Measurements are reported of differential cross sections for the production of a W boson, which decays into a muon and a neutrino, in association with jets, as a function of several variables, ...including the transverse momenta ( ) and pseudorapidities of the four leading jets, the scalar sum of jet transverse momenta ( ), and the difference in azimuthal angle between the directions of each jet and the muon. The data sample of pp collisions at a centre-of-mass energy of 7 TeV was collected with the CMS detector at the LHC and corresponds to an integrated luminosity of 5.0 fb super(-1). The measured cross sections are compared to predictions from Monte Carlo generators, MadGraph + pythia and sherpa, and to next-to-leading-order calculations from BlackHat + sherpa. The differential cross sections are found to be in agreement with the predictions, apart from the distributions of the leading jets at high values, the distributions of the at high- and low jet multiplicity, and the distribution of the difference in azimuthal angle between the leading jet and the muon at low values.
The clock and control signal distribution system for the NA48 experiment Jeitler, M.; Mikulec, I.; Neuhofer, G. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
11/1997, Letnik:
400, Številka:
1
Journal Article
Recenzirano
In the NA48 experiment at CERN, several detector subsystems located at distances of up to 200 m between each other produce data on a continuous basis and feed them into pipelines. Triggers are ...produced after variable delay times by two different systems for charged and for all-neutral kaon decays. To allow the retrieval of the corresponding data from the various subsystems and their merging into complex events by means of timestamps, a special, highly stable global clock distribution system has been developed. The design principles and the setup of the clock system are described and results for clock stability monitoring and automated correction of the signal transmission speed are reported.
A peaking structure in the J/ psi phi J/ psi phi mass spectrum near threshold is observed in B super( plus or minus ) arrow right J/ psi phi K super( plus or minus )B plus or minus arrow right J/ psi ...phi K plus or minus decays, produced in pp collisions at s=7 TeV collected with the CMS detector at the LHC. The data sample, selected on the basis of the dimuon decay mode of the J/ psi J/ psi , corresponds to an integrated luminosity of 5.2 fb super(-1). Fitting the structure to an S -wave relativistic Breit-Wigner lineshape above a three-body phase-space nonresonant component gives a signal statistical significance exceeding five standard deviations. The fitted mass and width values are m=4148.0 plus or minus 2.4(stat.) plus or minus 6.3(syst.)MeV and Gamma =28-11+15(stat.) plus or minus 19(syst.)MeV, respectively. Evidence for an additional peaking structure at higher J/ psi phi J/ psi phi mass is also reported.
(ProQuest: ... denotes formulae and/or non-USASCII text omitted; see image).Dijet production has been measured in ... collisions at a nucleon-nucleon centre-of-mass energy of 5.02... A data sample ...corresponding to an integrated luminosity of 35 ... was collected using the Compact Muon Solenoid detector at the Large Hadron Collider. The dijet transverse momentum balance, azimuthal angle correlations, and pseudorapidity distributions are studied as a function of the transverse energy in the forward calorimeters (...). For ... collisions, the dijet transverse momentum ratio and the width of the distribution of dijet azimuthal angle difference are comparable to the same quantities obtained from a simulated ... reference and insensitive to ... In contrast, the mean value of the dijet pseudorapidity is found to change monotonically with increasing ..., indicating a correlation between the energy emitted at large pseudorapidity and the longitudinal motion of the dijet frame. The pseudorapidity distribution of the dijet system in minimum bias ... collisions is compared with next-to-leading-order perturbative QCD predictions obtained from both nucleon and nuclear parton distribution functions, and the data more closely match the latter.
The NA62 experiment at CERN collected a large sample of charged kaon decays with a highly efficient trigger for decays into electrons in 2007. The kaon beam represents a source of tagged neutral pion ...decays in vacuum. A measurement of the electromagnetic transition form factor slope of the neutral pion in the time-like region from ∼1 million fully reconstructed π 0 Dalitz decay is presented. The limits on dark photon production in π 0 decays from the earlier kaon experiment at CERN, NA48/2, are also reported.
Results are presented of a search for compositeness in electrons and muons using a data sample of pp collisions at a center-of-mass energy s = 7 TeV collected with the CMS detector at the LHC and ...corresponding to an integrated luminosity of 5.0 fb - 1 . Excited leptons (a a) are assumed to be produced via contact interactions in conjunction with a standard model lepton and to decay via a a a a gamma , yielding a final state with two energetic leptons and a photon. The number of events observed in data is consistent with that expected from the standard model. The 95% confidence upper limits for the cross section for the production and decay of excited electrons (muons), with masses ranging from 0.6 to 2 TeV, are 1.48 to 1.24 fb (1.31 to 1.11 fb). Excited leptons with masses below 1.9 TeV are excluded for the case where the contact interaction scale equals the excited lepton mass. The limits on the cross sections are the most stringent ones published to date.
A measurement of the t t A= production cross section in pp collisions at s = 7 TeV is presented. The results are based on data corresponding to an integrated luminosity of 2.3 fb-1 collected by the ...CMS detector at the LHC. Selected events are required to have one isolated, high transverse momentum electron or muon, large missing transverse energy, and hadronic jets, at least one of which must be consistent with having originated from a b quark. The measured cross section is 158.1 +/- 2.1 (stat .) +/- 10.2 (syst .) +/- 3.5 (lum .) pb , in agreement with standard model predictions.
An updated search for heavy narrow resonances decaying to muon or electron pairs using the CMS detector is presented. Data samples from pp collisions at s = 7 TeV and 8 TeV at the LHC, with ...integrated luminosities of up to 5.3 and 4.1 fb - 1 , respectively, are combined. No evidence for a heavy narrow resonance is observed. The analysis of the combined data sets excludes, at 95% confidence level, a Sequential Standard Model Z SSM a2 resonance lighter than 2590 GeV, a superstring-inspired Z I a2 lighter than 2260 GeV, and KaluzaaKlein gravitons lighter than 2390 (2030) GeV, assuming that the coupling parameter k / M A= Pl is 0.10 (0.05). These are the most stringent limits to date.
From the 2002 data taking with a neutral kaon beam extracted from the CERN-SPS, the NA48/1 experiment observed 97 I 0 a IL + mu - I12 A= mu candidates with a background contamination of 30.8 +/- 4.2 ...events. From this sample, the BR (I 0 a IL + mu - I12 A= mu ) is measured to be (2.17 +/- 0.32 stat +/- 0.17 syst) X 10 - 6 .
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