120140050
Studies of radiation effects in the NA60 silicon pixel detectors
Abstract NA60 is a fixed target experiment at the CERN SPS, which studies dimuon production in proton- and ion-induced collisions. Downstream of the target system a silicon pixel telescope made with p-on-n silicon sensors measures the charged tracks originating from the interactions. During the 2003 data taking period with indium–indium collisions at 158 GeV per incident nucleon, a significant radiation dose with a very inhomogeneous distribution has been accumulated in the pixel telescope, leading to partially type-inverted silicon sensors. Measurements of the depletion voltage and leakage current performed during this run are shown and compared with simulation results. It is also shown that the operation of partially type-inverted sensors poses no major problem.
120443217
Low mass dimuon production in proton-nucleus collisions at 400-GeV/c
The NA60 experiment has studied low-mass muon pair production in proton-nucleus collisions with a system of Be, Cu, In, W, Pb and U targets using a 400 GeV/c proton beam at the CERN SPS. The mass spectrum is well described by the superposition of the two-body and Dalitz decays of the light neutral mesons η, ρ, ω, η′ and ϕ new measurement of the electromagnetic transition form factors of the η and ω was performed. The values found are Λη−2=1.950±0.059(stat.)±0.042(syst.)(GeV/c2)−2 and Λω−2=2.241±0.025(stat.)±0.028(syst.)(GeV/c2)−2. They agree with the previous available measurements, improving their uncertainty thanks to the higher statistics, and confirm the discrepancy with the prediction of the Vector Meson Dominance model in the case of the electromagnetic form factor of the ω meson. The comparison of the data to an improved calculation including also a direct point-like term is discussed. The nuclear dependence of the production cross sections of the ω, ρ and ϕ mesons was also studied. An increase of the ϕ production with respect to the ω is observed from p-Be to p-U collisions. Parameterizing the nuclear dependence of the production cross sections with the power law σpA∝Aα, one finds αω=0.841±0.014(stat.)±0.030(syst.) and αϕ=0.906±0.011(stat.)±0.025(syst.). A possible bias induced by the use of the light Be target is found. If it is excluded, the results are αω=0.801±0.037(stat.)±0.041(syst.) and αϕ=0.963±0.026(stat.)±0.017(syst.), showing an increase of αϕ and a decrease of αω.
196068018
NA60 Status Report
121035571
Low mass dimuon production in Indium-Indium collisions at 158 A GeV
Abstract.The NA60 experiment studies open charm and prompt dimuon production in proton-nucleus and nucleus-nucleus collisions at the CERN SPS. During 2003 the experiment collected data in Indium-Indium collisions at 158 GeV per nucleon. Almost 240 million dimuon events were recorded. New results on J/$\psi$ suppression, open-charm production and low mass dimuons should help clarify some interesting questions left open by previous experiments. After a brief detector description, this paper focuses on the analysis of the low mass dimuons. Preliminary results are presented on the $\phi/\omega$ production cross section ratios and on the $\phi$ transverse momentum distributions, both as a function of collision centrality.
202083233
New results from NA60 and other SPS experiments
NA60 has been the last heavy ion experiment running at the SPS. It has performed measurements on dimuon production with an indium beam at 158 AGeV/c and with a proton beam at 158 and 400 GeV/c, focusing on (i) the study of the p spectral function in nuclear collisions, (ii) the unambiguous determination of the open charm yield and the quantitative assessment of the production of thermal radiation in the intermediate mass region, and (iii) the study of the J/ψ suppression in a collision system other than Pb-Pb. This paper provides an overview of the latest results. In addition, several other SPS experiments are still producing physics results. Interesting highlights from WA98, NA45 and NA49 on (i) nuclear modification factors of neutral and charged pions, (ii) three particle correlations at high transverse momentum and (iii) net baryon distributions will be addressed at the end of the paper.
15347695
First results from the NA60 experiment at CERN
Since 1986, several heavy ion experiments have studied some signatures of the formation of the quark-gluon plasma and a few exciting results have been found. However, some important questions are still unanswered and require new measurements. The NA60 experiment, with a new detector concept that vastly improves dimuon detection in proton-nucleus and heavy-ion collisions, studies several of those open questions, including the production of open charm. This paper presents the experiment and some first results from data collected in 2002.
53052258
Signal Reconstruction of the ATLAS Hadronic Tile Calorimeter: implementation and performance
TileCal, the central hadronic section of the ATLAS Calorimeter, is a sampling calorimeter made of steel and scintillating tiles. The TileCal front-end electronics reads out about 10,000 photo-multipliers at 40 Msps measuring energies ranging from 30 MeV to 2 TeV. The read-out system is designed to provide the ATLAS High Level Trigger with reconstructed PMT signals within the time budget allowed by the First Level Trigger (LVL1) running at a maximum trigger rate of 75 KHz. The signal amplitude, time and a reconstruction quality factor are obtained for each PMT using optimal filtering techniques implemented in the Digital Signal Processors (DSP).
53139097
Implementation and performance of the ATLAS trigger muon "vertical slice"
The ATLAS (A Toroidal LHC ApparatuS) trigger system is designed to keep high effiency for interesting events while achieving a rejection of low transverse momentum ( p T ) physics of about 10 7 , thus reaching the ∼200 Hz data storage capability of the Data Aquisition system. A three levels structure has been implemented for this purpose, as described in this work for the case of the muon trigger system. After describing the implementation, some performance results are presented in terms of final trigger rates, resolutions, efficiencies, background rejection and algorithm latency.
120473193
Trigger of low pT muons with the ATLAS hadronic calorimeter
Abstract A strategy for tagging muons with the Tile Calorimeter at the second level trigger (LVL2) of the ATLAS experiment is presented and its efficiency and mistagging fraction are discussed. It is demonstrated that the Tile Calorimeter can identify muons with good efficiency down to p T =2 GeV /c where the stand-alone muon spectrometer has zero efficiency. A method of exploiting all information available at LVL2 to reduce spurious muon-tag and measure the candidate muon momentum is discussed. The effectiveness of this method is tested, in particular, in the case of b b events at low Large Hadron Collider luminosity (10 33 cm −1 s −2 ) with full simulation of experimental conditions.
198461351
Muons in the calorimeters: Energy loss corrections and muon tagging
6222401
Implementation and performance of the seeded reconstruction for the ATLAS event filter
ATLAS is one of the four major Large Hadron Collider (LHC) experiments that will start data taking in 2007. It is designed to cover a wide range of physics topics. The ATLAS trigger system has to be able to reduce an initial 40 MHz event rate, corresponding to an average of 23 proton-proton inelastic interactions per every 25 ns bunch crossing, to 200 Hz admissible by the Data Acquisition System. The ATLAS trigger is divided in three different levels. The first one provides a signal describing an event signature using dedicated custom hardware. This signature must be confirmed by the High Level Trigger (HLT) which using commercial computing farms performs an event reconstruction by running a sequence of algorithms. The validity of a signature is checked after every algorithm execution. A main characteristic of the ATLAS HLT is that only the data in a certain window around the position flagged by the first level trigger are analyzed. In this work, the performance of one sequence that runs at the Event Filter level (third level) is demonstrated. The goal of this sequence is to reconstruct and identify high transverse momentum electrons by performing cluster reconstruction at the electromagnetic calorimeter, track reconstruction at the Inner Detector, and cluster track matching.