Faculty Publications: January, 2015

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.

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Title:
The Fermi Bubbles
Authors:
Finkbeiner, Douglas P.
Publication:
American Astronomical Society, AAS Meeting #225, #235.01
Publication Date:
01/2015
Origin:
AAS
Abstract Copyright:
(c) 2015: American Astronomical Society
Bibliographic Code:
2015AAS...22523501F

Abstract

The Fermi Bubbles are a pair of giant lobes at the heart of the Milky Way, extending roughly 50 degrees north and south of the Galactic Center, and emitting photons with energies up to 100 GeV. This previously unknown structure could be evidence for past activity of the central supermassive black hole, or enhanced star formation towards the inner Galaxy. We will describe the path to discovery of the Bubbles in multiwavelength data, from the first hints in microwave radiation measured by WMAP and X-rays from ROSAT, to the unveiling of their shape and spectrum using public gamma-ray data from the Fermi Gamma-ray Space Telescope, to more recent measurements by Planck and XMM-Newton. We will outline the current state of knowledge of the Bubbles' spectrum, morphology and internal structure, and discuss theoretical proposals and numerical simulations for their nature and origin.

 

Title:
GeV excess electrons upscattering the CMB: a possible resolution to the "Photon Underproduction Crisis"
Authors:
Daylan, Tansu; Portillo, Stephen K. N.; Finkbeiner, Douglas P.
Publication:
American Astronomical Society, AAS Meeting #225, #255.19
Publication Date:
01/2015
Origin:
AAS
Abstract Copyright:
(c) 2015: American Astronomical Society
Bibliographic Code:
2015AAS...22525519D

Abstract

Recently a gamma-ray excess has been identified in the inner Milky Way, which may be associated with the final state photon shower following DM annihilation to standard model final states. In this scenario ~ GeV electrons are also produced and, given their long energy loss timescale (~ Gyr), they can diffuse and escape the galaxy before losing too much energy. If such an electron population exists in the IGM, one observable consequence would be inverse Compton scattering on the CMB, which would produce UV photons that can efficiently ionize the IGM. This may be a possible resolution to the "Photon Underproduction Crisis", recently pointed out by Kollmeier et al. (2014). Regardless of the relevance to this crisis, the existence of a ~ GeV electron population in the IGM can put constraints on DM annihilation parameters considering the known X-ray backgrounds.

 

Title:
A 100-3000 GHz model of thermal dust emission observed by Planck, DIRBE and IRAS
Authors:
Meisner, Aaron M.; Finkbeiner, Douglas P.
Publication:
American Astronomical Society, AAS Meeting #225, #256.14
Publication Date:
01/2015
Origin:
AAS
Abstract Copyright:
(c) 2015: American Astronomical Society
Bibliographic Code:
2015AAS...22525614M

Abstract

We apply the Finkbeiner et al. (1999) two-component thermal dust emission model to the Planck HFI maps. This parametrization of the far-infrared dust spectrum as the sum of two modified blackbodies serves as an important alternative to the commonly adopted single modified blackbody (MBB) dust emission model. Analyzing the joint Planck/DIRBE dust spectrum, we show that two-component models provide a better fit to the 100-3000 GHz emission than do single-MBB models, though by a lesser margin than found by Finkbeiner et al. (1999) based on FIRAS and DIRBE. We also derive full-sky 6.1' resolution maps of dust optical depth and temperature by fitting the two-component model to Planck 217-857 GHz along with DIRBE/IRAS 100mum data. Because our two-component model matches the dust spectrum near its peak, accounts for the spectrum's flattening at millimeter wavelengths, and specifies dust temperature at 6.1' FWHM, our model provides reliable, high-resolution thermal dust emission foreground predictions from 100 to 3000 GHz. We find that, in diffuse sky regions, our two-component 100-217 GHz predictions are on average accurate to within 2.2%, while extrapolating the Planck Collaboration (2013) single-MBB model systematically underpredicts emission by 18.8% at 100 GHz, 12.6% at 143 GHz and 7.9% at 217 GHz. We calibrate our two-component optical depth to reddening, and compare with reddening estimates based on stellar spectra. We find the dominant systematic problems in our temperature/reddening maps to be zodiacal light on large angular scales and the cosmic infrared background anistropy on small angular scales. We have recently released maps and associated software utilities for obtaining thermal dust emission and reddening predictions using our Planck-based two-component model.

 

Title:
A Generalized Method for Measuring RV in the Milky Way
Authors:
Lee, Albert; Green, Gregory; Ford Schlafly, Edward; Meisner, Aaron M.; Finkbeiner, Douglas P.
Publication:
American Astronomical Society, AAS Meeting #225, #256.16
Publication Date:
01/2015
Origin:
AAS
Abstract Copyright:
(c) 2015: American Astronomical Society
Bibliographic Code:
2015AAS...22525616L

Abstract

We present a simple but effective technique for measuring angular variation in RV across the sky. We divide stars from the Pan-STARRS1 catalog into Healpix pixels and determine the posterior distribution of reddening and RV for each pixel using a Metropolis-Hastings Monte Carlo. We find some agreement with previous high-precision photometric studies. Since current studies of RV are limited to isolated clouds, we hope to develop a systematic method for comparing RV values for the majority of observable dust.

 

Title:
3D Dust Mapping Reveals that Orion Forms Part of a Large Ring of Dust
Authors:
Ford Schlafly, Edward; Green, Gregory; Finkbeiner, Douglas P.; Rix, Hans-Walter
Publication:
American Astronomical Society, AAS Meeting #225, #256.18
Publication Date:
01/2015
Origin:
AAS
Abstract Copyright:
(c) 2015: American Astronomical Society
Bibliographic Code:
2015AAS...22525618F

Abstract

The Orion Molecular Complex is the nearest site of ongoing high-mass star formation, making it one of the most extensively studied molecular complexes in the Galaxy. We have developed a new technique for mapping the 3D distribution of dust in the Galaxy using Pan-STARRS1 photometry. We isolate the dust at the distance to Orion using this technique, revealing a large (100 pc, 14° diameter), previously unrecognized ring of dust, which we term the "Orion dust ring." The ring includes Orion A and B, and is not coincident with current Halpha features. The circular morphology suggests formation as an ancient bubble in the interstellar medium, though we have not been able to conclusively identify the source of the bubble. This hint at the history of Orion may have important consequences for models of high-mass star formation and triggered star formation.

 

Title:
Milky Way Dust and Stars in 3D
Authors:
Green, Gregory; Ford Schlafly, Eddie; Finkbeiner, Douglas P.
Publication:
American Astronomical Society, AAS Meeting #225, #256.19
Publication Date:
01/2015
Origin:
AAS
Abstract Copyright:
(c) 2015: American Astronomical Society
Bibliographic Code:
2015AAS...22525619G

Abstract

We present a three-dimensional map of dust reddening, along with a catalog of stellar distances and properties, determined from Pan-STARRS 1 and 2MASS photometry. Our method uses stars as tracers of the dust column; by inferring distances and reddenings to a billion stars, we determine reddening as a function of distance across three quarters of the sky. Our map has a typical angular resolution of ~7', a distance resolution of ~25%, and saturates at about 1.5 mag in E(B-V). Inferred distances to a large number of clouds agree well with literature distances, and the projected two-dimensional reddening agrees well with maps based on far-infrared dust emission (e.g., SFD '98) away from the Galactic plane. We envision many uses for a 3D map of dust and stars, among them: investigating the structure of the Milky Way and its stellar streams, correctly de-reddening photometry for objects embedded in the plane of the Galaxy, distance determinations to objects of known reddening, and studying the structure of star-forming regions.

 

Title:
Sharper Fermi LAT Images
Authors:
Portillo, Stephen; Finkbeiner, Douglas P.
Publication:
American Astronomical Society, AAS Meeting #225, #336.00
Publication Date:
01/2015
Origin:
AAS
Abstract Copyright:
(c) 2015: American Astronomical Society
Bibliographic Code:
2015AAS...22533600P

Abstract

The Large Area Telescope on the Fermi Gamma-ray Space Telescope has a point spread function with large tails, consisting of events affected by tracker ineffiencies, inactive volumes, and hard scattering; these tails can make source confusion a limiting factor. The parameter CTBCORE, available in the publicly available Extended Fermi LAT data, estimates the quality of each event's direction reconstruction; by implementing a cut in this parameter, the tails of the point spread function can be suppressed at the cost of losing effective area. We implement cuts on CTBCORE and present updated instrument response functions derived from the Fermi LAT data itself, along with all-sky maps generated with these cuts. Having shown the effectiveness of these cuts, especially at low energies, we encourage their use in analyses where angular resolution is more important than Poisson noise.

 

Title:
The Dark Energy Spectroscopic Instrument (DESI): The NOAO DECam Legacy Imaging Survey and DESI Target Selection
Authors:
Schlegel, David J.; Blum, Robert D.; Castander, Francisco Javier; Dey, Arjun; Finkbeiner, Douglas P.; Foucaud, Sebastien; Honscheid, Klaus; James, David; Lang, Dustin; Levi, Michael; Moustakas, John; Myers, Adam D.; Newman, Jeffrey; Nord, Brian; Nugent, Peter E.; Patej, Anna; Reil, Kevin; Rudnick, Gregory; Rykoff, Eli S.; Ford Schlafly, Eddie; Stark, Casey; Valdes, Francisco; Walker, Alistair R.; Weaver, Benjamin; DECam Legacy Survey Collaboration
Publication:
American Astronomical Society, AAS Meeting #225, #336.07
Publication Date:
01/2015
Origin:
AAS
Abstract Copyright:
(c) 2015: American Astronomical Society
Bibliographic Code:
2015AAS...22533607S

Abstract

The DECam Legacy Survey will conduct a 3-band imaging survey of the Sloan Digital Sky Survey (SDSS) extragalactic footprint. The Dark Energy Camera (DECam) will be used to image the 6700 square degree footprint overlapping SDSS in the region -20 < Dec < +30 deg, to depths of g=24.7, r=23.9, z=23.0. The survey will be conducted from Fall 2014 through Spring 2017, with periodic data releases beginning in March 2015. These releases will include catalogs constructed with the Tractor-based multi-wavelength forced photometry applied to the DECam and WISE satellite data.The Dark Energy Spectroscopic Instrument (DESI) will observe 24 million galaxies and quasars in a 14,000 square degree extragalactic footprint. The targeting in that footprint will be provided by a combination of these DECam data, the MOSAIC camera on the Mayall 4-meter, and the 90Prime camera on the Bok Telescope.

 

Title:
Modeling Thermal Dust Emission with Two Components: Application to the Planck High Frequency Instrument Maps
Authors:
Meisner, Aaron M.; Finkbeiner, Douglas P.
Publication:
The Astrophysical Journal, Volume 798, Issue 2, article id. 88, 19 pp. (2015). (ApJ Homepage)
Publication Date:
01/2015
Origin:
IOP
Astronomy Keywords:
dust, extinction, infrared: ISM, submillimeter: ISM
DOI:
10.1088/0004-637X/798/2/88
Bibliographic Code:
2015ApJ...798...88M

Abstract

We apply the Finkbeiner et al. two-component thermal dust emission model to the Planck High Frequency Instrument maps. This parameterization of the far-infrared dust spectrum as the sum of two modified blackbodies (MBBs) serves as an important alternative to the commonly adopted single-MBB dust emission model. Analyzing the joint Planck/DIRBE dust spectrum, we show that two-component models provide a better fit to the 100-3000 GHz emission than do single-MBB models, though by a lesser margin than found by Finkbeiner et al. based on FIRAS and DIRBE. We also derive full-sky 6.'1 resolution maps of dust optical depth and temperature by fitting the two-component model to Planck 217-857 GHz along with DIRBE/IRAS 100 mum data. Because our two-component model matches the dust spectrum near its peak, accounts for the spectrum's flattening at millimeter wavelengths, and specifies dust temperature at 6.'1 FWHM, our model provides reliable, high-resolution thermal dust emission foreground predictions from 100 to 3000 GHz. We find that, in diffuse sky regions, our two-component 100-217 GHz predictions are on average accurate to within 2.2%, while extrapolating the Planck Collaboration et al. single-MBB model systematically underpredicts emission by 18.8% at 100 GHz, 12.6% at 143 GHz, and 7.9% at 217 GHz. We calibrate our two-component optical depth to reddening, and compare with reddening estimates based on stellar spectra. We find the dominant systematic problems in our temperature/reddening maps to be zodiacal light on large angular scales and the cosmic infrared background anisotropy on small angular scales.

 

Title:
Development of high frequency and wide bandwidth Johnson noise thermometry
Authors:
Crossno, Jesse; Liu, Xiaomeng; Ohki, Thomas A.; Kim, Philip; Fong, Kin Chung
Publication:
Applied Physics Letters, Volume 106, Issue 2, id.023121 (ApPhL Homepage)
Publication Date:
01/2015
Origin:
AIP
Abstract Copyright:
2015: AIP Publishing LLC
DOI:
10.1063/1.4905926
Bibliographic Code:
2015ApPhL.106b3121C

Abstract

We develop a high frequency, wide bandwidth radiometer operating at room temperature, which augments the traditional technique of Johnson noise thermometry for nanoscale thermal transport studies. Employing low noise amplifiers and an analog multiplier operating at 2 GHz, auto- and cross-correlated Johnson noise measurements are performed in the temperature range of 3 to 300 K, achieving a sensitivity of 5.5 mK (110 ppm) in 1 s of integration time. This setup allows us to measure the thermal conductance of a boron nitride encapsulated monolayer graphene device over a wide temperature range. Our data show a high power law (T ˜ 4) deviation from the Wiedemann-Franz law above T ˜ 100 K.

 

Title:
Heralded quantum gates with integrated error detection in optical cavitites
Authors:
Borregaard, J.; Kómár, P.; Kessler, E. M.; Sørensen, A. S.; Lukin, M. D.
Publication:
eprint arXiv:1501.00956
Publication Date:
01/2015
Origin:
ARXIV
Keywords:
Quantum Physics
Comment:
15 pages - first 5 pages is the primary article and the remaining 10 pages is the supplemental material
Bibliographic Code:
2015arXiv150100956B

Abstract

We propose and analyze heralded quantum gates between qubits in optical cavities. They employ an auxiliary qubit to report if a successful gate occurred. In this manner, the errors, which would have corrupted a deterministic gate, are converted into a non-unity probability of success: once successful the gate has a much higher fidelity than a similar deterministic gate. Specifically, we describe that a heralded , near-deterministic controlled phase gate (CZ-gate) with the conditional error arbitrarily close to zero and the success probability that approaches unity as the cooperativity of the system, C, becomes large. Furthermore, we describe an extension to near-deterministic N- qubit Toffoli gate with a favorable error scaling. These gates can be directly employed in quantum repeater networks to facilitate near-ideal entanglement swapping, thus greatly speeding up the entanglement distribution.

 

Title:
A quantum dimer model for the pseudogap metal
Authors:
Punk, Matthias; Allais, Andrea; Sachdev, Subir
Publication:
eprint arXiv:1501.00978
Publication Date:
01/2015
Origin:
ARXIV
Keywords:
Condensed Matter - Strongly Correlated Electrons, High Energy Physics - Theory
Comment:
5+7 pages, 14 figures
Bibliographic Code:
2015arXiv150100978P

Abstract

We propose a quantum dimer model for the metallic state of the hole-doped cuprates at low hole density, p. The Hilbert space is spanned by spinless, neutral, bosonic dimers and spin S=1/2, charge +e fermionic dimers. The model realizes a `fractionalized Fermi liquid' with no symmetry-breaking and small hole pocket Fermi surfaces enclosing a total area determined by p. Exact diagonalization on lattices of sizes up to 8x8 shows anisotropic quasiparticle residue around the pocket Fermi surfaces. We discuss the relationship to experiments.

 

Title:
Persistence of activity in noisy motor-filament assemblies
Authors:
Chelakkot, Raghunath; Gopinath, Arvind; Mahadevan, L.
Publication:
eprint arXiv:1501.02791
Publication Date:
01/2015
Origin:
ARXIV
Keywords:
Physics - Biological Physics, Condensed Matter - Soft Condensed Matter, Quantitative Biology - Subcellular Processes
Comment:
4 figures
Bibliographic Code:
2015arXiv150102791C

Abstract

Long, elastic filaments cross-linked and deformed by active molecular motors occur in various natural settings. The overall macroscopic mechanical response of such a composite network depends on the coupling between the active and the passive properties of the underlying constituents and nonlocal interactions between different parts of the composite. In a simple one dimensional system, using a mean field model, it has been shown that the combination of motor activity and finite filament extensibility yields a persistence length scale over which strain decays. Here we study a similar system, in the complementary limit of strong noise and moderate extensibility, using Brownian multi-particle collision dynamics-based numerical simulations that includes the coupling between motor kinetics and local filament extensibility. While the numerical model shows deviations from the mean field predictions due to the presence of strong active noise caused by the variations in individual motor activity, several qualitative features are still retained. Specifically, for fixed motor attachment and detachment rates, the decay is length is set by the ratio of the passive elasticity to the active shear resistance generated by attached motors. Our study generalizes the notion of persistence in passive thermal systems to actively driven systems with testable predictions.

 

Title:
Persistence of strain in motor-filament assemblies
Authors:
Gopinath, Arvind; Chelakkot, Raghunath; Mahadevan, L.
Publication:
eprint arXiv:1501.02842
Publication Date:
01/2015
Origin:
ARXIV
Keywords:
Physics - Biological Physics, Quantitative Biology - Subcellular Processes
Bibliographic Code:
2015arXiv150102842G

Abstract

Crosslinked semi-flexible and flexible filaments that are actively deformed by molecular motors occur in various natural settings, such as the ordered eukaryotic flagellum, and the disordered cytoskeleton. The deformation of these composite systems is driven by active motor forces and resisted by passive filament elasticity, and structural constraints due to permanent cross-links. Using a mean field theory for a one-dimensional ordered system, we show that the combination of motor activity and finite filament extensibility yields a characteristic persistence length scale over which active strain decays. This decay length is set by the ability of motors to respond to combination of the weak extensional elasticity, passive shear resistance and the viscoelastic properties of the motor assembly, and generalizes the notion of persistence in purely thermal filaments to active systems.

 

Title:
Rotational state microwave mixing for laser cooling of complex diatomic molecules
Authors:
Yeo, Mark; Hummon, Matthew T.; Collopy, Alejandra L.; Yan, Bo; Hemmerling, Boerge; Chae, Eunmi; Doyle, John M.; Ye, Jun
Publication:
eprint arXiv:1501.04683
Publication Date:
01/2015
Origin:
ARXIV
Keywords:
Physics - Atomic Physics
Comment:
5 pages, 4 figures
Bibliographic Code:
2015arXiv150104683Y

Abstract

We demonstrate the mixing of rotational states in the ground electronic state using microwave radiation to enhance optical cycling in the molecule yttrium (II) monoxide (YO). This mixing technique is used in conjunction with a frequency modulated and chirped continuous wave laser to slow longitudinally a cryogenic buffer gas beam of YO. We generate a measurable flux of YO below 10~m/s, directly loadable into a three-dimensional magneto-optical trap. This technique opens the door for laser cooling of molecules with more complex structure.

 

Title:
Spin-Polarized Quantum Well States on Bi$_{2-x}$Fe$_x$Se$_3$
Authors:
Yee, Michael M.; Zhu, Z.-H.; Soumyanarayanan, Anjan; He, Yang; Song, Can-Li; Pomjakushina, Ekaterina; Salman, Zaher; Kanigel, Amit; Segawa, Kouji; Ando, Yoichi; Hoffman, Jennifer E.
Publication:
eprint arXiv:1501.05598
Publication Date:
01/2015
Origin:
ARXIV
Keywords:
Condensed Matter - Materials Science, Condensed Matter - Mesoscale and Nanoscale Physics, Condensed Matter - Strongly Correlated Electrons
Comment:
5 pages, 4 figures
Bibliographic Code:
2015arXiv150105598Y

Abstract

Low temperature scanning tunneling microscopy is used to image the doped topological insulator Bi$_{2-x}$Fe$_x$Se$_3$. Interstitial Fe defects allow the detection of quasiparticle interference (QPI), and the reconstruction of the empty state band structure. Quantitative comparison between measured data and density functional theory calculations reveals the unexpected coexistence of quantum well states (QWS) with topological surface states (TSS) on the atomically clean surface of Bi$_{2-x}$Fe$_x$Se$_3$. Spectroscopic measurements quantify the breakdown of linear dispersion due to hexagonal warping. Nonetheless, both QWS and TSS remain spin-polarized and protected from backscattering to almost 1 eV above the Dirac point, suggesting their utility for spin-based applications.

 

Title:
Dynamical Stability of a Many-body Kapitza Pendulum
Authors:
Citro, Roberta; Dalla Torre, Emanuele G.; DÁlessio, Luca; Polkovnikov, Anatoli; Babadi, Mehrtash; Oka, Takashi; Demler, Eugene
Publication:
eprint arXiv:1501.05660
Publication Date:
01/2015
Origin:
ARXIV
Keywords:
Quantum Physics, Condensed Matter - Quantum Gases
Comment:
11 pages, 11 figures
Bibliographic Code:
2015arXiv150105660C

Abstract

We consider a many-body generalization of the Kapitza pendulum: the periodically-driven sine-Gordon model. We show that this interacting system is dynamically stable to periodic drives with finite frequency and amplitude. This finding is in contrast to the common belief that periodically-driven unbounded interacting systems should always tend to an absorbing infinite-temperature state. The transition to an unstable absorbing state is described by a change in the sign of the kinetic term in the effective Floquet Hamiltonian and controlled by the short-wavelength degrees of freedom. We investigate the stability phase diagram through an analytic high-frequency expansion, a self-consistent variational approach, and a numeric semiclassical calculations. Classical and quantum experiments are proposed to verify the validity of our results.

 

Title:
Extremal Bundles on Calabi-Yau Threefolds
Authors:
Gao, Peng; He, Yang-Hui; Yau, Shing-Tung
Publication:
Communications in Mathematical Physics, Online First
Publication Date:
01/2015
Origin:
SPRINGER
Abstract Copyright:
(c) 2015: Springer-Verlag Berlin Heidelberg
DOI:
10.1007/s00220-014-2271-y
Bibliographic Code:
2015CMaPh.tmp...19G

Abstract

We study constructions of stable holomorphic vector bundles on Calabi-Yau threefolds, especially those with exact anomaly cancellation which we call extremal. By going through the known databases we find that such examples are rare in general and can be ruled out for the spectral cover construction for all elliptic threefolds. We then introduce a general Hartshorne-Serre construction and use it to find extremal bundles of general ranks and study their stability, as well as computing their Chern numbers. Based on both existing and our new constructions, we revisit the DRY conjecture for the existence of stable sheaves on Calabi-threefolds, and provide theoretical and numerical evidence for its correctness. Our construction can be easily generalized to bundles with no extremal conditions imposed.

 

Title:
Jet energy measurement and its systematic uncertainty in proton-proton collisions at TeV with the ATLAS detector
Authors:
Aad, G.; Abajyan, T.; Abbott, B.; ... Barreiro Guimarães da Costa, J.;... Franklin, M.;... Huth, J.;... Morii, M.;... ; and 2927 coauthors
Publication:
The European Physical Journal C, Volume 75, article id. #17, 101 pp. (EPJC Homepage)
Publication Date:
01/2015
Origin:
SPRINGER
Abstract Copyright:
(c) 2015: CERN for the benefit of the ATLAS collaboration
DOI:
10.1140/epjc/s10052-014-3190-y
Bibliographic Code:
2015EPJC...75...17A

Abstract

The jet energy scale (JES) and its systematic uncertainty are determined for jets measured with the ATLAS detector using proton-proton collision data with a centre-of-mass energy of TeV corresponding to an integrated luminosity of . Jets are reconstructed from energy deposits forming topological clusters of calorimeter cells using the anti- algorithm with distance parameters or , and are calibrated using MC simulations. A residual JES correction is applied to account for differences between data and MC simulations. This correction and its systematic uncertainty are estimated using a combination of in situ techniques exploiting the transverse momentum balance between a jet and a reference object such as a photon or a boson, for and pseudorapidities . The effect of multiple proton-proton interactions is corrected for, and an uncertainty is evaluated using in situ techniques. The smallest JES uncertainty of less than 1 % is found in the central calorimeter region () for jets with . For central jets at lower , the uncertainty is about 3 %. A consistent JES estimate is found using measurements of the calorimeter response of single hadrons in proton-proton collisions and test-beam data, which also provide the estimate for TeV. The calibration of forward jets is derived from dijet balance measurements. The resulting uncertainty reaches its largest value of 6 % for low- jets at . Additional JES uncertainties due to specific event topologies, such as close-by jets or selections of event samples with an enhanced content of jets originating from light quarks or gluons, are also discussed. The magnitude of these uncertainties depends on the event sample used in a given physics analysis, but typically amounts to 0.5-3 %.

 

Title:
Measurement of the production and lepton charge asymmetry of bosons in Pb+Pb collisions at with the ATLAS detector
Authors:
Aad, G.; Abbott, B.; Abdallah, J.; ... Barreiro Guimarães da Costa, J.;... Franklin, M.;... Huth, J.;... Morii, M.;... ; and 2884 coauthors
Publication:
The European Physical Journal C, Volume 75, article id. #23, 30 pp. (EPJC Homepage)
Publication Date:
01/2015
Origin:
SPRINGER
Abstract Copyright:
(c) 2015: CERN for the benefit of the ATLAS collaboration
DOI:
10.1140/epjc/s10052-014-3231-6
Bibliographic Code:
2015EPJC...75...23A

Abstract

A measurement of boson production in lead-lead collisions at is presented. It is based on the analysis of data collected with the ATLAS detector at the LHC in 2011 corresponding to an integrated luminosity of 0.14 and 0.15 in the muon and electron decay channels, respectively. The differential production yields and lepton charge asymmetry are each measured as a function of the average number of participating nucleons and absolute pseudorapidity of the charged lepton. The results are compared to predictions based on next-to-leading-order QCD calculations. These measurements are, in principle, sensitive to possible nuclear modifications to the parton distribution functions and also provide information on scaling of boson production in multi-nucleon systems.

 

Title:
Quasinormal quantization in de Sitter spacetime
Authors:
Jafferis, Daniel L.; Lupsasca, Alexandru; Lysov, Vyacheslav; Ng, Gim Seng; Strominger, Andrew
Publication:
Journal of High Energy Physics, Volume 2015, article id. #4, 19 pp.
Publication Date:
01/2015
Origin:
SPRINGER
Keywords:
Classical Theories of Gravity, Conformal and W Symmetry, Space-Time Symmetries, AdS-CFT Correspondence
Abstract Copyright:
(c) 2015: The Author(s)
DOI:
10.1007/JHEP01(2015)004
Bibliographic Code:
2015JHEP...01..004J

Abstract

A scalar field in four-dimensional deSitter spacetime (dS4) has quasinormal modes which are singular on the past horizon of the south pole and decay exponentially towards the future. These are found to lie in two complex highest-weight representations of the dS4 isometry group SO(4, 1). The Klein-Gordon norm cannot be used for quantization of these modes because it diverges. However a modified `R-norm', which involves reflection across the equator of a spatial S 3 slice, is nonsingular. The quasinormal modes are shown to provide a complete orthogonal basis with respect to the R-norm. Adopting the associated R-adjoint effectively transforms SO(4, 1) to the symmetry group SO(3, 2) of a 2+1-dimensional CFT. It is further shown that the conventional Euclidean vacuum may be defined as the state annihilated by half of the quasinormal modes, and the Euclidean Green function obtained from a simple mode sum. Quasinormal quantization contrasts with some conventional approaches in that it maintains manifest dS-invariance through-out. The results are expected to generalize to other dimensions and spins.

 

Title:
Measurement of the production cross-section as a function of jet multiplicity and jet transverse momentum in 7 TeV proton-proton collisions with the ATLAS detector
Authors:
Aad, G.; Abbott, B.; Abdallah, J.;... Barreiro Guimarães da Costa, J.;... Franklin, M.;... Huth, J.;... Morii, M.;... ; and 2875 coauthors
Publication:
Journal of High Energy Physics, Volume 2015, article id. #20, 67 pp.
Publication Date:
01/2015
Origin:
SPRINGER
Keywords:
Hadron-Hadron Scattering
Abstract Copyright:
(c) 2015: The Author(s)
DOI:
10.1007/JHEP01(2015)020
Bibliographic Code:
2015JHEP...01..020A

Abstract

The production cross-section dependence on jet multiplicity and jet transverse momentum is reported for proton-proton collisions at a centre-of-mass energy of 7 TeV in the single-lepton channel. The data were collected with the ATLAS detector at the CERN Large Hadron Collider and comprise the full 2011 data sample corresponding to an integrated luminosity of 4.6 fb-1. Differential cross-sections are presented as a function of the jet multiplicity for up to eight jets using jet transverse momentum thresholds of 25, 40, 60, and 80 GeV, and as a function of jet transverse momentum up to the fifth jet. The results are shown after background subtraction and corrections for all known detector effects, within a kinematic range closely matched to the experimental acceptance. Several QCD-based Monte Carlo models are compared with the results. Sensitivity to the parton shower modelling is found at the higher jet multiplicities, at high transverse momentum of the leading jet and in the transverse momentum spectrum of the fifth leading jet. The MC@NLO+HERWIG MC is found to predict too few events at higher jet multiplicities. [Figure not available: see fulltext.]

 

Title:
Measurement of the W W + W Z cross section and limits on anomalous triple gauge couplings using final states with one lepton, missing transverse momentum, and two jets with the ATLAS detector at TeV
Authors:
Aad, G.; Abbott, B.; Abdallah, J.;... Barreiro Guimarães da Costa, J.;... Franklin, M.;... Huth, J.;... Morii, M.;... ; and 2875 coauthors
Publication:
Journal of High Energy Physics, Volume 2015, article id. #49, 42 pp.
Publication Date:
01/2015
Origin:
SPRINGER
Keywords:
Hadron-Hadron Scattering
Abstract Copyright:
(c) 2015: The Author(s)
DOI:
10.1007/JHEP01(2015)049
Bibliographic Code:
2015JHEP...01..049A

Abstract

The production of a W boson decaying to enu or munu in association with a W or Z boson decaying to two jets is studied using 4 .6 fb-1 of proton-proton collision data at TeV recorded with the ATLAS detector at the LHC. The combined WW + WZ cross section is measured with a significance of 3.4 sigma and is found to be 68±7 (stat .)±19 (syst .) pb, in agreement with the Standard Model expectation of 61 .1±2 .2 pb. The distribution of the transverse momentum of the dijet system is used to set limits on anomalous contributions to the triple gauge coupling vertices and on parameters of an effective-field-theory model. [Figure not available: see fulltext.]

 

Title:
Searches for heavy long-lived charged particles with the ATLAS detector in proton-proton collisions at TeV
Authors:
Aad, G.; Abbott, B.; Abdallah, J.;... Barreiro Guimarães da Costa, J.;... Franklin, M.;... Huth, J.;... Morii, M.;... ; and 2886 coauthors
Publication:
Journal of High Energy Physics, Volume 2015, article id. #68, 51 pp.
Publication Date:
01/2015
Origin:
SPRINGER
Keywords:
Hadron-Hadron Scattering
Abstract Copyright:
(c) 2015: The Author(s)
DOI:
10.1007/JHEP01(2015)068
Bibliographic Code:
2015JHEP...01..068A

Abstract

Searches for heavy long-lived charged particles are performed using a data sample of 19.1 fb-1 from proton-proton collisions at a centre-of-mass energy of TeV collected by the ATLAS detector at the Large Hadron Collider. No excess is observed above the estimated background and limits are placed on the mass of long-lived particles in various supersymmetric models. Long-lived tau sleptons in models with gauge-mediated symmetry breaking are excluded up to masses between 440 and 385 GeV for tan beta between 10 and 50, with a 290 GeV limit in the case where only direct tau slepton production is considered. In the context of simplified LeptoSUSY models, where sleptons are stable and have a mass of 300 GeV, squark and gluino masses are excluded up to a mass of 1500 and 1360 GeV, respectively. Directly produced charginos, in simplified models where they are nearly degenerate to the lightest neutralino, are excluded up to a mass of 620 GeV. R-hadrons, composites containing a gluino, bottom squark or top squark, are excluded up to a mass of 1270, 845 and 900 GeV, respectively, using the full detector; and up to a mass of 1260, 835 and 870 GeV using an approach disregarding information from the muon spectrometer. [Figure not available: see fulltext.]

 

Title:
Search for the decay of the Standard Model Higgs boson in associated ( W/Z) H production with the ATLAS detector
Authors:
Aad, G.; Abbott, B.; Abdallah, J.;... Barreiro Guimarães da Costa, J.;... Franklin, M.;... Huth, J.;... Morii, M.;... ; and 2885 coauthors
Publication:
Journal of High Energy Physics, Volume 2015, article id. #69, 89 pp.
Publication Date:
01/2015
Origin:
SPRINGER
Keywords:
Hadron-Hadron Scattering
Abstract Copyright:
(c) 2015: The Author(s)
DOI:
10.1007/JHEP01(2015)069
Bibliographic Code:
2015JHEP...01..069A

Abstract

A search for the decay of the Standard Model Higgs boson is performed with the ATLAS experiment using the full dataset recorded at the LHC in Run 1. The integrated luminosities used are 4.7 and 20.3 fb-1 from pp collisions at and 8 TeV, respectively. The processes considered are associated ( W/Z) H production, where W --> enu/munu, Z --> ee/mumu and Z --> nunu. The observed (expected) deviation from the background-only hypothesis corresponds to a significance of 1.4 (2.6) standard deviations and the ratio of the measured signal yield to the Standard Model expectation is found to be mu = 0 .52 ± 0 .32 (stat .) ± 0 .24 (syst .) for a Higgs boson mass of 125.36 GeV. The analysis procedure is validated by a measurement of the yield of ( W/Z) Z production with in the same final states as for the Higgs boson search, from which the ratio of the observed signal yield to the Standard Model expectation is found to be 0 .74 ± 0 .09 (stat .) ± 0 .14 (syst .). [Figure not available: see fulltext.]

 

Title:
Stabilizing the false vacuum: Mott skyrmions
Authors:
Kanász-Nagy, M.; Dóra, B.; Demler, E. A.; Zaránd, G.
Publication:
Nature Scientific Reports, Volume 5, id. 7692 (2015).
Publication Date:
01/2015
Origin:
NATURE
Abstract Copyright:
(c) 2015: Macmillan Publishers Limited. All rights reserved
DOI:
10.1038/srep07692
Bibliographic Code:
2015NatSR...5E7692K

Abstract

Topological excitations keep fascinating physicists since many decades. While individual vortices and solitons emerge and have been observed in many areas of physics, their most intriguing higher dimensional topological relatives, skyrmions (smooth, topologically stable textures) and magnetic monopoles emerging almost necessarily in any grand unified theory and responsible for charge quantization remained mostly elusive. Here we propose that loading a three-component nematic superfluid such as 23Na into a deep optical lattice and thereby creating an insulating core, one can create topologically stable skyrmion textures. The skyrmion's extreme stability and its compact geometry enable one to investigate the skyrmion's structure, and the interplay of topology and excitations in detail. In particular, the superfluid's excitation spectrum as well as the quantum numbers are demonstrated to change dramatically due to the skyrmion, and reflect the presence of a trapped monopole, as imposed by the skyrmion's topology.

 

Title:
Search for s-channel single top-quark production in proton-proton collisions at &surd;{ s} = 8 TeV with the ATLAS detector
Authors:
Aad, G.; Abbott, B.; Abdallah, J.;... Barreiro Guimarães da Costa, J.;... Franklin, M.;... Huth, J.;... Morii, M.;... ; and 2882 coauthors
Publication:
Physics Letters B, Volume 740, p. 118-136.
Publication Date:
01/2015
Origin:
ELSEVIER
Keywords:
ATLAS, Top-quark, Electroweak production, s-Channel
Abstract Copyright:
(c) 2015 The Authors
DOI:
10.1016/j.physletb.2014.11.042
Bibliographic Code:
2015PhLB..740..118A

Abstract

This Letter presents a search at the LHC for s-channel single top-quark production in proton-proton collisions at a centre-of-mass energy of 8 TeV. The analyzed data set was recorded by the ATLAS detector and corresponds to an integrated luminosity of 20.3 fb-1. Selected events contain one charged lepton, large missing transverse momentum and exactly two b-tagged jets. A multivariate event classifier based on boosted decision trees is developed to discriminate s-channel single top-quark events from the main background contributions. The signal extraction is based on a binned maximum-likelihood fit of the output classifier distribution. The analysis leads to an upper limit on the s-channel single top-quark production cross-section of 14.6 pb at the 95% confidence level. The fit gives a cross-section of sigmas = 5.0 ± 4.3 pb, consistent with the Standard Model expectation.

 

Title:
Search for the Xb and other hidden-beauty states in the pi+pi- Upsilon (1 S) channel at ATLAS
Authors:
Aad, G.; Abbott, B.; Abdallah, J.;... Barreiro Guimarães da Costa, J.;... Franklin, M.;... Huth, J.;... Morii, M.;... ; and 2891 coauthors
Publication:
Physics Letters B, Volume 740, p. 199-217.
Publication Date:
01/2015
Origin:
ELSEVIER
Abstract Copyright:
(c) 2015 The Authors
DOI:
10.1016/j.physletb.2014.11.055
Bibliographic Code:
2015PhLB..740..199A

Abstract

This Letter presents a search for a hidden-beauty counterpart of the X (3872) in the mass ranges of 10.05-10.31 GeV and 10.40-11.00 GeV, in the channel Xb -->pi+pi- Upsilon (1 S) (-->mu+mu-), using 16.2 fb-1 of &surd;{ s} = 8 TeVpp collision data collected by the ATLAS detector at the LHC. No evidence for new narrow states is found, and upper limits are set on the product of the Xb cross section and branching fraction, relative to those of the Upsilon (2S), at the 95% confidence level using the CLS approach. These limits range from 0.8% to 4.0%, depending on mass. For masses above 10.1 GeV, the expected upper limits from this analysis are the most restrictive to date. Searches for production of the Upsilon (13DJ), Upsilon (10 860), and Upsilon (11 020) states also reveal no significant signals.

 

Title:
Search for H --> gammagamma produced in association with top quarks and constraints on the Yukawa coupling between the top quark and the Higgs boson using data taken at 7 TeV and 8 TeV with the ATLAS detector
Authors:
Aad, G.; Abbott, B.; Abdallah, J.;... Barreiro Guimarães da Costa, J.;... Franklin, M.;... Huth, J.;... Morii, M.;... ; and 2889 coauthors
Publication:
Physics Letters B, Volume 740, p. 222-242.
Publication Date:
01/2015
Origin:
ELSEVIER
Keywords:
Higgs boson, Diphoton decay, t t bar H, Top quark, Yukawa coupling, tH
Abstract Copyright:
(c) 2015 The Authors
DOI:
10.1016/j.physletb.2014.11.049
Bibliographic Code:
2015PhLB..740..222A

Abstract

A search is performed for Higgs bosons produced in association with top quarks using the diphoton decay mode of the Higgs boson. Selection requirements are optimized separately for leptonic and fully hadronic final states from the top quark decays. The dataset used corresponds to an integrated luminosity of 4.5 fb-1 of proton-proton collisions at a center-of-mass energy of 7 TeV and 20.3 fb-1 at 8 TeV recorded by the ATLAS detector at the CERN Large Hadron Collider. No significant excess over the background prediction is observed and upper limits are set on the t t bar H production cross section. The observed exclusion upper limit at 95% confidence level is 6.7 times the predicted Standard Model cross section value. In addition, limits are set on the strength of the Yukawa coupling between the top quark and the Higgs boson, taking into account the dependence of the t t bar H and tH cross sections as well as the H --> gammagamma branching fraction on the Yukawa coupling. Lower and upper limits at 95% confidence level are set at -1.3 and +8.0 times the Yukawa coupling strength in the Standard Model.

 

Title:
Detecting Majorana modes in one-dimensional wires by charge sensing
Authors:
Ben-Shach, Gilad; Haim, Arbel; Appelbaum, Ian; Oreg, Yuval; Yacoby, Amir; Halperin, Bertrand I.
Publication:
Physical Review B, Volume 91, Issue 4, id.045403 (PhRvB Homepage)
Publication Date:
01/2015
Origin:
APS
PACS Keywords:
Mesoscopic and nanoscale systems, Quantum wires, Multilayers superlattices heterostructures
Abstract Copyright:
2015: American Physical Society
DOI:
10.1103/PhysRevB.91.045403
Bibliographic Code:
2015PhRvB..91d5403B

Abstract

The electron number parity of the ground state of a semiconductor nanowire proximity coupled to a bulk superconductor can alternate between the quantized values ±1 if parameters such as the wire length L , the chemical potential mu , or the magnetic field B are varied inside the topological superconductor phase. The parity jumps, which may be interpreted as changes in the occupancy of the fermion state formed from the pair of Majorana modes at opposite ends of the wire, are accompanied by jumps delta N in the charge of the nanowire, whose values decrease exponentially with the wire length. We study theoretically the dependence of delta N on system parameters, and compare the locations in the mu -B plane of parity jumps when the nanowire is or is not proximity coupled to a bulk superconductor. We show that, despite the fact that the wave functions of the Majorana modes are localized near the two ends of the wire, the charge-density jumps have spatial distributions that are essentially uniform along the wire length, being proportional to the product of the two Majorana wave functions. We explain how charge measurements, say by an external single-electron transistor, could reveal these effects. Whereas existing experimental methods require direct contact to the wire for tunneling measurements, charge sensing avoids this issue and provides an orthogonal measurement to confirm recent experimental developments. Furthermore, by comparing density of states measurements which show Majorana features at the wire ends with the uniformly distributed charge measurements, one can rule out alternative explanations for earlier results. We shed light on a parameter regime for these wire-superconductor hybrid systems, and propose a related experiment to measure spin density.

 

Title:
Atomistic mechanisms for bilayer growth of graphene on metal substrates
Authors:
Chen, Wei; Cui, Ping; Zhu, Wenguang; Kaxiras, Efthimios; Gao, Yanfei; Zhang, Zhenyu
Publication:
Physical Review B, Volume 91, Issue 4, id.045408 (PhRvB Homepage)
Publication Date:
01/2015
Origin:
APS
PACS Keywords:
Ab initio calculations of adsorbate structure and reactions, Nucleation and growth, Theory and models of film growth
Abstract Copyright:
2015: American Physical Society
DOI:
10.1103/PhysRevB.91.045408
Bibliographic Code:
2015PhRvB..91d5408C

Abstract

Epitaxial growth on metal substrates has been shown to be the most powerful approach in producing large-scale high-quality monolayer graphene, yet it remains a major challenge to realize uniform bilayer graphene growth. Here we carry out a comparative study of the atomistic mechanisms for bilayer graphene growth on the (111) surfaces of Cu and Ni, using multiscale approaches combining first-principles calculations and rate-equation analysis. We first show that the relatively weak graphene-Cu interaction enhances the lateral diffusion and effective nucleation of C atoms underneath the graphene island, thereby making it more feasible to grow bilayer graphene on Cu. In contrast, the stronger graphene-Ni interaction suppresses the lateral mobility and dimerization of C atoms underneath the graphene, making it unlikely to achieve controlled growth of bilayer graphene on Ni. We then determine the critical graphene size beyond which nucleation of the second layer will take place. Intriguingly, the critical size exhibits an effective inverse "Ehrlich-Schwoebel barrier" effect, becoming smaller for faster C migration from the Cu surface to the graphene-Cu interface sites across the graphene edge. These findings allow us to propose a novel alternating growth scheme to realize mass production of bilayer graphene.

 

Title:
Measurement of differential production cross sections for Z /gamma* bosons in association with jets in p p ¯ collisions at &surd;{s }=1.96 TeV
Authors:
Aaltonen, T.; Amerio, S.; Amidei, D.;... Franklin, M.;... Guimaraes da Costa, J.;... ; and 397 coauthors; CDF Collaboration
Publication:
Physical Review D, Volume 91, Issue 1, id.012002 (PhRvD Homepage)
Publication Date:
01/2015
Origin:
APS
PACS Keywords:
Jets in large-Q2 scattering, Experimental tests, Hadron-induced high- and super-high-energy interactions, Z bosons
Abstract Copyright:
2015: American Physical Society
DOI:
10.1103/PhysRevD.91.012002
Bibliographic Code:
2015PhRvD..91a2002A

Abstract

Differential cross sections for the production of Z bosons or off-shell photons gamma* in association with jets are measured in proton-antiproton collisions at center-of-mass energy &surd;{s }=1.96 TeV using the full data set collected with the Collider Detector at Fermilab in Tevatron run II and corresponding to 9.6 fb-1 of integrated luminosity. Results include first measurements at CDF of differential cross sections in events with a Z /gamma* boson and three or more jets, the inclusive cross section for production of Z /gamma* and four or more jets, and cross sections as functions of various angular observables in lower jet-multiplicity final states. Measured cross sections are compared to several theoretical predictions.

 

Title:
Study of B±,0-->J /psi K+K-K±,0 and search for B0-->J /psi varphi at BaBar
Authors:
Lees, J. P.; Poireau, V.; Tisserand, V.;... Morii, M.;... and 333 coauthors.
Publication:
Physical Review D, Volume 91, Issue 1, id.012003 (PhRvD Homepage)
Publication Date:
01/2015
Origin:
APS
PACS Keywords:
Decays of bottom mesons, Determination of Kobayashi-Maskawa matrix elements, Charge conjugation parity time reversal and other discrete symmetries
Abstract Copyright:
2015: American Physical Society
DOI:
10.1103/PhysRevD.91.012003
Bibliographic Code:
2015PhRvD..91a2003L

Abstract

We study the rare B meson decays B±,0-->J /psi K+K-K±,0 , B±,0-->J /psi varphi K±,0 , and search for B0-->J /psi varphi , using 469 ×106 B B ¯ events collected at the Upsilon (4 S ) resonance with the BABAR detector at the PEP-II e+e- asymmetric energy collider. We present new measurements of branching fractions and a study of the J /psi varphi mass distribution in search of new charmonium-like states. In addition, we search for the decay B0-->J /psi varphi and find no evidence of a signal.

 

Title:
Study of quasielastic scattering using charged-current numu -iron interactions in the MINOS near detector
Authors:
Adamson, P.; Anghel, I.; Aurisano, A.;... Feldman, G. J.;... and 108 coauthors (Minos Collaboration)
Publication:
Physical Review D, Volume 91, Issue 1, id.012005 (PhRvD Homepage)
Publication Date:
01/2015
Origin:
APS
PACS Keywords:
Neutrino interactions, Protons and neutrons, Neutrino scattering, Neutrino muon pion and other elementary particle detectors, cosmic ray detectors
Abstract Copyright:
2015: American Physical Society
DOI:
10.1103/PhysRevD.91.012005
Bibliographic Code:
2015PhRvD..91a2005A

Abstract

Kinematic distributions from an inclusive sample of 1.41 ×106 charged-current numu interactions on iron, obtained using the MINOS near detector exposed to a wide-band beam with peak flux at 3 GeV, are compared to a conventional treatment of neutrino scattering within a Fermi gas nucleus. Results are used to guide the selection of a subsample enriched in quasielastic numuFe interactions, containing an estimated 123,000 quasielastic events of incident energies 1 <Enu<8 GeV , with nu>=2.79 GeV . Four additional subsamples representing topological and kinematic sideband regions to quasielastic scattering are also selected for the purpose of evaluating backgrounds. Comparisons using subsample distributions in four-momentum transfer Q2 show the Monte Carlo model to be inadequate at low Q2. Its shortcomings are remedied via inclusion of a Q2-dependent suppression function for baryon resonance production, developed from the data. A chi-square fit of the resulting Monte Carlo simulation to the shape of the Q2 distribution for the quasielastic-enriched sample is carried out with the axial-vector mass MA of the dipole axial-vector form factor of the neutron as a free parameter. The effective MA which best describes the data is 1.23-0.09+0.13(fit)-0.15+0.12(syst) GeV .

 

Title:
Measurements of Higgs boson production and couplings in the four-lepton channel in p p collisions at center-of-mass energies of 7 and 8 TeV with the ATLAS detector
Authors:
Aad, G.; Abbott, B.; Abdallah, J.;... Barreiro Guimarães da Costa, J.;... Franklin, M.;... Huth, J.;... Morii, M.;... ; and 2893 coauthors.
Publication:
Physical Review D, Volume 91, Issue 1, id.012006 (PhRvD Homepage)
Publication Date:
01/2015
Origin:
APS
PACS Keywords:
Standard-model Higgs bosons
Abstract Copyright:
2015: CERN
DOI:
10.1103/PhysRevD.91.012006
Bibliographic Code:
2015PhRvD..91a2006A

Abstract

The final ATLAS Run 1 measurements of Higgs boson production and couplings in the decay channel H -->Z Z*-->l+l-l'+l'- , where l , l'=e or mu , are presented. These measurements were performed using p p collision data corresponding to integrated luminosities of 4.5 and 20.3 fb-1 at center-of-mass energies of 7 and 8 TeV, respectively, recorded with the ATLAS detector at the LHC. The H -->Z Z*-->4 l signal is observed with a significance of 8.1 standard deviations, with an expectation of 6.2 standard deviations, at mH =125.36 GeV , the combined ATLAS measurement of the Higgs boson mass from the H -->gamma gamma and H -->Z Z*-->4 l channels. The production rate relative to the Standard Model expectation, the signal strength, is measured in four different production categories in the H -->Z Z*-->4 l channel. The measured signal strength, at this mass, and with all categories combined, is 1.44-0.33+0.40 . The signal strength for Higgs boson production in gluon fusion or in association with t t ¯ or b b ¯ pairs is found to be 1.7-0.4+0.5 , while the signal strength for vector-boson fusion combined with W H /Z H associated production is found to be 0.3-0.9+1.6.

 

Title:
Search for new phenomena in events with a photon and missing transverse momentum in p p collisions at &surd;{s }=8 TeV with the ATLAS detector
Authors:
Aad, G.; Abbott, B.; Abdallah, J.;... Barreiro Guimarães da Costa, J.;... Franklin, M.;... Huth, J.;... Morii, M.;... ; and 2866 coauthors.
Publication:
Physical Review D, Volume 91, Issue 1, id.012008 (PhRvD Homepage)
Publication Date:
01/2015
Origin:
APS
PACS Keywords:
Limits on production of particles, Inclusive production with identified leptons photons or other nonhadronic particles
Abstract Copyright:
2015: CERN
DOI:
10.1103/PhysRevD.91.012008
Bibliographic Code:
2015PhRvD..91a2008A

Abstract

Results of a search for new phenomena in events with an energetic photon and large missing transverse momentum with the ATLAS experiment at the LHC are reported. Data were collected in proton-proton collisions at a center-of-mass energy of 8 TeV and correspond to an integrated luminosity of 20.3 fb-1 . The observed data are well described by the expected Standard Model backgrounds. The expected (observed) upper limit on the fiducial cross section for the production of events with a photon and large missing transverse momentum is 6.1 (5.3) fb at 95% confidence level. Exclusion limits are presented on models of new phenomena with large extra spatial dimensions, supersymmetric quarks, and direct pair production of dark-matter candidates.

 

Title:
Consistent use of effective potentials
Authors:
Andreassen, Anders; Frost, William; Schwartz, Matthew D.
Publication:
Physical Review D, Volume 91, Issue 1, id.016009 (PhRvD Homepage)
Publication Date:
01/2015
Origin:
APS
PACS Keywords:
Spontaneous and radiative symmetry breaking, Electroweak radiative corrections
Abstract Copyright:
2015: American Physical Society
DOI:
10.1103/PhysRevD.91.016009
Bibliographic Code:
2015PhRvD..91a6009A

Abstract

It is well known that effective potentials can be gauge dependent while their values at extrema should be gauge invariant. Unfortunately, establishing this invariance in perturbation theory is not straightforward, since contributions from arbitrarily high-order loops can be of the same size. We show in massless scalar QED that an infinite class of loops can be summed (and must be summed) to give a gauge-invariant value for the potential at its minimum. In addition, we show that the exact potential depends on both the scale at which it is calculated and the normalization of the fields, but the vacuum energy does not. Using these insights, we propose a method to extract some physical quantities from effective potentials which is self-consistent order by order in perturbation theory, including improvement with the renormalization group.

 

Title:
Mobile Magnetic Impurities in a Fermi Superfluid: A Route to Designer Molecules
Authors:
Gopalakrishnan, Sarang; Parker, Colin V.; Demler, Eugene
Affiliation:
AA(Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA), AB(James Franck Institute and Department of Physics, University of Chicago, Chicago, Illinois 60637, USA), AC(Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA)
Publication:
Physical Review Letters, Volume 114, Issue 4, id.045301 (PhRvL Homepage)
Publication Date:
01/2015
Origin:
APS
PACS Keywords:
Mixtures of Bose and Fermi gases, Degenerate Fermi gases
Abstract Copyright:
2015: American Physical Society
DOI:
10.1103/PhysRevLett.114.045301
Bibliographic Code:
2015PhRvL.114d5301G

Abstract

A magnetic impurity in a fermionic superfluid hosts bound quasiparticle states known as Yu-Shiba-Rusinov states. We argue here that, if the impurity is mobile (i.e., has a finite mass), the impurity and its bound Yu-Shiba-Rusinov quasiparticle move together as a midgap molecule, which has an unusual "Mexican-hat" dispersion that is tunable via the fermion density. We map out the impurity dispersion, which consists of an "atomic" branch (in which the impurity is dressed by quasiparticle pairs) and a "molecular" branch (in which the impurity binds a quasiparticle). We discuss the experimental realization and detection of midgap Shiba molecules, focusing on Li-Cs mixtures, and comment on the prospects they offer for realizing exotic many-body states.

 

Title:
Atomic-Scale Nuclear Spin Imaging Using Quantum-Assisted Sensors in Diamond
Authors:
Ajoy, A.; Bissbort, U.; Lukin, M. D.; Walsworth, R. L.; Cappellaro, P.
Publication:
Physical Review X, Volume 5, Issue 1, id.011001
Publication Date:
01/2015
Origin:
APS
PACS Keywords:
Magnetometers for magnetic field measurements, Color centers and other defects, Optically detected magnetic resonance, NMR imaging
Abstract Copyright:
2015: authors
DOI:
10.1103/PhysRevX.5.011001
Bibliographic Code:
2015PhRvX...5a1001A

Abstract

Nuclear spin imaging at the atomic level is essential for the understanding of fundamental biological phenomena and for applications such as drug discovery. The advent of novel nanoscale sensors promises to achieve the long-standing goal of single-protein, high spatial-resolution structure determination under ambient conditions. In particular, quantum sensors based on the spin-dependent photoluminescence of nitrogen-vacancy (NV) centers in diamond have recently been used to detect nanoscale ensembles of external nuclear spins. While NV sensitivity is approaching single-spin levels, extracting relevant information from a very complex structure is a further challenge since it requires not only the ability to sense the magnetic field of an isolated nuclear spin but also to achieve atomic-scale spatial resolution. Here, we propose a method that, by exploiting the coupling of the NV center to an intrinsic quantum memory associated with the nitrogen nuclear spin, can reach a tenfold improvement in spatial resolution, down to atomic scales. The spatial resolution enhancement is achieved through coherent control of the sensor spin, which creates a dynamic frequency filter selecting only a few nuclear spins at a time. We propose and analyze a protocol that would allow not only sensing individual spins in a complex biomolecule, but also unraveling couplings among them, thus elucidating local characteristics of the molecule structure.

 

 


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