Study of Collective Phenomena in Heavy-Ion Collisions Using CMS Open Data

Abstract

In this work, we present preliminary results from a measurement of the recently proposed observable, $v_0(p_T)$, in lead-lead (PbPb) collisions at $\sqrt{s_{NN}}=2.76 \text{ TeV}$, using public data from the CMS Open Data portal. This observable is directly sensitive to radial flow and characterizes the transverse momentum ($p_T$) dependence of radial flow fluctuations, serving as probe of collective phenomena in the quark-gluon plasma (QGP) formed in heavy-ion collisions. Consistently with the ATLAS results at $\sqrt{s_{NN}}=5.02 \text{ TeV}$, we observe the three key features of collective radial flow: long-range correlations in pseudorapidity ($η$), a centrality-independent shape as a function of $p_T$, and factorization in $p_T$. The results presented in this work are generally compatible, within uncertainties, with the ATLAS measurements at $\sqrt{s_{NN}}=5.02\text{ TeV}$ reported in Phys. Rev. Lett. 136, 032301 (2026).

Figures (5)

• Figure 1: Scheme of the $p_T$ spectrum: the black curve represents the average spectrum over all events, while the blue and red curves represent events with a radial flow larger and smaller than the average, respectively. Events with a larger-than-average radial flow have a flatter spectrum, which is reflected in the covariance, that has a fixed zero-point at $p_T \approx \langle p_T \rangle$atlas-measurement.
• Figure 2: $v_0$ dependence on centrality (a) and the normalized covariance $v_0(p_T)v_0$(b), both measured in different $p_T^{ref}$ ranges.
• Figure 3: $v_0(p_T)$ observable in different $p_T^{ref}$ ranges and $\eta_{gap}=1$ in 50-60% centrality.
• Figure 4: $v_0(p_T)$ in different $\eta_{gap}$ values and $p_T^{ref} \in [0.5,2] \text{ GeV}$ in 50-60% centrality.
• Figure 5: $v_0(p_T)$ and $v_0(p_T)/v_0$ at default parameters in different centrality ranges.