Light Leptons Research Articles

Global fit to b→cτν anomalies as of Spring 2024

Recently, several new experimental results of the test of lepton flavor universality (LFU) in B→D(*) semileptonic decays were announced: the first result of RD from the LHCb run 1 data, the first results of RD and RD* from the LHCb run 2 data, and the first result of RD* from the Belle II collaboration. Including these new data, a global analysis still prefers the violation of the LFU between the tau and light leptons. A new world average of the data from the , LHCb, Belle, and Belle II collaborations is RD=0.342±0.026 and RD*=0.287±0.012. Including this new data, we update a circumstance of the b→cτν¯ measurements and their implications for new physics (NP). Incorporating recent developments for the B→D(*) form factors in the Standard Model, we observe a 4.4σ deviation from the Standard Model prediction. Our updates also include model-independent NP formulas for the related observables and the global fittings of parameters for leptoquark scenarios as well as single NP operator scenarios. Furthermore, we show future potential to indirectly distinguish different NP scenarios with the use of the precise measurements of the polarization observables in B→D(*)τν¯ at the Belle II and the high-pT flavored-tail searches at the LHC. We also discuss an impact on the LFU violation in ϒ→l+l−. Published by the American Physical Society 2024

Fractionary charged particles confronting lepton flavor violation and the muon’s anomalous magnetic moment

In light of the recent result published by the Fermilab Muon [Formula: see text] experiment, we investigate a simple model that includes particles of fractional electric charges: a color-singlet fermion and a scalar with charges [Formula: see text] and [Formula: see text], respectively. The impact of these particles on the muon anomalous magnetic moment is examined, particularly the restrictions on their Yukawa couplings with the light leptons. Given that lepton flavor violation processes impose stringent constraints on certain scenarios beyond the Standard Model, we evaluate the one-loop contribution of the new particles to [Formula: see text] in order to identify regions in the parameter space consistent with the Fermilab results and compatible with the current and projected limits on the branching ratio [Formula: see text]. Taking into account the current lower bound for the masses of fractionary charged particles, which is around 634[Formula: see text]GeV, we show that the mass of the scalar particle with fractional charge must exceed 1[Formula: see text]TeV. In particular, we present some estimatives for double production of the color-singlet fermion at the 14[Formula: see text]TeV LHC. Finally, we also study the validity of our model in light of the QCD lattice results on the muon [Formula: see text].

One-loop analysis of β decays in SMEFT

We perform a loop-level analysis of charged-current (CC) processes involving light leptons and quarks within the Standard Model Effective Field Theory (SMEFT). This work is motivated by the high precision reached in experiment and Standard Model calculations for CC decays of mesons, neutron, and nuclei, and by a lingering tension in the Cabibbo universality test. We identify the SMEFT operators that induce the largest loop-level contributions to CC processes. These include four-quark and four-fermion semileptonic operators involving two third-generation quarks. We discuss the available constraints on the relevant effective couplings and along the way we derive new loop-level bounds from K → πνν¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\pi \ u \\overline{\ u} $$\\end{document} on four-quark operators involving two top quarks. We find that low-energy CC processes are quite competitive with other probes, set constraints that do not depend on flavor-symmetry assumptions, and probe operators involving third-generation quarks up to effective scales of Λ ≃ 8 TeV. Finally, we briefly discuss single-field ultraviolet completions that could induce the relevant operators.

Model-independent extraction of form factors and |Vcb| in B¯→Dℓ−ν¯ℓ with hadronic tagging at BABAR

Using the entire ϒ(4S) dataset, the first two-dimensional unbinned angular analysis of the semileptonic decay B¯→Dℓ−ν¯ℓ is performed, employing hadronic reconstruction of the tag-side B meson from ϒ(4S)→BB¯. Here, ℓ denotes the light charged leptons e and μ. A novel data-driven signal-background separation procedure with minimal dependence on simulation is developed. This procedure preserves all multidimensional correlations present in the data. The expected sin2θℓ dependence of the differential decay rate in the Standard Model is demonstrated, where θℓ is the lepton helicity angle. Including input from the latest lattice QCD calculations and previously available experimental data, the underlying form factors are extracted using both model-independent (BGL) and dependent (CLN) methods. Comparisons with lattice calculations show flavor SU(3) symmetry to be a good approximation in the B(s)→D(s) sector. Using the BGL results, the CKM matrix element |Vcb|=(41.09±1.16)×10−3 and the Standard Model prediction of the lepton-flavor universality violation variable R(D)=0.300±0.004, are extracted. The value of |Vcb| from B¯→Dℓ−ν¯ℓ tends to be higher than that extracted using B¯→D*ℓ−ν¯ℓ. The Standard Model R(D) calculation is at a 1.97σ tension with the latest HFLAV experimental average. Published by the American Physical Society 2024

Search for leptoquark pair production decaying into te-t¯e+\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$te^- \\bar{t}e^+$$\\end{document} or tμ-t¯μ+\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$t\\mu ^- \\bar{t}\\mu ^+$$\\end{document} in multi-lepton final states in pp collisions at s=13TeV\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\sqrt{s} = 13\\,\ extrm{TeV}$$\\end{document} with the ATLAS detector

A search for leptoquark pair production decaying into te-t¯e+\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$te^- \\bar{t}e^+$$\\end{document} or tμ-t¯μ+\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$t\\mu ^- \\bar{t}\\mu ^+$$\\end{document} in final states with multiple leptons is presented. The search is based on a dataset of pp collisions at s=13TeV\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\sqrt{s}=13~\ ext {TeV} $$\\end{document} recorded with the ATLAS detector during Run 2 of the Large Hadron Collider, corresponding to an integrated luminosity of 139 fb-1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{-1}$$\\end{document}. Four signal regions, with the requirement of at least three light leptons (electron or muon) and at least two jets out of which at least one jet is identified as coming from a b-hadron, are considered based on the number of leptons of a given flavour. The main background processes are estimated using dedicated control regions in a simultaneous fit with the signal regions to data. No excess above the Standard Model background prediction is observed and 95% confidence level limits on the production cross section times branching ratio are derived as a function of the leptoquark mass. Under the assumption of exclusive decays into te-\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$te^{-}$$\\end{document} (tμ-\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$t\\mu ^{-}$$\\end{document}), the corresponding lower limit on the scalar mixed-generation leptoquark mass mLQmixd\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$m_{\ extrm{LQ}_{\ extrm{mix}}^{\ extrm{d}}}$$\\end{document} is at 1.58 (1.59) TeV and on the vector leptoquark mass mU~1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$m_{{\ ilde{U}}_1}$$\\end{document} at 1.67 (1.67) TeV in the minimal coupling scenario and at 1.95 (1.95) TeV in the Yang–Mills scenario.

Pauli-type coupling of spinors and curved spacetime

Abstract In this study we prove that the Pauli interaction---which is associated with a length parameter---emerges when the minimal coupling recipe is applied to the non-degenerate Dirac Lagrangian.
The conventional Dirac Lagrangian is rendered non-degenerate if supplemented by a particular term quadratic in the derivatives of the spinors.
For dimensional reasons, this non-degenerate Dirac Lagrangian is associated with a length parameter $\ell$.
It yields---just as the conventional degenerate Dirac Lagrangian---the standard free Dirac equation in Minkowski space as the $\ell$ terms cancel when setting up the Euler-Lagrange equations.
However, if the Dirac spinor is minimally coupled to gauge fields, then the length parameter~$\ell$ becomes a physical coupling constant yielding novel interactions.
For the U($1$) symmetry the Pauli coupling of fermions to electromagnetic fields arises, modifying the fermion's magnetic moment.
We discuss the impact of these findings on electrodynamics, and estimate the upper bound of the length parameter~$\ell$ from the yet existing discrepancy between the (SM) theory and measurement of the anomalous magnetic moment of light leptons.
This, and also recent studies of the renormalization theory, suggest that the Pauli coupling of leptons to the electromagnetic field is a necessary ingredient in QED, supporting the notion of a fundamental nature of the non-degenerate Dirac Lagrangian.

In a second step we then investigate how analogous ``Pauli-type'' couplings of gravity and matter arise if fermions are embedded in curved spacetime.
The diffeomorphism and Lorentz invariance of that system leads to an anomalous spin-torsion interaction and a curvature-dependent mass correction.
We calculate the mass correction in the De~Sitter geometry of vacuum with the cosmological constant $\Lambda$.
Possible implications for the existence of effective non-zero rest masses of neutrinos are addressed.
Finally, an outlook on the impact of mass correction on the physics of ``Big Bang'' cosmology, black holes, and of neutron stars is provided.

Test of new physics effects in overline{B}to left({D}^{left(ast right)},pi right){ell}^{-}{overline{nu}}_{ell } decays with heavy and light leptons

We study the overline{B}to Dleft({D}^{ast}right){ell}^{-}{overline{nu}}_{ell } decays based on the up-to-date available inputs from experiments and the lattice. First, we review the standard model (SM) predictions of the different observables associated with these decay channels. In the analyses, we consider new physics (NP) effects in the channels with the heavy (τ), as well as the light leptons (μ, e). We have extracted |Vcb| along with the new physics Wilson coefficients (WCs) from the available data on light leptons; the extracted value of |Vcb| is (40.3 ± 0.5) × 10−3. The extracted WCs are consistent with zero, but some could be of order 10−2. Also, we have done the simultaneous analysis of the data in overline{B}to {D}^{left(ast right)}left({mu}^{-},{e}^{-}right)overline{nu} alongside the inputs on Rleft({D}^{left(ast right)}right)=frac{Gamma left(overline{B}to {D}^{left(ast right)}{tau}^{-}{overline{nu}}_{tau}right)}{Gamma left(overline{B}to {D}^{left(ast right)}{ell}^{-}{overline{nu}}_{ell}right)} and the D∗ longitudinal polarisation fraction {F}_L^{D^{ast }} in different NP scenarios and extracted |Vcb| which is consistent with the number mentioned above. Also, the simultaneous explanation of R(D(∗)) and {F}_L^{D^{ast }} is not possible in the one-operator scenarios. However, the two operator scenarios with {mathcal{O}}_{S_2}^{tau }=left({overline{q}}_R{b}_Lright)left({overline{tau}}_R{nu}_{tau L}right) as one of the operators could explain all these three measurements. Finally, we have given predictions of all the related observables in overline{B}to {D}^{left(ast right)}left({tau}^{-},{mu}^{-},{e}^{-}right)overline{nu} decays in the NP scenarios, which could be tested in future experiments. We have repeated this exercise for overline{B}to pi {ell}^{-}{overline{nu}}_{ell } decays with the light lepton and extracted |Vub| and the new physics WCs. Finally, using all these available data for the light and heavy leptons, we have given bounds on the couplings of the relevant SM effective field theory (SMEFT) operators and the probable NP scale Λ.

Dephasingless laser wakefield acceleration in the bubble regime

Laser wakefield accelerators (LWFAs) have electric fields that are orders of magnitude larger than those of conventional accelerators, promising an attractive, small-scale alternative for next-generation light sources and lepton colliders. The maximum energy gain in a single-stage LWFA is limited by dephasing, which occurs when the trapped particles outrun the accelerating phase of the wakefield. Here, we demonstrate that a single space–time structured laser pulse can be used for ionization injection and electron acceleration over many dephasing lengths in the bubble regime. Simulations of a dephasingless laser wakefield accelerator driven by a 6.2-J laser pulse show 25 pC of injected charge accelerated over 20 dephasing lengths (1.3 cm) to a maximum energy of 2.1 GeV. The space–time structured laser pulse features an ultrashort, programmable-trajectory focus. Accelerating the focus, reducing the focused spot-size variation, and mitigating unwanted self-focusing stabilize the electron acceleration, which improves beam quality and leads to projected energy gains of 125 GeV in a single, sub-meter stage driven by a 500-J pulse.

Tests of Light-Lepton Universality in Angular Asymmetries of B^{0}→D^{*-}ℓν Decays.

We present the first comprehensive tests of the universality of the light leptons in the angular distributions of semileptonic B^{0}-meson decays to charged spin-1 charmed mesons. We measure five angular-asymmetry observables as functions of the decay recoil that are sensitive to lepton-universality-violating contributions. We use events where one neutral B is fully reconstructed in ϒ(4S)→BB[over ¯] decays in data corresponding to 189 fb^{-1} integrated luminosity from electron-positron collisions collected with the Belle II detector. We find no significant deviation from the standard model expectations.

Complete analysis on QED corrections to Bq → τ+τ−

Motivated by a dynamical enhancement of the electromagnetic corrections by a power of ΛQCD/mb in Bd,s→ μ+μ− at next-to-leading order (NLO), we extend the QED factorization effects on the leptonic B meson decays with light muon leptons to tauonic final states, Bd,s→ τ+τ−, using soft-collinear effective theory (SCET). This extension is necessary owing to the appearance of the large τ mass, which will lead to different power counting in SCET and also different results. We provide a complete NLO electromagnetic corrections to Bd,s→ τ+τ−, which include hard functions and hard-collinear functions below the bottom quark mass scale μb. The power enhanced electromagnetic effects from hard-collinear contributions on Bd,s→ μ+μ− discussed before also exist in Bd,s→ τ+τ−. However the logarithm term arising from contributions of hard-collinear photon and lepton virtualities for Bd,s→ τ+τ− is not large as it is in muon case due to the hard-collinear scale of τ mass, which lead to only approximately 0.04% QED corrections to the branching fraction of Bd,s→ τ+τ− compared with overall reduction about 0.5% in Bd,s→ μ+μ−.

Search for a new heavy scalar particle decaying into a Higgs boson and a new scalar singlet in final states with one or two light leptons and a pair of τ-leptons with the ATLAS detector

A search for a new heavy scalar particle X decaying into a Standard Model (SM) Higgs boson and a new singlet scalar particle S is presented. The search uses a proton-proton (pp) collision data sample with an integrated luminosity of 140 fb−1 recorded at a centre-of-mass energy of s\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\sqrt{s} $$\\end{document} = 13 TeV with the ATLAS detector at the Large Hadron Collider. The most sensitive mass parameter space is explored in X mass ranging from 500 to 1500 GeV, with the corresponding S mass in the range 200–500 GeV. The search selects events with two hadronically decaying τ-lepton candidates from H → τ+τ− decays and one or two light leptons (ℓ = e, μ) from S → VV (V = W, Z) decays while the remaining V boson decays hadronically or to neutrinos. A multivariate discriminant based on event kinematics is used to separate the signal from the background. No excess is observed beyond the expected SM background and 95% confidence level upper limits between 72 fb and 542 fb are derived on the cross-section σ(pp → X → SH) assuming the same SM-Higgs boson-like decay branching ratios for the S → VV decay. Upper limits on the visible cross-sections σ(pp → X → SH → WWττ) and σ(pp → X → SH → ZZττ) are also set in the ranges 3–26 fb and 6–33 fb, respectively.

Identification of light leptons and pions in the electromagnetic calorimeter of Belle II

The paper discusses new method for electron/pion and muon/pion separation in the Belle II detector at transverse momenta below 0.7 GeV/c, which is essential for efficient measurements of semi-leptonic decays of B mesons with tau lepton in the final state. The method is based on the analysis of patterns in the electromagnetic calorimeter by using a Convolutional Neural Network (CNN).

Search for lepton-flavor-violating τ decays into a lepton and a vector meson using the full Belle data sample

Charged-lepton-flavor-violation is predicted in several new physics scenarios. We update the analysis of τ lepton decays into a light charged lepton (ℓ = e± or μ±) and a vector meson (V0 = ρ0, ϕ, ω, K*0, or overline{K} *0) using 980 fb−1 of data collected with the Belle detector at the KEKB collider. No significant excess of such signal events is observed, and thus 90% credibility level upper limits are set on the τ → ℓV0 branching fractions in the range of (1.7–4.3) × 10−8. These limits are improved by 30% on average from the previous results.

Energy of Hard, Soft, and Nucleonic Components of Extensive Air Shower using Deasa Array

An extensive air shower is generated when a highly energetic cosmic ray enters the atmosphere resulting in soft, hard, and nucleonic components, which a mini array can measure. These studies have been done by Stockholm Educational Air Shower Array (SEASA) located at Sweden, which have 3 detectors per station observing temperature dependence with count rate. Similarly, School Cosmic Rays Outreach Detector (SCROD) located at Boston used educational array of 3 detectors per station to study the G.Z. cutoff. A similar experiment is being set up at Dayalbagh Educational Institute (DEI), Agra in which a mini array consisting of 8 plastic scintillation detectors having dimensions (100 x 100 x 2) cm3 separated by 8 m at 171 m above sea level. This simulation involves the study of energy deposition of hadrons, γ and lighter leptons (μ+ , μ - , e - , e + ) in extensive air shower using CERN based open simulation toolkit GEANT4. The energy range of secondary particles is 0.05 GeV < Ep< Eγ< Ee -< Ee+< Eμ -< 7000 GeV, 40 GeV < Eπ± -< 7000 GeV. The aim is to observe real life physics and carry out future studies of EAS based on mini array.

Impact of Λb→Λcτν measurement on new physics in b→clν transitions

Measurements of the branching ratios of $B \to D^{(*)}\tau\bar\nu/B \to D^{(*)}\ell\bar\nu$ and $B_c\to J/\psi\, \tau\bar\nu/B_c\to J/\psi\, \ell\bar\nu$ by the BaBar, Belle and LHCb collaborations consistently point towards an abundance of taus compared to channels with light leptons. However, the ratio $\Lambda_b \to\Lambda_c \tau\bar\nu/\Lambda_b \to\Lambda_c \ell\bar\nu$ shows a relative deficit in taus. In this paper, we critically address whether data still points towards a coherent pattern of deviations, in particular in light of the sum rule relating these decays in a model-independent way. We find that no common new physics explanation of all ratios is possible (within $2\sigma$ or $1.5\sigma$, depending on the ${\cal R}(\Lambda_c)$ normalization to light lepton channels). While this inconsistency could be a statistical fluctuation, further measurements are required in order to converge to a coherent pattern of experimental results.

Light lepton portal dark matter meets the LHC

We examine the sensitivity of the Large Hadron Collider (LHC) to light lepton portal dark matter with its mass below 10 GeV. The model features an extra doublet scalar field and singlet Dirac dark matter, which have Yukawa interactions with left-handed leptons. To correctly produce the dark matter abundance via the thermal freeze-out, a large mass splitting among the extra scalars is required, thus providing a light neutral scalar below mathcal{O}(10)textrm{GeV} and heavy neutral and charged scalars at the electroweak scale. In this paper, we focus on the electroweak pair-production of the extra scalars with subsequent model-specific scalar decays and evaluate the current constraints with the LHC Run 2 data and the discovery potential at the High Luminosity LHC (HL-LHC). It turns out that a large part of the theoretically allowed parameter space can be tested at the HL-LHC by taking into account complementarity between slepton searches and mono-Z plus missing transverse energy search. We also discuss same-sign charged scalar production as a unique prediction of the model, and the implication of the collider searches in the thermal dark matter scenario.

Testing entanglement and Bell inequalities in H→ZZ

We discuss quantum entanglement and violation of Bell inequalities in the $H\ensuremath{\rightarrow}ZZ$ decay, in particular when the two $Z$-bosons decay into light leptons. Although such process implies an important suppression of the statistics, this is traded by clean signals from a ``quasi maximally entangled'' system, which makes it very promising to check these crucial phenomena at high energy. In this paper we devise a novel framework to extract from $H\ensuremath{\rightarrow}ZZ$ data all significant information related to this goal, in particular spin correlation observables. In this context we derive sufficient and necessary conditions for entanglement in terms of only two parameters. Likewise, we obtain a sufficient and improved condition for the violation of Bell-type inequalities. The numerical analysis shows that with a luminosity of $L=300\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$ entanglement can be probed at $>3\ensuremath{\sigma}$ level. For $L=3\text{ }\text{ }{\mathrm{ab}}^{\ensuremath{-}1}$ (HL-LHC) entanglement can be probed beyond the $5\ensuremath{\sigma}$ level, while the sensitivity to a violation of the Bell inequalities is at the $4.5\ensuremath{\sigma}$ level.

Extra dimensions with light and heavy neutral leptons: an application to CEνNS

We explore the possibility of relating extra dimensions with light and heavy Dirac-type neutral leptons and develop a framework for testing them in various laboratory experiments. The Kaluza-Klein modes in the large extra dimension models of the light neutral leptons could mix with the standard model neutrinos and produce observable effects in the oscillation experiments. We show that the chirality flipping up-scattering processes occurring through either neutrino magnetic dipole moment or the weakly coupled scalar interactions can also produce heavy Kaluza-Klein modes of the corresponding right-handed neutral leptons propagating in one or more extra dimensions. However, to conserve the four- dimensional energy-momentum, their masses must be below the maximum energy of the neutrinos in the initial state. The appreciable size of extra dimensions connected with these heavy neutral leptons can thus affect the cross-sections of these processes. This framework applies to any up-scattering process. Our work here focuses only on its application to the coherent elastic neutrino-nucleus scattering process. We derive constraints on the size of extra dimensions using the COHERENT data in oscillation and up-scattering processes. For model with one large extra dimension for the light neutral leptons, we obtain the limits, R ~ 3 μm (NH) and R ~ 2.5 μm (IH), on the size of extra dimension corresponding to the absolute mass limit, m0 ≤ 3 × 10−3 eV at 90% C.L. from the short-baseline oscillations. Using the up-scattering process for heavy neutral leptons, we obtain new parameter spaces between the size of extra dimensions and parameters of the dipole or scalar interactions.

TAUOLA update for decay channels with e+e− pairs in the final state

With the arrival of high luminosity B-factories like the Belle II experiment, τ decay measurements have become more precise than ever, allowing rarer processes to be explored, and finer details of τ decays to be studied. These are important to understand the spectrum of intermediate particles produced in τ decays. Therefore Monte Carlo generators, like the TAUOLA program, have to facilitate precision analysis as well as confront new models that constantly emerge with the availability of high statistics experimental data. New decay channels and models may lead to large variation of matrix elements size within the available phase space, as in the case when e+e− pairs are present in final state. It requires appropriate presampler of the phase space generator and a proper documentation to help users introduce their own models. While releasing a new update, it is important for the TAUOLA Monte Carlo library to maintain the general structure of the previous versions to preserve backward compatibility. The aim is to minimize changes from the user perspective. This paper presents a demonstration of new models implementation facilitated by the current update. Program summaryProgram Title: tauola-bbbCPC Library link to program files:https://doi.org/10.17632/3hyw3f7v32.1Licensing provisions: GPLv2Programming language:FORTRAN/C++Journal reference of previous version: Comput. Phys. Comm., 232:220–236, 2018Does the new version supersede the previous version?: NoReasons for the new version: Meeting the needs of present day experiments.Summary of revisions: Phase space presamplers enriched with the possibility to generate narrow peaks of e+e− pairs, if present in matrix elements of 4- and 5-body decay channels and due to electromagnetic or New Physics interactions. The examples of physical models are implemented for: τ−→π−e−e+ντ, τ−→ν¯μμ−e−e+ντ and τ−→ν¯ee−e−e+ντ channels, which are used for the collected new algorithm validations.Nature of problem: Present day experiments, in particular Belle II, have the capability to measure extremely rare, not yet measured τ decays, as well as precise measurements of known decay channels. They require a Monte Carlo generator capable of generating all desired decays. They also need the possibility to modify and test new models for such decays. At the same time the default initialization of the event generator should contain decent modeling of known τ decays.Solution method: The new version supplements previous publications on TAUOLA. Phase-space presamplers and new decay channels with additional light lepton pairs are introduced.Additional comments including restrictions and unusual features: TAR BALL of the future versions of the program may become available through:http://wasm.web.cern.ch/wasm/Welcome.html; its sub-pages http://tauolapp.web.cern.ch/tauolapp/ or http://wasm.web.cern.ch/wasm/f77.html

|Vcb| , lepton flavor universality and SU(3)F symmetry breaking in Bs→Ds(*)ℓνℓ decays through unitarity and lattice QCD

In addition to the well-known $B \to D^{(*)} \ell \nu_\ell$ decays, semileptonic $B_s \to D_s^{(*)} \ell \nu_\ell$ processes offer the possibility to determine the Cabibbo-Kobayashi-Maskawa (CKM) matrix element $\vert V_{cb}\vert$. We implement the Dispersive Matrix (DM) approach to describe the hadronic Form Factors (FFs) for the $B_s \to D_s^{(*)}$ transition in the whole kinematical range, starting from recent Lattice QCD computations at large values of the 4-momentum transfer. We extract $\vert V_{cb} \vert$ from the experimental data, obtaining $\vert V_{cb} \vert \cdot 10^3 = (41.7 \pm 1.9)$ from $B_s \to D_s \ell \nu_\ell$ and $\vert V_{cb} \vert \cdot 10^3 =(40.7 \pm 2.4)$ from $B_s \to D_s^* \ell \nu_\ell$ decays. After averaging with the values of $\vert V_{cb} \vert$ obtained from the $B \to D^{(*)}$ channels [1,2] we get $\vert V_{cb} \vert \cdot 10^3 =(41.2 \pm 0.8)$, which is compatible with the most recent inclusive estimate $\vert V_{cb} \vert_{\rm{incl}} \cdot 10^3 = 42.16 \pm 0.50$ [3] at the $1 \sigma$ level. In addition we test the Lepton Flavour Universality (LFU) by computing the $\tau / \ell$ ratios of the total decay rates (where $\ell$ is a light lepton), obtaining $R(D_s) = 0.298\,(5)$ and $R(D_s^*)= 0.250\,(6)$. We also address the issue of the $SU(3)_F$ symmetry breaking by comparing the hadronic FFs entering the semileptonic $B \to D^{(*)}$ and $B_s \to D_s^{(*)}$ channels.