Overview of ALICE results on azimuthal correlations using neutral- and heavy-meson triggers

The ALICE detector is dedicated to studying the properties of hot and dense matter created in heavy-ion collisions. Among the probes used to investigate these properties are high-momentum particles, which originate in hard-scatterings occurring before the fireball creation. The fragments of hard scatterings interact with the hot and dense matter and via this interaction their spectra and azimuthal distributions are modified. This is probed by the measurement of the nuclear modification factor, where the $p_{\mathrm{T}}$ spectra obtained in Pb-Pb collisions are compared to a pp baseline. A strong suppression of charged hadrons as well as neutral- and heavy-flavor mesons was observed at $p_{\mathrm{T}} > 4$ GeV/$c$. Azimuthal correlations, using high-momentum ($p_{\mathrm{T}} > 4$ GeV/$c$) hadrons as triggers, can provide further insight into how the presence of the medium modifies the final kinematic distributions of the particles. Comparison with theoretical models can be used to test their predictions about the properties of the medium. We give an overview of ALICE azimuthal-correlation measurements of neutral- and heavy-flavor mesons with charged hadrons in pp collisions at $\sqrt{s}=7$ TeV and Pb-Pb collisions at $\sqrt{s_{\rm{NN}}}=2.76$ TeV. We also present a measurement of the $\pi^{0}$ correlation with jets in pp collisions at $\sqrt{s}=7$ TeV.Comment: Proceedings of '10th International Workshop on High-pT Physics at RHIC/LHC era' conference, 9-12 September 2014, 9 pages, 7 figure

Experimental treatment of Quark and Gluon Jets

The separate study of quark and gluon jets is vital for the interpretation of multiple variables behaviour observed in both high-energy hadron and heavy-ion collisions in the present and future experiments. We propose a set of jet-energy dependent cuts to be used to distinguish between quark and gluon jets experimentally based on a Monte-Carlo study of their properties. Further, we introduce the possibility to calibrate these cuts via gamma-jet and multi-jet events, which represent clean production channels for quark and gluon jets, respectively. The calibration can happen on real data and thus, reduces the dependence of the method performance on Monte-Carlo model predictions.Comment: 5 pages, 3 figures, presented at the 6th Intenational High-pT at LHC Workshop in Utrecht, 201

Topological study of three-jet events in ALICE

The ALICE experiment at LHC is dedicated to study matter formed in heavy-ion collisions, but also has a strong physics program for $pp$ collisions. In these collisions, protons will collide at energies never reached before under laboratory conditions. At the high energies, ALICE will enable us to study jet physics in detail, especially the production of multiple jet events, setting the baseline for heavy-ion. Three-jet events allow us to examine the properties of quark and gluon jets, providing a suitable tool for testing QCD experimentally. We discuss the selection method and topology of three-jet events in ALICE. The analysis was performed on two PYTHIA data sets, both involving $pp$ collisions at $\sqrt{s} = 14$ TeV with enhanced jet production. The results from the dedicated jet MC production are discussed and compared to previous studies at CDF and D\O. We investigate the possibilities to determine gluon jet candidates.Comment: 9 pages, 5 figures, contribution to the "High-Pt Physics at LHC '09" workshop in Pragu

Study of particle production from quark and gluon jets in proton-proton collisions

We investigate whether and how different fragmentation properties of quarks and gluons affect identified particle spectra. We present a systematic study of $\pi$, $K$ and $p$ production in minimum bias (inelastic, non-diffractive), two- and three-jet events at RHIC, Tevatron and LHC energies. Through the study of two- and three-jet events and various jet-production channels we can directly access the fragmentation properties of quark and gluon jets. We present MC estimate for the contribution of quark and gluon jets to individual particle species spectra, that can be compared to experimental results and test our current knowledge of the physics behind particle production inside jets.Comment: 5 pages, 3 figures, presented at Hot Quarks 201

Measurement of electrons from heavy-flavour hadron decays in p-Pb collisions at √sNN=5.02TeV

The production of electrons from heavy-flavour hadron decays was measured as a function of transverse momentum (p(T)) in minimum-bias p-Pb collisions at root s(NN) = 5.02 TeV using the ALICE detector at the LHC. The measurement covers the p(T) interval 0.5 < p(T) < 12 GeV/c and the rapidity range -1.065 < y(cms) < 0.135 in the centre-of-mass reference frame. The contribution of electrons from background sources was subtracted using an invariant mass approach. The nuclear modification factor R-pPb was calculated by comparing the p(T)-differential invariant cross section in p-Pb collisions to a pp reference at the same centre-of-mass energy, which was obtained by interpolating measurements at root s = 2.76 TeV and root s= 7 TeV. The R-pPb is consistent with unity within uncertainties of about 25%, which become larger for p(T) below 1 GeV/c. The measurement shows that heavy-flavour production is consistent with binary scaling, so that a suppression in the high-p(T) yield in Pb-Pb collisions has to be attributed to effects induced by the hot medium produced in the final state. The data in p-Pb collisions are described by recent model calculations that include cold nuclear matter effects. (C) 2015 CERN for the benefit of the ALICE Collaboration. Published by Elsevier B.V

Measurement of jet suppression in central Pb–Pb collisions at √sNN=2.76 TeV

The transverse momentum (pT) spectrum and nuclear modification factor (RAA) of recon- structed jets in 0–10% and 10–30% central Pb–Pb collisions at √sNN = 2.76 TeV were mea- sured. Jets were reconstructed using the anti-kT jet algorithm with a resolution parameter of R = 0.2 from charged and neutral particles, utilizing the ALICE tracking detectors and Elec- tromagnetic Calorimeter (EMCal). The jet pT spectra are reported in the pseudorapidity in- terval of |ηjet| 5 GeV/c to suppress jets constructed from the combinatorial background in Pb–Pb collisions. The leading charged particle requirement applied to jet spectra both in pp and Pb–Pb collisions had a negligible effect on the RAA. The nuclear modification factor RAA was found to be 0.28 ± 0.04 in 0–10% and 0.35 ± 0.04 in 10–30% collisions, indepen- dent of pT, jet within the uncertainties of the measurement. The observed suppression is in fair agreement with expectations from two model calculations with different approaches to jet quenching