p/pi Ratio in Di-Hadron Correlations

Particle ratios are important observables used to constrain models of particle production in heavy-ion collisions. In this work we report on a measurement of the p/pi ratio in the transverse momentum range 2.0 < p_{T,assoc} < 4.0 GeV/c, associated with a charged trigger particle of 5.0 < p_{T,trig} < 10.0 GeV/c, in 0-10% central Pb--Pb collisions at sqrt{s_{NN}}=2.76 TeV. The ratio is measured in the jet peak and in a region at large Delta eta separation from the peak (bulk region). The presented results are based on 14M minimum-bias Pb--Pb collisions, recorded by the ALICE detector. It is observed that the p/pi ratio in the bulk region is compatible with the p/pi ratio of an inclusive measurement, and is much larger than the p/pi ratio in the jet peak. The p/pi ratio in the jet peak is compatible with a PYTHIA reference, in which fragmentation in the vacuum is the dominant mechanism of particle production

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

Event-shape engineering for inclusive spectra and elliptic flow in Pb-Pb collisions at root(NN)-N-S=2.76 TeV

Peer reviewe

Elliptic flow of muons from heavy-flavour hadron decays at forward rapidity in Pb-Pb collisions at root s(NN)=2.76TeV

The elliptic flow, v(2), of muons from heavy-flavour hadron decays at forward rapidity (2.5 <y <4) is measured in Pb-Pb collisions at root s(NN)= 2.76TeVwith the ALICE detector at the LHC. The scalar product, two- and four-particle Q cumulants and Lee-Yang zeros methods are used. The dependence of the v(2) of muons from heavy-flavour hadron decays on the collision centrality, in the range 0-40%, and on transverse momentum, p(T), is studied in the interval 3 <p(T)<10 GeV/c. A positive v(2) is observed with the scalar product and two-particle Q cumulants in semi-central collisions (10-20% and 20-40% centrality classes) for the p(T) interval from 3 to about 5GeV/c with a significance larger than 3 sigma, based on the combination of statistical and systematic uncertainties. The v(2) magnitude tends to decrease towards more central collisions and with increasing pT. It becomes compatible with zero in the interval 6 <p(T)<10 GeV/c. The results are compared to models describing the interaction of heavy quarks and open heavy-flavour hadrons with the high-density medium formed in high-energy heavy-ion collisions. (C) 2015 CERN for the benefit of the ALICE Collaboration. Published by Elsevier B.V.Peer reviewe

Pseudorapidity and transverse-momentum distributions of charged particles in proton-proton collisions at root s=13 TeV

The pseudorapidity (eta) and transverse-momentum (p(T)) distributions of charged particles produced in proton-proton collisions are measured at the centre-of-mass energy root s = 13 TeV. The pseudorapidity distribution in vertical bar eta vertical bar <1.8 is reported for inelastic events and for events with at least one charged particle in vertical bar eta vertical bar <1. The pseudorapidity density of charged particles produced in the pseudorapidity region vertical bar eta vertical bar <0.5 is 5.31 +/- 0.18 and 6.46 +/- 0.19 for the two event classes, respectively. The transverse-momentum distribution of charged particles is measured in the range 0.15 <p(T) <20 GeV/c and vertical bar eta vertical bar <0.8 for events with at least one charged particle in vertical bar eta vertical bar <1. The evolution of the transverse momentum spectra of charged particles is also investigated as a function of event multiplicity. The results are compared with calculations from PYTHIA and EPOS Monte Carlo generators. (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

Centrality evolution of the charged-particle pseudorapidity density over a broad pseudorapidity range in Pb-Pb collisions at root s(NN)=2.76TeV

Peer reviewe

Identified particle yield associated with a high-pTp_T trigger particle at the LHC

Identified particle production ratios are important observables, used to constrain models of particle production in heavy-ion collisions. Measurements of the inclusive particle ratio in central heavy-ion collisions showed an increase of the baryon-to-meson ratio compared to proton-proton collisions at intermediate pT, the so-called baryon anomaly. One possible explanation of the baryon anomaly is that partons from the thermalized deconfined QCD matter hadronize in a different way compared to hadrons produced in a vacuum jet. In this work we extend on previous measurements by measuring particle ratios in the yield associated with a high-pT trigger particle. These measurements can potentially further constrain the models of particle production since they are sensitive to the difference between particles from a jet and particles that are produced in the bulk. We start by developing a particle identification method that uses both the specific energy loss of a particle and the time of flight. From there, we present a method to identify the particle yield associated with a high-pT trigger particle. We then measure the proton-to-pion and kaon-to-pion ratio in the jet peak and background of the associated yield in central Pb-Pb, central p-Pb and pp collisions. The observation that these particle ratios are higher in the background compared to the jet peak suggests that there is a difference between the mechanism of hadron production in the the underlying event and the jet. Furthermore, our results show that the particle ratios in the jet peak depend on the size of the system