QCD corrections to double J/psi production in e+e- annihilation at sqrt[s]=10.6 GeV

Optimized O(α_{s}^{2}) Correction to Exclusive Double-J/ψ Production at B Factories

The failure of observing the e^{+}e^{-}→J/ψJ/ψ events at B factories to date is often attributed to the significant negative order-α_{s} correction. In this work we compute the O(α_{s}^{2}) correction to this process for the first time. The magnitude of the next-to-next-to-leading order (NNLO) perturbative correction is substantially negative so that the standard nonrelativistic QCD prediction would suffer from an unphysical, negative cross section. This dilemma may be traced in the fact that the bulk contribution of the fixed-order radiative corrections stems from the perturbative corrections to the J/ψ decay constant. We thus implement an improved nonrelativistic QCD factorization framework, by decomposing the amplitude into the photon-fragmentation piece and the nonfragmentation piece. With the measured J/ψ decay constant as input, which amounts to resumming a specific class of radiative and relativistic corrections to all orders, the fragmentation-induced production rate can be predicted accurately and serves a benchmark prediction. The nonfragmentation type of the amplitude is then computed through NNLO in α_{s} and at lowest order in velocity. Both the O(α_{s}) and O(α_{s}^{2}) corrections in the interference term become positive and exhibit a decent convergence behavior. Our finest prediction is σ(e^{+}e^{-}→J/ψJ/ψ)=2.13_{-0.06}^{+0.30}  fb at sqrt[s]=10.58  GeV. With the projected integrated luminosity of 50  ab^{-1}, the prospect to observe this exclusive process at Belle 2 experiment appears to be bright.

Next-to-leading-order QCD corrections to e+e- -->J/psi gg at the B factories

We calculate the next-to-leading-order (NLO) QCD corrections to e;{+}e;{-}-->J/psi gg via color singlet J/psi(3S1) at the B factories. The result shows that the cross section is enhanced to 0.373 pb by a K factor (NLO/LO) of about 1.21. By considering its dependence on the charm quark mass and renormalization scale, the NLO cross section can range from 0.294 to 0.409 pb. Further including the psi;{'} feed-down, sigma[e;{+}e;{-}-->J/psi X(non-cc[over ])] is enhanced by another factor of about 1.29 and reach 0.482 pb. In addition, the momentum distributions of J/psi production and polarization are presented. Recent measurements from Belle agree well with our prediction for the cross section and momentum distribution. It is expected that this process can serve as a very good channel to clarify the J/psi polarization puzzle by performing further experimental measurements.

QCD corrections to e+e- -->J/psi+gg at B factories

In heavy quarkonium production, the measured ratio R_{cc[over ]}=sigma[J/psi+cc[over ]+X]/sigma[J/psi+X] at B factories is much larger than existing theoretical predictions. To clarify this discrepancy, in nonrelativistic QCD we find the next-to-leading-order (NLO) QCD correction to e;{+}e;{-}-->J/psi+gg can enhance the cross section by about 20%. Together with the calculated NLO result for e;{+}e;{-}-->J/psi+cc[over ], we show that the NLO corrections can significantly improve the fit to the ratio R_{cc[over ]}. The effects of leading logarithm resummation near the end point on the J/psi momentum distribution and total cross section are also considered. Comparison of the calculated cross section for e;{+}e;{-}-->J/psi+gg with the observed cross section for e;{+}e;{-}-->J/psi+non-(cc[over ]) is expected to provide unique information on the issue of color-octet contributions.

Next-to-leading-order QCD corrections to J/psi polarization at Tevatron and Large-Hadron-Collider energies

We calculate the next-to-leading-order QCD corrections to J/psi polarization at the Fermilab Tevatron and CERN Large Hadron Collider. Our results show that the J/psi polarization status drastically changes from transverse-polarization dominant at leading order to longitudinal-polarization dominant at next-to-leading order. Although the theoretical evaluation predicts a larger longitudinal polarization than the value measured at the Tevatron, it may provide a solution towards the previous large discrepancy for J/psi polarization between theoretical predication and experimental measurement.