Inclusive and differential measurements of the tt@? charge asymmetry in pp collisions at s=8 TeV

North-Holland Pub. Co 2016 Physics letters: B Vol.757 No.-

<P>The t (t) over bar charge asymmetry is measured in proton-proton collisions at a centre-of-mass energy of 8 TeV. The data, collected with the CMS experiment at the LHC, correspond to an integrated luminosity of 19.7 fb(-1). Selected events contain an electron or a muon and four or more jets, where at least one jet is identified as originating from b-quark hadronization. The inclusive charge asymmetry is found to be 0.0010 +/- 0.0068 (stat)+/- 0.0037 (syst). In addition, differential charge asymmetries as a function of rapidity, transverse momentum, and invariant mass of the If system are studied. For the first time at the LHC, the measurements are also performed in a reduced fiducial phase space of top quark pair production, with an integrated result of -0.0035 +/- 0.0072 (stat) +/- 0.0031 (syst). All measurements are consistent within two standard deviations with zero asymmetry as well as with the predictions of the standard model. (C) 2016 CERN for the benefit of the CMS Collaboration. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). Funded by SCOAP(3).</P>

Transverse momentum spectra of inclusive b jets in pPb collisions at s_NN=5.02 TeV

North-Holland Pub. Co 2016 Physics letters: B Vol.754 No.-

<P>We present a measurement of b jet transverse momentum (p(T)) spectra in proton-lead (pPb) collisions using a dataset corresponding to about 35nb(-1) collected with the CMS detector at the LHC. Jets from b quark fragmentation are found by exploiting the long lifetime of hadrons containing a b quark through tagging methods using distributions of the secondary vertex mass and displacement. Extracted cross sections for b jets are scaled by the effective number of nucleon-nucleon collisions and are compared to a reference obtained from PYTHIA simulations of pp collisions. The PYTHIA-based estimate of the nuclear modification factor is found to be 1.22 +/- 0.15 (stat + syst pPb) +/- 0.27 (syst PYTHIA) averaged over all jets with p(T) between 55 and 400 GeV/c and with |eta(lab)| < 2. We also compare this result to predictions from models using perturbative calculations in quantum chromodynamics. (C) 2016 CERN for the benefit of the CMS Collaboration. Published by Elsevier B.V.</P>

Search for neutral MSSM Higgs bosons decaying to μ⁺μ^- in pp collisions at s=7 and 8 TeV

North-Holland Pub. Co 2016 Physics letters: B Vol.752 No.-

<P>search for neutral Higgs bosons predicted in the minimal supersymmetric standard model (MSSM) for mu(+) mu(-) decay channels is presented. The analysis uses data collected by the CMS experiment at the LHC in proton-proton collisions at centre-of-mass energies of 7 and 8 TeV, corresponding to integrated luminosities of 5.1 and 19.3 fb(-1), respectively. The search is sensitive to Higgs bosons produced either through the gluon fusion process or in association with a b (b) over bar quark pair. No statistically significant excess is observed in the mu(+) mu(-) mass spectrum. Results are interpreted in the framework of several benchmark scenarios, and the data are used to set an upper limit on the MSSM parameter tan beta as a function of the mass of the pseudoscalar A boson in the range from 115 to 300 GeV. Model independent upper limits are given for the product of the cross section and branching fraction for gluon fusion and b quark associated production at root s = 8 TeV. They are the most stringent limits obtained to date in this channel. (C) 2015 CERN for the benefit of the CMS Collaboration. Published by Elsevier B.V.</P>

Search for pair-produced resonances decaying to jet pairs in proton-proton collisions at s=8 TeV

North-Holland Pub. Co 2015 Physics letters. Section B Vol.747 No.-

<P>Results are reported of a general search for pair production of heavy resonances decaying to pairs of hadronic jets in events with at least four jets. The study is based on up to 19.4 fb(-1) of integrated luminosity from proton-proton collisions at a center-of-mass energy of 8 TeV, recorded with the CMS detector at the LHC. Limits are determined on the production of scalar top quarks (top squarks) in the framework of R-parity violating supersymmetry and on the production of color-octet vector bosons (colorons). First limits at the LHC are placed on top squark production for two scenarios. The first assumes decay to a bottom quark and a light-flavor quark and is excluded for masses between 200 and 385 GeV, and the second assumes decay to a pair of light-flavor quarks and is excluded for masses between 200 and 350 GeV at 95% confidence level. Previous limits on colorons decaying to light-flavor quarks are extended to exclude masses from 200 to 835 GeV. (C) 2015 CERN for the benefit of the CMS Collaboration. Published by Elsevier B.V. This is an open access article under the CC BY license.</P>

A search for pair production of new light bosons decaying into muons

North-Holland Pub. Co 2016 Physics letters. Section B Vol.752 No.-

<P>A search for the pair production of new light bosons, each decaying into a pair of muons, is performed with the CMS experiment at the LHC, using a dataset corresponding to an integrated luminosity of 20.7 fb(-1) collected in proton-proton collisions at center-of-mass energy of root s = 8 TeV. No excess is observed in the data relative to standard model background expectation and a model independent upper limit on the product of the cross section, branching fraction, and acceptance is derived. The results are compared with two benchmark models, the first one in the context of the next-to-minimal super-symmetric standard model, and the second one in scenarios containing a hidden sector, including those predicting a nonnegligible light boson lifetime. (C) 2015 CERN for the benefit of the CMS Collaboration. Published by Elsevier B.V.</P>

Search for supersymmetry in events with a photon, a lepton, and missing transverse momentum in pp collisions at s=8 TeV

North-Holland Pub. Co 2016 Physics letters. Section B Vol.757 No.-

<P>A search for supersymmetry involving events with at least one photon, one electron or muon, and large missing transverse momentum has been performed by the CMS experiment. The data sample corresponds to an integrated luminosity of 19.7 fb(-1) of pp collisions at root s = 8 TeV, produced at the CERN LHC. No excess of events is observed beyond expectations from standard model processes. The result of the search is interpreted in the context of a general model of gauge-mediated supersymmetry breaking, where the charged and neutral winos are the next-to-lightest supersymmetric particles. Within this model, winos with a mass up to 360 GeV are excluded at the 95% confidence level. Two simplified models inspired by gauge-mediated supersymmetry breaking are also examined, and used to derive upper limits on the production cross sections of specific supersymmetric processes. (C) 2016 CERN for the benefit of the CMS Collaboration. Published by Elsevier B.V.</P>

Search for a new bottomonium state decaying to @?(1S)π⁺π^- in pp collisions at s=8 TeV

North-Holland Pub. Co 2013 Physics letters: B Vol.727 No.1

The results of a search for the bottomonium counterpart, denoted as X<SUB>b</SUB>, of the exotic charmonium state X(3872) is presented. The analysis is based on a sample of pp collisions at s=8 TeV collected by the CMS experiment at the LHC, corresponding to an integrated luminosity of 20.7 fb<SUP>-1</SUP>. The search looks for the exclusive decay channel X<SUB>b</SUB>→@?(1S)π<SUP>+</SUP>π<SUP>-</SUP> followed by @?(1S)→μ<SUP>+</SUP>μ<SUP>-</SUP>. No evidence for an X<SUB>b</SUB> signal is observed. Upper limits are set at the 95% confidence level on the ratio of the inclusive production cross sections times the branching fractions to @?(1S)π<SUP>+</SUP>π<SUP>-</SUP> of the X<SUB>b</SUB> and the @?(2S). The upper limits on the ratio are in the range 0.9-5.4% for X<SUB>b</SUB> masses between 10 and 11 GeV. These are the first upper limits on the production of a possible X<SUB>b</SUB> at a hadron collider.

Search for top-squark pairs decaying into Higgs or Z bosons in pp collisions at s=8 TeV

Elsevier 2014 Physics letters: B Vol.736 No.-

A search for supersymmetry through the direct pair production of top squarks, with Higgs (H) or Z bosons in the decay chain, is performed using a data sample of proton-proton collisions at s=8 TeV collected in 2012 with the CMS detector at the LHC. The sample corresponds to an integrated luminosity of 19.5 fb<SUP>-1</SUP>. The search is performed using a selection of events containing leptons and bottom-quark jets. No evidence for a significant excess of events over the standard model background prediction is observed. The results are interpreted in the context of simplified supersymmetric models with pair production of a heavier top-squark mass eigenstate t@?<SUB>2</SUB> decaying to a lighter top-squark mass eigenstate t@?<SUB>1</SUB> via either t@?<SUB>2</SUB>→Ht@?<SUB>1</SUB> or t@?<SUB>2</SUB>→Zt@?<SUB>1</SUB>, followed in both cases by t@?<SUB>1</SUB>→tχ@?<SUB>1</SUB><SUP>0</SUP>, where χ@?<SUB>1</SUB><SUP>0</SUP> is an undetected, stable, lightest supersymmetric particle. The interpretation is performed in the region where the mass difference between the t@?<SUB>1</SUB> and χ@?<SUB>1</SUB><SUP>0</SUP> states is approximately equal to the top-quark mass (m<SUB>t@?'1</SUB>-m<SUB>χ@?'1^0</SUB>~m<SUB>t</SUB>), which is not probed by searches for direct t@?<SUB>1</SUB> squark pair production. The analysis excludes top squarks with masses m<SUB>t@?'2</SUB><575 GeV and m<SUB>t@?'1</SUB><400 GeV at a 95% confidence level.

Search for resonant pair production of Higgs bosons decaying to two bottom quark-antiquark pairs in proton-proton collisions at 8 TeV

North-Holland Pub. Co 2015 Physics letters. Section B Vol.749 No.-

A model-independent search for a narrow resonance produced in proton-proton collisions at s=8 TeV and decaying to a pair of 125 GeV Higgs bosons that in turn each decays into a bottom quark-antiquark pair is performed by the CMS experiment at the LHC. The analyzed data correspond to an integrated luminosity of 17.9 fb<SUP>-1</SUP>. No evidence for a signal is observed. Upper limits at a 95% confidence level on the production cross section for such a resonance, in the mass range from 270 to 1100 GeV, are reported. Using these results, a radion with decay constant of 1 TeV and mass from 300 to 1100 GeV, and a Kaluza-Klein graviton with mass from 380 to 830 GeV are excluded at a 95% confidence level.

Search for new physics in events with opposite-sign leptons, jets, and missing transverse energy in pp collisions at s=7 TeV

CMS Collaboration,Chatrchyan, S.,Khachatryan, V.,Sirunyan, A.M.,Tumasyan, A.,Adam, W.,Bergauer, T.,Dragicevic, M.,Ero, J.,Fabjan, C.,Friedl, M.,Fruhwirth, R.,Ghete, V.M.,Hammer, J.,Hormann, N.,Hrubec, North-Holland Pub. Co 2013 Physics letters: B Vol.718 No.3

A search is presented for physics beyond the standard model (BSM) in final states with a pair of opposite-sign isolated leptons accompanied by jets and missing transverse energy. The search uses LHC data recorded at a center-of-mass energy s=7 TeV with the CMS detector, corresponding to an integrated luminosity of approximately 5 fb<SUP>-1</SUP>. Two complementary search strategies are employed. The first probes models with a specific dilepton production mechanism that leads to a characteristic kinematic edge in the dilepton mass distribution. The second strategy probes models of dilepton production with heavy, colored objects that decay to final states including invisible particles, leading to very large hadronic activity and missing transverse energy. No evidence for an event yield in excess of the standard model expectations is found. Upper limits on the BSM contributions to the signal regions are deduced from the results, which are used to exclude a region of the parameter space of the constrained minimal supersymmetric extension of the standard model. Additional information related to detector efficiencies and response is provided to allow testing specific models of BSM physics not considered in this Letter.