Review of Tau physics Emilie Passemar Indiana University/Jefferson Laboratory Searching for Physics Beyond the Standard Model Using Charged Leptons COFI Workshop, Puerto Rico, May 21, 2018 Emilie Passemar Outline : 1. Tau lepton as a laboratory to explore the Standard Model and possible extensions 2. Lepton Flavour Violation 3. CP violation in tau decays 4. Other interesting topics in tau physics: 1. Lepton Universality 2. Extraction of Vus from hadronic Tau decays and test of the CKM unitarity 5. Conclusion and outlook Emilie Passemar 1. Introduction and Motivation Emilie Passemar 1.1 Quest for New Physics • New era in particle physics : (unexpected) success of the Standard Model: a successful theory of G. G.Isidori Isidori – Kaon– Kaon Physics: Physics: the the next next step step Kaon Kaon 2016, 2016, Birmingham, Birmingham, Sept Sept 2016 2016 microscopic phenomena with no intrinsic energy limitation • Where do we look? Everywhere! G. Isidori searchLepton –Lepton Kaon for New Physics:Flavor Flavor Physics the Universality next Universality with step broad Kaon 2016, Birmingham, Sept 2016 search strategy given lack of clear indications onG. Isidori the – SM-EFT Kaon Physics: boundaries the next step Kaon 2016, Birmingham, Sept 2016 (both in energies and effective couplings) A Arenewed renewed2.2 Lepton interest interest in universalityin possible possible violations violations & NP of of LFU LFU has has been been triggered triggered by by two two Leptonveryvery different LeptonFlavordifferent Flavor sets Universality sets Universalityof of observations observations in in B Bphysics physics: : • HintA renewed from Binterest physics in possible anomalies? violations of LFU has been triggered by two A I)renewed I)LFU LFU• testA testinterestrenewed in inb →b ininterest→ c possible chargedc charged in possible violationscurrents currents violations: τ : of vs.τ vs.LFU light of light LFU has leptons leptonshas been been ( triggeredμ (, μ triggerede,) e) by by two two b → veryc charged different currents:sets of observations in B physics: very differentvery differentsets of observationssets of observations in B physics in B physics:: τ vs.I) light LFU leptonstest in b →(µ, c e)charged [R(D), currents R(D*)]: τ vs. light leptons (μ, e) I) LFU test1. in LFU b → test c charged in b → c currentscharged currents:: τ vs. light τ vs. leptons light leptons (μ, e (µ,) e) : b c b c b b L c c L b bL Lc c New Belle result L L L L L L L L W NP NPNP τL WW νL τL νL EmilieEmilie Passemar Passemar b c b c 4 LτL τL LνL νL LτL τL νLL νL SMW prediction quite solid:NP f.f. uncertainty cancel (to a good extent...) in the ratio Consistent results by 3 different exps. → 4σ excess over SM (combining D and D*) τ SM predic*on solid: ν τ f.f. uncertainty ν L D & D*L channelsL are well consistent L with a universal enhancement (~15%) of the SMSMcancels (to a good extent...) prediction prediction quite quite solid: solid: f.f. f.f. uncertainty uncertainty cancel cancel (to ( toa gooda good extent... extent...) in) in the the ratio ratio SM bL → cL τL νL amplitude (RH or scalar amplitudes disfavored) ConsistentConsistentin the ra*o results results by by 3 different3 different exps. exps. → → 4σ 4σ excess excess over over SM SM (combining (combining D Dand and D* D*) ) D D&Consistent results by 3 different &D* D* channels channels are are well well consistent consistentexps with 4σ excess over SM (combining D and D with a universala universal enhancement enhancement (~15%) (~15%) of *of )the the SM prediction quite solid: f.f. uncertainty cancel (to a good extent...) in the ratio SMSM b b → → c c τ τν ν amplitude amplitude ( RH (RH or or scalar scalar amplitudes amplitudes disfavored disfavored) ) Consistent L L New resultsL resultsLL LL byL from3 different LHCb on exps. Friday, → see 4σ talkexcess by Kristof over De SMBruyn (combining D and D*) Emilie Passemar 22 D & D* channels are well consistent with a universal enhancement (~15%) of the SM bL → cL τL νL amplitude (RH or scalar amplitudes disfavored) 1.1 Quest for New Physics • New era in particle physics : G.G. Isidori Isidori – – SimultaneousSimultaneous (unexpected explanations) success ofof B-physicsB-physics of the anomalies anomaliesStandard Model : a successful theory PSI, of PSI, Dec. Dec. 2017 2017 microscopic phenomena with no intrinsic energy limitation • EFT-typeEFT-typeWhere do considerationsconsiderationswe look? Everywhere! search for New Physics with broad Recentsearch data strategy show given some lack convincing of clear indicationsevidences ofon L theepton SM-EFT Flavor boundaries Universality Recent(both indata energies show some and effective convincing couplings evidences) of Lepton Flavor Universality violationsviolations bb →→ c charged currentscurrents:: τ τ vs. vs. light light leptons leptons• Hint ( μ(,μ e,from )e )[ R [ BDR, D physicsR, D*RD*] ] anomalies? bb →→ s neutral currents:currents: μμ vs. vs. e e [R [RKK, ,R RK*K*b →(+ (+ cP 5Pcharged 5et et al. al.) ]) currents:] τ vs. light leptons (µ, e) [R(D), R(D*)] b Lb L c LcL bL b L c L cL WW NPNP τ , ℓ ν τ ν Lτ L , LℓL L νL L τL L νL R(D)Key and unique R(D*) role consistent of Tau physics with a R(D) and R(D*) consistent with a EmilieEmilie Passemar Passemar universaluniversal enhancement enhancement (~30%) (~30%) of5 of the SM b → c τ ν amplitude the SM LbL →L cLL τ LL νL amplitude The new physics flavor scale 1.2 τ lepton as a unique probeThe of newnew physicsphysics flavor scale • In theK questphysics: of NewϵK Physics, can be sensitive to veryK highphysics: scale: ϵK E sdsd 5 2 ⇒ Λ ! 10 TeV – Kaon physics: sΛdsd 5 2 ⇒ Λ ! 10 TeV [εK] Λ ΛNP Charged leptons: µ → eγ, µ → e,etc. Charged leptons: µ → eγ, µ → e,etc. – Tau Leptons: τµµeff 342 2 ⇒ Λ ! 10 TeV [τ → µγ] µΛeff 3 2 ⇒ Λ ! 10 TeV Λ There is no exact symmetry that can forbid such • At low energy: lots of experiments e.g., operatorsThere is no exact symmetry that can forbid such BaBar, Belle, BESIII, LHCb important operators improvementsAll other bounds on measurements on NP, like proton and bounds decay, maybe due obtainedtoAll exact other and symmetry boundsmore expected on NP, like(Belle proton II, LHCb decay,, ATLAS, maybe due CMSto) exact symmetry ΛLE • In many cases no SM background: Y. Grossman Charged lepton theory Lecce, May 6, 2013 p. 10 e.g., LFV, EDMs Y. Grossman Charged lepton theory Lecce, May 6, 2013 p. 10 • For some modes accurate calculations of hadronic uncertainties essential, e.g. CPV in hadronic Tau decays, Vus, αS extraction, etc Tau leptons very important to look for New Physics! 6 1.2 τ lepton as a unique probe of new physics • Unique probe of Lepton Universaity and Charged Lepton Flavour Violation No SM background Indirect probe of flavor-violating NP occurring at energies not directly accessible at accelerators • Tool to search for New Physics at colliders: Ex: h à τ τ, LFV in h à τ µ Emilie Passemar 7 1.2 τ lepton as a unique probe of new physics • Unique probe of Lepton Universaity and Charged Lepton Flavour Violation No SM background Indirect probe of flavor-violating NP occurring at energies not directly accessible at accelerators • Tool to search for New Physics at colliders: Ex: h à τ τ, LFV in h à τ µ • Studying its hadronic decays: inclusive & exclusive – Unique probe of some of the fundamental SM parameters αS, |Vus|, ms Emilie Passemar 8 1.2 τ lepton as a unique probe of new physics • Unique probe of Lepton Universaity and Charged Lepton Flavour Violation No SM background Indirect probe of flavor-violating NP occurring at energies not directly accessible at accelerators • Tool to search for New Physics at colliders: Ex: h à τ τ, LFV in h à τ µ • Studying its hadronic decays: inclusive & exclusive – Unique probe of some of the fundamental SM parameters αS, |Vus|, ms – Ideal set-up for the “R&D” of theory tools about non perturbative & perturbative dynamics: OPE, Chiral Perturbation Theory, Resonances, large Nc, dispersion relations lattice QCD, etc… improve our understanding of the SM and QCD at low energy Emilie Passemar 9 1.2 τ lepton as a unique probe of new physics • Unique probe of Lepton Universaity and Charged Lepton Flavour Violation No SM background Indirect probe of flavor-violating NP occurring at energies not directly accessible at accelerators • Tool to search for New Physics at colliders: Ex: h à τ τ, LFV in h à τ µ • Studying its hadronic decays: inclusive & exclusive – Unique probe of some of the fundamental SM parameters αS, |Vus|, ms – Ideal set-up for the “R&D” of theory tools about non perturbative & perturbative dynamics: OPE, Chiral Perturbation Theory, Resonances, large Nc, dispersion relations lattice QCD, etc… – Inputs for the muon g-2 Emilie Passemar 10 1.2 τ lepton as a unique probe of new physics • A lot of progress in tau physics since its discovery on all the items described before important experimental efforts from LEP, CLEO, B factories: Babar, Belle, BES, VEPP-2M, LHCb, neutrino experiments,… Experiment Number of τ pairs More to come from LHCb, BES, LEP ~3x105 VEPP-2M, Belle II, CMS, ATLAS CLEO ~1x107 BaBar ~5x108 Belle ~9x108 • But τ physics has still potential Belle II ~1012 “unexplored frontiers” deserve future exp. & th. efforts • In the following, some selected examples and J. Berryman will give more Emilie Passemar 11 1.3The The veryProgram basic of charged leptons Adapted from Talk by Y. Grossman@CLFV2013 Muon LFV Intensity Frontier Charged Lepton µ+ → e+γ νe ↔ νµ − WG’13 µ+ → e+e+e νe ↔ ντ − − µ N → e N νµ ↔ ντ µ−N → e+N′ µ+e− → µ−e+ NeutrinoOscillations τ → ℓγ → + − µ → µγ LFV τ ℓℓi ℓj − (g 2)µ, (EDM)µ τ → ℓ + hadrons Tau LFV Muon LFC τ → τγ (g − 2)τ , (EDM)τ CPV in τ → Kπν τ τ → Kππν Tau LFC τ τ → Nπν τ Emilie Passemar Thanks to Babu 12 Y.