Faculty Publications: August, 2013
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Title: | Response times to conceptual questions | |
Authors: | Lasry, Nathaniel; Watkins, Jessica; Mazur, Eric; Ibrahim, Ahmed | |
Publication: | American Journal of Physics, Volume 81, Issue 9, pp. 703-706 (2013). | |
Publication Date: | 09/2013 | |
Origin: | AIP | |
Keywords: | cognition, physics education | |
PACS Keywords: | Research in physics education | |
Abstract Copyright: | (c) 2013: American Institute of Physics | |
DOI: | 10.1119/1.4812583 | |
Bibliographic Code: | 2013AmJPh..81..703L |
Abstract
We measured the time taken by students to respond to individual Force Concept Inventory (FCI) questions. We examine response time differences between correct and incorrect answers, both before and after instruction. We also determine the relation between response time and expressed confidence. Our data reveal three results of interest. First, response times are longer for incorrect answers than for correct ones, indicating that distractors are not automatic choices. Second, response times increase after instruction for both correct and incorrect answers, supporting the notion that instruction changes students' approach to conceptual questions. Third, response times are inversely related to students' expressed confidence; the lower their confidence, the longer it takes to respond.
Abstract
We describe the design and data analysis of the DEEP2 Galaxy Redshift Survey, the densest and largest high-precision redshift survey of galaxies at z ~ 1 completed to date. The survey was designed to conduct a comprehensive census of massive galaxies, their properties, environments, and large-scale structure down to absolute magnitude MB = -20 at z ~ 1 via ~90 nights of observation on the Keck telescope. The survey covers an area of 2.8 deg2 divided into four separate fields observed to a limiting apparent magnitude of R AB = 24.1. Objects with z <~ 0.7 are readily identifiable using BRI photometry and rejected in three of the four DEEP2 fields, allowing galaxies with z > 0.7 to be targeted ~2.5 times more efficiently than in a purely magnitude-limited sample. Approximately 60% of eligible targets are chosen for spectroscopy, yielding nearly 53,000 spectra and more than 38,000 reliable redshift measurements. Most of the targets that fail to yield secure redshifts are blue objects that lie beyond z ~ 1.45, where the [O II] 3727 Å doublet lies in the infrared. The DEIMOS 1200 line mm-1 grating used for the survey delivers high spectral resolution (R ~ 6000), accurate and secure redshifts, and unique internal kinematic information. Extensive ancillary data are available in the DEEP2 fields, particularly in the Extended Groth Strip, which has evolved into one of the richest multiwavelength regions on the sky. This paper is intended as a handbook for users of the DEEP2 Data Release 4, which includes all DEEP2 spectra and redshifts, as well as for the DEEP2 DEIMOS data reduction pipelines. Extensive details are provided on object selection, mask design, biases in target selection and redshift measurements, the spec2d two-dimensional data-reduction pipeline, the spec1d automated redshift pipeline, and the zspec visual redshift verification process, along with examples of instrumental signatures or other artifacts that in some cases remain after data reduction. Redshift errors and catastrophic failure rates are assessed through more than 2000 objects with duplicate observations. Sky subtraction is essentially photon-limited even under bright OH sky lines; we describe the strategies that permitted this, based on high image stability, accurate wavelength solutions, and powerful B-spline modeling methods. We also investigate the impact of targets that appear to be single objects in ground-based targeting imaging but prove to be composite in Hubble Space Telescope data; they constitute several percent of targets at z ~ 1, approaching ~5%-10% at z > 1.5. Summary data are given that demonstrate the superiority of DEEP2 over other deep high-precision redshift surveys at z ~ 1 in terms of redshift accuracy, sample number density, and amount of spectral information. We also provide an overview of the scientific highlights of the DEEP2 survey thus far.Based on observations taken at the W. M. Keck Observatory, which is operated jointly by the University of California and the California Institute of Technology, and on observations made with the NASA/ESO Hubble Space Telescope, obtained from the data archives at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555, and from the Canadian Astronomy Data Centre.
Title: | Asymmetric Mutualism in Two and Three Dimensions | |
Authors: | Lavrentovich, Maxim O.; Nelson, David R. | |
Publication: | eprint arXiv:1309.0273 | |
Publication Date: | 09/2013 | |
Origin: | ARXIV | |
Keywords: | Quantitative Biology - Populations and Evolution, Condensed Matter - Statistical Mechanics | |
Comment: | 9 pages, 13 figures | |
Bibliographic Code: | 2013arXiv1309.0273L |
Abstract
Genetic drift at the frontiers of two-dimensional range expansions of microorganisms can frustrate local cooperation between different genetic variants, demixing the population into distinct sectors. In a biological context, mutualistic or antagonistic interactions will typically be asymmetric between variants. Taking into account both the asymmetry and the interaction strength, we explore the much weaker demixing in three dimensions and show how the symmetric directed percolation transition to a mutualistic phase becomes pinned to an exactly soluble voter model point. We also demonstrate that expansions with undulating fronts roughen dramatically at the boundaries of the mutualistic phase, with severe consequences for the population genetics along the transition lines.
Title: | Stability of Branched Flow from a Quantum Point Contact | |
Authors: | Liu, Bo; Heller, Eric J. | |
Publication: | eprint arXiv:1309.1814 | |
Publication Date: | 09/2013 | |
Origin: | ARXIV | |
Keywords: | Condensed Matter - Mesoscale and Nanoscale Physics | |
Comment: | 4 figures | |
Bibliographic Code: | 2013arXiv1309.1814L |
Abstract
In classically chaotic systems, small differences in initial conditions are exponentially magnified over time. However, it was observed experimentally that the (necessarily quantum) "branched flow" pattern of electron flux from a quantum point contact (QPC) traveling over a random background potential in two-dimensional electron gases(2DEGs) remains substantially invariant to large changes in initial conditions. Since such a potential is classically chaotic and unstable to changes in initial conditions, it was conjectured that the origin of the observed stability is purely quantum mechanical, with no classical analog. In this paper, we show that the observed stability is a result of the physics of the QPC and the nature of the experiment. We show that the same stability can indeed be reproduced classically, or quantum mechanically. In addition, we explore the stability of the branched flow with regards to changes in the eigenmodes of quantum point contact.
Title: | Enhanced anti-ferromagnetic exchange between magnetic impurities in a superconducting host | |
Authors: | Yao, Norman Y.; Glazman, Leonid I.; Demler, Eugene A.; Lukin, Mikhail D.; Sau, Jay D. | |
Publication: | eprint arXiv:1309.2633 | |
Publication Date: | 09/2013 | |
Origin: | ARXIV | |
Keywords: | Condensed Matter - Mesoscale and Nanoscale Physics, Condensed Matter - Strongly Correlated Electrons, Condensed Matter - Superconductivity | |
Comment: | 9 pages, 3 figures | |
Bibliographic Code: | 2013arXiv1309.2633Y |
Abstract
It is generally believed that superconductivity only weakly affects the indirect exchange between magnetic impurities. If the distance r between impurities is smaller than than the superconducting coherence length (r < \xi), this exchange is thought to be dominated by RKKY interactions, identical to the those in a normal metallic host. This perception is based upon a perturbative treatment of the exchange interaction. Here, we provide a non-perturbative analysis and demonstrate that the presence of Yu-Shiba-Rusinov bound states induces a strong 1/r^2 anti-ferromagnetic interaction that can dominate over conventional RKKY even at distances significantly smaller than the coherence length. Experimental signatures, implications and applications are discussed.
Title: | Single-photon nonlinear optics with graphene plasmons | |
Authors: | Gullans, M.; Chang, D. E.; Koppens, F. H. L.; García de Abajo, F. J.; Lukin, M. D. | |
Publication: | eprint arXiv:1309.2651 | |
Publication Date: | 09/2013 | |
Origin: | ARXIV | |
Keywords: | Condensed Matter - Mesoscale and Nanoscale Physics, Physics - Optics, Quantum Physics | |
Comment: | 4+ pages, 3 Figures | |
Bibliographic Code: | 2013arXiv1309.2651G |
Abstract
We show theoretically that it is possible to realize significant nonlinear optical interactions at the few photon level in graphene nanostructures. Our approach takes advantage of the electric field enhancement associated with the strong confinement of graphene plasmons and the large intrinsic nonlinearity of graphene. Such a system could provide a powerful platform for quantum nonlinear optical control of light. As an example, we consider an integrated optical device that exploits this large nonlinearity to realize a single photon switch.
Title: | The dynamics of quantum criticality: Quantum Monte Carlo and holography | |
Authors: | Witczak-Krempa, William; Sorensen, Erik; Sachdev, Subir | |
Publication: | eprint arXiv:1309.2941 | |
Publication Date: | 09/2013 | |
Origin: | ARXIV | |
Keywords: | Condensed Matter - Strongly Correlated Electrons, Condensed Matter - Quantum Gases, General Relativity and Quantum Cosmology, High Energy Physics - Theory | |
Comment: | 13+9 pages, 5+1 figures | |
Bibliographic Code: | 2013arXiv1309.2941W |
Abstract
Understanding the real time dynamics of systems near quantum critical points at non-zero temperatures constitutes an important yet challenging problem, especially in two spatial dimensions where interactions are strong. We present detailed quantum Monte Carlo results for two separate realizations of the superfluid-insulator transition of bosons on a lattice: their low-frequency conductivities are found to have the same universal dependence on imaginary frequency and temperature. We then use the structure of the real time dynamics of conformal field theories described by the holographic gauge/gravity duality to make progress on the difficult problem of analytically continuing the Monte Carlo data to real time. Our method yields quantitative and experimentally testable results on the frequency-dependent conductivity at the quantum critical point, and on the spectrum of quasinormal modes in the vicinity of the superfluid-insulator quantum phase transition. Extensions to other observables and universality classes are discussed.
Title: | The theory of coherent dynamic nuclear polarization in quantum dots | |
Authors: | Neder, Izhar; Rudner, Mark S.; Halperin, Bertrand I. | |
Publication: | eprint arXiv:1309.3027 | |
Publication Date: | 09/2013 | |
Origin: | ARXIV | |
Keywords: | Condensed Matter - Mesoscale and Nanoscale Physics | |
Comment: | 22 pages, 6 figures | |
Bibliographic Code: | 2013arXiv1309.3027N |
Abstract
We consider the dynamic nuclear spin polarization (DNP) using two electrons in a double quantum dot in presence of external magnetic field and spin-orbit interaction, in various schemes of periodically repeated sweeps through the S-T+ avoided crossing. By treating the problem semi-classically, we find that generally the DNP have two distinct contributions - a geometrical polarization and a dynamic polarization, which have different dependence on the control parameters such as the sweep rates and waiting times in each period. Both terms show non-trivial dependence on those control parameter. We find that even for small spin-orbit term, the dynamical polarization dominates the DNP in presence of a long waiting period near the S-T+ avoided crossing, of the order of the nuclear Larmor precession periods. A detailed numerical analysis of a specific control regime can explain the oscillations observed by Foletti et.~al.~in arXiv:0801.3613.
Title: | Observation of D0-D0bar Mixing using the CDF II Detector | |
Authors: | CDF Collaboration; Aaltonen, T.; Amerio, S.; Amidei, D.;... Franklin, M.; ...Guimaraes da Costa, J.;... and 403 coauthors | |
Publication: | eprint arXiv:1309.4078 | |
Publication Date: | 09/2013 | |
Origin: | ARXIV | |
Keywords: | High Energy Physics - Experiment | |
Comment: | 8 pages, 4 figures, submitted to Phys. Rev. Lett | |
Bibliographic Code: | 2013arXiv1309.4078C |
Abstract
We measure the time dependence of the ratio of decay rates for D0 -> K+ pi- to the Cabibbo-favored decay D0 -> K- pi+. The charge conjugate decays are included. A signal of 3.3 x 10^4 D*+ -> pi+ D0, D0 -> K+ pi- decays is obtained with D0 proper decay times between 0.75 and 10 mean D0 lifetimes. The data were recorded with the CDF II detector at the Fermilab Tevatron and correspond to an integrated luminosity of 9.6 fb-1 for p-pbar collisions at sqrt(s) = 1.96 TeV. Assuming CP conservation, we search for D0-D0bar mixing and measure the mixing parameters to be R_D = (3.51 +/- 0.35) x 10^{-3}, y' = (4.3 +/- 4.3) x 10^{-3}, and x'^2 = (0.08 +/- 0.18) x 10^{-3}. We report Bayesian probability intervals in the x'^2 - y' plane and find that the significance of excluding the no-mixing hypothesis is equivalent to 6.1 Gaussian standard deviations, providing the second observation of D0-D0bar mixing from a single experiment.
Title: | Jet Cleansing: Pileup Removal at High Luminosity | |
Authors: | Krohn, David; Low, Matthew; Schwartz, Matthew D.; Wang, Lian-Tao | |
Publication: | eprint arXiv:1309.4777 | |
Publication Date: | 09/2013 | |
Origin: | ARXIV | |
Keywords: | High Energy Physics - Phenomenology | |
Comment: | 5 pages, 4 figures, 2 tables | |
Bibliographic Code: | 2013arXiv1309.4777K |
Abstract
One of the greatest impediments to extracting useful information from high luminosity hadron-collider data is radiation from secondary collisions (i.e. pileup) which can overlap with that of the primary interaction. In this paper we introduce a simple jet-substructure technique termed cleansing which can consistently correct for large amounts of pileup in an observable independent way. Cleansing works at the subjet level, combining tracker and calorimeter-based data to reconstruct the pileup-free primary interaction. The technique can be used on its own, with various degrees of sophistication, or in concert with jet grooming. We apply cleansing to both kinematic and jet shape reconstruction, finding in all cases a marked improvement over previous methods both in the correlation of the cleansed data with uncontaminated results and in measures like S/rt(B). Cleansing should improve the sensitivity of new-physics searches at high luminosity and could also aid in the comparison of precision QCD calculations to collider data.
Title: | Silicon-Vacancy Color Centers in Nanodiamonds: Cathodoluminescence Imaging Marker in the Near Infrared | |
Authors: | Zhang, Huiliang; Aharonovich, Igor; Glenn, David R.; Schalek, R.; Magyar, Andrew P.; Lichtman, Jeff W.; Hu, Evelyn L.; Walsworth, Ronald L. | |
Publication: | eprint arXiv:1309.5169 | |
Publication Date: | 09/2013 | |
Origin: | ARXIV | |
Keywords: | Condensed Matter - Materials Science | |
Bibliographic Code: | 2013arXiv1309.5169Z |
Abstract
We demonstrate that nanodiamonds fabricated to incorporate silicon-vacancy (Si-V) color centers provide bright, spectrally narrow, and stable cathodoluminescence (CL) in the near-infrared. Si-V color centers containing nanodiamonds are promising as non-bleaching optical markers for correlated CL and secondary electron microscopy, including applications to nanoscale bioimaging.
Title: | Study of orbitally excited $B$ mesons and evidence for a new $B\pi$ resonance | |
Authors: | Aaltonen, T.; Amerio, S.; Amidei, D.; Anastassov, A.;... Franklin, M.;... Guimaraes da Costa, J.;... and 404 coauthors | |
Publication: | eprint arXiv:1309.5961 | |
Publication Date: | 09/2013 | |
Origin: | ARXIV | |
Keywords: | High Energy Physics - Experiment | |
Comment: | submitted to Phys. Rev. D | |
Bibliographic Code: | 2013arXiv1309.5961A |
Abstract
Using the full CDF Run II data sample, we report evidence for a new resonance, which we refer to as B(5970), found simultaneously in the $B^0\pi^+$ and $B^+\pi^-$ mass distributions with a significance of 4.4 standard deviations. We further report the first study of resonances consistent with orbitally excited $B^{+}$ mesons and an updated measurement of the properties of orbitally excited $B^0$ and $B_s^0$ mesons. Using samples of approximately 8400 $B^{**0}$, 3300 $B^{**+}$, 1350 $B^{**0}_s$, 2600 $B(5970)^0$, and 1400 $B(5970)^+$ decays, we measure the masses and widths of all states, as well as the product of the relative production rate of $B_1$ and $B_2^*$ states times the branching fraction into a $B^{0,+}$ meson and a charged particle. Furthermore, we measure the branching fraction of the $B_{s2}^{*0} \rightarrow B^{*+} K^-$ decay relative to the $B_{s2}^{*0} \rightarrow B^{+} K^-$ decay, the production rate times the branching fraction of the B(5970) state relative to the $B_{2}^{*0,+}$ state, and the production rate of the orbitally excited $B^{0,+}$ states relative to the $B^{0,+}$ ground state. The masses of the new B(5970) resonances are $5978\pm5(\textrm{stat})\pm12(\textrm{syst}) \textrm{MeV/c}^{2}$ for the neutral state and $5961\pm5(\textrm{stat})\pm12(\textrm{syst}) \textrm{MeV/c}^{2}$ for the charged state, assuming that the resonance decays into $B\pi$ final states. The properties of the orbitally excited and the new $B(5970)^{0,+}$ states are compatible with isospin symmetry.
Title: | Angular fluctuations of a multi-component order describe the pseudogap regime of the cuprate superconductors | |
Authors: | Hayward, Lauren E.; Hawthorn, David G.; Melko, Roger G.; Sachdev, Subir | |
Publication: | eprint arXiv:1309.6639 | |
Publication Date: | 09/2013 | |
Origin: | ARXIV | |
Keywords: | Condensed Matter - Superconductivity, Condensed Matter - Strongly Correlated Electrons, High Energy Physics - Theory | |
Comment: | 9+9 pages, 8 figures | |
Bibliographic Code: | 2013arXiv1309.6639H |
Abstract
The hole-doped cuprate high temperature superconductors enter the pseudogap regime as their superconducting critical temperature, Tc, falls with decreasing hole density. Experiments have probed this regime for over two decades, but we argue that decisive new information has emerged from recent X-ray scattering experiments (arXiv:1207.0915, arXiv:1206.4333, arXiv:1207.3667). The experiments observe incommensurate charge density wave fluctuations whose strength rises gradually over a wide temperature range above Tc, but then decreases as the temperature is lowered below Tc. We propose a theory in which the superconducting and charge-density wave orders exhibit angular fluctuations in a 6-dimensional space. The theory provides a natural quantitative fit to the X-ray data, and is consistent with other observed characteristics of the pseudogap.
Title: | On a functional equation appearing in characterization of distributions by the optimality of an estimate | |
Authors: | Feldman, G.; Graczyk, P. | |
Publication: | eprint arXiv:1309.6770 | |
Publication Date: | 09/2013 | |
Origin: | ARXIV | |
Keywords: | Mathematics - Probability | |
Bibliographic Code: | 2013arXiv1309.6770F |
Abstract
Let $X$ be a second countable locally compact Abelian group containing no subgroup topologically isomorphic to the circle group $\mathbb{T}$. Let $\mu$ be a probability distribution on $X$ such that its characteristic function $\hat\mu(y)$ does not vanish and $\hat\mu(y)$ for some $n \geq 3$ satisfies the equation $$ \prod_{j=1}^{n} \hat\mu(y_j + y) = \prod_{j=1}^{n}\hat\mu(y_j - y), \quad \sum_{j=1}^{n} y_j = 0, \quad y_1,\dots,y_n,y \in Y. $$ Then $\mu$ is a convolution of a Gaussian distribution and a distribution supported in the subgroup of $X$ generated by elements of order 2.
Title: | Non-Minimal Higher-Spin DS4/CFT3 | |
Authors: | Chang, Chi-Ming; Pathak, Abhishek; Strominger, Andrew | |
Publication: | eprint arXiv:1309.7413 | |
Publication Date: | 09/2013 | |
Origin: | ARXIV | |
Keywords: | High Energy Physics - Theory | |
Bibliographic Code: | 2013arXiv1309.7413C |
Abstract
We conjecture that the level k U(N) Chern-Simons theory coupled to free anticommuting scalar matter in the fundamental is dual to non-minmal higher-spin Vasiliev gravity in dS4 with parity-violating phase \theta0 = \pi N/2k and Neumann boundary conditions for the scalar. Related conjectures are made for fundamental commuting spinor matter and critical theories. This generalizes a recent conjecture relating the minimal Type A Vasiliev theory in dS4 to the Sp(N) model with fundamental real anti-commuting scalars.
Title: | Search for new physics in trilepton events and limits on the associated chargino-neutralino production at CDF | |
Authors: | CDF Collaboration; Aaltonen, T.; Amerio, S.; Amidei, D.;... Franklin, M.; ...Guimaraes da Costa, J.;... and 402 coauthors | |
Publication: | eprint arXiv:1309.7509 | |
Publication Date: | 09/2013 | |
Origin: | ARXIV | |
Keywords: | High Energy Physics - Experiment | |
Comment: | 8 pages, 4 figures | |
Bibliographic Code: | 2013arXiv1309.7509C |
Abstract
We perform a search for new physics using final states consisting of three leptons and a large imbalance in transverse momentum resulting from proton-antiproton collisions at 1.96 TeV center-of-mass energy. We use data corresponding to 5.8 fb-1 of integrated luminosity recorded by the CDF II detector at the Tevatron collider. Our main objective is to investigate possible new low-momentum (down to 5 GeV/c) multi-leptonic final states not investigated by LHC experiments. Relative to previous CDF analyses, we expand the geometric and kinematic coverage of electrons and muons and utilize tau leptons that decay hadronically. Inclusion of tau leptons is particularly important for supersymmetry (SUSY) searches. The results are consistent with standard-model predictions. By optimizing our event selection to increase sensitivity to the minimal supergravity (mSUGRA) SUSY model, we set limits on the associated production of chargino and neutralino, the SUSY partners of the electroweak gauge bosons. We exclude cross sections up to 0.1 pb and chargino masses up to 168 GeV/c^2 at 95% CL, for a suited set of mSUGRA parameters. We also exclude a region of the two-dimensional space of the masses of the neutralino and the supersymmetric partner of the tau lepton, not previously excluded at the Tevatron.
Title: | Search for the production of ZW and ZZ boson pairs decaying into charged leptons and jets in proton-antiproton collisions at sqrt(s)=1.96 TeV | |
Authors: | CDF Collaboration; Aaltonen, T.; Amerio, S.; Amidei, D.; ... Franklin, M.; ...Guimaraes da Costa, J.;... and 402 coauthors | |
Publication: | eprint arXiv:1310.0086 | |
Publication Date: | 09/2013 | |
Origin: | ARXIV | |
Keywords: | High Energy Physics - Experiment | |
Comment: | 17 pages, 10 figures. Submitted to Phys. Rev. D | |
Bibliographic Code: | 2013arXiv1310.0086C |
Abstract
We present a measurement of the production cross section for ZW and ZZ boson pairs in final states with a pair of charged leptons, from the decay of a Z boson, and at least two jets, from the decay of a W or Z boson, using the full sample of proton-antiproton collisions recorded with the CDF II detector at the Tevatron, corresponding to 8.9 fb^(-1) of integrated luminosity. We increase the sensitivity to vector boson decays into pairs of quarks using a neural network discriminant that exploits the differences between the spatial spread of energy depositions and charged-particle momenta contained within the jet of particles originating from quarks and gluons. Additionally, we employ new jet energy corrections to Monte Carlo simulations that account for differences in the observed energy scales for quark and gluon jets. The number of signal events is extracted through a simultaneous fit to the dijet mass spectrum in three classes of events: events likely to contain jets with a heavy-quark decay, events likely to contain jets originating from light quarks, and events that fail these identification criteria. We determine the production cross section to be 2.5 +2.0 -1.0 pb (< 6.1 pb at the 95% confidence level), consistent with the standard model prediction of 5.1 pb.
Title: | Generalized dephasing relation for fidelity and application as an efficient propagator | |
Authors: | Kocia, Lucas; Heller, Eric J. | |
Publication: | Journal of Chemical Physics, Volume 139, Issue 12, pp. 124110-124110-7 (2013). (JChPh Homepage) | |
Publication Date: | 09/2013 | |
Origin: | AIP | |
Keywords: | chaos, Monte Carlo methods, quantum theory | |
PACS Keywords: | Semiclassical theories and applications, Quantum chaos, semiclassical methods, Quantum Monte Carlo methods | |
Abstract Copyright: | (c) 2013: American Institute of Physics | |
DOI: | 10.1063/1.4820880 | |
Bibliographic Code: | 2013JChPh.139l4110K |
Abstract
The dephasing relation (DR), a linearization of semiclassical fidelity, is generalized to include the overlap of ``off-diagonal'' elements. The accuracy of the formulation is tested in integrable and chaotic systems and its scaling with dimensionality is studied in a Caldeira-Leggett model with many degrees of freedom. It is shown that the DR is often in very good agreement with numerically analytic quantum results and frequently outperforms an alternative semiclassical treatment. Most importantly, since there is no computationally expensive prefactor, and Monte Carlo Metropolis sampling is used to facilitate the calculation, the DR is found to scale remarkably well with increasing dimension. We further demonstrate that a propagator based on the DR can include more quantum coherence and outperform other popular linearized semiclassical methods, such as forward-backward semiclassical dynamics (FBSD) and the linearized semiclassical initial value representation (LSC-IVR).
Title: | Four-State Sub-12-nm FETs Employing Lattice-Matched II-VI Barrier Layers | |
Authors: | Jain, F.; Chan, P.-Y.; Suarez, E.; Lingalugari, M.; Kondo, J.; Gogna, P.; Miller, B.; Chandy, J.; Heller, E. | |
Publication: | Journal of Electronic Materials, Online First | |
Publication Date: | 09/2013 | |
Origin: | SPRINGER | |
Keywords: | Multistate FETs, four-state QDG FETs, four-state QDSL FETs, four-channel SWS FETs, multiple quantum well/dot channel FETs | |
Abstract Copyright: | (c) 2013: TMS | |
DOI: | 10.1007/s11664-013-2758-x | |
Bibliographic Code: | 2013JEMat.tmp..498J |
Abstract
Three-state behavior has been demonstrated in Si and InGaAs field-effect transistors (FETs) when two layers of cladded quantum dots (QDs), such as SiO x -cladded Si or GeO x -cladded Ge, are assembled on the thin tunnel gate insulator. This paper describes FET structures that have the potential to exhibit four states. These structures include: (1) quantum dot gate (QDG) FETs with dissimilar dot layers, (2) quantum dot channel (QDC) with and without QDG layers, (3) spatial wavefunction switched (SWS) FETs with multiple coupled quantum well channels, and (4) hybrid SWS-QDC structures having multiple drains/sources. Four-state FETs enable compact low-power novel multivalued logic and two-bit memory architectures. Furthermore, we show that the performance of these FETs can be enhanced by the incorporation of II-VI nearly lattice-matched layers in place of gate oxides and quantum well/dot barriers or claddings. Lattice-matched high-energy gap layers cause reduction in interface state density and control of threshold voltage variability, while providing a higher dielectric constant than SiO2. Simulations involving self-consistent solutions of the Poisson and Schrödinger equations, and transfer probability rate from channel (well or dot layer) to gate (QD layer) are used to design sub-12-nm FETs, which will aid the design of multibit logic and memory cells.
Title: | Monopoles in 2 + 1-dimensional conformal field theories with global U(1) symmetry | |
Authors: | Pufu, Silviu S.; Sachdev, Subir | |
Publication: | Journal of High Energy Physics, Volume 2013, article id. #127 | |
Publication Date: | 09/2013 | |
Origin: | SPRINGER | |
Keywords: | Solitons Monopoles and Instantons, Field Theories in Higher Dimensions, Global Symmetries | |
Abstract Copyright: | (c) 2013: SISSA, Trieste, Italy | |
DOI: | 10.1007/JHEP09(2013)127 | |
Bibliographic Code: | 2013JHEP...09..127P |
Abstract
In 2 + 1-dimensional conformal field theories with a global U(1) symmetry, monopoles can be introduced through a background gauge field that couples to the U(1) conserved current. We use the state-operator correspondence to calculate scaling dimensions of such monopole insertions. We obtain the next-to-leading term in the 1 /N b expansion of the Wilson-Fisher fixed point in the theory of N b complex bosons.
Title: | Search for excited electrons and muons in \sqrt {s}=8 TeV proton-proton collisions with the ATLAS detector | |
Authors: | Aad, G.; Abajyan, T.; Abbott, B.;...Guimaraes da Costa, J.;... Huth, J.;... Morii, M.;...; and 2929 coauthors. | |
Publication: | New Journal of Physics, Volume 15, Issue 9, article id. 093011 (2013). | |
Publication Date: | 09/2013 | |
Origin: | IOP | |
DOI: | 10.1088/1367-2630/15/9/093011 | |
Bibliographic Code: | 2013NJPh...15i3011A |
Abstract
The ATLAS detector at the Large Hadron Collider is used to search for excited electrons and excited muons in the channel pp → ℓℓ* → ℓℓγ, assuming that excited leptons are produced via contact interactions. The analysis is based on 13 fb-1 of pp collisions at a centre-of-mass energy of 8 TeV. No evidence for excited leptons is found, and a limit is set at the 95% credibility level on the cross section times branching ratio as a function of the excited-lepton mass mℓ*. For mℓ* ⩾ 0.8 TeV, the respective upper limits on σB(ℓ* → ℓγ) are 0.75 and 0.90 fb for the e* and μ* searches. Limits on σB are converted into lower bounds on the compositeness scale Λ. In the special case where Λ = mℓ*, excited-electron and excited-muon masses below 2.2 TeV are excluded.
Title: | Fractional and integer quantum Hall effects in the zeroth Landau level in graphene | |
Authors: | Abanin, Dmitry A.; Feldman, Benjamin E.; Yacoby, Amir; Halperin, Bertrand I. | |
Publication: | Physical Review B, vol. 88, Issue 11, id. 115407 (PhRvB Homepage) | |
Publication Date: | 09/2013 | |
Origin: | APS | |
PACS Keywords: | Quantum Hall effects, Quantum phase transitions | |
DOI: | 10.1103/PhysRevB.88.115407 | |
Bibliographic Code: | 2013PhRvB..88k5407A |
Abstract
Experiments on the fractional quantized Hall effect in the zeroth Landau level of graphene have revealed some striking differences between filling factors in the ranges 0<|ν|<1 and 1<|ν|<2. We argue that these differences can be largely understood as a consequence of the effects of terms in the Hamiltonian which break SU(2) valley symmetry, which we find to be important for |ν|<1 but negligible for |ν|>1. The effective absence of valley anisotropy for |ν|>1 means that states with an odd numerator, such as |ν|=5/3 or 7/5, can accommodate charged excitations in the form of large-radius valley skyrmions, which should have a low energy cost and may be easily induced by coupling to impurities. The absence of observed quantum Hall states at these fractions is likely due to the effects of valley skyrmions. For |ν|<1, the anisotropy terms favor phases in which electrons occupy states with opposite spins, similar to the antiferromagnetic state previously hypothesized to be the ground state at ν=0. The anisotropy and Zeeman energies suppress large-area skyrmions, so that quantized Hall states can be observable at a set of fractions similar to those in GaAs two-dimensional electron systems. In a perpendicular magnetic field B, the competition between the Coulomb energy, which varies as B1/2, and the Zeeman energy, which varies as B, can explain the observation of apparent phase transitions as a function of B for fixed ν, as transitions between states with different degrees of spin polarization. In addition to an analysis of various fractional states from this point of view and an examination of the effects of disorder on valley skyrmions, we present new experimental data for the energy gaps at integer fillings ν=0 and ν=-1, as a function of magnetic field, and we examine the possibility that valley skyrmions may account for the smaller energy gaps observed at ν=-1.
Title: | Ballistic versus diffusive transport in graphene | |
Authors: | Borunda, Mario F.; Hennig, H.; Heller, Eric J. | |
Publication: | Physical Review B, vol. 88, Issue 12, id. 125415 (PhRvB Homepage) | |
Publication Date: | 09/2013 | |
Origin: | APS | |
PACS Keywords: | Ballistic transport, Scattering by point defects dislocations surfaces and other imperfections | |
DOI: | 10.1103/PhysRevB.88.125415 | |
Bibliographic Code: | 2013PhRvB..88l5415B |
Abstract
We investigate the transport of electrons in disordered and pristine graphene devices. Fano shot noise, a standard metric to assess the mechanism for electronic transport in mesoscopic devices, has been shown to produce almost the same magnitude (≈1/3) in ballistic and diffusive graphene devices and is therefore of limited applicability. We consider a two-terminal geometry where the graphene flake is contacted by narrow metallic leads. We propose that the dependence of the conductance on the position of one of the leads, a conductance profile, can give us insight into the charge flow, which can in turn be used to analyze the transport mechanism. Moreover, we simulate scanning probe microscopy (SPM) measurements for the same devices, which can visualize the flow of charge inside the device, thus complementing the transport calculations. From our simulations, we find that both the conductance profile and SPM measurements are excellent tools to assess the transport mechanism differentiating ballistic and diffusive graphene systems.
Title: | Measurement of the D*(2010)^{+} natural linewidth and the D*(2010)^{+}-D^{0} mass difference | |
Authors: | Lees, J. P.; Poireau, V.; Tisserand, V.;... ; Morii, M.;... and 337 coauthors.. | |
Publication: | Physical Review D, vol. 88, Issue 5, id. 052003 (PhRvD Homepage) | |
Publication Date: | 09/2013 | |
Origin: | APS | |
PACS Keywords: | Decays of charmed mesons, Charmed mesons, Experimental tests, Relativistic quark model | |
DOI: | 10.1103/PhysRevD.88.052003 | |
Bibliographic Code: | 2013PhRvD..88e2003L |
Abstract
We measure the mass difference, Δm_{0}, between the D^{*}(2010)^{+} and the D^{0} and the natural linewidth, Γ, of the transition D^{*}(2010)^{+}→D^{0}π^{+}. The data were recorded with the BABAR detector at center-of-mass energies at and near the Υ(4S) resonance, and correspond to an integrated luminosity of approximately 477fb^{-1}. The D^{0} is reconstructed in the decay modes D^{0}→K^{-}π^{+} and D^{0}→K^{-}π^{+}π^{-}π^{+}. For the decay mode D^{0}→K^{-}π^{+} we obtain Γ=(83.4±1.7±1.5)keV and Δm_{0}=(145425.6±0.6±1.8)keV, where the quoted errors are statistical and systematic, respectively. For the D^{0}→K^{-}π^{+}π^{-}π^{+} mode we obtain Γ=(83.2±1.5±2.6)keV and Δm_{0}=(145426.6±0.5±2.0)keV. The combined measurements yield Γ=(83.3±1.2±1.4)keV and Δm_{0}=(145425.9±0.4±1.7)keV; the width is a factor of approximately 12 times more precise than the previous value, while the mass difference is a factor of approximately 6 times more precise.
Title: | Searches for the Higgs boson decaying to W^{+}W^{-}→ℓ^{+}νℓ^{-}ν¯ with the CDF II detector | |
Authors: | Aaltonen, T.; Amerio, S.; Amidei, D.;... Franklin, M.;... Guimaraes da Costa, J.;... and 416 coauthors | |
Publication: | Physical Review D, vol. 88, Issue 5, id. 052012 (PhRvD Homepage) | |
Publication Date: | 09/2013 | |
Origin: | APS | |
PACS Keywords: | Limits on production of particles, Standard-model Higgs bosons | |
DOI: | 10.1103/PhysRevD.88.052012 | |
Bibliographic Code: | 2013PhRvD..88e2012A |
Abstract
We present a search for a standard model Higgs boson decaying to two W bosons that decay to leptons using the full data set collected with the CDF II detector in s=1.96TeV pp¯ collisions at the Fermilab Tevatron, corresponding to an integrated luminosity of 9.7fb^{-1}. We obtain no evidence for production of a standard model Higgs boson with mass between 110 and 200GeV/c^{2}, and place upper limits on the production cross section within this range. We exclude standard model Higgs boson production at the 95% confidence level in the mass range between 149 and 172GeV/c^{2}, while expecting to exclude, in the absence of signal, the range between 155 and 175GeV/c^{2}. We also interpret the search in terms of standard model Higgs boson production in the presence of a fourth generation of fermions and within the context of a fermiophobic Higgs boson model. For the specific case of a standard-model-like Higgs boson in the presence of fourth-generation fermions, we exclude at the 95% confidence level Higgs boson production in the mass range between 124 and 200GeV/c^{2}, while expecting to exclude, in the absence of signal, the range between 124 and 221GeV/c^{2}.
Title: | Combination of searches for the Higgs boson using the full CDF data set | |
Authors: | Aaltonen, T.; Amerio, S.; Amidei, D.;... Franklin, M.;... Guimaraes da Costa, J.;... and 405 coauthors | |
Publication: | Physical Review D, vol. 88, Issue 5, id. 052013 (PhRvD Homepage) | |
Publication Date: | 09/2013 | |
Origin: | APS | |
PACS Keywords: | Limits on production of particles, Standard-model Higgs bosons | |
DOI: | 10.1103/PhysRevD.88.052013 | |
Bibliographic Code: | 2013PhRvD..88e2013A |
Abstract
We present a combination of searches for the standard model Higgs boson using the full CDF run II data set, which corresponds to an integrated luminosity of 9.45-10.0fb^{-1} collected from s=1.96TeV pp¯ collisions at the Fermilab Tevatron. The searches consider Higgs boson production from gluon-gluon fusion, vector-boson fusion, and associated production with either a W or Z boson or a tt¯ pair. Depending on the production mode, Higgs boson decays to W^{+}W^{-}, ZZ, bb¯, τ^{+}τ^{-}, and γγ are examined. We search for a Higgs boson with masses (m_{H}) in the range 90-200GeV/c^{2}. In the absence of a signal, we expect based on combined search sensitivity to exclude at the 95% credibility level the mass regions 90<m_{H}<94GeV/c^{2}, 96<m_{H}<106GeV/c^{2}, and 153<m_{H}<175GeV/c^{2}. The observed exclusion regions are 90<m_{H}<102GeV/c^{2} and 149<m_{H}<172GeV/c^{2}. A moderate excess of signal-like events relative to the background expectation at the level of 2.0 standard deviations is present in the data for the m_{H}=125GeV/c^{2} search hypothesis. We also present interpretations of the data within the context of a fermiophobic model and an alternative standard model incorporating a fourth generation of fermions. Finally, for the hypothesis of a new particle with mass 125GeV/c^{2}, we constrain the coupling strengths of the new particle to W^{±} bosons, Z bosons, and fermions.
Title: | Higgs boson studies at the Tevatron | |
Authors: | Aaltonen, T.; Abazov, V. M.; Abbott, B.;... and 766 coauthors | |
Publication: | Physical Review D, vol. 88, Issue 5, id. 052014 (PhRvD Homepage) | |
Publication Date: | 09/2013 | |
Origin: | APS | |
PACS Keywords: | Limits on production of particles, Standard-model Higgs bosons | |
DOI: | 10.1103/PhysRevD.88.052014 | |
Bibliographic Code: | 2013PhRvD..88e2014A |
Abstract
We combine searches by the CDF and D0 Collaborations for the standard model Higgs boson with mass in the range 90-200GeV/c^{2} produced in the gluon-gluon fusion, WH, ZH, tt¯H, and vector boson fusion processes, and decaying in the H→bb¯, H→W^{+}W^{-}, H→ZZ, H→τ^{+}τ^{-}, and H→γγ modes. The data correspond to integrated luminosities of up to 10fb^{-1} and were collected at the Fermilab Tevatron in pp¯ collisions at s=1.96TeV. The searches are also interpreted in the context of fermiophobic and fourth generation models. We observe a significant excess of events in the mass range between 115 and 140GeV/c^{2}. The local significance corresponds to 3.0 standard deviations at m_{H}=125GeV/c^{2}, consistent with the mass of the Higgs boson observed at the LHC, and we expect a local significance of 1.9 standard deviations. We separately combine searches for H→bb¯, H→W^{+}W^{-}, H→τ^{+}τ^{-}, and H→γγ. The observed signal strengths in all channels are consistent with the presence of a standard model Higgs boson with a mass of 125GeV/c^{2}.
Title: | Combination of CDF and D0 W-Boson mass measurements | |
Authors: | Aaltonen, T.; Abazov, V. M.; Abbott, B.;... and 770 coauthors | |
Publication: | Physical Review D, vol. 88, Issue 5, id. 052018 (PhRvD Homepage) | |
Publication Date: | 09/2013 | |
Origin: | APS | |
PACS Keywords: | W bosons, Applications of electroweak models to specific processes, Decays of W bosons, Inclusive production with identified leptons photons or other nonhadronic particles | |
DOI: | 10.1103/PhysRevD.88.052018 | |
Bibliographic Code: | 2013PhRvD..88e2018A |
Abstract
We summarize and combine direct measurements of the mass of the W boson in s=1.96TeV proton-antiproton collision data collected by CDF and D0 experiments at the Fermilab Tevatron Collider. Earlier measurements from CDF and D0 are combined with the two latest, more precise measurements: a CDF measurement in the electron and muon channels using data corresponding to 2.2fb^{-1} of integrated luminosity, and a D0 measurement in the electron channel using data corresponding to 4.3fb^{-1} of integrated luminosity. The resulting Tevatron average for the mass of the W boson is M_{W}=80387±16MeV. Including measurements obtained in electron-positron collisions at LEP yields the most precise value of M_{W}=80385±15MeV.
Title: | An on-shell approach to factorization | |
Authors: | Feige, Ilya; Schwartz, Matthew D. | |
Publication: | Physical Review D, vol. 88, Issue 6, id. 065021 (PhRvD Homepage) | |
Publication Date: | 09/2013 | |
Origin: | APS | |
PACS Keywords: | Gauge field theories, General properties of QCD | |
DOI: | 10.1103/PhysRevD.88.065021 | |
Bibliographic Code: | 2013PhRvD..88f5021F |
Abstract
Factorization is possible due to the universal behavior of Yang-Mills theories in soft and collinear limits. Here, we take a small step towards a more transparent understanding of these limits by proving a form of perturbative factorization at tree level using on-shell spinor helicity methods. We present a concrete and self-contained expression of factorization in which matrix elements in QCD are related to products of other matrix elements in QCD up to leading order in a power-counting parameter determined by the momenta of certain physical on-shell states. Our approach uses only the scaling of momenta in soft and collinear limits, avoiding any assignment of scaling behavior to unphysical (and gauge-dependent) fields. The proof of factorization exploits many advantages of helicity spinors, such as the freedom to choose different reference vectors for polarizations in different collinear sectors. An advantage of this approach is that once factorization is shown to hold in QCD, the transition to soft-collinear effective theory is effortless.
Title: | Search for CP Violation in B^{0}- B¯^{0} Mixing Using Partial Reconstruction of B^{0}→D^{*-}Xℓ^{+}ν_{ℓ} and a Kaon Tag | |
Authors: | Lees, J. P.; Poireau, V.; Tisserand, V.;... ; Morii, M.;... and 333 coauthors | |
Publication: | Physical Review Letters, vol. 111, Issue 10, id. 101802 (PhRvL Homepage) | |
Publication Date: | 09/2013 | |
Origin: | APS | |
PACS Keywords: | Decays of bottom mesons, Charge conjugation parity time reversal and other discrete symmetries, Decays of J/psi Upsilon and other quarkonia, Decays of charmed mesons | |
DOI: | 10.1103/PhysRevLett.111.101802 | |
Bibliographic Code: | 2013PhRvL.111j1802L |
Abstract
We present results of a search for CP violation in B^{0}-B¯^{0} mixing with the BABAR detector. We select a sample of B^{0}→D^{*-}Xℓ^{+}ν decays with a partial reconstruction method and use kaon tagging to assess the flavor of the other B meson in the event. We determine the CP violating asymmetry A_{CP}≡[N(B^{0}B^{0})-N(B¯^{0}B¯^{0})]/[N(B^{0}B^{0})+N(B¯^{0}B¯^{0})]=(0.06±0.17_{-0.32}^{+0.38})%, corresponding to Δ_{CP}=1-|q/p|=(0.29±0.84_{-1.61}^{+1.88})×10^{-3}.
Title: | Proposal for Coherent Coupling of Majorana Zero Modes and Superconducting Qubits Using the 4π Josephson Effect | |
Authors: | Pekker, David; Hou, Chang-Yu; Manucharyan, Vladimir E.; Demler, Eugene | |
Publication: | Physical Review Letters, vol. 111, Issue 10, id. 107007 (PhRvL Homepage) | |
Publication Date: | 09/2013 | |
Origin: | APS | |
PACS Keywords: | Josephson junction arrays and wire networks, Quantum wires, Nonconventional mechanisms, Tunneling phenomena, point contacts weak links Josephson effects | |
DOI: | 10.1103/PhysRevLett.111.107007 | |
Bibliographic Code: | 2013PhRvL.111j7007P |
Abstract
We propose to use an ancilla fluxonium qubit to interact with a Majorana qubit hosted by a topological one-dimensional wire. The coupling is obtained using the Majorana qubit-controlled 4π Josephson effect to flux bias the fluxonium qubit. We demonstrate how this coupling can be used to sensitively identify topological superconductivity, to measure the state of the Majorana qubit, to construct 2-qubit operations, and to implement quantum memories with topological protection.
Title: | Measurement of the D^{*}(2010)^{+} Meson Width and the D^{*}(2010)^{+}-D^{0} Mass Difference | |
Authors: | Lees, J. P.; Poireau, V.; Tisserand, V.;... ; Morii, M.;... and 339 coauthors | |
Publication: | Physical Review Letters, vol. 111, Issue 11, id. 111801 (PhRvL Homepage) | |
Publication Date: | 09/2013 | |
Origin: | APS | |
PACS Keywords: | Decays of charmed mesons, Experimental tests, Relativistic quark model, Charmed mesons | |
DOI: | 10.1103/PhysRevLett.111.111801 | |
Bibliographic Code: | 2013PhRvL.111k1801L |
Abstract
We measure the mass difference Δm_{0} between the D^{*}(2010)^{+} and the D^{0} and the natural linewidth Γ of the transition D^{*}(2010)^{+}→D^{0}π^{+}. The data were recorded with the BABAR detector at center-of-mass energies at and near the Υ(4S) resonance, and correspond to an integrated luminosity of approximately 477fb^{-1}. The D^{0} is reconstructed in the decay modes D^{0}→K^{-}π^{+} and D^{0}→K^{-}π^{+}π^{-}π^{+}. For the decay mode D^{0}→K^{-}π^{+} we obtain Γ=(83.4±1.7±1.5)keV and Δm_{0}=(145425.6±0.6±1.8)keV, where the quoted errors are statistical and systematic, respectively. For the D^{0}→K^{-}π^{+}π^{-}π^{+} mode we obtain Γ=(83.2±1.5±2.6)keV and Δm_{0}=(145426.6±0.5±2.0)keV. The combined measurements yield Γ=(83.3±1.2±1.4)keV and Δm_{0}=(145425.9±0.4±1.7)keV; the width is a factor of approximately 12 times more precise than the previous value, while the mass difference is a factor of approximately 6 times more precise.
Title: | Femtosecond laser induced surface melting and nanojoining for plasmonic circuits | |
Authors: | Hu, A.; Deng, G. L.; Courvoisier, S.; Reshef, O.; Evans, C. C.; Mazur, E.; Zhou, Y. | |
Publication: | Proceedings of the SPIE, Volume 8809, id. 880907 6 pp. (2013). (SPIE Homepage) | |
Publication Date: | 09/2013 | |
Origin: | SPIE | |
Abstract Copyright: | (c) 2013: SPIE. Downloading of the abstract is permitted for personal use only. | |
Comment: | ISBN: 9780819496591 | |
DOI: | 10.1117/12.2022482 | |
Bibliographic Code: | 2013SPIE.8809E..07H |