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Paper proposal for phi meson v1

Updated on Wed, 2025-05-28 05:39. Originally created by gyz on 2025-05-16 02:11.

Paper Title: Observation of Strong ϕ meson Directed Flow at High Baryon Density Region  


Target journal: PRL
 

PAs: Xin Dong, Chenlu Hu, Hongcan Li, Like Liu, Yaping Wang, Shusu Shi, Guannan Xie, Nu Xu, Guangyu Zheng*


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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Paper figures:

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 measurement.




Fig. 2. Reconstructed ϕ-meson invariant mass distributions from the √sNN = 3 GeV Au+Au collisions in the corresponding pT-y regions. Panel (a) represents K+K- invariant mass distributions of foreground, combinatorial background and signals. Panel (b) represents the reconstructed v1 as a function of invariant mass.




Fig. 3. ϕ-meson v1 as a function of rapidity, from the √sNN = 3 - 4.5 GeV 10-40% Au +Au collisions at RHIC. Fitted with 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, respectively.
 

Fig. 4. Energy Dependence of mid-rapidity 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.For comparison, calculations of transport models are shown as dash line from JAM with baryonic mean field and bars from modified UrQMD.
 
 

 


 

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Conclusions:

      In summary, we report the measurements of energy dependence of ϕ-meson directed flow v1 from the √sNN  = 3.0, 3.2, 3.5, 3.9, 4.5 and 7.7 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-meson can qualitatively reproduce the observed data. 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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