$J/\psi$ and $\Upsilon$ Polarization in Hadronic Production Processes

Both charm and bottom quarks form nonrelativistic bound states analogous to positronium. The J/ψ and ψ(2S) charmonium states and the first three Ψ(nS) bottomonium states, all spin-triplet S-wave quarkonium states below open heavy-flavor thresholds, have relatively large branching ratios to e^−e^+ or μ^−μ^+ pairs. In hadron collisions, experiments measuring lepton pairs can determine polarization by using angular correlation techniques. The polarization, in turn, can be related theoretically to the production mechanism for the bound state. This review summarizes experimental studies with proton beams at fixed-target and colliding-beam accelerators, covering a center-of-mass energy range from 39 to 7,000 GeV for nucleon and antiproton targets. Analyses using various polarization frames and spin-quantization axes are described and results compared. A pattern emerges that connects experimental results over the whole energy span. The theoretical implications of the pattern are presented, and a set of new measurements is proposed.

Note:

28 pages, 5 figures; prepared for Volume 64 of the Annual Review of Nuclear and Particle Science

quarkonium
polarization
hadroproduction
review
p nucleon: interaction
anti-p p: interaction
quarkonium: hadroproduction
psi mesons: leptonic decay
upsilon mesons: leptonic decay
quarkonium: polarization

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J/ψJ/\psiJ/ψ and Υ\UpsilonΥ Polarization in Hadronic Production Processes

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$J/\psi$ and $\Upsilon$ Polarization in Hadronic Production Processes