Heavy Quark Fragmentation to Polarised Quarkonium

Abstract

We calculate the polarisation of $\psi$'s and ${\rm Y}$'s produced by the fragmentation of heavy quarks. We find that fragmentation to transversely aligned quarkonium is slightly enhanced relative to longitudinally polarised. This net alignment corresponds to a $\sim 5\%$ asymmetry in the angular distribution of leptons produced in the subsequent decay of the quarkonium. We point out that the leading gluon contribution to $\psi$ and ${\rm Y}$ production arises from the evolution of the charm quark fragmentation function, rather than from direct gluon fragmentation.

Comments: 8 pages, 1 figure included, uses harvmac.tex and epsf.tex, UCSD/PTH 93-06, CALT-68-1864, SLAC-PUB-6175