Study of the readout chip and silicon sensor degradation for the CMS pixel upgrade

Hybrid silicon pixel detectors are currently used in the innermost tracking system of the Compact Muon Solenoid (CMS) experiment. Radiation tolerance up to fluences expected for a few years of running of the Large Hadron Collider (LHC) has already been proved, although some degradation of the part of the silicon detector closer to the interaction point is expected. During the LHC upgrade phases, the level of dose foreseen for the silicon pixel detector will be much higher. To face this aspect, dedicated irradiation tests with fluences above $\mathcal{O}(10^{15})$ n$_{\textrm{eq}}$/cm$^2$ have been performed on the silicon sensor and readout chip. Changes in the operation of the sensor and readout chip as a function of the fluence are presented. The charge collection efficiency has been studied: partial recovery of the detector efficiency can be achieved by operating the detectors in a controlled environment and at higher bias voltage.Comment: conference; 6 pages; 5 figure

Measurement of inclusive bb-quark production at s=\sqrt{s}=7 TeV with the CMS experiment

Measurements performed by the CMS experiment of the cross section for inclusive $b$-quark production in proton-proton collisions at $\sqrt{s}= 7$ TeV are presented. The measurements are based on different methods, such as inclusive jet measurements with secondary vertex tagging or selecting a sample of events containing jets and at least one muon, where the transverse momentum of the muon with respect to the closest jet axis discriminates $b$-events from the background. The results are compared with predictions based on perturbative QCD calculations at leading and next-to-leading order.Comment: conference; 7 page

Search for pair-produced dijet resonances in four-jet final states in pp collisions at s√=7 TeV

This is the publisher's version, also available electronically from http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.110.141802.A search for the pair production of a heavy, narrow resonance decaying into two jets has been performed using events collected in s√=7  TeV pp collisions with the CMS detector at the LHC. The data sample corresponds to an integrated luminosity of 5.0  fb(−1). Events are selected with at least four jets and two dijet combinations with similar dijet mass. No resonances are found in the dijet mass spectrum. The upper limit at 95% confidence level on the product of the resonance pair production cross section, the branching fractions into dijets, and the acceptance varies from 0.22 to 0.005 pb, for resonance masses between 250 and 1200 GeV. Pair-produced colorons decaying into qq-bar are excluded for coloron masses between 250 and 740 GeV

Search for heavy quarks decaying into a top quark and a W or Z boson using lepton + jets events in pp collisions at s√=7 TeV

This is the publisher's version, also available electronically from http://link.springer.com/article/10.1007%2FJHEP01%282013%29154.Results are presented from a search for the pair-production of heavy quarks, QQ-bar , that decay exclusively into a top quark and a W or Z boson. The search is performed using a sample of proton-proton collisions at s√=7 TeV corresponding to an integrated luminosity of 5.0 fb(−1), collected by the Compact Muon Solenoid experiment. The signal region is defined using a sample of events containing one electron or muon, missing transverse momentum, and at least four jets with large transverse momenta, where one jet is likely to originate from the decay of a bottom quark. No significant excess of events is observed with respect to the standard model expectations. Assuming a strong pair-production mechanism, quark masses below 675 (625) GeV decaying into tW (tZ) are excluded at the 95 % confidence level

Search for supersymmetry in final states with a single lepton, b-quark jets, and missing transverse energy in proton-proton collisions at s√=7 TeV

This is the publisher's version, also available electronically from http://journals.aps.org/prd/abstract/10.1103/PhysRevD.87.052006.A search motivated by supersymmetric models with light top squarks is presented using proton-proton collision data recorded with the CMS detector at a center-of-mass energy of s√=7  TeV during 2011, corresponding to an integrated luminosity of 4.98  fb(−1). The analysis is based on final states with a single lepton, b-quark jets, and missing transverse energy. Standard model yields are predicted from data using two different approaches. The observed event numbers are found to be compatible with these predictions. Results are interpreted in the context of the constrained minimal supersymmetric standard model and of a simplified model with four top quarks in the final state

Search in leptonic channels for heavy resonances decaying to long-lived neutral particles

This is the publisher's version, also available electronically from http://link.springer.com/article/10.1007%2FJHEP02%282013%29085.A search is performed for heavy resonances decaying to two long-lived massive neutral particles, each decaying to leptons. The experimental signature is a distinctive topology consisting of a pair of oppositely charged leptons originating at a separated secondary vertex. Events were collected by the CMS detector at the LHC during pp collisions at s√=7 TeV, and selected from data samples corresponding to 4.1 (5.1) fb(−1) of integrated luminosity in the electron (muon) channel. No significant excess is observed above standard model expectations, and an upper limit is set with 95% confidence level on the production cross section times the branching fraction to leptons, as a function of the long-lived massive neutral particle lifetime

Study of the Mass and Spin-Parity of the Higgs Boson Candidate via Its Decays to Z Boson Pairs

This is the publisher's version, also available electronically from http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.110.081803.A study is presented of the mass and spin-parity of the new boson recently observed at the LHC at a mass near 125 GeV. An integrated luminosity of 17.3  fb(−1), collected by the CMS experiment in proton-proton collisions at center-of-mass energies of 7 and 8 TeV, is used. The measured mass in the ZZ channel, where both Z bosons decay to e or μ pairs, is 126.2±0.6(stat)±0.2(syst)  GeV. The angular distributions of the lepton pairs in this channel are sensitive to the spin-parity of the boson. Under the assumption of spin 0, the present data are consistent with the pure scalar hypothesis, while disfavoring the pure pseudoscalar hypothesis