Abstract
Exclusive quarkonium pair production in electron–positron collisions is studied in non-relativistic QCD. The obtained cross section for J/ψηc production in the leading order is confronted against the recent measurements by the Belle Collaboration at KEKB. It is shown that a large renormalization K-factor is necessary to explain the experimental data. We point out that the JPC=0−+ nature of the hadronic systems that are assigned to be ηc should be tested by the triple angular distributions in terms of the scattering angle, and, polar and azimuthal angles of J/ψ into leptons. We further study J/ψJ/ψ and ϒϒ productions at LEP energies. Although the axial–vector couplings of the Z-boson to charm and bottom quarks allow production of such pairs when one of them is polarized transversally and the other longitudinally, we find that the integrated luminosity at Z pole accumulated by LEP is not large enough to observe the exclusive pair production of quarkonium.
Highlights
IntroductionThe e+ + e− → J/ψ + ccprocess seemed to dominate the threshold region (z → 1) of the energy spectra of the differential cross section comparing to the COM process e++e− → J/ψ+g and colour-singlet process e+ + e− → J/ψ + gg, contrary to the theoretical expectation in [10, 11, 12, 13, 14]
Quarkonium production and decays have long been considered as an ideal means to investigate the bound-state formation in QCD
While the quarkonium physics has been studied for more than twenty years, the recent interest in the field has been focused on the colour-octet scenario [1] which was triggered by the high-pT J/ψ surplus production discovered by the CDF collaboration at the Tevatron in 1992 [2, 3, 4]
Summary
The e+ + e− → J/ψ + ccprocess seemed to dominate the threshold region (z → 1) of the energy spectra of the differential cross section comparing to the COM process e++e− → J/ψ+g and colour-singlet process e+ + e− → J/ψ + gg, contrary to the theoretical expectation in [10, 11, 12, 13, 14] In their second report (based on 41.8f b−1 data set) [15], the direct measurement of the e+ + e− → J/ψ + ccprocess is presented simultaneously and it is found that experimental result is about 10 times larger than the theoretical prediction for this process. Motivated by the observed large cross section of the J/ψ ηc production by Belle, we further consider the heavy quarkonium pair production at LEP energies For this purpose, we include the formulae for the Z intermediated processes.
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