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تسجيل مستخدم جديد$J/psi$ polarization in p+p collisions at $sqrt{s}$ = 200 GeV in STAR
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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 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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