OPMD

Abstract:

A search for excited leptons is carried out with the CMS detector at the LHC, using 36 pb-1 of pp collision data recorded at s=7 TeV. The search is performed for associated production of a lepton and an oppositely charged excited lepton pp→ℓℓ*, followed by the decay ℓ*→ℓγ, resulting in the ℓℓγ final state, where ℓ=e,μ. No excess of events above the standard model expectation is observed. Interpreting the findings in the context of ℓ* production through four-fermion contact interactions and subsequent decay via electroweak processes, first upper limits are reported for ℓ* production at this collision energy. The exclusion region in the compositeness scale Λ and excited lepton mass Mℓ* parameter space is extended beyond previously established limits. For Λ=Mℓ*, excited lepton masses are excluded below 1070 GeV/c2 for e* and 1090 GeV/c2 for μ* at the 95% confidence level. © 2011 CERN.

Abstract:

Measurements of primary charged hadron multiplicity distributions are presented for non-single-diffractive events in proton-proton collisions at centre-of-mass energies of √s = 0.9, 2.36, and 7TeV, in five pseudorapidity ranges from |η| < 0.5 to |η| < 2.4. The data were collected with the minimum-bias trigger of the CMS experiment during the LHC commissioning runs in 2009 and the 7TeV run in 2010. The multiplicity distribution at √s = 0.9 TeV is in agreement with previous measurements. At higher energies the increase of the mean multiplicity with √s is underestimated by most event generators. The average transverse momentum as a function of the multiplicity is also presented. The measurement of higher-order moments of the multiplicity distribution confirms the violation of Koba-Nielsen-Olesen scaling that has been observed at lower energies.

Abstract:

The charged particle transverse momentum (pT) spectra are presented for pp collisions at √s = 0:9 and 7TeV. The data samples were collected with the CMS detector at the LHC and correspond to integrated luminosities of 231 μb-1and 2.96 pb-1, respectively. Calorimeter-based high-transverse-energy triggers are employed to enhance the statistical reach of the high-pT measurements. The results are compared with leading and next-toleading order QCD and with an empirical scaling of measurements at different collision energies using the scaling variable xT - 2pT=ps over the pT range up to 136 GeV/c. Using a combination of xT scaling and direct interpolation at fixed pT, a reference transverse momentum spectrum at √s = 2:76TeV is constructed, which can be used for studying high-pT particle suppression in the dense QCD medium produced in heavy-ion collisions at that centre-of-mass energy. Copyright CERN.

Abstract:

Measurements of the jet energy calibration and transverse momentum resolution in CMS are presented, performed with a data sample collected in proton-proton collisions at a centre-of-mass energy of 7TeV, corresponding to an integrated luminosity of 36pb-1. The transverse momentum balance in dijet and γ/Z+jets events is used to measure the jet energy response in the CMS detector, as well as the transverse momentum resolution. The results are presented for three different methods to reconstruct jets: a calorimeter-based approach, the "Jet-Plus-Track" approach, which improves the measurement of calorimeter jets by exploiting the associated tracks, and the "Particle Flow" approach, which attempts to reconstruct individually each particle in the event, prior to the jet clustering, based on information from all relevant subdetectors.