Alignment of the ALICE Inner Tracking System with cosmic-ray tracks

37 pages, 15 figures, revised version, accepted by JINSTALICE (A Large Ion Collider Experiment) is the LHC (Large Hadron Collider) experiment devoted to investigating the strongly interacting matter created in nucleus-nucleus collisions at the LHC energies. The ALICE ITS, Inner Tracking System, consists of six cylindrical layers of silicon detectors with three different technologies; in the outward direction: two layers of pixel detectors, two layers each of drift, and strip detectors. The number of parameters to be determined in the spatial alignment of the 2198 sensor modules of the ITS is about 13,000. The target alignment precision is well below 10 micron in some cases (pixels). The sources of alignment information include survey measurements, and the reconstructed tracks from cosmic rays and from proton-proton collisions. The main track-based alignment method uses the Millepede global approach. An iterative local method was developed and used as well. We present the results obtained for the ITS alignment using about 10^5 charged tracks from cosmic rays that have been collected during summer 2008, with the ALICE solenoidal magnet switched off.Peer reviewe

First proton-proton collisions at the LHC as observed with the ALICE detector: Measurement of the charged-particle pseudorapidity density at √s = 900 GeV

On 23rd November 2009, during the early commissioning of the CERN Large Hadron Collider (LHC), two counter-rotating proton bunches were circulated for the first time concurrently in the machine, at the LHC injection energy of 450 GeV per beam. Although the proton intensity was very low, with only one pilot bunch per beam, and no systematic attempt was made to optimize the collision optics, all LHC experiments reported a number of collision candidates. In the ALICE experiment, the collision region was centred very well in both the longitudinal and transverse directions and 284 events were recorded in coincidence with the two passing proton bunches. The events were immediately reconstructed and analyzed both online and offline. We have used these events to measure the pseudorapidity density of charged primary particles in the central region. In the range |η|<0.5, we obtain dNch/dη=3. 10±0. 13(stat.)±0. 22(syst.) for all inelastic interactions, and dNch/dη=3.51±0. 15(stat.)±0. 25(syst.) for non-single diffractive interactions. These results are consistent with previous measurements in proton-antiproton interactions at the same centre-of-mass energy at the CERN SppS̄ collider. They also illustrate the excellent functioning and rapid progress of the LHC accelerator, and of both the hardware and software of the ALICE experiment, in this early start-up phase

Centrality, rapidity and transverse momentum dependence of J/\u3c8 suppression in Pb-Pb collisions at 1asNN= 2.76TeV

The inclusive J/.nuclear modification factor (R-AA) in Pb-Pb collisions at root(NN)-N-S = 2.76TeVhas been measured by ALICE as a function of centrality in the e+ e-decay channel at mid-rapidity (| y| < 0.8) and as a function of centrality, transverse momentum and rapidity in the + -decay channel at forward-rapidity (2.5 < y < 4). The J/.yields measured in Pb-Pb are suppressed compared to those in ppcollisions scaled by the number of binary collisions. The RAAintegrated over a centrality range corresponding to 90% of the inelastic Pb-Pb cross section is 0.72 - 0.06(stat.) - 0.10(syst.) at mid-rapidity and 0.58 - 0.01(stat.) - 0.09(syst.) at forward-rapidity. At low transverse momentum, significantly larger values of RAAare measured at forward-rapidity compared to measurements at lower energy. These features suggest that a contribution to the J/.yield originates from charm quark (re) combination in the deconfined partonic medium

Multiplicity dependence of pion, kaon, proton and lambda production in p–Pb collisions at √sNN = 5.02 TeV

Inthis Letter, comprehensive results on π±,K±,K0S, p(pbar) and Λ(Λbar) production at mid-rapidity (0< yCMS < 0.5) in p–Pb collisions at √sNN = 5.02 TeV, measured by the ALICE detector at the LHC, are reported. The transverse momentum distributions exhibit a hardening as a function of event multiplicity, which is stronger for heavier particles. This behavior is similar to what has been observed in pp and Pb–Pb collisions at the LHC. The measured pT distributions are compared to d–Au, Au–Au and Pb–Pb results at lower energy and with predictions based on QCD-inspired and hydrodynamic models

Gamma-aminobutyric acid uptake and the termination of inhibitory synaptic potentials in the rat hippocampal slice.

Intracellular recordings were made from CA1 pyramidal cells in the rat hippocampal slice to study the processes that influence the time course of inhibitory post-synaptic potentials (i.p.s.p.s) mediated by gamma-aminobutyric acid (GABA), and conductance changes evoked by ionophoretically applied GABA. The GABA-uptake inhibitors, nipecotic acid and cis-4-OH-nipecotic acid (1 mM), greatly prolonged conductance increases associated with both hyperpolarizing and depolarizing responses to ionophoretically applied GABA. In contrast to their effects on GABA-evoked conductances, uptake inhibitors only slightly prolonged antidromically evoked i.p.s.p.s. Their primary effect occurred after the i.p.s.p. had decayed to 5-30% of its peak. 4-OH-isonipecotic acid, a nipecotic acid analogue that does not inhibit GABA uptake, did not prolong i.p.s.p.s or ionophoretically evoked conductance changes. Sodium pentobarbitone (100 microM), a drug that prolongs the open time of GABA-activated chloride channels, potentiated both i.p.s.p.s and responses to ionophoretically applied GABA. Whereas pentobarbitone also prolonged i.p.s.p.s, it did not prolong responses to ionophoretically applied GABA. The prolongation of i.p.s.p.s by pentobarbitone occurred equally in both the early and late phases of the i.p.s.p., in contrast to the effects of GABA-uptake inhibitors. I.p.s.p.s did not usually decay exponentially. The observation that uptake inhibitors prolonged the late but not the early decay phase of the i.p.s.p., together with the previous finding that the conductance change persists for the duration of the i.p.s.p., indicate that GABA is present in the synapse throughout much of the i.p.s.p. These data suggest that diffusion of GABA out of the synapse, a non-exponential process, is an important determinant of the i.p.s.p. decay time course. Increasing the extracellular potassium concentration from 3.5 to 8.5 mM resulted in spontaneously occurring, synchronous burst firing of pyramidal cells. Cis-4-OH-nipecotic acid significantly reduced the number and amplitude of extracellularly recorded population spikes within each burst. We conclude that diffusion, channel open time and GABA uptake all influence the time course of GABA-mediated i.p.s.p.s. The time course of a single, brief i.p.s.p. is determined predominantly by post-synaptic channel kinetics and diffusion of GABA out of the synapse, whereas the inhibition produced by prolonged synaptic bursts or relatively long application of exogenous GABA can be markedly influenced by GABA uptake.(ABSTRACT TRUNCATED AT 400 WORDS

Two-pion Bose-Einstein correlations in pp collisions at root s=900 GeV

We report on the measurement of two-pion correlation functions from pp collisions at root s = 900 GeV performed by the ALICE experiment at the Large Hadron Collider. Our analysis shows an increase of the Hanbury Brown-Twiss radius with increasing event multiplicity, in line with other measurements done in particle- and nuclear collisions. Conversely, the strong decrease of the radius with increasing transverse momentum, as observed at the Relativistic Heavy Ion Collider and at Tevatron, is not manifest in our data

Midrapidity antiproton-to-proton ratio in pp collisons root s=0.9 and 7 TeV measured by the ALICE experiment

The ratio of the yields of antiprotons to protons in pp collisions has been measured by the ALICE experiment at root s = 0.9 and 7 TeV during the initial running periods of the Large Hadron Collider. The measurement covers the transverse momentum interval 0.45 < p(t) < 1.05 GeV/c and rapidity vertical bar y vertical bar < 0.5. The ratio is measured to be R-vertical bar y vertical bar<0.5 = 0.957 +/- 0.006(stat) +/- 0.0014(syst) at 0.9 Tev and R-vertical bar y vertical bar<0.5 = 0.991 +/- 0.005 +/- 0.014(syst) at 7 TeV and it is independent of both rapidity and transverse momentum. The results are consistent with the conventional model of baryon-number transport and set stringent limits on any additional contributions to baryon-number transfer over very large rapidity intervals in pp collisions

Midrapidity Antiproton-to-Proton Ratio in pp Collisons root s=0.9 and 7 TeV Measured by the ALICE Experiment

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)The ratio of the yields of antiprotons to protons in pp collisions has been measured by the ALICE experiment at root s = 0.9 and 7 TeV during the initial running periods of the Large Hadron Collider. The measurement covers the transverse momentum interval 0.45 < p(t) < 1.05 GeV/c and rapidity vertical bar y vertical bar < 0.5. The ratio is measured to be R-vertical bar y vertical bar<0.5 = 0.957 +/- 0.006(stat) +/- 0.0014(syst) at 0.9 Tev and R-vertical bar y vertical bar<0.5 = 0.991 +/- 0.005 +/- 0.014(syst) at 7 TeV and it is independent of both rapidity and transverse momentum. The results are consistent with the conventional model of baryon-number transport and set stringent limits on any additional contributions to baryon-number transfer over very large rapidity intervals in pp collisions.1057Calouste Gulbenkian Foundation from LisbonConselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Financiadora de Estudos e Projetos (FINEP)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)National Natural Science Foundation of China (NSFC)Chinese Ministry of Education (CMOE)Ministry of Science and Technology of China (MSTC)Ministry of Education and Youth of the Czech RepublicDanish Natural Science Research CouncilCarlsberg FoundationDanish National Research FoundationThe European Research CouncilHelsinki Institute of PhysicsAcademy of FinlandFrench CNRS-IN2P3Region Pays de LoireRegion AlsaceRegion AuvergneCEA, FranceGerman BMBFHelmholtz AssociationHungarian OTKANational Office for Research and Technology (NKTH)Department of Atomic EnergyDepartment of Science and Technology of the Government of IndiaIstituto Nazionale di Fisica Nucleare (INFN) of ItalyMEXT, JapanJoint Institute for Nuclear Research, DubnaKorea Foundation for International Cooperation of Science and Technology (KICOS)CONACYTDGAPA, MexicoALFA-ECHELEN Program (High-Energy physics Latin-American-European Network)Stichting voor Fundamenteel Onderzoek der Materie (FOM)Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO), The NetherlandsResearch Council of Norway (NFR)Polish Ministry of Science and Higher EducationNational Authority for Scientific Research-NASR (Autontatea Nationala pentru Cercetare Stiintifica-ANCS)Federal Agency of Science of the Ministry of Education and Science of Russian FederationInternational Science and Technology CenterRussian Academy of SciencesRussian Federal Agency of Atomic EnergyRussian Federal Agency for Science and InnovationsCERN-INTASMinistry of Education of SlovakiaCIEMATEELAMinisterio de Educacion y Ciencia of SpainXunta de Galicia (Conselleria de Educacion)CEADENCubaenergia, CubaIAEA (International Atomic Energy Agency)Swedish Reseach CouncilKnut & Alice Wallenberg FoundationUkraine Ministry of Education and ScienceUnited Kingdom Science and Technology Facilities Council (STFC)The United States Department of EnergyUnited States National Science Foundation, State of TexasSwiss Fonds Kidagan, ArmeniaUnited States National Science Foundation, the State of OhioConselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP

Midrapidity Antiproton-to-Proton Ratio in pp Collisons root s=0.9 and 7 TeV Measured by the ALICE Experiment

The ratio of the yields of antiprotons to protons in pp collisions has been measured by the ALICE experiment at root s = 0.9 and 7 TeV during the initial running periods of the Large Hadron Collider. The measurement covers the transverse momentum interval 0.45 < p(t) < 1.05 GeV/c and rapidity vertical bar y vertical bar < 0.5. The ratio is measured to be R(vertical bar y vertical bar<0.5) = 0.957 +/- 0.006(stat) +/- 0.0014(syst) at 0.9 Tev and R(vertical bar y vertical bar<0.5) = 0.991 +/- 0.005 +/- 0.014(syst) at 7 TeV and it is independent of both rapidity and transverse momentum. The results are consistent with the conventional model of baryon-number transport and set stringent limits on any additional contributions to baryon-number transfer over very large rapidity intervals in pp collisions

D Meson Elliptic Flow in Noncentral Pb-Pb Collisions at root(S)(NN)=2.76 TeV

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Azimuthally anisotropic distributions of D-0, D+, and D*+ mesons were studied in the central rapidity region (vertical bar y vertical bar < 0.8) in Pb-Pb collisions at a center-of-mass energy root(S)(NN) = 2.76 TeV per nucleon-nucleon collision, with the ALICE detector at the LHC. The second Fourier coefficient upsilon(2) (commonly denoted elliptic flow) was measured in the centrality class 30%-50% as a function of the D meson transverse momentum p(T), in the range 2-16 GeV/c. The measured upsilon(2) of D mesons is comparable in magnitude to that of light-flavor hadrons. It is positive in the range 2 < p(T) < 6 GeV/c with 5.7 sigma significance, based on the combination of statistical and systematic uncertainties.11110State Committee of ScienceWorld Federation of Scientists (WFS)Swiss Fonds Kidagan, ArmeniaConselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Financiadora de Estudos e Projetos (FINEP)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)National Natural Science Foundation of China (NSFC)Chinese Ministry of Education (CMOE)Ministry of Science and Technology of China (MSTC)Ministry of Education and Youth of the Czech RepublicDanish Natural Science Research CouncilCarlsberg FoundationDanish National Research FoundationEuropean Research Council under the European CommunityHelsinki Institute of PhysicsAcademy of FinlandFrench CNRS-IN2P3, FranceRegion Pays de Loire, FranceRegion Alsace, FranceRegion Auvergne, FranceCEA, FranceGerman BMBFHelmholtz AssociationGeneral Secretariat for Research and Technology, Ministry of Development, GreeceHungarian OTKANational Office for Research and Technology (NKTH)Department of Atomic EnergyDepartment of Science and Technology of the Government of IndiaIstituto Nazionale di Fisica Nucleare (INFN)Centro Fermi-Museo Storico della Fisica e Centro Studi e Ricerche 'Enrico Fermi,' ItalyMEXT, JapanJoint Institute for Nuclear Research, DubnaNational Research Foundation of Korea (NRF)CONACYT, MexicoDGAPA, MexicoALFA-ECEPLANET Program (European Particle Physics Latin American Network) Stichting voor Fundamenteel Onderzoek der Materie (FOM), NetherlandsNederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO), NetherlandsResearch Council of Norway (NFR)Polish Ministry of Science and Higher EducationNational Authority for Scientific Research-NASR (Autoritatea Nationala pentru Cercetare Stiintifica-ANCS)Ministry of Education and Science of Russian FederationRussian Academy of SciencesRussian Federal Agency of Atomic EnergyRussian Federal Agency for Science and InnovationsRussian Foundation for Basic ResearchMinistry of Education of SlovakiaDepartment of Science and Technology, South AfricaCIEMATEELAMinisterio de Economia y Competitividad (MINECO) of SpainXunta de Galicia (Conselleria de Educacion)CEADENCubaenergiaCubaIAEA (International Atomic Energy Agency)Swedish Research Council (VR)Knut & Alice Wallenberg Foundation (KAW)Ukraine Ministry of Education and ScienceUnited Kingdom Science and Technology Facilities Council (STFC)United States Department of EnergyUnited States National Science FoundationState of TexasState of OhioConselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP