Extracting the speed of sound of QCD from transverse momentum fluctuations
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arXiv
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| Format: | Preprint |
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2026
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| author | Alqahtani, Mubarak Parida, Tribhuban Ollitrault, Jean-Yves |
| author_facet | Alqahtani, Mubarak Parida, Tribhuban Ollitrault, Jean-Yves |
| contents | We extract the speed of sound ($c_s$) in the quark-gluon plasma from ATLAS data on the probability distribution of the transverse momentum per particle, $[p_T]$, in ultra-central Pb+Pb collisions. With an ideal detector, $c_s$ can be inferred from the rise of the mean $[p_T]$ with the collision multiplicity. In practice, however, low-$p_T$ particles escape detection, which biases the analysis. We show how to correct for this bias by using data on the variance of $[p_T]$, as well as information from the recently-measured $v_0(p_T)$. We also introduce a systematic method for deblurring the noise from the hadronization process. Assuming that the size of the quark-gluon plasma is independent of the hadron multiplicity in collisions at zero impact parameter, which is the scenario preferred both by high-energy QCD and heavy-ion data, we obtain $c_s/c=0.496\pm 0.008$ at temperature $T=221\pm 13$ MeV, in perfect agreement with first-principles calculations from lattice QCD. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2603_09647 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | Extracting the speed of sound of QCD from transverse momentum fluctuations Alqahtani, Mubarak Parida, Tribhuban Ollitrault, Jean-Yves High Energy Physics - Phenomenology High Energy Physics - Experiment Nuclear Experiment Nuclear Theory We extract the speed of sound ($c_s$) in the quark-gluon plasma from ATLAS data on the probability distribution of the transverse momentum per particle, $[p_T]$, in ultra-central Pb+Pb collisions. With an ideal detector, $c_s$ can be inferred from the rise of the mean $[p_T]$ with the collision multiplicity. In practice, however, low-$p_T$ particles escape detection, which biases the analysis. We show how to correct for this bias by using data on the variance of $[p_T]$, as well as information from the recently-measured $v_0(p_T)$. We also introduce a systematic method for deblurring the noise from the hadronization process. Assuming that the size of the quark-gluon plasma is independent of the hadron multiplicity in collisions at zero impact parameter, which is the scenario preferred both by high-energy QCD and heavy-ion data, we obtain $c_s/c=0.496\pm 0.008$ at temperature $T=221\pm 13$ MeV, in perfect agreement with first-principles calculations from lattice QCD. |
| title | Extracting the speed of sound of QCD from transverse momentum fluctuations |
| topic | High Energy Physics - Phenomenology High Energy Physics - Experiment Nuclear Experiment Nuclear Theory |
| url | https://arxiv.org/abs/2603.09647 |