Observation of Polarization in Bottomonium Production at sqrt(s)=38.8 GeV

TL;DR

This paper reports the measurement of bottomonium polarization in p-Cu collisions at 38.8 GeV, revealing significant transverse polarization at certain kinematic ranges, and compares results with NRQCD predictions.

Contribution

First measurement of bottomonium polarization at this energy and collision system, providing new experimental data for testing QCD models.

Findings

Upsilon(1S) shows no polarization at small xF and pT but significant transverse polarization at higher pT or xF.

Upsilon(2S+3S) states exhibit large transverse polarization across all measured xF and pT.

Results align with NRQCD predictions of transverse polarization from quark-antiquark and gluon-gluon fusion.

Abstract

We present a measurement of the polarization observed for bottomonium states produced in p-Cu collisions at sqrt(s)=38.8 GeV. The angular distribution of the decay dimuons of the Upsilon(1S) state show no polarization at small xF and pT but significant positive transverse production polarization for either pT > 1.8 GeV/c or for xF > 0.35. The Upsilon(2S+3S) unresolved states show a large transverse production polarization at all values of xF and pT measured. These observations are compared with an NRQCD calculation that predicts a transverse polarization in bottomonium production arising from quark-antiquark fusion and gluon-gluon fusion diagrams.