Search for flavor changing neutral currents in top quark decays in pp collisions at 7 TeV

The results of a search for flavor changing neutral currents in top quark decays $\mathrm{t}\to \mathrm{Zq}$ in events with a topology compatible with the decay chain $\mathrm{t}\overline{\mathrm{t}}\to \mathrm{Wb}+\mathrm{Zq}\to ?\nu \mathrm{b}+??\mathrm{q}$ are presented. The search is performed with a data sample corresponding to an integrated luminosity of $5.0{\text{fb}}^{?1}$ of proton–proton collisions at a center-of-mass energy of 7 TeV, collected with the CMS detector at the LHC. The observed number of events agrees with the standard model prediction and no evidence for flavor changing neutral currents in top quark decays is found. A $\mathrm{t}\to \mathrm{Zq}$ branching fraction greater than 0.21% is excluded at the 95% confidence level.     

Search for dijet resonances in 7 TeV pp collisions at CMS

A search for narrow resonances in the dijet mass spectrum is performed using data corresponding to an integrated luminosity of 2.9 pb?1 collected by the CMS experiment at the Large Hadron Collider. Upper limits at the 95% confidence level are presented on the product of the resonance cross section, branching fraction into dijets, and acceptance, separately for decays into quark-quark, quark-gluon, or gluon-gluon pairs. The data exclude new particles predicted in the following models at the 95% confidence level: string resonances, with mass less than 2.50 TeV, excited quarks, with mass less than 1.58 TeV, and axigluons, colorons, and E6 diquarks, in specific mass intervals. This extends previously published limits on these models.     

Measurement of dijet angular distributions and search for quark compositeness in pp collisions at √s = 7 TeV

Dijet angular distributions are measured over a wide range of dijet invariant masses in pp collisions at √s = 7 TeV, at the CERN LHC. The event sample, recorded with the CMS detector, corresponds to an integrated luminosity of 36 pb?1. The data are found to be in good agreement with the predictions of perturbative QCD, and yield no evidence of quark compositeness. With a modified frequentist approach, a lower limit on the contact interaction scale for left-handed quarks of Λ? = 5.6 TeV (Λ? = 6.7 TeV) for destructive (constructive) interference is obtained at the 95% confidence level.     

Indications of suppression of excited Υ states in Pb-Pb collisions at √(s(NN))=2.76 TeV

A comparison of the relative yields of Υ resonances in the μ(+)μ(-) decay channel in Pb-Pb and pp collisions at a center-of-mass energy per nucleon pair of 2.76 TeV is performed with data collected with the CMS detector at the LHC. Using muons of transverse momentum above 4 GeV/c and pseudorapidity below 2.4, the double ratio of the Υ(2S) and Υ(3S) excited states to the Υ(1S) ground state in Pb-Pb and pp collisions, [Υ(2S+3S)/Υ(1S)](Pb-Pb)/[Υ(2S+3S)/Υ(1S)](pp), is found to be 0.31(-0.15)(+0.19)(stat)±0.03(syst). The probability to obtain the measured value, or lower, if the true double ratio is unity, is calculated to be less than 1%.