A Measurement of the J/Psi Spin Alignment in CDF Run II Data

We present a measurement of the spin alignment of J/&psi mesons having rapidity |y| < 0.6 and 5 &le pT< 30 GeV/c using the J/&psi &rarr &mu+ &mu- decay channel. The analysis is performed using data from pp collisions at 1.96 TeV with an integrated luminosity of 800 pb-1 taken from June 2004 to February 2006 with the CDF II detector at the Fermilab Tevatron. Promptly-produced J/&psi mesons are isolated from those produced in heavy flavor decays by impact parameter selections on the two muon tracks. The analysis procedure is similar to that used in Run I, employing a template method to account for acceptance and trigger efficiency effects. We use experimentally-derived trigger efficiency funtions to produce the templates.

We measure the polarization &alphaB=-0.066 ± 0.050 for the B-decay events.
We find negative (longitudinal) polarization in the higher pT region for the prompt J/&psi events, in contrast to expectations from NRQCD.

A more detailed summary of the results can be found here: ps , pdf .
This result supersedes the previous measurement performed with 188 pb-1.

Recent theory prediction for the prompt J/&psi polarization [1]:
[1] V.A. Khoze, A.D. Martin, M.G. Ryskin, and W.J. Stirling, Eur. Phys. J. C 39, 163-171 (2005), hep-ph/0410020

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