Search for tau LFV with polarized beams Alberto Cervelli INFN & Universita’ di Pisa SuperB Physics Meeting Frascati Alberto Cervelli

Outline Introduction Data Sample Used Spin Correlation in single t decays Spin Correlation between decaying t Conclusions SuperB Physics Meeting Frascati Alberto Cervelli

Introduction Measure effects of polarization in t decays especially the recently implemented LFV modes Improve bkg rejection for LFV events produced by polarized beams SuperB Physics Meeting Frascati Alberto Cervelli

Data Sample Produced 50k events with Fast Sim V0.1.1 with new routines for polarized tmg production in tauola+KK2f t+p+n t-m-g Electrons in HER have 80% polarization g m- t- polarization e- e+ t+ n p+ SuperB Physics Meeting Frascati Alberto Cervelli

t+p+n decays Vs t-m-g The matrix element for tpn includes a spin dependent factor for the momentum helicity angle qh. t produced along beam lines are longitudinnaly polarized t polrization is transverse if emitted at large angles Polarization has same direction and sign for the two ts For LFV (V-A) models helicity angles for m, p are positively correlated t+ rest frame qh p+ t- SuperB Physics Meeting Frascati Alberto Cervelli

Helicity Angle Correlation I When summed over all thetas some correlation is visible Correlations for -0.1< qtcm <0.1 No clear correlation observed for large q since spin is projected on a direction orthogonal to the polarization vector SuperB Physics Meeting Frascati Alberto Cervelli

Helicity Angle Correlation II Correlations for qtcm <-0.8 Correlation between pion and muon direction is clear Angle distribution show clear non uniform shapes SuperB Physics Meeting Frascati Alberto Cervelli

Longitudinal Correlation III Correlations for qtcm >0.8 Correlation is visible and the angles are flipped w.r.t. Backward emitted taus as expected SuperB Physics Meeting Frascati Alberto Cervelli

Correlation between decay planes When taus are emitted at large angles they are expected to have transverse polarization. For the time being we only looked for transverse polarization correlation CM frame p+ n NO correlation is observed Double checking in progress Looking for new observables t+ q g t- m- SuperB Physics Meeting Frascati Alberto Cervelli

Possible Explanations Routines producing the decaying taus in LFV final states are being studied in detail Cross check is being performed looking spin-spin correlation using tpn decays for both t Maybe our procedure computing spin spin correlation is flawed when boosting in CM frame Still debugging SuperB Physics Meeting Frascati Alberto Cervelli

Future Plans Measure spin-spin correlation from FastSim simulated tau decays Exploit transverse and longitudinal tau polarization for bkg reduction in LFV searches Check the implementation of LFV decays in tauola in polarized beam scenarios (in more than one model (V-A), (V+A) etc) Estimate experimental sensitivities using only reconstructed quantities SuperB Physics Meeting Frascati Alberto Cervelli

Conclusions Longitudinal polarization well reproduced by MC Transverse polarization should be investigated, open questions: Are we missing something? Is the MC reproducing transverse spin correlations? Unfortunately we could not reach sound conclusions for this meeting Still a lot of work in progress SuperB Physics Meeting Frascati Alberto Cervelli