Physics PAN Seminar by Prof. Peter Christiansen (Lund University, Sweden)

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Date: September 10, 2021
Time: 3:30 p.m. - 4:30 p.m.
Location: Virtual event
Category: Seminar

Physics PAN Seminar by Prof. Peter Christiansen (Lund University, Sweden) 

Title: Studying dense QCD dynamics with quantum number balance

Abstract: The strangeness enhancement observed by ALICE in small collision systems has lead to a confrontation between traditional pp models, in which high-multiplicity pp collisions are an almost incoherent sum of parton-parton collisions (e.g PYTHIA), and QGP-like models, where the parton-parton collisions leads to the formation of a medium. To differentiate between these models (and their extensions), we have done a new series of measurements where we have tried to determine how the strangeness and baryon number of a Xi baryon (B=+1, S=-2) is balanced (B=-1, S=+2) by other hadrons. In this way, we wanted to measure if there is evidence that the quarks directly form hadrons (close correlations in momentum space) or that there is significant diffusion between quark production and hadronization (longer range correlations). The data seems to favor short-to-medium range correlations and a weak multiplicity dependence (unlike for the strangeness enhancement itself).

In the second half of the talk, I will therefore speculate that maybe these correlations are limited by an intermediate phase that we denote the gluon plasma (GP) and where there are few light quarks. In this picture, the hydrodynamization ("modern version of thermalization") is driven by gluons and it is first late that quark pairs appear and therefore their diffusion is small. This scenario, related to the old idea of Hot Glue, has potentially many nice features (photon flow and little or no CME). To test this idea we propose to extend the Xibaryon studies to study how charm and anticharm hadrons balance, since charm will be produced in the initial interactions and therefore be able to probe the full evolution of the collision. Finally, we also discuss how these ideas can be used to test the idea of J/psi regeneration.


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September 2021