123564706
Pioneering instrumentation aspects of NA60
NA60 is taking data with proton and heavy-ion beams at the CERN SPS. Although building up on previous experiments, the dimuon physics programme of NA60 places very demanding requirements on its new detectors, in terms of radiation tolerance, granularity and read-out electronics speed. We start by comparing dimuon detection strategies in NA60 with those of previous experiments. We then describe the new detectors used in NA60, placing particular emphasis on their technological pioneering aspects as well as on their contributions to the overall physics performance of the experiment.
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.
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.
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.
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.
202109678
Search for charginos nearly mass degenerate with the lightest neutralino in e(+)e(-) collisions at centre-of-mass energies up to 209 GeV
A search for charginos nearly mass degenerate with the lightest neutralino is performed with the data collected by the ALEPH detector at LEP, at centre-of-mass energies between 189 and 209 GeV, corresponding to an integrated luminosity of 628 pb(-1). The analysis is based on the detection of isolated and energetic initial state radiation photons, produced in association with chargino pairs whose decay products have little visible energy. The number of candidate events observed is in agreement with that expected from Standard Model background sources. These results are combined with those of other direct searches for charginos, and a lower limit of 88 GeV/c(2) at 95% confidence level is derived for the chargino mass in the case of heavy sfermions, irrespective of the chargino-neutralino mass difference. (C) 2002 Elsevier Science B.V. All rights reserved.
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
122387957
Search for pentaquark states in Z decays
Exotic hadrons made of five quarks (pentaquarks) are searched for in hadronic Z decays collected by the ALEPH detector at LEP. No significant signal is observed. At 95% C.L., upper limits are set on the production rates N of such particles and their charge-conjugate state per Z decay: N Theta(1535)+ . BR(Theta(1535)^+ -> pK0s xi^- pi^-) Xi^-pi^+ D*-p) D^-p) < 31 x 10^-4.
120612135
Bose-Einstein correlations in W-pair decays with an event-mixing technique
Bose-Einstein correlations in W-pair decays are studied using data collected by the ALEPH detector at LEP at e+e- centre-of-mass energies from 183 to 209 GeV. The analysis is based on the comparison of WW-->qqqq events to ``mixed'' events constructed with the hadronic part of WW-->qqlnu events. The data are in agreement with the hypothesis that Bose-Einstein correlations are present only for pions from the same W decay. The JETSET model with Bose-Einstein correlations between pions from different W bosons is disfavoured.
118266013
Electroweak Measurements in Electron-Positron Collisions at W-Boson-Pair Energies at LEP
Electroweak measurements performed with data taken at the electron-positron collider LEP at CERN from 1995 to 2000 are reported. The combined data set considered in this report corresponds to a total luminosity of about 3 fb$^{-1}$ collected by the four LEP experiments ALEPH, DELPHI, L3 and OPAL, at centre-of-mass energies ranging from 130 GeV to 209 GeV. Combining the published results of the four LEP experiments, the measurements include total and differential cross-sections in photon-pair, fermion-pair and four-fermion production, the latter resulting from both double-resonant WW and ZZ production as well as singly resonant production. Total and differential cross-sections are measured precisely, providing a stringent test of the Standard Model at centre-of-mass energies never explored before in electron-positron collisions. Final-state interaction effects in four-fermion production, such as those arising from colour reconnection and Bose-Einstein correlations between the two W decay systems arising in WW production, are searched for and upper limits on the strength of possible effects are obtained. The data are used to determine fundamental properties of the W boson and the electroweak theory. Among others, the mass and width of the W boson, $M_W$ and $\Gamma_W$, the branching fraction of W decays to hadrons, $B(W\to\mathrm{had})$, and the trilinear gauge-boson self-couplings $g^Z_1$, $\kappa_\gamma$ and $\lambda_\gamma$ are determined to be: M_W = 80.376 \pm 0.033 ~GeV \Gamma_W = 2.195 \pm 0.083 ~GeV B(W\to\mathrm{had}) = 67.41 \pm 0.27 % g^Z_1 = 0.984 ^{+0.018}_{-0.020} \kappa_\gamma = 0.982 \pm 0.042 \lambda_\gamma = -0.022 \pm 0.019