Observation of the decay Λ b 0 → ψ(2S)pπ−

Abstract

The Λ0 b baryon is the isospin-singlet ground state of a bound system of a beauty quark and two light quarks. The high production rate of b quarks at the Large Hadron Collider (LHC) [1-5], along with the excellent mass resolution and hadron-identification capabilities of the LHCb detector, give access to a variety of decay channels of the Λ0 b baryon, including multibody, rare, charmless and semileptonic decays [6-25]. The high signal yield of the Λ0 b → J/ψpK− decay [15] facilitated a precise measurement of the Λ0 b lifetime [26], while the relatively low energy released in the Λ0 b→ ψ(2S)pK− and Λ0 b→ χcpK− decays allowed for precise measurements of the Λ0 b mass [16, 22]. A six-dimensional amplitude analysis of the Λ0 b → J/ψpK− decay resulted in the observation of the Pc(4380)+ and Pc(4450)+ pentaquark states decaying into the J/ψp final state [27]. Later, these states were confirmed using a model-independent technique [28]. Subsequently, an analysis of Cabibbo-suppressed Λ0 b → J/ψpπ − decays found evidence for contributions from the Pc(4380)+ and Pc(4450)+ pentaquarks and from the Zc(4200)− tetraquark [29].