386 research outputs found
CMS Software Distribution on the LCG and OSG Grids
The efficient exploitation of worldwide distributed storage and computing
resources available in the grids require a robust, transparent and fast
deployment of experiment specific software. The approach followed by the CMS
experiment at CERN in order to enable Monte-Carlo simulations, data analysis
and software development in an international collaboration is presented. The
current status and future improvement plans are described.Comment: 4 pages, 1 figure, latex with hyperref
Distributed Computing Grid Experiences in CMS
The CMS experiment is currently developing a computing system capable of serving, processing and archiving the large number of events that will be generated when the CMS detector starts taking data. During 2004 CMS undertook a large scale data challenge to demonstrate the ability of the CMS computing system to cope with a sustained data-taking rate equivalent to 25% of startup rate. Its goals were: to run CMS event reconstruction at CERN for a sustained period at 25 Hz input rate; to distribute the data to several regional centers; and enable data access at those centers for analysis. Grid middleware was utilized to help complete all aspects of the challenge. To continue to provide scalable access from anywhere in the world to the data, CMS is developing a layer of software that uses Grid tools to gain access to data and resources, and that aims to provide physicists with a user friendly interface for submitting their analysis jobs. This paper describes the data challenge experience with Grid infrastructure and the current development of the CMS analysis system
Long-Lived Neutralino NLSPs
We investigate the collider signatures of heavy, long-lived, neutral
particles that decay to charged particles plus missing energy. Specifically, we
focus on the case of a neutralino NLSP decaying to Z and gravitino within the
context of General Gauge Mediation. We show that a combination of searches
using the inner detector and the muon spectrometer yields a wide range of
potential early LHC discoveries for NLSP lifetimes ranging from 10^(-1)-10^5
mm. We further show that events from Z(l+l-) can be used for detailed kinematic
reconstruction, leading to accurate determinations of the neutralino mass and
lifetime. In particular, we examine the prospects for detailed event study at
ATLAS using the ECAL (making use of its timing and pointing capabilities)
together with the TRT, or using the muon spectrometer alone. Finally, we also
demonstrate that there is a region in parameter space where the Tevatron could
potentially discover new physics in the delayed Z(l+l-)+MET channel. While our
discussion centers on gauge mediation, many of the results apply to any
scenario with a long-lived neutral particle decaying to charged particles.Comment: 31 pages, 12 figure
Transverse Momentum Fluctuations in Nuclear Collisions at 158 AGeV
Results are presented on event-by-event fluctuations in transverse momentum
of charged particles, produced at forward rapidities in p+p, C+C, Si+Si and
Pb+Pb collisions at 158 AGeV. Three different characteristics are discussed:
the average transverse momentum of the event, the Phi_pT fluctuation measure
and two-particle transverse momentum correlations. In the kinematic region
explored, the dynamical fluctuations are found to be small. However, a
significant system size dependence of Phi_pT is observed, with the largest
value measured in peripheral Pb+Pb interactions. The data are compared with
predictions of several models.Comment: will be submitted to Phys. Rev.
System size dependence of strange particle yields and spectra at sqrt(s)=17.3 GeV
Yields and spectra of strange hadrons (K+, K-, phi, Lambda and Antilambda) as
well as of charged pions were measured in near central C+C and Si+Si collisions
at 158 AGeV beam energy with the NA49 detector. Together with earlier data for
p+p, S+S and Pb+Pb reactions the system size dependence can be studied.
Relative strangeness production rises fast and saturates at about 60
participating nucleons; the net hyperon spectra show an increasing shift
towards midrapidity for larger colliding nuclei. An interpretation based on the
formation of coherent systems of increasing volume is proposed. The transverse
mass spectra can be described by a blast wave ansatz. Increasing flow velocity
is accompanied by decreasing temperatures for both kinetic and chemical freeze
out. The increasing gap between inelastic and elastic decoupling leaves space
for rescattering.Comment: 8 pages, 6 figures, Proceedings of the Hot Quarks 2004 worksho
Event-by-Event Fluctuations of Particle Ratios in Central Pb+Pb Collisions at 20 to 158 AGeV
In the vicinity of the QCD phase transition, critical fluctuations have been
predicted to lead to non-statistical fluctuations of particle ratios, depending
on the nature of the phase transition. Recent results of the NA49 energy scan
program show a sharp maximum of the ratio of K+ to Pi+ yields in central Pb+Pb
collisions at beam energies of 20-30 AGeV. This observation has been
interpreted as an indication of a phase transition at low SPS energies. We
present first results on event-by-event fluctuations of the kaon to pion and
proton to pion ratios at beam energies close to this maximum.Comment: 4 pages, 4 figures, Quark Matter 2004 proceeding
Multiplicity fluctuations in nuclear collisions at 158 A GeV
System size dependence of multiplicity fluctuations of charged particles
produced in nuclear collisions at 158 A GeV was studied in the NA49 CERN
experiment. Results indicate a non-monotonic dependence of the scaled variance
of the multiplicity distribution with a maximum for semi-peripheral Pb+Pb
interactions with number of projectile participants of about 35. This effect is
not observed in a string-hadronic model of nuclear collision HIJING.Comment: Presented at "Focus on Multiplicity", 17-19 of June, Bari, Ital
Report from NA49
The most recent data of NA49 on hadron production in nuclear collisions at
CERN SPS energies are presented. Anomalies in the energy dependence of pion and
kaon production in central Pb+Pb collisions are observed. They suggest that the
onset of deconfinement is located at about 30 AGeV. Large multiplicity and
transverse momentum fluctuations are measured for collisions of intermediate
mass systems at 158 AGeV. The need for a new experimental programme at the CERN
SPS is underlined.Comment: invited talk presented at Quark Matter 2004, 10 page
System-size dependence of strangeness production in nucleus-nucleus collisions at sqrt{s_{NN}}=17.3 GeV
Emission of pi, K, phi and Lambda was measured in near-central C+C and Si+Si
collisions at 158 AGeV beam energy. Together with earlier data for p+p, S+S and
Pb+Pb, the system-size dependence of relative strangeness production in
nucleus-nucleus collisions is obtained. Its fast rise and the saturation
observed at about 60 participating nucleons can be understood as onset of the
formation of coherent partonic subsystems of increasing size.Comment: Phys.Rev.Lett in print; version2: changes made according to the
request of the referee
Omega and Antiomega production in central Pb+Pb collisions at 40 and 158 AGeV
Results are presented on Omega production in central Pb+Pb collisions at 40
and 158 AGeV beam energy. Given are transverse-mass spectra, rapidity
distributions, and total yields for the sum Omega+Antiomega at 40 AGeV and for
Omega and Antiomega separately at 158 AGeV. The yields are strongly
under-predicted by the string-hadronic UrQMD model and are in better agreement
with predictions from a hadron gas models.Comment: 5 papes, 4 figures, 1 table, updated figure 4 and table 1. Final
version, including some editorial changes, as published in PR
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