Further tests of lepton flavor universality from the charged lepton energy distribution in 
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 semileptonic decays: The case of 
<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msub><mml:mi mathvariant="normal">Λ</mml:mi><mml:mi>b</mml:mi></mml:msub><mml:mo stretchy="false">→</mml:mo><mml:msub><mml:mi mathvariant="normal">Λ

Penalva, Neus; Hernández, E.; Nieves, J.

doi:10.1103/physrevd.100.113007

“…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.…”

Section: Introductionmentioning

confidence: 99%

Inclusive semileptonic Λb decays in the Standard Model and beyond

Colangelo

¹

,

Fazio

²

,

Loparco

³

2020

J. High Energ. Phys.

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Inclusive semileptonic decays of beauty baryons are studied using the heavy quark expansion to $$ \mathcal{O}\left(1/{m}_b^3\right) $$ O 1 / m b 3 , at leading order in αs. The case of a polarized decaying baryon is examined, with reference to Λb. An extension of the Standard Model effective Hamiltonian inducing b → $$ U\mathrm{\ell}{\overline{\nu}}_{\mathrm{\ell}} $$ U ℓ ν ¯ ℓ transitions (U = u, c and ℓ = e, μ, τ) is considered, which comprises the full set of D=6 semileptonic operators with left-handed neutrinos. The effects of the new operators in several observables are described.

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“…Quite remarkably, the coefficients of the quadratic energy dependence A 2 (q 2 ) and A P 2 (q 2 ) depend only on q 2 and not on the mass m e of the lepton [18]. For these two coefficients one finds…”

Section: Electron Energy Distributionsmentioning

confidence: 96%

“…In the following we therefore assume that the form factors F V /A i are relatively real and shall not further discuss the T -odd observables. It is convenient and by now common practise to rewrite the angular decay distribution (18) in terms of the three Legendre polynomials P 0 (cos θ) = 1, P 1 (cos θ) = cos θ and P 2 (cos θ) = (3 cos 2 θ − 1)/2. One obtains…”

Section: Four-fold Angular Decay Distributionmentioning

confidence: 99%

“…We have also listed the corresponding range of √ δ e which determines the flip suppression for the transverse polarization of the electron to be discussed later on. The total rate as well as the partial rates vanish at threshold q 2 = m 2 e (maximal recoil) and at zero recoil q 2 = (M n − M p ) 2 due to the overall kinematical factors (q 2 − m 2 e ) 2 and p ∼ ((M n − M p ) 2 − q 2 ) 1/2 in the rate expression (18). At zero recoil one has dΓ hf /dΓ nf = (1…”

Section: Unpolarized Neutron Decaysmentioning

confidence: 99%

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A new angle on an old problem: helicity approach to neutron beta decay in the Standard Model

Groote

¹

,

Körner

²

,

Melić

³

2019

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We elaborate on the dichotomy between the description of the semileptonic decays of heavy hadrons on the one hand and the semileptonic decays of light hadrons such as neutron β decays on the other hand. For example, almost without exception the semileptonic decays of heavy baryons are described in cascade fashion as a sequence of two two-body decays B1 → B2 + W off−shell and W off−shell → ℓ+ν ℓ whereas neutron β decays are analyzed as true three-body decays n → p+e − +νe. Within the cascade approach it is possible to define a set of seven angular observables for polarized neutron β decays as well as the longitudinal, transverse and normal polarization of the decay electron. We determine the dependence of the observables on the usual vector and axial vector form factors. In order to be able to assess the importance of recoil corrections we expand the rate and the q 2 averages of the observables up to NLO and NNLO in the recoil parameter δ = (Mn − Mp)/(Mn + Mp) = 0.689 · 10 −3 . Remarkably, we find that the rate and three of the four parity conserving polarization observables that we analyze are protected from NLO recoil corrections when the second class current contributions are set to zero.

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“…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.…”

Section: Jhep02(2021)183mentioning

confidence: 99%

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

Hu

¹

,

Li

²

,

Yang

³

et al. 2021

J. High Energ. Phys.

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In $$ {\Lambda}_b^0\to {\Lambda}_c^{+}\left(\to {\Lambda}^0{\pi}^{+}\right){\tau}^{-}{\overline{v}}_{\tau } $$ Λ b 0 → Λ c + → Λ 0 π + τ − v ¯ τ decay, the solid angle of the final-state particle τ− cannot be determined precisely since the decay products of the τ− include an undetected ντ. Therefore, the angular distribution of this decay cannot be measured. In this work, we construct a measurable angular distribution by considering the subsequent decay τ−→ π−ντ. The full cascade decay is $$ {\Lambda}_b^0\to {\Lambda}_c^{+}\left(\to {\Lambda}^0{\pi}^{+}\right){\tau}^{-}\left(\to {\pi}^{-}{v}_{\tau}\right){\overline{v}}_{\tau } $$ Λ b 0 → Λ c + → Λ 0 π + τ − → π − v τ v ¯ τ . The three-momenta of the final-state particles Λ0, π+, and π− can be measured. Considering all Lorentz structures of the new physics (NP) effective operators and an unpolarized initial Λb state, the five-fold differential angular distribution can be expressed in terms of ten angular observables $$ {\mathcal{K}}_i\left({q}^2,{E}_{\pi}\right) $$ K i q 2 E π . By integrating over some of the five kinematic parameters, we define a number of observables, such as the Λc spin polarization $$ {P}_{\Lambda_c}\left({q}^2\right) $$ P Λ c q 2 and the forward-backward asymmetry of π− meson AFB(q2), both of which can be represented by the angular observables $$ {\hat{\mathcal{K}}}_i\left({q}^2\right) $$ K ̂ i q 2 . We provide numerical results for the entire set of the angular observables $$ {\hat{\mathcal{K}}}_i\left({q}^2\right) $$ K ̂ i q 2 and $$ {\hat{\mathcal{K}}}_i $$ K ̂ i both within the Standard Model and in some NP scenarios, which are a variety of best-fit solutions in seven different NP hypotheses. We find that the NP which can resolve the anomalies in $$ \overline{B}\to {D}^{\left(\ast \right)}{\tau}^{-}{\overline{v}}_{\tau } $$ B ¯ → D ∗ τ − v ¯ τ decays has obvious effects on the angular observables $$ {\hat{\mathcal{K}}}_i\left({q}^2\right) $$ K ̂ i q 2 , except $$ {\hat{\mathcal{K}}}_{1 ss}\left({q}^2\right) $$ K ̂ 1 ss q 2 and $$ {\hat{\mathcal{K}}}_{1 cc}\left({q}^2\right) $$ K ̂ 1 cc q 2 .

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Further tests of lepton flavor universality from the charged lepton energy distribution in b→c semileptonic decays: The case of Λb→Λ

Cited by 32 publications

References 36 publications

Inclusive semileptonic Λb decays in the Standard Model and beyond

Inclusive semileptonic Λb decays in the Standard Model and beyond

A new angle on an old problem: helicity approach to neutron beta decay in the Standard Model

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

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