Title: Measurement of Proton and Light Nuclei Production in Au+Au Collisions at √sNN = 3 GeV by RHIC-STAR

PAs: Daniel Cebra, Xin Dong, Benjamin Kimelman, Hui Liu, Xiaofeng Luo, Junlin Wu, Guannan Xie, Nu Xu, Ning Yu, Dingwei Zhang

Target Journal: Physical Review C

Paper draft:  In preparation 
Analysis Note:  In preparation 
Paper proposal: https://drupal.star.bnl.gov/STAR/system/files/PaperProposal_LightNucleiProduction_3GeV_HuiLiu.pdf

Abstract:
Light nuclei production is expected to be sensitive to baryon density fluctuations and can be used to probe the signatures of QCD critical point and/or first order phase transition in heavy-ion collisions. In this paper, we will present the protons (p) and light nuclei (d, t, ³He, ⁴He) productions in Au+Au collisions at √sNN = 3 GeV measured in 2018 by STAR experiment under Fixed-target mode. We will show the transverse momentum spectra (p_T) of proton (p), deuteron (d), triton (t), ³He and ⁴He at various rapidity slices. The rapidity and centrality dependence of coalescence parameters B₂(d), B₃(t) and B₃(³He), particle ratios (d/p, t/p, t/d, ³He/p and ⁴He/p), and yield ratios of N_p*N_t/N_d², N_⁴He*N_p/(N_³He*N_d) and N_⁴He*N_t*N_p²/(N_³He*N_d³) will be also presented. Their physics implications will be discussed.

Figure 1:
 
Fig. 1. (left) The <dE/dx> of charged tracks versus rigidity in Au+Au collisions at √sNN = 3 GeV. The dotted lines are Bichsel theoretical curves for the corresponding particles. (right)  The m2/q2 of particle versus rigidity distribution at √sNN = 3 GeV.

Figure 2:

Fig. 2. Transverse momentum versus rapidity of particles in Au+Au collisions at √sNN = 3 GeV. The purple boxes indicate the pT and rapidity ranges of each particle in the  analysis.

Figure 3:

Fig. 3. (top) Proton transverse momentum spectra for different rapidity ranges and centrality bins(0-10%, 10-20%, 20-40% and 40-80%) in Au+Au collisions at √sNN = 3 GeV. To  distinguish spectra clearly, they are scaled by a factor from 1 at mid-rapidity to 10e-9 at beam rapidity. Systematics uncertainties are represented by boxes. The dotted lines are fit by  blast wave function. (bottom) Deuteron transverse momentum spectra for different rapidity ranges and centrality bins(0-10%, 10-20%, 20-40% and 40-80%) in Au+Au collisions  at √sNN = 3 GeV.

Figure 4:

Fig. 4.  (top) Triton transverse momentum spectra for different rapidity ranges and centrality bins(0-10%, 10-20%, 20-40% and 40-80%) in Au+Au collisions at √sNN = 3 GeV. To  distinguish spectra clearly, they are scaled by a factor from 1 at mid-rapidity to 10e-9 at beam rapidity. Systematics uncertainties are represented by boxes. The dotted lines are fit by  blast wave function. (middle) Helium3 transverse momentum spectra for different rapidity ranges and centrality bins(0-10%, 10-20%, 20-40% and 40-80%) in Au+Au collisions  at √sNN = 3 GeV. (bottom) Helium4 transverse momentum spectra for different rapidity ranges and centrality bins(0-10%, 10-20%, 20-40% and 40-80%) in Au+Au collisions  at √sNN = 3 GeV.

Figure 5:

Fig. 5. The rapidity density distributions(dN/dy) of particles for different centrality bins in Au+Au collisions at √sNN = 3 GeV. The solid markers indicate the measured rapidity ranges, the open markers are reflected by measured results. The boxes indicate the systematical uncertainties.

Figures 6:

Fig. 6. Rapidity dependence of <pT> of particles for different centrality bins in Au+Au collisions at √sNN = 3 GeV. The solid markers indicate the measured rapidity ranges, the open markers are reflected by measured results. The boxes indicate the systematical uncertainties. 

Figure 7:

Fig. 7. (a) dN/dy normalized by spin degeneracy factor as an exponential function of the particle mass in Au+Au collisions at √sNN = 3 GeV. Rapidity windows are distinguished by different colorful Markers. The boxes indicate the systematical uncertainties. The solid lines represent the fit with exponential function. (b) <pT> as a linear function of the particle mass in Au+Au collisions at √sNN = 3 GeV. Rapidity windows are distinguished by different colorful Markers. The boxes indicate the systematical uncertainties.

Figure 8:

Fig. 8. The rapidity dependence of dN/dy of particles in Au+Au collisions at √sNN = 3 GeV. The solid lines represent the distribution fit by 3 gaussians function. The dashed lines represent the distribution fit by 2 generalized gaussians + 1 gaussian function.

Figure 9:

Fig. 9. 4pi yield as an exponential function of the particle mass in Au+Au collisions at √sNN = 3 GeV. The boxes represent the quadratic sums of the measured errors and the extrapolation uncertainties.

Figure 10:

Fig. 10. Rapidity dependence of d/p, t/d, t/p, he3/p and he4/p for different centrality bins in Au+Au collisions at √sNN = 3 GeV. The boxes indicate the systematical uncertainties.

Figure 11:

Fig. 11. Energy dependence of d/p and anti-d/anti-p yield ratios. The vertical lines indicate statistical uncertainties. The boxes indicate the systematical uncertainties. The curves represent the thermal model results.

Figure 12:

Fig. 12. Rapidity dependence of the coalescence parameter for B2(d), √B3(t) and √B3(He3) at pT/A = 0.65 GeV/c for different centrality bins in Au+Au collisions at √sNN = 3 GeV. The bands represent the systematical uncertainties.

Figure 13:

Fig. 13. Coalescence parameters B2(d), √B3(t) and √B3(He3) as a function of pT/A for different centrality bins in Au+Au collisions at √sNN = 3 GeV. The boxes represent the systematical uncertainties.

Figure 14:

Fig. 14. Energy dependence of the coalescence parameters for B₂(d) and B₃(³He) from central collisions. The vertical lines indicate statistical uncertainties. The boxes indicate the systematical uncertainties.

Figure 15:

Fig. 15. Rapidity dependence of the yield ratio for N_p*N_t/N_d², N_⁴He*N_p/(N_³He*N_d) and N_⁴He*N_t*N_p²/(N_³He*N_d³) for different centrality bins in Au+Au collisions at √sNN = 3 GeV. The bands represent the systematical uncertainties.

Figure 16:

Fig. 16. Energy dependence of N_p*N_t/N_d² at central collisions. The error bars represent statistical errors. The boxes indicate the systematical uncertainties.

Summary:
we have measured proton and light nuclei(d, t, ³He and ⁴He) production in Au+Au collisions at √sNN = 3 GeV from STAR experiment and presented the p_T spectra, dN/dy and <p_T> of particles from mid-rapidity to backward rapidity. we also calculated the 4pi yield of particles.

The coalescence parameters B_A(d, t and ³He) and particle ratio (d/p, t/p) at mid-rapidity of central collisions follow the energy dependence trend as observed in STAR Beam Energy Scan-I and other experiment groups.

The yield ratio N_p*N_t/N_d² of mid-rapidity measured at 3 GeV follow the trend of world data.

Supporting materials:

presentations in PWG:
https://drupal.star.bnl.gov/STAR/system/files/201207light_nuclei_production_at_FXT_3GeV.pdf
https://drupal.star.bnl.gov/STAR/system/files/201214light_nuclei_production_at_FXT_3GeV.pdf
https://drupal.star.bnl.gov/STAR/system/files/210104light_nuclei_production_at_FXT_3GeV_SL20d.pdf

STAR collaboration meeting:
https://drupal.star.bnl.gov/STAR/system/files/210302_STARCollaborationMeeting_huiliu.pdf

APS 2021:
https://drupal.star.bnl.gov/STAR/system/files/APS2021_LightNuclei_HuiLiu.pdf