Measurement of jet spectra and in pp and Pb–Pb collisions at with the ALICE detector
Introduction
The study of jets in ultra-relativistic heavy-ion collisions is intimately connected to the investigation of the properties of the Quark–Gluon Plasma (QGP). The QGP is a deconfined state of matter, in which the relevant degrees of freedom are those of strongly-interacting quarks and gluons. Simple quantum-mechanical considerations, based on the Heisenberg principle of indetermination, imply that hard-scattering processes, with a large momentum transfer, happen at a much smaller time scale as compared to that of the QGP formation, which is driven by many low momentum scatterings. The subsequent transport of the hard scattered parton through the medium and its fragmentation are expected to be considerably modified through elastic collisions and medium-induced radiation [1]. These phenomena are usually referred to as “jet quenching”. Measurements at both RHIC [2], [3] and the LHC [4], [5], [6] have confirmed these predictions using a variety of observables. Jet reconstruction can take advantage of the more accurate estimate of the energy of the parton compared to high transverse momentum single hadron measurements, which are often used as proxies for jets.
In these proceedings we report measurements of the jet nuclear modification factor and charged jet performed by the ALICE experiment for Pb–Pb collisions at . These results are based on data collected by ALICE in 2011 and extend previous measurements reported in Refs. [7], [8].
Section snippets
Experimental setup and analysis techniques
For a complete description of the ALICE detector and its performance see Refs. [10] and [11], respectively. The main sub-detectors used in the present measurement are the VZERO, the central tracking system and the Electromagnetic Calorimeter (EMCal). The VZERO detector consists of segmented scintillators covering the full azimuth at forward rapidity. It is used to measure the centrality of the Pb–Pb events and also provides the set of minimum bias and centrality triggers used to collect the
Results
Fig. 2(a) shows the anti- jet spectra at mid-rapidity for the 0–10% and the 10–30% centrality classes. In order to compare with the same measurement performed in pp collisions at the same [14], the jet yield in Pb–Pb has been divided by the number of binary collisions calculated in a Monte Carlo Glauber model [9] that assumes independent binary nucleon–nucleon collisions. The systematic uncertainty is dominated by the tracking efficiency uncertainty and the unfolding
Conclusions
In these proceedings we have reported new measurements of jet suppression performed by the ALICE experiment. The measured suppression for both central and semi-central events is in qualitative agreement with both the YaJEM and JEWEL models. In order to obtain a tighter constraint on the models the path-length dependence of the parton energy loss has been explored by measuring the charged jet , which shows hints of such an effect for semi-central events. ALICE has also measured jet yields in
References (26)
- et al.
Phys. Lett. B
(1995) Phys. Lett. B
(2014)- et al.
Phys. Lett. B
(2008) - et al.
NIM A
(1996) NIM
(1995)Nucl. Phys. A
(2014)Phys. Rev. Lett.
(2003)Phys. Rev. C
(2004)Phys. Rev. C
(2011)J. High Energy Phys.
(2014)
Phys. Lett. B
J. Phys. Conf. Ser.
J. Phys. Conf. Ser.
Cited by (8)
Overview of ALICE results at Quark Matter 2014
2014, Nuclear Physics ACitation Excerpt :Among the main topics are precision measurements of jet quenching in heavy-ion collisions as well as further understanding of possible collectivity in proton–lead collisions. This proceedings can only present a subset of the results, for more information the reader is referred to [1–33]. These discuss light flavor [2,3,6,18,25], heavy flavor [5,8,15,21,28], jet [1,13,23,32], photon [10,24], quarkonia [4,9,11,12,20], dielectron [19] and correlation [7,14,16,22,26,30,33] measurements as well as ultra-peripheral collisions [27], event characterization [31] and the ALICE upgrade [17,29].
Experimental results on p(d)+A collisions at RHIC and the LHC
2014, Nuclear Physics ATransverse momentum distribution of primary charged particles in the p -Pb interactions using HIJING 1.0
2016, International Journal of Modern Physics APhysics perspectives of heavy-ion collisions at very high energy
2016, Science China: Physics, Mechanics and AstronomyJet production in pp, p-Pb and Pb-Pb collisions measured by ALICE
2015, Journal of Physics: Conference SeriesHeavy-ion physics at the LHC
2015, The Large Hadron Collider: Harvest of Run 1
- 1
A list of members of the ALICE Collaboration and acknowledgments can be found at the end of this issue.