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

Transverse momentum spectra of charged particles in proton-proton collisions at s=900\sqrt{s} = 900 GeV with ALICE at the LHC

The inclusive charged particle transverse momentum distribution is measured in proton-proton collisions at $\sqrt{s} = 900$ GeV at the LHC using the ALICE detector. The measurement is performed in the central pseudorapidity region $(|\eta|<0.8)$ over the transverse momentum range $0.15<p_{\rm T}<10$ GeV/$c$. The correlation between transverse momentum and particle multiplicity is also studied. Results are presented for inelastic (INEL) and non-single-diffractive (NSD) events. The average transverse momentum for $|\eta|<0.8$ is $\left<p_{\rm T}\right>_{\rm INEL}=0.483\pm0.001$ (stat.) $\pm0.007$ (syst.) GeV/$c$ and \left_{\rm NSD}=0.489\pm0.001 (stat.) $\pm0.007$ (syst.) GeV/$c$, respectively. The data exhibit a slightly larger $\left<p_{\rm T}\right>$ than measurements in wider pseudorapidity intervals. The results are compared to simulations with the Monte Carlo event generators PYTHIA and PHOJET.Comment: 20 pages, 8 figures, 2 tables, published version, figures at http://aliceinfo.cern.ch/ArtSubmission/node/390

VM-based infrastructure for simulating different cluster and storage solutions used on ATLAS tier3 sites

ATLAS is a particle physics experiment on Large Hadron Collider at CERN. The experiment produces petabytes of data every year. The ATLAS Computing model embraces the Grid paradigm and originally included three levels of computing centres to be able to operate such large volume of data. With the formation of small computing centres, usually based at universities, the model was expanded to include them as Tier3 sites. The experiment supplies all necessary software to operate typical Grid-site, but Tier3 sites do not support Grid services of the experiment or support them partially. Tier3 centres comprise a range of architectures and many do not possess Grid middleware, thus, monitoring of storage and analysis software used on Tier2 sites becomes unavailable for Tier3 site system administrator and, also, Tier3 sites activity becomes unavailable for virtual organization of the experiment. In this paper we present ATLAS off-Grid sites monitoring software suite, which enables monitoring on sites, which are not under operation of ATLAS Distributed Computing software

VM-based infrastructure for simulating different cluster and storage solutions in ATLAS

The current ATLAS Tier3 infrastructure consists of a variety of sites of different sizes and with a mix of local resource management systems (LRMS) and mass storage system (MSS) implementations. The Tier3 monitoring suite, having been developed in order to satisfy the needs of Tier3 site administrators and to aggregate Tier3 monitoring information on the global VO level, needs to be validated for various combinations of LRMS and MSS solutions along with the corresponding Ganglia and/or Nagios plugins. For this purpose the Testbed infrastructure, which allows simulation of various computational cluster and storage solutions, had been set up at JINR (Dubna). This infrastructure provides the ability to run testbeds with various LRMS and MSS implementations, and with the capability to quickly redeploy particular testbeds or their components. Performance of specific components is not a critical issue for development and validation, whereas easy management and deployment are crucial. Therefore virtual machines were chosen for implementation of the validation infrastructure which, though initially developed for Tier3 monitoring project, can be exploited for other purposes. Load generators for simulation of the computing activities at the farm were developed as a part of this task. The poster will cover concrete implementation, including deployment scenarios, hypervisor details and load simulators

Charged-particle multiplicity measurement in proton–proton collisions at sqrt(s)=0.9 and 2.36 TeV with ALICE at LHC

Charged-particle production was studied in proton–proton collisions collected at the LHC with the ALICE detector at centre-of-mass energies 0.9 TeV and 2.36 TeV in the pseudorapidity range |η| &lt; 1.4. In the central region (|η| &lt; 0.5), at 0.9 TeV, we measure charged-particle pseudorapidity density dNch/dη = 3.02 ± 0.01(stat.) +0.08 −0.05(syst.) for inelastic interactions, and dNch/dη = 3.58 ± 0.01 (stat.) +0.12 −0.12(syst.) for non-single-diffractive interactions. At 2.36 TeV, we find dNch/dη = 3.77 ± 0.01(stat.) +0.25 −0.12(syst.) for inelastic, and dNch/dη = 4.43 ± 0.01(stat.) +0.17 −0.12(syst.) for non-single-diffractive collisions. The relative increase in charged-particle multiplicity from the lower to higher energy is 24.7% ± 0.5%(stat.) +5.7 −2.8%(syst.) for inelastic and 23.7% ± 0.5%(stat.) +4.6 −1.1%(syst.) for non-single-diffractive interactions. This increase is consistent with that reported by the CMS collaboration for non-single-diffractive events and larger than that found by a number of commonly used models. The multiplicity distribution was measured in different pseudorapidity intervals and studied in terms of KNO variables at both energies. The results are compared to proton– antiproton data and to model predictions

Charged-particle multiplicity measurement in proton-proton collisions at root s=7 TeV with ALICE at LHC

The pseudorapidity density and multiplicity distribution of charged particles produced in proton-proton collisions at the LHC, at a centre-of-mass energy root s = 7 TeV, were measured in the central pseudorapidity region vertical bar eta vertical bar < 1. Comparisons are made with previous measurements at root s = 0.9 TeV and 2.36 TeV. At root s = 7 TeV, for events with at least one charged particle in |eta vertical bar| < 1, we obtain dN(ch)/d eta = 6.01 +/- 0.01(stat.)(-0.12)(+0.20) (syst.). This corresponds to an increase of 57.6%+/-0.4%(stat.)(-1.8%)(+3.6) (syst.) relative to collisions at 0.9 TeV, significantly higher than calculations from commonly used models. The multiplicity distribution at 7 TeV is described fairly well by the negative binomial distribution