RARE DILEPTONIC DECAYS OF Λ_bIN A QUARK MODEL

Abstract

<jats:p>Hadronic form factors for the rare weak transitions Λ<jats:sub>b</jats:sub>→ Λ<jats:sup>(*)</jats:sup>are calculated using a nonrelativistic quark model. The form factors are extracted in two ways. An analytic extraction using single-component wave functions (SCA) with the quark current being reduced to its nonrelativistic Pauli form is employed in the first method. In the second method, the form factors are extracted numerically using the full quark model wave function (MCN) with the full relativistic form of the quark current. Although there are differences between the two sets of form factors, both sets satisfy the relationships expected from the heavy quark effective theory (HQET). Differential decay rates, branching ratios (BRs) and forward–backward asymmetries (FBAs) are calculated for the dileptonic decays Λ<jats:sub>b</jats:sub>→ Λ<jats:sup>(*)</jats:sup>ℓ<jats:sup>+</jats:sup>ℓ<jats:sup>-</jats:sup>, for transitions to both ground state and excited daughter baryons. Inclusion of the long distance contributions from charmonium resonances significantly enhances the decay rates. In the MCN model the Λ(1600) mode is the dominant mode in the μ channel when charmonium resonances are considered; the Λ(1520) mode is also found to have a comparable BR to that of the ground state in the μ channel.</jats:p>

Differential branching fraction and angular analysis of Λ0 b → Λμ+μ− decays

“…Theoretical aspects of the Λ 0 b → Λµ + µ − decay have been considered both in the SM and in some of its extensions [3][4][5][6][7][8][9][10][11][12][13][14][15][16]. Although based on the same effective Hamiltonian as that for the corresponding mesonic transitions, the hadronic form factors for the Λ 0 b baryon case are less well-known due to the less stringent experimental constraints.…”

“…The decay has a non-trivial angular structure which, in the case of unpolarised Λ 0 b production, is described by the helicity angles of the muon and proton, the angle between the planes defined by the Λ decay products and the two muons, and the square of the dimuon invariant mass, q 2 . In theoretical investigations, the differential branching fraction, and forward-backward asymmetries for both the dilepton and the hadron systems of the decay, have received particular attention [3,11,[15][16][17]. Different treatments of form factors are used depending on the q 2 region and can be tested by comparing predictions with data as a function of q 2 .…”

Towards an assessment of the ATLAS data on the branching ratioΓ(Λb0→ψ(2S)Λ

“…The set of fit values lead to branching ratios within 0.1 deviation from 0.8. We mention that there have been a number of theoretical quark model calculations for the decay Λ b → Λ + J/ψ based on the factorization hypothesis [9]- [15] two of which we will return to when we present our numerical results.…”

“…7 we plot the dependence of the ratios R H and R Λ b on the dipole mass using an approximation where It is interesting to compare our results with the predictions of Refs. [14,15] who have conveniently supplied parametrizations of their model form factors. The predictions of both models [14,15] for the branching fraction B(Λ b → Λ + J/ψ) are close to our result.…”

“…[14,15] who have conveniently supplied parametrizations of their model form factors. The predictions of both models [14,15] for the branching fraction B(Λ b → Λ + J/ψ) are close to our result. However, the predictions for the branching fraction B(Λ b → Λ+ψ(2S)) considerably differ from our result leading to very different results on the branching ratio R Λ b .…”