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Paper proposal for phi meson v1

Updated on Fri, 2025-05-16 02:35. Originally created by gyz on 2025-05-16 02:11.

Paper Title: Energy Dependence of ϕ meson Directed Flow at High Baryon Density Region

Target journal: PRL
 

PAs: Xin Dong, Chenlu Hu, Hongcan Li, Guannan Xie, Nu Xu, Guangyu Zheng, etc.

PA representative: Guangyu Zheng

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Abstract:

 

In this paper we report the observation of ϕ-meson directed flow v1 at  high  baryon density region mid-central(10-40%) Au+Au collisions at RHIC.This is part of the beam energy scan program carried out by the STAR experiment at the relativistic collider. ϕ-meson candidates were reconstructed through K+K- decay channels. We observe ϕ-meson exhibit significant anistropic directed flow (v1) in heavy-ion collisions. The collectivity of the ϕ-meson will be compared with that of proton, Λ baryon and kaon. It is observed that at high baryon density region, ϕ meson v1 has the similar strength with that of proton and Λ baryon while Kaon v1 is much smaller.This suggests that ϕ-meson production is closely coupled to baryons.
 

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Fig. 1. ϕ meson acceptance,shown as transverse momentum pT versus rapidity y, from the  √sNN = 3 and 4.5 GeV Au +Au collisions. Dashed rectangular boxes illustrate the acceptance regions used for directed flow analysis.



Fig. 2. Reconstructed ϕ meson invariant mass distributions from the √sNN = 3 GeV Au+Au collisions in the corresponding pT -y regions shown in Panel (b). Panel (a) are invariant mass distributions of reconstructed data, combinatoral bacground and residual signal. Panel (b) is v1 of reconstructed data as a function of invariant mass.



Fig. 3. ϕ meson v1 ,shown as a function of rapidity, from the √sNN = 3 - 4.5 GeV 10-40% Au +Au collisions at RHIC. Fitting results, from a first-order polynomial function, are shown as the red dash lines. Results of the transport model calculations w/ and w/o baryonic mean field are shown as blue and black bands.

Fig. 4. Energy Dependence of mid-rapdiity v1 slope for ϕ, Kaon mesons and proton, Λ baryons in 10-40% Au+Au collisions. The statistical and systematic uncertainties are presented by gray bands and square brackets, respectively. 
 

 
Paper figures:

 

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Conclusions:

In summary, we report the measurements of energy dependence of ϕ meson directed flow v1 from the √sNN = 3 - 4.5 GeV mid-central (10-40%) Au+Au collisions at RHIC. The v1 slope of ϕ meson decreases in magnitude with increasing collision energy and exhibits a similar strength to that of proton and Λ baryons while Kaon shows significantly smaller v1 slope;
      Transport model calculations using JAM2 and UrQMD indicate that the baryonic mean-field is necessary to reproduce the v1 of proton and Λ baryons at high baryon density region and its effect on mesons is typically secondary; however, it has a strong impact on ϕ meson v1. Furthermore, a modified UrQMD model that includes additional decay channels from high-mass baryon resonances to ϕ can qualitatively reproduce the observed trend. These suggest that the unexpectedly large v1 of ϕ meson originates primarily from its production mechanism, likely inherited at the moment of generation rather than being developed through subsequent medium evolution. Our findings imply that ϕ meson production is closely coupled to the baryons at high baryon density region.  
 

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Presentations: 

FCV weekly meeting presentation:
https://drupal.star.bnl.gov/STAR/system/files/phi_FXT_flow_9.25_fcv.pdf

Collaboration meeting:
https://drupal.star.bnl.gov/STAR/meetings/STAR-Collaboration-Meeting-October-2024/Flow-Chirality-and-Vorticity-FCV-Parallel-session-3
https://drupal.star.bnl.gov/STAR/meetings/STAR-Collaboration-Meeting-March-2025/FCV-PWG-Parallel-session-II/Measurement-phi-meson-dir

Preliminary Request :
https://drupal.star.bnl.gov/STAR/blog/gyz/Preliminary-Request-phi-meson-directed-and-Elliptic-flow-3-45-GeV-QM2025
https://drupal.star.bnl.gov/STAR/system/files/phi_flowFXT_preliminaryRequest.pdf

Poster at QM25 and 20th-NC-14th-Symp-MHENP:
https://drupal.star.bnl.gov/STAR/presentations/Quark-Matter-2025/Measurement-phi-meson-directed-flow-sqrtsrm-NN-3-196-GeV-AuAu-collis
https://drupal.star.bnl.gov/STAR/presentations/20th-NC-14th-Symp-MHENP/Measurement-%CF%95-meson-production-and-collectivity-AuAu-collision


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