Two-pion Bose-Einstein correlations in central Pb-Pb collisions at sNN\sqrt{s_{\rm NN}} = 2.76 TeV

The first measurement of two-pion Bose-Einstein correlations in central Pb-Pb collisions at $\sqrt{s_{\rm NN}} = 2.76$ TeV at the Large Hadron Collider is presented. We observe a growing trend with energy now not only for the longitudinal and the outward but also for the sideward pion source radius. The pion homogeneity volume and the decoupling time are significantly larger than those measured at RHIC.Comment: 17 pages, 5 captioned figures, 1 table, authors from page 12, published version, figures at http://aliceinfo.cern.ch/ArtSubmission/node/388

Suppression of charged particle production at large transverse momentum in central Pb-Pb collisions at sNN=2.76\sqrt{s_{\rm NN}} = 2.76 TeV

Inclusive transverse momentum spectra of primary charged particles in Pb-Pb collisions at $\sqrt{s_{_{\rm NN}}}$ = 2.76 TeV have been measured by the ALICE Collaboration at the LHC. The data are presented for central and peripheral collisions, corresponding to 0-5% and 70-80% of the hadronic Pb-Pb cross section. The measured charged particle spectra in $|\eta|<0.8$ and $0.3 < p_T < 20$ GeV/$c$ are compared to the expectation in pp collisions at the same $\sqrt{s_{\rm NN}}$, scaled by the number of underlying nucleon-nucleon collisions. The comparison is expressed in terms of the nuclear modification factor $R_{\rm AA}$. The result indicates only weak medium effects ($R_{\rm AA} \approx$ 0.7) in peripheral collisions. In central collisions, $R_{\rm AA}$ reaches a minimum of about 0.14 at $p_{\rm T}=6$-7GeV/$c$ and increases significantly at larger $p_{\rm T}$. The measured suppression of high-$p_{\rm T}$ particles is stronger than that observed at lower collision energies, indicating that a very dense medium is formed in central Pb-Pb collisions at the LHC.Comment: 15 pages, 5 captioned figures, 3 tables, authors from page 10, published version, figures at http://aliceinfo.cern.ch/ArtSubmission/node/98

New global bifurcation diagrams for piecewise smooth systems: Transversality of homoclinic points does not imply chaos

In this paper we consider some piecewise smooth $2$-dimensional systems having a possibly non-smooth homoclinic $gamma(t)$. We assume that the critical point $ec0$ lies on the discontinuity surface $Omega^0$. We consider $4$ scenarios which differ for the presence or not of sliding close to $ec0$ and for the possible presence of a transversal crossing between $gamma(t)$ and $Omega^0$. We assume that the systems are subject to a small non-autonomous perturbation, and we obtain $4$ new bifurcation diagrams. In particular we show that, in one of these scenarios, the existence of a transversal homoclinic point guarantees the persistence of the homoclinic trajectory but chaos cannot occur. Further we illustrate the presence of new phenomena involving an uncountable number of sliding homoclinics

CREAM: A simple, Grid-accessible, Job Management System for local Computational Resources

Efficient and robust system for accessing computational resources and managing job operations is a key component of any Grid framework designed to support large distributed computing environment. Computing Resource Execution and Management (CREAM) is a simple, minimal system designed to provide efficient processing of a large number of requests for computation on managed resources. Requests are accepted from distributed clients via a Web Service based interface. The CREAM architecture is designed to be a robust, scalable and fault tolerant service of a Grid middleware. In this paper we describe the CREAM architecture and the provided functionality. We also discuss how CREAM is integrated within the EGEE gLite middleware in general, and with the gLite Workload Management System in particular

Flexible Job Submission Using Web Services: the gLite WMProxy Experience

Contemporary Grids are characterized by a middleware that provides the necessary virtualization of computation and data resources for the shared working environment of the Grid. In a large-scale view, different middleware technologies and implementations have to coexist. The SOA approach provides the needed architectural backbone for interoperable environments, where different providers can offer their solutions without restricting users to just one specific implementation. The WMProxy (Workload Manager Proxy) is a new service providing access to the gLite Workload Management System (WMS) functionality through a simple Web Services-based interface. The WMProxy was designed to efficiently handle a large number of requests for job submission and control to the WMS and the service interface addresses the Web Services and SOA architecture standards, in particular adhering to the WS- Interoperability basic profile. In this paper we describe the WMProxy service: from its architecture, independent from the used Web Services container, up to the provided functionality, all together with the rationale behind the decisions made during both the design and implementation phases. In particular, we provide a description of how the WMProxy is integrated with the gLite Workload Management System; the used technologies, focusing on the Web Services features; the mechanisms adopted to improve performances still keeping high reliability and fault-tolerance; the changes in the job submission operation chain with respect to the previous generation of Workload Management Systems and the new operations provided in order to support bulk- submission and improve Client-Server interaction capabilities

J/\u3a8 production and nuclear effects in p-Pb collisions at 1asNN=5.02 TeV

Inclusive J/\u3a8 production has been studied with the ALICE detector in p-Pb collisions at the nucleon-nucleon center of mass energy 1asNN = 5.02TeV at the CERN LHC. The measurement is performed in the center of mass rapidity domains 2.03 < ycms < 3.53 and ?4.46 < ycms < ?2.96, down to zero transverse momentum, studying the \u3bc+\u3bc? decay mode. In this paper, the J/\u3a8 production cross section and the nuclear modification factor RpPb for the rapidities under study are presented. While at forward rapidity, corresponding to the proton direction, a suppression of the J/\u3a8 yield with respect to binary-scaled pp collisions is observed, in the backward region no suppression is present. The ratio of the forward and backward yields is also measured differentially in rapidity and transverse momentum. Theoretical predictions based on nuclear shadowing, as well as on models including, in addition, a contribution from partonic energy loss, are in fair agreement with the experimental results

Femtoscopy of pp collisions at sqrt[s]=0.9 and 7\ua0TeV at the LHC with two-pion Bose-Einstein correlations

We report on the high statistics two-pion correlation functions from pp collisions at root s = 0.9 TeV and root s = 7 TeV, measured by the ALICE experiment at the Large Hadron Collider. The correlation functions as well as the extracted source radii scale with event multiplicity and pair momentum. When analyzed in the same multiplicity and pair transverse momentum range, the correlation is similar at the two collision energies. A three-dimensional femtoscopic analysis shows an increase of the emission zone with increasing event multiplicity as well as decreasing homogeneity lengths with increasing transverse momentum. The latter trend gets more pronounced as multiplicity increases. This suggests the development of space-momentum correlations, at least for collisions producing a high multiplicity of particles. We consider these trends in the context of previous femtoscopic studies in high-energy hadron and heavy-ion collisions and discuss possible underlying physics mechanisms. Detailed analysis of the correlation reveals an exponential shape in the outward and longitudinal directions, while the sideward remains a Gaussian. This is interpreted as a result of a significant contribution of strongly decaying resonances to the emission region shape. Significant nonfemtoscopic correlations are observed, and are argued to be the consequence of "mini-jet"-like structures extending to low p(t). They are well reproduced by the Monte-Carlo generators and seen also in pi(+)pi(-) correlations

Centrality dependence of \u3c0, K, and p production in Pb-Pb collisions at sqrt[s_{NN}]=2.76 TeV

In this paper measurements are presented of \u3c0\ub1, K\ub1, p, and p(bar) production at midrapidity (|y| < 0.5), in Pb-Pb collisions at 1asNN= 2.76 TeV as a function of centrality. The measurement covers the transverse-momentum (pT ) range from 100, 200, and 300 MeV/c up to 3, 3, and 4.6 GeV/c for \u3c0, K, and p, respectively. The measured pT distributions and yields are compared to expectations based on hydrodynamic, thermal and recombination models. The spectral shapes of central collisions show a stronger radial flow than measured at lower energies, which can be described in hydrodynamic models. In peripheral collisions, the pT distributions are not well reproduced by hydrodynamic models. Ratios of integrated particle yields are found to be nearly independent of centrality. The yield of protons normalized to pions is a factor 3c1.5 lower than the expectation from thermal models