First measurement of Bose-Einstein correlations in proton-proton collisions at √s=0.9 and 2.36 TeV at the LHC

Bose-Einstein correlations have been measured using samples of proton-proton collisions at 0.9 and 2.36 TeV center-of-mass energies, recorded by the CMS experiment at the CERN Large Hadron Collider. The signal is observed in the form of an enhancement of pairs of same-sign charged particles with small relative four-momentum. The size of the correlated particle emission region is seen to increase significantly with the particle multiplicity of the event

Search for large extra dimensions in the diphoton final state at the Large Hadron Collider

28 páginas, 3 figuras, 3 tablas.-- CMS Collaboration: et al.-- Open Access: This article is distributed under the terms of the Creative Commons Attribution Noncommercial License.A search for large extra spatial dimensions via virtual-graviton exchange in the diphoton channel has been carried out with the CMS detector at the LHC. No excess of events above the standard model expectations is found using a data sample collected in proton-proton collisions at ps = 7TeV and corresponding to an integrated luminosity of 36 pb-1. New lower limits on the e ective Planck scale in the range of 1.6-2.3TeV at the 95% con dence level are set, providing the most restrictive bounds to date on models with more than two large extra dimensions.Peer reviewe

CMS tracking performance results from early LHC operation

The first LHC pp collisions at centre-of-mass energies of 0.9 and 2.36 TeV were recorded by the CMS detector in December 2009. The trajectories of charged particles produced in the collisions were reconstructed using the all-silicon Tracker and their momenta were measured in the 3.8 T axial magnetic field. Results from the Tracker commissioning are presented including studies of timing, efficiency, signal-to-noise, resolution, and ionization energy. Reconstructed tracks are used to benchmark the performance in terms of track and vertex resolutions, reconstruction of decays, estimation of ionization energy loss, as well as identification of photon conversions, nuclear interactions, and heavy-flavour decays

Measurement of W+W− production and search for the Higgs boson in pp collisions at s=7 TeV

AbstractA measurement of W+W− production in pp collisions at s=7 TeV and a search for the Higgs boson are reported. The W+W− candidates are selected in events with two leptons, either electrons or muons. The measurement is performed using LHC data recorded with the CMS detector, corresponding to an integrated luminosity of 36 pb−1. The pp → W+W− cross section is measured to be 41.1±15.3(stat)±5.8(syst)±4.5(lumi)pb, consistent with the standard model prediction. Limits on WWγ and WWZ anomalous triple gauge couplings are set. The search for the standard model Higgs boson in the W+W− decay mode does not reveal any evidence of excess above backgrounds. Limits are set on the production of the Higgs boson in the context of the standard model and in the presence of a sequential fourth family of fermions with high masses. In the latter context, a Higgs boson with mass between 144 and 207 GeV/c2 is ruled out at 95% confidence level

Measurement of the B+ Production Cross Section in pp Collisions at root s=7 TeV

Measurements of the total and differential cross sections d sigma/dp(T)(B) and d sigma/dy(B) for B+ mesons produced in pp collisions at root s = 7 TeV are presented. The data correspond to an integrated luminosity of 5.8 pb(-1) collected by the CMS experiment operating at the LHC. The exclusive decay B+ -> J/psi K+, with J/psi -> mu(+)mu(-), is used to detect B+ mesons and to measure the production cross section as a function of p(T)(B) and y(B). The total cross section for p(T)(B) > 5 GeV and vertical bar y(B)vertical bar < 2.4 is measured to be 28.1 +/- 2.4 +/- 2.0 +/- 3.1 mu b, where the first uncertainty is statistical, the second is systematic, and the last is from the luminosity measurement

Measurement of the charge ratio of atmospheric muons with the CMS detector

AbstractWe present a measurement of the ratio of positive to negative muon fluxes from cosmic ray interactions in the atmosphere, using data collected by the CMS detector both at ground level and in the underground experimental cavern at the CERN LHC. Muons were detected in the momentum range from 5 GeV/c to 1 TeV/c. The surface flux ratio is measured to be 1.2766±0.0032(stat.)±0.0032(syst.), independent of the muon momentum, below 100 GeV/c. This is the most precise measurement to date. At higher momenta the data are consistent with an increase of the charge ratio, in agreement with cosmic ray shower models and compatible with previous measurements by deep-underground experiments

Study of Z Boson Production in PbPb Collisions at √sNN=2.76 TeV

A search for Z bosons in the μ+μ− decay channel has been performed in PbPb collisions at √sNN=2.76  TeV with the CMS detector at the LHC, in a 7.2  μb−1 data sample. The number of opposite-sign muon pairs observed in the 60–120  GeV/c2 invariant mass range is 39, corresponding to a yield per unit of rapidity (y) and per minimum bias event of [33.8±5.5(stat)±4.4(syst)]×10−8, in the |y|<2.0 range. Rapidity, transverse momentum, and centrality dependencies are also measured. The results agree with next-to-leading order QCD calculations, scaled by the number of incoherent nucleon-nucleon collisions.ISSN:0031-9007ISSN:1079-711

First measurement of the underlying event activity at the LHC with √ = 0.9 TeV

A measurement of the underlying activity in scattering processes with pT scale in the GeV region is performed in proton-proton collisions at √ = 0.9 TeV, using data collected by the CMS experiment at the LHC. Charged particle production is studied with reference to the direction of a leading object, either a charged particle or a set of charged particles forming a jet. Predictions of several QCD-inspired models as implemented in PYTHIA are compared, after full detector simulation, to the data. The models generally predict too little production of charged particles with pseudorapidity {pipe}η{pipe} 0.5 GeV/c, and azimuthal direction transverse to that of the leading object. © 2010 CERN for benefit of the CMS collaboration

Inclusive b-hadron production cross section with muons in pp collisions at root s=7 TeV

A measurement of the b-hadron production cross section in proton-proton collisions at root s = 7 TeV is presented. The dataset, corresponding to 85 nb(-1), was recorded with the CMS experiment at the LHC using a low-threshold single-muon trigger. Events are selected by the presence of a muon with transverse momentum p(T)(mu) > 6 GeV with respect to the beam direction and pseudorapidity vertical bar eta(mu)vertical bar b + X -> mu + X') = 1.32 +/- 0.01(stat) +/- 0: 30(syst) +/- 0.15(lumi)mu b

Search for microscopic black hole signatures at the Large Hadron Collider

AbstractA search for microscopic black hole production and decay in pp collisions at a center-of-mass energy of 7 TeV has been conducted by the CMS Collaboration at the LHC, using a data sample corresponding to an integrated luminosity of 35 pb−1. Events with large total transverse energy are analyzed for the presence of multiple high-energy jets, leptons, and photons, typical of a signal expected from a microscopic black hole. Good agreement with the standard model backgrounds, dominated by QCD multijet production, is observed for various final-state multiplicities and model-independent limits on new physics in these final states are set. Using simple semi-classical approximation, limits on the minimum black hole mass are derived as well, in the range 3.5–4.5 TeV. These are the first direct limits on black hole production at a particle accelerator