X(3872) Production in Relativistic Heavy-Ion Collisions

Abstract

Heavy ion collisions provide a unique opportunity to study the nature of X(3872) compared with electron-positron and proton-proton (antiproton) collisions. With the abundant charm pairs produced in heavy-ion collisions, the production of multicharm hadrons and molecules can be enhanced by the combination of charm and anticharm quarks in the medium. We investigate the centrality and momentum dependence of X(3872) in heavy-ion collisions via the Langevin equation and instant coalescence model (LICM). When X( 3872) is treated as a compact tetraquark state, the tetraquarks are produced via the coalescence of heavy and light quarks near the quantum chromodynamic (QCD) phase transition due to the restoration of the heavy quark potential at T → T c . In the molecular scenario, loosely bound X(3872) is produced via the coalescence of D 0 -D * 0 mesons in a hadronic medium after kinetic freeze-out. The phase space distributions of the charm quarks and D mesons in a bulk medium are studied with the Langevin equation, while the coalescence probability between constituent particles is controlled by the Wigner function, which encodes the internal structure of the formed particle.First, we employ the LICM to explain both D 0 and J/ψ production as a benchmark. Then, we give predictions regarding X(3872) production. We find that the total yield of tetraquark is several times larger than the molecular production in Pb-Pb collisions. Although the geometric size of the molecule is huge, the coalescence probability is small due to strict constraints on the relative momentum between D 0 and D * 0 in the molecular Wigner function, which significantly suppresses the molecular yield.

On the Ground-state Energy of a Mixture of Two Different Oppositely Polarized Fermionic Gases

“…-According to a recent study [62], the compact tetraquark and loosely bound molecule are produced at different medium temperatures: a tetraquark is formed in QGP above the critical temperature, while a molecule is formed only in the hadronic medium after the kinetic freeze-out. Moreover, in Ref.…”

Chiral perturbation theory for heavy hadrons and chiral effective field theory for heavy hadronic molecules

“…[221]. The CMS Collaboration reported the evidence of the X(3872) production in relativistic heavy ion collisions for the first time [222], which provides a novel insight into the nature of X(3872) [223,224,225,226].…”

$B_c^+$ Formation from Random Charm and Anti-bottom Quarks in the Quark-Gluon Plasma

“…It depends on the relative distance x r and relative momenta q r between b and c quarks when they move to the regions with T ≤ T coal . The Instantaneous Coalescence Model (ICM) to describe the formation of B + c is written as [28],…”

“…This coalescence probability will be significantly enhanced if the numbers of charm and bottom pairs become large in the medium. As heavy quarks, especially bottom quarks, are hard to reach kinetic equilibrium due to their large * baoyi.chen@tju.edu.cn masses, we will employ the Langevin equations to study the realistic dynamical evolutions of heavy quarks in the QGP and the Instantaneous Coalesncece Model (ICM) to study the reaction of b + c → B + c + g (where g represents a gluon) [25][26][27][28]. Considering both the cold nuclear matter effect (such as the shadowing effect) and hot medium effects on heavy quarks and B + c mesons, we calculate the final spectrum of B + c mesons in Pb-Pb collisions and compare with the recent experimental data.…”