[Show abstract][Hide abstract] ABSTRACT: The anisotropy of the azimuthal distributions of charged particles produced in PbPb collisions with a nucleon-nucleon center-of-mass energy of 2.76 TeV is studied with the CMS experiment at the LHC. The elliptic anisotropy parameter defined as the second coefficient in a Fourier expansion of the particle invariant yields, is extracted using the event-plane method, two- and four-particle cumulants, and Lee--Yang zeros. The anisotropy is presented as a function of transverse momentum (pt), pseudorapidity (eta) over a broad kinematic range: 0.3 < pt < 20 GeV, abs(eta) < 2.4, and in 12 classes of collision centrality from 0 to 80%. The results are compared to those obtained at lower center-of-mass energies, and various scaling behaviors are examined. When scaled by the geometric eccentricity of the collision zone, the elliptic anisotropy is found to obey a universal scaling with the transverse particle density for different collision systems and center-of-mass energies.
[Show abstract][Hide abstract] ABSTRACT: A search is presented in proton-proton collisions at root s = 7 TeV for fermionic triplet states expected in type Ill seesaw models. The search is performed using final states with three isolated charged leptons and an imbalance in transverse momentum. The data, collected with the CMS detector at the LHC, correspond to an integrated luminosity of 4.9 fb(-1). No excess of events is observed above the background predicted by the standard model, and the results are interpreted in terms of limits on production cross sections and masses of the heavy partners of the neutrinos in type Ill seesaw models. Depending on the considered scenarios, lower limits are obtained on the mass of the heavy partner of the neutrino that range from 180 to 210 GeV. These are the first limits on the production of type III seesaw fermionic triplet states reported by an experiment at the LHC.
Physics Letters B 12/2012; 718(2):348-368. DOI:10.1016/j.physletb.2012.10.070 · 6.13 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A search for resonances decaying to top quark-antiquark pairs is performed
using a dilepton+jets data sample recorded by the CMS experiment at the LHC in
pp collisions at sqrt(s) = 7 TeV corresponding to an integrated luminosity of
5.0 inverse femtobarns. No significant deviations from the standard model
background are observed. Upper limits are presented for the production cross
section times branching fraction of top quark-antiquark resonances for masses
from 750 to 3000 GeV. In particular, the existence of a leptophobic topcolor
particle Z' is excluded at the 95% confidence level for resonance masses M[Z']
< 1.3 TeV for Gamma[Z'] = 0.012 M[Z'], and M[Z'] < 1.9 TeV for Gamma[Z'] = 0.10
Physical Review D 11/2012; 87(7). DOI:10.1103/PhysRevD.87.072002 · 4.64 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A search is presented for charge-asymmetric production of a W' boson that has been proposed to accommodate the forward-backward asymmetry observed in the production of top-antitop quark pairs at the Tevatron. The new heavy W' boson would be produced in association with a top quark and would decay into top and down quarks. The data correspond to an integrated luminosity of 5.0 fb(-1) in pp collisions at a center-of-mass energy of 7 TeV, recorded by the CMS detector at the LHC. No significant excess above the standard model expectations is observed, and, from a combination of the electron-plus-jets and muon-plus-jets channels, a 95% confidence level lower limit of 840 GeV/c(2) is set on the W' boson mass for a W' boson model with values for coupling constants to top and down quarks g(L) = 0 and g(R) = 2. In addition, a kinematic reconstruction of the W' resonance mass using the inherent charge asymmetry of this model finds no indication of the presence of W' events in the data.
Physics Letters B 10/2012; 717(4-5):351-370. DOI:10.1016/j.physletb.2012.09.048 · 6.13 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Results are presented from a search for new physics in the final state containing a photon (γ) and missing transverse energy (E[combininb /](T)). The data correspond to an integrated luminosity of 5.0 fb(-1) collected in pp collisions at √[s]=7 TeV by the CMS experiment. The observed event yield agrees with standard-model expectations for the γ+E[combininb /](T) events. Using models for the production of dark-matter particles (χ), we set 90% confidence level (C.L.) upper limits of 13.6-15.4 fb on χ production in the γ+E[combininb /](T) state. These provide the most sensitive upper limits for spin-dependent χ-nucleon scattering for χ masses (M(χ)) between 1 and 100 GeV. For spin-independent contributions, the present limits are extended to M(χ)<3.5 GeV. For models with 3-6 large extra dimensions, our data exclude extra-dimensional Planck scales between 1.64 and 1.73 TeV at 95% C.L.
[Show abstract][Hide abstract] ABSTRACT: A measurement of the electron charge asymmetry in inclusive pp→W+X→eν+X production at sqrt[s]=7 TeV is presented based on data recorded by the CMS detector at the LHC and corresponding to an integrated luminosity of 840 pb(-1). The electron charge asymmetry reflects the unequal production of W(+) and W(-) bosons in pp collisions. The electron charge asymmetry is measured in bins of the absolute value of electron pseudorapidity in the range of |η|<2.4. The asymmetry rises from about 0.1 to 0.2 as a function of the pseudorapidity and is measured with a relative precision better than 7%. This measurement provides new stringent constraints for parton distribution functions.
[Show abstract][Hide abstract] ABSTRACT: A search is presented for physics beyond the standard model (BSM) in events with a Z boson, jets, and missing transverse energy (E-T(miss)) This signature is motivated by BSM physics scenarios, including supersymmetry. The study is performed using a sample of proton-proton collision data collected at root s = 7 TeV with the CMS experiment at the LHC, corresponding to an integrated luminosity of 4.98 fb(-1). The contributions from the dominant standard model backgrounds are estimated from data using two complementary strategies, the jet-Z balance technique and a method based on modeling E-T(miss) with data control samples. In the absence of evidence for BSM physics, we set limits on the non-standard-model contributions to event yields in the signal regions and interpret the results in the context of simplified model spectra. Additional information is provided to facilitate tests of other BSM physics models.
Physics Letters B 09/2012; 716(2):260-284. DOI:10.1016/j.physletb.2012.08.026 · 6.13 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Evidence is presented for the associated production of a single top quark and
W boson in pp collisions at sqrt(s) = 7 TeV with the CMS experiment at the LHC.
The analyzed data corresponds to an integrated luminosity of 4.9 inverse
femtobarns. The measurement is performed using events with two leptons and a
jet originated from a b quark. A multivariate analysis based on kinematic
properties is utilized to separate the t t-bar background from the signal. The
observed signal has a significance of 4.0 sigma and corresponds to a cross
section of (16 +5 -4) pb, in agreement with the standard model expectation of
(15.6 +/- 0.4 (+ 1.0 -1.2)) pb.
[Show abstract][Hide abstract] ABSTRACT: The top-quark mass is measured in proton-proton collisions at sqrt(s) = 7 TeV
using a data sample corresponding to an integrated luminosity of 5.0 inverse
femtobarns collected by the CMS experiment at the LHC. The measurement is
performed in the dilepton decay channel t t-bar to ell+ nu[ell] b, ell-
anti-nu[ell] b-bar, where ell=e,mu. Candidate top-quark decays are selected by
requiring two leptons, at least two jets, and imbalance in transverse momentum.
The mass is reconstructed with an analytical matrix weighting technique using
distributions derived from simulated samples. Using a maximum-likelihood fit,
the top-quark mass is determined to be 172.5 +/- 0.4 (stat) +/- 1.5 (syst) GeV.
European Physical Journal C 09/2012; 72(10). DOI:10.1140/epjc/s10052-012-2202-z · 5.08 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The Lambda b differential production cross section and the cross section ratio sigma((Lambda) over bar (b))/sigma(Lambda(b)) are measured as functions of transverse momentum p(T)(Lambda b) rapidity vertical bar y(Lambda b)vertical bar in pp collisions at root s = 7 TeV using data collected by the CMS experiment at the LHC. The measurements are based on Lambda(b) decays reconstructed in the exclusive final state J/psi Lambda, with the subsequent decays J/psi -> mu(+)mu(-) and Lambda -> p pi, using a data sample corresponding to an integrated luminosity of 1.9 fb(-1). The product sigma(Lambda(b)) x B(Lambda(b) -> J/psi Lambda) versus p(T)(Lambda b) falls faster than that of b mesons. The measured value of sigma(Lambda(b)) x B(Lambda(b) -> J/psi Lambda) for p(T)(Lambda b) > 10 GeV and vertical bar y(Lambda b)vertical bar < 2.0 is 1.16 +/- 0.06 +/- 0.12 nb, and the integrated sigma(<(Lambda)over bar>(b))/sigma(Lambda(b)) ratio is 1.02 +/- 0.07 +/- 0.09, where the uncertainties are statistical and systematic, respectively.
Physics Letters B 08/2012; 714(2-5):136-157. DOI:10.1016/j.physletb.2012.05.063 · 6.13 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The first measurement of the charged component of the underlying event using the novel "jet-area/median" approach is presented for proton-proton collisions at centre-of-mass energies of 0.9 and 7TeV. The data were recorded in 2010 with the CMS experiment at the LHC. A new observable, sensitive to soft particle production, is introduced and investigated inclusively and as a function of the event scale defined by the transverse momentum of the leading jet. Various phenomenological models are compared to data, with and without corrections for detector effects. None of the examined models describe the data satisfactorily.
Journal of High Energy Physics 08/2012; 2012(8). DOI:10.1007/JHEP08(2012)130 · 6.11 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The t t-bar charge asymmetry is measured in events containing a charged
lepton (electron or muon) and at least four jets, one of which is identified as
originating from b-quark hadronization. The analyzed dataset corresponds to an
integrated luminosity of 5.0 inverse femtobarns collected with the CMS detector
at the LHC. An inclusive and three differential measurements of the t t-bar
charge asymmetry as a function of rapidity, transverse momentum, and invariant
mass of the t t-bar system are presented. The measured inclusive t t-bar charge
asymmetry is A(C) = 0.004 +/- 0.010 (stat.) +/- 0.011 (syst.). This result and
the three differential measurements are consistent with zero asymmetry as well
as with the predictions of the standard model.
[Show abstract][Hide abstract] ABSTRACT: Dijet production in PbPb collisions at a nucleon-nucleon center-of-mass energy of 2.76 TeV is studied with the CMS detector at the LHC. A data sample corresponding to an integrated luminosity of 150 mu b(-1) is analyzed. Jets are reconstructed using combined information from tracking and calorimetry, using the anti-k(T) algorithm with R = 0.3. The dijet momentum balance and angular correlations are studied as a function of collision centrality and leading jet transverse momentum. For the most peripheral PbPb collisions, good agreement of the dijet momentum balance distributions with pp data and reference calculations at the same collision energy is found, while more central collisions show a strong imbalance of leading and subleading jet transverse momenta attributed to the jet-quenching effect. The dijets in central collisions are found to be more unbalanced than the reference, for leading jet transverse momenta up to the highest values studied.
Physics Letters B 06/2012; 712(3):176-197. DOI:10.1016/j.physletb.2012.04.058 · 6.13 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The top quark pair production cross section is measured in dilepton events with one electron or muon, and one hadronically decaying tau lepton from the decay t (t) over bar -> (l nu(l))((sic)(h)nu((sic)))b (b) over bar, (l = e, mu). The data sample corresponds to an integrated luminosity of 2.0 fb(-1) for the electron channel and 2.2 fb(-1) for the muon channel, collected by the CMS detector at the LHC. This is the first measurement of the t (t) over bar cross section explicitly including tau leptons in proton- proton collisions at root s = 7 TeV. The measured value sigma(t (t) over bar) = 143 +/- 14(stat) +/- 22(syst) +/- 3(lumi) pb is consistent with the standard model predictions.
Physical Review D 06/2012; 85(11-11). DOI:10.1103/PhysRevD.85.112007 · 4.64 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Results are presented from a search for large, extra spatial dimensions in events with either two isolated muons or two isolated electrons. The data are from proton-proton interactions at root s = 7 TeV collected with the CMS detector at the LHC. The size of the data sample corresponds to an integrated luminosity of approximately 2 fb(-1). The observed dimuon and dielectron mass spectra are found to be consistent with standard-model expectations. Depending on the number of extra dimensions, the 95% confidence level limits from the combined mu mu and ee channels range from M-s > 2.4 TeV to M-s > 3.8 TeV, where M-s characterizes the scale for the onset of quantum gravity.
Physics Letters B 05/2012; 711(1):15-34. DOI:10.1016/j.physletb.2012.03.029 · 6.13 Impact Factor