Angular analysis of Λb→ Λc(→ Λπ) ℓ$$ \overline{\nu} $$

Abstract

We revisit the decay Λ 0 b → Λ + c −ν (= e, µ, τ) with a subsequent two-body decay Λ + c → Λ 0 π + in the Standard Model and in generic New Physics models. The decay's joint four-differential angular distribution can be expressed in terms of ten angular observables, assuming negligible polarization of the initial Λ b state. We present compact analytical results for all angular observables, which enables us to discuss their possible New Physics reach. We find that the decay at hand probes more and complementary independent combinations of Wilson coefficients compared to its mesonic counter parts B → D (*) −ν. Our result for the angular distribution disagrees with some of the results on scalar-vector interference terms in the literature. We provide numerical estimates for all angular observables based on lattice QCD results for the Λ b → Λ c form factors and account for a recent measurement of the parity-violating parameter in Λ + c → Λ 0 π + decays by BESIII. A numerical implementation of our results is made publicly available as part of the EOS software.

Inclusive semileptonic Λb decays in the Standard Model and beyond

“…However, a sizable longitudinal Λ b polarization is expected for b quarks produced in Z and top quark decays, as shown by the measurements at LEP [35][36][37]. For this reason, the effects beyond the Standard Model (BSM) in the polarized case have been scrutinized for the exclusive Λ b → Λ c −ν modes [38][39][40][41], in addition to the case of unpolarized baryon [42][43][44][45][46][47]. The plan of our study is as follows.…”

The measurable angular distribution of $$ {\Lambda}_b^0\to {\Lambda}_c^{+}\left(\to {\Lambda}^0{\pi}^{+}\right){\tau}^{-}\left(\to {\pi}^{-}{v}_{\tau}\right){\overline{v}}_{\tau } $$ decay

“…[16] as our BP7 scenario BP7: Next, we should discuss the entire set of angular observables, including the functions K i (q 2 ) and the numbers K i , within the SM and in these NP scenarios respectively. For angular observables K i with i = 2ss, 2cc, 2c, 3sc, 3s, 4sc, and 4s, we factor out the asymmetry parameter α Λc = −0.82 ± 0.09 [60], because it can bring great uncertainty to these observables, thus interfering with the emergence of the NP effects. 2.…”

“…The large production cross section of Λ 0 b on the LHC and the clear Λ 0 b → Λ + c transition form factors [46][47][48][49][50][51] make Λ 0 b → Λ + c τ −ν τ decay a good candidate to complement theB → D ( * ) τ −ν τ decays. In the previous studies of the NP contributions in Λ 0 b → Λ + c τ −ν τ decay [14,[52][53][54][55][56][57], especially in some studies considering the angular distribution of the cascade decay Λ 0 b → Λ + c (→ Λ 0 π + )τ −ν τ [58][59][60][61], the information of the polar and azimuthal angles (θ τ , φ τ ) of the final-state particle τ − may be used. However, as pointed out in ref.…”

“…[47], which has also been checked by refs. [14,60]. Since we have integrated over all the leptonside kinematic parameters, the observables constructed above are not affected by τ decay dynamics, so they are also applicable to light leptons = µ, e (Necessary replacement m τ → m and removal of factor B(τ → π − ν τ ) are required).…”

Relations between b → cτν decay modes in scalar models

“…s τ ν, B c → J/ψτ ν, B c → η c τ ν, as well as baryonic decays [19][20][21][22][23][24][25][26]. A 1.8σ-tension has been seen in B c → J/ψτ ν decays R(J/ψ) = 0.71 ± 0.17 ± 0.18 , [27] (1.7)…”