Excited cluster states: A new source for proton number fluctuations in the high baryon density regime

TL;DR

This paper investigates how decay products of excited nuclear cluster states influence proton number fluctuations in high baryon density collisions, highlighting their significance at low energies and importance for future precise measurements.

Contribution

It introduces the calculation of excited nuclear cluster decay contributions to proton fluctuations within the statistical model, emphasizing their impact on cumulant ratios at low energies.

Findings

Excited cluster states significantly affect proton fluctuation cumulants at low energies.

The contribution ranges from 1% to 100% depending on the cumulant order.

Impact diminishes at collision energies above 3.5 GeV.

Abstract

We calculate the contribution of the decay products of excited nuclear cluster states to the event-by-event fluctuations of protons in the energy range from $\sqrt{s_{NN}}=2-5$~GeV within the statistical model. We find that the inclusion of the excited nuclear clusters yields corrections to all cumulant ratios, ranging from 1\% for ratio of second to first-order cumulant to 100\% for the sixth to second order cumulant towards the lowest inspected energy. As expected the contribution of excited cluster states is most important at low energies $\sqrt{s_{NN}}<3.5$~GeV and becomes negligible at higher collision energies. Especially in light of the expected ultra-high precision data from CBM at FAIR, this new contribution is important to allow for a quantitative comparison with (potentially later available) lattice QCD or effective model results.