Nita Sinha The Institute of Mathematical Sciences Chennai

CPV in Charged Leptons  CP violation has been observed in K meson and B meson decays and perhaps (?) recently even in the D meson decays  SM cannot produce the observed matter vs antimatter asymmetry  Look elsewhere—Neutrinos Charged leptons Electric Dipole Moments  Will hopefully simultaneously be able to pin down the kind of New Physics

BABAR Rapid Communications PRD 85, (2012 ) t: (V ts V * td ) 2 ~ 10, m t 2 c: (V cs V * cd ) 2 ~ 2, m c 2 u: (V us V * ud ) 2 ~ 2, m u 2 c dominates The BaBar collaboration reported a measurement of a rate asymmetry in this tau decay mode

In the presence of CPV, the observed neutral Kaon states of definite mass and lifetime are: Asymmetry from Neutral Kaon Mixing The observed asymmetry has the opposite sign The observed asymmetry has the opposite sign !

Sign of the Asymmetry In fact, the sign of such an CP asymmetry expected to be opposite to the CP Asymmetry in charged D decays in charged D decays

Careful Analysis 1

2 The discrepancy from expectation (if confirmed with higher statistical significance) needs to be explained

 Except for neutral K mixing, tau decays can only be affected by Direct CPV Direct CPV  CP asymmetries in semi-hadronic final states can probe both CPV coming from New hadronic and leptonic physics. coming from New hadronic and leptonic physics.  Once the well measured Kaon oscillation contribution to CP asymmetry is accounted for, any further deviations provide asymmetry is accounted for, any further deviations provide clean signals of New Physics clean signals of New Physics  Except for neutral K mixing, tau decays can only be affected by Direct CPV Direct CPV  CP asymmetries in semi-hadronic final states can probe both CPV coming from New hadronic and leptonic physics. coming from New hadronic and leptonic physics.  Once the well measured Kaon oscillation contribution to CP asymmetry is accounted for, any further deviations provide asymmetry is accounted for, any further deviations provide clean signals of New Physics clean signals of New Physics Why is this interesting?

Decay Rate In Standard Model Where, the leptonic term: and the hadronic term is given in terms of the hadronic vector current which is parameterized in terms of scalar and vector form factors as:

No Vector –Scalar Interference term Form Factors parameterized in terms of Briet -Wigner forms with energy dependent widths l=1 p wave vector state l=0 s wave scalar state

Note:  For CP asymmetry need strong and weak phases  Strong phase-provided by the resonances!  No Weak phase in SM, can come from New Physics (complex coupling) (complex coupling) CP Asymmetry CP asymmetry being linear in NP has higher sensitivity to it than effects like lfv or edms

 For charged Higgs, no new FF, only modification, so calculable  Interference of scalar and vector FF term vanishes after the angular integration, so cannot give the decay rate asymmetry angular integration, so cannot give the decay rate asymmetry although can give asymmetry in distributions although can give asymmetry in distributions  The Vector contribution being odd under parity, interference of vector-scalar is odd, hence vanishes when integrated over the vector-scalar is odd, hence vanishes when integrated over the full (parity even ) phase space full (parity even ) phase space BUT Additional Scalar Interaction (Charged Higgs) ?  Naively expect a charged scalar boson to provide the additional NSI amplitude, NSI amplitude,  With a complex weak coupling and strong phase difference of scalar and vector FF scalar and vector FF  CP Asymmetry

Belle and Cleo Analysis

Other Options-Tensor interaction? Complex coupling NP amplitude HadronicCurrent

This interference survives even after full phase space integration, as both vector and tensor terms are odd under parity vector and tensor terms are odd under parity

 Use the observed BR and ACP to determine the coupling strength of this new tensor interaction and its CP violating phase.  Small coupling will not affect the fits to BR, as it will appeared squared, yet its linear interference term will be sufficient to generate the asymmetry.  Strong phases determined from the complex form of the form factors (vector and scalar) Numerical estimates of NP Parameters Case I

Case II

Future

SummarySummary  KM Mechanism of CPV verified, explains all measured CPV  BAU requires larger CPV  Explore the lepton sector– Neutrinos Charged leptons Charged leptons  Other possible sources of CPV and NP need to be explored  Observation of a CP asymmetry in the tau decay mode is interesting and if the deviation from the expected SM value confirmed at higher statistical significance deviation from the expected SM value confirmed at higher statistical significance It will be an excellent probe of NP It will be an excellent probe of NP  In a model independent way we explored the possibility if tensor interactions could possibly explain the observed asymmetry. possibly explain the observed asymmetry.

Thank You