# $J/\psi$ polarization in p+p collisions at $\sqrt{s}$ = 200 GeV in STAR

Abstract : We report on a polarization measurement of inclusive $J/\psi$ mesons in the di-electron decay channel at mid-rapidity at 2 $< p_T <$ 6 GeV/c in p+p collisions at $\sqrt{s}$ = 200 GeV. Data were taken with the STAR detector at RHIC. The $J/\psi$ polarization measurement should help to distinguish between the different models of the $J/\psi$ production mechanism since they predict different $p_T$ dependences of the $J/\psi$ polarization. In this analysis, $J/\psi$ polarization is studied in the helicity frame. The polarization parameter $\lambda_{\theta}$ measured at RHIC becomes smaller towards high $p_T$, indicating more longitudinal $J/\psi$ polarization as $p_T$ increases. The result is compared with predictions of presently available models.
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Journal articles
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http://hal.in2p3.fr/in2p3-00913294
Contributor : Dominique Girod <>
Submitted on : Tuesday, December 3, 2013 - 2:50:02 PM
Last modification on : Thursday, February 7, 2019 - 3:18:12 PM

### Citation

L. Adamczyk, W. Borowski, S. Kabana. $J/\psi$ polarization in p+p collisions at $\sqrt{s}$ = 200 GeV in STAR. Physics Letters B, Elsevier, 2013, 739, pp.180-188. ⟨10.1016/j.physletb.2014.10.049⟩. ⟨in2p3-00913294⟩

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