Speaker
Description
Event-by-event fluctuations of the mean transverse momentum of particles provide a direct probe of collective radial expansion of the system formed in high-energy collisions. We present the first measurement of transverse-momentum-dependent radial flow fluctuations, characterized by the observable $v_0(p_{\mathrm{T}})$, in small collision systems. The measurement is performed using CMS data from pp collisions at $\sqrt{s}=13~\mathrm{TeV}$, pPb collisions at $\sqrt{s_{\mathrm{NN}}}=8.16~\mathrm{TeV}$, and OO, NeNe and peripheral PbPb collisions at $\sqrt{s_{\mathrm{NN}}}=5.36~\mathrm{TeV}$. The observable is measured from two-particle correlations with a pseudorapidity gap to suppress short-range nonflow contributions. The transverse-momentum dependence is investigated through the normalized quantity $v_0(p_{\mathrm{T}})/v_0$ as a function of $p_{\mathrm{T}}/\langle p_{\mathrm{T}}\rangle$, providing a systematic comparison across multiplicity and collision systems. The results are compared with hydrodynamic calculations based on TRENTO+MUSIC initial conditions, as well as predictions from the nonthermal event generators PYTHIA and HIJING. This study provides a new experimental handle on radial-flow fluctuations and their possible collective origin in small collision systems.
