Evidence ofϒ(1S)→J/ψ+χc1and sear

Abstract

Using data samples of 102 × 10 6 Υ(1S) and 158 × 10 6 Υ(2S) events collected with the Belle detector, a first experimental search has been made for double-charmonium production in the exclusive decays Υ(1S, 2S) → J/ψ(ψ ′ ) + X, where X = η c , χ cJ (J = 0, 1, 2), η c (2S), X(3940), and X(4160). No significant signal is observed in the spectra of the mass recoiling against the reconstructed J/ψ or ψ ′ except for the evidence of χ c1 production with a significance of 4.6σ for Υ(1S) → J/ψ + χ c1 . The measured branching fraction B(Υ(1S) → J/ψ + χ c1 ) is (3.90 ± 1.21(stat.) ± 0.23(syst.)) × 10 −6 . The 90% confidence level upper limits on the branching fractions of the other modes having a significance of less than 3σ are determined. These results are consistent with theoretical calculations using the nonrelativistic QCD factorization approach. [4][5][6][7][8][9]. Later the double-charmonium productions of J/ψX(3940) [10,11] and J/ψX(4160) [12] were observed in e + e − annihilation by Belle as well. Numerous theoretical investigations in the following years had attempted to alleviate this disquieting discrepancy, and it is now believed that one can achieve agreement within reasonable uncertainties when both the QCD radiative and relativistic corrections of the order of υ 2 (where υ is the quark relative velocity)are taken into account [13][14][15][16][17][18][19][20][21].Inspired by the unexpectedly high double-charmonium production in e + e − annihilation, interest has turned to the double-charmonium states produced in bottomonium decays. Several theoretical calculations have focused on these processes in perturbative QCD, e.g., η b → J/ψJ/ψ [22][23][24][25] and χ b0,1,2 → J/ψJ/ψ [26][27][28][29]. Experimentally, however, such studies are extremely sparse, apart from the recent searches for several channels of χ bJ into double charmonia for the first time by the Belle Collaboration [30]. The measurements are consistent with NRQCD predictions, though no significant signals are observed; it is reasonable to extend the search for double-charmonium production to the C-odd Υ decays. Compared with the Υ(4S) resonance with its rather broad width, the first three Υ resonances are so narrow that the resonant decay contributions dominate over the continuum ones. This provides a further opportunity to probe the potential properties of double-charmonium production at these Υ peaks.Comprehensive studies of the exclusive decay of Υ into a vector-plus-pseudoscalar charmonium[31], as well as the S-wave charmonium J/ψ plus the P-wave charmonium χ cJ (J = 0, 1, 2) [32] have been performed in the NRQCD factorization approach, where the contributions from the strong, electromagnetic, and radiative channels were considered and the strong decay was taken as dominant. The branching fractions are predicted to be of order 10 −6 for Υ(nS) → J/ψ(ψ ′ ) + η c (η c (2S)) (n = 1, 2, 3) [31]; for Υ → J/ψ + η c , in particular, the predicted branching fraction is consistent with the previous calculation of 1.7 × 10 −6 with only the three-gluon c...

Systematics of fully heavy tetraquarks

“…In the full-charm sector, the charmonium pair production had also been observed by the NA3 [28,29], D0 [30], LHCb [31] and Belle [32] collaborations. Very recently, the LHCb collaboration observed a narrow structure and a wide structure in the J/ψ-pair invariant mass spectrum in the range of 6.2 ∼ 7.2 GeV, which could be all-charm hadrons [33].…”

Higher-order QCD corrections to $Υ$ decay into double charmonia

“…The two uncertainties in the theoretical predictions are from the ambiguities of the heavy quark masses and renormalization scale. For comparison, we also juxtapose the Belle data [14] J/ψ + η c . The branching fraction for Υ → J/ψ + χ c1 is predicted to be 3.65 +4.99+0.12 −2.02−1.20 × 10 −6 , where the uncertainties are from the ambiguities of the charm/bottom mass and renormalization scale, which agrees perfectly with the Belle measurement (3.90 ± 1.21 ± 0.23) × 10 −6 .…”

“…It is worth noting that the theoretical prediction on the branching fraction of Υ → J/ψ + χ c1 based on NRQCD at leading order (LO) in α s [13] is larger than the experimental measurement [14]. More seriously, the dominant theoretical predictions are proportional to α 6 s , and thereby contaminated with strong renormalization scale dependence, which may usually be improved by radiative corrections.…”