Λ b decays into Λc∗ℓν¯ℓ and Λc∗ π- [Λc∗=Λc(2595) and Λ c (2625)] and heavy quark spin symmetry

We study the implications for Λb→Λ∗cℓν¯ℓ and Λb→Λ∗cπ− [Λ∗c=Λc(2595) and Λc(2625)] decays that can be deduced from heavy quark spin symmetry (HQSS). Identifying the odd parity Λc(2595) and Λc(2625) resonances as HQSS partners, with total angular momentum–parity jPq=1− for the light degrees of freedom, we find that the ratios Γ(Λb→Λc(2595)π−)/Γ(Λb→Λc(2625)π−) and Γ(Λb→Λc(2595)ℓν¯ℓ)/Γ(Λb→Λc(2625)ℓν¯ℓ) agree, within errors, with the experimental values given in the Review of Particle Physics. We discuss how future, and more precise, measurements of the above branching fractions could be used to shed light into the inner HQSS structure of the narrow Λc(2595) odd-parity resonance. Namely, we show that such studies would constrain the existence of a sizable jPq=0− component in its wave-function, and/or of a two-pole pattern, in analogy to the case of the similar Λ(1405) resonance in the strange sector, as suggested by most of the approaches that describe the Λc(2595) as a hadron molecule. We also investigate the lepton flavor universality ratios R[Λ∗c]=B(Λb→Λ∗cτν¯τ)/B(Λb→Λ∗cμν¯μ), and discuss how R[Λc(2595)] may be affected by a new source of potentially large systematic errors if there are two Λc(2595) poles.This research has been supported by the Spanish Ministerio de Ciencia, Innovación y Universidades and European FEDER funds under Contracts FIS2017-84038-C2-1-P and SEV-2014-0398. S. Sakai acknowledges the support by NSFC and DFG through funds provided to the Sino-German CRC110 “Symmetries and the Emergence of Structure in QCD” (NSFC Grant No. 11621131001), by the NSFC (Grant Nos. 11747601 and 11835015), by the CAS Key Research Program of Frontier Sciences (Grant No. QYZDB-SSW-SYS013), by the CAS Key Research Program (Grant No. XDPB09) and by the CAS President’s International Fellowship Initiative (PIFI) (No. 2019PM0108).Peer reviewe