Search

For J/ψ pair production at hadron colliders, we present the full next-to-leading order (NLO) calculations with the color-singlet channel in nonrelativistic QCD. We find that the NLO result can reasonably well describe the LHCb measured cross section, but exhibits very different behaviors from the CMS data in the transverse momentum distribution and mass distribution of the J/ψ pair. Moreover, by adding contributions of gluon fragmentation and quark fragmentation, which occur at even higher order in αs, it is still unable to reduce the big differences. In particular, the observed flat distribution in the large invariant mass region is hard to explain. New processes or mechanisms are needed to understand the CMS data for J/ψ pair production. [ABSTRACT FROM AUTHOR]

We investigate the ratio of the branching fractions of the molecular candidates decaying into the ground and radially excited states within the quark-interchange model. Our numerical results suggest that these molecular candidates are more likely to decay into the radially excited states than into ground states. In particular, the ratio Γ[Zc(4430) πψ(2S)]/Γ[Zc(4430) πJ/ψ]~ 9.9 is close to the experimental measurement, which supports the interpretation of Zc(4430) as the DD*(2S) molecular state. The ratios of the branching fractions of Zb(10610) and Zb(10650) to πϒ(2S,3S) and πϒ(1S) agrees very well with the Belle Collaboration's measurement. We also predict the similar ratios for Zc(3900), Zc(4020), RZc(3900) ≈ 1.4, and RZc(4020) ≈ 4.8. Hopefully, the πψ(2S) mode and the ratios RZc(3900) and RZc(4020) will be measured by the BESIII and Belle collaborations in the near future, which shall be very helpful for understanding the underlying dynamics of these exotic states. [ABSTRACT FROM AUTHOR]