2,611 research outputs found
Production and assembly of the ALICE silicon drift detectors
No full textAbstract The ALICE experiment at the LHC will study collisions of heavy-ions at a centre-of-mass energy $5:5 TeV per nucleon. The main aim of the experiment is to study in detail the behaviour of nuclear matter at high densities and temperatures, in view of probing deconfinement and chiral symmetry restoration. Silicon Drift Detectors (SDDs) have been selected to equip the two intermediate layers of the ALICE Inner Tracking System (ITS) [ALICE Collaboration, Technical Design Report, CERN/LHCC 99-12], since they couple a very good multi-track capability with dE=dx information and excellent spatial resolution as described in [E. Gatti, P. Rehak, Nucl. Instr. and Meth. A 225 (1984) 608; S. Beole´, et al., Nucl. Instr. and Meth. A 377 (1996) 393; S. Beole´, et al., Il Nuovo Cimento 109A (9) (1996)]. In this paper we describe the different components of the SDD system as well as the different procedure of the system assembly.
Transverse momentum dependence of charmonium suppression in Pb - Pb collisions at the CERN SPS
No full textCharmonium suppression in Pb-Pb collisions at 158 GeV/c per nucleon is investigated in detail with the study of the transverse momentum distributions of J/psi as a function of the centrality of the collision. It is shown that the observed J/psi suppression in Pb-Pb interactions is particularly significant mainly at low transverse momentum where it strongly depends on centrality. For peripheral Pb-Pb collisions, the transverse momentum dependence of the J/psi cross section is, as a function of centrality, qualitatively similar to the dependence observed in p-A and S-U collisions. Comparing peripheral and central Pb-Pb collisions, the data show a relative suppression in the whole p(T) range although its amplitude significantly decreases with increasing p(T) and becomes almost p(T) independent for the highest p(T) values. RI Alexa, Calin/F-6345-2010; Cortese, Pietro/G-6754-2012; beole', stefania/G-9353-201
The ALICE Inner Tracking System: Performance with Proton and Lead Beams
No full textThe Inner Tracking System (ITS) of the ALICE experiment consists of six cylindrical layers of silicon detectors. Each layer has hermetic structure and it is coaxial with the beam pipe. The ITS covers the pseudorapidity range |η|≤ 0.9 and the distance from the nominal beam line ranges from 3.9 cm for the innermost layer up to 43 cm for the outermost. The two innermost layers are made of Silicon Pixel Detectors (SPD), the two central layers of Silicon Drift Detectors (SDD) and the two outermost layers of double sided Silicon Strip Detectors (SSD). The ITS has the main purposes of providing both primary and secondary vertices reconstruction and of improving the ALICE barrel tracking capabilities in the vicinity of the interaction point. Furthermore, as a standalone tracker, the ITS recovers particles which do not reach or are missed by the external barrel detector, due to acceptance limitations and momentum cutoff. After a short summary on the status of spatial alignment and detector calibration, this paper will focus on the ITS performances with with proton and lead beams in 2010 for what concerns vertexing and tracking
Designing a Linear Silicon Drift Detector
No full textThe design and 2D simulation results of a Silicon Drift Chamber with a rectangular configuration are presented, The proposed structure is intended to allow a test of the technology used in the production of the device and serve as a basis to verify different solutions in the design of drift detectors
Measuring (KSK +/-)-K-0 interactions using Pb-Pb collisions at root S-NN=2.76 TeV
No full textWe present the first ever measurements of femtoscopic correlations between the K-S(0) and K-+/- particles. The analysis was performed on the data from Pb-Pb collisions at root S-NN = 2.76 TeV measured by the ALICE experiment. The observed femtoscopic correlations are consistent with final-state interactions proceeding via the a(0)(980) resonance. The extracted kaon source radius and correlation strength parameters for (KSK-)-K-0 are found to be equal within the experimental uncertainties to those for (KSK+)-K-0. Comparing the results of the present study with those from published identical-kaon femtoscopic studies by ALICE, mass and coupling parameters for the a(0) resonance are tested. Our results are also compatible with the interpretation of the a(0) having a tetraquark structure instead of that of a diquark. (c) 2017 The Author. Published by Elsevier B.V
Charmonia and Drell-Yan production in proton-nucleus collisions at the CERN SPS
No full textCharmonium production in p-A collisions is a unique tool for the study of the interaction of bound c (c) over bar states in nuclear matter, It can provide details on the basic features of the resonance formation mechanism and, in particular, on its non-perturbative aspects. In this Letter, we present an experimental study of charmonia and Drell-Yan production in proton-nucleus collisions at 450 GeV/c. The results are analyzed in the framework of the Glauber model and lead to the values of the nuclear absorption cross-section sigma(pA)(abs) for J/psi and psi'. Then, we compare the J/psi absorption in proton-nucleus and sulphur-uranium interactions, using NA38 data. We obtain that, for the J/psi, sigma(pA)(abs) and sigma(SU)(abs) are compatible, showing that no sizeable additional suppression mechanism is present in S-U collisions, and confirming that the anomalous J/psi suppression only sets in for Pb-Pb interactions, (C) 2002 Elsevier Science B.V. All rights reserved. RI Alexa, Calin/F-6345-2010; Rato Mendes, Pedro/F-8827-2010; Cortese, Pietro/G-6754-2012; beole', stefania/G-9353-2012Charmonium production in p-A collisions is a unique tool for the study of the interaction of bound c (c) over bar states in nuclear matter, It can provide details on the basic features of the resonance formation mechanism and, in particular, on its non-perturbative aspects. In this Letter, we present an experimental study of charmonia and Drell-Yan production in proton-nucleus collisions at 450 GeV/c. The results are analyzed in the framework of the Glauber model and lead to the values of the nuclear absorption cross-section sigma(pA)(abs) for J/psi and psi'. Then, we compare the J/psi absorption in proton-nucleus and sulphur-uranium interactions, using NA38 data. We obtain that, for the J/psi, sigma(pA)(abs) and sigma(SU)(abs) are compatible, showing that no sizeable additional suppression mechanism is present in S-U collisions, and confirming that the anomalous J/psi suppression only sets in for Pb-Pb interactions, (C) 2002 Elsevier Science B.V. All rights reserved
Measurement of beauty-quark production in pp collisions at s = 13 TeV via non-prompt D mesons
No full textAbstract The p T-differential production cross sections of non-prompt D0, D+, and D s + mesons originating from beauty-hadron decays are measured in proton–proton collisions at a centre-of-mass energy s = 13 TeV. The measurements are performed at midrapidity, |y| < 0.5, with the data sample collected by ALICE from 2016 to 2018. The results are in agreement with predictions from several perturbative QCD calculations. The fragmentation fraction of beauty quarks to strange mesons divided by the one to non-strange mesons, f s /(f u + f d), is found to be 0.114 ± 0.016 (stat.) ± 0.006 (syst.) ± 0.003 (BR) ± 0.003 (extrap.). This value is compatible with previous measurements at lower centre-of-mass energies and in different collision systems in agreement with the assumption of universality of fragmentation functions. In addition, the dependence of the non-prompt D meson production on the centre-of-mass energy is investigated by comparing the results obtained at s = 5.02 and 13 TeV, showing a hardening of the non-prompt D-meson p T-differential production cross section at higher s . Finally, the b b ¯ production cross section per unit of rapidity at midrapidity is calculated from the non-prompt D0, D+, D s + , and Λ c + hadron measurements, obtaining d σ / d y = 75.2 ± 3.2 stat . ± 5.2 syst . − 3.2 + 12.3 extrap . μb
Centrality dependence of the pseudorapidity density distribution for charged particles in Pb-Pb collisions at root s(NN)=5.02 TeV
No full textWe present the charged-particle pseudorapidity density in Pb-Pb collisions at root s(NN) = 5.02 TeV in centrality classes measured by ALICE. The measurement covers a wide pseudorapidity range from -3.5 to 5, which is sufficient for reliable estimates of the total number of charged particles produced in the collisions. For the most central (0-5%) collisions we find 21 400 +/- 1 300, while for the most peripheral (80-90%) we find 230 +/- 38. This corresponds to an increase of (27 +/- 4)% over the results at root s(NN) = 2.76 TeV previously reported by ALICE. The energy dependence of the total number of charged particles produced in heavy-ion collisions is found to obey a modified power-law like behaviour. The charged-particle pseudorapidity density of the most central collisions is compared to model calculations-none of which fully describes the measured distribution. We also present an estimate of the rapidity density of charged particles. The width of that distribution is found to exhibit a remarkable proportionality to the beam rapidity, independent of the collision energy from the top SPS to LHC energies. (C) 2017 The Author(s). Published by Elsevier B.V
K S 0 - and (anti-) Λ -hadron correlations in pp collisions at s = 13 TeV
No full textAbstract Two-particle Azimuthal correlations are measured with the ALICE apparatus in pp collisions at s = 13 TeV to explore strangeness- and multiplicity-related effects in the fragmentation of jets and the transition regime between bulk and hard production, probed with the condition that a strange meson ( K S 0 ) or baryon ( Λ ) with transverse momentum p T > 3 GeV/ c is produced. Azimuthal correlations between kaons or Λ hyperons with other hadrons are presented at midrapidity for a broad range of the trigger ( 3 < p T trigg < 20 GeV/ c ) and associated particle p T (1 GeV/ c < p T assoc < p T trigg ), for minimum-bias events and as a function of the event multiplicity. The near- and away-side peak yields are compared for the case of either K S 0 or Λ ( Λ ¯ ) being the trigger particle with that of inclusive hadrons (a sample dominated by pions). In addition, the measurements are compared with predictions from PYTHIA 8 and EPOS LHC event generators
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