Abstract
The production of light neutral mesons in AA collisions probes the physics of the Quark-Gluon Plasma (QGP), which is formed in heavy-ion collisions at the LHC. More specifically, the centrality dependent neutral meson spectra in AA collisions compared to its spectra in minimum-bias pp collisions, scaled with the number of hard collisions, provides information on the energy loss of partons traversing the QGP. The measurement allows to test with high precision the predictions of theoretical model calculations. In addition, the decay of the π0 and η mesons are the dominant back- grounds for all direct photon measurements. Therefore, pushing the limits of the precision of neutral meson production is key to learning about the temperature and space-time evolution of the QGP.In the ALICE experiment neutral mesons can be detected via their decay into two photons. The latter can be reconstructed using the two calorimeters EMCal and PHOS or via conversions in the detector material. The excellent momentum resolution of the conversion photons down to very low pT and the high reconstruction efficiency and triggering capability of calorimeters at high pT, allow us to measure the pT dependent invariant yield of light neutral mesons over a wide kinematic range.Combining state-of-the-art reconstruction techniques with the high statistics delivered by the LHC in Run 2 gives us the opportunity to enhance the precision of our measurements. In these proceedings, new ALICE run 2 preliminary results for neutral meson production in pp and Pb–Pb collisions at LHC energies are presented.
Highlights
In the field of heavy-ion physics we are faced with fundamental questions: What are the different particle production mechanisms across different system sizes? Can we find the onset of the Quark-Gluon Plasma (QGP) in heavy-ion collisions? Is there a QGP droplet formed in small collision systems [1]? In proton–proton collisions the particle production mechanism at high pT ( 6 GeV/c) is expected to be dominated by the fragmentation of high momentum partons in jet-like structures
=of5nTeeuVtraal npdioPnbs–(Plebftc)oallnisdioηnsmaetso√nssNN(ri=gh5t) as function of transverse TeV. It is measured using photons reconstructed with η/π0 ratio for pp collisions
The neutral meson invariant yield in pp and Pb–Pb collisions has been measured with the ALICE detector, utilising all the available photon reconstruction methods and combining the neutral meson measurements, improving the precision and extending the pT range
Summary
In the field of heavy-ion physics we are faced with fundamental questions: What are the different particle production mechanisms across different system sizes? Can we find the onset of the QGP in heavy-ion collisions? Is there a QGP droplet formed in small collision systems [1]? In proton–proton collisions the particle production mechanism at high pT ( 6 GeV/c) is expected to be dominated by the fragmentation of high momentum partons in jet-like structures. M. Sas. Studying the particle production mechanisms is key to understand the physics governing both small and large systems. Identified hadron spectra are a good probe to study both the production mechanisms in pp collisions [2], as well as the parton energy loss in high-energy heavy-ion collisions. Among these identified hadrons are the neutral pion (π0) and η meson, which are abundant and have large branching ratios into two photons, making them suitable probes to study details of particle production. Measuring neutral mesons grants the possibility of extracting the direct photon signal that is seen as an excess yield above the photons fW√roseNmNpr=heas5de.rn0ot2ntihTceedVien,cvaaasyrimsa,neatansyduierielsddporwof ibtthhinetghπee0.Aga.nLdtIhCηe Emtedmeespoteencrstaoitnur.rpepoaf tth√e
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