Abstract
One of the key signatures of the Quark-Gluon Plasma (QGP) is the modification of hadron transverse momentum differential cross-sections in heavy-ion collisions (HIC) as compared to proton-proton (pp) collisions. Suppression of hadron production at high transverse momenta (pT) in HIC has been explained by the energy loss of the partons produced in the hard scattering processes which traverse the deconfined quantum chromodynamic (QCD) matter. The dependence of the observed suppression on the pT of the measured hadron towards higher pT is an important input for the theoretical understanding of jet quenching effects in the QGP and the nature of the energy loss, while suppression towards lower pT gives information about collective behaviour. The ALICE experiment at the Large Hadron Collider (LHC) performs a variety of measurements including the spectra of neutral mesons and kaons at mid-rapidity in a wide pT range in pp, p-Pb and Pb-Pb collisions. An overview of ALICE results in HIC and pp collisions at = 2.76 TeV of neutral pions, kaons and eta mesons as a function of transverse momentum (pT) and centrality will be presented. Ratios η/π0, K±/π± as well as comparisons to model calculations will also be discussed.
Highlights
Light mesons offer an opportunity to study the Quark-Gluon Plasma (QGP) and quantify its properties
Suppression of hadron production at high transverse momenta in heavy-ion collisions (HIC) has been explained by the energy loss of the partons produced in the hard scattering processes which traverse the deconfined quantum chromodynamic (QCD) matter
A suppression of π0 and η is observed via comparisons of the Pb-Pb invariant yields to scaled pp NLO pQCD
Summary
Light mesons offer an opportunity to study the QGP and quantify its properties. At low pT, mesons give insight about bulk properties and collective effects. Gluons are expected to suffer a larger energy loss in the medium than quarks (Casimir factor) This effect may give rise to differences in suppression patterns between π0 and η which can be quantified with RA√A measurements. The π0 and η results are compared in two centrality classes to NLO pQCD predictions of the corresponding production in pp collisions [7] scaled by Ncoll These comparisons show a suppression in the Pb-Pb data with respect to scaled NLO pQCD. K± and π± in the 0-5% centrality class (Fig. 3) are compared to corresponding pp measurements (open markers), where a zoom to the pT region below 5 GeV/c indicate differences in the spectra with respect to pp that is attributed to radial flow [10]
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