Third Moments of Conserved Charges as Probes of QCD Phase Structure

Abstract

The third moments of conserved charges, the baryon and electric charge numbers, and energy, as well as their mixed moments, carry more information on the state around the QCD phase boundary than previously proposed fluctuation observables and higher order moments. In particular, their signs give plenty of information on the location of the state created in relativistic heavy ion collisions in the temperature and baryon chemical potential plane. We demonstrate this with an effective model.

Exploring the QCD Phase Structure with Beam Energy Scan in Heavy-ion Collisions

“…Fluctuations of conserved quantities, such as baryon (B), charge (Q) and strangeness (S) numbers, have been proposed as a sensitive probe to search for the signature of the QCD critical point in heavy-ion collisions [24]. These fluctuations are sensitive to the correlation length (ξ) [24] and can be directly connected to the susceptibility of the system computed in theoretical calculations, such as Lattice QCD [25,26,27] and HRG models [28].…”

“…These fluctuations are sensitive to the correlation length (ξ) [24] and can be directly connected to the susceptibility of the system computed in theoretical calculations, such as Lattice QCD [25,26,27] and HRG models [28]. The STAR experiment has measured various order fluctuations of net-proton (N p − Np, proxy for net-baryon), net-charge and net-kaon (proxy for net-strangeness) numbers in the Au+Au collisons at √ s NN =7.7, 11.5, 14.5, 19.6, 27, 39, 62.4 and 200 GeV [29,30,31].…”

Highlights from the heavy-ion program in STAR

“…The critical point is characteristic by large correlation length of the dynamical system which manifests in large event-by-event fluctuations of conserved quantities, such as net-baryon number (B), net-charge (Q), and net-strangeness(S) [16][17][18]. The experimentally accessible order moments of these quantities, variance (σ 2 ), skewness (S), and kurtosis (κ), are directly connected to the theoretically calculated thermodynamic susceptibilities.…”

Results from the RHIC Beam Energy Scan

“…A common strategy for locating the critical end point (CEP) is to scan the phase diagram by varying the √ s NN , and look for an increase/divergence or a non-monotonic behavior of experimental observables sensitive to the correlation length (ξ) [31]. Large fluctuations in the event-by-event distributions of conserved quantities, such as net-charge, net-baryon number, and net-strangeness have been proposed as possible experimental signatures of the QCD CEP [36].…”