Low-mass dielectrons in pp, p–Pb and Pb–Pb collisions measured by the ALICE Experiment

Dielectrons produced in ultra-relativistic heavy-ion collisions at the LHC provide a unique probe of the system evolution as they are unperturbed by final-state interactions. The dielectron continuum is extremely rich in physics sources: on top of ordinary Dalitz and resonance decays of pseudoscalar and vector mesons, thermal black-body radiation is of particular interest as it carries information about the temperature of the hot and dense system created in such collisions. The dielectron invariant-mass distribution is furthermore sensitive to medium modifications of the spectral function of short-lived vector mesons that are linked to the potential restoration of chiral symmetry at high temperatures. Correlated electron pairs from semi-leptonic charm and beauty decays provide complementary information about the heavy-quark energy loss

Measurement of heavy-flavour production in ALICE

The ALICE experiment, currently in the commissioning phase, will study nucleus-nucleus and proton-proton collisions at the CERN Large Hadron Collider (LHC). We review the ALICE heavy-flavour physics program and present a selection of results on the expected performance for the case of proton-proton collisions.Comment: 5 pages, 2 figures, prepared for the proceedings of the "5th Italian Workshop on p-p Physics at LHC", Perugia, January 200

Scattering Studies with Low-Energy Kaon-Proton Femtoscopy in Proton-Proton Collisions at the LHC

The study of the strength and behavior of the antikaon-nucleon ((K) over bar N) interaction constitutes one of the key focuses of the strangeness sector in low-energy quantum chromodynamics (QCD). In this Letter a unique high-precision measurement of the strong interaction between kaons and protons, close and above the kinematic threshold, is presented. The femtoscopic measurements of the correlation function at low pair-frame relative momentum of (K+ p circle plus K- (p) over bar) and (K- p circle plus K+ (p) over bar) pairs measured in pp collisions at root s = 5, 7, and 13 TeV are reported. A structure observed around a relative momentum of 58 MeV/c in the measured correlation function of (K- p circle plus K+ (p) over bar) with a significance of 4.4 sigma constitutes the first experimental evidence for the opening of the ((K) over bar (0)(n) circle plus K-0 (n) over bar) breaking channel due to the mass difference between charged and neutral kaons. The measured correlation functions have been compared to Julich and Kyoto models in addition to the Coulomb potential. The high-precision data at low relative momenta presented in this work prove femtoscopy to be a powerful complementary tool to scattering experiments and provide new constraints above the (K) over barN threshold for low-energy QCD chiral models.Peer reviewe

Connecting the underlying event with jet properties in pp collisions at s\sqrt{s} = 7 TeV with the ALICE experiment

A preliminary study of the fragmentation properties of charged particle jets as a function of the Underlying Multiplicity (UM) is presented. The UM is defined such that it can be related to the global soft event characteristics by excluding the contribution due to jet fragmentation. The measurement of jet properties as a function of the UM might be connected to the impact parameter dependence of the transverse nucleon structure as described via Generalized Parton Distributions. The results from the studies are compared to Monte Carlo (MC) models.Comment: Proceedings submitted for the 28th Winter Workshop on Nuclear Dynamics, Puerto Rico, April 7-14, 201

Measurement of beauty production via non-prompt D-0 mesons in Pb-Pb collisions at root s(NN)=5.02 TeV

Peer reviewe

Femtoscopy and energy-momentum conservation effects in proton-proton collisions at 900 GeV in ALICE

Two particle correlations are used to extract information about the characteristic size of the system for proton-proton collisions at 900 GeV measured by the ALICE (A Large Ion Collider experiment) detector at CERN. The correlation functions obtained show the expected Bose-Einstein effect for identical particles, but there are also long range correlations present that shift the baseline from the expected flat behavior. A possible source of these correlations is the conservation of energy and momentum, especially for small systems, where the energy available for particle production is limited. A new technique, first introduced by the STAR collaboration, of quantifying these long range correlations using energy-momentum conservation considerations is presented here. It is shown that the baseline of the two particle correlation function can be described using this technique.Comment: Hot Quarks 2010 conference proceedings, to appear in Journal of Physics: Conference Series (JPCS

Medium information from anisotropic flow and jet quenching in relativistic heavy ion collisions

Within a multiphase transport (AMPT) model, where the initial conditions are obtained from the recently updated HIJING 2.0 model, the recent anisotropic flow and suppression data for charged hadrons in Pb+Pb collisions at the LHC center of mass energy of 2.76 TeV are explored to constrain the properties of the partonic medium formed. In contrast to RHIC, the measured centrality dependence of charged hadron multiplicity dN_ch/deta at LHC provides severe constraint to the largely uncertain gluon shadowing parameter s_g. We find final-state parton scatterings reduce considerably hadron yield at midrapidity and enforces a smaller s_g to be consistent with dN_ch/deta data at LHC. With the parton shadowing so constrained, hadron production and flow over a wide transverse momenta range are investigated in AMPT. The model calculations for the elliptic and triangular flow are found to be in excellent agreement with the RHIC data, and predictions for the flow coefficients v_n(p_T, cent) at LHC are given. The magnitude and pattern of suppression of the hadrons in AMPT are found consistent with the measurements at RHIC. However, the suppression is distinctly overpredicted in Pb+Pb collisions at the LHC energy. Reduction of the QCD coupling constant alpha_s by ~30% in the higher temperature plasma formed at LHC reproduces the measured hadron suppression.Comment: Talk given by Subrata Pal at the 11th International Conference on Nucleus-Nucleus Collisions (NN2012), San Antonio, Texas, USA, May 27-June 1, 2012. To appear in the NN2012 Proceedings in Journal of Physics: Conference Series (JPCS

Status of the Fast Interaction Trigger for ALICE Upgrade

Publisher Copyright: © Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND 4.0).The Fast Interaction Trigger (FIT) denotes a set of three new detectors being part of the upgrade of ALICE in preparation for Run 3 of the LHC at CERN. To fulfill its physics objectives, ALICE aims to collect in Run 3 all minimum-bias data at the target interaction rate of 50 kHz for Pb-Pb and up to 1 MHz for pp collisions. This challenging increase in data rates of almost two orders of magnitude compared with Run 1 and Run 2 requires major improvements in all ALICE subdetectors, especially in their readout. While some of the upgraded ALICE detectors can operate in a continuous readout mode others need the fast trigger, specifically: Transition Radiation Detector (TRD), Charged-Particle Veto (CPV), High Momentum Particle Identification (HMPID), calorimeters and Photon Spectrometer (PHOS). Besides generating triggers for them, the FIT detectors will monitor luminosity, will provide the collision start time for particle identification via the time of flight, will measure the particle multiplicity in the forward direction, the centrality and the event plane, and will participate in diffractive physics measurements. The FIT consists of the following three detectors: FT0 - a set of two fast Cherenkov arrays specializing in minimum-bias trigger generation and luminosity measurement, located on both sides of the interaction point; FV0 - a large segmented scintillator disk focusing on multiplicity triggers and event plane determination, attached to the FT0 array located opposite to the Muon Spectrometer; and FDD (Forward Diffractive Detector) - also a scintillator located at very high pseudorapidities, concentrating on background monitoring and diffractive physics. The assembly of FIT detectors is close to completion. All components are on time for installation at ALICE between December 2020 and May 2021 according to the present schedule.Peer reviewe

Measurement of the electromagnetic dissociation cross section of Pb nuclei at sNN\sqrt{s_{\rm NN}} = 2.76 TeV

Electromagnetic dissociation of heavy nuclei in ultra-peripheral interactions at high energies can be used to monitor the beam luminosity at colliders. In ALICE neutrons emitted by the excited nuclei close to beam rapidity are detected by the Zero Degree Calorimeters (ZDCs), providing a precise measurement of the event rate. During the 2010 Pb run, a dedicated data taking was performed triggering on electromagnetic processes with the ZDCs. These data, combined with the results from a Van der Meer scan, allowed to measure the electromagnetic dissociation cross-section of Pb nuclei at $\sqrt{s_{\rm NN}}$~=~2.76~TeV. Experimental results on various cross-sections are presented together with a comparison to the available predictions.Comment: 4 pages, 3 figure