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ABSTRACT: The doubledifferential cross sections of promptly produced J/ψ and ψ(2S) mesons are measured in pp collisions at sqrt[s]=7 TeV, as a function of transverse momentum p_{T} and absolute rapidity y. The analysis uses J/ψ and ψ(2S) dimuon samples collected by the CMS experiment, corresponding to integrated luminosities of 4.55 and 4.90 fb^{1}, respectively. The results are based on a twodimensional analysis of the dimuon invariant mass and decay length, and extend to p_{T}=120 and 100 GeV for the J/ψ and ψ(2S), respectively, when integrated over the interval y<1.2. The ratio of the ψ(2S) to J/ψ cross sections is also reported for y<1.2, over the range 10<p_{T}<100 GeV. These are the highest p_{T} values for which the cross sections and ratio have been measured.Physical Review Letters 05/2015; 114(19):191802. · 7.51 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: A measurement of the Higgs boson mass is presented based on the combined data samples of the ATLAS and CMS experiments at the CERN LHC in the H→γγ and H→ZZ→4ℓ decay channels. The results are obtained from a simultaneous fit to the reconstructed invariant mass peaks in the two channels and for the two experiments. The measured masses from the individual channels and the two experiments are found to be consistent among themselves. The combined measured mass of the Higgs boson is m_H=125.09±0.21 (stat)±0.11 (syst) GeV.Physical Review Letters 05/2015; 114(19):191803. · 7.51 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: The standard model of particle physics describes the fundamental particles and their interactions via the strong, electromagnetic and weak forces. It provides precise predictions for measurable quantities that can be tested experimentally. The probabilities, or branching fractions, of the strangeB meson (B0s ) andtheB0meson decaying into two oppositely charged muons (μ+ and μ) are especially interesting because of their sensitivity to theories that extend the standard model. The standard model predicts that the B0s→μ+μ and B0s→μ+μ decays are very rare, with about four of the former occurring for every billion B0s mesons produced, and one of the latter occurring for every ten billion B0 mesons1. A difference in the observed branching fractions with respect to the predictions of the standard model would provide a direction in which the standard model should be extended. Before the Large Hadron Collider (LHC) at CERN2 started operating, no evidence for either decay mode had been found. Upper limits on the branching fractions were an order of magnitude above the standard model predictions. The CMS (CompactMuonSolenoid) andLHCb(LargeHadronCollider beauty) collaborations have performed a joint analysis of the data from proton'proton collisions that they collected in 2011 at a centreofmass energy of seven teraelectronvolts and in 2012 at eight teraelectronvolts. Here we report the first observation of the B0s→μ+μ decay, with a statistical significance exceeding six standard deviations, and the best measurement so far of its branching fraction. Furthermore, we obtained evidence for the B0s→μ+μ decay with a statistical significance of three standard deviations. Both measurements are statistically compatible with standard model predictions and allow stringent constraints to be placed on theories beyond the standardmodel. The LHCexperimentswill resume taking data in 2015, recording proton'proton collisions at a centreofmass energy of 13 teraelectronvolts, which will approximately double the production rates of B0s and B0 mesons and lead to further improvements in the precision of these crucial tests of the standard model.Nature 05/2015; 522(7554). DOI:10.1038/nature14474 · 41.46 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: A search is presented for the decay ϒ(1S)→γA[superscript 0], A[superscript 0] → c[bar over c], where A[superscript 0] is a candidate for the CPodd Higgs boson of the nexttominimal supersymmetric standard model. The search is based on data collected with the BABAR detector at the ϒ(2S) resonance. A sample of ϒ(1S) mesons is selected via the decay ϒ(2S) → π[superscript +]π[superscript ]ϒ(1S). The A[superscript 0] → c[bar over c] decay is identified through the reconstruction of hadronic D[superscript 0], D[superscript +], and D[superscript *](2010)[superscript +] meson decays. No significant signal is observed. The measured 90% confidencelevel upper limits on the product branching fraction B(ϒ(1S) → γA[superscript 0]) × B(A[superscript 0] → c[bar over c]) range from 7.4 × 10[superscript 5] to 2.4 × 10[superscript 3] for A[superscript 0] masses from 4.00 to 8.95 GeV/c[superscript 2] and 9.10 to 9.25 GeV/c[superscript 2], where the region between 8.95 and 9.10 GeV/c[superscript 2] is excluded because of background from ϒ(2S) → γχ[subscript bJ](1P), χ[subscript bJ](1P) → γϒ(1S) decays.  [Show abstract] [Hide abstract]
ABSTRACT: We perform a measurement of the τ → lγν[bar over ν] (l = e,μ) branching fractions for a minimum photon energy of 10 MeV in the τ rest frame, using 431 fb[superscript 1] of e[superscript +]e[superscript ] collisions collected at the centerofmass energy of the ϒ(4S) resonance with the BABAR detector at the PEPII storage rings. We find B(τ → μγν[bar over ν]) = (3.69 ± 0.03 ± 0.10) × 10[superscript 3] and B(τ → eγν[bar over ν]) = (1.847 ± 0.015 ± 0.052) × 10[superscript 2], where the first quoted error is statistical and the second is systematic. These results are substantially more precise than previous measurements.  [Show abstract] [Hide abstract]
ABSTRACT: Based on a sample of 500 million e[superscript +]e[superscript ] → c[bar over c] events recorded by the BABAR detector at c.m. energies of close to 10.6 GeV, we report on a study of the decay D[superscript 0] → π[superscript ]e[superscript +]ν[subscript e]. We measure the ratio of branching fractions, R[subscript D] = B(D[superscript 0] → π[superscript ]e[superscript +]ν[subscript e])/B(D[superscript 0] → K[superscript ]π[superscript +]) = 0.0713 ± 0.0017[subscript stat] ± 0.0024[subscript syst], and use the present world average for B(D[superscript 0] → K[superscript ]π[superscript +] to obtain B(D[superscript 0] → π[superscript ]e[superscript +]ν[subscript e]) = (2.770 ± 0.068[subscript stat] ± 0.092[subscript syst] ± 0.037[subscript ext]) × 10[superscript 3] where the third error accounts for the uncertainty on the branching fraction for the reference channel. The measured dependence of the differential branching fraction on q[superscript 2], the fourmomentum transfer squared between the D and the π meson, is compared to various theoretical predictions for the hadronic form factor, f[π over +,D](q[superscript 2]), and the normalization V[subscript cd] × f[π over +,D](q[superscript 2] = 0) = 0.1374 ± 0.0038[subscript stat] ± 0.0022[subscript syst] ± 0.0009[subscript ext] is extracted from a fit to data. Using the most recent LQCD prediction of f[π over +,D](q[superscript 2] = 0) = 0.666 ± 0.029, we obtain V[subscript cd] = 0.206 ± 0.007[subscript exp] ± 0.009[subscript LQCD]. Assuming, instead, V[subscript cd] = V[subscript us] = 0.2252 ± 0.0009, we obtain f[π over +,D](q[superscript 2] = 0) = 0.610 ± 0.020subscript exp] ± 0.005[subscript ext]. The q[superscript 2] dependence of f[π over +,D](q[superscript 2]) is compared to a variety of multipole parametrizations. This information is applied to B[superscript 0] → π[superscript ]e[superscript +]ν[subscript e] decays and, combined with an earlier B[superscript 0] → π[superscript ]e[superscript +]ν[subscript e] measurement by BABAR, is used to derive estimates of V[subscript ub].  [Show abstract] [Hide abstract]
ABSTRACT: Abstract: The production of Z bosons is studied in the dimuon and dielectron decay channels in PbPb and pp collisions at (Formula presented.) TeV, using data collected by the CMS experiment at the LHC. The PbPb data sample corresponds to an integrated luminosity of about 166 μb−1, while the pp data sample collected in 2013 at the same nucleonnucleon centreofmass energy has an integrated luminosity of 5.4 pb−1. The Z boson yield is measured as a function of rapidity, transverse momentum, and collision centrality. The ratio of PbPb to pp yields, scaled by the number of inelastic nucleonnucleon collisions, is found to be 1.06 ± 0.05 (stat) ± 0.08 (syst) in the dimuon channel and 1.02 ± 0.08 (stat) ± 0.15 (syst) in the dielectron channel, for centralityintegrated Z boson production. This binary collision scaling is seen to hold in the entire kinematic region studied, as expected for a colourless probe that is unaffected by the hot and dense QCD medium produced in heavy ion collisions.Journal of High Energy Physics 03/2015; 2015(3). DOI:10.1007/JHEP03(2015)022 · 6.11 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We present Dalitz plot analyses for the decays of B mesons to D[superscript −]D[superscript 0]K[superscript +] and [bar over D][superscript 0]D[superscript 0]K[superscript +]. We report the observation of the D[* over s1](2700)[superscript +] resonance in these two channels and obtain measurements of the mass M(D[* over s1](2700)[superscript +]) = 2699[+14 over −7] MeV/c[superscript 2] and of the width Γ(D[* over s1](2700)[superscript +]) = 127[+24 over −19] MeV, including statistical and systematic uncertainties. In addition, we observe an enhancement in the D[superscript 0]K[superscript +] invariant mass around 2350–2500 MeV/c[superscript 2] in both decays B[superscript 0] → D[superscript −]D[superscript 0]K[superscript +] and B[superscript +] → [bar over D][superscript 0]D[superscript 0]K[superscript +], which we are not able to interpret. The results are based on 429 fb[superscript −1] of data containing 471×10[superscript 6]B[bar over B] pairs collected at the ϒ(4S) resonance with the BABAR detector at the SLAC National Accelerator Laboratory.  [Show abstract] [Hide abstract]
ABSTRACT: We report the observation of the baryonic decay [bar over B][superscript 0 → Λ[+ over c][bar over p]K[superscript ]K[superscript +] using a data sample of 471 × 10[superscript 6] B[bar over B] pairs produced in e[superscript +]e[superscript ] annihilations at √s = 10.58 GeV. This data sample was recorded with the BABAR detector at the PEPII storage ring at SLAC. We find B([bar over B][superscript 0 → Λ[+ over c][bar over p]K[superscript ]K[superscript +]) = (2.5 ± 0.4[subscript (stat)] ± 0.2[subscript (syst)] ± 0.6[subscript B(Λ[+ over c])) × 10[superscript 5], where the uncertainties are statistical, systematic, and due to the uncertainty of the Λ[+ over c] → pK[superscript ]π[superscript +] branching fraction, respectively. The result has a significance corresponding to 5.0 standard deviations, including all uncertainties. For the resonant decay [bar over B][superscript 0] → Λ[+ over c][bar over p]ϕ, we determine the upper limit B([bar over B][superscript 0] → Λ[+ over c][bar over p]ϕ) < 1.2 × 10[superscript 5] at 90% confidence level.  [Show abstract] [Hide abstract]
ABSTRACT: We present a measurement of the asymmetry A[subscript CP] between samesign inclusive dilepton samples ℓ[superscript +]ℓ[superscript +] and ℓ[superscript −]ℓ[superscript −] (ℓ=e, μ) from semileptonic B decays in Υ(4S)→B[bar over B] events, using the complete data set recorded by the BABAR experiment near the Υ(4S) resonance, corresponding to 471×10[superscript 6] B[bar over B] pairs. The asymmetry A[subscript CP] allows comparison between the mixing probabilities P([bar over B][superscript 0]→B[superscript 0]) and P(B[superscript 0]→[bar over B][superscript 0]), and therefore probes CP and T violation. The result, A[subscript CP]=[−3.9±3.5(stat)±1.9(syst)]×10[superscript −3], is consistent with the standard model expectation.  [Show abstract] [Hide abstract]
ABSTRACT: A search for new longlived particles decaying to leptons is presented using protonproton collisions produced by the LHC at sqrt[s]=8 TeV. Data used for the analysis were collected by the CMS detector and correspond to an integrated luminosity of 19.7 fb^{1}. Events are selected with an electron and muon with opposite charges that both have transverse impact parameter values between 0.02 and 2 cm. The search has been designed to be sensitive to a wide range of models with nonprompt eμ final states. Limits are set on the "displaced supersymmetry" model, with pair production of top squarks decaying into an eμ final state via Rparityviolating interactions. The results are the most restrictive to date on this model, with the most stringent limit being obtained for a top squark lifetime corresponding to cτ=2 cm, excluding masses below 790 GeV at 95% confidence level.Physical Review Letters 02/2015; 114(6):061801. · 7.51 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: A search for new physics is performed based on events with jets and a pair of isolated, samesign leptons. The results are obtained using a sample of protonproton collision data collected by the CMS experiment at a centreofmass energy of 8 TeV at the LHC, corresponding to an integrated luminosity of 19.5 fb1. In order to be sensitive to a wide variety of possible signals beyond the standard model, multiple search regions defined by the missing transverse energy, the hadronic energy, the number of jets and bquark jets, and the transverse momenta of the leptons in the events are considered. No excess above the standard model background expectation is observed and constraints are set on a number of models for new physics, as well as on the samesign topquark pair and quadrupletopquark production cross sections. Information on event selection efficiencies is also provided, so that the results can be used to confront an even broader class of new physics models. [Figure not available: see fulltext.]Journal of High Energy Physics 01/2015; 2015(1). DOI:10.1007/JHEP01(2015)014 · 6.11 Impact Factor 
Article: Search for new π[superscript 0]like particles produced in association with a τlepton pair
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ABSTRACT: We report on a search in e[superscript +]e[superscript ] annihilations for new π[superscript 0]like particles produced in association with a τlepton pair. These objects, with a similar mass and similar decay modes to π[superscript 0] mesons, could provide an explanation for the nonasymptotic behavior of the pionphoton transition form factor observed by the BABAR Collaboration. No significant signal is observed, and limits on the production cross section at the level of 73 fb or 370 fb, depending on the model parameters, are determined at 90% confidence level. These upper limits lie below the cross section values needed to explain the BABAR form factor data.  [Show abstract] [Hide abstract]
ABSTRACT: We use (121 ± 1) million Υ(3S) and (98 ± 1) million Υ(2S) mesons recorded by the BABAR detector at the PEPII e[superscript +]e[superscript ] collider at SLAC to perform a study of radiative transitions involving the χ[subscript bJ](1P,2P) states in exclusive decays with μ[superscript +]μ[superscript ]γγ final states. We reconstruct twelve channels in four cascades using two complementary methods. In the first we identify both signal photon candidates in the electromagnetic calorimeter (EMC), employ a calorimeter timingbased technique to reduce backgrounds, and determine branchingratio products and fine mass splittings. These results include the best observational significance yet for the χ[subscript b0](2P) → γΥ(2S) and χ[subscript b0](1P) → γΥ(1S) transitions. In the second method, we identify one photon candidate in the EMC and one which has converted into an e[superscript +]e[superscript ] pair due to interaction with detector material, and we measure absolute product branching fractions. This method is particularly useful for measuring Υ(3S) → γχ[subscript b1,2](1P) decays. Additionally, we provide the most uptodate derived branching fractions, matrix elements and mass splittings for χ[subscript b] transitions in the bottomonium system. Using a new technique, we also measure the two lowestorder spindependent coefficients in the nonrelativistic QCD Hamiltonian.  [Show abstract] [Hide abstract]
ABSTRACT: This article reports world averages of measurements of $b$hadron, $c$hadron, and $\tau$lepton properties obtained by the Heavy Flavor Averaging Group (HFAG) using results available through summer 2014. For the averaging, common input parameters used in the various analyses are adjusted (rescaled) to common values, and known correlations are taken into account. The averages include branching fractions, lifetimes, neutral meson mixing parameters, $CP$ violation parameters, parameters of semileptonic decays and CKM matrix elements.  [Show abstract] [Hide abstract]
ABSTRACT: Searches are presented for heavy scalar (H) and pseudoscalar (A) Higgs bosons posited in the two doublet model (2HDM) extensions of the standard model (SM). These searches are based on a data sample of pp collisions collected with the CMS experiment at the LHC at a centerofmass energy of s=8TeV and corresponding to an integrated luminosity of 19.5fb1. The decays H→hh and A→Zh, where h denotes an SMlike Higgs boson, lead to events with three or more isolated charged leptons or with a photon pair accompanied by one or more isolated leptons. The search results are presented in terms of the H and A production cross sections times branching fractions and are further interpreted in terms of 2HDM parameters. We place 95% C.L. cross section upper limits of approximately 7 pb on σB for H→hh and 2 pb for A→Zh. Also presented are the results of a search for the rare decay of the top quark that results in a charm quark and an SM Higgs boson, t→ch, the existence of which would indicate a nonzero flavorchanging Yukawa coupling of the top quark to the Higgs boson. We place a 95% C.L. upper limit of 0.56% on B(t→ch).Physical Review D 12/2014; 90(11). DOI:10.1103/PhysRevD.90.112013 · 4.64 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: Searches for supersymmetry (SUSY) are presented based on the electroweak pair production of neutralinos and charginos, leading to decay channels with Higgs, Z, and W bosons and undetected lightest SUSY particles (LSPs). The data sample corresponds to an integrated luminosity of about 19.5 fb[superscript −1] of protonproton collisions at a centerofmass energy of 8 TeV collected in 2012 with the CMS detector at the LHC. The main emphasis is neutralino pair production in which each neutralino decays either to a Higgs boson (h) and an LSP or to a Z boson and an LSP, leading to hh, hZ, and ZZ states with missing transverse energy (E[miss over T]). A second aspect is charginoneutralino pair production, leading to hW states with E[miss over T]. The decays of a Higgs boson to a bottomquark pair, to a photon pair, and to final states with leptons are considered in conjunction with hadronic and leptonic decay modes of the Z and W bosons. No evidence is found for supersymmetric particles, and 95% confidence level upper limits are evaluated for the respective pair production cross sections and for neutralino and chargino mass values.  [Show abstract] [Hide abstract]
ABSTRACT: We present measurements of Collins asymmetries in the inclusive process e[superscript +]e[superscript −] → ππX, where π stands for charged pions, at a centerofmass energy of 10.6 GeV. We use a data sample of 468 fb[superscript 1] collected by the BABAR experiment at the PEPII B factory at SLAC, and consider pairs of charged pions produced in opposite hemispheres of hadronic events. We observe clear asymmetries in the distributions of the azimuthal angles in two distinct reference frames. We study the dependence of the asymmetry on several kinematic variables, finding that it increases with increasing pion momentum and momentum transverse to the analysis axis, and with increasing angle between the thrust and beam axis.  [Show abstract] [Hide abstract]
ABSTRACT: Dark sectors charged under a new Abelian interaction have recently received much attention in the context of dark matter models. These models introduce a light new mediator, the socalled dark photon (A[superscript ′]), connecting the dark sector to the standard model. We present a search for a dark photon in the reaction e[superscript +] e[superscript ] →γA[superscript ′], A[superscript ′] → e[superscript +]e[superscript ], μ[superscript +]μ[superscript ] using 514 fb[superscript −1] of data collected with the BABAR detector. We observe no statistically significant deviations from the standard model predictions, and we set 90% confidence level upper limits on the mixing strength between the photon and dark photon at the level of 10[superscript 4] − 10[superscript 3] for dark photon masses in the range 0.02–10.2 GeV. We further constrain the range of the parameter space favored by interpretations of the discrepancy between the calculated and measured anomalous magnetic moment of the muon. 
Article: Measurements of Direct CP Asymmetries in B → X[subscript s]γ Decays Using Sum of Exclusive Decays
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ABSTRACT: We measure the direct CP violation asymmetry, A[subscript CP], in B → X[subscript s]γ and the isospin difference of the asymmetry, ΔA[subscript CP], using 429 fb[superscript 1] of data collected at ϒ(4S) resonance with the BABAR detector at the PEPII asymmetricenergy e[superscript +]e[superscript ] storage rings operating at the SLAC National Accelerator Laboratory. B mesons are reconstructed from ten charged B final states and six neutral B final states. We find A[subscript CP] = +(1.7 ± 1.9 ± 1.0)%, which is in agreement with the Standard Model prediction and provides an improvement on the world average. Moreover, we report the first measurement of the difference between A[subscript CP] for charged and neutral decay modes, ΔA[subscript CP] = +(5.0 ± 3.9 ± 1.5)%. Using the value of ΔA[subscript CP], we also provide 68% and 90% confidence intervals on the imaginary part of the ratio of the Wilson coefficients corresponding to the chromomagnetic dipole and the electromagnetic dipole transitions.
Publication Stats
6k  Citations  
3,708.29  Total Impact Points  
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Institutions

2013

Yerevan Physics Institute
Ayrivan, Yerevan, Armenia


19832013

University of Colorado at Boulder
 Department of Physics
Boulder, Colorado, United States


2011

Brandenburg University of Technology Cottbus  Senftenberg
Kottbus, Brandenburg, Germany


20062009

Université de Savoie
Chambéry, RhôneAlpes, France


20012007

RuhrUniversität Bochum
 Institut für Experimentalphysik I
Bochum, North RhineWestphalia, Germany


19952000

Carleton University
Ottawa, Ontario, Canada


19912000

The Ohio State University
 Department of Educational Studies
Columbus, Ohio, United States


1997

Harvard University
Cambridge, Massachusetts, United States


19941996

Cornell University
 Department of Electrical and Computer Engineering
Ithaca, New York, United States
