Abstract
LHCb has recently reported the observation of exotic structures in the J /ψp channel, in Λb → J /ψ K − p decay, which we discuss here and refer to as charmoniumpentaquarkstates. The data sample corresponds to an integrated luminosity of 3.0 fb−1 acquired with the LHCb detector from 7 and 8 TeV pp collisions. An amplitude analysisof the three-body final state reproduces the two-body mass and angular distributions. Toobtain a satisfactory fit of the structures seen in the J /ψp mass spectrum, it is necessaryto include two Breit-Wigner amplitudes that each describe a resonant state. Details aregiven on the significance, and prefered quantum numbers, of these two resonances.
Highlights
LHCb has recently reported the observation of exotic structures in the J/ψp channel, in Λb → J/ψK− p decay, which we discuss here and refer to as charmoniumpentaquark states
The K− p system must form a vertex with χ2 < 16, as must the two muons from
As structures are seen in both K− p and J/ψp mass distributions a full amplitude analysis is performed, using the available angular variables in addition to the mass distributions, in order to determine the resonances present
Summary
The two interfering processes shown in Fig. Λ∗ → K− p and Λ0b → P+c K−, P+c → J/ψp, with. The helicity couplings can be further expressed in terms of LS couplings (BLS ), when the decay proceeds with orbital angular momentum L and total spin S of the A and B system. The helicity couplings are expressed in terms of LS couplings (BLS ), where L is the orbital angular momentum in the decay, and S is the total spin of A plus B. The orbital angular momentum between the decay products of Λ0b is denoted as LΛX0b. The matrix element given by Eq 2 is a six dimensional function of mKp and Ω and depends on the fit parameters ω, which represent independent helicity or LS couplings, and masses and widths of resonances M = M(mKp, Ω | ω). After accounting for the selection efficiency, the probability density function (PDF) described in Section 2 is obtained
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