Faculty Publications: February, 2013

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Title:   Relaxation dynamics of colloidal particles at liquid interfaces
Authors:   Wang, Anna; Kaz, David M.; McGorty, Ryan; Manoharan, Vinothan N.
Publication:   4TH INTERNATIONAL SYMPOSIUM ON SLOW DYNAMICS IN COMPLEX SYSTEMS: Keep Going Tohoku. AIP Conference Proceedings, Volume 1518, pp. 336-343 (2013). (AIPC Homepage)
Publication Date:   02/2013
Origin:   AIP
Abstract Copyright:   (c) 2013: American Institute of Physics
DOI:   10.1063/1.4794594
Bibliographic Code:   2013AIPC.1518..336W

Abstract

We study the dynamics of colloidal particles as they approach and breach a water-oil interface. We use a fast 3D imaging technique, digital holographic microscopy, to track particles with 2 nm precision and sub-millisecond time resolution. We find that polystyrene particles dispersed in water or water-glycerol mixtures relax logarithmically with time after breaching the interface and do not reach equilibrium on experimental timescales. By contrast, decane-dispersed PMMA particles show fast dynamics and reach a steady-state height within milliseconds. We attribute the difference to the surface properties of the particles. We also probe the dependence of the relaxation rate on surface charge by studying carboxyl-functionalized particles under varying acid concentrations. We conclude that the slow relaxation may be due to contact-line pinning on topographical defects rather than surface charges.
 

Title:   A search for high-mass resonances decaying to τ+τ in pp collisions at s=7 TeV with the ATLAS detector
Authors:   Atlas Collaboration; Aad, G.; Abajyan, T.; Abbott, B.;... Franklin, M.;... Guimaraes da Costa, J.;... Huth, J.;... Morii, M.;...; and 2904 coauthors.
Publication:   Physics Letters B, Volume 719, Issue 4, p. 242-260.
Publication Date:   02/2013
Origin:   ELSEVIER
Keywords:   Exotics, Z′, Ditau, Resonance, Search
Abstract Copyright:   CERN
DOI:   10.1016/j.physletb.2013.01.040
Bibliographic Code:   2013PhLB..719..242A

Abstract

This Letter presents a search for high-mass resonances decaying into τ+τ final states using proton–proton collisions at s=7 TeV produced by the Large Hadron Collider. The data were recorded with the ATLAS detector and correspond to an integrated luminosity of 4.6 fb‑1. No statistically significant excess above the Standard Model expectation is observed; 95% credibility upper limits are set on the cross section times branching fraction of Z resonances decaying into τ+τ pairs as a function of the resonance mass. As a result, Z bosons of the Sequential Standard Model with masses less than 1.40 TeV are excluded at 95% credibility.
 

Title:   Measurement of the jet radius and transverse momentum dependence of inclusive jet suppression in lead–lead collisions at sNN=2.76 TeV with the ATLAS detector
Authors:   ATLAS Collaboration: Aad, G.; Abbott, B.; Abdallah, J.;...Guimaraes da Costa, J.;... Huth, J.;... Morii, M.;...; and 2858 coauthors.
Publication:   Physics Letters B, Volume 719, Issue 4, p. 220-241.
Publication Date:   02/2013
Origin:   ELSEVIER
Keywords:   LHC, ATLAS, Heavy ion, Jets
Abstract Copyright:   CERN
DOI:   10.1016/j.physletb.2013.01.024
Bibliographic Code:   2013PhLB..719..220A

Abstract

Measurements of inclusive jet suppression in heavy ion collisions at the LHC provide direct sensitivity to the physics of jet quenching. In a sample of lead–lead collisions at sNN=2.76 TeV corresponding to an integrated luminosity of approximately 7 μb‑1, ATLAS has measured jets with a calorimeter system over the pseudorapidity interval |η|<2.1 and over the transverse momentum range 38<pT<210 GeV. Jets were reconstructed using the anti-kt algorithm with values for the distance parameter that determines the nominal jet radius of R=0.2, 0.3, 0.4 and 0.5. The centrality dependence of the jet yield is characterized by the jet "central-to-peripheral ratio," RCP. Jet production is found to be suppressed by approximately a factor of two in the 10% most central collisions relative to peripheral collisions. RCP varies smoothly with centrality as characterized by the number of participating nucleons. The observed suppression is only weakly dependent on jet radius and transverse momentum. These results provide the first direct measurement of inclusive jet suppression in heavy ion collisions and complement previous measurements of dijet transverse energy imbalance at the LHC.
 

Title:   Search for supersymmetry in events with photons, bottom quarks, and missing transverse momentum in proton–proton collisions at a centre-of-mass energy of 7 TeV with the ATLAS detector
Authors:   Atlas Collaboration; Aad, G.; Abajyan, T.; Abbott, B.;... Franklin, M.;... Guimaraes da Costa, J.;... Huth, J.;... Morii, M.;...; and 2890 coauthors.
Publication:   Physics Letters B, Volume 719, Issue 4, p. 261-279.
Publication Date:   02/2013
Origin:   ELSEVIER
Keywords:   Supersymmetry, Gauge mediation, Higgs boson
Abstract Copyright:   CERN
DOI:   10.1016/j.physletb.2013.01.041
Bibliographic Code:   2013PhLB..719..261A

Abstract

A search has been performed for the experimental signature of an isolated photon with high transverse momentum, at least one jet identified as originating from a bottom quark, and high missing transverse momentum. Such a final state may originate from supersymmetric models with gauge-mediated supersymmetry breaking in events in which one of a pair of higgsino-like neutralinos decays into a photon and a gravitino while the other decays into a Higgs boson and a gravitino. The search is performed using the full dataset of 7 TeV proton–proton collisions recorded with the ATLAS detector at the LHC in 2011, corresponding to an integrated luminosity of 4.7 fb. A total of 7 candidate events are observed while 7.5±2.2 events are expected from the Standard Model background. The results of the search are interpreted in the context of general gauge mediation to exclude certain regions of a benchmark plane for higgsino-like neutralino production.
 

Title:   Search for long-lived, heavy particles in final states with a muon and multi-track displaced vertex in proton–proton collisions at s=7 TeV with the ATLAS detector
Authors:   Atlas Collaboration; Aad, G.; Abajyan, T.; Abbott, B.;... Franklin, M.;... Guimaraes da Costa, J.;... Huth, J.;... Morii, M.;...; and 2908 coauthors.
Publication:   Physics Letters B, Volume 719, Issue 4, p. 280-298.
Publication Date:   02/2013
Origin:   ELSEVIER
Abstract Copyright:   CERN
DOI:   10.1016/j.physletb.2013.01.042
Bibliographic Code:   2013PhLB..719..280A

Abstract

Many extensions of the Standard Model posit the existence of heavy particles with long lifetimes. In this Letter, results are presented of a search for events containing one or more such particles, which decay at a significant distance from their production point, using a final state containing charged hadrons and an associated muon. This analysis uses a data sample of proton–proton collisions at s=7 TeV corresponding to an integrated luminosity of 4.4 fb-1 collected in 2011 by the ATLAS detector operating at the Large Hadron Collider. Results are interpreted in the context of R-parity violating supersymmetric scenarios. No events in the signal region are observed and limits are set on the production cross section for pair production of supersymmetric particles, multiplied by the square of the branching fraction for a neutralino to decay to charged hadrons and a muon, based on the scenario where both of the produced supersymmetric particles give rise to neutralinos that decay in this way. However, since the search strategy is based on triggering on and reconstructing the decay products of individual long-lived particles, irrespective of the rest of the event, these limits can easily be reinterpreted in scenarios with different numbers of long-lived particles per event. The limits are presented as a function of neutralino lifetime, and for a range of squark and neutralino masses.
 

Title:   A search for prompt lepton-jets in pp collisions at s=7TeV with the ATLAS detector
Authors:   Atlas Collaboration; Aad, G.; Abajyan, T.; Abbott, B.;... Franklin, M.;... Guimaraes da Costa, J.;... Huth, J.;... Morii, M.;...; and 2879 coauthors.
Publication:   Physics Letters B, Volume 719, Issue 4, p. 299-317.
Publication Date:   02/2013
Origin:   ELSEVIER
Abstract Copyright:   CERN
DOI:   10.1016/j.physletb.2013.01.034
Bibliographic Code:   2013PhLB..719..299A

Abstract

We present a search for a light (mass <2GeV) boson predicted by Hidden Valley supersymmetric models that decays into a final state consisting of collimated muons or electrons, denoted "lepton-jets". The analysis uses 5fb of s=7TeV proton–proton collision data recorded by the ATLAS detector at the Large Hadron Collider to search for the following signatures: single lepton-jets with at least four muons; pairs of lepton-jets, each with two or more muons; and pairs of lepton-jets with two or more electrons. This study finds no statistically significant deviation from the Standard Model prediction and places 95% confidence-level exclusion limits on the production cross section times branching ratio of light bosons for several parameter sets of a Hidden Valley model.
 

Title:   Quantum logic between remote quantum registers
Authors:   Yao, N. Y.; Gong, Z.-X.; Laumann, C. R.; Bennett, S. D.; Duan, L.-M.; Lukin, M. D.; Jiang, L.; Gorshkov, A. V.
Publication:   Physical Review A, vol. 87, Issue 2, id. 022306 (PhRvA Homepage)
Publication Date:   02/2013
Origin:   APS
PACS Keywords:   Quantum computation, Quantum communication, Lattice theory and statistics, Spin chain models
DOI:   10.1103/PhysRevA.87.022306
Bibliographic Code:   2013PhRvA..87b2306Y

Abstract

We consider two approaches to dark-spin-mediated quantum computing in hybrid solid-state spin architectures. First, we review the notion of eigenmode-mediated unpolarized spin-chain state transfer and extend the analysis to various experimentally relevant imperfections: quenched disorder, dynamical decoherence, and uncompensated long-range coupling. In finite-length chains, the interplay between disorder-induced localization and decoherence yields a natural optimal channel fidelity, which we calculate. Long-range dipolar couplings induce a finite intrinsic lifetime for the mediating eigenmode; extensive numerical simulations of dipolar chains of lengths up to L=12 show remarkably high fidelity despite these decay processes. We further briefly consider the extension of the protocol to bosonic systems of coupled oscillators. Second, we introduce a quantum mirror based architecture for universal quantum computing that exploits all of the dark spins in the system as potential qubits. While this dramatically increases the number of qubits available, the composite operations required to manipulate dark-spin qubits significantly raise the error threshold for robust operation. Finally, we demonstrate that eigenmode-mediated state transfer can enable robust long-range logic between spatially separated nitrogen-vacancy registers in diamond; disorder-averaged numerics confirm that high-fidelity gates are achievable even in the presence of moderate disorder.
 

Title:   Using electric fields to prevent mirror-trapped antiprotons in antihydrogen studies
Authors:   Richerme, P.; Gabrielse, G.; Ettenauer, S.; Kalra, R.; Tardiff, E.; Fitzakerley, D. W.; George, M. C.; Hessels, E. A.; Storry, C. H.; Weel, M.; Müllers, A.; Walz, J.
Publication:   Physical Review A, vol. 87, Issue 2, id. 023422 (PhRvA Homepage)
Publication Date:   02/2013
Origin:   APS
PACS Keywords:   Atom cooling methods, Exotic atoms and molecules, Applied classical electromagnetism, Other topics in electromagnetism; electron and ion optics
DOI:   10.1103/PhysRevA.87.023422
Bibliographic Code:   2013PhRvA..87b3422R

Abstract

The signature of trapped antihydrogen (H¯) atoms is the annihilation signal detected when the magnetic trap that confines the atoms is suddenly switched off. This signal would be difficult to distinguish from the annihilation signal of any trapped p¯ that is released when the magnetic trap is switched off. This work deduces the large cyclotron energy (>137 eV) required for magnetic trapping of p¯, considers the possibility that such p¯ are produced, and explores the effectiveness of an electric field applied to clear charged particles from the trapping volume before H¯ detection. No mechanisms are found that can give a p¯ such a large cyclotron energy and allow it to mimic an H¯ annihilation. The method used to release H¯ atoms from their magnetic trap without removing the magnetic field gradient that could possibly confine p¯ with a high cyclotron energy is also discussed.
 

Title:   Keldysh approach for nonequilibrium phase transitions in quantum optics: Beyond the Dicke model in optical cavities
Authors:   Torre, Emanuele G. Dalla; Diehl, Sebastian; Lukin, Mikhail D.; Sachdev, Subir; Strack, Philipp
Publication:   Physical Review A, vol. 87, Issue 2, id. 023831 (PhRvA Homepage)
Publication Date:   02/2013
Origin:   APS
PACS Keywords:   Quantum optical phenomena in absorbing, dispersive and conducting media, Decoherence; open systems; quantum statistical methods, Nonequilibrium and irreversible thermodynamics, Path-integral methods
DOI:   10.1103/PhysRevA.87.023831
Bibliographic Code:   2013PhRvA..87b3831T

Abstract

We investigate nonequilibrium phase transitions for driven atomic ensembles interacting with a cavity mode and coupled to a Markovian dissipative bath. In the thermodynamic limit and at low frequencies, we show that the distribution function of the photonic mode is thermal, with an effective temperature set by the atom-photon interaction strength. This behavior characterizes the static and dynamic critical exponents of the associated superradiance transition. Motivated by these considerations, we develop a general Keldysh path-integral approach that allows us to study physically relevant nonlinearities beyond the idealized Dicke model. Using standard diagrammatic techniques, we take into account the leading-order corrections due to the finite number N of atoms. For finite N, the photon mode behaves as a damped classical nonlinear oscillator at finite temperature. For the atoms, we propose a Dicke action that can be solved for any N and correctly captures the atoms’ depolarization due to dissipative dephasing.
 

Title:   Efficient calculation of the effective single-particle potential and its application in electron microscopy
Authors:   Wang, Wei L.; Kaxiras, Efthimios
Publication:   Physical Review B, vol. 87, Issue 8, id. 085103 (PhRvB Homepage)
Publication Date:   02/2013
Origin:   APS
PACS Keywords:   Density functional theory, local density approximation, gradient and other corrections
DOI:   10.1103/PhysRevB.87.085103
Bibliographic Code:   2013PhRvB..87h5103W

Abstract

We present an efficient method for obtaining the effective single-particle potential for electrons within density functional theory (DFT). In contrast to the independent atom model (IAM) often used to interpret microscopy experiments, our method includes the contributions from charge redistribution and exchange-correlation interactions in a realistic system. The method allows calculation of the effective potential through the widely used pseudopotential formalism instead of the costly all-electron calculations. A transferable and spin-independent core potential for each element is calculated once and for all. The nonlinear exchange-correlation interaction is treated explicitly. This scheme can be readily implemented in pseudopotential DFT codes. We demonstrate the usefulness of our method by calculating the scattering potential and simulating images of nitrogen point defects in graphene for transmission electron microscopy (TEM). The results are in good agreement with experiments.
 

Title:   Multipoint correlators of conformal field theories: Implications for quantum critical transport
Authors:   Chowdhury, Debanjan; Raju, Suvrat; Sachdev, Subir; Singh, Ajay; Strack, Philipp
Publication:   Physical Review B, vol. 87, Issue 8, id. 085138 (PhRvB Homepage)
Publication Date:   02/2013
Origin:   APS
PACS Keywords:   Quantum transport, Gauge/string duality, Field theories in dimensions other than four
DOI:   10.1103/PhysRevB.87.085138
Bibliographic Code:   2013PhRvB..87h5138C

Abstract

We compute three-point correlators between the stress-energy tensor and the conserved currents of conformal field theories (CFTs) in 2+1 dimensions. We first compute the correlators in the large-flavor-number expansion of conformal gauge theories and then perform the computation using holography. In the holographic approach, the correlators are computed from an effective action on (3+1)-dimensional anti-de Sitter space (AdS4) and depend upon the coefficient γ of a four-derivative term in the action. We find a precise match between the CFT and the holographic results, thus, fixing the values of γ. The CFTs of free fermions and bosons take the values γ=1/12,‑1/12, respectively, and so saturate the bound |γ|≤1/12 obtained earlier from the holographic theory; the correlator of the conserved gauge flux of U(1) gauge theories takes intermediate values of γ. The value of γ also controls the frequency dependence of the conductivity and other properties of quantum critical transport at nonzero temperatures. Our results for the values of γ lead to an appealing physical interpretation of particlelike or vortexlike transport near quantum phase transitions of interest in condensed-matter physics. This paper includes Appendices reviewing key features of the AdS-CFT correspondence for condensed-matter physicists.
 

Title:   Search for di-muon decays of a low-mass Higgs boson in radiative decays of the Υ(1S)
Authors:   Lees, J. P.; Poireau, V.; Tisserand, V.; ... Morii, M.;...; and 357 coauthors.
Publication:   Physical Review D, vol. 87, Issue 3, id. 031102 (PhRvD Homepage)
Publication Date:   02/2013
Origin:   APS
PACS Keywords:   Extensions of electroweak Higgs sector, Supersymmetric models, Decays of J/psi, Upsilon, and other quarkonia, Decays of muons
DOI:   10.1103/PhysRevD.87.031102
Bibliographic Code:   2013PhRvD..87c1102L

Abstract

We search for di-muon decays of a low-mass Higgs boson (A0) produced in radiative Υ(1S) decays. The Υ(1S) sample is selected by tagging the pion pair in the Υ(2S,3S)→π+π-Υ(1S) transitions, using a data sample of 92.8×106 Υ(2S) and 116.8×106 Υ(3S) events collected by the BABAR detector. We find no evidence for A0 production and set 90% confidence level upper limits on the product branching fraction B(Υ(1S)→γA0)×B(A0→μ+μ-) in the range of (0.28-9.7)×10-6 for 0.212≤mA0≤9.20GeV/c2. The results are combined with our previous measurements of Υ(2S,3S)→γA0, A0→μ+μ- to set limits on the effective coupling of the b quark to the A0.
 

Title:   Dissolution-driven convection in a Hele-Shaw cell
Authors:   Slim, Anja C.; Bandi, M. M.; Miller, Joel C.; Mahadevan, L.
Publication:   Physics of Fluids, Volume 25, Issue 2, pp. 024101-024101-20 (2013). (PhFl Homepage)
Publication Date:   02/2013
Origin:   AIP
Keywords:   carbon capture and storage, carbon compounds, convection, diffusion, dissolving, geochemistry, geophysical fluid dynamics, potassium compounds
PACS Keywords:   Environmental studies, Geochemistry, Natural convection, Viscosity, diffusion, and thermal conductivity
Abstract Copyright:   (c) 2013: American Institute of Physics
DOI:   10.1063/1.4790511
Bibliographic Code:   2013PhFl...25b4101S

Abstract

Motivated by convection in the context of geological carbon-dioxide (CO2) storage, we present an experimental study of dissolution-driven convection in a Hele-Shaw cell for Rayleigh numbers in the range 100<<1700. We use potassium permanganate (KMnO4) in water as an analog for CO2 in brine and infer concentration profiles at high spatial and temporal resolution and accuracy from transmitted light intensity. We describe behavior from first contact up to 65% average saturation and measure several global quantities including dissolution flux, average concentration, amplitude of perturbations away from pure one-dimensional diffusion, and horizontally averaged concentration profiles. We show that the flow evolves successively through distinct regimes starting with a simple one-dimensional diffusional profile. This is followed by linear growth in which fingers are initiated and grow quasi-exponentially, independently of one-another. Once the fingers are well-established, a flux-growth regime begins as fresh fluid is brought to the interface and contaminated fluid removed, with the flux growing to a local maximum. During this regime, fingers still propagate independently. However, beyond the flux maximum, fingers begin to interact and zip together from the root down in a merging regime. Several generations of merging occur before only persistent primary fingers remain. Beyond this, the reinitiation regime begins with new fingers created between primary existing ones before merging into them. Through appropriate scaling, we show that the regimes are universal and independent of layer thickness (equivalently ) until the fingers hit the bottom. At this time, progression through these regimes is interrupted and the flow transitions to a saturating regime. In this final regime, the flux gradually decays in a manner well described by a Howard-style phenomenological model.
 

Title:   Measurement of the flavour composition of dijet events in pp collisions at sqrt{s}=7 {TeV} with the ATLAS detector
Authors:   Aad, G.; Abajyan, T.; Abbott, B.;...Guimaraes da Costa, J.;... Huth, J.;... Morii, M.;...; and 2902 coauthors.
Publication:   The European Physical Journal C, Volume 73, article id. #2301 (EPJC Homepage)
Publication Date:   02/2013
Origin:   SPRINGER
Abstract Copyright:   (c) 2013: CERN for the benefit of the ATLAS collaboration
DOI:   10.1140/epjc/s10052-013-2301-5
Bibliographic Code:   2013EPJC...73.2301A

Abstract

This paper describes a measurement of the flavour composition of dijet events produced in pp collisions at sqrt{s} =7{ TeV} using the ATLAS detector. The measurement uses the full 2010 data sample, corresponding to an integrated luminosity of 39 pb-1. Six possible combinations of light, charm and bottom jets are identified in the dijet events, where the jet flavour is defined by the presence of bottom, charm or solely light flavour hadrons in the jet. Kinematic variables, based on the properties of displaced decay vertices and optimised for jet flavour identification, are used in a multidimensional template fit to measure the fractions of these dijet flavour states as functions of the leading jet transverse momentum in the range 40 GeV to 500 GeV and jet rapidity | y|<2.1. The fit results agree with the predictions of leading- and next-to-leading-order calculations, with the exception of the dijet fraction composed of bottom and light flavour jets, which is underestimated by all models at large transverse jet momenta. The ability to identify jets containing two b-hadrons, originating from e.g. gluon splitting, is demonstrated. The difference between bottom jet production rates in leading and subleading jets is consistent with the next-to-leading-order predictions.
 

Title:   Search for the Higgs boson in the all-hadronic final state using the full CDF data set
Authors:   Aaltonen, T.; Álvarez González, B.; Amerio, S.;... Franklin, M.;... Guimaraes da Costa, J.;... and 471 coauthors.
Publication:   Journal of High Energy Physics, Volume 2013, article id. #4
Publication Date:   02/2013
Origin:   SPRINGER
Keywords:   Hadron-Hadron Scattering
Abstract Copyright:   (c) 2013: SISSA
DOI:   10.1007/JHEP02(2013)004
Bibliographic Code:   2013JHEP...02..004A

Abstract

This paper reports the result of a search for the standard model Higgs boson in events containing four reconstructed jets associated with quarks. For masses below 135 GeV/ c 2, the Higgs boson decays to bottom-antibottom quark pairs are dominant and result primarily in two hadronic jets. An additional two jets can be produced in the hadronic decay of a W or Z boson produced in association with the Higgs boson, or from the incoming quarks that produced the Higgs boson through the vector-boson fusion process. The search is performed using a sample of sqrt{s}=1.96 TeV proton-antiproton collisions corresponding to an integrated luminosity of 9.45 fb-1 recorded by the CDF II detector. The data are in agreement with the background model and 95% credibility level upper limits on Higgs boson production are set as a function of the Higgs boson mass. The median expected (observed) limit for a 125 GeV/ c 2 Higgs boson is 11.0 (9.0) times the predicted standard model rate.[Figure not available: see fulltext.]
 

Title:   Search for the neutral Higgs bosons of the minimal supersymmetric standard model in pp collisions at sqrt{s}=7 TeV with the ATLAS detector
Authors:   Aad, G.; Abajyan, T.; Abbott, B.;...Guimaraes da Costa, J.;... Huth, J.;... Morii, M.;...; and 2879 coauthors.
Publication:   Journal of High Energy Physics, Volume 2013, article id. #95
Publication Date:   02/2013
Origin:   SPRINGER
Keywords:   Hadron-Hadron Scattering
Abstract Copyright:   (c) 2013: CERN for the benefit of the ATLAS collaboration
DOI:   10.1007/JHEP02(2013)095
Bibliographic Code:   2013JHEP...02..095A

Abstract

A search for neutral Higgs bosons of the Minimal Supersymmetric Standard Model (MSSM) is reported. The analysis is based on a sample of proton-proton collisions at a centre-of-mass energy of 7 TeV recorded with the ATLAS detector at the Large Hadron Collider. The data were recorded in 2011 and correspond to an integrated luminosity of 4.7 fb-1 to 4.8 fb-1. Higgs boson decays into oppositely-charged muon or τ lepton pairs are considered for final states requiring either the presence or absence of b-jets. No statistically significant excess over the expected background is observed and exclusion limits at the 95% confidence level are derived. The exclusion limits are for the production cross-section of a generic neutral Higgs boson, ϕ, as a function of the Higgs boson mass and for h/ A/ H production in the MSSM as a function of the parameters m A and tan β in the m_h^{max } scenario for m A in the range of 90 GeV to 500 GeV.[Figure not available: see fulltext.]
 

Title:   Measurement of the Λb0 lifetime and mass in the ATLAS experiment
Authors:   Aad, G.; Abajyan, T.; Abbott, B.;...Guimaraes da Costa, J.;... Huth, J.;... Morii, M.;...; and 2867 coauthors.
Publication:   Physical Review D, vol. 87, Issue 3, id. 032002 (PhRvD Homepage)
Publication Date:   02/2013
Origin:   APS
PACS Keywords:   Bottom baryons
DOI:   10.1103/PhysRevD.87.032002
Bibliographic Code:   2013PhRvD..87c2002A

Abstract

A measurement of the Λb0 lifetime and mass in the decay channel Λb0→J/ψ(μ+μ-0(pπ-) is presented. The analysis uses a signal sample of about 2200 Λb0 and Λ¯b0 decays that are reconstructed in 4.9fb-1 of ATLAS pp collision data collected in 2011 at the LHC center-of-mass energy of 7 TeV. A simultaneous mass and decay time maximum likelihood fit is used to extract the Λb0 lifetime and mass. They are measured to be τΛb=1.449±0.036(stat)±0.017(syst)ps and mΛb=5619.7±0.7(stat)±1.1(syst)MeV.
 

Title:   Branching fraction measurement of B+→ωℓ+ν decays
Authors:   Lees, J. P.; Poireau, V.; Tisserand, V.; ... Morii, M.;...; and 362 coauthors.
Publication:   Physical Review D, vol. 87, Issue 3, id. 032004 (PhRvD Homepage)
Publication Date:   02/2013
Origin:   APS
PACS Keywords:   Bottom mesons, Determination of Kobayashi-Maskawa matrix elements, Decays of bottom mesons
DOI:   10.1103/PhysRevD.87.032004
Bibliographic Code:   2013PhRvD..87c2004L

Abstract

We present a measurement of the B+→ωℓ+ν branching fraction based on a sample of 467 million BB¯ pairs recorded by the BABAR detector at the SLAC PEP-II e+e- collider. We observe 1125±131 signal decays, corresponding to a branching fraction of B(B+→ωℓ+ν)=(1.21±0.14±0.08)×10-4, where the first error is statistical and the second is systematic. The dependence of the decay rate on q2, the invariant mass squared of the leptons, is compared to QCD predictions of the form factors based on a quark model and light-cone sum rules.
 

Title:   Comparisons of annual modulations in MINOS with the event rate modulation in CoGeNT
Authors:   Adamson, P.; Anghel, I.; Barr, G.;... Feldman, G. J.;...
Publication:   Physical Review D, vol. 87, Issue 3, id. 032005 (PhRvD Homepage)
Publication Date:   02/2013
Origin:   APS
PACS Keywords:   Neutrino, muon, pion, and other elementary particles; cosmic rays, Scintillation detectors, Dark matter
DOI:   10.1103/PhysRevD.87.032005
Bibliographic Code:   2013PhRvD..87c2005A

Abstract

The CoGeNT Collaboration has recently published results from a fifteen month data set which indicate an annual modulation in the event rate similar to what is expected from weakly interacting massive particle interactions. It has been suggested that the CoGeNT modulation may actually be caused by other annually modulating phenomena, specifically the flux of atmospheric muons underground or the radon level in the laboratory. We have compared the phase of the CoGeNT data modulation to that of the concurrent atmospheric muon and radon data collected by the MINOS experiment which occupies an adjacent experimental hall in the Soudan Underground Laboratory. The results presented are obtained by performing a shape-free χ2 data-to-data comparison and from a simultaneous fit of the MINOS and CoGeNT data to phase-shifted sinusoidal functions. Both tests indicate that the phase of the CoGeNT modulation is inconsistent with the phases of the MINOS muon and radon modulations at the 3.0σ level.
 

Title:   Collectively Enhanced Interactions in Solid-State Spin Qubits
Authors:   Weimer, Hendrik; Yao, Norman Y.; Lukin, Mikhail D.
Publication:   Physical Review Letters, vol. 110, Issue 6, id. 067601 (PhRvL Homepage)
Publication Date:   02/2013
Origin:   APS
PACS Keywords:   Color centers and other defects, Quantum computation, Magnetic impurity interactions
DOI:   10.1103/PhysRevLett.110.067601
Bibliographic Code:   2013PhRvL.110f7601W

Abstract

We propose and analyze a technique to collectively enhance interactions between solid-state quantum registers composed from random networks of spin qubits. In such systems, disordered dipolar interactions generically result in localization. Here, we demonstrate the emergence of a single collective delocalized eigenmode as one turns on a transverse magnetic field. The interaction strength between this symmetric collective mode and a remote spin qubit is enhanced by the square root of the number of spins participating in the delocalized mode. Mediated by such collective enhancement, long-range quantum logic between remote spin registers can occur at distances consistent with optical addressing. A specific implementation utilizing nitrogen-vacancy defects in diamond is discussed and the effects of decoherence are considered.
 

Title:   Measurement of W-boson polarization in top-quark decay using the full CDF Run II data set
Authors:   Aaltonen, T.; Amerio, S.; Amidei, D.;... Guimaraes da Costa, J.;... Franklin, M.;... and 406 coauthors.
Publication:   Physical Review D, vol. 87, Issue 3, id. 031104 (PhRvD Homepage)
Publication Date:   02/2013
Origin:   APS
PACS Keywords:   W bosons, Polarization in interactions and scattering, Top quarks
DOI:   10.1103/PhysRevD.87.031104
Bibliographic Code:   2013PhRvD..87c1104A

Abstract

We measure the polarization of W bosons from top-quark (t) decays into final states with a charged lepton and jets, tt¯→W+bW-b¯→ℓνbqq¯'b¯, using the full Run II data set collected by the CDF II detector, corresponding to an integrated luminosity of 8.7fb-1. A model-independent method simultaneously determines the fraction of longitudinal (f0) and right-handed (f+) W bosons to yield f0=0.726±0.066(stat)±0.067(syst) and f+=-0.045±0.044(stat)±0.058(syst) with a correlation coefficient of -0.69. Additional results are presented under various standard model assumptions. No significant discrepancies with the standard model are observed.
 

Title:   Topological Blockade and Measurement of Topological Charge
Authors:   van Heck, B.; Burrello, M.; Yacoby, A.; Akhmerov, A. R.
Publication:   Physical Review Letters, vol. 110, Issue 8, id. 086803 (PhRvL Homepage)
Publication Date:   02/2013
Origin:   APS
PACS Keywords:   Quantum Hall effects, Fractional statistics systems, Quantum computation
DOI:   10.1103/PhysRevLett.110.086803
Bibliographic Code:   2013PhRvL.110h6803V

Abstract

The fractionally charged quasiparticles appearing in the 5/2 fractional quantum Hall plateau are predicted to have an extra nonlocal degree of freedom, known as topological charge. We show how this topological charge can block the tunneling of these particles, and how such topological blockade can be used to read out their topological charge. We argue that the short time scale required for this measurement is favorable for the detection of the non-Abelian anyonic statistics of the quasiparticles. We also show how topological blockade can be used to measure braiding statistics, and to couple a topological qubit with a conventional one.
 

Title:   Tuning the Electronic and Chemical Properties of Monolayer MoS2Adsorbed on Transition Metal Substrates
Authors:   Chen, Wei; Santos, Elton J. G.; Zhu, Wenguang; Kaxiras, Efthimios; Zhang, Zhenyu
Publication:   Nano Letters, vol. 13, issue 2, pp. 509-514
Publication Date:   02/2013
Origin:   CROSSREF
DOI:   10.1021/nl303909f
Bibliographic Code:   2013NanoL..13..509C

Abstract

Not Available
 

Title:   Measurement of W-boson polarization in top-quark decay using the full CDF Run II data set
Authors:   Aaltonen, T.; Amerio, S.; Amidei, D.; ...; Franklin, M.;... Guimaraes da Costa, J.;... and 406 coauthors.
Publication:   Physical Review D, vol. 87, Issue 3, id. 031104 (PhRvD Homepage)
Publication Date:   02/2013
Origin:   APS
PACS Keywords:   W bosons, Polarization in interactions and scattering, Top quarks
DOI:   10.1103/PhysRevD.87.031104
Bibliographic Code:   2013PhRvD..87c1104A

Abstract

We measure the polarization of W bosons from top-quark (t) decays into final states with a charged lepton and jets, tt¯→W+bW-b¯→ℓνbqq¯'b¯, using the full Run II data set collected by the CDF II detector, corresponding to an integrated luminosity of 8.7fb-1. A model-independent method simultaneously determines the fraction of longitudinal (f0) and right-handed (f+) W bosons to yield f0=0.726±0.066(stat)±0.067(syst) and f+=-0.045±0.044(stat)±0.058(syst) with a correlation coefficient of -0.69. Additional results are presented under various standard model assumptions. No significant discrepancies with the standard model are observed.
 

Title:   Study of the decay $\bar{B}^{0}\rightarrow\Lambda_{c}^{+}\bar{p}\pi^{+}\pi^{-}$ and its intermediate states
Authors:   The Babar Collaboration; Lees, J. P.; Poireau, V.; Tisserand, V.; ... Morii, M.;...; and 350 coauthors.
Publication:   eprint arXiv:1302.0191
Publication Date:   02/2013
Origin:   ARXIV
Keywords:   High Energy Physics - Experiment
Comment:   20 pages, 30 figures
Bibliographic Code:   2013arXiv1302.0191T

Abstract

We study the decay $\bar{B}^{0}\rightarrow\Lambda_{c}^{+}\bar{p}\pi^{+}\pi^{-}$, reconstructing the \Lambda_{c}^{+} baryon in the $p K^{-}\pi^{+}$ mode, using a data sample of $467\times 10^{6}$ $B\bar{B}$ pairs collected with the BaBar detector at the PEP-2 storage rings at SLAC. We measure branching fractions for decays with intermediate $\Sigma_{c}$ baryons to be ${\cal B}[\bar{B}^{0}\rightarrow\Sigma_{c}(2455)^{++}\bar{p}\pi^{-}]=(21.3 \pm 1.0 \pm 1.0 \pm 5.5) \times 10^{-5}$, ${\cal B}[\bar{B}^{0}\rightarrow\Sigma_{c}(2520)^{++}\bar{p}\pi^{-}]=(11.5\pm 1.0 \pm 0.5 \pm 3.0)\times 10^{-5}$, ${\cal B}[\bar{B}^{0}\rightarrow\Sigma_{c}(2455)^{0}\bar{p}\pi^{+}]=(9.1 \pm 0.7 \pm 0.4 \pm 2.4)\times10^{-5}$, and ${\cal B}[\bar{B}^{0}\rightarrow\Sigma_{c}(2520)^{0}\bar{p}\pi^{+}]= (2.2 \pm 0.7 \pm 0.1\pm 0.6) \times 10^{-5}$, where the uncertainties are statistical, systematic, and due to the uncertainty on the $\Lambda_{c}^{+}\rightarrow\proton\Km\pi^{+}$ branching fraction, respectively. For decays without $\Sigma_{c}(2455)$ or $\Sigma_{c}(2520)$ resonances, we measure ${\cal B}[\bar{B}^{0}\rightarrow\Lambda_{c}^{+}\bar{p}\pi^{+}\pi^{-}]_{\mathrm{non-\Sigma_{c}}}=(79 \pm 4 \pm 4 \pm 20)\times10^{-5}$. The total branching fraction is determined to be ${\cal B}[\bar{B}^{0}\rightarrow\Lambda_{c}^{+}\bar{p}\pi^{+}\pi^{-}]_{\mathrm{total}}=(123 \pm 5 \pm 7 \pm 32)\times10^{-5}$. We examine multibody mass combinations in the resonant three-particle $\Sigma_{c}\bar{p}\pi$ final states and in the four-particle $\Lambda_{c}^{+}\bar{p}\pi^{+}\pi^{-}$ final state, and observe different characteristics for the $\bar{p}\pi$ combination in neutral versus doubly-charged $\Sigma_{c}$ decays.
 

Title:   Dispersing quasinormal modes in 2+1 dimensional conformal field theories
Authors:   Witczak-Krempa, William; Sachdev, Subir
Publication:   eprint arXiv:1302.0847
Publication Date:   02/2013
Origin:   ARXIV
Keywords:   Condensed Matter - Strongly Correlated Electrons, General Relativity and Quantum Cosmology, High Energy Physics - Theory
Comment:   31+9 pages, 11+4 figures. v2: added refs & minor modifications
Bibliographic Code:   2013arXiv1302.0847W

Abstract

We study the charge response of conformal field theories (CFTs) at non-zero temperature in 2+1 dimensions using the AdS/CFT correspondence. A central role is played by the quasinormal modes (QNMs), specifically, the poles and zeros of the current correlators. We generalize our recent study of the QNMs of the a.c. charge conductivity to include momentum dependence. This sheds light on the various excitations in the CFT. We begin by discussing the R-current correlators of the N=8 SU(N) super-Yang-Mills theory at its conformal fixed point using holography. For instance, transitions in the QNM spectrum as a function of momentum clearly identify hydrodynamic-to-relativistic crossovers. We then extend our study to include four-derivative terms in the gravitational description allowing us to study more generic charge response as well as the role of S-duality, which plays a central role in understanding the correlators. The presence of dispersing Drude-like QNMs can lead to new behavior, distinct from what occurs in the aforementioned gauge theory. We also extend previous conductivity sum rules to finite momentum and discuss their interpretation in the gravity picture. A comparison is finally made with the conformal fixed point of the vector O(N) model in the large-N limit.
 

Title:   A semi-local holographic minimal model
Authors:   Chang, Chi-Ming; Yin, Xi
Publication:   eprint arXiv:1302.4420
Publication Date:   02/2013
Origin:   ARXIV
Keywords:   High Energy Physics - Theory
Comment:   31 pages
Bibliographic Code:   2013arXiv1302.4420C

Abstract

We present a conjecture on the complete spectrum of single-trace operators in the infinite N limit of W(N) minimal model and evidences for the conjecture. We further propose that the holographic dual of W(N) minimal model in the 't Hooft limit is an unusual "semi-local" higher spin gauge theory on AdS3 x S^1. At each point on the S^1 lives a copy of three-dimensional Vasiliev theory, that contains an infinite tower of higher spin gauge fields coupled to a single massive complex scalar propagating in AdS3. The Vasiliev theories at different points on the S^1 are correlated only through the AdS3 boundary conditions on the massive scalars. All but one single tower of higher spin symmetries are broken by the boundary conditions.
 

Title:   Swarming, swirling and stasis in sequestered bristle-bots
Authors:   Giomi, L.; Hawley-Weld, N.; Mahadevan, L.
Publication:   eprint arXiv:1302.5952
Publication Date:   02/2013
Origin:   ARXIV
Keywords:   Condensed Matter - Soft Condensed Matter, Condensed Matter - Statistical Mechanics, Nonlinear Sciences - Adaptation and Self-Organizing Systems
Comment:   21 pages, 15 figures, supplementary videos at https://www.youtube.com/user/BristleBotChannel; Proc. R. Soc. A 469, 20120637 (2013); doi:10.1098/rspa.2012.0637
Bibliographic Code:   2013arXiv1302.5952G

Abstract

The collective ability of organisms to move coherently in space and time is ubiquitous in any group of autonomous agents that can move and sense each other and the environment. Here we investigate the origin of collective motion and its loss using macroscopic self-propelled Bristle-Bots, simple automata made from a toothbrush and powered by an onboard cell phone vibrator-motor, that can sense each other through shape-dependent local interactions, and can also sense the environment non-locally via the effects of confinement and substrate topography. We show that when Bristle-Bots are confined to a limited arena with a soft boundary, increasing the density drives a transition from a disordered and uncoordinated motion to organized collective motion either as a swirling cluster or a collective dynamical stasis. This transition is regulated by a single parameter, the relative magnitude of spinning and walking in a single automaton. We explain this using quantitative experiments and simulations that emphasize the role of the agent shape, environment, and confinement via boundaries. Our study shows how the behavioral repertoire of these physically interacting automatons controlled by one parameter translates into the mechanical intelligence of swarms.
 

Title:   Glycans pattern the phase behaviour of lipid membranes
Authors:   Subramaniam, Anand Bala; Guidotti, Guido; Manoharan, Vinothan N.; Stone, Howard A.
Publication:   Nature Materials, Volume 12, Issue 2, pp. 128-133 (2013).
Publication Date:   02/2013
Origin:   NATURE
Abstract Copyright:   (c) 2013: Nature Publishing Group
DOI:   10.1038/nmat3492
Bibliographic Code:   2013NatMa..12..128S

Abstract

Hydrated networks of glycans (polysaccharides)—in the form of cell walls, periplasms or gel-like matrices—are ubiquitously present adjacent to cellular plasma membranes. Yet, despite their abundance, the function of glycans in the extracellular milieu is largely unknown. Here we show that the spatial configuration of glycans controls the phase behaviour of multiphase model lipid membranes: inhomogeneous glycan networks stabilize large lipid domains at the characteristic length scale of the network, whereas homogeneous networks suppress macroscopic lipid phase separation. We also find that glycan-patterned phase separation is thermally reversible—thus indicating that the effect is thermodynamic rather than kinetic—and that phase patterning probably results from a preferential interaction of glycans with ordered lipid phases. These findings have implications for membrane-mediated transport processes, potentially rationalize long-standing observations that differentiate the behaviour of native and model membranes and may indicate an intimate coupling between cellular lipidomes and glycomes.
 

Title:   Comparisons of annual modulations in MINOS with the event rate modulation in CoGeNT
Authors:   Adamson, P.; Anghel, I.; Barr, G.;... Feldman, G. J.; ...; and 101 coauthors.
Publication:   Physical Review D, vol. 87, Issue 3, id. 032005 (PhRvD Homepage)
Publication Date:   02/2013
Origin:   APS
PACS Keywords:   Neutrino, muon, pion, and other elementary particles; cosmic rays, Scintillation detectors, Dark matter
DOI:   10.1103/PhysRevD.87.032005
Bibliographic Code:   2013PhRvD..87c2005A

Abstract

The CoGeNT Collaboration has recently published results from a fifteen month data set which indicate an annual modulation in the event rate similar to what is expected from weakly interacting massive particle interactions. It has been suggested that the CoGeNT modulation may actually be caused by other annually modulating phenomena, specifically the flux of atmospheric muons underground or the radon level in the laboratory. We have compared the phase of the CoGeNT data modulation to that of the concurrent atmospheric muon and radon data collected by the MINOS experiment which occupies an adjacent experimental hall in the Soudan Underground Laboratory. The results presented are obtained by performing a shape-free χ2 data-to-data comparison and from a simultaneous fit of the MINOS and CoGeNT data to phase-shifted sinusoidal functions. Both tests indicate that the phase of the CoGeNT modulation is inconsistent with the phases of the MINOS muon and radon modulations at the 3.0σ level.


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