Abstract
Based on the coalescence model for light nuclei production, we show that the yield ratio $\mathcal{O}_\text{p-d-t} = N_{^3\text{H}} N_p / N_\text{d}^2$ of $p$, d, and $^3$H in heavy-ion collisions is sensitive to the neutron relative density fluctuation $\Delta n= \langle (\delta n)^2\rangle/\langle n\rangle^2$ at kinetic freeze-out. From recent experimental data in central Pb+Pb collisions at $\sqrt{s_{NN}}=6.3$~GeV, $7.6$~GeV, $8.8$~GeV, $12.3$~GeV and $17.3$~GeV measured by the NA49 Collaboration at the CERN Super Proton Synchrotron (SPS), we find a possible non-monotonic behavior of $\Delta n$ as a function of the collision energy with a peak at $\sqrt{s_{NN}}=8.8$~GeV, indicating that the density fluctuations become the largest in collisions at this energy. With the known chemical freeze-out conditions determined from the statistical model fit to experimental data, we obtain a chemical freeze-out temperature of $\sim 144~$MeV and baryon chemical potential of $\sim 385~$MeV at this collision energy, which are close to the critical endpoint in the QCD phase diagram predicted by various theoretical studies. Our results thus suggest the potential usefulness of the yield ratio of light nuclei in relativistic heavy-ion collisions as a direct probe of the large density fluctuations associated with the QCD critical phenomena.
Highlights
Op-d-t = N3HNp/Nd2 of p, d, and 3H in heavy-ion collisions is sensitive to the neutron relative density fluctuation ∆n = tral Pb+Pb collisions at
With the known chemical freeze-out conditions determined from the statistical model fit to experimental data, we obtain a chemical freeze-out temperature of ∼ 144 MeV and baryon chemical potential of ∼ 385 MeV at this collision energy, which are close to the critical endpoint in the QCD phase diagram predicted by various theoretical studies
Our results suggest the potential usefulness of the yield ratio of light nuclei in relativistic heavy-ion collisions as a direct probe of the large density fluctuations associated with the QCD critical phenomena
Summary
E √sNN centrality ∆n (α = −0.2) ∆n (α = −0.1) ∆n (α = 0) ∆n (α = 0.1) ∆n (α = 0.2). 158 17.3 0 − 12% 0.542±0.084 0.594±0.101 0.668±0.127 0.782±0.175 1.002±0.345 freeze-out. To take into account density fluctuations of nucleons, we express the neutron and proton density in the emission source as n(r). Where · denotes the average value over space and δn(r) (δnp(r)) with δn = 0 ( δnp = 0) denotes the fluctuation of neutron (proton) density from its average value n ( np ). Assuming δnp(r) = c(r)δn(r), where the function c(r) can be positive or negative, we can express the correlation between δn(r) and δnp(r) as δnδnp drδn(r)δnp(r) dr c(r)(δn(r))
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