May 13 – 19, 2018
Venice, Italy
Europe/Zurich timezone
The organisers warmly thank all participants for such a lively QM2018! See you in China in 2019!

Quarkonium Production and Polarization in an Improved Color Evaporation Model

May 16, 2018, 5:50 PM
Sala Mosaici-2, 3rd Floor (Palazzo del Casinò)

Sala Mosaici-2, 3rd Floor

Palazzo del Casinò

Parallel Talk Quarkonia Quarkonia


Ramona Vogt (LLNL)


An improved version of the color evaporation model (ICEM) has been introduced to describe heavy quarkonium production [1]. 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 $\psi^\prime$ over $J/\psi$ better than the traditional color evaporation model.

The ICEM has been extended to calculate the polarization of prompt $J/\psi$ and $\Upsilon$(1S) production for the first time in the color evaporation approach. The first calculations were made at leading order. The polarization parameter $\lambda_\vartheta$ 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 compared to experimental results in $p$+Cu and $\pi$+W collisions [2,3]. The next step of calculating the $p_T$ dependence of the polarization has been taken, with a calculation in the $k_T$-factorization approach [4].

This talk will 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. It will also present the polarization results and make comparison to polarization data from RHIC, the Tevatron and the LHC.

[1] Y.-Q. Ma and R. Vogt, Phys. Rev. D {\bf 94} (2016) 114029.

[2] V. Cheung and R. Vogt, Phys. Rev. D {\bf 95} (2017) 074021.

[3] V. Cheung and R. Vogt, Phys. Rev. D {\bf 96} (2017) 054014.

[4] V. Cheung and R. Vogt, in preparation.

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