τ lepton is a fundamental particle in the standard model, and its mass is a very sensitive quantity in testing the lepton-universality.
BESIII gave the most precise τ mass value in a single measurement in 2014, but the accuracy is still much lower than those of electron and muon.
In order to improve the accuracy of τ mass measurement, more than 130 pb-1 τ mass scan data were collected in...
The Belle II experiment is a substantial upgrade of the Belle detector, operating at the SuperKEKB energy-asymmetric e+e− collider. The design luminosity of the machine is 8 × 10^35 cm−2s−1, and the Belle II experiment aims to record 50 ab−1 of data, a factor of 50 more than its predecessor. From February to July 2018, the machine has completed a commissioning run and the main operation of...
In this talk I will present the calculation of the QED third order correction to the muon lifetime. This result is obtained in the so-called heavy daughter approximation, i.e. the decay rate is computed in the limit of equal muon and electron masses which yields crucial simplifications in the evaluation of multi-loop Feynman diagrams. Despite the electron being about 207 times lighter that the...
I will provide a short overview on deviations of the Standard Model symmetries within tau lepton processes. I will consider from dynamic dependent symmetries such as universality to the breaking of global symmetries, namely lepton flavor, lepton number or baryon number violations.
In the last couple of decades, there has been a tremendous growth of interest in testing fundamental symmetries, such as CPT and the Lorentz invariance of special relativity. Using effective field theory, it has been possible to parameterize a much broader range of symmetry violations that had previously been envisioned or tested. The new possibilities include different patterns of symmetry...
In the quest to map out the structure of the proton in exquisite detail, the Electron Ion Collider (EIC) will collide electrons and protons at high energy with unprecedented luminosity.
In this talk I will discuss how to exploit the features of the EIC to explore physics beyond the Standard Model. I will focus on charged-lepton-flavor-violating (CLFV) interactions in which an electron is...
Within the Standard Model Effective Field Theory framework, with operators up to dimension 6, we perform a model-independent analysis of the lepton-flavour-violating processes involving tau leptons. Namely, we study hadronic tau decays and $\ell$-$\tau$ conversion in nuclei, with $\ell = e,\mu$. Based on available experimental limits, we establish constraints on the Wilson coefficients of the...
Lorentz invariance is among the most fundamental and tested symmetries in physics. Measurements from over two decades of experiments place stringent constraints on many Lorentz-violating interactions affecting the particles of the Standard Model. However, a large class of interactions inducing charged-lepton-flavor violation remains largely unexamined. In this talk, we discuss dominant...
We present in full analytic form the partial widths for the lepton flavor violating decays $L^\pm \to \ell^\pm \ell'^{+} \ell'^{-}$, with $L = \tau, \mu$ and $\ell^{(\prime)} = \mu, e$, mediated by neutrino oscillations in the one-loop diagrams. Compared to the first result by Petcov:1976ff, which was obtained in the nonphysical zero momentum limit $\mathcal{P} \ll m_{\nu} \ll M_W$, we retain...
We report on the first search for electron-muon flavor violation in the decay of a b quark and anti-b quark bound state. A search for the LFV decay Υ(3S) → e± μ∓ in a sample of 118 million Υ(3S) mesons from 27 fb−1 of data collected with the BABAR detector at the SLAC PEP-II e+e− collider operating with a 10.36 GeV center-of-mass energy revealed no signal. We set a limit on the branching...
Many theories beyond the Standard Model predict new phenomena, such as Z’, W’ bosons, or heavy leptons, in final states with isolated, high-pt leptons (e/mu/tau). Searches for new physics with such signatures, produced either resonantly or non-resonantly, are performed using the ATLAS experiment at the LHC. This includes a novel search that exploits the lepton-charge asymmetry in events with...
In the past half a dozen years or so, the tau lepton has become the central focus for many reasons. Foremost in this is the fact that there are strong experimental hints that the tau is intimately involved in strong indications of lepton universality violations (LUV). Moreover, it is no longer just one type of experiments but rather three different types are involved and in each case the...
The charged Lepton Flavor Violation (cLFV) is highly suppressed in the Standard Model (SM) by the finite but tiny neutrino masses. Its branching fraction is calculated to be at a negligible level and so far none has been found in all the historical experiments, including searches in lepton ($\mu$,$\tau$) decays, pseudoscalar meson (K,$\pi$) decays, vector meson ($\phi$,$J/\psi$,$\Upsilon$)...
We report the result of a search for \tau \to \ell \gamma (\ell = e, \mu) using the full data sample at Belle. Charged lepton flavor violation (CLFV) is forbidden in the Standard Model but possible in several new physics scenarios.
In many of these models, the radiative decays $\tau \to \ell\gamma$ are predicted to have a sizeable probability and are thus particularly interesting CLFV...
We have measured the electric dipole moment (EDM) of the tau lepton using an 833 fb^-1 data sample collected with the Belle detector at the KEKB asymmetric-energy e^+e^- collider. Using an optimal observable method, we obtain the EDM result with O(10^-17) ecm uncertainty. The result is consistent with no EDM at the present level of experimental sensitivity and improves the sensitivity by about...
We study charged lepton flavor violation associated with a light leptophilic axion-like particle (ALP), $X$, at the $B$-factory experiment Belle II.
We focus on production of the ALP in the tau decays $\tau \to X l$ with $l=e,\mu$, followed by its decay via $X\to l^- l^+$.
The ALP can be either promptly decaying or long-lived.
We perform Monte-Carlo simulations, recasting a prompt search...
I will briefly review the interesting collection of flavor anomalies that continue to accumulate from various experiment campaigns. What are they trying to tell us and, might there be connections? To add evidence to the experimental findings, a group of us is forming to develop a next-generation rare pion decay experiment. We aim to improve on the lepton flavor universality violation (LFUV)...
COMET is an experiment at J-PARC, Japan, which will search for neutrinoless conversion of muons into electrons in the field of a nucleus (μ− + N → e− + N); a lepton flavor violating process. The experimental sensitivity goal for this process is order of 10^{−15} for Phase-I and 10^{−17} for Phase-II experiment, which is a factor of 100–10,000 improvements correspondingly over existing limits....
The Mu2e experiment will measure the charged lepton flavor violating (CLFV), neutrino-less conversion of a negative muon into an electron in the field of a nucleus. The process has never been observed, but is predicted to occur in many Beyond the Standard Model scenarios at rates within the reach of the Mu2e experiment. The goal of the experiment is to improve the previous upper limit by four...
An economical theoretical framework for combined explanations of the flavor physics anomalies involving muons, (g-2)_mu, RK(*) and b->s mu mu supplements the Standard Model (SM) with a lepton-flavored U(1)_X gauge group where the auge boson has mass of O(0.1) GeV and a TeV-scale leptoquark. We explore the theory space of the chiral, anomaly-free U(1)_X gauge extensions and carry out a...
Lepton flavor is not an exact symmetry of nature as indicated by neutrino oscillations. Moreover, the hints for discrepancy between the measured data and the theoretical prediction of numerous observables related to the ratio between events containing electrons to those containing muons, e.g. R_D(*) and R_K, points towards new physics exhibiting lepton non-universality. These examples also...
Leptoquarks (LQ) are predicted by many new physics theories to describe the similarities between the lepton and quark sectors of the Standard Model and offer an attractive potential explanation for the lepton flavour anomalies observed at LHCb and flavour factories. The ATLAS experiment has a broad program of direct searches for leptoquarks, coupling to the first-, second- or third-generation...
We report on a precision measurement of the ratio R^Υ(3S)_τμ = B[Υ(3S) → τ+τ−] / B[Υ(3S) → μ+μ−] using data collected with the BaBar detector at the SLAC PEP-II e+e− collider. The measurement is based on a 28 fb−1 data sample collected at a center-of-mass energy of 10.355 GeV corresponding to a sample of 122 million Υ(3S) mesons. The ratio is measured to be R^Υ(3S)_τμ = 0.966 ± 0.008 (stat) ±...
The Belle II experiment at SuperKEKB, an asymmetric e+e- collider, aims at a total integrated luminosity of 50 ab-1, to pursue a rich program of Standard Model and Beyond the Standard Model physics. In its first year of operation, approximately 10 fb-1 were collected at the Upsilon(4S) resonance, with about 100 fb-1 expected by the end of 2020. This results in a sizeable sample of tau pairs,...
Many models of dark matter and hidden sectors predict new particles with masses below the electroweak scale. Low-energy electron-positron colliders such as BABAR are ideally suited to discover these hidden-sector particles. We present two recent BABAR searches for low-mass hidden-sector particles, including new searches for prompt and long-lived leptonically decaying hidden scalars produced in...
After a brief review of semileptonic tau decays in the Standard Model, I will discuss the usefulness of these channels in several new physics searches.
The calculation of radiative corrections (radcorr) in semileptonic decays requires a good description of photon-hadron interactions at all energies. We present a calculation of the radcorr to $\tau^- \to P^- \nu_{\tau}$ decays ($P$ a pseudoscalar meson) where photon-hadron form factors obeys the expected QCD constraints at very small and very large virtual photon momenta. The implications for...
The radiative two-pion tau decay process is studied in this work. The resonance chiral theory is used to calculate the relevant form factors. Different light-flavor vector resonance dynamics are revealed in several different two-particle invariant mass distributions. Interesting studies on the T-odd asymmetry distributions arising from the radiative two-pion tau decay process are explored as...
The rare second-class decay mode of the $\tau$ into $\eta\pi\nu$ could be
observed for the first time at Belle II. It is important to try to derive
a reliable evaluation of the branching fraction and of the energy
distribution of this mode within the standard-model. Many predictions
exist already in the literature which, unfortunately, can differ by one to
two orders of magnitude. In...
Pion-kaon ($\pi K$) pairs occur frequently as final states in heavy-particle decays.
A consistent treatment of $\pi K$ scattering and production amplitudes over a wide energy range is therefore mandatory for multiple applications:
in Standard Model tests; to describe crossed channels in the quest for exotic hadronic states; and for an improved spectroscopy of excited kaon resonances.
In...
We present updated determinations of |Vus| using tau decays that include a preliminary updated HFLAV global fit of the tau branching fractions, up-to-date lattice hadronic form factors and decay constants, and novel determinations published in 2019 of the electromagnetic and strong isospin-breaking corrections to the π+→μ+ν[γ] and K+→μ+ν[γ] leptonic decay rates obtained with lattice QCD+QED.
In the framework of precision experiments, the search for electric dipole moments and the precise determination of magnetic dipole moments (g-2)
have since long be of prime interest. Tau leptons play a particular role owing to the large mass as compared to the electron and muon.
The precision of these measurements is, at the one hand, dominated by radiative corrections, which govern the...
Hadronic decays of $\tau$ lepton provide a unique possibility to study dynamics in a three-body hadronic system. Particularly, $\tau^-\to \pi^+\pi^-\pi^-\,\nu$ and $\tau^-\to K^-K^+\pi^-\,\nu$ gives a clear sample of the $a_1(1260)$ decays. While the pionic system is dominated by the $\rho$ intermediate resonance and the system with kaons shows mostly $K^*$ resonances, the two final states are...
The discrepancy between the FOPT and CIPT predictions for the hadronic tau decay rate (and other spectral function moments) has been a subject of intense investigations for many years and constitutes a major theoretical uncertainty for strong coupling determinations from hadronic tau decay spectral data. We demonstrate that the discrepancy may be understood since the Borel representations...
We use a new, more precise, non-strange, inclusive vector
isovector spectral function to determine the strong coupling at the
tau mass scale employing finite energy sum rules. The new spectral
function is obtained from a combination of (i) ALEPH and OPAL results
for the 2 pion and 4 pion tau decay channels, (ii) recent BaBar
results for the tau K Kbar decay distribution, and...
Tau-based finite-energy sum rule (FESR) analyses often assume that scales
s_0~m_tau^2 are large enough that (i) integrated duality violations (DVs)
can be neglected, and (ii) contributions from non-perturbative OPE
condensates of dimension D scale as ~(Lambda_{QCD}/m_tau )^D, allowing the
OPE series to be truncated at low dimension. The latter assumption is not
true in general since the...
Testing the Yukawa couplings of the Higgs boson to quarks and leptons is important to understand the origin of fermion masses. ATLAS has recently measured the properties of the Higgs boson decays to two tau leptons, with an analysis based on the full dataset of pp collisions collected at 13 TeV at the LHC. The talk will present details on the analysis techniques used to measure the inclusive...
In the past two decades, several results from short-baseline neutrino experiments have hinted that sterile neutrinos could be present. If confirmed, these new particles would be a definite proof of physics beyond the Standard Model and would offer attractive solutions to many unanswered questions in our field. After briefly reviewing selected results, I will present the current experimental...
Among the Higgs boson decay channels, the one to tau leptons can offer insight into the properties of the Higgs boson. The structure under CP symmetry of the Yukawa coupling between the Higgs boson and tau leptons was investigated in CMS by reconstructing the decay planes of the two tau leptons and measuring their angular separation. Tau decay planes are reconstructed depending on the studied...
In this talk I will review the short baseline anomalies and recent developments relevant to this topic. I will discuss theoretical interpretations of these anomalies, including sterile neutrinos, decaying neutrinos, and novel gauge forces. Limitations of the theoretical interpretations will be highlighted.
The LHC Run 2 data-taking period was characterized by an increase in instantaneous luminosity and center-of-mass energy. Several techniques have been deployed in the CMS experiment to reconstruct and identify tau leptons in this environment. The DeepTau identification algorithm is used to identify hadronically decaying tau leptons from quark and gluon induced jets, electrons, and muons....
I will give a summary talk on long baseline neutrino measurements, with attention to topics and searches related to tau neutrinos. I will cover the latest results from T2K, NOvA, and OPERA, and future prospects from DUNE and Hyper-K.
The Muon 𝑔−2 experiment at Fermilab has recently confirmed Brookhaven's earlier measurement of the muon anomalous magnetic moment. This new result increases the muon g-2 discrepancy with the Standard Model prediction and strengthens its "new physics" interpretation, as well as the quest for its underlying origin. I will discuss the connection of the muon g-2 discrepancy to precision...
Kilometer-scale neutrino detectors, like the IceCube Neutrino Observatory deployed in the ice cap at the South Pole, are uniquely capable of detecting energetic tau neutrinos and tau leptons. IceCube has sensitivity to tau neutrinos with energies at and above the threshold for tau lepton production, and has sufficiently large volume to contain tau leptons that travel hundreds of meters. The...
During the last 15 years the "Radio MontecarLow (“Radiative Corrections and Monte Carlo Generators for Low Energies”) Working Group, see www.lnf.infn.it/wg/sighad/, has been providing valuable support to
the development of radiative corrections and Monte Carlo generators for low energy e+e- data and tau-lepton decays. Its operation which started
in 2006 proceeded until the last few years...
This talk will provide of overview on searches for particle dark matter, including direct, indirect, and accelerator searches that cover different energy and mass scales. I will highlight the future directions in particle dark matter searches, and how experiments can be complementary in maximizing the sensitivity to a broad range of viable models.
The Monte Carlo for lepton pair production and tau decays consist
of KKMC for lepton pair production, Tauola for tau lepton decays and
Photos for radiative corrections in decays.
An effort for adaptation of the system for precision data to be collected
at Belle II experiment lead to extension of phase space generation modules
both in Photos and Tauola to enable decays and/or radiative...
The neutrino astronomy is polluted by the atmospheric noise up TeVs energy. Anyway Icecube claimed an astrophysical signature (just above a few tens TeV energy), since the 2013. They discovered a sudden increase in the cascade event rate, surprisingly more abundant than the previous TeVs muon neutrino tracks. Such a flavor switch might be also mimic by an atmospheric charm rising presence....
The VEPP-2000 ee collider has been operating at BINP (Novosibirsk) from 2010 in the center-of-mass energy range from 0.3 to 2 GeV. The project luminosity of this machine, exploiting the idea of the round beams, has to amount to 1032cm-2s-1. By now the luminosity up to 51031cm-2s-1 was achieved. Two detectors, CMD-3 and SND, are running at two interaction regions of the VEPP-2000. Each...
Observation of neutrinoless double beta decay would profoundly impact our understanding of the neutrino. This lepton-number violating process requires new beyond Standard Model physics, would imply that neutrinos are Majorana particles, and provide insight into the nature of neutrino mass. It is thus a highly-sensitive and promising probe of new physics. In this talk, I will present the...
Total amount of about 320 pb^{-1} of integrated luminocity has been collected with SND detector at VEPP-2000 collider. Here we present recent results on e+e- annihilation to hadrons below 2 GeV based on part of the data. In particular, we discuss measurements of the e^+e^-\to pi^+\pi^- and e^+e^- \to n\bar{n} cross sections, and study of the radiative processes e^+e^- \to \eta\gamma, e^+e^-...
The MINOS/MINOS+ experiment, which consisted of two magnetised steel-scintillator tracking calorimeters, observed neutrino and antineutrino flavour change over a baseline of 735 km in the NuMI beam from Fermilab.
With 11 years of collected data in configurations with peak energies at 3 GeV and 6 GeV, the experiment, which has performed precision measurements of neutrino...
FASER$\nu$ at the LHC is designed to directly detect collider neutrinos for the first time and study their properties at TeV energies, where no such measurements currently exist. The detector will be located 480 m downstream of the ATLAS interaction point. With FASERnu, the three-flavor neutrino cross-sections will be measured in the currently unexplored energy range between 360 GeV and 5 TeV....
SND@LHC is a compact and stand-alone experiment to perform measurements with neutrinos produced at the LHC in a hitherto unexplored pseudo-rapidity region of 7.2 < 𝜂 < 8.6, complementary to all the other experiments at the LHC. The experiment is to be located 480 m downstream of IP1 in the unused TI18 tunnel. The detector is composed of a hybrid system based on an 800 kg target mass of...
Nearly twenty years ago a team from Brookhaven National Lab measured the anomalous part of the muon's dipole moment ($a_\mu$) finding a ~three-sigma discrepancy against contemporary Standard Model predictions. The mystery lingered for a time as there were no further measurements, but within a few years a small dedicated team set into motion a plan to revive the technique at Fermilab. This team...
The recent Fermilab result has confirmed the long standing discrepancy between the direct measurement and the Standard Model (SM) prediction of the anomalous magnetic moment of the muon aμ=(gµ-2)/2. The possibility to improve the SM prediction using data-driven approaches has motivated the BESIII collaboration to embark on a dedicated experimental program. The high statistics data samples...
The recent result from the Fermilab experiment on the anomalous magnetic moment of the muon ($g-2$) has revived the interest on this observable, that exhibits an interesting —and persistent— $4\sigma$ discrepancy with respect to its theoretical value.
Future runs at Fermilab will help deciphering the nature of such discrepancy, but that will require a commensurate improvement on the theory...
In my talk, I will present a dispersive estimate of the $f_0(980)$ contribution to $(g-2)_\mu$. The performed analysis is a coupled-channel extension of the previous work, where $f_0(500)$ has already been addressed. Important ingredients are $\gamma^*\gamma^*\to \pi \pi$ and $\gamma^*\gamma^*\to K\bar{K}$ S-wave helicity amplitudes which rely on the novel unitarizaiton scheme for studying...
KLOE-2, the continuation of the KLOE experiment at the Frascati $\phi-$factory, completed its data-taking by acquiring about 5 fb$^{-1}$ at the $\phi$ meson peak.
One of its distinctive feature is the possibility to study $e^+e^- \to \gamma^{\ast}\gamma^{\ast}e^+e^-\to \pi^0 e^+e^-$ processes by tagging final state leptons with two stations installed in both arms of the DA$\Phi$NE...
The hadronic light-by-light contribution to the muon g-2 can now
be calculated using first principles lattice QCD+QED methods. Independent results from two collaborations are available. I will review the status and recent developments.
We study the HLbL contribution to g-2 in the kinematic region where the three loop momenta are large. We show how, even when the fourth photon is in the static limit, the massless quark loop gives the leading term of an operator product expansion. Power corrections are found to be small. Gluonic corrections are also included and the expansion is found to be well-behaved at relatively...
The largest part of the hadronic-vacuum-polarization (HVP) contribution to the muon anomalous magnetic moment is due to the intermediate state of two pions. Analyticity and unitarity do not only allow us to write this contribution in terms of the pion vector form factor (VFF), but also constrain the VFF itself. I will discuss fits of a dispersive representation of the pion VFF to $e^+e^-$...
We review the isospin-breaking and electromagnetic corrections to the $\tau^-\to\pi^-\pi^0\nu_\tau$ decays, which are used as an input to the two-pion contributions to the hadronic vacuum polarization (at LO) of the anomalous magnetic moment ($a_\mu$). We extend previous analyses by Cirigliano et al. working with ChPT with resonances. As an outcome, we improve the agreement between this...
We discuss a method for calculating the heavy quark vacuum polarisation contribution to the muon anomalous magnetic moment, $a_\mu$, using perturbative QCD up to ${\cal O}\left(\alpha_s^3\right)$. This approach is independent of $e^+e^-$ cross-section data allowing a fully theoretical evaluation of these contributions. This method confirms an existing result at lower orders in $\alpha_s$ and...
We present a continuum determination of a_mu^SIB, the strong isospin-breaking contribution to a_mu, the anomalous magnetic moment of the muon, using ChPT and the formulation of a_mu as a weighted integral of the electromagnetic current two-point function over Euclidean Q^2. Flavor-breaking hadronic tau decay sum rules are shown to provide a determination of a key higher-order chiral LEC...
The SM predicts zero values of CPV & TV in the decays of tau leptons except \tau^- \to \nu K^0_S [\pi,\pi\pi]. With neutrino oscillations I would give the golden medals for CPV & TV. I think that tau decays can get bronze medals in \tau^- \to \nu K [pi, \pi\pi, \eta]. Their hadronic final states are enough `complex'.
The Super Charm-Tau Factory (SCTF) project proposed at Budker Institute of Nuclear Physics is discussed. An electron-positron collider with the luminosity of about
10^35 1/cm^2/s operated at the center-of-mass energies from 3 to 7 GeV, and modern particle detector allow one to study on the new level of precision the physics of charmonium, exotic charmonium-like states, charmed mesons and...
Anomalous magnetic moment of the tau lepton, $a_\tau = (g_\tau -2)/2$, is a sensitive probe of new physics but is extremely difficult to measure precisely in contrast to electron and muon moments. The best experimental limits were set by the DELPHI collaboration more than 15 years ago in the studies of the ditau production in the $e^+e^- \to e^+e^-\tau^+\tau^-$ process. Ultra-peripheral...
For now two decades, an extensive neutrino oscillations experimental era dramatically improved our knowledge on the 3-neutrino oscillations paradigm. This program, though, almost only focused on the electron and muon neutrinos, and our knowledge on the tau neutrino mostly relies on leptonic universality.
DUNE (Deep Underground Neutrino Experiment) is a next generation of neutrino...
Following the many contributions KLOE-2 has done to Dark Matter (DM) searches, an alternative model, where the Dark Force mediator is an hypothetical leptophobic B boson, in contra-position to the U boson or "dark photon", is investigated. The B boson couples mainly to quarks and it can be searched in the Phi decay to eta-B where B will decay in p0-gamma. So far, investigation of the pi0-gamma...
We investigate vector-like fermionic dark matter and flavor anomalies in a simple extension of standard model, with doublet vector-like fermions of quark and lepton type and also a $S_1(\bar{\textbf{3}},\textbf{1},1/3)$ scalar leptoquark. An additional vector-like lepton singlet is included, whose admixture with vector-like lepton doublet plays the role of dark matter and is examined in relic...
The presence of new relic sterile neutrinos at eV energy mass, their clustering as dark warm matter halos, their target for ZeV UHE neutrinos, might lead to UHECR uncorrelated signals with nearby sources, overcoming the GZK cut off. The ability of sterile neutrinos to solve at once different puzzle of theoretical physics and astrophysics will be shown in details.
In the poster, we have taken $L_e-L_\tau$ gauge symmetry to study neutrino phenomenology in the framework of type-(I+II) seesaw mechanism. In the model, three heavy right-handed neutrinos, a scalar singlet, and one scalar triplet are added to the Standard Model. As a result, the active neutrino-mass matrix has a two-zero $A_1$ texture which helps explain neutrino oscillation parameters like...
We analyse the rare semileptonic decays of $B$ meson to axial vector mesons $K_1(1270)$ and $K_1(1400)$ mediated by the flavor changing neutral current $b \to s ll$ quark level transition, in an effective field theory approach. We perform a global fit to all the relevant and up-to-date $b \to sl^+ l^-$ data for various sets of (axial)vector couplings. We then look over the implications of the...
Several indications of lepton non universality ratios, $R_{D^*}$, $R_{J/ \psi}$ and the measurements on hadronic and $\tau$ longitudinal polarizations in $b \to c \tau \bar{\nu_\tau}$ processes have attracted a lot of attentions. By considering the most general effective Lagrangian, we carry out a model independent analysis of the semileptonic $\Lambda_b$ decays, to inspect the nature of new...
LFV processes have been studied extensively in this model (JHEP 07 (2019) 154). We study systematically the phenomenological consequences of introducing inverse see-saw neutrino masses in the model (according to JHEP 12 (2019) 154) and obtain predictions on the $\tau \rightarrow \ell \gamma $ and $\tau \rightarrow \ell \ell' \ell'$ decays (other LFV decays are also analyzed) which are close to...
Discrete symmetries are being preferred to explain the neutrino phenomenology, we chose the simplest $S_3$ group and explore the implication of its modular form on neutrino masses and mixing. Non-trivial transformations of Yukawa couplings under this symmetry, make the model phenomenologically interesting by reducing the requirement of multiple scalar fields. This symmetry imposes a specific...
We realize neutrino phenomenology via Type-(I+II) seesaw
mechanism in a simple $U(1)_{L_e-L_\mu}$ gauge extension of standard model. With three additional right-handed neutrinos and a scalar triplet, we obtain two-zero $A_2$ texture in active neutrino mass matrix. We constrain the model parameters consistent with current neutrino oscillation data. Furthermore, we obtain new contributions to...
In this work, a flavour theory, of a neutrino mass model implementing an $A_4$ family symmetry is proposed. This scheme provides a simple way to derive tribimaximal mixing in the neutrino sector via spontaneous breaking of $A_4 $ symmetric model leading to acceptable values of $\theta_{13}$ and maximal CP violation. A $z_2 \times z_2$ invariant perturbations in this model is introduced in the...
Tau leptons can have lepton-flavor-violating (LFV) couplings to a muon or an electron and an Axion-Like Particle (ALP). ALPs are pseudo Nambu-Goldstone bosons associated with the spontaneously broken global $U(1)_{\mathrm{PQ}}$ symmetry. LFV ALPs have been of a great interest in the last several decades as they can solve some of the SM long-lasting problems. Assuming a future muon collider...
New results are presented for a search for charged lepton flavor violating decays of tau leptons to three muons with the CMS detector. The search employs tau leptons produced in decays of heavy flavor B/D mesons and W bosons.
The fluorescence detector (FD) of the Pierre Auger Observatory is sensitive to upward-going air showers for energies above 10^17 eV. Given its operation time and wide field of view, the FD has the potential to support or constrain the recent "anomalous" observations by the ANITA detector, interpreted as upward-going air showers of unexplained nature.
We have used 14 years of data collected...
Lepton flavor violating interactions are absent in the standard model but are expected in various beyond-standard models. In this work, the potential of the future circular electron-positron collider to probe the four-fermion lepton flavor couplings via the e-e+ → eτ process is revisited by means of an effective field theory approach. We provide constraints at 95% C.L. on the dimension-six...
The future experiments like SHiP, DsTau, and DUNE are proposed to study the properties and the production cross sections of the $\tau$ lepton and its corresponding neutrino ($\nu_{\tau}$). Recently we have performed [1,2,3], a theoretical study of the production cross section as well as the polarization observables of the $\tau$ lepton and the final nucleon/hyperon produced in the quasielastic...
The tau-lepton lifetime represents a fundamental parameter within the Standard Model framework, contributing to the test of lepton flavor universality. Exploiting the vertex detector resolution and the tiny beam spot size at the interaction point, Belle II is expected to improve the present tau-lifetime value. The event topology where one tau decays to three charged pions (3-prong) and the...
Using the Belle II data from the early Phase III data taking, we reconstructed the tau
leptons using the 3-prong τ decays. This decay mode is used for the tau-lepton mass
measurement using the pseudomass technique developed by the ARGUS experiment. Though
this measurement is expected to be limited by statistics and imperfect knowledge of
the detector performance, we foresee that Belle II...
The proposed FCC-ee collider provides optimal conditions for ultimate statstics studies of the
four heaviest particles of the Standard Model, the Z, W and Higgs bosons and the top quark.
With the phenomenal sample of 5x10^12 Z decays in the very clean e+e- environment it also
provides optimal conditions for precision studies of heavy flavour, among that studies of the
tau lepton....
The latest measurement of the muon g-2, recently announced at Fermilab, exhibits a 4.2$\sigma$ discrepancy from the currently accepted Standard Model prediction. The leading hadronic contribution $a_{\mu}^{HLO}$ represents the main source of uncertainty on the theoretical value, and is traditionally determined by a data-driven dispersive approach. In contrast, a recent evaluation of...
Having the SuperKEKB e+e- collider upgraded with a polarized e- beam is under consideration, providing a unique program of precision electroweak and other physics at 10.6 GeV, thereby opening exciting new windows in search of new physics. Measurements of left-right asymmetries ($A_{LR}$) of e+e- transitions to pairs of taus, muons, electrons, c- and b-quarks would yield improvements to the...
Using about 200 fb-1 of data from electron-positron annihilations, we present searches for dark leptophilic scalars produced in association with tau-pair decays at the Belle II experiment. The goal of this analysis is to discover dark matter or find upper limits of the dark coupling constant as a function of the dark scalar mass.
Searches for the violation of lepton flavor universality (LFU) are critical precision tests of the standard model (SM) motivated by the growing number of anomalies reported in several measurements in the flavor sector (quarks and leptons) in the last decades. At the Belle II experiment, thanks to the large amount of tau-lepton pairs produced in electron-positron annihilation, it is possible to...
Test 2
This is a test from Sergi
Using the Belle II data from the early Phase III data taking, we reconstructed the tau
leptons using the 3-prong τ decays. This decay mode is used for the tau-lepton mass
measurement using the pseudomass technique developed by the ARGUS experiment. Though
this measurement is expected to be limited by statistics and imperfect knowledge of
the detector performance, we foresee that Belle II...
