[J over ψ] polarization in p+p collisions at √s = 200 TeV in STAR

Abstract

We report on a polarization measurement of inclusive [J over ψ] mesons in the di-electron decay channel at mid-rapidity at 2<p[subscript T]<6 GeV/c in p+p collisions at √s = 200 GeV. Data were taken with the STAR detector at RHIC. The [J over ψ] polarization measurement should help to distinguish between different models of the [J over ψ] production mechanism since they predict different p[subscript T] dependences of the [J over ψ] polarization. In this analysis, [J over ψ] polarization is studied in the helicity frame. The polarization parameter λ[subscript θ] measured at RHIC becomes smaller towards high p[subscript T], indicating more longitudinal [J over ψ] polarization as p[subscript T] increases. The result is compared with predictions of presently available models.