Speaker
Description
The collision of a proton and a lead nucleus is asymmetric in nature, leading to an asymmetric rapidity distribution (more particles produced in the Pb-going side) of the produced particles at ultrarelativistic energies. We study multiplicity in such collision as a function of pseudorapidity, and centrality defined from the energy deposited in a calorimeter. In particular, we focus on the ultracentral regime (high-multiplicity collisions), where the asymmetry is more pronounced. We show that in this region, fluctuations of the multiplicity and the centrality estimator are predominantly due to quantum fluctuations, with impact parameter fluctuations playing negligible role. The joint probability distribution of multiplicity and the centrality estimator can be well approximated by a correlated gamma distribution. We show that this simple model can reproduce existing ATLAS data, and we make quantitative predictions for two more centrality bins in the ultracentral regime, namely $0-0.1\%$ and $0-0.01\%$, which could be verified experimentally. Predictions for more central events (e.g. $0-0.001\%$) are also possible by the same model. We also argue that by repeating the same analysis with a different centrality estimator, direct information can be obtained about the rapidity decorrelation in particle production.
Based on Samanta, Ollitrault, Phys. Lett. B 855 (2024), 138834 [arXiv: 2405.14671]
| Category | Theory |
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