Title: Beam-energy dependence of identified two-particle angular correlations in Au+Au collisions at RHIC

PA's: S. Jowzaee, W. J. Llope

Target Journal: PRC

PWG: Bulkcorr

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Abstract:
Two-particle correlation function of pions, kaons and protons have been studied in 7.7 GeV to 200 GeV Au+Au collisions measured by STAR at RHIC. These correlations were measured for both like-sign and unlike-sign charge combinations versus the centrality. The correlations of pions and kaons show the expected near-side peak resulting from the short-range mechanisms like jet fragmentation, resonance decays and femtoscopy effects. These correlations decrease with increasing the beam energy. However, protons exhibit strong anti-correlations in this near-side region. This behavior of protons is reported for the first time in an A+A system. The anti-correlation is pT-independent and decreases with increases of the beam energy and decreases with the centrality. The experimental results have also compared to the Monte Carlo models of UrQMD, Hijing and AMPT.
   

PACS numbers: 25.75.-q, 25.75.Gz




Figures: 


                                                     
Fig. 1: R2(∆y, ∆phi) of like-sign (left) and unlike-sign (right) pions in Au+Au collisions at mid centrality 30%-40% and 0.2<pT<2.0

GeV/c in different beam energies from 7.7 GeV (top left) to 200 GeV (bottom right). 

                
Fig. 2: R2(∆y, ∆phi) of like-sign(left) and unlike-sign (right) protons in Au+Au collisions at mid centrality 30%-40% and 0.4<pT<2.0 GeV/c in different beam energies from 7.7 GeV (top left) to 200 GeV (bottom right). Due to the large statistical fluctuations in large ∆y bins, the plots are presented in the range of |∆y|<1.   


                   
Fig. 3: R2(∆y, ∆phi) of like-sign(left) and unlike-sign (right) kaons in Au+Au collisions at 200 GeV, mid centrality 30%-40% and 0.2<pT<1.6 GeV/c.


          
Fig. 4: <R2(∆y)> projection of like-sign (red) and unlike-sign (blue) pions (left) and protons (right) in Au+Au collisions at 30%-40% centrality and eight different energies from 7.7 GeV (top left) to 200 GeV (bottom right). Also shown at the highest beam energies in the right frames are the antiproton-antiproton correlations.


            
Fig. 5: Near-side and away-side <R2(∆y)> projections of like-sign (red) and unlike-sign (blue) pions (left) and protons (right) in Au+Au collisions at 14.5 GeV (top) and 62.4 GeV (bottom), 30%-40% centrality.


              
Fig. 6: <R2(∆y)> projection of like-sign (red) and unlike-sign (blue) pions (left) and protons (right) in Au+Au collisions at 14.5 GeV (top) and 62.4 GeV (bottom), 30%-40% centrality compared with the UrQMD (solid line) and Hijing (dash-dotted line), and AMPT (dashed line) simulations.


             
Fig. 7: <R2(∆y)> projection of like-sign (red) and unlike-sign (blue) pions (left) and protons (right) in Au+Au collisions at 14.5 GeV (top) and 62.4 GeV (bottom) for the most central 0%-5%, mid central 30%-40% and peripheral 60%-70% events.


              
Fig. 8: <R2(∆y)> projection of like-sign (red) and unlike-sign (blue) pions (left) and protons (right) in low and high pT in Au+Au collisions at 14.5 Gev (top) and 62.4 GeV (bottom), 30%-40% centrality.


Conclusion:

Two-particle angular correlation function have been studied for like-sign and unlike-sign pion, kaon and proton pairs in BES I dataset at RHIC. The energy, centrality and pT dependence of correlations were investigated. No non-monotonic behavior was observed in the two-particle angular correlations of mesons and baryons as a function of the beam energies from 7.7 to 200 GeV. The expected near-side peak was observed in the correlation function of pions and kaons associated with the short-range mechanisms. The correlations decrease with the beam energy and decrease with the centrality, and are is pT independent. A strong near-side ring-shaped enhancement was observed in unlike-sign kaons due to the Phi(1020) resonance decay to K+K-. In contrast to mesons, protons exhibit a significant near-side anti-correlation at all beam energies. This anti-correlation was observed in both like-sign and unlike-sign (anti)proton pairs, and it is wider in relative rapidity, ∆y, for the like-sign charge combination as compared to the unlike-sign combination. The proton anti-correlation is pT independent and decreases with increasing the beam energy and decreases with centrality. These experimental results were compared with the UrQMD, Hijing and AMPT models. The observed short-range enhancement in the correlation of pions was not seen in none of the models, while UrQMD and AMPT quantitatively described the unlike-sign and like-sign proton results, respectively.



Analysis code for PSN0707:
CVS_psn0707


Supporting Material:
QM2017_talk
Tracking_comparison_presentation
STARanalmtg_Nov2017
Bulkcorr_mtg_Feb2018
Bulkcorr_mtg_March2018
APS2018_presentation
Bulkcorr_mtg_June2018