[Show abstract][Hide abstract] ABSTRACT: Dijet production has been measured in collisions at a nucleon-nucleon centre-of-mass energy of 5.02. A data sample corresponding to an integrated luminosity of 35 was collected using the Compact Muon Solenoid detector at the Large Hadron Collider. The dijet transverse momentum balance, azimuthal angle correlations, and pseudorapidity distributions are studied as a function of the transverse energy in the forward calorimeters (). For collisions, the dijet transverse momentum ratio and the width of the distribution of dijet azimuthal angle difference are comparable to the same quantities obtained from a simulated reference and insensitive to . In contrast, the mean value of the dijet pseudorapidity is found to change monotonically with increasing , indicating a correlation between the energy emitted at large pseudorapidity and the longitudinal motion of the dijet frame. The pseudorapidity distribution of the dijet system in minimum bias collisions is compared with next-to-leading-order perturbative QCD predictions obtained from both nucleon and nuclear parton distribution functions, and the data more closely match the latter.
European Physical Journal C 07/2014; 74(7-ARTN 2951). DOI:10.1140/epjc/s10052-014-2951-y · 5.08 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A peaking structure in the mass spectrum near threshold is observed in decays, produced in pp collisions at collected with the CMS detector at the LHC. The data sample, selected on the basis of the dimuon decay mode of the , corresponds to an integrated luminosity of 5.2 fb−1. Fitting the structure to an S-wave relativistic Breit–Wigner lineshape above a three-body phase-space nonresonant component gives a signal statistical significance exceeding five standard deviations. The fitted mass and width values are and , respectively. Evidence for an additional peaking structure at higher mass is also reported.
Physics Letters B 06/2014; 734:261-281. DOI:10.1016/j.physletb.2014.05.055 · 6.13 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A search is reported for massive resonances decaying into a quark and a
vector boson (W or Z), or two vector bosons (WW, WZ, or ZZ). The analysis is
performed on an inclusive sample of multijet events corresponding to an
integrated luminosity of 19.7 inverse femtobarns, collected in proton-proton
collisions at a centre-of-mass energy of 8 TeV with the CMS detector at the
LHC. The search uses novel jet-substructure identification techniques that
provide sensitivity to the presence of highly boosted vector bosons decaying
into a pair of quarks. Exclusion limits are set at a confidence level of 95% on
the production of: (i) excited quark resonances q* decaying to qW and qZ for
masses less than 3.2 TeV and 2.9 TeV, respectively, (ii) a Randall-Sundrum
graviton G[RS] decaying into WW for masses below 1.2 TeV, and (iii) a heavy
partner of the W boson W' decaying into WZ for masses less than 1.7 TeV. For
the first time mass limits are set on W' to WZ and G[RS] to WW in the all-jets
final state. The mass limits on q* to qW, q* to qZ, W' to WZ, G[RS] to WW are
the most stringent to date. A model with a "bulk" graviton G[Bulk] that decays
into WW or ZZ bosons is also studied.
Journal of High Energy Physics 05/2014; 2014(8-UNSP 173). DOI:10.1007/JHEP08(2014)173 · 6.11 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Results are presented of a search for a "natural" supersymmetry scenario with gauge mediated symmetry breaking. It is assumed that only the supersymmetric partners of the top quark (the top squark) and the Higgs boson (Higgsino) are accessible. Events are examined in which there are two photons forming a Higgs boson candidate, and at least two b-quark jets. In 19.7 fb-1 of proton-proton collision data at s=8 TeV, recorded in the CMS experiment, no evidence of a signal is found and lower limits at the 95% confidence level are set, excluding the top squark mass below 360 to 410 GeV, depending on the Higgsino mass.
[Show abstract][Hide abstract] ABSTRACT: A search for WV gamma triple vector boson production is presented based on
events containing a W boson decaying to a muon or an electron and a neutrino, a
second V (W or Z) boson, and a photon. The data correspond to an integrated
luminosity of 19.3 inverse femtobarns collected in 2012 with the CMS detector
at the LHC in pp collisions at sqrt(s) = 8 TeV. An upper limit of 311 fb on the
fiducial cross section for the WV gamma production process is obtained at 95%
confidence level for photons with a transverse energy above 30 GeV and with an
absolute value of pseudorapidity of less than 1.44. This limit is approximately
a factor of 3.4 larger than the standard model predictions that are based on
next-to-leading order QCD calculations. Since no evidence of anomalous WW gamma
gamma or WWZ gamma quartic gauge boson couplings is found, this paper presents
the first experimental limits on the dimension-8 parameter f[T,0] and the
CP-conserving WWZ gamma parameters kappa[0,W] and kappa[C,W]. Limits are also
obtained for the WW gamma gamma parameters a[0,W] and a[C,W].
[Show abstract][Hide abstract] ABSTRACT: The production of \( Y \)(1S), \( Y \)(2S), and \( Y \)(3S) is investigated in pPb and pp collisions at centre-of-mass energies per nucleon pair of 5.02 TeV and 2.76 TeV, respectively. The datasets correspond to integrated luminosities of about 31 nb−1 (pPb) and 5.4 pb−1 (pp), collected in 2013 by the CMS experiment at the LHC. Upsilons that decay into muons are reconstructed within the rapidity interval |y
CM| < 1.93 in the nucleon-nucleon centre-of-mass frame. Their production is studied as a function of two measures of event activity, namely the charged-particle multiplicity measured in the pseudorapidity interval |η| < 2.4, and the sum of transverse energy deposited at forward pseudorapidity, 4.0 < |η| < 5.2. The \( Y \) cross sections normalized by their event activity integrated values, \( Y \)(nS)/〈\( Y \)(nS)〉, are found to rise with both measures of the event activity in pp and pPb. In both collision systems, the ratios of the excited to the ground state cross sections, \( Y \)(nS)/
\( Y \)(1S), are found to decrease with the charged-particle multiplicity, while as a function of the transverse energy the variation is less pronounced. The event activity integrated double ratios, [\( Y \)(nS)/
\( Y \)(1S)]pPb
/[\( Y \)(nS)/
\( Y \)(1S)]pp, are also measured and found to be 0.83 ± 0.05 (stat.) ± 0.05 (syst.) and 0.71 ± 0.08 (stat.) ± 0.09 (syst.) for \( Y \)(2S) and \( Y \)(3S), respectively.
Journal of High Energy Physics 04/2014; 2014(4-ARTN 103). DOI:10.1007/JHEP04(2014)103 · 6.11 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A search for baryon number violation (BNV) in top-quark decays is performed using pp collisions produced by the LHC at . The top-quark decay considered in this search results in one light lepton (muon or electron), two jets, but no neutrino in the final state. Data used for the analysis were collected by the CMS detector and correspond to an integrated luminosity of 19.5 fb−1. The event selection is optimized for top quarks produced in pairs, with one undergoing the BNV decay and the other the standard model hadronic decay to three jets. No significant excess of events over the expected yield from standard model processes is observed. The upper limits at 95% confidence level on the branching fraction of the BNV top-quark decay are calculated to be 0.0016 and 0.0017 for the muon and the electron channels, respectively. Assuming lepton universality, an upper limit of 0.0015 results from the combination of the two channels. These limits are the first that have been obtained on a BNV process involving the top quark.
Physics Letters B 04/2014; 731:173-196. DOI:10.1016/j.physletb.2014.02.033 · 6.13 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A search for invisible decays of Higgs bosons is performed using the vector
boson fusion and associated ZH production modes. In the ZH mode, the Z boson is
required to decay to a pair of charged leptons or a b b-bar quark pair. The
searches use the 8 TeV pp collision dataset collected by the CMS detector at
the LHC, corresponding to an integrated luminosity of up to 19.7 inverse
femtobarns. Certain channels include data from 7 TeV collisions corresponding
to an integrated luminosity of 4.9 inverse femtobarns. The searches are
sensitive to non-standard-model invisible decays of the recently observed Higgs
boson, as well as additional Higgs bosons with similar production modes and
large invisible branching fractions. In all channels, the observed data are
consistent with the expected standard model backgrounds. Limits are set on the
production cross section times invisible branching fraction, as a function of
the Higgs boson mass, for the vector boson fusion and ZH production modes. By
combining all channels, and assuming standard model Higgs boson cross sections
and acceptances, the observed (expected) upper limit on the invisible branching
fraction at m[H]=125 GeV is found to be 0.58 (0.44) at 95% confidence level. We
interpret this limit in terms of a Higgs-portal model of dark matter
European Physical Journal C 04/2014; 74(8):2980. DOI:10.1140/epjc/s10052-014-2980-6 · 5.08 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A search is presented for a massive particle, generically referred to as a Z', decaying into a tt̄ pair. The search focuses on Z' resonances that are sufficiently massive to produce highly Lorentz-boosted top quarks, which yield collimated decay products that are partially or fully merged into single jets. The analysis uses new methods to analyze jet substructure, providing suppression of the non-top multijet backgrounds. The analysis is based on a data sample of proton-proton collisions at a center-of-mass energy of 7 TeV, corresponding to an integrated luminosity of 5 fb -1. Upper limits in the range of 1 pb are set on the product of the production cross section and branching fraction for a topcolor Z' modeled for several widths, as well as for a Randall-Sundrum Kaluza-Klein gluon. In addition, the result contrain any enhancement in tt̄ production beyond expectations of the standard mode for tt invariant mass larger than 1TeV/c 2.
Journal of High Energy Physics 03/2014; 2012(3). DOI:10.1007/JHEP03(2014)132 · 6.11 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A search for three-jet hadronic resonance production in pp collisions at a centre-of-mass energy of 8 TeV has been conducted by the CMS Collaboration at the LHC with a data sample corresponding to an integrated luminosity of . The search method is model independent, and events are selected that have high jet multiplicity and large values of jet transverse momenta. The signal models explored assume R-parity-violating supersymmetric gluino pair production and have final states with either only light-flavour jets or both light- and heavy-flavour jets. No significant deviation is found between the selected events and the expected standard model multijet and background. For a gluino decaying into light-flavour jets, a lower limit of 650 GeV on the gluino mass is set at a 95% confidence level, and for a gluino decaying into one heavy- and two light-flavour jets, gluino masses between 200 and 835 GeV are, for the first time, likewise excluded.
Physics Letters B 03/2014; 730:193-214. DOI:10.1016/j.physletb.2014.01.049 · 6.13 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Results are presented from a search for the production of a heavy gauge boson
W' decaying into a top and a bottom quark, using a data set collected by the
CMS experiment at sqrt(s)=8 TeV and corresponding to an integrated luminosity
of 19.5 inverse femtobarns. Various models of W'-boson production are studied
by allowing for an arbitrary combination of left- and right-handed couplings.
The analysis is based on the detection of events with a lepton (e, mu), jets,
and missing transverse energy in the final state. No evidence for W'-boson
production is found and 95% confidence level upper limits on the production
cross section times branching fraction are obtained. For W' bosons with purely
right-handed couplings, and for those with left-handed couplings assuming no
interference effects, the observed 95% confidence level limit is M(W')>2.05
TeV. For W' bosons with purely left-handed couplings, including interference
effects, the observed 95% confidence level limit is M(W')>1.84 TeV. The results
presented in this paper are the most stringent limits published to date.
Journal of High Energy Physics 02/2014; 1405(5). DOI:10.1007/JHEP05(2014)108 · 6.11 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A measurement of total and fiducial inclusive W and Z boson production cross
sections in pp collisions at sqrt(s)=8 TeV is presented. Electron and muon
final states are analyzed in a data sample collected with the CMS detector
corresponding to an integrated luminosity of 18.2 +/- 0.5 inverse picobarns.
The measured total inclusive cross sections times branching fractions are
sigma(pp to W X) B(W to l nu ) = 12.21 +/- 0.03 (stat.) +/- 0.24 (syst.) +/-
0.32 (lum.) nb and sigma(pp to Z X) B(Z to l+ l-) = 1.15 +/- 0.01 (stat.) +/-
0.02 (syst.) +/- 0.03 (lum.) nb for the dilepton mass in the range of 60 to 120
GeV. The measured values agree with next-to-next-to-leading-order QCD cross
section calculations. Ratios of cross sections are reported with a precision of
2%. This is the first measurement of inclusive W and Z boson production in
proton-proton collisions at sqrt(s)=8 TeV.
[Show abstract][Hide abstract] ABSTRACT: A search for the standard model Higgs boson decaying to a W-boson pair at the LHC is reported. The event sample corresponds to an integrated luminosity of 4.9 fb(-1) and 19.4 fb(-1) collected with the CMS detector in pp collisions at = 7 and 8 TeV, respectively. The Higgs boson candidates are selected in events with two or three charged leptons. An excess of events above background is observed, consistent with the expectation from the standard model Higgs boson with a mass of around 125 GeV. The probability to observe an excess equal or larger than the one seen, under the background-only hypothesis, corresponds to a significance of 4.3 standard deviations for m (H) = 125.6 GeV. The observed signal cross section times the branching fraction to WW for m (H) = 125.6 GeV is times the standard model expectation. The spin-parity J (P) = 0(+) hypothesis is favored against a narrow resonance with J (P) = 2(+) or J (P) = 0(-) that decays to a W-boson pair. This result provides strong evidence for a Higgs-like boson decaying to a W-boson pair.
Journal of High Energy Physics 01/2014; 2014(1-ARTN 096). DOI:10.1007/JHEP01(2014)096 · 6.11 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The first observation of the associated production of a single top quark and
a W boson is presented. The analysis is based on a data set corresponding to an
integrated luminosity of 12.2 inverse femtobarns of proton-proton collisions at
sqrt(s) = 8 TeV recorded by the CMS experiment at the LHC. Events with two
leptons and a jet originating from a b quark are selected. A multivariate
analysis based on kinematic and topological properties is used to separate the
signal from the dominant t t-bar background. An excess consistent with the
signal hypothesis is observed, with a significance which corresponds to 6.1
standard deviations above a background-only hypothesis. The measured production
cross section is 23.4 +/- 5.4 pb, in agreement with the standard model