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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In $$ {B}_c^{-} $$ B c − → J/ψ(→ μ+μ−)τ−$$ {\overline{\nu}}_{\tau } $$ ν ¯ τ decay, the three-momentum $$ {\boldsymbol{p}}_{\tau^{-}} $$ p τ − cannot be determined accurately due to the decay products of τ− inevitably include an undetected ντ. As a consequence, 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 $$ {B}_c^{-} $$ B c − → J/ψ(→ μ+μ−)τ−(→ π−ντ)$$ {\overline{\nu}}_{\tau } $$ ν ¯ τ , in which the three-momenta $$ {\boldsymbol{p}}_{\mu^{+}},{\boldsymbol{p}}_{\mu^{-}} $$ p μ + , p μ − , and $$ {\boldsymbol{p}}_{\pi^{-}} $$ p π − can be measured. The five-fold differential angular distribution containing all Lorentz structures of the new physics (NP) effective operators can be written in terms of twelve angular observables ℐi(q2, Eπ). Integrating over the energy of pion Eπ, we construct twelve normalized angular observables $$ {\hat{\mathrm{\mathcal{I}}}}_i $$ ℐ ̂ i (q2) and two lepton-flavor-universality ratios $$ R\left({P}_{L,T}^{J/\psi}\right) $$ R P L , T J / ψ (q2). Based on the Bc → J/ψ form factors calculated by the latest lattice QCD and sum rule, we predict the q2 distribution of all $$ {\hat{\mathrm{\mathcal{I}}}}_i $$ ℐ ̂ i and $$ R\left({P}_{L,T}^{J/\psi}\right) $$ R P L , T J / ψ both within the Standard Model and in eight NP benchmark points. We find that the benchmark BP2 (corresponding to the hypothesis of tensor operator) has the greatest effect on all ℐi and $$ R\left({P}_{L,T}^{J/\psi}\right) $$ R P L , T J / ψ , except $$ {\hat{\mathrm{\mathcal{I}}}}_5 $$ ℐ ̂ 5 . The ratios $$ R\left({P}_{L,T}^{J/\psi}\right) $$ R P L , T J / ψ are more sensitive to the NP with pseudo-scalar operators than the ℐi. Finally, we discuss the symmetries in the angular observables and present a model-independent method to determine the existence of tensor operators.

Section: Angular Observables I I (Q 2 )mentioning

confidence: 72%

Section: Jhep06(2021)075mentioning

confidence: 99%

Section: A the Calculation Of The Angular Distributionmentioning

confidence: 99%

“…The modified leptonic helicity amplitudes are L (λ,λ ) , which can be obtained directly from the appendix of ref. [80].…”

Section: A1 Definitions and Conventionsmentioning

confidence: 99%

“…The dimensionless factors induced in the calculation of V * → τ − (→ π − ν τ )ν τ are as follows [80] S…”

Section: A3 Dimensionless Factorsmentioning

confidence: 99%

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New physics in the angular distribution of $$ {B}_c^{-} $$ → J/ψ(→ μ+μ−)τ−(→ π−ντ)$$ {\overline{\nu}}_{\tau } $$ decay

et al. 2021

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Study of new physics effects in $$ {\overline{B}}_s\to {D}_s^{\left(\ast \right)}{\tau}^{-}{\overline{\nu}}_{\tau } $$ semileptonic decays using lattice QCD form factors and heavy quark effective theory

Penalva,

Flynn,

Hernández

et al. 2024

We benefit from the lattice QCD determination by the HPQCD of the Standard Model (SM) form factors for the $$ {\overline{B}}_s\to {D}_s $$ B ¯ s → D s [Phys. Rev. D101 (2020) 074513] and the SM and tensor ones for the $$ {\overline{B}}_s\to {D}_s^{\ast } $$ B ¯ s → D s ∗ (arXiv:2304.03137 [hep-lat]) semileptonic decays, and the heavy quark effective theory (HQET) relations for the analogous B → D(*) decays obtained by F.U. Bernlochner et al. in Phys. Rev. D95 (2017) 115008, to extract the leading and sub-leading Isgur-Wise functions for the $$ {\overline{B}}_s\to {D}_s^{\left(\ast \right)} $$ B ¯ s → D s ∗ decays. Further use of the HQET relations allows us to evaluate the corresponding scalar, pseudoscalar and tensor form factors needed for a phenomenological study of new physics (NP) effects on the $$ {\overline{B}}_s\to {D}_s^{\left(\ast \right)} $$ B ¯ s → D s ∗ semileptonic decay. At present, the experimental values for the ratios $$ {\mathcal{R}}_{D^{\left(\ast \right)}}=\Gamma \left[\overline{B}\to {D}^{\left(\ast \right)}{\tau}^{-}{\overline{\nu}}_{\tau}\left]/\Gamma \right[\overline{B}\to {D}^{\left(\ast \right)}{e}^{-}\left({\mu}^{-}\right){\overline{\nu}}_{e\left(\mu \right)}\right] $$ R D ∗ = Γ B ¯ → D ∗ τ − ν ¯ τ / Γ B ¯ → D ∗ e − μ − ν ¯ e μ are the best signal in favor of lepton flavor universality violation (LFUV) seen in charged current (CC) b → c decays. In this work we conduct a study of NP effects on the $$ {\overline{B}}_s\to {D}_s^{\left(\ast \right)}{\tau}^{-}{\overline{\nu}}_{\tau } $$ B ¯ s → D s ∗ τ − ν ¯ τ semileptonic decays by comparing tau spin, angular and spin-angular asymmetry distributions obtained within the SM and three different NP scenarios. As expected from SU(3) light-flavor symmetry, we get results close to the ones found in a similar analysis of the $$ \overline{B}\to {D}^{\left(\ast \right)} $$ B ¯ → D ∗ case. The measurement of the $$ {\overline{B}}_s\to {D}_s^{\left(\ast \right)}\ell {\overline{\nu}}_{\ell } $$ B ¯ s → D s ∗ ℓ ν ¯ ℓ semileptonic decays, which is within reach of present experiments, could then be of relevance in helping to establish or rule out LFUV in CC b → c transitions.

Visible energy and angular distributions of the charged particle from the τ −decay in $$ b\to c\tau \left(\mu {\overline{\nu}}_{\mu }{\nu}_{\tau },{\pi \nu}_{\tau },{\rho \nu}_{\tau}\right){\overline{\nu}}_{\tau } $$ reactions

Penalva

Hernández

Nieves

2022

We study the d2Γd/(dωd cos θd), dΓd/d cos θd and dΓd/dEd distributions, which are defined in terms of the visible energy and polar angle of the charged particle from the τ −decay in $$ b\to c\tau \left(\mu {\overline{\nu}}_{\mu }{\nu}_{\tau },{\pi \nu}_{\tau },{\rho \nu}_{\tau}\right){\overline{\nu}}_{\tau } $$ b → cτ μ ν ¯ μ ν τ πν τ ρν τ ν ¯ τ reactions. These differential decay widths could be measured in the near future with certain precision. The first two contain information on the transverse tau-spin, tau-angular and tau-angular-spin asymmetries of the $$ {H}_b\to {H}_c\tau {\overline{\nu}}_{\tau } $$ H b → H c τ ν ¯ τ parent decay and, from a dynamical point of view, they are richer than the commonly used one, d2Γd/(dωdEd), since the latter only depends on the tau longitudinal polarization. We pay attention to the deviations with respect to the predictions of the standard model (SM) for these new observables, considering new physics (NP) operators constructed using both right- and left-handed neutrino fields, within an effective field-theory approach. We present results for $$ {\Lambda}_b\to {\Lambda}_c\tau \left(\mu {\overline{\nu}}_{\mu }{\nu}_{\tau },{\pi \nu}_{\tau },{\rho \nu}_{\tau}\right){\overline{\nu}}_{\tau } $$ Λ b → Λ c τ μ ν ¯ μ ν τ πν τ ρν τ ν ¯ τ and $$ \overline{B}\to {D}^{\left(\ast \right)}\tau \left(\mu {\overline{\nu}}_{\mu }{\nu}_{\tau },{\pi \nu}_{\tau },{\rho \nu}_{\tau}\right){\overline{\nu}}_{\tau } $$ B ¯ → D ∗ τ μ ν ¯ μ ν τ πν τ ρν τ ν ¯ τ sequential decays and discuss their use to disentangle between different NP models. In this respect, we show that dΓd/d cos θd, which should be measured with sufficiently good statistics, becomes quite useful, especially in the τ → πντ mode. The study carried out in this work could be of special relevance due to the recent LHCb measurement of the lepton flavor universality ratio $$ {\mathrm{\mathcal{R}}}_{\Lambda_c} $$ ℛ Λ c in agreement with the SM. The experiment identified the τ using its hadron decay into π−π+π−ντ, and this result for $$ {\mathrm{\mathcal{R}}}_{\Lambda_c} $$ ℛ Λ c , which is in conflict with the phenomenology from the b-meson sector, needs confirmation from other tau reconstruction channels.