Antonio Pich
The very high statistics, low backgrounds and clean back-to-back kinematics of a TeraZ facility would provide an optimal laboratory for precision measurements of the $τ$ properties. A few important topics in $τ$ physics where very relevant contributions could be made are highlighted.
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This Fifth International WEIN Symposium is devoted to physics beyond the standard model. This talk is about tau lepton physics, but I begin with the question: do we know how to find new physics in the world of elementary particles? This question is interwoven with the various tau physics topics. These topics are: searching for unexpected tau decay modes; searching for additional tau decay mechanisms; radiative tau decays; tau decay modes of the W, B, and D; decay of the Z^0 to tau pairs; searching for CP violation in tau decay; the tau neutrino, dreams and odd ideas in tau physics; and tau res…
The prospects for tau physics at future high-luminosity facilities are briefly discussed. Although important (and often complementary) contributions will be made from other machines, the unique experimental environment near threshold makes the Tau-Charm Factory the best experimental tool for $τ$ physics.
The present status of some selected topics on tau physics is presented: charged-current universality tests, bounds on lepton-flavour violation, the determination of alpha_s from the inclusive tau hadronic width, the measurement of |V_{us}| through the Cabibbo-suppressed decays of the tau, and the theoretical description of the "tau -> nu_tau K pi" spectrum.
Status of neutrino oscillation study is briefly reviewed. Some aspects relevant to tau physics are also described.
Some important aspects of hadronic tau decays are reviewed: the determination of alpha_s from the inclusive tau hadronic width, the measurement of |V_{us}| through the Cabibbo-suppressed decays of the tau, and the theoretical description of the tau -> nu_tau K pi spectrum. The present status of other relevant electroweak topics, such as charged-current universality tests or bounds on lepton-flavour violation, has been already summarized in a previous review.
The Tau-Charm Factory combines the optimum conditions to perform a high-precision investigation of the $τ$ and $ν_τ$ leptons, the $c$ quark, and light-quark, glueball and hybrid spectroscopy. An overview of the broad physics program that this facility will address is presented.
The leptonic decays of the tau lepton provide relevant tests on the structure of the weak currents and the universality of their couplings to the gauge bosons. The hadronic tau decay modes constitute an ideal tool for studying low--energy effects of the strong interaction in very clean conditions. Accurate determinations of the QCD coupling and the strange quark mass have been obtained with tau decay data. New physics phenomena, such as a non-zero tau neutrino mass or violations of conservation laws can also be searched for with tau decays.
Because of their narrow width, tau decays can be well separated from their production process. Only spin degrees of freedom connect these two parts of the physics process of interest for high energy collision experiments. In the following, we present a Monte Carlo algorithm which is based on that property. The interface supplements events generated by other programs, with tau decays. Effects of spin, genuine weak corrections or of new physics may be taken into account at the time when a tau decay is generated and written into an event record.
The pure leptonic or semileptonic character of tau decays makes them a good laboratory to test the structure of the weak currents and the universality of their couplings to the gauge bosons. The hadronic tau decay modes constitute an ideal tool for studying low-energy effects of the strong interactions in very clean conditions; a well-known example is the precise determination of the QCD coupling from tau-decay data. New physics phenomena, such as a non-zero tau-neutrino mass or violations of (flavour / CP) conservation laws can also be searched for with tau decays.
We study effects of unparticle physics on muon g-2 and LFV tau decay processes. LFV interactions between the Standard Model sector and unparticles can explain the difference of experimental value of muon g-2 from the Standard Model prediction. While the same couplings generate LFV tau decay, we found that LFV coupling can be of O(0.1 ... 1) without conflict with experimental bounds of LFV tau decay if the scaling dimension of unparticle operator d_{U} > 1.6.
The charm physics program accessible to a Tau-Charm Factory is summarized. Semileptonic, leptonic, hadronic, rare and forbidden charm decay modes are discussed, as well as \dmix\ mixing and CP violation in the charm sector. The theoretical expectations in the Standard Model and beyond as well as the experimental capabilities of a Tau-Charm Factory are examined for each of the above processes. {To appear in {\it The Tau-Charm Factory in the Era of B-Factories and CESR}, Stanford, CA, August 15-16, 1994}
A complete discussion of the constraints on the Michel parameters and the ambiguities of their interpretation is presented. Estimators of new physics, optimized for a very wide class of hypotheses and models, are proposed.
The pure leptonic or semileptonic character of tau decays makes them a good laboratory to test the structure of the weak currents and the universality of their couplings to the gauge bosons. The hadronic $τ$ decay modes constitute an ideal tool for studying low--energy effects of the strong interactions in very clean conditions. New physics phenomena, such as a non-zero $m_{ν_τ}$ or violations of conservation laws can also be searched for with tau decays. The present experimental and theoretical status of tau physics is summarized.
Precise measurements of the tau lepton properties provide stringent tests of the Standard Model structure and accurate determinations of its parameters. We overview the present status of a few selected topics: lepton universality, QCD tests and the determination of alpha_s, m_s and V_us from hadronic tau decays, and lepton flavor violation phenomena.
Motivated by the strong experimental evidence of large nu_mu - nu_tau neutrino oscillations, we study existing constraints for related mu - tau flavor violation. Using a general bottom-up approach, we construct dimension-6 effective fermionic operators whose coefficients encode the scale of new physics associated with mu - tau flavor violation, which is a piece in the puzzle of the origin of neutrino oscillations. We survey existing experimental bounds on this scale, which arise mostly from tau and B decays. In many cases the new physics scale is constrained to be above a few TeV. We also disc…
This talk summarizes the status of the charmonium system, with particular emphasis on outstanding problems in QCD spectroscopy which a tau-charm factory can address.
We analyze in details the impact of the $10$ $ν_τ$ events seen in the OPERA experiment in constraining the Non Standard Interaction parameter $\varepsilon_{μτ}$ affecting neutrino propagation in matter and the allowed parameter space of models with one sterile neutrino of the $3+1$ type.
We study the possible effects of TeV scale new physics (NP) on the rate for Higgs boson decays to charged leptons, focusing on the tau tau channel which can be readily studied at the Large Hadron collider. Using an SU(3)_C X SU(2)_L X U(1)_Y invariant effective theory valid below a NP scale Lambda, we determine all effective operators up to dimension six that could generate appreciable contributions to the decay rate and compute the dependence of the rate on the corresponding operator coefficients. We bound the size of these operator coefficients based on the scale of the tau mass, naturalness…
Recent theoretical results in tau lepton physics and their implications for the experimental analysis are presented. The paper is split into the following chapters: 1. Introduction, 2. Weak Couplings, 3. Inclusive Decays, Perturbative QCD and Sum Rules, 4. Exclusive Decays, 5. Beyond the Standard Model.
The usage of polarimetry and spin-correlation tests to determine the {\em complete Lorentz structure} of the tau lepton's charged and neutral-current couplings is reviewed. The emphasis is on tests for ``something'' in a $(V-A) + $ ``something'' structure in ${J^{Charged}}_{Lepton}$ current, so as to bound the scales $Λ$ for ``new physics" such as arising from tau weak magnetism, weak electricity, and/or second-class currents. Tests for $T$ and for $CP$ violation are discussed.
Simulation of tau decays, ambiguities and anomalous couplings
本研究通过KKMC蒙特卡洛方法评估τ对形成质量，利用Collins-Soper和Mustraal框架解决新物理过程的歧义，并提出相关项目用于τ极化矢量和手性标签的应用。
Tau Physics Opportunities at the Super Tau-Charm Facility
本文概述了超级陶-粲装置在极高统计量、可控系统误差和低本底条件下，对陶轻子性质进行高精度研究的广泛物理项目。
Monte Carlos for tau lepton -- Standard Model and New Physics signatures
本文介绍τ轻子物理中的蒙特卡罗方法，重点描述KKMC模拟器对e+e-→τ+τ-(nγ)过程、额外轻子对产生及反常磁偶极矩效应的模拟能力，以支持标准模型检验与新物理搜索。
Overview of tau lepton physics at a super tau-charm facility
本文介绍了超 tau-charm 厂房在tau轻子物理中的研究重点和未来发展方向
We study the spin polarizations of both tau leptons in the decay b -> s tau+ tau-. In addition to the polarization asymmetries involving a single tau, we construct asymmetries for the case where both polarizations are simultaneously measured. We also study forward-backward asymmetries with polarized tau's. We find that a large number of asymmetries are predicted to be large, >~ 10%. This permits the measurement of all Wilson coefficients and the b-quark mass, thus allowing the standard model (SM) to be exhaustively tested. Furthermore, there are many unique signals for the presence of new phys…
Radiative corrections to one- and two-meson tau decays for precise new physics tests
该研究回顾了τ→P(P)ν_τ[γ]衰变的辐射修正，分析其对轻子普适性、CKM幺正性等标准模型检验的影响，为精确新物理检验提供支持。
In tau physics, we are at the frontier between the completion of the LEP program and the start of analyses from b-factories, which are expected to produce results in the coming years. Nice results from CLEO are steadily delivered in the meantime. For charm, impressive progress have been achieved by fixed target experiments in the search for CP violation and D^0 - \bar D^0 oscillations. First results from b-factories demonstrate the power of these facilities in such areas. The novel measurement of the D* width by CLEO happens to be rather different from current expectations. The absence of a ch…
Hadronic decays rates of the $τ$ lepton into multi meson final states are presented. The structure of the hadronic matrix elements for various decay modes is discussed. The formalism of structure functions allows for a detailed test of these matrix elements. Various correlations are discussed which are sensitive to possible CP violation and new physics effects in the decay modes.
We analyze the sensitivity of hadronic tau decays to non-standard interactions within the model-independent framework of the Standard Model Effective Field Theory (SMEFT). Both exclusive and inclusive decays are studied, using the latest lattice data and QCD dispersion relations. We show that there are enough theoretically clean channels to disentangle all the effective couplings contributing to these decays, with the $τ\to ππν_τ$ channel representing an unexpected powerful New Physics probe. We find that the ratios of non-standard couplings to the Fermi constant are bound at the sub-percent l…
INVITED TALK AT SECOND WORKSHOP ON TAU LEPTON PHYSICS, COLOMBUS, OHIO, SEPTEMBER 1992
The B Factories have generated a large amount of new results on the tau lepton. The present status of some selected topics on tau physics is presented: charged-current universality tests, bounds on lepton-flavour violation, the determination of alpha_s from the inclusive tau hadronic width, and the measurement of |V_{us}| through the Cabibbo-suppressed decays of the tau lepton.
The recently measured B -> tau nu branching ratio allows to test the Standard Model by probing virtual effects of new heavy particles, such as a charged Higgs boson. The accuracy of the test is currently limited by the experimental error on BR(B -> tau nu) and by the uncertainty on the parameters fB and |Vub|. The redundancy of the Unitarity Triangle fit allows to reduce the error on these parameters and thus to perform a more precise test of the Standard Model. Using the current experimental inputs, we obtain BR(B -> tau nu)_SM = (0.84 +- 0.11)x10^{-4}, to be compared with BR(B -> tau nu)_exp…
The pure leptonic or semileptonic character of tau decays makes them a good laboratory to test the structure of the weak currents and the universality of their couplings to the gauge bosons. The hadronic tau decay modes constitute an ideal tool for studying low-energy effects of the strong interactions in very clean conditions; a well-known example is the precise determination of the QCD coupling from tau-decay data. New physics phenomena, such as a non-zero tau-neutrino mass or violations of (flavour / CP) conservation laws can also be searched for with tau decays.
We consider the possibility of studying new physics that singles out the tau-lepton at the LHC. We concentrate on the tau-lepton charge asymmetry in tau+tau- pair production as a tool to probe this physics beyond the Standard Model. We consider two generic scenarios for the new physics. We first study a non-universal Z' boson as an example of a new resonance that can single out tau-leptons. We then consider vector lepto-quarks coupling of the first generation quarks with the third generation leptons as an example of non-resonant new physics. We find that in both cases the charge asymmetry can …
We report the recent results of a search for lepton-flavor-violating tau decays and a search for CP violation in tau to nu Ks pi using a large data sample accumulated with the Belle detector at the KEKB asymmetric-energy e^+e^- collider. The sensitivity to these modes is significantly improved compared to previous experiments.
Hadronic tau decays represent a clean laboratory for the precise study of quantum chromodynamics (QCD). Observables (sum rules) based on the spectral functions of hadronic tau decays can be related to QCD quark-level calculations to determine fundamental quantities like the strong coupling constant, parameters of the chiral Lagrangian, |V_us|, the mass of the strange quark, and to simultaneously test the concept of quark-hadron duality. Using the best available measurements and a revisited analysis of the theoretical framework, the value alpha_s(m_tau) = 0.345 +- 0.004[exp] +- 0.009[theo] is o…
Machine Learning (ML) techniques are rapidly finding a place among the methods of High Energy Physics data analysis. Different approaches are explored concerning how much effort should be put into building high-level variables based on physics insight into the problem, and when it is enough to rely on low-level ones, allowing ML methods to find patterns without explicit physics model. In this paper we continue the discussion of previous publications on the CP state of the Higgs boson measurement of the H to tau tau decay channel with the consecutive tau^pm to rho^pm nu; rho^pm to pi^pm pi^0 an…
A large amount of new results have been presented at TAU2006. The highlights of the workshop, the present status of a few selected topics on lepton physics (universality, QCD tests, V_{us} determination from tau decay, g-2, neutrino oscillations, lepton-flavour violation) and the prospects for future improvements are briefly summarized.
By exploiting the relatively long lifetime of the tau lepton, we propose several novel methods for searching for new physics at an electron-positron collider. We consider processes that involve final states consisting of a tau lepton pair plus two missing particles. The mass and spin of the new physics particles can be measured in 3-prong tau decays. The tau polarization, which reflects the coupling to new physics, can be measured from the $τ\to πν$ decay channel using the impact parameter distribution of the charged pion. We also discuss the corresponding backgrounds for these measurements, t…
In this talk I discuss the role of heavy quarks in new physics searches with tau leptons. I focus on new physics effects associated to the scalar sector which are naturally enhanced for the heaviest fermions due to the large hierarchy of the fermion masses. I will discuss two topics within this context: lepton flavour violation in the $τ- \ell$ ($\ell=e,μ$) sector and violations of lepton universality in tauonic $B$ decays.
Many models for physics beyond the Standard Model predict lepton-flavour violating decays of charged leptons at a level which may become observable very soon. We investigate the decays of a Tau-lepton into three charged leptons (Tau -> lll', l(') = e,μin a generic way. Using effective-field-theory methods, the relevant operators are classified according to their chirality structure. For each case, we work out the Dalitz plots for the decay distributions, including interference terms which arise from four-lepton operators and radiatively induced processes. We discuss phenomenological implicatio…
The deviation between the standard model prediction and the measurement of the muon g-2 is currently at 3-4 sigma (can be up to 7 sigma in the upcoming experiment E989). If new physics is responsible for such discrepancy, it is expected that the new contributions to tau g-2 are even larger than that for muon due to its large mass. In spite of that, the tau g-2 is much more difficult to be directly measured because of its short lifetime. In this paper, we consider the effect of the tau g-2 at $e^-e^+$ colliders in a model independent way. Using the tau pair production channel at the Large Elect…
Different aspects of Tau physics are discussed, both as a New Physics probe and as a tool to study Standard Model physics. The goal of this Tau2014 opening talk is to introduce (some of) the many research directions currently being pursued with tau leptons, which will be discussed in great technical detail in the following talks.
Workshop on Tau Lepton Physics: $\mathbf{30^{th}}$ Anniversary
本文回顾了自1990年首届Tau Lepton Physics研讨会举办以来的领域演变与物理亮点，基于此后十五届$τ$研讨会的讨论进行总结。
The physics of tau and charm started in early 70's after J/$ψ$ and $τ$ were discovered. Since then several dedicated accelerators and experiments were built with increasing luminosities and studies on light hadron spectroscopy, charmonium, electroweak and QCD were never interupted. New interests and surprises are not rare in this area. With the newly built BEPCII/BESIII, an even brighter future is foreseen.
B physics has played a prominent role in investigations of new physics effects at low-energies. Presently, the largest discrepancy between a standard model prediction and experimental measurements appears in the branching ratio of the charged current mediated B to tau nu decay, where the large tau mass lifts the helicity suppression arising in leptonic B decays. Less significant systematic deviations are also observed in the semileptonic B to D(*) tau nu rates. Due to the rich spin structure of the final state, the decay mode B to D* tau nu offers a number of tests of such possible standard mo…
The TauSpinner algorithm is a tool that allows to modify the physics model of the Monte Carlo generated samples due to the changed assumptions of event production dynamics, but without the need of re-generating events. With the help of weights $τ$-lepton production or decay processes can be modified accordingly to a new physics model. In a recent paper a new version TauSpinner ver.2.0.0 has been presented which includes a provision for introducing non-standard states and couplings and study their effects in the vector-boson-fusion processes by exploiting the spin correlations of $τ$-lepton pai…
We discuss the potential of $τ$-charm and B factories for the search of new physics through the study of rare $τ$ decays. We consider decays that involve the violation of lepton flavour conservation. Such decays bear a close relationship to the physics of neutrino mass and the properties of the lepton sector of the electroweak theory.
We study the longitudinal, transverse, and normal polarization components of the tau lepton in the decays $\bar{B}^0 \to D^{(\ast)} τ^- \barν_τ$ and discuss their role in searching for new physics (NP) beyond the standard model (SM). Starting with a model-independent effective Hamiltonian including non-SM four-Fermi operators, we obtain experimental constraints on different NP scenarios and investigate their effects on the polarization observables. In the SM the longitudinal and transverse polarizations of the tau lepton differ substantially from the corresponding zero lepton mass values of $P…
Any axionlike particle (ALP) intrinsically possesses flavorful couplings to the standard model (SM) fermions arising as a consequence of the right-handed flavor rotation within the SM. In this paper we discuss this intrinsically flavored ALP, and explore the correlation of a minimal set of the couplings in a view of coherence in flavor physics observables. We focus particularly on the tau-lepton flavor violation (LFV). The ALP is assumed to be tau-philic on a current-eigenstate basis, a la Pecci-Quinn. The ALP has the intrinsic flavorful coupling structure for fermions, which allows coupling a…
The doubly-charged scalar boson H^{--} is involved in several new physics models for generating neutrino masses. Depending on new physics models, H^{--} has the Yukawa interaction with a pair of left-handed charged leptons or a pair of right-handed ones. In this talk, we see that these two Yukawa interactions can be distinguished by measuring energy distributions of charged pions produced by decays of tau leptons if pair-produced H^{++} H^{--} can decay sufficiently into four charged leptons which involve one or two tau leptons. The information on the Yukawa interaction of H^{--} will help to …
The main highlights discussed at TAU2012 are briefly summarized. Besides the standard topics on lepton physics covered also at previous conferences (universality, QCD tests, V_{us} determination from tau decay, g-2, neutrino oscillations, lepton-flavour violation), the tau lepton is playing now a very important role in searches for new physics phenomena.
Precise measurements of the lepton properties provide stringent tests of the Standard Model and accurate determinations of its parameters. We overview the present status of tau physics, highlighting the most recent developments, and discuss the prospects for future improvements. The leptonic decays of the tau lepton probe the structure of the weak currents and the universality of their couplings to the W boson. The universality of the leptonic Z couplings has also been tested through leptonic Z decays. The hadronic tau decay modes constitute an ideal tool for studying low-energy effects of the…
CP violating dipole moments of leptons vanish at least to three loop order and are estimated to be $({m_l\over Mev})\times 1.6\times 10^{- 40}$ e-cm in the standard model (SM), where $m_l$ is the mass of the lepton. However they can receive potentially large contributions in some beyond SM scenarios and this makes them very sensitive probes of new physics. In this article we show that a non universal interaction, involving leptoquarks to the quark-lepton pair of the third generation through helicity unsuppressed couplings of the order of ordinary gauge couplings, can generate electric and weak…
Recent experimental results on exclusive semi-tauonic B meson decays, B -> D(*) tau nu, showing sizable deviations from the standard model prediction, suggest a new physics in which the structure of the relevant weak charged interaction may differ from that of the standard model. We study the exclusive semi-tauonic B decays in a model-independent manner using the most general set of four-Fermi interactions in order to clarify possible structures of the charged current in new physics. It turns out that correlations among observables including tau and D* polarizations and q^2 distributions are u…
Behind the observed pattern of lepton flavor mixing is a partial or approximate mu-tau flavor symmetry --- a milestone on our road to the true origin of neutrino masses and flavor structures. In this review article we first describe the features of mu-tau permutation and reflection symmetries, and then explore their various consequences on model building and neutrino phenomenology. We pay particular attention to soft mu-tau symmetry breaking, which is crucial for our deeper understanding of the fine effects of flavor mixing and CP violation.
Comment on "Radiative corrections to tau -> pi(K) nu_tau[gamma]: A reliable new physics test"
研究对τ→Pν_τγ结构依赖振幅的结果进行评论，指出相关约定字典轴向项符号错误，修正后GR10振幅与轴向扇区手征预测相符但与矢量扇区手征反常符号相反，数值影响小。
Rare $B$ decays provide an opportunity to probe for new physics beyond the Standard Model. In this paper, we propose to measure the tau polarization in the inclusive decay $B\to X_sτ^+τ^-$ and discuss how it can be used, in conjunction with other observables, to completely determine the parameters of the flavor-changing low-energy effective Hamiltonian. Both the Standard Model and several new physics scenarios are examined. This process has a large enough branching fraction, $\sim {\rm few}\times 10^{-7}$, such that sufficient statistics will be provided by the B-Factories currently under cons…
The central aspect of my personal scientific activity, has focused on calculations useful for interpretation of High Energy accelerator experimental results, especially in a domain of precision tests of the Standard Model. My activities started in early 80's, when computer support for algebraic manipulations was in its infancy. But already then it was important for my work. It brought a multitude of benefits, but at the price of some inconvenience for physics intuition. Calculations became more complex, work had to be distributed over teams of researchers and due to automatization, some aspect…
Charged lepton flavor violation has long been recognized as unambiguous signature of New Physics. Here we describe the physics capabilities and discovery potential of New Physics models with charged lepton flavor violation in the tau sector as its experimental signature. Current experimental status from the B-Factory experiments BaBar, Belle and Belle II, and future prospects at Super Tau Charm Factory, LHC, EIC and FCC-ee experiments to discover New Physics via charged lepton flavor violation in the tau sector are discussed in detail. Submitted to the Proceedings of the US Community Study on …
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