A
bstract
A search for the standard model Higgs boson produced in association with a top-quark pair
t
t
¯
H
is presented, using data samples corresponding to integrated luminosities of up to 5.1 fb
...−1
and 19.7 fb
−1
collected in pp collisions at center-of-mass energies of 7 TeV and 8 TeV respectively. The search is based on the following signatures of the Higgs boson decay: H → hadrons, H → photons, and H → leptons. The results are characterized by an observed
t
t
¯
H
signal strength relative to the standard model cross section,
μ
=
σ/σ
SM
,under the assumption that the Higgs boson decays as expected in the standard model. The best fit value is
μ
= 2.8 ± 1.0 for a Higgs boson mass of 125.6 GeV.
(ProQuest: ... denotes formulae and/or non-USASCII text omitted; see image) Abstract Azimuthal dihadron correlations of charged particles have been measured in PbPb collisions at ...=2.76TeV by the ...CMS collaboration, using data from the 2011 LHC heavy-ion run. The data set includes a sample of ultra-central (0-0.2% centrality) PbPb events collected using a trigger based on total transverse energy in the hadron forward calorimeters and the total multiplicity of pixel clusters in the silicon pixel tracker. A total of about 1.8 million ultra-central events were recorded, corresponding to an integrated luminosity of 120 mub-1. The observed correlations in ultra-central PbPb events are expected to be particularly sensitive to initial-state fluctuations. The single-particle anisotropy Fourier harmonics, from v ^sub 2^ to v ^sub 6^, are extracted as a function of particle transverse momentum. At higher transverse momentum, the v ^sub 2^ harmonic becomes significantly smaller than the higher-order v ^sub n^ (ngreater than or equal to3). The p ^sub T^-averaged v ^sub 2^ and v ^sub 3^ are found to be equal within 2%, while higher-order v ^sub n^ decrease as n increases. The breakdown of factorization of dihadron correlations into single-particle azimuthal anisotropies is observed. This effect is found to be most prominent in the ultra-central PbPb collisions, where the initial-state fluctuations play a dominant role. A comparison of the factorization data to hydrodynamic predictions with event-by-event fluctuating initial conditions is also presented. Figure not available: see fulltext.
Abstract A search for new resonances decaying to WW, ZZ, or WZ is presented. Final states are considered in which one of the vector bosons decays leptonically and the other hadronically. Results are ...based on data corresponding to an integrated luminosity of 19.7 fb-1 recorded in proton-proton collisions at ... = 8 TeV with the CMS detector at the CERN LHC. Techniques aiming at identifying jet substructures are used to analyze signal events in which the hadronization products from the decay of highly boosted W or Z bosons are contained within a single reconstructed jet. Upper limits on the production of generic WW, ZZ, or WZ resonances are set as a function of the resonance mass and width. We increase the sensitivity of the analysis by statistically combining the results of this search with a complementary study of the all-hadronic final state. Upper limits at 95% confidence level are set on the bulk graviton production cross section in the range from 700 to 10 fb for resonance masses between 600 and 2500 GeV, respectively. These limits on the bulk graviton model are the most stringent to date in the diboson final state. Figure not available: see fulltext.
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 fb-1, 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 GRS 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' arrow right WZ and GRS arrow right WW in the all-jets final state. The mass limits on q* arrow right qW, q* arrow right qZ, W' arrow right WZ, GRS arrow right WW are the most stringent to date. A model with a "bulk" graviton Gbulk that decays into WW or ZZ bosons is also studied. Figure not available: see fulltext.
(ProQuest: ... denotes formulae and/or non-USASCII text omitted; see image) Abstract Measurements of the differential and double-differential Drell-Yan cross sections are presented using an ...integrated luminosity of 4.5 (4.8) fb^sup -1^ in the dimuon (dielectron) channel of proton-proton collision data recorded with the CMS detector at the LHC at ... = 7 TeV. The measured inclusive cross section in the Z-peak region (60-120 GeV) is sigma() = 986.4±0.6 (stat.)±5.9 (exp. syst.)±21.7 (th. syst.)±21.7 (lum.) pb for the combination of the dimuon and dielectron channels. Differential cross sections dsigma/dm for the dimuon, dielectron, and combined channels are measured in the mass range 15 to 1500 GeV and corrected to the full phase space. Results are also presented for the measurement of the double-differential cross section d^sup 2^sigma/dm d|y| in the dimuon channel over the mass range 20 to 1500 GeV and absolute dimuon rapidity from 0 to 2.4. These measurements are compared to the predictions of perturbative QCD calculations at next-to-leading and next-to-next-to-leading orders using various sets of parton distribution functions. Figure not available: see fulltext.
A
bstract
The production of a Z boson, decaying into two leptons and produced in association with one or more b jets, is studied using proton-proton collisions delivered by the LHC at a ...centre-of-mass energy of 7 TeV. The data were recorded in 2011 with the CMS detector and correspond to an integrated luminosity of 5 fb
−1
. The Z(
ℓℓ
) + b-jets cross sections (where
ℓℓ
=
μμ
or ee) are measured separately for a Z boson produced with exactly one b jet and with at least two b jets. In addition, a cross section ratio is extracted for a Z boson produced with at least one b jet, relative to a Z boson produced with at least one jet. The measured cross sections are compared to various theoretical predictions, and the data favour the predictions in the five-flavour scheme, where b quarks are assumed massless. The kinematic properties of the reconstructed particles are compared with the predictions from the M
ad
G
raph
event generator using the
pythia
parton shower simulation.
A
bstract
A search is presented for massive spin-1 Z
′
resonances decaying to a top quark and a heavy vector-like top quark partner T. The search is based on a 2.6 fb
−1
sample of proton-proton ...collisions at 13 TeV collected with the CMS detector at the LHC. The analysis is optimized for final states in which the T quark decays to a W boson and a bottom quark. The focus is on all-jet final states in which both the W boson and the top quark decay into quarks that evolve into jets. The decay products of the top quark and of the W boson are assumed to be highly Lorentz-boosted and cannot be reconstructed as separate jets, but are instead reconstructed as merged, wide jets. Techniques for the identification of jet substructure and jet flavour are used to distinguish signal from background events. Several models for Z
′
bosons decaying to T quarks are excluded at 95% confidence level, with upper limits on the cross section ranging from 0.13 to 10 pb, depending on the chosen hypotheses. This is the first search for a neutral spin-1 heavy resonance decaying to a top quark and a vector-like T quark in the all-hadronic final state.
(ProQuest: ... denotes formulae and/or non-USASCII text omitted; see image) Abstract A search for narrow resonances and quantum black holes is performed in inclusive and b-tagged dijet mass spectra ...measured with the CMS detector at the LHC. The data set corresponds to 5 fb^sup -1^ of integrated luminosity collected in pp collisions at ... TeV. No narrow resonances or quantum black holes are observed. Model-independent upper limits at the 95% confidence level are obtained on the product of the cross section, branching fraction into dijets, and acceptance for three scenarios: decay into quark-quark, quark-gluon, and gluon-gluon pairs. Specific lower limits are set on the mass of string resonances (4.31 TeV), excited quarks (3.32 TeV), axigluons and colorons (3.36 TeV), scalar color-octet resonances (2.07 TeV), E^sub 6^ diquarks (3.75 TeV), and on the masses of W' (1.92 TeV) and Z' (1.47 TeV) bosons. The limits on the minimum mass of quantum black holes range from 4 to 5.3 TeV. In addition, b-quark tagging is applied to the two leading jets and upper limits are set on the production of narrow dijet resonances in a model-independent fashion as a function of the branching fraction to b-jet pairs.Figure not available: see fulltext.
Abstract A study of proton-proton collisions in which two b hadrons are produced in association with a Z boson is reported. The collisions were recorded at a centre-of-mass energy of 7 TeVwith the ...CMS detector at the LHC, for an integrated luminosity of 5.2 fb^sup -1^. The b hadrons are identified by means of displaced secondary vertices, without the use of reconstructed jets, permitting the study of b-hadron pair production at small angular separation. Differential cross sections are presented as a function of the angular separation of the b hadrons and the Z boson. In addition, inclusive measurements are presented. For both the inclusive and differential studies, different ranges of Z boson momentum are considered, and each measurement is compared to the predictions from different event generators at leading-order and next-to-leading-order accuracy. Figure not available: see fulltext.
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