Improved quark coalescence model for spin alignments of vector mesons

Xin-Li Sheng,G David,S Mukherjee,A Kalweit,T Ullrich,Z Xu,I.-K Yoo,P Garg

doi:10.1051/epjconf/202225911013

Xin-Li Sheng, G David + Show 6 more

Open Access

https://doi.org/10.1051/epjconf/202225911013

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Abstract

We propose an improved quark coalescence model for spin alignment of vector mesons by spin density matrix with phase space dependence. Within this model we propose an understanding of spin alignments of vector mesons ϕ and K*0 in the static limit: a large positive deviation of ρ00 for ϕ mesons from 1/3 may come from the electric part of the vector ϕ field, while a negative deviation of ρ00 for K*0 mesons may come from the electric part of vorticity fields. In the low-pT region, ρ00 for K*0 mesons is proportional to pT2, which is qualitatively agree with experimental results.

Highlights

In ultra-relativistic heavy-ion collisions, a huge orbital angular momentum (OAM) can be generated in the direction perpendicular to the reaction plane
We have argued in Ref. [9] that the dominant contribution to ρφ00 may possibly be from the electric part Eφ, which results in the positive deviation from 1/3 for φ mesons’ spin alignment [6,7,8]
The spin alignment of K∗0 is dominated by vorticity fields and will be smaller than 1/3 for nearly static K∗0, which qualitatively agrees with experimental results obtained by ALICE and STAR [6,7,8]

Summary

Introduction

In ultra-relativistic heavy-ion collisions, a huge orbital angular momentum (OAM) can be generated in the direction perpendicular to the reaction plane. During the evolution of the fireball, the OAM is transferred to the spin polarization of quarks through the spin-orbit coupling in nonlocal scatterings [1]. The spin alignment of vector mesons can be measured through the angular distribution of decay daughters [4]. We give a general relation between the density matrix of vector mesons and that of quarks. Using the spin polarization of quarks in vorticity and vector meson fields, predicted by the Wigner function approach [3], we derive spin alignments of vector mesons φ and K∗0. This work should be tested by a detailed and comprehensive simulation of vorticity tensor fields and vector meson fields in heavy ion collisions. The momentum integration measure is denoted using shorthand notation [d3p] ≡ d3p/(2π)

Spin density matrix and quark coalescence model in phase space

E p1 E p2

Summary