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Rare Tau Decay at Belle – Search for Lepton Flavor Violation –

Rare Tau Decay at Belle – Search for Lepton Flavor Violation –. Takayoshi Ohshima Nagoya University Belle Collaboration New data on t  mg & t  mh EPS2003, Aachen.

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Rare Tau Decay at Belle – Search for Lepton Flavor Violation –

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  1. Rare Tau Decay at Belle– Search for Lepton Flavor Violation – Takayoshi OhshimaNagoya UniversityBelle Collaboration New data on tmg & tmh EPS2003, Aachen We, Belle collaboration, search for LFVing tau-decay at KEKB-factory experiment. I would like to present the latest results on t->mg and mh.

  2. KEKB asymmetric e+e– collider - e+ / e– : 3.5 / 8 GeV - CM energy: 10.58 GeV - Design luminosity: 1034/cm2/s KEKB & Belle spectrometer KEKB is an asymmetric electron-positron collider in Japan which attained the world highest peak luminosity of 1× 10^34 this May. We now accumulate about 160/fb data, corrsponding to about 140 M tau-pairs produced at an energy of 10.6 GeV, by this general purpose Belle detector.

  3. Forbidden in SM, while New physics allows LFV decay. SUSY predicts LFV ( , e, …, e ) Enhancement due to high mass Br() ~ 105-6Br(e) Physics oftmg This LFVing decay is forbidden in SM but is allowed in new physics beyond the SM. Some SUSY models predict rather a large branching fraction accessible at Belle. The best limit is so far achieved by CLEO and Belle as 1×10^-6 in the branching fraction.

  4. Search for (mg)+(m+ ng>0 + neutrino(s)) 86.3/fb data analyzed (78.5 M tt) From the previous studies,we know that gttand gmm form the prominent BG; (2) Non-zero candidate events are foundto exist in signal region. Therefore, BG reduction & knowledge of its distribution are essential to extract the number of signal events. In order to remove BG,we newly introducea cut, pmissing-Mmissingcut Event selection

  5. Event selection (dominant BG)

  6. pmissing vs. Mmissing cut & Blind analysis 98% tt and 86% mm removed , 76% signals survived. Signal MC is indicated by yellow. Signal yield is evaluated inDE-vs-Mmg (DE=EmgCM-EbeamCM) In order to avoid bias on analysis, we Blind the signal region 1.70 GeV < Mmg< 1.85 GeV

  7. BG in the signal region • BG comprises (1)ttgand • (2) mmg(one m misidentified as m)and (3) small cont. • For BG, ttgand cont. are obtained by MC, • For mmg, mmgfrom data and multiplied by m-ID inefficiencyk. • BG probability density (Si) is expressed by Gaussian and Landau functions. Thus obtained B spectrum at the blinded region is shown here by the curves. BG can be also obtained from actual data by averaging their distributions at both side-bands, as indicated by the histogram. Curve and histogram agree very well. Finally, we open the blinded area. Dots are the remaining data. It well agree with the expected BGs. Yellow shows the expected signal distribution.

  8. DE vs. Mmg Event distribution where the blinded region is unveiled. (1) Due to initial radiation and energy leakage of photon calorimeter, the distribution has a long tail. Resolution DE： 65.40.6 MeV Mmg：20.30.9 MeV/c2 (2) 5s region (e = 11.0%) (3) In order to evaluate the number of signal events, we take 5s region indicated here, which provides 10.3 % of detection efficiency.

  9. Unbinned EML fit S. Ahmed et. al., PR D61 071101 (200) Probability densities for a sum of BG and signal are displayed by dark and bright pattern, and the data by dots. From these figures it can be seen, the events observed are much more characteristic of BG than of signal.

  10. Systematic uncertainty on s0 Continuum & k : +0.06/-0.11 ev. BG function: 0.3 ev. Fit region: 0.07 ev. Br(tmg) <3.2 x 10 -7 at 90% CL. Systematic uncertaintyon 2eNtt Track rec. eff. : 2.0% Photon rec. eff. : 2.8% Cut selection : 2.2% Luminosity : 1.4% Trigger efficiency : 1.6% MC statistics : 0.8% ------------------------------------ Total : 4.7% (LFV interaction structure & spin correlation: < 0.1%) Br(tmg)

  11. The constrained MSSM Higgs-mediated model. An attractive process to give the most strigent bound on Higgs-mediated LFV in MSSM. Especially, large tanb would provide large Br. M. Sher, PR D66 057301 (2002); K.S. Bubu and C. Kolda, PRL 89, 241802 (2002); A. Dedes, J. Ellis, and M. Raidal, PL B549, 159 (2002) Br(t  mh) is 8.4 times larger than Br(t  mmm) color facor  3 Higgs coupling  (ms/mm)2 Current upper limit from CLEO　（Ldt = 4.7fb-1） Using h  gg mode. Br(tmh) < 9.62×10-6 ;Br(teh) < 8.19×10-6 Physics ofLFVtmh

  12. Essentially, very similar to tmg Two h decay-modes hgg (Br = 39.4%): 2 tracks + ng > 2 + missing hp+p-p0(Br = 22.6%): 4 tracks + ng > 2 + missing (m is not required) 84.3/fb data used Event selection hgg mass hp+p-p0 mass s12 MeV s5 MeV a resolution normalized h-mass in gg mode, and p0 and h-mass for 3p modes.

  13. hgg h3p From MC Resolutions: DE: 60.4 2.6 MeV, 38.5  2.0 MeV Mmh: 22.5  0.6 MeV/c2, 12.1  0.3 MeV/c2 Signal-ellipse: 90% acceptance BG: from MC mostly tt, and uds cont. and mm. From data Remaining events: (after kinematical cuts)18 events 60 events (within 10s but out of ellipse)7events 2 events (MC=3.72.4) (MC=0) Open blind (within region)0 events 0 events (MC=0.9) (MC=0) Backgrounds & Resolution Blind analysis is performed as same as the mg case, and the signal region is defined, this time, by an ellipse, as shown here, which gives a 90% acceptance. DE-Mmhplot

  14. Number of signals & Br evaluation hp+p-p0 hgg s0: upper limit of signal events = 2.3 These are the events distributions in DE vs mhMass plane. Dots are the data, open circle is tt MC events and square is continuum. The ellipses are the signal region with an acceptance of 90%. • Branching fraction • hgg 3p gg+3p • e Brh3.3% 1.1% 4.4% • Ntt76.9  106 • Br (10-7)< 4.5 < 13.6 < 3.4

  15. Br(tmh) Systematic uncertainties(%) hgg h3p Luminosity1.4 1.4 Brh0.7 1.8 Beam BG2.3 2.1 Trigger eff.1.4 1.4 Tracking eff.2.0 2.0 p0 veto5.5 -- h/p0 recon. eff.2.0 4.2 m ID eff.4.0 4.0 MC stat.1.3 2.1 Sum8.1 7.3 Br(tmh) < 3.4 10-7 at 90% CL. Include systematic uncertainty into an upper limit at 90% CL. S: detection sensitivity, b: BG R.Cousins and V.Highland, NIM A320, 331 (1992)

  16. Summary • We attain upper limits of • Br(tmg) < 3.2  10-7 & Br(tmh) < 3.4  10-7 • at 90% CL using 85/fb data. • 2. For the first data sensitivity reaches 10-7 level. • 3. They provide some constraint on physics beyond the SM. Dedes, J. Ellis, and M. Raidal, PL B549, 159 (2002) K.S. Bubu and C. Kolda, PRL 89, 241802 (2002) 4. Additional available data of 75/fb should improve these sensitivities soon.

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