Eliecer Hernández

Universidad de Salamanca

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Universidad de Salamanca

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Eliecer Hernández has a total of 86 co-authors. Here are the top co-authors by number of shared publications:

Juan Nieves
Instituto de Fisica Corpuscular
65 shared publications
Conrado Albertus
Universidad de Salamanca
23 shared publications
E. Oset
Centro Mixto Universidad de Valencia-CSIC, Institutos de Investigación de Paterna
16 shared publications
Manuel Jose Vicente Vacas
Departamento de Física Teorica and Instituto de Fisica Corpuscular (IFIC), Centro Mixto UVEG-CSIC, Valencia E-46071, Spain
13 shared publications
Neus Penalva
Instituto de Física Corpuscular (centro mixto CSIC-UV), Institutos de Investigación de Paterna, Paterna, Spain
11 shared publications
Alfons J. Buchmann
Institute for Theoretical Physics University of Tübingen D-72076 Tübingen Germany
10 shared publications

Latest Publications

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- 4 November 2026
- Published by American Physical Society (APS) in Physical Review D
Erratum: Probing new physics and C P violation in ν τ n → Λ c τ − ( π − ν τ ) and ν ¯ τ p → Λ τ ...
by E. Hernández, J. Nieves, J. E. Sobczyk
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- 4 November 2026
- Published by American Physical Society (APS) in Physical Review D
Open Access
Erratum: Probing new physics and C P violation in ν τ n → Λ c τ − ( π − ν τ ) and ν ¯ τ p → Λ τ ...
by E. Hernández, J. Nieves, J. E. Sobczyk
Open Access
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- 5 May 2026
- Published by American Physical Society (APS) in Physical Review D
Probing new physics and C P violation in ν τ n → Λ c τ − ( π − ν τ ) and ν ¯ τ p → Λ τ + ( π + ν ¯ τ )
by E. Hernández, J. Nieves, J. E. Sobczyk
We study the processes ν τ n → Λ c τ − ( π − ν τ ) and ν ¯ τ p → Λ τ + ( π + ν ¯ τ ) , with particular emphasis on the pion energy and angular distributions, as a possible signal for lepton flavor universality violation, and in general of physics beyond the Standard Model (SM), as well as a sensitive probe of the τ polarization vector. We work within an effective low-energy extension of the SM with all dimension-six four-fermion operators. In this framework, complex Wilson coefficients which encode new physics can generate C P -violating contributions. We propose an observable that provides a genuine C P -odd signal due to its sensitivity to particular transverse components of the τ polarization vector. Namely, we show that the asymmetry in the azimuthal-angle distribution of the pion in the decay τ ± → π ± ν τ constitutes a smoking-gun prediction of such a beyond the SM scenario. We estimate the strength of this effect extrapolating nucleon-hyperon form factors recently obtained from lattice QCD calculations.
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- 5 May 2026
- Published by American Physical Society (APS) in Physical Review D
Open Access
Probing new physics and C P violation in ν τ n → Λ c τ − ( π − ν τ ) and ν ¯ τ p → Λ τ + ( π + ν ¯ τ )
by E. Hernández, J. Nieves, J. E. Sobczyk
We study the processes ν τ n → Λ c τ − ( π − ν τ ) and ν ¯ τ p → Λ τ + ( π + ν ¯ τ ) , with particular emphasis on the pion energy and angular distributions, as a possible signal for lepton flavor universality violation, and in general of physics beyond the Standard Model (SM), as well as a sensitive probe of the τ polarization vector. We work within an effective low-energy extension of the SM with all dimension-six four-fermion operators. In this framework, complex Wilson coefficients which encode new physics can generate C P -violating contributions. We propose an observable that provides a genuine C P -odd signal due to its sensitivity to particular transverse components of the τ polarization vector. Namely, we show that the asymmetry in the azimuthal-angle distribution of the pion in the decay τ ± → π ± ν τ constitutes a smoking-gun prediction of such a beyond the SM scenario. We estimate the strength of this effect extrapolating nucleon-hyperon form factors recently obtained from lattice QCD calculations.
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Cited by 2
- 22 September 2025
- Published by American Physical Society (APS) in Physical Review D
Inclusive quasielastic neutrino and antineutrino scattering off nuclei within the Standard Model and beyond
by E. Hernández, J. Nieves, J. E. Sobczyk
We derive fully general expressions for the inclusive (anti-)neutrino-induced nuclear quasielastic production of a strange or charmed baryon Y , considering all dimension-six new-physics operators relevant to the semileptonic q → q ′ ℓ ν ℓ transition with both left- and right-handed neutrino fields. We illustrate the formalism by applying it to the Λ c production in neutrino-nucleus scattering. The nuclear response is computed using a state-of-the-art spectral function, based on realistic nuclear many-body wave functions obtained via the coupled-cluster method and a nuclear Hamiltonian derived from chiral effective field theory. We also highlight the role played by the final state interactions between the produced Y hyperon and the residual nuclear system, which can obscure potential new physics signals in this (anti-)neutrino–nucleus reaction. Our results improve upon previous studies that neglected nuclear corrections and uncertainties—effects we show to be comparable to, or even larger than, those expected from new physics.
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- 22 September 2025
- Published by American Physical Society (APS) in Physical Review D
Open Access
Inclusive quasielastic neutrino and antineutrino scattering off nuclei within the Standard Model and beyond
by E. Hernández, J. Nieves, J. E. Sobczyk
We derive fully general expressions for the inclusive (anti-)neutrino-induced nuclear quasielastic production of a strange or charmed baryon Y , considering all dimension-six new-physics operators relevant to the semileptonic q → q ′ ℓ ν ℓ transition with both left- and right-handed neutrino fields. We illustrate the formalism by applying it to the Λ c production in neutrino-nucleus scattering. The nuclear response is computed using a state-of-the-art spectral function, based on realistic nuclear many-body wave functions obtained via the coupled-cluster method and a nuclear Hamiltonian derived from chiral effective field theory. We also highlight the role played by the final state interactions between the produced Y hyperon and the residual nuclear system, which can obscure potential new physics signals in this (anti-)neutrino–nucleus reaction. Our results improve upon previous studies that neglected nuclear corrections and uncertainties—effects we show to be comparable to, or even larger than, those expected from new physics.
Cited by 2
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Cited by 7
- 18 October 2024
- Published by Springer Nature in Journal of High Energy Physics
The Λc → Λ ℓ+νℓ weak decay including new physics
by Fernando Alvarado, Luis Alvarez-Ruso, Eliecer Hernández, Juan Nieves, Neus Penalva
We investigate the Λ_c → Λℓ⁺ν_ℓ decay with a focus on potential new physics (NP) effects in the ℓ = μ channel. We employ an effective Hamiltonian within the framework of the Standard Model Effective Field Theory (SMEFT) to consider generalized dimension-6 semileptonic c → s operators of scalar, pseudoscalar, vector, axial-vector and tensor types. We rely on Lattice QCD (LQCD) for the hadronic transition form factors, using heavy quark spin symmetry (HQSS) to determine those that have not yet been obtained on the lattice. Uncertainties due to the truncation of the NP Hamiltonian and different implementations of HQSS are taken into account. As a result, we unravel the NP discovery potential of the Λ_c → Λ semileptonic decay in different observables. Our findings indicate high sensitivity to NP in lepton flavour universality ratios, probing multi-TeV scales in some cases. On the theoretical side, we identify LQCD uncertainties in axial and vector form factors as critical for improving NP sensitivity, alongside better SMEFT uncertainty estimations.
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- 18 October 2024
- Published by Springer Nature in Journal of High Energy Physics
Open Access
The Λc → Λ ℓ+νℓ weak decay including new physics
by Fernando Alvarado, Luis Alvarez-Ruso, Eliecer Hernández, Juan Nieves, Neus Penalva
We investigate the Λ_c → Λℓ⁺ν_ℓ decay with a focus on potential new physics (NP) effects in the ℓ = μ channel. We employ an effective Hamiltonian within the framework of the Standard Model Effective Field Theory (SMEFT) to consider generalized dimension-6 semileptonic c → s operators of scalar, pseudoscalar, vector, axial-vector and tensor types. We rely on Lattice QCD (LQCD) for the hadronic transition form factors, using heavy quark spin symmetry (HQSS) to determine those that have not yet been obtained on the lattice. Uncertainties due to the truncation of the NP Hamiltonian and different implementations of HQSS are taken into account. As a result, we unravel the NP discovery potential of the Λ_c → Λ semileptonic decay in different observables. Our findings indicate high sensitivity to NP in lepton flavour universality ratios, probing multi-TeV scales in some cases. On the theoretical side, we identify LQCD uncertainties in axial and vector form factors as critical for improving NP sensitivity, alongside better SMEFT uncertainty estimations.
Cited by 7
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Cited by 8
- 25 January 2024
- Published by Springer Nature in Journal of High Energy Physics
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
by Neus Penalva, Jonathan M. Flynn, Eliecer Hernández, Juan Nieves
We benefit from the lattice QCD determination by the HPQCD of the Standard Model (SM) form factors for the $$ {\overline{B}}_s\to {D}_s $$ ${\bar{B}}_{s} \to D_{s}$ [Phys. Rev. D 101 (2020) 074513] and the SM and tensor ones for the $$ {\overline{B}}_s\to {D}_s^{\ast } $$ ${\bar{B}}_{s} \to D_{s}^{*}$ (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. D 95 (2017) 115008, to extract the leading and sub-leading Isgur-Wise functions for the $$ {\overline{B}}_s\to {D}_s^{\left(\ast \right)} $$ ${\bar{B}}_{s} \to D_{s}^{(*)}$ 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 $$ {\overline{B}}_s\to {D}_s^{\left(\ast \right)} $$ ${\bar{B}}_{s} \to D_{s}^{(*)}$ semileptonic decay. At present, the experimental values for the ratios $$ {\mathcal{R}}_{D^{\left(\ast \right)}}=\Gamma \left[\overline{B}\to {D}^{\left(\ast \right)}{\tau}^{-}{\overline{\nu}}_{\tau}\left]/\Gamma \right[\overline{B}\to {D}^{\left(\ast \right)}{e}^{-}\left({\mu}^{-}\right){\overline{\nu}}_{e\left(\mu \right)}\right] $$ $R_{D^{(*)}} = Γ (\bar{B} \to D^{(*)} τ^{-} {\bar{ν}}_{τ} (/ Γ) \bar{B} \to D^{(*)} e^{-} (μ^{-}) {\bar{ν}}_{e (μ)})$ 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 $$ {\overline{B}}_s\to {D}_s^{\left(\ast \right)}{\tau}^{-}{\overline{\nu}}_{\tau } $$ ${\bar{B}}_{s} \to D_{s}^{(*)} τ^{-} {\bar{ν}}_{τ}$ 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 $$ \overline{B}\to {D}^{\left(\ast \right)} $$ $\bar{B} \to D^{(*)}$ case. The measurement of the $$ {\overline{B}}_s\to {D}_s^{\left(\ast \right)}\ell {\overline{\nu}}_{\ell } $$ ${\bar{B}}_{s} \to D_{s}^{(*)} ℓ {\bar{ν}}_{ℓ}$ 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.
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- 25 January 2024
- Published by Springer Nature in Journal of High Energy Physics
Open Access
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
by Neus Penalva, Jonathan M. Flynn, Eliecer Hernández, Juan Nieves
We benefit from the lattice QCD determination by the HPQCD of the Standard Model (SM) form factors for the $$ {\overline{B}}_s\to {D}_s $$ ${\bar{B}}_{s} \to D_{s}$ [Phys. Rev. D 101 (2020) 074513] and the SM and tensor ones for the $$ {\overline{B}}_s\to {D}_s^{\ast } $$ ${\bar{B}}_{s} \to D_{s}^{*}$ (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. D 95 (2017) 115008, to extract the leading and sub-leading Isgur-Wise functions for the $$ {\overline{B}}_s\to {D}_s^{\left(\ast \right)} $$ ${\bar{B}}_{s} \to D_{s}^{(*)}$ 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 $$ {\overline{B}}_s\to {D}_s^{\left(\ast \right)} $$ ${\bar{B}}_{s} \to D_{s}^{(*)}$ semileptonic decay. At present, the experimental values for the ratios $$ {\mathcal{R}}_{D^{\left(\ast \right)}}=\Gamma \left[\overline{B}\to {D}^{\left(\ast \right)}{\tau}^{-}{\overline{\nu}}_{\tau}\left]/\Gamma \right[\overline{B}\to {D}^{\left(\ast \right)}{e}^{-}\left({\mu}^{-}\right){\overline{\nu}}_{e\left(\mu \right)}\right] $$ $R_{D^{(*)}} = Γ (\bar{B} \to D^{(*)} τ^{-} {\bar{ν}}_{τ} (/ Γ) \bar{B} \to D^{(*)} e^{-} (μ^{-}) {\bar{ν}}_{e (μ)})$ 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 $$ {\overline{B}}_s\to {D}_s^{\left(\ast \right)}{\tau}^{-}{\overline{\nu}}_{\tau } $$ ${\bar{B}}_{s} \to D_{s}^{(*)} τ^{-} {\bar{ν}}_{τ}$ 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 $$ \overline{B}\to {D}^{\left(\ast \right)} $$ $\bar{B} \to D^{(*)}$ case. The measurement of the $$ {\overline{B}}_s\to {D}_s^{\left(\ast \right)}\ell {\overline{\nu}}_{\ell } $$ ${\bar{B}}_{s} \to D_{s}^{(*)} ℓ {\bar{ν}}_{ℓ}$ 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.
Cited by 8
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Cited by 3
- 2 March 2023
- Published by Springer Nature in Journal of High Energy Physics
Erratum to: 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
by Neus Penalva, Eliecer Hernández, Juan Nieves
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- 2 March 2023
- Published by Springer Nature in Journal of High Energy Physics
Open Access
Erratum to: 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
by Neus Penalva, Eliecer Hernández, Juan Nieves
Cited by 3
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Cited by 15
- 21 December 2022
- Published by American Physical Society (APS) in Physical Review D
Is the $Λ_{c} (2625)^{+}$ the heavy quark spin symmetry partner of the $Λ_{c} (2595)^{+}$ ?
by Meng-Lin Du, Eliecer Hernández, Juan Nieves
We use a $O (α_{s}, Λ_{QCD} / m_{c})$ heavy quark effective theory scheme, where only $O (Λ_{QCD} / m_{b})$ corrections are neglected, to study the matrix elements of the scalar, pseudoscalar, vector, axial-vector and tensor currents between the $Λ_{b}$ ground state and the odd parity charm $Λ_{c} (2595)^{+}$ and $Λ_{c} (2625)^{+}$ resonances. We show that in the near-zero recoil regime, the scheme describes reasonably well, taking into account uncertainties, the results for the 24 form factors obtained in lattice QCD (LQCD) just in terms of only four Isgur-Wise (IW) functions. We also find some support for the possibility that the $Λ_{c} (2595)^{+}$ and $Λ_{c} (2625)^{+}$ resonances might form a heavy quark spin symmetry (HQSS) doublet. However, we argue that the available LQCD description of these two resonances is not accurate enough to disentangle the possible effects of the $Σ_{c} π$ and $Σ_{c}^{*} π$ thresholds, located only a few MeV above their position, and that it cannot be ruled out that these states are not HQSS partners. Finally, we study the ratio $\frac{d Γ [Λ_{b} \to Λ_{c, 1 / 2^{-}}^{*} ℓ {\bar{ν}}_{ℓ}] / d q^{2}}{d Γ [Λ_{b} \to Λ_{c, 3 / 2^{-}}^{*} ℓ {\bar{ν}}_{ℓ}] / d q^{2}}$ of the Standard Model differential semileptonic decay widths, with $q$ the four-momentum transferred between the initial and final hadrons. We provide a natural explanation for the existence of large deviations, near the zero recoil, of this ratio from $1 / 2$ (value predicted in the infinite heavy quark mass limit, assuming that the $Λ_{c, 1 / 2^{-}}^{*}$ and $Λ_{c, 3 / 2^{-}}^{*}$ are the two members of a HQSS doublet) based on S-wave contributions to the $Λ_{b} \to Λ_{c, 1 / 2^{-}}^{*}$ decay amplitude driven by a subleading IW function.
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- 21 December 2022
- Published by American Physical Society (APS) in Physical Review D
Open Access
Is the $Λ_{c} (2625)^{+}$ the heavy quark spin symmetry partner of the $Λ_{c} (2595)^{+}$ ?
by Meng-Lin Du, Eliecer Hernández, Juan Nieves
We use a $O (α_{s}, Λ_{QCD} / m_{c})$ heavy quark effective theory scheme, where only $O (Λ_{QCD} / m_{b})$ corrections are neglected, to study the matrix elements of the scalar, pseudoscalar, vector, axial-vector and tensor currents between the $Λ_{b}$ ground state and the odd parity charm $Λ_{c} (2595)^{+}$ and $Λ_{c} (2625)^{+}$ resonances. We show that in the near-zero recoil regime, the scheme describes reasonably well, taking into account uncertainties, the results for the 24 form factors obtained in lattice QCD (LQCD) just in terms of only four Isgur-Wise (IW) functions. We also find some support for the possibility that the $Λ_{c} (2595)^{+}$ and $Λ_{c} (2625)^{+}$ resonances might form a heavy quark spin symmetry (HQSS) doublet. However, we argue that the available LQCD description of these two resonances is not accurate enough to disentangle the possible effects of the $Σ_{c} π$ and $Σ_{c}^{*} π$ thresholds, located only a few MeV above their position, and that it cannot be ruled out that these states are not HQSS partners. Finally, we study the ratio $\frac{d Γ [Λ_{b} \to Λ_{c, 1 / 2^{-}}^{*} ℓ {\bar{ν}}_{ℓ}] / d q^{2}}{d Γ [Λ_{b} \to Λ_{c, 3 / 2^{-}}^{*} ℓ {\bar{ν}}_{ℓ}] / d q^{2}}$ of the Standard Model differential semileptonic decay widths, with $q$ the four-momentum transferred between the initial and final hadrons. We provide a natural explanation for the existence of large deviations, near the zero recoil, of this ratio from $1 / 2$ (value predicted in the infinite heavy quark mass limit, assuming that the $Λ_{c, 1 / 2^{-}}^{*}$ and $Λ_{c, 3 / 2^{-}}^{*}$ are the two members of a HQSS doublet) based on S-wave contributions to the $Λ_{b} \to Λ_{c, 1 / 2^{-}}^{*}$ decay amplitude driven by a subleading IW function.
Cited by 15
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Cited by 2
- 9 December 2022
- Published by Elsevier in Physics Letters B
Erratum to: Tau longitudinal and transverse polarizations from visible kinematics in (anti-)neutrino nucleus scattering [Phys. Lett. B 829 (2022) 137046]
by E. Hernández, J. Nieves, F. Sánchez, J.E. Sobczyk
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- 9 December 2022
- Published by Elsevier in Physics Letters B
Erratum to: Tau longitudinal and transverse polarizations from visible kinematics in (anti-)neutrino nucleus scattering [Phys. Lett. B 829 (2022) 137046]
by E. Hernández, J. Nieves, F. Sánchez, J.E. Sobczyk
Cited by 2
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Cited by 20
- 26 September 2022
- Published by American Physical Society (APS) in Physical Review D
New physics effects on $Λ_{b} \to Λ_{c}^{*} τ {\bar{ν}}_{τ}$ decays
by Meng-Lin Du, Neus Penalva, Eliecer Hernández, Juan Nieves
We benefit from a recent lattice determination of the full set of vector, axial and tensor form factors for the $Λ_{b} \to Λ_{c}^{*} (2595) τ {\bar{ν}}_{τ}$ and $Λ_{c}^{*} (2625) τ {\bar{ν}}_{τ}$ semileptonic decays to study the possible role of these two reactions in lepton flavor universality violation studies. Using an effective theory approach, we analyze different observables that can be accessed through the visible kinematics of the charged particles produced in the tau decay, for which we consider the $π^{-} ν_{τ}, ρ^{-} ν_{τ}$ and $μ^{-} {\bar{ν}}_{μ} ν_{τ}$ channels. We compare the results obtained in the Standard Model and other schemes containing new physics (NP) interactions, with either left-handed or right-handed neutrino operators. We find a discriminating power between models similar to the one of the $Λ_{b} \to Λ_{c}$ decay, although somewhat hindered in this case by the larger errors of the $Λ_{b} \to Λ_{c}^{*}$ lattice form factors. Notwithstanding this, the analysis of these reactions is already able to discriminate between some of the NP scenarios and its potentiality will certainly improve when more precise form factors are available.
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- 26 September 2022
- Published by American Physical Society (APS) in Physical Review D
Open Access
New physics effects on $Λ_{b} \to Λ_{c}^{*} τ {\bar{ν}}_{τ}$ decays
by Meng-Lin Du, Neus Penalva, Eliecer Hernández, Juan Nieves
We benefit from a recent lattice determination of the full set of vector, axial and tensor form factors for the $Λ_{b} \to Λ_{c}^{*} (2595) τ {\bar{ν}}_{τ}$ and $Λ_{c}^{*} (2625) τ {\bar{ν}}_{τ}$ semileptonic decays to study the possible role of these two reactions in lepton flavor universality violation studies. Using an effective theory approach, we analyze different observables that can be accessed through the visible kinematics of the charged particles produced in the tau decay, for which we consider the $π^{-} ν_{τ}, ρ^{-} ν_{τ}$ and $μ^{-} {\bar{ν}}_{μ} ν_{τ}$ channels. We compare the results obtained in the Standard Model and other schemes containing new physics (NP) interactions, with either left-handed or right-handed neutrino operators. We find a discriminating power between models similar to the one of the $Λ_{b} \to Λ_{c}$ decay, although somewhat hindered in this case by the larger errors of the $Λ_{b} \to Λ_{c}^{*}$ lattice form factors. Notwithstanding this, the analysis of these reactions is already able to discriminate between some of the NP scenarios and its potentiality will certainly improve when more precise form factors are available.
Cited by 20
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Cited by 25
- 6 April 2022
- Published by Springer Nature in Journal of High Energy Physics
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
by Neus Penalva, Eliecer Hernández, Juan Nieves
We study the d²Γ_d/(dωd cos θ_d), dΓ_d/d cos θ_d and dΓ_d/dE_d distributions, which are defined in terms of the visible energy and polar angle of the charged particle from the τ −decay in $$ b\to c\tau \left(\mu {\overline{\nu}}_{\mu }{\nu}_{\tau },{\pi \nu}_{\tau },{\rho \nu}_{\tau}\right){\overline{\nu}}_{\tau } $$ $b \to cτ (μ {\bar{ν}}_{μ} ν_{τ}, {πν}_{τ}, {ρν}_{τ}) {\bar{ν}}_{τ}$ 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 $$ {H}_b\to {H}_c\tau {\overline{\nu}}_{\tau } $$ $H_{b} \to H_{c} τ {\bar{ν}}_{τ}$ parent decay and, from a dynamical point of view, they are richer than the commonly used one, d²Γ_d/(dωdE_d), 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 $$ {\Lambda}_b\to {\Lambda}_c\tau \left(\mu {\overline{\nu}}_{\mu }{\nu}_{\tau },{\pi \nu}_{\tau },{\rho \nu}_{\tau}\right){\overline{\nu}}_{\tau } $$ $Λ_{b} \to Λ_{c} τ (μ {\bar{ν}}_{μ} ν_{τ}, {πν}_{τ}, {ρν}_{τ}) {\bar{ν}}_{τ}$ and $$ \overline{B}\to {D}^{\left(\ast \right)}\tau \left(\mu {\overline{\nu}}_{\mu }{\nu}_{\tau },{\pi \nu}_{\tau },{\rho \nu}_{\tau}\right){\overline{\nu}}_{\tau } $$ $\bar{B} \to D^{(*)} τ (μ {\bar{ν}}_{μ} ν_{τ}, {πν}_{τ}, {ρν}_{τ}) {\bar{ν}}_{τ}$ sequential decays and discuss their use to disentangle between different NP models. In this respect, we show that dΓ_d/d cos θ_d, which should be measured with sufficiently good statistics, becomes quite useful, especially in the τ → πν_τ 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⁻ν_τ, 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.
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- 6 April 2022
- Published by Springer Nature in Journal of High Energy Physics
Open Access
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
by Neus Penalva, Eliecer Hernández, Juan Nieves
We study the d²Γ_d/(dωd cos θ_d), dΓ_d/d cos θ_d and dΓ_d/dE_d distributions, which are defined in terms of the visible energy and polar angle of the charged particle from the τ −decay in $$ b\to c\tau \left(\mu {\overline{\nu}}_{\mu }{\nu}_{\tau },{\pi \nu}_{\tau },{\rho \nu}_{\tau}\right){\overline{\nu}}_{\tau } $$ $b \to cτ (μ {\bar{ν}}_{μ} ν_{τ}, {πν}_{τ}, {ρν}_{τ}) {\bar{ν}}_{τ}$ 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 $$ {H}_b\to {H}_c\tau {\overline{\nu}}_{\tau } $$ $H_{b} \to H_{c} τ {\bar{ν}}_{τ}$ parent decay and, from a dynamical point of view, they are richer than the commonly used one, d²Γ_d/(dωdE_d), 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 $$ {\Lambda}_b\to {\Lambda}_c\tau \left(\mu {\overline{\nu}}_{\mu }{\nu}_{\tau },{\pi \nu}_{\tau },{\rho \nu}_{\tau}\right){\overline{\nu}}_{\tau } $$ $Λ_{b} \to Λ_{c} τ (μ {\bar{ν}}_{μ} ν_{τ}, {πν}_{τ}, {ρν}_{τ}) {\bar{ν}}_{τ}$ and $$ \overline{B}\to {D}^{\left(\ast \right)}\tau \left(\mu {\overline{\nu}}_{\mu }{\nu}_{\tau },{\pi \nu}_{\tau },{\rho \nu}_{\tau}\right){\overline{\nu}}_{\tau } $$ $\bar{B} \to D^{(*)} τ (μ {\bar{ν}}_{μ} ν_{τ}, {πν}_{τ}, {ρν}_{τ}) {\bar{ν}}_{τ}$ sequential decays and discuss their use to disentangle between different NP models. In this respect, we show that dΓ_d/d cos θ_d, which should be measured with sufficiently good statistics, becomes quite useful, especially in the τ → πν_τ 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⁻ν_τ, 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.
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