Title: Measurements of Multiplicity Dependent v2 and v3 in O+O and d+Au Collisions

PA

Shengli Huang(1), Jinhui Chen(2), Roy Lacey(1), Jiangyong Jia(1), Prithwish Tribedy(3), Zaining Wang(2), Zhengxi Yan(1), ChunjianZhang(2)
1.SBU 2.Fudan 3. BNL

Analysis note:
drupal.star.bnl.gov/STAR/system/files/ANdAuOORun21.pdf

PWG presentation:

•For O+O:

•https://drupal.star.bnl.gov/STAR/blog/slhuang/OO-Glauber-Update

•https://drupal.star.bnl.gov/STAR/blog/slhuang/di-hadron-correlation-OO

•https://drupal.star.bnl.gov/STAR/system/files/OOnewpreliminary.pdf

•https://drupal.star.bnl.gov/STAR/blog/slhuang/Qm2023-preliminary

•https://drupal.star.bnl.gov/STAR/system/files/OOPWGMay-17-2023-Shengli.pdf

•https://drupal.star.bnl.gov/STAR/system/files/OOPWGMay10-2023-Shengli.pdf

 

•For d+Au: 

•https://drupal.star.bnl.gov/STAR/blog/slhuang/PWGJune112024

•https://drupal.star.bnl.gov/STAR/blog/slhuang/PWGJun182024

Abstract:

In this paper, flow harmonics (v2, v3) in symmetric (O+O) and asymmetric (d+Au) collisions are measured as a function of multiplicity. v2, measured using both two- and four-particle correlations, shows a strong system dependence, while v3 is nearly system-independent. This indicates that both final state interactions and initial geometry play significant roles in anisotropy in small systems. The eccentricity scaling (vn/εn) suggests that the initial geometry contains sub-nucleon fluctuations. Furthermore, we found that while v2{4}/v2{2} is consistent with ε2{4}/ε2{2} in central d+Aucollisions, it is lower than ε2{4}/ε2{2} in central O+O collisions, based on two types of ab initio effective field QCD calculations. This finding helps constrain these models and enhances our understanding of nucleon-nucleon correlations.

Figure 1:

The v2{2} and v3{2}  measured using two-particle correlations in 1.0<∣Δη∣<3.01.0<∣Δη∣<3.0 for O+O and d+Au collisions at 200 GeV. The left panel shows vn​ without subtraction, while the right panel shows the nonflow-subtracted vn​. Before and after subtraction, v2{2}  is significantly enhanced in central d+Au collisions but shows weak dependence on multiplicity in central O+O. v3{2}  exhibits weak system dependence between d+Au and O+O collisions.

Figure 2:

The v2{2}/ε2{2} and v3{2}/ε2{2} for O+O and d+Au collisions at 200 GeV. The eccentricity is calculated using the  Glauber + AFDMC model. The left panel shows vn{2}/εn{2} ​ with nuclear Glauber, while the right panel shows vn{2}/εn{2} ​ with sub-nuclear Glauber. vn{2}/εn{2} demonstrates good scaling for sub-nuclear fluctuations between d+Au and O+O collisions.

Figure3:

The v2{2} and v2{4} for O+O(right panel) and d+Au(left panel) collisions at 200 GeV. Both v2{2} and v2{4}  

show significant enhancement in central d+Au collisions. In contrast, v2{2}exhibits weak multiplicity dependence, while v2{4} drops significantly in central O+O collisions.

Figure 4:

The v2{4} /v2{2} for O+O (right panel) and d+Au (left panel) collisions at 200 GeV. v2{4}/v2{2} is found to be consistent with ε2{4}/ε2{2}  in central d+Aucollisions. In O+O collisions, we compare v2{4}/v2{2} with ε2{4}/ε2{2}  from four different models: two (AFDMC and NLEFT) based on ab initio EFT models, and the two two using a single-body distribution that fits the nucleon distribution from AFDMC and NLEFT. All models predict values above the measured v2{4}/v2{2} when including sub-nucleon fluctuations, though the ε2{4}/ε2{2} from AFDMC is closer to the measurements than others