A fully pipelined 40MHz “dead-time-free” trigger system for neutral K0 decays for the NA48 experiment2Cagliari, Cambridge, CERN, Dubna, Edinburgh, Ferrara, Firenze, Mainz, Orsay, Perugia, Pisa, ...Saclay, Siegen, Torino, Warszawa, Wien Collaboration.2 at CERN is described. The NA48 experiment studies CP-violation using the high intensity beam of the CERN SPS accelerator. The trigger system sums, digitises, filters and processes signals from 13 340 channels of the liquid krypton electro-magnetic calorimeter. In 1996 the calorimeter and part of the trigger electronics were installed and tested. In 1997 the system was completed and prepared to be used in the first NA48 physics data taking period.
A search is presented for charge-asymmetric production of a W ' boson that has been proposed to accommodate the forward-backward asymmetry observed in the production of top-antitop quark pairs at the ...Tevatron. The new heavy W ' boson would be produced in association with a top quark and would decay into top and down quarks. The data correspond to an integrated luminosity of 5.0 fb-1 in pp collisions at a center-of-mass energy of 7 TeV, recorded by the CMS detector at the LHC. No significant excess above the standard model expectations is observed, and, from a combination of the electron-plus-jets and muon-plus-jets channels, a 95% confidence level lower limit of 840 GeV / c 2 is set on the W ' boson mass for a W ' boson model with values for coupling constants to top and down quarks g L = 0 and g R = 2 . In addition, a kinematic reconstruction of the W ' resonance mass using the inherent charge asymmetry of this model finds no indication of the presence of W ' events in the data.
A search is presented for physics beyond the standard model (BSM) in events with a Z boson, jets, and missing transverse energy (E T miss). This signature is motivated by BSM physics scenarios, ...including supersymmetry. The study is performed using a sample of proton-proton collision data collected at s = 7 TeV with the CMS experiment at the LHC, corresponding to an integrated luminosity of 4.98 fb-1. The contributions from the dominant standard model backgrounds are estimated from data using two complementary strategies, the jet-Z balance technique and a method based on modeling E T miss with data control samples. In the absence of evidence for BSM physics, we set limits on the non-standard-model contributions to event yields in the signal regions and interpret the results in the context of simplified model spectra. Additional information is provided to facilitate tests of other BSM physics models.
The results of a search for pair production of a heavy, top-like quark, t ' , in the decay mode t ' t A= ' ? bW + b A= W - ? b l + ? b A= l - ? A= are presented. The search is performed with a data ...sample corresponding to an integrated luminosity of 5.0 fb - 1 in pp collisions at a center-of-mass energy of 7 TeV, collected by the CMS experiment at the LHC. The observed number of events agrees with the expectation from standard model processes, and no evidence of t ' t A= ' production is found. Upper limits on the production cross section as a function of t ' mass are presented, and t ' masses below 557 GeV / c 2 are excluded at the 95% confidence level.
A search for high-mass resonances decaying into t + t - is performed using a data sample of pp collisions at s = 7 TeV . The data were collected with the CMS detector at the LHC and correspond to an ...integrated luminosity of 4.9 fb-1. The number of observed events is in agreement with the standard model prediction. An upper limit on the product of the resonance cross section and branching fraction into t-lepton pairs is calculated as a function of the resonance mass. Using the sequential standard model resonance Z SSM ' and the superstring-inspired E 6 model with resonance Z ? ' as benchmarks, resonances with standard model couplings with masses below 1.4 and 1.1 TeV, respectively, are excluded at 95% confidence level.
A measurement is presented of W-boson production in PbPb collisions carried out at a nucleon-nucleon (NN) centre-of-mass energy s NN of 2.76 TeV at the LHC using the CMS detector. In data ...corresponding to an integrated luminosity of 7.3 mu b - 1 , the number of W ? mu ? mu decays is extracted in the region of muon pseudorapidity | ? mu | 25 GeV / c . Yields of muons found per unit of pseudorapidity correspond to (159 +/- 10 (stat.) +/- 12 (syst.)) X 10 - 8 W + and (154 +/- 10 (stat.) +/- 12 (syst.)) X 10 - 8 W - bosons per minimum-bias PbPb collision. The dependence of W production on the centrality of PbPb collisions is consistent with a scaling of the yield by the number of incoherent NN collisions. The yield of W bosons is also studied in a sample of pp interactions at s = 2.76 TeV corresponding to an integrated luminosity of 231 nb - 1 . The individual W + and W - yields in PbPb and pp collisions are found to agree, once the neutron and proton content in Pb nuclei is taken into account. Likewise, the difference observed in the dependence of the positive and negative muon production on pseudorapidity is consistent with next-to-leading-order perturbative QCD calculations.
A search for narrow, high-mass resonances decaying to electron or muon pairs has been performed using pp collision data collected at s = 7 TeV by the CMS experiment in 2011. The data sample ...corresponds to an integrated luminosity of approximately 5 fba1. The event yields observed in the signal regions are consistent with predictions of the standard model backgrounds, and upper limits on the cross section times branching fraction for a resonance decaying to dileptons are extracted from a shape analysis of the dilepton invariant mass distribution. The resulting mass limits at 95% confidence level are 2330 GeV for the Z a2 in the Sequential Standard Model, 2000 GeV for the superstring-inspired Z I a2 resonance, 890 (540) GeV for the Stueckelberg extension Z St a2 with the mass parameter Im = 0.06 (0.04), and 2140 (1810) GeV for Kaluza-Klein gravitons with the coupling parameter k / M A= Pl of 0.10 (0.05). These limits are the most stringent to date.
The I b differential production cross section and the cross section ratio I ( I A= b ) / I ( I b ) are measured as functions of transverse momentum p T I b and rapidity | y I b | in p p collisions at ...s = 7 TeV using data collected by the CMS experiment at the LHC. The measurements are based on I b decays reconstructed in the exclusive final state J / I I , with the subsequent decays J / I a mu + mu a and I a p I , using a data sample corresponding to an integrated luminosity of 1.9 fb a 1 . The product I ( I b ) X B ( I b a J / I I ) versus p T I b falls faster than that of b mesons. The measured value of I ( I b ) X B ( I b a J / I I ) for p T I b > 10 GeV and | y I b | < 2.0 is 1.16 +/- 0.06 +/- 0.12 nb , and the integrated I ( I A= b ) / I ( I b ) ratio is 1.02 +/- 0.07 +/- 0.09 , where the uncertainties are statistical and systematic, respectively.
The NA48 experiment at the CERN SPS accelerator aims to measure Re(ε′/ε), the direct CP violation parameter in
K
0 → 2π decays, to the precision of 2 × 10
−4. In the year 1999, the NA48 collaboration ...has published its first measurement based on the 1997 data. The presented result is a preliminary measurement from data collected in the 1998 run which contain 2.5 times more
K
L
→ 2π
0 decays than the 1997 data. A combined result of Re(ε′/ε)=(14.0±4.3)×10
−4 has been obtained.
A search for neutral Higgs bosons decaying to tau pairs at a center-of-mass energy of 7 TeV is performed using a dataset corresponding to an integrated luminosity of 4.6 fba1 recorded by the CMS ...experiment at the LHC. The search is sensitive to both the standard model Higgs boson and to the neutral Higgs bosons predicted by the minimal supersymmetric extension of the standard model (MSSM). No excess of events is observed in the tau-pair invariant-mass spectrum. For a standard model Higgs boson in the mass range of 110a145 GeV upper limits at 95% confidence level (CL) on the production cross section are determined. We exclude a Higgs boson with m H = 115 GeV with a production cross section 3.2 times of that predicted by the standard model. In the MSSM, upper limits on the neutral Higgs boson production cross section times branching fraction to tau pairs, as a function of the pseudoscalar Higgs boson mass, m A , sets stringent new bounds in the parameter space, excluding at 95% CL values of tan I2 as low as 7.1 at m A = 160 GeV in the m h max benchmark scenario.
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