J/psi and Upsilon Polarization in Hadronic Production Processes

Abstract

Both charm and bottom quarks form nonrelativistic bound states analogous to positronium. The J/psi and psi(2S) charmonium states and the first three Upsilon(nS) bottomonium states, all spin-triplet S-wave quarkonium states below open-heavy-flavor thresholds, have relatively large branching ratios to e- e+ or mu- mu+ 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 7000 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.

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

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Cited by in corpus (7)

• $J/\psi$ production and polarization within a jet
• Measurement of the ${\rm Y}$ polarizations in $pp$ collisions at $\sqrt{s}$=7 and 8TeV
• Fragmentation functions of polarized heavy quarkonium
• On the Rotational Invariance and Non-Invariance of Lepton Angular Distributions in Drell-Yan and Quarkonium Production
• $J/\psi$ and $\psi$(2S) polarization in proton-proton collisions at energies available at the CERN Large Hadron Collider using PYTHIA8
• Quarkonium production and polarization in pp collisions with the CMS detector
• The Hadronization Impact on $J/\psi$ Energy Correlators: A Pythia8 Study from Partonic to Hadronic Observables