CMS Barrel Pixel Detector Overview

The pixel detector is the innermost tracking device of the CMS experiment at the LHC. It is built from two independent sub devices, the pixel barrel and the end disks. The barrel consists of three concentric layers around the beam pipe with mean radii of 4.4, 7.3 and 10.2 cm. There are two end disks on each side of the interaction point at 34.5 cm and 46.5 cm. This article gives an overview of the pixel barrel detector, its mechanical support structure, electronics components, services and its expected performance.Comment: Proceedings of Vertex06, 15th International Workshop on Vertex Detector

Measurements of tt‾t\overline{t} spin correlations and top quark polarization using dilepton final states in pp collisions at s\sqrt{s} = 8 TeV

Measurements of the top quark-antiquark ($t\overline{t}$) spin correlations and the top quark polarization are presented for $t\overline{t}$ pairs produced in pp collisions at $\sqrt{s}$=8  TeV. The data correspond to an integrated luminosity of 19.5  fb$^{−1}$ collected with the CMS detector at the LHC. The measurements are performed using events with two oppositely charged leptons (electrons or muons) and two or more jets, where at least one of the jets is identified as originating from a bottom quark. The spin correlations and polarization are measured from the angular distributions of the two selected leptons, both inclusively and differentially, with respect to the invariant mass, rapidity, and transverse momentum of the $t\overline{t}$ system. The measurements are unfolded to the parton level and found to be in agreement with predictions of the standard model. A search for new physics in the form of anomalous top quark chromo moments is performed. No evidence of new physics is observed, and exclusion limits on the real part of the chromo-magnetic dipole moment and the imaginary part of the chromo-electric dipole moment are evaluated

Forward-backward asymmetry of Drell–Yan lepton pairs in pp collisions at s\sqrt{s} = 8 TeV

A measurement of the forward-backward asymmetry AFB of oppositely charged lepton pairs (μμ and ee) produced via Z/γ∗ boson exchange in pp collisions at $\sqrt{s}$ = 8 TeV is presented. The data sample corresponds to an integrated luminosity of 19.7 fb$^{−1}$ collected with the CMS detector at the LHC. The measurement of $A_{FB}$ is performed for dilepton masses between 40 GeV and 2 TeV and for dilepton rapidity up to 5. The $A_{FB}$ measurements as a function of dilepton mass and rapidity are compared with the standard model predictions

Measurement of the CP-violating weak phase ϕsϕ_s and the decay width difference ΔΓsΔΓ_s using the Bs0→J/ψϕ(1020)B^{0}_{s}→J/ψϕ(1020) decay channel in pp collisions at s=8\sqrt{s} = 8 TeV

The CP-violating weak phase $ϕ_s$ of the $B^{0}_{s}$ meson and the decay width difference $ΔΓ_s$ of the Bs0 light and heavy mass eigenstates are measured with the CMS detector at the LHC using a data sample of $B^{0}_{s}→J/ψϕ(1020)→μ^{+}μ^{−}K^{+}K^{−}$ decays. The analysed data set corresponds to an integrated luminosity of 19.7fb$^{−1}$ collected in pp collisions at a centre-of-mass energy of 8TeV . A total of 49 200 reconstructed $B^{0}_{s}$ decays are used to extract the values of $ϕ_s$ and $ΔΓ_s$ by performing a time-dependent and flavour-tagged angular analysis of the $μ^{+}μ^{−}K^{+}K^{−}$ final state. The weak phase is measured to be $ϕ_s$=−0.075±0.097(stat)±0.031(syst) rad , and the decay width difference is $ΔΓ_s$=0.095±0.013(stat)±0.007(syst) ps$^{−1}$

Search for lepton flavour violating decays of the Higgs boson to eττ and eμ in proton–proton collisions at s\sqrt{s} = 8 TeV

A direct search for lepton flavour violating decays of the Higgs boson (H) in the H→eτ and H→eμ channels is described. The data sample used in the search was collected in proton–proton collisions at $\sqrt{s}$=8 TeV with the CMS detector at the LHC and corresponds to an integrated luminosity of 19.7 fb$^{−1}$. No evidence is found for lepton flavour violating decays in either final state. Upper limits on the branching fractions, B(H→eτ)<0.69% and B(H→eμ)<0.035% , are set at the 95% confidence level. The constraint set on B(H→eτ) is an order of magnitude more stringent than the existing indirect limits. The limits are used to constrain the corresponding flavour violating Yukawa couplings, absent in the standard model

Search for supersymmetry in electroweak production with photons and large missing transverse energy in pp collisions at s=8 TeV\sqrt{s} = 8\mathrm{\,Te\kern -0.1em V}

Results are reported from a search for supersymmetry with gauge-mediated supersymmetry breaking in electroweak production. Final states with photons and large missing transverse energy ( $E^{miss}_{T}$ ) were examined. The data sample was collected in pp collisions at $\sqrt{s}$ =8TeV with the CMS detector at the LHC and corresponds to 7.4 fb$^{−1}$ . The analysis focuses on scenarios in which the lightest neutralino has bino- or wino-like components, resulting in decays to photons and gravitinos, where the gravitinos escape undetected. The data were obtained using a specially designed trigger with dedicated low thresholds, providing good sensitivity to signatures with photons, $E^{miss}_{T}$ , and low hadronic energy. No excess of events over the standard model expectation is observed. The results are interpreted using the model of general gauge mediation. With the wino mass fixed at 10 $GeV$ above that of the bino, wino masses below 710 $GeV$ are excluded at 95% confidence level. Constraints are also set in the context of two simplified models, for which the analysis sets the lowest cross section limits on the electroweak production of supersymmetric particles

Measurement of the Zγ→νν‾γZγ → ν\overline{ν}γ production cross section in pp collisions at s\sqrt{s} = 8 TeV and limits on anomalous ZZγ and Zγγ trilinear gauge boson couplings

An inclusive measurement of the $Zγ → ν\overline{ν}γ$ production cross section in pp collisions at $\sqrt{s}$=8TeV is presented, using data corresponding to an integrated luminosity of 19.6 fb$^{−1}$ collected with the CMS detector at the LHC. This measurement is based on the observation of events with large missing energy and with a single photon with transverse momentum above 145 GeV and absolute pseudorapidity in the range |η|<1.44 . The measured Zγ→νν‾γ production cross section, 52.7±2.1 (stat)±6.4 (syst)±1.4 (lumi) fb , agrees well with the standard model prediction of 50.0−2.2+2.4 fb . A study of the photon transverse momentum spectrum yields the most stringent limits to date on the anomalous ZZγ and Zγγ trilinear gauge boson couplings

Phenomenological MSSM interpretation of CMS searches in pp collisions at s\sqrt{s} = 7 and 8 TeV

Searches for new physics by the CMS collaboration are interpreted in the framework of the phenomenological minimal supersymmetric standard model (pMSSM). The data samples used in this study were collected at $\sqrt{s}$ = 7 and 8 TeV and have integrated luminosities of 5.0 fb$^{−1}$ and 19.5 fb$^{−1}$, respectively. A global Bayesian analysis is performed, incorporating results from a broad range of CMS supersymmetry searches, as well as constraints from other experiments. Because the pMSSM incorporates several well-motivated assumptions that reduce the 120 parameters of the MSSM to just 19 parameters defined at the electroweak scale, it is possible to assess the results of the study in a relatively straightforward way. Approximately half of the model points in a potentially accessible subspace of the pMSSM are excluded, including all pMSSM model points with a gluino mass below 500 GeV, as well as models with a squark mass less than 300 GeV. Models with chargino and neutralino masses below 200 GeV are disfavored, but no mass range of model points can be ruled out based on the analyses considered. The nonexcluded regions in the pMSSM parameter space are characterized in terms of physical processes and key observables, and implications for future searches are discussed

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

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

Measurement of prompt ψ\psi(2S) to J/ψ\psi yield ratios in Pb-Pb and p-p collisions at sNN\sqrt {sNN} = 2.76 TeV

The ratio between the prompt ψ(2S) and J/ψ yields, reconstructed via their decays into μ+μ-, is measured in Pb-Pb and p-p collisions at sNN=2.76  TeV. The analysis is based on Pb-Pb and p-p data samples collected by CMS at the Large Hadron Collider, corresponding to integrated luminosities of 150  μb-1 and 5.4  pb-1, respectively. The double ratio of measured yields (Nψ(2S)/NJ/ψ)Pb-Pb/(Nψ(2S)/NJ/ψ)p-p is computed in three Pb-Pb collision centrality bins and two kinematic ranges: one at midrapidity, |y|<1.6, covering the transverse momentum range 6.5<pT<30  GeV/c, and the other at forward rapidity, 1.6<|y|<2.4, extending to lower pT values, 3<pT<30  GeV/c. The centrality-integrated double ratio changes from 0.45±0.13(stat)±0.07(syst) in the first range to 1.67±0.34(stat)±0.27(syst) in the second. This difference is most pronounced in the most central collisions