2025/05/27 by Xin Liu, Liu, Xin, Hsiang-nan Li +3
Physics and Astronomy · #Particle physics theoretical and experimental studies #Quantum Chromodynamics and Particle Interactions #Atomic and Subatomic Physics Research
paper · pdf · doi:10.48550/arxiv.2505.20605
Motivated by the recent LHCb measurements of the ratios between the branching ratios (BRs), R_χc2/J/ψ ≡ \rm BR(Bc+ → χc2 π+)/\rm BR(Bc+ → J/ψπ+) and R_χc1/χc2 ≡ \rm BR(Bc+ → χc1 π+)/\rm BR(Bc+ → χc2 π+), we analyze the decays Bc+ → χcJ (P, V)+ in the improved perturbative QCD (iPQCD) formalism, where χcJ denotes the p-wave charmonia with J=0, 1, 2, and P (V) denotes the pseudoscalars π and K (the vectors ρ and K^*). Our results R_χc2/J/ψ = 0.32 ± 0.05 and R_χc1/χc2= 0.11 ± 0.01 at leading order in the strong coupling αs agree well with the data within uncertainties. The result R_χc0/J/ψ ≡ \rm BR(Bc+ → χc0 π+)/\rm BR(Bc+ → J/ψπ+) = 0.17 ± 0.02 is lower than 1.41+0.50-0.45 inferred by the Bc+ → χc0 π+ measurement. The large longitudinal polarization fractions imply that these components dominate the Bc+ → χc1,c2 ρ+ BRs. A peculiar constructive (destructive) interference between the twist-2 and twist-3 contributions is identified in the Bc+→ χc1 ρ+ (Bc+→ χc1 π+) mode, but not in the corresponding ones with χc0,c2 mesons. Inputting the BRs of the strong decays χc0,c2 → π+ π- / K+ K- and χcJ → π+π-(π+ π-/K+K-) reported by the BESIII Collaboration, we obtain those of Bc+ → χcJ (ρ, π)+ followed by secondary decay chains under the narrow-width approximation. All the above iPQCD predictions can be confronted by more precise experiments in the future to deepen our understanding of QCD dynamics in Bc→χcJ transitions.