Transverse momentum dependence of J/psi polarization at midrapidity in p+p collisions at sqrt(s)=200 GeV

Abstract

We report the measurement of the transverse momentum dependence of inclusive J/psi polarization in p+p collisions at sqrt(s)=200 GeV performed by the PHENIX Experiment at RHIC. The polarization is studied in the helicity, Gottfried-Jackson, and Collins-Soper frames for p_T < 5 GeV/c and |y| < 0.35. The J/psi polarization in the helicity and Gottfried-Jackson frames is consistent with zero for all transverse momenta, with a slight (1.8 sigma) trend towards longitudinal polarization for transverse momenta above 2 GeV/c. No conclusion is allowed due to the limited acceptance in the Collins-Soper frame and the uncertainties of the current data. The results are compared to observations for other collision systems and center of mass energies and to different quarkonia production models.

Figures (7)

• Figure 1: Definition of the polarization frames: helicity(HX), Gottfried-Jackson(GJ) and Collins-Soper(CS) frames.
• Figure 2: Invariant mass of dielectrons in the $J/\psi~$ mass range. Dashed lines represents the mass range used in the polarization analysis.
• Figure 3: Distribution of single electrons versus the $Z$ coordinate of the track in the drift chamber for real (open boxes) and simulated (closed boxes) data for different sectors (0 is the bottom and 3 is the top ones) in the east (left) and west (right) detector arms. The box-height for each point corresponds to its statistical uncertainty.
• Figure 4: Single electron identification efficiency estimated using full reconstructed Dalitz decays from real data (open circles) and simulation (full squares). Dotted line represents the minimum $p_T$ for the electron used to reconstruct $J/\psi~$ decays.
• Figure 7: (top) Same as in As in Fig. \ref{['fig:costheta_HX_GJ']}, but now for the Collins-Soper frame. Dotted lines on bottom panel correspond to Eq. (\ref{['eq:costheta']}) for $\lambda=\pm1$.