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1. chinaXiv:201609.00830 [pdf]

Measurement of differential and integrated fiducial cross sections for Higgs boson production in the four-lepton decay channel in pp collisions at $ \sqrt{s}=$ 7 and 8 TeV

Khachatryan, Vardan and others
Subjects: Physics >> Nuclear Physics

Integrated fiducial cross sections for the production of four leptons via the H to 4l decays (l = e, mu) are measured in pp collisions at sqrt(s) = 7 and 8 TeV. Measurements are performed with data corresponding to integrated luminosities of 5.1 inverse femtobarns at 7 TeV, and 19.7 inverse femtobarns at 8 TeV, collected with the CMS experiment at the LHC. Differential cross sections are measured using the 8 TeV data, and are determined as functions of the transverse momentum and rapidity of the four-lepton system, accompanying jet multiplicity, transverse momentum of the leading jet, and difference in rapidity between the Higgs boson candidate and the leading jet. A measurement of the Z to 4l cross section, and its ratio to the H to 4l cross section is also performed. All cross sections are measured within a fiducial phase space defined by the requirements on lepton kinematics and event topology. The integrated H to 4l fiducial cross section is measured to be 0.56 +0.67-0.44 (stat) +0.21-0.06 (syst) fb at 7 TeV, and 1.11 +0.41-0.35 (stat) +0.14-0.10 (syst) fb at 8 TeV. The measurements are found to be compatible with theoretical calculations based on the standard model.

submitted time 2016-09-12 Hits576Downloads323 Comment 0

2. chinaXiv:201609.00829 [pdf]

Search for supersymmetry in events with soft leptons, low jet multiplicity, and missing transverse energy in proton–proton collisions at $\sqrt{s}$=8 TeV

Khachatryan, Vardan and others
Subjects: Physics >> Nuclear Physics

Results are presented from a search for supersymmetric particles in scenarios with a compressed mass spectrum. The data sample corresponds to 19.7 inverse femtobarns of proton-proton collisions recorded by the CMS experiment at sqrt(s) = 8 TeV. The search targets top squark pair production in scenarios with mass differences Delta m = m(top squark) - m(neutralino) below the W-boson mass and with top-squark decays in the four-body mode (top squark to b l nu neutralino), where the neutralino is assumed to be the lightest supersymmetric particle (LSP). The signature includes a high transverse momentum (pt) jet associated with initial-state radiation, one or two low-pt leptons, and significant missing transverse energy. The event yields observed in data are consistent with the expected background contributions from standard model processes. Limits are set on the cross section for top squark pair production as a function of the top squark and LSP masses. Assuming a 100% branching fraction for the four-body decay mode, top-squark masses below 316 GeV are excluded for Delta m = 25 GeV at 95% CL. The dilepton data are also interpreted under the assumption of chargino-neutralino production, with subsequent decays to sleptons or sneutrinos. Assuming a difference between the common lightest chargino/next lightest neutralino mass and the LSP mass of 20 GeV and a tau-enriched decay scenario, masses in the range m(chargino) < 307 GeV are excluded at 95% CL.

submitted time 2016-09-12 Hits496Downloads289 Comment 0

3. chinaXiv:201609.00823 [pdf]

Study of Z boson production in pPb collisions at $\sqrt{s} NN $=5.02TeV

Khachatryan, Vardan and others
Subjects: Physics >> Nuclear Physics

The production of Z bosons in pPb collisions at sqrt(s[NN]) = 5.02 TeV is studied by the CMS experiment via the electron and muon decay channels. The inclusive cross section is compared to pp collision predictions, and found to scale with the number of elementary nucleon-nucleon collisions. The differential cross sections as a function of the Z boson rapidity and transverse momentum are measured. Though they are found to be consistent within uncertainty with theoretical predictions both with and without nuclear effects, the forward-backward asymmetry suggests the presence of nuclear effects at large rapidities. These results provide new data for constraining nuclear parton distribution functions.

submitted time 2016-09-12 Hits540Downloads297 Comment 0

4. chinaXiv:201609.00822 [pdf]

Measurement of the inclusive jet cross section in pp collisions at $\sqrt{s} =$ 2.76 TeV

Khachatryan, Vardan and others
Subjects: Physics >> Nuclear Physics

The double-differential inclusive jet cross section is measured as a function of jet transverse momentum pT and absolute rapidity y, using proton-proton collision data collected with the CMS experiment at the LHC, at a center-of-mass energy of sqrt(s) = 2.76 TeV and corresponding to an integrated luminosity of 5.43 inverse picoboarns. Jets are reconstructed within the pT range of 74 to 592 GeV and the rapidity range |y| < 3.0. The reconstructed jet spectrum is corrected for detector resolution. The measurements are compared to the theoretical prediction at next-to-leading-order QCD using different sets of parton distribution functions. This inclusive cross section measurement explores a new kinematic region and is consistent with QCD predictions.

submitted time 2016-09-12 Hits550Downloads314 Comment 0

5. chinaXiv:201609.00804 [pdf]

Search for narrow resonances decaying to dijets in proton-proton collisions at $\sqrt{s} =$ 13 TeV

Khachatryan, Vardan and others
Subjects: Physics >> Nuclear Physics

A search for narrow resonances in proton-proton collisions at sqrt(s) = 13 TeV is presented. The invariant mass distribution of the two leading jets is measured with the CMS detector using a data set corresponding to an integrated luminosity of 2.4 inverse femtobarns. The highest observed dijet mass is 6.1 TeV. The distribution is smooth and no evidence for resonant particles is observed. Upper limits at 95% confidence level are set on the production cross section for narrow resonances with masses above 1.5 TeV. When interpreted in the context of specific models, the limits exclude string resonances with masses below 7.0 TeV, scalar diquarks below 6.0 TeV, axigluons and colorons below 5.1 TeV, excited quarks below 5.0 TeV, color-octet scalars below 3.1 TeV, and W' bosons below 2.6 TeV. These results significantly extend previously published limits.

submitted time 2016-09-12 Hits495Downloads285 Comment 0

6. chinaXiv:201609.00802 [pdf]

Event generator tunes obtained from underlying event and multiparton scattering measurements

Khachatryan, Vardan and others
Subjects: Physics >> Nuclear Physics

New sets of parameters ("tunes") for the underlying-event (UE) modeling of the PYTHIA8, PYTHIA6 and HERWIG++ Monte Carlo event generators are constructed using different parton distribution functions. Combined fits to CMS UE proton-proton (pp) data at sqrt(s) = 7 TeV and to UE proton-antiproton (p p-bar) data from the CDF experiment at lower sqrt(s), are used to study the UE models and constrain their parameters, providing thereby improved predictions for proton-proton collisions at 13 TeV. In addition, it is investigated whether the values of the parameters obtained from fits to UE observables are consistent with the values determined from fitting observables sensitive to double-parton scattering processes. Finally, comparisons of the UE tunes to "minimum bias" (MB) events, multijet, and Drell-Yan (q q-bar to Z / gamma* to lepton-antilepton + jets) observables at 7 and 8 TeV are presented, as well as predictions for MB and UE observables at 13 TeV.

submitted time 2016-09-12 Hits489Downloads261 Comment 0

7. chinaXiv:201609.00800 [pdf]

Search for dark matter and unparticles produced in association with a Z boson in proton-proton collisions at $\sqrt{s}=$ 8  TeV

Khachatryan, Vardan and others
Subjects: Physics >> Nuclear Physics

A search for evidence of particle dark matter (DM) and unparticle production at the LHC has been performed using events containing two charged leptons, consistent with the decay of a Z boson, and large missing transverse momentum. This study is based on data collected with the CMS detector corresponding to an integrated luminosity of 19.7 inverse femtobarns of pp collisions at the LHC at a center-of-mass energy of 8 TeV. No significant excess of events is observed above the number expected from the standard model contributions. The results are interpreted in terms of 90% confidence level limits on the DM-nucleon scattering cross section, as a function of the DM particle mass, for both spin-dependent and spin-independent scenarios. Limits are set on the effective cutoff scale Lambda, and on the annihilation rate for DM particles, assuming that their branching fraction to quarks is 100%. Additionally, the most stringent 95% confidence level limits to date on the unparticle model parameters are obtained.

submitted time 2016-09-12 Hits524Downloads300 Comment 0

8. chinaXiv:201609.00796 [pdf]

Measurement of spin correlations in $t\bart$ production using the matrix element method in the muon+jets final state in pp collisions at $\sqrt{s} =$ 8 TeV

Khachatryan, Vardan and others
Subjects: Physics >> Nuclear Physics

The consistency of the spin correlation strength in top quark pair production with the standard model (SM) prediction is tested in the muon + jets final state. The events are selected from pp collisions, collected by the CMS detector, at a centre-of-mass energy of 8 TeV, corresponding to an integrated luminosity of 19.7 inverse femtobarns. The data are compared with the expectation for the spin correlation predicted by the SM and with the expectation of no correlation. Using a template fit method, the fraction of events that show SM spin correlations is measured to be 0.72 +/- 0.08 (stat) +0.15 -0.13 (syst), representing the most precise measurement of this quantity in the lepton + jets final state to date.

submitted time 2016-09-12 Hits590Downloads358 Comment 0

9. chinaXiv:201609.00790 [pdf]

Search for anomalous single top quark production in association with a photon in pp collisions at $ \sqrt{s}=8 $ TeV

Khachatryan, Vardan and others
Subjects: Physics >> Nuclear Physics

The result of a search for flavor changing neutral currents (FCNC) through single top quark production in association with a photon is presented. The study is based on proton-proton collisions at a center-of-mass energy of 8 TeV using data collected with the CMS detector at the LHC, corresponding to an integrated luminosity of 19.8 inverse femtobarns. The search for t gamma events where t to Wb and W to mu nu is conducted in final states with a muon, a photon, at least one hadronic jet with at most one being consistent with originating from a bottom quark, and missing transverse momentum. No evidence of single top quark production in association with a photon through a FCNC is observed. Upper limits at the 95% confidence level are set on the tu gamma and tc gamma anomalous couplings and translated into upper limits on the branching fraction of the FCNC top quark decays: B(t to u gamma) < 1.3E-4 and B(t to c gamma) < 1.7E-3. Upper limits are also set on the cross section of associated t gamma production in a restricted phase-space region. These are the most stringent limits currently available.

submitted time 2016-09-12 Hits524Downloads301 Comment 0

10. chinaXiv:201609.00789 [pdf]

Search for a low-mass pseudoscalar Higgs boson produced in association with a $b\barb$ pair in pp collisions at $\sqrt{s} =$ 8 TeV

Khachatryan, Vardan and others
Subjects: Physics >> Nuclear Physics

A search is reported for a light pseudoscalar Higgs boson decaying to a pair of tau leptons, produced in association with a b b-bar pair, in the context of two-Higgs-doublet models. The results are based on pp collision data at a centre-of-mass energy of 8 TeV collected by the CMS experiment at the LHC and corresponding to an integrated luminosity of 19.7 inverse femtobarns. Pseudoscalar boson masses between 25 and 80 GeV are probed. No evidence for a pseudoscalar boson is found and upper limits are set on the production cross section times branching fraction to tau pairs between 7 and 39 pb at the 95% confidence level. This excludes pseudoscalar A bosons with masses between 25 and 80 GeV, with standard model-like Higgs boson negative couplings to down-type fermions, produced in association with b b-bar pairs, in Type-II, two-Higgs-doublet models.

submitted time 2016-09-12 Hits494Downloads285 Comment 0

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