NBI Heavy-ion Seminar (online): Can QCD thermodynamics be probed from the multiplicity and mean transverse momentum of ultracentral heavy-ion collisions?

Tuesday 25 Nov 2025, 15:00 → 16:30 Europe/Copenhagen

NBB (NBI)

You Zhou (Niels Bohr Institute)

Title: Can QCD thermodynamics be probed from the multiplicity and mean transverse momentum of ultracentral heavy-ion collisions?

Speaker: Dr. Henry Hirvonen  (Vanderbilt University)

Abstract: Recent measurements show that the mean transverse momentum of hadrons exhibits a power-law dependence on hadronic multiplicity in ultracentral relativistic heavy-ion collisions. It has been proposed that the exponent of this power law provides a direct measurement of the speed of sound at temperatures determined from the mean transverse momentum. In this talk, we examine the validity of this claim and discuss the assumptions required to connect the speed of sound with the experimental observable. We demonstrate that modest modifications to the original argument can lead to a thermodynamic quantity that differs from the speed of sound. Furthermore, using numerical simulations, we show that the observable is sensitive to a type of fluctuations that induce the changes in particle multiplicity, and that enforcing an experimentally inaccessible quantity, called "effective volume", to be constant leads to discrepancies between the speed of sound and the extracted exponent. Finally, we illustrate how variations in the equation of state affect the correlation between the observable and the speed of sound. Our findings suggest that the most effective use of this observable is within a global analysis, where it may provide additional constraints on the properties of QCD matter.

Time: November 25th, 2025, at 3 PM

Location: Online via Zoom