Spectra–flow correlation as a probe of thermo-geometric fluctuations in the QGP initial state

by Dr Rupam Samanta (Institute of Nuclear Physics (IFJ, PAN), Poland)

Monday 2 Nov 2026, 16:00 → 18:00 Europe/Zurich

Initial-state fluctuations in heavy-ion collisions leave imprints on the hadron transverse-momentum spectrum. This was recently shown at the LHC through v0(pT), which correlates the spectra with the event-by-event mean transverse momentum [pT]. I will introduce a new observable, v02(pT), which correlates the spectra with the squared elliptic flow v2^2. As a three-particle correlator, it is much less sensitive to nonflow, especially at high pT. A principal component analysis of the joint fluctuations of the spectra, [pT], and v2^2 splits the spectral fluctuations into a thermal mode and a geometric mode at fixed temperature. I will show that v0(pT) is solely governed by the thermal mode, while v02(pT) has a sizable geometric contribution that grows in non-central collisions and causes a sign change at low pT. Additionally, using ideal hydrodynamics for Pb+Pb collisions at 5.02 TeV, corrected with the measured v2(pT), I will present predictions of a decrease of v02(pT) at high pT, a clear meson–baryon splitting, and a doubly sign-changing proton v02(pT) at low pT in mid-central and peripheral collisions. This makes v02(pT) a clean probe of the QGP initial state and motivates its measurement at the LHC.