Faculty Publications: November, 2018

Query Results from the Smithsonian/NASA Astrophysics Data System (ADS)

The following are Harvard Physics faculty members' publications, added to the ADS database last month. Please note that some publications which appeared in print last month may not be included in the database (and therefore may not appear on this list) until the following month.

Title:
A microwave-assisted spectroscopy technique for determining charge state in nitrogen-vacancy ensembles in diamond
Authors:
Aude Craik, D. P. L.; Kehayias, P.; Greenspon, A. S.; Zhang, X.; Turner, M. J.; Schloss, J. M.; Bauch, E.; Hart, C. A.; Hu, E. L.; Walsworth, R. L.
Publication:
eprint arXiv:1811.01972
Publication Date:
11/2018
Origin:
ARXIV
Keywords:
Condensed Matter - Mesoscale and Nanoscale Physics, Quantum Physics
Comment:
10 pages, 6 figures
Bibliographic Code:
2018arXiv181101972A

Abstract

We present a microwave-assisted spectroscopy technique for determining the relative concentrations of nitrogen vacancy (NV) centers in diamond that are negatively-charged (NV${}^-$) and neutrally-charged (NV${}^0$). Our method is based on selectively modulating the NV${}^-$ fluorescence with a spin-state-resonant microwave drive to isolate, in-situ, the spectral shape of the NV${}^-$ and, subsequently, NV${}^0$ contributions to an NV-ensemble sample's fluorescence. The sample-specific nature of this method accounts for any sample-to-sample variations in the spectral shape of the NV${}^-$ and NV${}^0$ fluorescence; and permits the investigation of the effect of material parameters, such as local strain and nitrogen concentration, on the steady-state charge-state distribution in NV ensembles. Our method does not rely on a specific illumination sequence, and can be applied with any illumination conditions of interest, as long as they produce fluorescence contrast between the NV${}^-$ spin states. The techniques presented here may be generalized to determine relative concentrations of other solid-state defects whose fluorescence can be selectively modulated by means of a microwave drive.

 

Title:
Evaluating Quasi-local Angular Momentum and Center-of-Mass at Null Infinity
Authors:
Keller, Jordan; Wang, Ye-Kai; Yau, Shing-Tung
Publication:
eprint arXiv:1811.02383
Publication Date:
11/2018
Origin:
ARXIV
Keywords:
Mathematics - Differential Geometry, General Relativity and Quantum Cosmology
Comment:
35 pages, no figure
Bibliographic Code:
2018arXiv181102383K

Abstract

We calculate the limits of the quasi-local angular momentum and center-of-mass defined by Chen-Wang-Yau \cite{CWY} for a family of spacelike two-spheres approaching future null infinity in an asymptotically flat spacetime admitting a Bondi-Sachs expansion. Our result complements earlier work of Chen-Wang-Yau \cite{CWY2}, where the authors calculate the limits of the quasi-local energy and linear momentum at null infinity. Finiteness of the center-of-mass limit requires that the spacetime be in the so-called center-of-mass frame, a mild assumption on the mass aspect function amounting to vanishing of linear momentum at null infinity. With this condition and the assumption that the Bondi mass is non-trivial, we obtain explicit expressions for the angular momentum and center-of-mass at future null infinity in terms of the observables appearing in the Bondi-Sachs expansion of the spacetime metric.

 

Title:
First Measurement of $\nu_{\mu}$ Charged-Current $\pi^{0}$ Production on Argon with a LArTPC
Authors:
MicroBooNE collaboration; Adams, C.; Alrashed, M.; An, R.; Anthony, J.;... Guenette, R.;... and 170 coauthors
Publication:
eprint arXiv:1811.02700
Publication Date:
11/2018
Origin:
ARXIV
Keywords:
High Energy Physics - Experiment, Physics - Instrumentation and Detectors
Bibliographic Code:
2018arXiv181102700M

Abstract

We report the first measurement of the flux-integrated cross section of $\nu_{\mu}$ charged-current single $\pi^{0}$ production on argon. This measurement is performed with the MicroBooNE detector, an 85 ton active mass liquid argon time projection chamber exposed to the Booster Neutrino Beam at Fermilab. This result on argon is compared to past measurements on lighter nuclei to investigate the scaling assumptions used in models of the production and transport of pions in neutrino-nucleus scattering. The techniques used are an important demonstration of the successful reconstruction and analysis of neutrino interactions producing electromagnetic final states using a liquid argon time projection chamber operating at the earth's surface.

 

Title:
Moment maps, nonlinear PDE, and stability in mirror symmetry
Authors:
Collins, Tristan C.; Yau, Shing-Tung
Publication:
eprint arXiv:1811.04824
Publication Date:
11/2018
Origin:
ARXIV
Keywords:
Mathematics - Differential Geometry, Mathematics - Algebraic Geometry
Comment:
94 pages, 3 figures
Bibliographic Code:
2018arXiv181104824C

Abstract

We study the deformed Hermitian-Yang-Mills (dHYM) equation, which is mirror to the special Lagrangian equation, from the variational point of view via an infinite dimensional GIT problem mirror to Thomas' GIT picture for special Lagrangians. This gives rise to infinite dimensional manifold $\mathcal{H}$ mirror to Solomon's space of positive Lagrangians. In the hypercritical phase case we prove the existence of smooth approximate geodesics, and weak geodesics with $C^{1,\alpha}$ regularity. This is accomplished by proving sharp with respect to scale estimates for the Lagrangian phase operator on collapsing manifolds with boundary. We apply these results to the infinite dimensional GIT problem for deformed Hermitian-Yang-Mills. We associate algebraic invariants to certain birational models of $X\times \Delta$, where $\Delta \subset \mathbb{C}$ is a disk. Using the existence of regular weak geodesics we prove that these invariants give rise to obstructions to the existence of solutions to the dHYM equation. Furthermore, we show that these invariants fit into a stability framework closely related to Bridgeland stability. Finally, we use a Fourier-Mukai transform on toric K\"ahler manifolds to describe degenerations of Lagrangian sections of SYZ torus fibrations of Landau-Ginzburg models $(Y,W)$. We speculate on the resulting algebraic invariants, and discuss the implications for relating Bridgeland stability to the existence of special Lagrangian sections of $(Y,W)$.

 

Title:
Gaussian states for the variational study of (1+1)-dimensional lattice gauge models
Authors:
Sala, P.; Shi, T.; Kühn, S.; Bañuls, M. C.; Demler, E.; Cirac, J. I.
Publication:
eprint arXiv:1811.04899
Publication Date:
11/2018
Origin:
ARXIV
Keywords:
High Energy Physics - Lattice, Condensed Matter - Strongly Correlated Electrons, Quantum Physics
Comment:
7 pages, 2 figures, proceedings of the 36th Annual International Symposium on Lattice Field Theory, 22-28 July, 2018 Michigan State University, East Lansing, Michigan, USA
Bibliographic Code:
2018arXiv181104899S

Abstract

We introduce a variational ansatz based on Gaussian states for (1+1)-dimensional lattice gauge models. To this end we identify a set of unitary transformations which decouple the gauge degrees of freedom from the matter fields. Using our ansatz, we study static aspects as well as real-time dynamics of string breaking in two (1+1)-dimensional theories, namely QED and two-color QCD. We show that our ansatz captures the relevant features and is in excellent agreement with data from numerical calculations with tensor networks.

 

Title:
Gauge theory for the cuprates near optimal doping
Authors:
Sachdev, Subir; Scammell, Harley D.; Scheurer, Mathias S.; Tarnopolsky, Grigory
Publication:
eprint arXiv:1811.04930
Publication Date:
11/2018
Origin:
ARXIV
Keywords:
Condensed Matter - Strongly Correlated Electrons, High Energy Physics - Theory
Comment:
57 pages, 16 figures
Bibliographic Code:
2018arXiv181104930S

Abstract

We describe the phase diagram of a 2+1 dimensional SU(2) gauge theory of fluctuating incommensurate spin density waves for the hole-doped cuprates. Our primary assumption is that all low energy fermionic excitations are gauge neutral and electron-like, while the spin density wave order is fractionalized into Higgs fields transforming as adjoints of the gauge SU(2). The confining phase of the gauge theory is a conventional Fermi liquid with a large Fermi surface (and its associated $d$-wave superconductor). There is a quantum phase transition to a Higgs phase describing the `pseudogap' at lower doping. Depending upon the quartic terms in the Higgs potential, the Higgs phase exhibits one or more of charge density wave, Ising-nematic, time-reversal odd scalar spin chirality, and $\mathbb{Z}_2$ topological orders. It is notable that the emergent broken symmetries in our theory of fluctuating spin density waves co-incide with those observed in diverse experiments. For the electron-doped cuprates, the spin density wave fluctuations are at wavevector $(\pi,\pi)$, and then the corresponding SU(2) gauge theory only has a crossover between the confining and Higgs regimes, with an exponentially large confinement scale deep in the Higgs regime. On the Higgs side, for both the electron- and hole-doped cases, and at scales shorter than the confinement scale (which can be infinite when $\mathbb{Z}_2$ topological order is present), the electron spectral function has a `fractionalized Fermi liquid (FL*)' form with small Fermi surfaces. We also describe the deconfined quantum criticality of the Higgs transition in the limit of a large number of Higgs flavors, and perturbatively discuss its coupling to fermionic excitations.

 

Title:
Density wave probes cuprate quantum phase transition
Authors:
Webb, Tatiana A.; Boyer, Michael C.; Yin, Yi; Chowdhury, Debanjan; He, Yang; Kondo, Takeshi; Takeuchi, T.; Ikuta, H.; Hudson, Eric W.; Hoffman, Jennifer E.; Hamidian, Mohammad H.
Publication:
eprint arXiv:1811.05968
Publication Date:
11/2018
Origin:
ARXIV
Keywords:
Condensed Matter - Superconductivity, Condensed Matter - Strongly Correlated Electrons
Comment:
9 pages, 4 figures
Bibliographic Code:
2018arXiv181105968W

Abstract

In cuprate materials, the strong correlations in proximity to the antiferromagnetic Mott insulating state give rise to an array of unconventional phenomena beyond high temperature superconductivity. Developing a complete description of the ground state evolution is crucial to decoding the complex phase diagram. Here we use the structure of broken translational symmetry, namely $d$-form factor charge modulations in (Bi,Pb)$_2$(Sr,La)$_2$CuO$_{6+\delta}$, as a probe of the ground state reorganization which occurs at the transition from truncated Fermi arcs to a large Fermi surface. We use real space imaging of local electronic inhomogeneity as a tool to access a range of dopings within each sample, and we firmly establish the spectral gap $\Delta$ as a proxy for local hole doping. From the $\Delta$-dependence of the charge modulation wavevector, we discover a commensurate to incommensurate transition that is coincident with the Fermi surface transition from arcs to large hole pocket, demonstrating the qualitatively distinct nature of the electronic correlations governing the two sides of this quantum phase transition. Furthermore, the doping dependence of the incommensurate wavevector on the overdoped side is at odds with a simple Fermi surface driven instability.

 

Title:
Imaging magnetic polarons in the doped Fermi-Hubbard model
Authors:
Koepsell, Joannis; Vijayan, Jayadev; Sompet, Pimonpan; Grusdt, Fabian; Hilker, Timon A.; Demler, Eugene; Salomon, Guillaume; Bloch, Immanuel; Gross, Christian
Publication:
eprint arXiv:1811.06907
Publication Date:
11/2018
Origin:
ARXIV
Keywords:
Condensed Matter - Quantum Gases, Quantum Physics
Bibliographic Code:
2018arXiv181106907K

Abstract

Polarons are among the most fundamental quasiparticles emerging in interacting many-body systems, forming already at the level of a single mobile dopant. In the context of the two-dimensional Fermi-Hubbard model, such polarons are predicted to form around charged dopants in an antiferromagnetic background in the low doping regime close to the Mott insulating state. Macroscopic transport and spectroscopy measurements related to high $T_{c}$ materials have yielded strong evidence for the existence of such quasiparticles in these systems. Here we report the first microscopic observation of magnetic polarons in a doped Fermi-Hubbard system, harnessing the full single-site spin and density resolution of our ultracold-atom quantum simulator. We reveal the dressing of mobile doublons by a local reduction and even sign reversal of magnetic correlations, originating from the competition between kinetic and magnetic energy in the system. The experimentally observed polaron signatures are found to be consistent with an effective string model at finite temperature. We demonstrate that delocalization of the doublon is a necessary condition for polaron formation by contrasting this mobile setting to a scenario where the doublon is pinned to a lattice site. Our work paves the way towards probing interactions between polarons, which may lead to stripe formation, as well as microscopically exploring the fate of polarons in the pseudogap and bad metal phase.

 

Title:
Non-Hermitian Quasi-Localization and Ring Attractor Neural Networks
Authors:
Tanaka, Hidenori; Nelson, David R.
Publication:
eprint arXiv:1811.07433
Publication Date:
11/2018
Origin:
ARXIV
Keywords:
Condensed Matter - Disordered Systems and Neural Networks, Condensed Matter - Statistical Mechanics, Quantitative Biology - Neurons and Cognition
Bibliographic Code:
2018arXiv181107433T

Abstract

Eigenmodes of a broad class of "sparse" random matrices, with interactions concentrated near the diagonal, exponentially localize in space, as initially discovered in 1957 by Anderson for quantum systems. Anderson localization plays ubiquitous roles in varieties of problems from electrons in solids to mechanical and optical systems. However, its implications in neuroscience (where the connections can be strongly asymmetric) have been largely unexplored, mainly because synaptic connectivity matrices of neural systems are often "dense", which makes the eigenmodes spatially extended. Here, we explore roles that Anderson localization could be playing in neural networks by focusing on "spatially structured" disorder in synaptic connectivity matrices. Recently, neuroscientists have experimentally confirmed that the local excitation and global inhibition (LEGI) ring attractor model can functionally represent head direction cells in Drosophila melanogaster central brain. We first study a non-Hermitian (i.e. asymmetric) tight-binding model with disorder and then establish a connection to the LEGI ring attractor model. We discover that (i) Principal eigenvectors of the LEGI ring attractor networks with structured nearest neighbor disorder are "quasi-localized", even with fully dense inhibitory connections. (ii) The quasi-localized eigenvectors play dominant roles in the early time neural dynamics, and the location of the principal quasi-localized eigenvectors predict an initial location of the "bump of activity" re

 

Title:
4-manifolds and topological modular forms
Authors:
Gukov, Sergei; Pei, Du; Putrov, Pavel; Vafa, Cumrun
Publication:
eprint arXiv:1811.07884
Publication Date:
11/2018
Origin:
ARXIV
Keywords:
High Energy Physics - Theory, Mathematical Physics, Mathematics - Algebraic Topology, Mathematics - Geometric Topology
Comment:
74 pages
Bibliographic Code:
2018arXiv181107884G

Abstract

We build a connection between topology of smooth 4-manifolds and the theory of topological modular forms by considering topologically twisted compactification of 6d (1,0) theories on 4-manifolds with flavor symmetry backgrounds. The effective 2d theory has (0,1) supersymmetry and, possibly, a residual flavor symmetry. The equivariant topological Witten genus of this 2d theory then produces a new invariant of the 4-manifold equipped with a principle bundle, valued in the ring of equivariant weakly holomorphic (topological) modular forms. We describe basic properties of this map and present a few simple examples. As a byproduct, we obtain some new results on 't Hooft anomalies of 6d (1,0) theories and a better understanding of the relation between 2d (0,1) theories and TMF spectra.

 

Title:
From spinon band topology to the symmetry quantum numbers of monopoles in Dirac spin liquids
Authors:
Song, Xue-Yang; He, Yin-Chen; Vishwanath, Ashvin; Wang, Chong
Publication:
eprint arXiv:1811.11182
Publication Date:
11/2018
Origin:
ARXIV
Keywords:
Condensed Matter - Strongly Correlated Electrons, High Energy Physics - Lattice, High Energy Physics - Theory
Comment:
26 pages, 7 figures
Bibliographic Code:
2018arXiv181111182S

Abstract

The interplay of symmetry and topology have been at the forefront of recent progress in quantum matter. Here we uncover an unexpected connection between band topology and the description of competing orders in a quantum magnet. Specifically we show that aspects of band topology protected by crystalline symmetries determine key properties of the Dirac spin liquid (DSL) which can be defined on the honeycomb, square, triangular and kagom\'e lattices. At low energies, the DSL on all these lattices is described by an emergent Quantum Electrodynamics (QED$_3$) with $N_f=4$ flavors of Dirac fermions coupled to a $U(1)$ gauge field. However the symmetry properties of the magnetic monopoles, an important class of critical degrees of freedom, behave very differently on different lattices. In particular, we show that the lattice momentum and angular momentum of monopoles can be determined from the charge (or Wannier) centers of the corresponding spinon insulator. We also show that for DSLs on bipartite lattices, there always exists a monopole that transforms trivially under all microscopic symmetries owing to the existence of a parent SU(2) gauge theory. We connect our results to generalized Lieb-Schultz-Mattis theorems and also derive the time-reversal and reflection properties of monopoles. Our results indicate that recent insights into free fermion band topology can also guide the description of strongly correlated quantum matter.

 

Title:
Unifying Description of Competing Orders in Two Dimensional Quantum Magnets
Authors:
Song, Xue-Yang; Wang, Chong; Vishwanath, Ashvin; He, Yin-Chen
Publication:
eprint arXiv:1811.11186
Publication Date:
11/2018
Origin:
ARXIV
Keywords:
Condensed Matter - Strongly Correlated Electrons, High Energy Physics - Lattice, High Energy Physics - Theory
Comment:
13+9 pages, 7 figures
Bibliographic Code:
2018arXiv181111186S

Abstract

Quantum magnets provide the simplest example of strongly interacting quantum matter, yet they continue to resist a comprehensive understanding above one spatial dimension (1D). In 1D, a key ingredient to progress is Luttinger liquid theory which provides a unified description. Here we explore a promising analogous framework in two dimensions, the Dirac spin liquid (DSL), which can be constructed on several different lattices. The DSL is a version of Quantum Electrodynamics ( QED$_3$) with four flavors of Dirac fermions coupled to photons. Importantly, its excitations also include magnetic monopoles that drive confinement. By calculating the complete action of symmetries on monopoles on the square, honeycomb, triangular and kagom\`e lattices, we answer previously open key questions. We find that the stability of the DSL is enhanced on the triangular and kagom\`e lattices as compared to the bipartite (square and honeycomb) lattices. We obtain the universal signatures of the DSL on the triangular and kagom\`e lattices, including those that result from monopole excitations, which serve as a guide to numerics and to experiments on existing materials. Interestingly, the familiar 120 degree magnetic orders on these lattices can be obtained from monopole proliferation. Even when unstable, the Dirac spin liquid unifies multiple ordered states which could help organize the plethora of phases observed in strongly correlated two-dimensional materials.

 

Title:
Using Attribution to Decode Dataset Bias in Neural Network Models for Chemistry
Authors:
McCloskey, Kevin; Taly, Ankur; Monti, Federico; Brenner, Michael P.; Colwell, Lucy
Publication:
eprint arXiv:1811.11310
Publication Date:
11/2018
Origin:
ARXIV
Keywords:
Computer Science - Machine Learning, Statistics - Machine Learning
Bibliographic Code:
2018arXiv181111310M

Abstract

Deep neural networks have achieved state of the art accuracy at classifying molecules with respect to whether they bind to specific protein targets. A key breakthrough would occur if these models could reveal the fragment pharmacophores that are causally involved in binding. Extracting chemical details of binding from the networks could potentially lead to scientific discoveries about the mechanisms of drug actions. But doing so requires shining light into the black box that is the trained neural network model, a task that has proved difficult across many domains. Here we show how the binding mechanism learned by deep neural network models can be interrogated, using a recently described attribution method. We first work with carefully constructed synthetic datasets, in which the 'fragment logic' of binding is fully known. We find that networks that achieve perfect accuracy on held out test datasets still learn spurious correlations due to biases in the datasets, and we are able to exploit this non-robustness to construct adversarial examples that fool the model. The dataset bias makes these models unreliable for accurately revealing information about the mechanisms of protein-ligand binding. In light of our findings, we prescribe a test that checks for dataset bias given a hypothesis. If the test fails, it indicates that either the model must be simplified or regularized and/or that the training dataset requires augmentation.

 

Title:
Classifying Snapshots of the Doped Hubbard Model with Machine Learning
Authors:
Bohrdt, Annabelle; Chiu, Christie S.; Ji, Geoffrey; Xu, Muqing; Greif, Daniel; Greiner, Markus; Demler, Eugene; Grusdt, Fabian; Knap, Michael
Publication:
eprint arXiv:1811.12425
Publication Date:
11/2018
Origin:
ARXIV
Keywords:
Condensed Matter - Quantum Gases, Condensed Matter - Disordered Systems and Neural Networks, Condensed Matter - Strongly Correlated Electrons
Comment:
4 pages, 3 figures + 4 pages, 5 figures
Bibliographic Code:
2018arXiv181112425B

Abstract

Quantum gas microscopes for ultracold atoms can provide high-resolution real-space snapshots of complex many-body systems. We implement machine learning to analyze and classify such snapshots of ultracold atoms. Specifically, we compare the data from an experimental realization of the two-dimensional Fermi-Hubbard model to two theoretical approaches: a doped quantum spin liquid state of resonating valence bond type, and the geometric string theory, describing a state with hidden spin order. This approach considers all available information without a potential bias towards one particular theory by the choice of an observable and can therefore select the theory which is more predictive in general. Up to intermediate doping values, our algorithm tends to classify experimental snapshots as geometric-string-like, as compared to the doped spin liquid. Our results demonstrate the potential for machine learning in processing the wealth of data obtained through quantum gas microscopy for new physical insights.

 

Title:
Performance of missing transverse momentum reconstruction with the ATLAS detector using proton-proton collisions at √{s}=13 TeV
Authors:
Aaboud, M.; Aad, G.; Abbott, B.; Abdinov, O.;... Franklin, M.;... Huth, J.;... Morii, M.;... and 2860 coauthors
Publication:
The European Physical Journal C, Volume 78, Issue 11, article id. 903, 46 pp. (EPJC Homepage)
Publication Date:
11/2018
Origin:
SPRINGER
Abstract Copyright:
(c) 2018
DOI:
10.1140/epjc/s10052-018-6288-9
Bibliographic Code:
2018EPJC...78..903A

Abstract

The performance of the missing transverse momentum (ET^{miss}) reconstruction with the ATLAS detector is evaluated using data collected in proton-proton collisions at the LHC at a centre-of-mass energy of 13 TeV in 2015. To reconstruct ET^{miss}, fully calibrated electrons, muons, photons, hadronically decaying τ {-leptons}, and jets reconstructed from calorimeter energy deposits and charged-particle tracks are used. These are combined with the soft hadronic activity measured by reconstructed charged-particle tracks not associated with the hard objects. Possible double counting of contributions from reconstructed charged-particle tracks from the inner detector, energy deposits in the calorimeter, and reconstructed muons from the muon spectrometer is avoided by applying a signal ambiguity resolution procedure which rejects already used signals when combining the various ET^{miss} contributions. The individual terms as well as the overall reconstructed ET^{miss} are evaluated with various performance metrics for scale (linearity), resolution, and sensitivity to the data-taking conditions. The method developed to determine the systematic uncertainties of the ET^{miss} scale and resolution is discussed. Results are shown based on the full 2015 data sample corresponding to an integrated luminosity of 3.2 fb^{-1}.

 

Title:
Search for Higgs boson pair production in the γ γ b\overline{b} final state with 13 TeV pp collision data collected by the ATLAS experiment
Authors:
Aaboud, M.; Aad, G.; Abbott, B.; Abdinov, O.;... Franklin, M.;... Huth, J.;... Morii, M.;... and 2910 coauthors
Publication:
Journal of High Energy Physics, Volume 2018, Issue 11, article id. 40, 44 pp.
Publication Date:
11/2018
Origin:
SPRINGER
Keywords:
Hadron-Hadron scattering (experiments), Higgs physics
Abstract Copyright:
(c) 2018
DOI:
10.1007/JHEP11(2018)040
Bibliographic Code:
2018JHEP...11..040A

Abstract

A search is performed for resonant and non-resonant Higgs boson pair production in the γ γ b\overline{b} final state. The data set used corresponds to an integrated luminosity of 36.1 fb-1 of proton-proton collisions at a centre-of-mass energy of 13 TeV recorded by the ATLAS detector at the CERN Large Hadron Collider. No significant excess relative to the Standard Model expectation is observed. The observed limit on the non-resonant Higgs boson pair cross-section is 0.73 pb at 95% confidence level. This observed limit is equivalent to 22 times the predicted Standard Model cross-section. The Higgs boson self-coupling ( κ λ = λ HHH / λ HHH SM ) is constrained at 95% confidence level to -8.2 < κ λ < 13.2. For resonant Higgs boson pair production through X\to HH\to γ γ b\overline{b} , the limit is presented, using the narrow-width approximation, as a function of m X in the range 260 GeV < m X < 1000 GeV. The observed limits range from 1.1 pb to 0.12 pb over this mass range.

 

Title:
Search for charged Higgs bosons decaying into top and bottom quarks at √{s}=13 TeV with the ATLAS detector
Authors:
Aaboud, M.; Aad, G.; Abbott, B.; Abdinov, O.;... Franklin, M.;... Huth, J.;... Morii, M.;... and 2915 coauthors
Publication:
Journal of High Energy Physics, Volume 2018, Issue 11, article id. 85, 55 pp.
Publication Date:
11/2018
Origin:
SPRINGER
Keywords:
Beyond Standard Model, Hadron-Hadron scattering (experiments), Higgs physics
Abstract Copyright:
(c) 2018
DOI:
10.1007/JHEP11(2018)085
Bibliographic Code:
2018JHEP...11..085A

Abstract

A search for charged Higgs bosons heavier than the top quark and decaying via H ± → tb is presented. The data analysed corresponds to 36.1 fb-1 of pp collisions at √{s}=13 TeV and was recorded with the ATLAS detector at the LHC in 2015 and 2016. The production of a charged Higgs boson in association with a top quark and a bottom quark, pp → tbH ±, is explored in the mass range from m H ± = 200 to 2000 GeV using multi-jet final states with one or two electrons or muons. Events are categorised according to the multiplicity of jets and how likely these are to have originated from hadronisation of a bottom quark. Multivariate techniques are used to discriminate between signal and background events. No significant excess above the background-only hypothesis is observed and exclusion limits are derived for the production cross-section times branching ratio of a charged Higgs boson as a function of its mass, which range from 2.9 pb at mH ± = 200 GeV to 0.070 pb at mH ± = 2000 GeV. The results are interpreted in two benchmark scenarios of the Minimal Supersymmetric Standard Model. [Figure not available: see fulltext.]

 

Title:
Visible-Spanning Flat Supercontinuum for Astronomical Applications
Authors:
Ravi, Aakash; Beck, Matthias; Phillips, David F.; Bartels, Albrecht; Sasselov, Dimitar; Szentgyorgyi, Andrew; Walsworth, Ronald L.
Affiliation:
AA(0000-0003-1312-8161), AG(0000-0003-0311-4751)
Publication:
Journal of Lightwave Technology, vol. 36, issue 22, pp. 5309-5315
Publication Date:
11/2018
Origin:
CROSSREF
DOI:
10.1109/JLT.2018.2872423
Bibliographic Code:
2018JLwT...36.5309R

Abstract

We demonstrate a broad, flat, visible supercontinuum spectrum that is generated by a dispersion-engineered tapered photonic crystal fiber pumped by a 1 GHz repetition rate turn-key Ti:sapphire laser outputting $\sim$ 30 fs pulses at 800 nm. At a pulse energy of 100 pJ, we obtain an output spectrum that is flat to within 3 dB over the range 490-690 nm with a blue tail extending below 450 nm. The mode-locked laser combined with the photonic crystal fiber forms a simple visible frequency comb system that is extremely well-suited to the precise calibration of astrophysical spectrographs, among other applications.

 

Title:
Observation of H → b b bar decays and VH production with the ATLAS detector
Authors:
Aaboud, M.; Aad, G.; Abbott, B.; Abdinov, O.;... Franklin, M.;... Huth, J.;... Morii, M.;... and 2929 coauthors
Publication:
Physics Letters B, Volume 786, p. 59-86.
Publication Date:
11/2018
Origin:
ELSEVIER
Abstract Copyright:
(c) 2018 Elsevier Science B.V. All rights reserved.
DOI:
10.1016/j.physletb.2018.09.013
Bibliographic Code:
2018PhLB..786...59A

Abstract

A search for the decay of the Standard Model Higgs boson into a b b bar pair when produced in association with a W or Z boson is performed with the ATLAS detector. The data, corresponding to an integrated luminosity of 79.8fb-1 were collected in proton-proton collisions during Run 2 of the Large Hadron Collider at a centre-of-mass energy of 13TeV. For a Higgs boson mass of 125GeV, an excess of events over the expected background from other Standard Model processes is found with an observed (expected) significance of 4.9 (4.3) standard deviations. A combination with the results from other searches in Run 1 and in Run 2 for the Higgs boson in the b b bar decay mode is performed, which yields an observed (expected) significance of 5.4 (5.5) standard deviations, thus providing direct observation of the Higgs boson decay into b-quarks. The ratio of the measured event yield for a Higgs boson decaying into b b bar to the Standard Model expectation is 1.01 ± 0.12(stat.)-0.15+0.16 (syst .) . Additionally, a combination of Run 2 results searching for the Higgs boson produced in association with a vector boson yields an observed (expected) significance of 5.3 (4.8) standard deviations.

 

Title:
Combined measurement of differential and total cross sections in the H → γγ and the H → ZZ* → 4ℓ decay channels at √{ s } = 13 TeV with the ATLAS detector
Authors:
Aaboud, M.; Aad, G.; Abbott, B.; Abdinov, O.;... Franklin, M.;... Huth, J.;... Morii, M.;... and 2913 coauthors
Publication:
Physics Letters B, Volume 786, p. 114-133.
Publication Date:
11/2018
Origin:
ELSEVIER
Abstract Copyright:
(c) 2018 Elsevier Science B.V. All rights reserved.
DOI:
10.1016/j.physletb.2018.09.019
Bibliographic Code:
2018PhLB..786..114A

Abstract

A combined measurement of differential and inclusive total cross sections of Higgs boson production is performed using 36.1 fb-1 of 13 TeV proton-proton collision data produced by the LHC and recorded by the ATLAS detector in 2015 and 2016. Cross sections are obtained from measured H → γγ and H → ZZ* → 4 ℓ event yields, which are combined taking into account detector efficiencies, resolution, acceptances and branching fractions. The total Higgs boson production cross section is measured to be 57.0-5.9+6.0 (stat.) -3.3+4.0 (syst.) pb, in agreement with the Standard Model prediction. Differential cross-section measurements are presented for the Higgs boson transverse momentum distribution, Higgs boson rapidity, number of jets produced together with the Higgs boson, and the transverse momentum of the leading jet. The results from the two decay channels are found to be compatible, and their combination agrees with the Standard Model predictions.

 

Title:
Searches for exclusive Higgs and Z boson decays into J/ψ γ, ψ(2S) γ, and ϒ(nS) γ at √{ s } = 13TeV with the ATLAS detector
Authors:
Aaboud, M.; Aad, G.; Abbott, B.; Abdinov, O.;... Franklin, M.;... Huth, J.;... Morii, M.;... and 2910 coauthors
Publication:
Physics Letters B, Volume 786, p. 134-155.
Publication Date:
11/2018
Origin:
ELSEVIER
Abstract Copyright:
(c) 2018 Elsevier Science B.V. All rights reserved.
DOI:
10.1016/j.physletb.2018.09.024
Bibliographic Code:
2018PhLB..786..134A

Abstract

Searches for the exclusive decays of the Higgs and Z bosons into a J / ψ, ψ (2 S), or ϒ (nS) (n = 1 , 2 , 3) meson and a photon are performed with a pp collision data sample corresponding to an integrated luminosity of 36.1fb-1 collected at √{ s } = 13TeV with the ATLAS detector at the CERN Large Hadron Collider. No significant excess of events is observed above the expected backgrounds, and 95% confidence-level upper limits on the branching fractions of the Higgs boson decays to J / ψ γ, ψ (2 S) γ, and ϒ (nS) γ of 3.5 ×10-4, 2.0 ×10-3, and (4.9 , 5.9 , 5.7) ×10-4, respectively, are obtained assuming Standard Model production. The corresponding 95% confidence-level upper limits for the branching fractions of the Z boson decays are 2.3 ×10-6, 4.5 ×10-6 and (2.8 , 1.7 , 4.8) ×10-6, respectively.

 

Title:
Constraints on off-shell Higgs boson production and the Higgs boson total width in ZZ → 4ℓ and ZZ → 2ℓ2ν final states with the ATLAS detector
Authors:
Aaboud, M.; Aad, G.; Abbott, B.; Abdinov, O.;... Franklin, M.;... Huth, J.;... Morii, M.;... and 2926 coauthors
Publication:
Physics Letters B, Volume 786, p. 223-244.
Publication Date:
11/2018
Origin:
ELSEVIER
Abstract Copyright:
(c) 2018 Elsevier Science B.V. All rights reserved.
DOI:
10.1016/j.physletb.2018.09.048
Bibliographic Code:
2018PhLB..786..223A

Abstract

A measurement of off-shell Higgs boson production in the ZZ → 4 ℓ and ZZ → 2 ℓ 2 ν decay channels, where ℓ stands for either an electron or a muon, is performed using data from proton-proton collisions at a centre-of-mass energy of √{ s } = 13 TeV. The data were collected by the ATLAS experiment in 2015 and 2016 at the Large Hadron Collider, and they correspond to an integrated luminosity of 36.1fb-1. An observed (expected) upper limit on the off-shell Higgs signal strength, defined as the event yield normalised to the Standard Model prediction, of 3.8 (3.4) is obtained at 95% confidence level (CL). Assuming the ratio of the Higgs boson couplings to the Standard Model predictions is independent of the momentum transfer of the Higgs production mechanism considered in the analysis, a combination with the on-shell signal-strength measurements yields an observed (expected) 95% CL upper limit on the Higgs boson total width of 14.4 (15.2) MeV.

 

Title:
Classical approach to collision complexes in ultracold chemical reactions
Authors:
Soley, Micheline B.; Heller, Eric J.
Publication:
Physical Review A, Volume 98, Issue 5, id.052702 (PhRvA Homepage)
Publication Date:
11/2018
Origin:
APS
Abstract Copyright:
2018: American Physical Society
DOI:
10.1103/PhysRevA.98.052702
Bibliographic Code:
2018PhRvA..98e2702S

Abstract

Inspired by Wannier's threshold law, we recognize that collision-complex decay meets the requirements of quantum-classical correspondence in sufficiently exothermic ultracold reactions. We make use of this correspondence to elucidate the classical foundations of ultracold reactions and to help bring calculations currently beyond the capabilities of quantum mechanics within reach. A classical method with a simplified model of many-body interactions is provided for the determination of the collision-complex lifetime and demonstrated for a reduced-dimensional system, as preliminary to the calculation of collision-complex lifetimes in the full-dimensional system.

 

Title:
Dynamical signature of fractionalization at a deconfined quantum critical point
Authors:
Ma, Nvsen; Sun, Guang-Yu; You, Yi-Zhuang; Xu, Cenke; Vishwanath, Ashvin; Sandvik, Anders W.; Meng, Zi Yang
Publication:
Physical Review B, Volume 98, Issue 17, id.174421 (PhRvB Homepage)
Publication Date:
11/2018
Origin:
APS
Abstract Copyright:
2018: American Physical Society
DOI:
10.1103/PhysRevB.98.174421
Bibliographic Code:
2018PhRvB..98q4421M

Abstract

Deconfined quantum critical points govern continuous quantum phase transitions at which fractionalized (deconfined) degrees of freedom emerge. Here we study dynamical signatures of the fractionalized excitations in a quantum magnet (the easy-plane J-Q model) that realize a deconfined quantum critical point with emergent O(4) symmetry. By means of large-scale quantum Monte Carlo simulations and stochastic analytic continuation of imaginary-time correlation functions, we obtain the dynamic spin-structure factors in the Sx and Sz channels. In both channels, we observe broad continua that originate from the deconfined excitations. We further identify several distinct spectral features of the deconfined quantum critical point, including the lower edge of the continuum and its form factor on moving through the Brillouin zone. We provide field-theoretical and lattice model calculations that explain the overall shapes of the computed spectra, which highlight the importance of interactions and gauge fluctuations to explain the spectral-weight distribution. We make further comparisons with the conventional Landau O(2) transition in a different quantum magnet, at which no signatures of fractionalization are observed. The distinctive spectral signatures of the deconfined quantum critical point suggest the feasibility of its experimental detection in neutron scattering and nuclear magnetic resonance experiments.

 

Title:
Density functional theory beyond the Born-Oppenheimer approximation: Accurate treatment of the ionic zero-point motion
Authors:
Kolesov, Grigory; Kaxiras, Efthimios; Manousakis, Efstratios
Publication:
Physical Review B, Volume 98, Issue 19, id.195112 (PhRvB Homepage)
Publication Date:
11/2018
Origin:
APS
Abstract Copyright:
2018: American Physical Society
DOI:
10.1103/PhysRevB.98.195112
Bibliographic Code:
2018PhRvB..98s5112K

Abstract

We introduce a method to carry out zero-temperature calculations within density functional theory (DFT) but without relying on the Born-Oppenheimer (BO) approximation for the ionic motion. Our approach is based on the finite-temperature many-body path-integral formulation of quantum mechanics by taking the zero-temperature limit and treating the imaginary-time propagation of the electronic variables in the context of DFT. This goes beyond the familiar BO approximation and is limited from being an exact treatment of both electrons and ions only by the approximations involved in the DFT component. We test our method in two simple molecules, H2 and benzene. We demonstrate that the method produces a difference from the results of the BO approximation which is significant for many physical systems, especially those containing light atoms such as hydrogen; in these cases, we find that the fluctuations of the distance from its equilibrium position, due to the zero-point motion, is comparable to the interatomic distances. The method is suitable for use with conventional condensed-matter approaches and currently is implemented on top of the periodic pseudopotential code siesta.

 

Title:
Probing one-dimensional systems via noise magnetometry with single spin qubits
Authors:
Rodriguez-Nieva, Joaquin F.; Agarwal, Kartiek; Giamarchi, Thierry; Halperin, Bertrand I.; Lukin, Mikhail D.; Demler, Eugene
Publication:
Physical Review B, Volume 98, Issue 19, id.195433 (PhRvB Homepage)
Publication Date:
11/2018
Origin:
APS
Abstract Copyright:
2018: American Physical Society
DOI:
10.1103/PhysRevB.98.195433
Bibliographic Code:
2018PhRvB..98s5433R

Abstract

The study of exotic one-dimensional states, particularly those at the edges of topological materials, demand new experimental probes that can access the interplay between charge and spin degrees of freedom. One potential approach is to use a single spin probe, such as a nitrogen vacancy center in diamond, which has recently emerged as a versatile tool to probe nanoscale systems in a noninvasive fashion. Here, we present a theory describing how noise magnetometry with spin probes can directly address several questions that have emerged in experimental studies of 1D systems, including those in topological materials. We show that by controlling the spin degree of freedom of the probe, it is possible to measure locally and independently local charge and spin correlations of 1D systems. Visualization of 1D edge states, as well as sampling correlations with wave-vector resolution can be achieved by tuning the probe-to-sample distance. Furthermore, temperature-dependent measurements of magnetic noise can clearly delineate the dominant scattering mechanism (impurities versus interactions)—this is of particular relevance to quantum spin Hall measurements where conductance quantization is not perfect. The possibility to probe both charge and spin excitations in a wide range of length scales opens new pathways to bridging the large gap between atomic scale resolution of scanning probes and global transport measurements.

 

Title:
Quantum field theory for the chiral clock transition in one spatial dimension
Authors:
Whitsitt, Seth; Samajdar, Rhine; Sachdev, Subir
Publication:
Physical Review B, Volume 98, Issue 20, id.205118 (PhRvB Homepage)
Publication Date:
11/2018
Origin:
APS
Abstract Copyright:
(c) 2018: American Physical Society
DOI:
10.1103/PhysRevB.98.205118
Bibliographic Code:
2018PhRvB..98t5118W

Abstract

We describe the quantum phase transition in the N -state chiral clock model in spatial dimension d =1 . With couplings chosen to preserve time-reversal and spatial inversion symmetries, such a model is in the universality class of recent experimental studies of the ordering of pumped Rydberg states in a one-dimensional chain of trapped ultracold alkali atoms. For such couplings and N =3 , the clock model is expected to have a direct phase transition from a gapped phase with a broken global ZN symmetry, to a gapped phase with the ZN symmetry restored. The transition has dynamical critical exponent z ≠1 , and so cannot be described by a relativistic quantum field theory. We use a lattice duality transformation to map the transition onto that of a Bose gas in d =1 , involving the onset of a single-boson condensate in the background of a higher-dimensional N -boson condensate. We present a renormalization group analysis of the strongly coupled field theory for the Bose gas transition in an expansion in 2 -d , with 4 -N chosen to be of order 2 -d . At two-loop order, we find a regime of parameters with a renormalization group fixed point which can describe a direct phase transition. We also present numerical density-matrix renormalization group studies of lattice chiral clock and Bose gas models for N =3 , finding good evidence for a direct phase transition, and obtain estimates for z and the correlation length exponent ν.

 

Title:
Search for pair production of Higgsinos in final states with at least three b -tagged jets in √{s }=13 TeV p p collisions using the ATLAS detector
Authors:
Aaboud, M.; Aad, G.; Abbott, B.; Abdinov, O.;... Franklin, M.;... Huth, J.;... Morii, M.;... and 2886 coauthors
Publication:
Physical Review D, Volume 98, Issue 9, id.092002 (PhRvD Homepage)
Publication Date:
11/2018
Origin:
APS
Abstract Copyright:
2018: CERN
DOI:
10.1103/PhysRevD.98.092002
Bibliographic Code:
2018PhRvD..98i2002A

Abstract

A search for pair production of the supersymmetric partners of the Higgs boson (higgsinos H ˜) in gauge-mediated scenarios is reported. Each higgsino is assumed to decay to a Higgs boson and a gravitino. Two complementary analyses, targeting high- and low-mass signals, are performed to maximize sensitivity. The two analyses utilize LHC p p collision data at a center-of-mass energy √{s }=13 TeV , the former with an integrated luminosity of 36.1 fb-1 and the latter with 24.3 fb-1, collected with the ATLAS detector in 2015 and 2016. The search is performed in events containing missing transverse momentum and several energetic jets, at least three of which must be identified as b -quark jets. No significant excess is found above the predicted background. Limits on the cross section are set as a function of the mass of the H ˜ in simplified models assuming production via mass-degenerate higgsinos decaying to a Higgs boson and a gravitino. Higgsinos with masses between 130 and 230 GeV and between 290 and 880 GeV are excluded at the 95% confidence level. Interpretations of the limits in terms of the branching ratio of the higgsino to a Z boson or a Higgs boson are also presented, and a 45% branching ratio to a Higgs boson is excluded for mH ˜≈400 GeV .

 

Title:
Measurement of dijet azimuthal decorrelations in p p collisions at √{s }=8 TeV with the ATLAS detector and determination of the strong coupling
Authors:
Aaboud, M.; Aad, G.; Abbott, B.; Abdinov, O.;... Franklin, M.;... Huth, J.;... Morii, M.;... and 2884 coauthors
Publication:
Physical Review D, Volume 98, Issue 9, id.092004 (PhRvD Homepage)
Publication Date:
11/2018
Origin:
APS
Abstract Copyright:
2018: CERN
DOI:
10.1103/PhysRevD.98.092004
Bibliographic Code:
2018PhRvD..98i2004A

Abstract

A measurement of the rapidity and transverse momentum dependence of dijet azimuthal decorrelations is presented, using the quantity RΔ ϕ. The quantity RΔ ϕ specifies the fraction of the inclusive dijet events in which the azimuthal opening angle of the two jets with the highest transverse momenta is less than a given value of the parameter Δ ϕmax. The quantity RΔ ϕ is measured in proton-proton collisions at √{s }=8 TeV as a function of the dijet rapidity interval, the event total scalar transverse momentum, and Δ ϕmax. The measurement uses an event sample corresponding to an integrated luminosity of 20.2 fb-1 collected with the ATLAS detector at the CERN Large Hadron Collider. Predictions of a perturbative QCD calculation at next-to-leading order in the strong coupling with corrections for nonperturbative effects are compared to the data. The theoretical predictions describe the data in the whole kinematic region. The data are used to determine the strong coupling αS and to study its running for momentum transfers from 260 GeV to above 1.6 TeV. Analysis that combines data at all momentum transfers results in αS(mZ)=0.1127-0.0027+0.0063.

 

Title:
Search for pair production of heavy vectorlike quarks decaying into hadronic final states in p p collisions at √{s }=13 TeV with the ATLAS detector
Authors:
Aaboud, M.; Aad, G.; Abbott, B.; Abdinov, O.;... Franklin, M.;... Huth, J.;... Morii, M.;... and 2884 coauthors
Publication:
Physical Review D, Volume 98, Issue 9, id.092005 (PhRvD Homepage)
Publication Date:
11/2018
Origin:
APS
Abstract Copyright:
2018: CERN
DOI:
10.1103/PhysRevD.98.092005
Bibliographic Code:
2018PhRvD..98i2005A

Abstract

A search is presented for the pair production of heavy vectorlike quarks, T T ¯ or B B ¯, that decay into final states with jets and no reconstructed leptons. Jets in the final state are classified using a deep neural network as arising from hadronically decaying W /Z bosons, Higgs bosons, top quarks, or background. The analysis uses data from the ATLAS experiment corresponding to 36.1 fb-1 of proton-proton collisions with a center-of-mass energy of √{s }=13 TeV delivered by the Large Hadron Collider in 2015 and 2016. No significant deviation from the Standard Model expectation is observed. Results are interpreted assuming the vectorlike quarks decay into a Standard Model boson and a third-generation-quark, T →W b ,H t ,Z t or B →W t ,H b ,Z b , for a variety of branching ratios. At 95% confidence level, the observed (expected) lower limit on the vectorlike B -quark mass for a weak-isospin doublet (B , Y ) is 950 (890) GeV, and the lower limits on the masses for the pure decays B →H b and T →H t , where these results are strongest, are 1010 (970) GeV and 1010 (1010) GeV, respectively.

 

Title:
Search for lepton-flavor violation in different-flavor, high-mass final states in p p collisions at √{s }=13 TeV with the ATLAS detector
Authors:
Aaboud, M.; Aad, G.; Abbott, B.; Abdinov, O.;... Franklin, M.;... Huth, J.;... Morii, M.;... and 2912 coauthors
Publication:
Physical Review D, Volume 98, Issue 9, id.092008 (PhRvD Homepage)
Publication Date:
11/2018
Origin:
APS
Abstract Copyright:
2018: CERN
DOI:
10.1103/PhysRevD.98.092008
Bibliographic Code:
2018PhRvD..98i2008A

Abstract

A search is performed for a heavy particle decaying into different-flavor, dilepton pairs (e μ , e τ or μ τ ), using 36.1 fb-1 of proton-proton collision data at √{s }=13 TeV collected in 2015-2016 by the ATLAS detector at the Large Hadron Collider. No excesses over the Standard Model predictions are observed. Bayesian lower limits at the 95% credibility level are placed on the mass of a Z' boson, the mass of a supersymmetric τ -sneutrino, and on the threshold mass for quantum black-hole production. For the Z' and sneutrino models, upper cross-section limits are converted to upper limits on couplings, which are compared with similar limits from low-energy experiments and which are more stringent for the e τ and μ τ modes.

 

Title:
Search for lepton-flavor-violating decays of the Z boson into a τ lepton and a light lepton with the ATLAS detector
Authors:
Aaboud, M.; Aad, G.; Abbott, B.; Abdinov, O.;... Franklin, M.;... Huth, J.;... Morii, M.;... and 2914 coauthors
Publication:
Physical Review D, Volume 98, Issue 9, id.092010 (PhRvD Homepage)
Publication Date:
11/2018
Origin:
APS
Abstract Copyright:
2018: CERN
DOI:
10.1103/PhysRevD.98.092010
Bibliographic Code:
2018PhRvD..98i2010A

Abstract

Direct searches for lepton flavor violation in decays of the Z boson with the ATLAS detector at the LHC are presented. Decays of the Z boson into an electron or muon and a hadronically decaying τ lepton are considered. The searches are based on a data sample of proton-proton collisions collected by the ATLAS detector in 2015 and 2016, corresponding to an integrated luminosity of 36.1 fb-1 at a center-of-mass energy of √{s }=13 TeV . No statistically significant excess of events above the expected background is observed, and upper limits on the branching ratios of lepton-flavor-violating decays are set at the 95% confidence level: B (Z →e τ )<5.8 ×10-5 and B (Z →μ τ )<2.4 ×10-5. This is the first limit on B (Z →e τ ) with ATLAS data. The upper limit on B (Z →μ τ ) is combined with a previous ATLAS result based on 20.3 fb-1 of proton-proton collision data at a center-of-mass energy of √{s }=8 TeV and the combined upper limit at 95% confidence level is B (Z →μ τ )<1.3 ×10-5.

 

Title:
Search for chargino-neutralino production using recursive jigsaw reconstruction in final states with two or three charged leptons in proton-proton collisions at √{s }=13 TeV with the ATLAS detector
Authors:
Aaboud, M.; Aad, G.; Abbott, B.; Abdinov, O.;... Franklin, M.;... Huth, J.;... Morii, M.;... and 2909 coauthors
Publication:
Physical Review D, Volume 98, Issue 9, id.092012 (PhRvD Homepage)
Publication Date:
11/2018
Origin:
APS
Abstract Copyright:
2018: CERN
DOI:
10.1103/PhysRevD.98.092012
Bibliographic Code:
2018PhRvD..98i2012A

Abstract

A search for electroweak production of supersymmetric particles is performed in two-lepton and three-lepton final states using recursive jigsaw reconstruction, a technique that assigns reconstructed objects to the most probable hemispheres of the decay trees, allowing one to construct tailored kinematic variables to separate the signal and background. The search uses data collected in 2015 and 2016 by the ATLAS experiment in √{s }=13 TeV proton-proton collisions at the CERN Large Hadron Collider corresponding to an integrated luminosity of 36.1 fb-1. Chargino-neutralino pair production, with decays via W /Z bosons, is studied in final states involving leptons and jets and missing transverse momentum for scenarios with large and intermediate mass splittings between the parent particle and lightest supersymmetric particle, as well as for the scenario where this mass splitting is close to the mass of the Z boson. The latter case is challenging since the vector bosons are produced with kinematic properties that are similar to those in Standard Model processes. Results are found to be compatible with the Standard Model expectations in the signal regions targeting large and intermediate mass splittings, and chargino-neutralino masses up to 600 GeV are excluded at 95% confidence level for a massless lightest supersymmetric particle. Excesses of data above the expected background are found in the signal regions targeting low mass splittings, and the largest local excess amounts to 3.0 standard deviations.

 

Title:
Gravitational lensing and the power spectrum of dark matter substructure: Insights from the ETHOS N -body simulations
Authors:
Díaz Rivero, Ana; Dvorkin, Cora; Cyr-Racine, Francis-Yan; Zavala, Jesús; Vogelsberger, Mark
Publication:
Physical Review D, Volume 98, Issue 10, id.103517 (PhRvD Homepage)
Publication Date:
11/2018
Origin:
APS
Abstract Copyright:
2018: American Physical Society
DOI:
10.1103/PhysRevD.98.103517
Bibliographic Code:
2018PhRvD..98j3517D

Abstract

Strong gravitational lensing has been identified as a promising astrophysical probe to study the particle nature of dark matter. In this paper we present a detailed study of the power spectrum of the projected mass density (convergence) field of substructure in a Milky Way-sized halo. This power spectrum has been suggested as a key observable that can be extracted from strongly-lensed images and yield important clues about the matter distribution within the lens galaxy. We use two different N -body simulations from the ETHOS framework: one with cold dark matter and another with self-interacting dark matter and a cutoff in the initial power spectrum. Despite earlier works that identified k ≳100 kpc-1 as the most promising scales to learn about the particle nature of dark matter we find that even at lower wave numbers—which are actually within reach of observations in the near future—we can gain important information about dark matter. Comparing the amplitude and slope of the power spectrum on scales 0.1 ≲k /kpc-1≲10 from lenses at different redshifts can help us distinguish between cold dark matter and other exotic dark matter scenarios that alter the abundance and central densities of subhalos. Furthermore, by considering the contribution of different mass bins to the power spectrum we find that subhalos in the mass range 1 07-108 M are on average the largest contributors to the power spectrum signal on scales 2 ≲k /kpc-1≲15 , despite the numerous subhalos with masses >108 M in a typical lens galaxy. Finally, by comparing the power spectra obtained from the subhalo catalogs to those from the particle data in the simulation snapshots we find that the seemingly-too-simple halo model is in fact a fairly good approximation to the much more complex array of substructure in the lens.

 

Title:
Search for Resonant and Nonresonant Higgs Boson Pair Production in the b b ¯τ+τ- Decay Channel in p p Collisions at √{s }=13 TeV with the ATLAS Detector
Authors:
Aaboud, M.; Aad, G.; Abbott, B.; Abdinov, O.;... Franklin, M.;... Huth, J.;... Morii, M.;... and 2918 coauthors
Publication:
Physical Review Letters, Volume 121, Issue 19, id.191801 (PhRvL Homepage)
Publication Date:
11/2018
Origin:
APS
Abstract Copyright:
2018: CERN
DOI:
10.1103/PhysRevLett.121.191801
Bibliographic Code:
2018PhRvL.121s1801A

Abstract

A search for resonant and nonresonant pair production of Higgs bosons in the b b ¯τ+τ- final state is presented. The search uses 36.1 fb-1 of p p collision data with √{s }=13 TeV recorded by the ATLAS experiment at the LHC in 2015 and 2016. Decays of the τ -lepton pairs with at least one τ lepton decaying to final states with hadrons and a neutrino are considered. No significant excess above the expected background is observed in the data. The cross-section times branching ratio for nonresonant Higgs boson pair production is constrained to be less than 30.9 fb, 12.7 times the standard model expectation, at 95% confidence level. The data are also analyzed to probe resonant Higgs boson pair production, constraining a model with an extended Higgs sector based on two doublets and a Randall-Sundrum bulk graviton model. Upper limits are placed on the resonant Higgs boson pair production cross-section times branching ratio, excluding resonances X in the mass range 305 GeV <mX<402 GeV in the simplified hMSSM minimal supersymmetric model for tan β =2 and excluding bulk Randall-Sundrum gravitons GKK in the mass range 325 GeV <mGKK<885 GeV for k /M¯ Pl=1.

 

Title:
Combination of the Searches for Pair-Produced Vectorlike Partners of the Third-Generation Quarks at √{s }=13 TeV with the ATLAS Detector
Authors:
Aaboud, M.; Aad, G.; Abbott, B.; Abdinov, O.;... Franklin, M.;... Huth, J.;... Morii, M.;... and 2923 coauthors
Publication:
Physical Review Letters, Volume 121, Issue 21, id.211801 (PhRvL Homepage)
Publication Date:
11/2018
Origin:
APS
Abstract Copyright:
2018: CERN
DOI:
10.1103/PhysRevLett.121.211801
Bibliographic Code:
2018PhRvL.121u1801A

Abstract

A combination of the searches for pair-produced vectorlike partners of the top and bottom quarks in various decay channels (T →Z t /W b /H t , B →Z b /W t /H b ) is performed using 36.1 fb-1 of p p collision data at √{s }=13 TeV with the ATLAS detector at the Large Hadron Collider. The observed data are found to be in good agreement with the standard model background prediction in all individual searches. Therefore, combined 95% confidence-level upper limits are set on the production cross section for a range of vectorlike quark scenarios, significantly improving upon the reach of the individual searches. Model-independent limits are set assuming the vectorlike quarks decay to standard model particles. A singlet T is excluded for masses below 1.31 TeV and a singlet B is excluded for masses below 1.22 TeV. Assuming a weak isospin (T ,B ) doublet and |VT b|≪|Vt B|, T and B masses below 1.37 TeV are excluded.

 

Title:
Observation of Centrality-Dependent Acoplanarity for Muon Pairs Produced via Two-Photon Scattering in Pb +Pb Collisions at √{sN N }=5.02 TeV with the ATLAS Detector
Authors:
Aaboud, M.; Aad, G.; Abbott, B.; Abdinov, O.;... Franklin, M.;... Huth, J.;... Morii, M.;... and 2910 coauthors
Publication:
Physical Review Letters, Volume 121, Issue 21, id.212301 (PhRvL Homepage)
Publication Date:
11/2018
Origin:
APS
Abstract Copyright:
2018: CERN
DOI:
10.1103/PhysRevLett.121.212301
Bibliographic Code:
2018PhRvL.121u2301A

Abstract

This Letter presents a measurement of γ γ →μ+μ- production in Pb +Pb collisions recorded by the ATLAS detector at the Large Hadron Collider at √{sNN}=5.02 TeV with an integrated luminosity of 0.49 nb-1. The azimuthal angle and transverse momentum correlations between the muons are measured as a function of collision centrality. The muon pairs are produced from γ γ through the interaction of the large electromagnetic fields of the nuclei. The contribution from background sources of muon pairs is removed using a template fit method. In peripheral collisions, the muons exhibit a strong back-to-back correlation consistent with previous measurements of muon pair production in ultraperipheral collisions. The angular correlations are observed to broaden significantly in central collisions. The modifications are qualitatively consistent with rescattering of the muons while passing through the hot matter produced in the collision.

 

Title:
3D Magneto-Optical Trap of Yttrium Monoxide
Authors:
Collopy, Alejandra L.; Ding, Shiqian; Wu, Yewei; Finneran, Ian A.; Anderegg, Loïc; Augenbraun, Benjamin L.; Doyle, John M.; Ye, Jun
Affiliation:
AA(JILA, National Institute of Standards and Technology and Department of Physics, University of Colorado, Boulder, Colorado 80309, USA), AB(JILA, National Institute of Standards and Technology and Department of Physics, University of Colorado, Boulder, Colorado 80309, USA), AC(JILA, National Institute of Standards and Technology and Department of Physics, University of Colorado, Boulder, Colorado 80309, USA), AD(JILA, National Institute of Standards and Technology and Department of Physics, University of Colorado, Boulder, Colorado 80309, USA), AE(Department of Physics and Center for Ultracold Atoms, Harvard University, Cambridge, Massachusetts 02138, USA), AF(Department of Physics and Center for Ultracold Atoms, Harvard University, Cambridge, Massachusetts 02138, USA), AG(Department of Physics and Center for Ultracold Atoms, Harvard University, Cambridge, Massachusetts 02138, USA), AH(JILA, National Institute of Standards and Technology and Department of Physics, University of Colorado, Boulder, Colorado 80309, USA)
Publication:
Physical Review Letters, Volume 121, Issue 21, id.213201 (PhRvL Homepage)
Publication Date:
11/2018
Origin:
APS
Abstract Copyright:
2018: American Physical Society
DOI:
10.1103/PhysRevLett.121.213201
Bibliographic Code:
2018PhRvL.121u3201C

Abstract

We report three-dimensional trapping of an oxide molecule (YO), using a radio-frequency magneto-optical trap (MOT). The total number of molecules trapped is ˜1.5 ×104 , with a temperature of 4.1(5) mK. This diversifies the frontier of molecules that are laser coolable and paves the way for the second-stage narrow-line cooling in this molecule to the microkelvin regime. Futhermore, the new challenges of creating a 3D MOT of YO resolved here indicate that MOTs of more complex nonlinear molecules should be feasible as well.

 

Title:
Constraints on Primordial Gravitational Waves Using Planck, WMAP, and New BICEP2/Keck Observations through the 2015 Season
Authors:
BICEP2 Collaboration; Keck Array Collaboration; Ade, P. A. R.; Ahmed, Z.; Aikin, R. W.;... Dvorkin, C.;... Kovac, J. M.;... and 73 coauthors
Publication:
Physical Review Letters, Volume 121, Issue 22, id.221301 (PhRvL Homepage)
Publication Date:
11/2018
Origin:
APS
Abstract Copyright:
2018: American Physical Society
DOI:
10.1103/PhysRevLett.121.221301
Bibliographic Code:
2018PhRvL.121v1301B

Abstract

We present results from an analysis of all data taken by the bicep2/Keck CMB polarization experiments up to and including the 2015 observing season. This includes the first Keck Array observations at 220 GHz and additional observations at 95 and 150 GHz. The Q and U maps reach depths of 5.2, 2.9, and 26 μ KCMB arcmin at 95, 150, and 220 GHz, respectively, over an effective area of ≈400 square degrees. The 220 GHz maps achieve a signal to noise on polarized dust emission approximately equal to that of Planck at 353 GHz. We take auto and cross spectra between these maps and publicly available WMAP and Planck maps at frequencies from 23 to 353 GHz. We evaluate the joint likelihood of the spectra versus a multicomponent model of lensed-Λ CDM +r +dust+synchrotron+noise . The foreground model has seven parameters, and we impose priors on some of these using external information from Planck and WMAP derived from larger regions of sky. The model is shown to be an adequate description of the data at the current noise levels. The likelihood analysis yields the constraint r0.05<0.07 at 95% confidence, which tightens to r0.05<0.06 in conjunction with Planck temperature measurements and other data. The lensing signal is detected at 8.8 σ significance. Running a maximum likelihood search on simulations we obtain unbiased results and find that σ (r )=0.020 . These are the strongest constraints to date on primordial gravitational waves.

 

Title:
Tuning Methods for Semiconductor Spin Qubits
Authors:
Botzem, Tim; Shulman, Michael D.; Foletti, Sandra; Harvey, Shannon P.; Dial, Oliver E.; Bethke, Patrick; Cerfontaine, Pascal; McNeil, Robert P. G.; Mahalu, Diana; Umansky, Vladimir; Ludwig, Arne; Wieck, Andreas; Schuh, Dieter; Bougeard, Dominique; Yacoby, Amir; Bluhm, Hendrik
Publication:
Physical Review Applied, Volume 10, Issue 5, id.054026
Publication Date:
11/2018
Origin:
APS
Abstract Copyright:
2018: American Physical Society
DOI:
10.1103/PhysRevApplied.10.054026
Bibliographic Code:
2018PhRvP..10e4026B

Abstract

We present efficient methods to reliably characterize and tune gate-defined semiconductor spin qubits. Our methods are developed for double quantum dots in Ga As heterostructures, but they can easily be adapted to other quantum-dot-based qubit systems. These tuning procedures include the characterization of the interdot tunnel coupling, the tunnel coupling to the surrounding leads, and the identification of various fast initialization points for the operation of the qubit. Since semiconductor-based spin qubits are compatible with standard semiconductor process technology and hence promise good prospects of scalability, the challenge of efficiently tuning the dot's parameters will only grow in the near future, once the multiqubit stage is reached. With the anticipation of being used as the basis for future automated tuning protocols, all measurements presented here are fast-to-execute and easy-to-analyze characterization methods. They result in quantitative measures of the relevant qubit parameters within a couple of seconds and require almost no human interference.

 

Title:
Thermal characterization of gallium oxide Schottky barrier diodes
Authors:
Chatterjee, Bikramjit; Jayawardena, Asanka; Heller, Eric; Snyder, David W.; Dhar, Sarit; Choi, Sukwon
Publication:
Review of Scientific Instruments, Volume 89, Issue 11, id.114903 (RScI Homepage)
Publication Date:
11/2018
Origin:
AIP
Abstract Copyright:
2018: Author(s)
DOI:
10.1063/1.5053621
Bibliographic Code:
2018RScI...89k4903C

Abstract

The higher critical electric field of β-gallium oxide (Ga2O3) gives promise to the development of next generation power electronic devices with improved size, weight, power, and efficiency over current state-of-the-art wide bandgap devices based on 4H-silicon carbide (SiC) and gallium nitride (GaN). However, it is expected that Ga2O3 devices will encounter serious thermal issues due to the poor thermal conductivity of the material. In this work, self-heating in Ga2O3 Schottky barrier diodes under different regimes of the diode operation was investigated using diverse optical thermography techniques including thermoreflectance thermal imaging, micro-Raman thermography, and infrared thermal microscopy. 3D coupled electro-thermal modeling was used to validate experimental results and to understand the mechanism of heat generation for the diode structures. Measured top-side and cross-sectional temperature fields suggest that device and circuit engineers should account for the concentrated heat generation that occurs near the anode/Ga2O3 interface and/or the lightly doped drift layer under both forward and high voltage reverse bias conditions. Results of this study suggest that electro-thermal co-design techniques and top-side thermal management solutions are necessary to exploit the full potential of the Ga2O3 material system.

 

Title:
Photon-mediated interactions between quantum emitters in a diamond nanocavity
Authors:
Evans, R. E.; Bhaskar, M. K.; Sukachev, D. D.; Nguyen, C. T.; Sipahigil, A.; Burek, M. J.; Machielse, B.; Zhang, G. H.; Zibrov, A. S.; Bielejec, E.; Park, H.; Lončar, M.; Lukin, M. D.
Publication:
Science, Volume 362, Issue 6415, pp. 662-665 (2018). (Sci Homepage)
Publication Date:
11/2018
Category:
PHYSICS
Origin:
SCIENCE
Abstract Copyright:
(c) 2018: Science
DOI:
10.1126/science.aau4691
Bibliographic Code:
2018Sci...362..662E

Abstract

Photon-mediated interactions between quantum systems are essential for realizing quantum networks and scalable quantum information processing. We demonstrate such interactions between pairs of silicon-vacancy (SiV) color centers coupled to a diamond nanophotonic cavity. When the optical transitions of the two color centers are tuned into resonance, the coupling to the common cavity mode results in a coherent interaction between them, leading to spectrally resolved superradiant and subradiant states. We use the electronic spin degrees of freedom of the SiV centers to control these optically mediated interactions. Such controlled interactions will be crucial in developing cavity-mediated quantum gates between spin qubits and for realizing scalable quantum network nodes.

 

Title:
Mechanics of biomimetic 4D printed structures
Authors:
van Rees, Wim M.; Matsumoto, Elisabetta A.; Gladman, A. Sydney; Lewis, Jennifer A.; Mahadevan, L.
Publication:
Soft Matter, vol. 14, issue 43, pp. 8771-8779
Publication Date:
11/2018
Origin:
CROSSREF
DOI:
10.1039/C8SM00990B
Bibliographic Code:
2018SMat...14.8771V

Abstract

Not Available

 

Title:
Mapping Distances across the Perseus Molecular Cloud Using CO Observations, Stellar Photometry, and Gaia DR2 Parallax Measurements
Authors:
Zucker, Catherine; Schlafly, Edward F.; Speagle, Joshua S.; Green, Gregory M.; Portillo, Stephen K. N.; Finkbeiner, Douglas P.; Goodman, Alyssa A.
Publication:
The Astrophysical Journal, Volume 869, Issue 1, article id. 83, 27 pp. (2018). (ApJ Homepage)
Publication Date:
12/2018
Origin:
IOP
Astronomy Keywords:
dust, extinction, ISM: clouds, methods: statistical
DOI:
10.3847/1538-4357/aae97c
Bibliographic Code:
2018ApJ...869...83Z

Abstract

We present a new technique to determine distances to major star-forming regions across the Perseus Molecular Cloud, using a combination of stellar photometry, astrometric data, and 12CO spectral-line maps. Incorporating the Gaia DR2 parallax measurements when available, we start by inferring the distance and reddening to stars from their Pan-STARRS1 and Two Micron All Sky Survey photometry, based on a technique presented by Green et al. and implemented in their 3D “Bayestar” dust map of three-quarters of the sky. We then refine their technique by using the velocity slices of a CO spectral cube as dust templates and modeling the cumulative distribution of dust along the line of sight toward these stars as a linear combination of the emission in the slices. Using a nested sampling algorithm, we fit these per-star distance–reddening measurements to find the distances to the CO velocity slices toward each star-forming region. This results in distance estimates explicitly tied to the velocity structure of the molecular gas. We determine distances to the B5, IC 348, B1, NGC 1333, L1448, and L1451 star-forming regions and find that individual clouds are located between ≈275 and 300 pc, with typical combined uncertainties of ≈5%. We find that the velocity gradient across Perseus corresponds to a distance gradient of about 25 pc, with the eastern portion of the cloud farther away than the western portion. We determine an average distance to the complex of 294 ± 17 pc, about 60 pc further than the distance derived to the western portion of the cloud using parallax measurements of water masers associated with young stellar objects. The method we present is not limited to the Perseus Complex, but may be applied anywhere on the sky with adequate CO data in the pursuit of more accurate 3D maps of molecular clouds in the solar neighborhood and beyond.

 


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