Sharif Digital Repository

The observation of a new b baryon via its strong decay into Ξb-π + (plus charge conjugates) is reported. The measurement uses a data sample of pp collisions at √s=7TeV collected by the CMS experiment at the LHC, corresponding to an integrated luminosity of 5.3fb -1. The known Ξb- baryon is reconstructed via the decay chain Ξb-→J/ψΞ -→μ +μ -Λ0π -, with Λ0→pπ -. A peak is observed in the distribution of the difference between the mass of the Ξb-π + system and the sum of the masses of the Ξb- and π +, with a significance exceeding 5 standard deviations. The mass difference of the peak is 14.84±0.74(stat)±0.28(syst)MeV. The new state most likely corresponds to the JP=3/2 + companion of the Ξ b  

A search for the rare decays Bs0→μ+μ- and B0→μ+μ- is performed in pp collisions at √s=7TeV, with a data sample corresponding to an integrated luminosity of 1.14fb-1, collected by the CMS experiment at the LHC. In both cases, the number of events observed after all selection requirements is consistent with expectations from background and standard-model signal predictions. The resulting upper limits on the branching fractions are B(Bs0→μ +μ-)<1.9×10-8 and B(B0→μ+μ-)<4.6×10-9, at 95% confidence level  

A measurement of the electron charge asymmetry in inclusive pp→W+X→eν+X production at √s=7TeV is presented based on data recorded by the CMS detector at the LHC and corresponding to an integrated luminosity of 840pb -1. The electron charge asymmetry reflects the unequal production of W + and W - bosons in pp collisions. The electron charge asymmetry is measured in bins of the absolute value of electron pseudorapidity in the range of |η|<2.4. The asymmetry rises from about 0.1 to 0.2 as a function of the pseudorapidity and is measured with a relative precision better than 7%. This measurement provides new stringent constraints for parton distribution functions  

Measurements of the differential production cross sections dσ/dpTB and dσ/dyB for B0 mesons produced in pp collisions at √s=7TeV are presented. The data set used was collected by the CMS experiment at the LHC and corresponds to an integrated luminosity of 40pb-1. The production cross section is measured from B0 meson decays reconstructed in the exclusive final state J/ψKS0, with the subsequent decays J/ψ→μ +μ- and KS0→π+π-. The total cross section for pTB>5GeV and <2.2 is measured to be 33.2±2.5±3.5μb, where the first uncertainty is statistical and the second is systematic  

The suppression of the individual Υ(nS) states in PbPb collisions with respect to their yields in pp data has been measured. The PbPb and pp data sets used in the analysis correspond to integrated luminosities of 150μb -1 and 230nb-1, respectively, collected in 2011 by the CMS experiment at the LHC, at a center-of-mass energy per nucleon pair of 2.76TeV. The Υ(nS) yields are measured from the dimuon invariant mass spectra. The suppression of the Υ(nS) yields in PbPb relative to the yields in pp, scaled by the number of nucleon-nucleon collisions, RAA, is measured as a function of the collision centrality. Integrated over centrality, the RAA values are 0.56±0.08(stat)±0.07(syst),... 

A search is performed in pp collisions at √s=7TeV for exotic particles decaying via WZ to final states with electrons and muons. The data sample corresponds to an integrated luminosity of approximately 5fb -1. No significant excess is observed in the data above the expected standard model background. Upper bounds at 95% confidence level are set on the production cross section of the W ′ boson described by the sequential standard model and on the W ′ WZ coupling. W ′ bosons with masses below 1143 GeV are excluded. Limits are also set in the context of low-scale technicolor models, under a range of assumptions concerning the model parameters  

The azimuthal anisotropy of charged particles in Pb-Pb collisions at √s NN=2.76TeV is measured with the CMS detector at the LHC over an extended transverse momentum (p T) range up to approximately 60GeV/c. The data cover both the low-p T region associated with hydrodynamic flow phenomena and the high-p T region where the anisotropies may reflect the path-length dependence of parton energy loss in the created medium. The anisotropy parameter (v 2) of the particles is extracted by correlating charged tracks with respect to the event-plane reconstructed by using the energy deposited in forward-angle calorimeters. For the six bins of collision centrality studied, spanning the range of 0-60%... 

Results are presented from a search for new physics in the final state containing a photon (γ) and missing transverse energy (E T). The data correspond to an integrated luminosity of 5.0fb -1 collected in pp collisions at √s=7TeV by the CMS experiment. The observed event yield agrees with standard-model expectations for the γ+E T events. Using models for the production of dark-matter particles (χ), we set 90% confidence level (C.L.) upper limits of 13.6-15.4 fb on χ production in the γ+E T state. These provide the most sensitive upper limits for spin-dependent χ-nucleon scattering for χ masses (M χ) between 1 and 100 GeV. For spin-independent contributions, the present limits are extended to... 

A search for a Higgs boson in the four-lepton decay channel H→ZZ, with each Z boson decaying to an electron or muon pair, is reported. The search covers Higgs boson mass hypotheses in the range of 110100GeV (with 13 below 160GeV), while 67.1±6.0 (9.5±1.3) events are expected from background. The four-lepton mass distribution is consistent with the expectation of standard model background production of ZZ pairs. Upper limits at 95% confidence level exclude the...