19794101
J/psi production in Indium-Indium collisions at 158 GeV/nucleon.
The NA60 experiment studies muon pair production at the CERN Super Proton Synchrotron. In this Letter we report on a precision measurement of J/psi in In-In collisions. We have studied the J/psi centrality distribution, and we have compared it with the one expected if absorption in cold nuclear matter were the only active suppression mechanism. For collisions involving more than approximately 80 participant nucleons, we find that an extra suppression is present. This result is in qualitative agreement with previous Pb-Pb measurements by the NA50 experiment, but no theoretical explanation is presently able to coherently describe both results.
121815577
The NA60 silicon pixel tracker
Abstract NA60 is a fixed target experiment at the CERN SPS designed to study the production of open charm and prompt dimuons in proton–nucleus and heavy-ion collisions. To access the kinematics of the charged particles produced in the collisions already at the vertex level, a tracker made from radiation-tolerant silicon pixel detectors has been placed inside a 2.5 T magnetic field close to the target. In 2003 the vertex spectrometer, made from 12 tracking planes with 96 ALICE1LHCb pixel chips, was successfully operated in a run with a 158 GeV/nucleon indium ion beam incident on indium targets. During the five weeks of data taking, the detector was exposed to high and inhomogeneously distributed radiation levels. For the 2004 proton run, the tracker was upgraded with ATLAS pixel detector modules, to allow higher interaction rates. This paper describes the setup of the pixel tracker, its performance and the radiation damage it suffered.
122731585
Search for $B^0_s \to \mu^+ \mu^-$ and $B^0 \to \mu^+ \mu^-$ decays
A search for the rare decays B_s to mu+ mu- and B^0 to mu^+ mu^- is performed in pp collisions at sqrt(s) = 7 TeV, with a data sample corresponding to an integrated luminosity of 5 inverse femtobarns 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 Br(B_s to mu^+ mu^-) < 7.7E-9 and Br(B^0 to mu^+ mu^-) < 1.8E-9 at 95% confidence level.
464926
The silicon vertex telescope of the NA60 experiment
The NA60 experiment at CERN studies the production of open charm and prompt dimuons in collisions of high energy protons or heavy ions with target nuclei. The physics program relies on the precise measurement of the charged particles’ positions and momenta at the vertex. Tracking starts already a few centimetres away from the target in a radiation tolerant silicon detector placed in a 2.5 T dipole magnetic field. During several weeks of running in 2003 and 2004, this vertex tracker was exposed to high levels of inhomogeneously distributed radiation. In this paper we describe the construction, operation and performance of this novel, LHC-era detector.
122818028
Fine Synchronization of the CMS Muon Drift-Tube Local Trigger using Cosmic Rays
The CMS experiment uses self-triggering arrays of drift tubes in the barrel muon trigger to perform the identification of the correct bunch crossing. The identification is unique only if the trigger chain is correctly synchronized. In this paper, the synchronization performed during an extended cosmic ray run is described and the results are reported. The random arrival time of cosmic ray muons allowed several synchronization aspects to be studied and a simple method for the fine synchronization of the Drift Tube Local Trigger at LHC to be developed.
123126552
Experience with the NA60 silicon pixel vertex tracker in a harsh radiation environment
Abstract The NA60 experiment at CERN's Super Proton Synchrotron studies the production of open charm and prompt dimuons in collisions induced by heavy-ion and proton beams on nuclear targets. The experimental setup includes a dimuon spectrometer previously used in the NA50 experiment, and a new silicon vertex tracker: a telescope built from 12 stations of radiation tolerant pixel detectors placed close to the target inside of a 2.5 T dipole field. For the first time under such harsh radiation conditions, the pixel telescope tracks the large number of charged particles produced at the target. Its good spatial and momentum resolution enables the reconstruction of primary and secondary vertices, and the matching of two of the tracks with the two muons that gave the trigger in the muon spectrometer, placed behind the hadron absorber. In Fall 2003, the NA60 experiment performed a five week long physics run with a beam of 158 GeV/nucleon Indium ions colliding with a segmented Indium target. The run yielded data from several hundred million dimuon and minimum bias triggers. The pixel detectors were exposed to high levels of radiation inhomogeneously distributed over its acceptance. The silicon sensors closest to the beam axis underwent type inversion. This article discusses selected aspects of the silicon pixel detector's design and operation. Its performance is illustrated, in particular, by the vastly improved dimuon mass resolution. The last section discusses the re-utilization of the irradiated pixel detectors in a vertex tracker optimized for NA60's proton-nucleus run in 2004.
122002257
Production of D**s mesons in hadronic Z decays
The production rates of the orbitally excited Ds** mesons, Ds1 and Ds2*, are measured with the 4.1 million hadronic Z decays recorded by the ALEPH detector during 1991--1995. The Ds** mesons are reconstructed in the decay modes Ds1+ -> D*+ K0, Ds1+ -> D*0 K+ and Ds2*+ -> D0 K+. The production rate of the Ds1 is measured to be n(Z->Ds1+-)=(0.52+-0.09+-0.06)%, under the assumption that the two considered decay modes of the Ds1 saturate the branching ratio. The production rate of the Ds2* is determined to be n(Z->Ds2*+-)=(0.83+-0.29+0.07-0.13)%, assuming that the branching fraction of the decay Ds2*+ -> D0 K+ is 45%. The production rates in Z->cc and Z->bbar decays are measured separately.
202111272
Measurement of the hadronic photon structure function F-2(gamma)(x,Q(2)) in two-photon collisions at LEP
The hadronic photon structure function F-2(gamma)(x,Q(2)) is measured from data taken with the ALEPH detector at LEP. At centre-of-mass energies between roots=189 GeV and 207 GeV an integrated luminosity of 548.4 pb(-1) is analyzed in two ranges of Q(2) with [Q(2)] =17.3 GeV2 and 67.2 GeV2. Detector effects and acceptance are corrected for with a Tikhonov unfolding procedure. The results are compared to theoretical predictions and measurements from other experiments.
17926047
Study of the fragmentation of b quarks into B mesons at the Z peak
The fragmentation of b quarks into B mesons is studied with four million hadronic Z decays collected by the ALEPH experiment during the years 1991-1995. A semi-exclusive reconstruction of B->l nu D(*) decays is performed, by combining lepton candidates with fully reconstructed D(*) mesons while the neutrino energy is estimated from the missing energy of the event. The mean value of xewd, the energy of the weakly-decaying B meson normalised to the beam energy, is found to be mxewd = 0.716 +- 0.006 (stat) +- 0.006 \, (syst) using a model-independent method; the corresponding value for the energy of the leading B meson is mxel = 0.736 +- 0.006 (stat) +- 0.006 (syst). The reconstructed spectra are compared with different fragmentation models.
14187092
Inclusive semileptonic branching ratios of b hadrons produced in Z decays
A measurement of the inclusive semileptonic branching ratios of b hadrons produced in Z decay is presented, using four million hadronic events collected by the ALEPH detector from 1991 to 1995. Electrons and muons are selected opposite to b-tagged hemispheres. Two different methods are explored to distinguish the contributions from direct $\bl$ and cascade $\bcl$ dec ays to the total lepton yield. One is based on the lepton transverse momentum spectrum, the other makes use of the correlation between the charge of the lepton and charge estimators built from tracks in the opposite hemisphere of the event. The latter method reduces the dependence on the modelling of semileptonic b decays. The results obtained by averaging the two techniques are BR(b->l) = 0.1070 +- 0.0010 +- 0.0023 +- 0.0026 BR(b->c->l) = 0.0818 +- 0.0015 +- 0.0022 + 0.0022 -0.0014
122560479
Deuteron and Anti-deuteron Production in e+e- Collisions at the Z Resonance
Deuteron and anti-deuteron production in Z decays has been observed in the ALEPH experiment at LEP. The production rate of anti-deuterons is measured to be 5.9+-1.8+-0.5 10^-6 per hadronic Z decay in the anti-deuteron momentum range 0.62 to 1.03 GeV/c. The coalescence parameter B_2, which characterizes the likelihood of anti-deuteron production, is measured to be 0.0033+-0.0013 GeV^2 in Z dedays. These measurements indicate that the production of anti-deuterons is suppressed in e+e- collisions compared to pp and photoproduction collisions.