Quarkonium Production and Polarization in an Improved Color Evaporation Model

Journal Article · 22 January 2019 · Nuclear Physics. A

DOI: https://doi.org/10.1016/j.nuclphysa.2018.08.003 · OSTI ID:1513116

Vogt, R.  ^[1]

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1. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States). Nuclear and Chemical Sciences Division; Univ. of California, Davis, CA (United States). Physics Dept.

An improved version of the color evaporation model (ICEM) has been introduced to describe heavy quarkonium production. In contrast to the traditional color evaporation model, the constraint was imposed that the invariant mass of the intermediate heavy quark-antiquark pair must be larger than the mass of produced quarkonium. A momentum shift between heavy quark-antiquark pair and the quarkonium was also introduced. Calculations show that the model can describe the charmonium yields as well as ratio of $$\psi$$' over $$J$$/$$\psi$$ better than the traditional color evaporation model. The ICEM has been extended to calculate the polarization of prompt $$J$$/$$\psi$$ and $$Υ$$($1S$) production for the first time in the color evaporation approach. The first calculations were made at leading order. The polarization parameter λ$$_\vartheta$$ was calculated as a function of center of mass energy and rapidity in p + p collisions. The x_F dependence of the polarization was also calculated and compred to experimental results in p+Cu and π+W collisions. The next step of calculating the p_T dependence of the polarization has been taken, with a calculation in the k_T-factorization approach. We compare the unpolarized p_T distributions for the $$J$$/$$\psi$$ and $$\psi$$, as well as the $$\psi$$ to $$J$$/$$\psi$$ ratio, in p + p collisions at RHIC and the LHC for several energies. We also present the polarization results and make comparison to polarization data.

• Research Organization: Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)
• Sponsoring Organization: USDOE National Nuclear Security Administration (NNSA)
• Grant/Contract Number: AC52-07NA27344
• OSTI ID: 1513116
• Report Number(s): LLNL-JRNL--753547; 940193
• Journal Information: Nuclear Physics. A, Journal Name: Nuclear Physics. A Journal Issue: C Vol. 982; ISSN 0375-9474
• Publisher: ElsevierCopyright Statement
• Country of Publication: United States
• Language: English