Speaker
Description
High-order net-proton cumulants and the event volume definition in A+A collisions at NICA energies.
G. Feofilov, St. Petersburg State University, St. Petersburg, RF
E-mail: g.feofilov@spbu.ru
Thermodynamic predictions [1] have indicated that the non-Gaussian fluctuations of the event-by-event observables, such as the net electric charge, the net strangeness and the net baryon number, could be a very sensitive signal of the proximity of the critical point (CP) of strongly interactive matter. This CP is being extensively searched at present in high-energy nucleus-nucleus collisions at the SPS at CERN and in BES-I and -II programs at RHIC. In particular, the higher-order cumulants of net-protons are being used as a proxy for net baryon number. Relevant studies are also in preparation with the MPD experiment at NICA at JINR.
However, the non-dynamical, trivial volume fluctuations of protons and net-protons could dominate over the genuine physical signals of interest [2,3]. This is due to the fact that, in currently applied procedures, any selected class of collision centrality will contain the inevitable mixture of the events with different impact parameters (see in [4]). Thus the relevant trivial volume fluctuations will dominate over the signal of interest.
We propose in this report the procedure to use, in the analysis of A+A collisions at NICA, the event-vise definition of the interaction volume in order to mitigate the influence of trivial fluctuations on the values of high-order net-proton cumulants. This could be done event-by-event using the ML technique, similar to [5], for the number of nucleons-participants (Npart) in the given collision. The value of Npart estimated for the event is more relevant then the mean impact paparemeter, and it is also of particular importance due to the well known effect of nucleon stopping at NICA energies that leads to the bias of the net-proton number.
Acknowlegments: The author acknowledges Saint-Petersburg State University for a research project 103821868.
1. M.A.Stepanov, Phys. Rev. Lett. 102, (2009) 032301.
2. V. Skokov, B. Friman and K. Redlich, “Volume fluctuations and higher order cumulants of the net baryon number”. arXiv:1205.4756v2.
3. P.Braun-Munzinger, A.Rustamov, J.Stachel, Nuclear Physics A960 (2017) 114–130.
4. T. A. Drozhzhova,V. N. Kovalenko,A. Yu. Seryakov,G. A. Feofilov, Physics of Atomic Nuclei, 2016, V 79, Issue 5, pp 737–748
5. K. Galaktionov, V. Rudnev and F. Valiev, Physics of Particles and Nuclei, 2023, Vol. 54, No. 3, pp. 446–448.
