Transverse momentum distribution of charged particles and identified hadrons in p-Pb collisions at the LHC with ALICE

Hadron production has been measured at mid-rapidity by the ALICE experiment at the LHC in proton-lead (p-Pb) collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV. The transverse momentum ($p_{\rm T}$) distribution of primary charged particles and of identified light-flavoured hadrons ($\pi^{\pm}$, K$^{\pm}$, K$^{0}_{\rm S}$, p, $\bar{\rm p}$, $\Lambda$, $\bar{\Lambda}$) are presented in this report. Charged-particle tracks are reconstructed in the central barrel over a wide momentum range. Furthermore they can be identified by exploiting specific energy loss (d$E$/d$x$), time-of-flight and topological particle-identification techniques. Particle-production yields, spectral shapes and particle ratios are measured in several multiplicity classes and are compared with results obtained in Pb-Pb collisions at the LHC. The measurement of charged-particle transverse momentum spectra and nuclear modification factor R$_{\rm pPb}$ indicates that the strong suppression of high-$p_{\rm T}$ hadrons observed in Pb-Pb collisions is not due to initial-state effects, but it is rather a fingerprint of jet quenching in hot QCD matter. The systematic study of the hadronic spectral shapes as a function of the particle mass and of particle ratios as a function of charged-particle density provides insights into collective phenomena, as observed in Pb-Pb collisions. Similar features, that could be present in high-multiplicity p-Pb collisions, will also be discussed.Comment: 7 pages, 5 figures, presented at the The European Physical Society Conference on High Energy Physics - EPS-HEP2013, 18-24 July 2013, Stockholm, Swede

Transverse momentum spectra of identified charged hadrons with the ALICE detector in Pb--Pb collisions at sNN\sqrt{s_{NN}} = 2.76 TeV

The measurement of identified charged-hadron production at mid-rapidity ($|y| < 0.5$) performed with the ALICE experiment is presented for Pb--Pb collisions at $\sqrt{s_{\rm NN}} = \rm .76 TeV$. The transverse momentum spectra of $\pi^{\pm}$, $K^{\pm}$, $p$ and $\bar{p}$ are measured from 100 MeV/c up to 3 GeV/c for pions, from 200 MeV/c up to 2 GeV/c for kaons and from 300 MeV/c up to 3 GeV/c for protons and antiprotons using the \emph{dE/dx} and the \emph{time-of-flight} particle-identification techniques. Preliminary results on charged hadron production yields and particle ratios are reported as a function of $p_{T}$ and collision centrality. Finally, the results are discussed in terms of hydrodynamics-inspired models and compared with published RHIC data in Au--Au collisions at $\sqrt{s_{\rm NN}} = \rm 200 GeV$ and predictions for the LHC.Comment: 4 pages, 5 figures, talk at the 2011 Europhysics Conference on High Energy Physics, EPS-HEP 2011, July 21-27, 2011 Grenoble, Rh\^one-Alpes, Franc

Spectra of identified hadrons with the ALICE detector in pp and Pb-Pb collisions at the LHC

The measurement of identified charged-hadron production at mid-rapidity ($|y| < 0.5$) performed with the ALICE experiment at the LHC is presented for pp collisions at $\sqrt{s}$ = 900 GeV and 7 TeV and for Pb--Pb collisions at $\sqrt{s_{NN}}$ = 2.76 TeV. Transverse momentum spectra of $\pi^{\pm}$, K$^{\pm}$, p, $\rm \bar{p}$ and multi-strange baryons are measured over a wide momentum range using the $dE/dx$, the time-of-flight and topological particle-identification techniques. In this report, the particle-identification detectors and techniques, as well as the achieved performance, are shortly reviewed. Proton-proton results on particle production yields, spectral shapes and particle ratios are presented as a function of the collision energy and compared to previous experiments and commonly-used Monte Carlo models. Particle spectra, yields and ratios in Pb--Pb are measured as a function of the collision centrality and the results are compared with published RHIC data in Au--Au collisions at $\sqrt{s_{NN}}$ = 200 GeV and predictions for the LHC.Comment: 8 pages, 9 figures, presented at the first ECTP International Conference on "Primordial QCD matter in LHC era: implications of QCD results on the early Universe", Cairo, Egypt, December 4-8, 201

Ligth-flavour identified charged-hadron production in pp and Pb-Pb collisions at the LHC

Thanks to the unique detector design adopted to fulfill tracking and particle-identification (PID) requirements (e.g. low momentum cut-off and low material budget), the ALICE experiment provides significant information about hadron production both in pp and Pb-Pb collisions. In particular, the $p_{\rm T}$-differential and integrated production yields of identified particles play a key role in the study of the collective and thermal properties of the matter formed in high-energy heavy-ion collisions. Furthermore, the production of high-$p_{\rm T}$ particles provides insights into the property of the hot medium created in such collisions and the in-medium energy-loss mechanisms. Transverse momentum spectra of $\pi^{\pm}$, K$^{\pm}$, p and $\bar{\rm p}$ are measured at mid-rapidity ($\left|y\right| <~0.5$) over a wide momentum range, from $\sim$~100 MeV/$c$ up to $\sim$~20 GeV/$c$. The current results on light-flavour charged-hadron production will be presented for pp collisions at $\sqrt{s}$ = 0.9, 2.76 and 7 TeV and for Pb-Pb collisions at $\sqrt{s_{\rm NN}}$ = 2.76 TeV. Integrated production yields, transverse momentum spectra and particle ratios in pp are discussed as a function of the collision energy and compared to previous experiments and commonly-used Monte Carlo models. Pb-Pb collisions at the LHC feature the highest radial flow ever observed and an unexpectedly low p/$\pi$ production ratio. The results are presented as a function of collision centrality and compared to RHIC data in Au-Au collisions at $\sqrt{s_{\rm NN}}$ = 200 GeV and predictions from thermal and hydrodynamic models. The nuclear modification factor ($R_{\rm AA}$) of identified hadrons will also be discussed and compared to unidentified charged particles and theoretical predictions. This is observed to be identical for all particle species at high-$p_{\rm T}$.Comment: 10 pages, 11 figures, prepared for the Proceedings of the International Workshop On Physics At The LHC (Kruger 2012) December 3 - 7, 2012 Protea Hotel, Kruger Gate South Afric

Small systems at the LHC

In these proceedings, I report on a selection of recent LHC results in small systems from ALICE, ATLAS and CMS experiments. Due to the fact that the investigation of QCD in small systems at high multiplicity is becoming an increasingly large subject, interesting the heavy-ion community and more in general the high-energy physics community, not all the related topics can be discussed in this paper. The focus will be given to some of the measurements addressing the physics of collective phenomena in small systems and to the recent results on strangeness enhancement in proton-proton collisions. The reader must be informed that a large number of interesting results did not find space in the discussion reported here.Comment: Prepared for the Proceeding of the SQM 2017 conferenc

Identified-particle production and spectra with the ALICE detector in pp and Pb-Pb collisions at the LHC

Thanks to its unique capabilities the ALICE experiment can measure the production of identified particles and resonances over a wide momentum range both in pp and Pb-Pb collisions at the LHC. In this report, particle-identification detectors and techniques, as well as achieved performance, are shortly reviewed. The current results on hadron transverse momentum spectra measured in pp collisions at $\sqrt{s}$ = 0.9 TeV and 7 TeV, and in Pb-Pb collisions at $\sqrt{s_{\rm NN}}$ = 2.76 TeV are shown. In particular, proton-proton results on particle production yields, spectral shapes and particle ratios are presented as a function of the collision energy and compared to previous experiments and commonly-used Monte Carlo models. Particle spectra, yields and ratios in Pb-Pb are measured as a function of the collision centrality and the results are compared with published RHIC data in Au-Au collisions at $\sqrt{s_{\rm NN}}$ = 0.2 TeV and predictions for the LHC.Comment: 8 pages, 11 figures, Presented at Strangeness in Quark Matter, 18-24 September 2011, Crakow, Polan

Confronting experimental data with heavy-ion models: Rivet for heavy ions

The Rivet library is an important toolkit in particle physics, and serves as a repository for analysis data and code. It allows for comparisons between data and theoretical calculations of the final state of collision events. This paper outlines several recent additions and improvements to the framework to include support for analysis of heavy ion collision simulated data. The paper also presents examples of these recent developments and their applicability in implementing concrete physics analyses

Azimuthal anisotropy of charged jet production in root s(NN)=2.76 TeV Pb-Pb collisions

We present measurements of the azimuthal dependence of charged jet production in central and semi-central root s(NN) = 2.76 TeV Pb-Pb collisions with respect to the second harmonic event plane, quantified as nu(ch)(2) (jet). Jet finding is performed employing the anti-k(T) algorithm with a resolution parameter R = 0.2 using charged tracks from the ALICE tracking system. The contribution of the azimuthal anisotropy of the underlying event is taken into account event-by-event. The remaining (statistical) region-to-region fluctuations are removed on an ensemble basis by unfolding the jet spectra for different event plane orientations independently. Significant non-zero nu(ch)(2) (jet) is observed in semi-central collisions (30-50% centrality) for 20 <p(T)(ch) (jet) <90 GeV/c. The azimuthal dependence of the charged jet production is similar to the dependence observed for jets comprising both charged and neutral fragments, and compatible with measurements of the nu(2) of single charged particles at high p(T). Good agreement between the data and predictions from JEWEL, an event generator simulating parton shower evolution in the presence of a dense QCD medium, is found in semi-central collisions. (C) 2015 CERN for the benefit of the ALICE Collaboration. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).Peer reviewe

Forward-central two-particle correlations in p-Pb collisions at root s(NN)=5.02 TeV

Two-particle angular correlations between trigger particles in the forward pseudorapidity range (2.5 2GeV/c. (C) 2015 CERN for the benefit of the ALICE Collaboration. Published by Elsevier B. V.Peer reviewe