Jet production rates in association with W and Z bosons in pp collisions at √s = 7 TeV

Measurements of jet production rates in association with W and Z bosons for jet transverse momenta above 30 GeV are reported, using a sample of proton-proton collision events recorded by CMS at √s = 7TeV, corresponding to an integrated luminosity of 36 pb^(-1). The study includes the measurement of the normalized inclusive rates of jets σ(V+ ≥n jets)/σ(V), where V represents either a W or a Z. In addition, the ratio of W to Z cross sections and the W charge asymmetry as a function of the number of associated jets are measured. A test of scaling at √s = 7TeV is also presented. The measurements provide a stringent test of perturbative-QCD calculations and are sensitive to the possible presence of new physics. The results are in agreement with the predictions of a simulation that uses explicit matrix element calculations for nal states with jets

Measurement of the tt production cross section in pp collisions at √s = 7 TeV in dilepton final states containing a τ

The top quark pair production cross section is measured in dilepton events with one electron or muon, and one hadronically decaying τ lepton from the decay tt →(ℓν_ℓ)(τ_hν_τ)bb, (ℓ=e,μ). The data sample corresponds to an integrated luminosity of 2.0  fb^(-1) for the electron channel and 2.2  fb^(-1) for the muon channel, collected by the CMS detector at the LHC. This is the first measurement of the tt cross section explicitly including τ leptons in proton-proton collisions at √s=7  TeV. The measured value σ_(tt) =143±14(stat)±22(syst)±3(lumi)  pb is consistent with the standard model predictions

Search for quark compositeness in dijet angular distributions from pp collisions at √s = 7 TeV

A search for quark compositeness using dijet angular distributions from pp collisions at √s = 7 TeV is presented. The search has been carried out using a data sample corresponding to an integrated luminosity of 2.2 fb^(−1), recorded by the CMS experiment at the LHC. Normalized dijet angular distributions have been measured for dijet invariant masses from 0.4 TeV to above 3 TeV and compared with a variety of contact interaction models, including those which take into account the effects of next-to-leading-order QCD corrections. The data are found to be in agreement with the predictions of perturbative QCD, and lower limits are obtained on the contact interaction scale, ranging from 7.5 up to 14.5 TeV at 95 % confidence level

Inclusive b-jet production in pp collisions at √s = 7 TeV

The inclusive b-jet production cross section in pp collisions at a center-of mass energy of 7 TeV is measured using data collected by the CMS experiment at the LHC. The cross section is presented as a function of the jet transverse momentum in the range 18 < p_T  < 200 GeV for several rapidity intervals. The results are also given as the ratio of the b-jet production cross section to the inclusive jet production cross section. The measurement is performed with two different analyses, which differ in their trigger selection and b-jet identification: a jet analysis that selects events with a b jet using a sample corresponding to an integrated luminosity of 34 pb^(−1), and a muon analysis requiring a b jet with a muon based on an integrated luminosity of 3 pb^(−1). In both approaches the b jets are identified by requiring a secondary vertex. The results from the two methods are in agreement with each other and with next-to-leading order calculations, as well as with predictions based on the pythia event generator

Measurement of the charge asymmetry in top-quark pair production in proton–proton collisions at √s = 7 TeV

The difference in angular distributions between top quarks and antiquarks, commonly referred to as the charge asymmetry, is measured in pp collisions at the LHC with the CMS experiment. The data sample corresponds to an integrated luminosity of 1.09 fb^(−1) at a centre-of-mass energy of 7 TeV. Top-quark pairs are selected in the final state with an electron or muon and four or more jets. At least one jet is identified as originating from b-quark hadronization. The charge asymmetry is measured in two variables, one based on the pseudorapidities (η) of the top quarks and the other on their rapidities (y). The results A^η_C = −0.017 ± 0.032 (stat.) ^(+0.025)_(−0.036) (syst.) and A^y_C = −0.013 ± 0.028 (stat.) ^(+0.029)_(−0.031) (syst.) are consistent within uncertainties with the standard-model predictions

Measurement of isolated photon production in pp and PbPb collisions at √snn = 2.76 TeV

Isolated photon production is measured in proton–proton and lead–lead collisions at nucleon–nucleon centre-of-mass energies of 2.76 TeV in the pseudorapidity range |η|<1.44 and transverse energies E_T between 20 and 80 GeV with the CMS detector at the LHC. The measured E_T spectra are found to be in good agreement with next-to-leading-order perturbative QCD predictions. The ratio of PbPb to pp isolated photon E_T-differential yields, scaled by the number of incoherent nucleon–nucleon collisions, is consistent with unity for all PbPb reaction centralities

Effects of temperature and ocean acidification on shell characteristics of Argopecten purpuratus: implications for scallop aquaculture in an upwelling-influenced area

Coastal upwelling regions already constitute hot spots of ocean acidification as naturally acidified waters are brought to the surface. This effect could be exacerbated by ocean acidification and warming, both caused by rising concentrations of atmospheric CO2. Along the Chilean coast, upwelling supports highly productive fisheries and aquaculture activities. However, during recent years, there has been a documented decline in the national production of the native scallop Argopecten purpuratus. We assessed the combined effects of temperature and pCO2-driven ocean acidification on the growth rates and shell characteristics of this species farmed under the natural influence of upwelling waters occurring in northern Chile (30° S, Tongoy Bay). The experimental scenario representing current conditions (14°C, pH ~8.0) were typical of natural values recorded in Tongoy Bay, whilst conditions representing the low pH scenario were typical of an adjacent upwelling area (pH ~7.6). Shell thickness, weight, and biomass were reduced under low pH (pH ~7.7)and increased temperature (18°C) conditions. At ambient temperature (14°C) and low pH, scallops showed increased shell dissolution and low growth rates. However, elevated temperatures ameliorated the impacts of low pH, as evidenced by growth rates in both pH treatments at the higher temperature treatment that were not significantly different from the control treatment. The impact of low pH at current temperature on scallop growth suggests that the upwelling could increase the time required for scallops to reach marketable size. Mortality of farmed scallops is discussed in relation to our observations of multiple environmental stressors in this upwelling-influenced area

Search for B^0_s → µ^+µ^- and B^0 → µ^+µ^- decays

A search for the rare decays B^0_s → μ^+μ^− and B^0 → μ^+μ^− is performed in pp collisions at √s = 7TeV , with a data sample corresponding to an integrated luminosity of 5 fb^(−1) collected by the CMS experiment at the LHC. In both decays, the number of events observed after all selection requirements is consistent with the expectation from background plus standard model signal predictions. The resulting upper limits on the branching fractions are B(B^0_s → µ^+µ^−7.7x10^(−9) and B(B^0 → µ^+µ^−) 1.8x10^(−9) at 95% confidence level