1. Search for LFV  decays involving     ’ at Belle Y. Enari, Belle collaboration Nagoya University

2. 9/15/2004Search for LFV tau decay involving neutral meson at Belle2 Motivation In MSSM at large tan    may have a  large branching ratio by Higgs mediated process. Comparison other mode. M slepton > weak scale, Br(    is not large. M. Sher, Phys.Rev.D66 05731(2002) K.S.Babu PRL,89,241802 (2002) A. Dedes, et.al. PLB 549,2442 (2002)    is important process!! Br(    ) : Br(   3  ) : Br(    ) =  a. (m s /m  ) 2 b. color factor c. phase space

3. 9/15/2004Search for LFV tau decay involving neutral meson at Belle3 1  10 -7 Status of LFV  decay search Belle    3 l CLEO result (PDG2004) Today’s report. 1/ L @  ~ 9% 1/ L @  ~ 3% In MSSM, Br of LFV decay may have O (10 -7 ~10 -9 ). Babar   3 l 1/ L @  ~ 3% Efficiency  BG level   l  3 l.   l    

4. 9/15/2004Search for LFV tau decay involving neutral meson at Belle4 KEKB & Belle detector L peak = 13.9  10 33 /cm 2 /sec  Ldt = 287.85 fb -1 Cross section @ s =10.58GeV     : 0.9 nb BB : 1.0 nb KEKB is  Factory!!!.  -ID eff. = 87.5% fake = 1.4 % e-ID eff. = 92.4% fake = 0.25 %

5. 9/15/2004Search for LFV tau decay involving neutral meson at Belle5 Analysis. Modes –    e     –    e             –    e  ’,  ’  ’       Blind analysis Blind region ±10  ±5  ±10  Invariant mass : M  = E 2  - p 2  Energy difference :  E = E  – E beam * Blind region: -0.5<  E < 0.5(GeV), -5  < M  < 5  Evaluation # of signal event - Low BG level  Counting signal candidates using elliptical region

6. 9/15/2004Search for LFV tau decay involving neutral meson at Belle6               ’    Selection criteria (    l    l  l  ’) Signal event reconstruction signal side ( e    ’) + tag side (1 trk + n   + missing.) BG suppression For QED BG. –NOT  (e) (for 1-1prong) –5 < E CM < 10.GeV For qq and  BG –  0 veto for  ’s  –0.5 < cos   < 0.95 –M tag < 1.777 GeV/c 2 –missing momentum towards tag side. –p miss vs. m miss 2 2-D cut. total Br(   1 prong) = 84 % (1prong or 3 prong)

7. 9/15/2004Search for LFV tau decay involving neutral meson at Belle7 Background suppression (1) Bhabha, , 2photon process  Total energy  not-(e or  in tag side. (Only 1-1 prong modes) Hadronic process (u,d,s,c)  generic process  Opening angle signal : 5% loss  : 80% reject. sig : 2% loss  : 67% rej. uds: 65% rej.

8. 9/15/2004Search for LFV tau decay involving neutral meson at Belle8 Background suppression(2) missing particle : p miss towards detectable regions. signal event : is in only tag side cos  thrust-miss < -0.55  BG event : are in both sides  Effective missing mass black: signal MC Blue:  generic After all kinematical cut applied: (except e/  ID for signal side) eff.(  = 3.8  10 -6. eff.(uds) = 3.0  10 -7. eff.(  = 3.4  10 -8. eff.(ee) = 3.0  10 -7. signal : 17% loss  : 95% reject

9. 9/15/2004Search for LFV tau decay involving neutral meson at Belle9 Mass distribution    ’ mass peak. (  ID; 1.3<M  <2.1; with Blind)    ~5.2 MeV/c 2  ~ 14 MeV/c 2  m  ’   region   m   – m        ~12 MeV/c 2  m   – m     data:57ev. MC:48.1±4.0 data: 77ev. MC:81.6 ± 8.4 data:109ev. MC:100±5.9 BG: Fake  /K (80%)   l  0 : true  0 others : mis-combination

10. 9/15/2004Search for LFV tau decay involving neutral meson at Belle10  E vs M inv. :   l  0, l , l  ’ BG estimation N exp is calculated from the side band events with assuming a flat distribution. Open blind. N exp =3.1±1.0 N exp =0.15±0.15

11. 9/15/2004Search for LFV tau decay involving neutral meson at Belle11  E vs M inv. :   l  0, l , l  ’ BG estimation N exp is calculated from the side band events with assuming a flat distribution. Open blind. N exp =3.1±1.0 N exp =0.15±0.15 Systematic uncertainties - eID:1%,  ID: 2%, track: 2%,  0 veto 5.5% Beam BG:2.3% Trigger:1.4%  4.5~8.7% - BG estimation: If N exp <1, assume N exp =0.

12. 9/15/2004Search for LFV tau decay involving neutral meson at Belle12 Result Br is obtained from Upper limit evaluation (POisson Limit Estimator program) –Feldman-Cousins method s0 2(  B X N  ) B = s0: signal events  : efficiency N  : # of  pairs B X : B of sub-decay Systematic uncertainty: using the Gaussian error. First search!! J. Conrad et al., PRD 012002 (2003) Preliminary 10-70 times tighter limit from PDG2004  140M 

13. 9/15/2004Search for LFV tau decay involving neutral meson at Belle13 Discussion -    - (1) Statistics4.7fb -1 154fb -1 Signal efficiency    7.2%  B  8.0%  B          not use 7.2%  B  Observed events 0 1 CLEOBelle  33  1.7 Keeping BG level low. Comparison with CLEO result B (    ) < 1.3  10 -7 @ 90% C.L. Upper limit : B (    ) < 9.6  10 -6

14. 9/15/2004Search for LFV tau decay involving neutral meson at Belle14 Discussion -    - (2) Constraint on tan  vs m A Preliminary CDF result : measurement (pp  A/  bb  bbbb) LEP result : LEP Higgs Working Group, PRL 86,4472 (2002) http://lephiggs.web.cern/LEPHIGGS/paper/Note2001-04 B (    ) < 1.3  10 -7 @ 90% C.L.

15. 9/15/2004Search for LFV tau decay involving neutral meson at Belle15 Search for   l    l  l  ’ meson mode using 154fb -1. No indication of signal events. B (   l    l  l  ’) < 1.3 ~ 10  10 –7 @ 90%C.L..  10-70 times tighter bounds.  First searches in   e  ’,  ’. Summary 1/ L @  ~ 9% 1/ L @  ~ 3%   l  3 l.   l     Preliminary

16. 9/15/2004Search for LFV tau decay involving neutral meson at Belle16 Backup slides

17. 9/15/2004Search for LFV tau decay involving neutral meson at Belle17 Signal efficiency and BG - muon mode - side band MC : data : b 0 12.5±2.7 13 2.7 ± 0.7 0.8 ± 0.3 2 0.6 ± 0.4 9.2 ± 2.3 9 3.1 ± 1.0 5.5 ± 1.9 5 1.4 ± 0.6 (153.8, 428, 232, 160 fb -1 )

18. 9/15/2004Search for LFV tau decay involving neutral meson at Belle18 Signal efficiency and BG - electron modes - side band MC : data : b 0 0.7±0.7 0 0 – 0.0 0.0 ± 0.7 1 0.23 ± 0.23 0.0 ± 0.7 1 0.15 ± 0.15 0.8 ± 0.3 1 0.16 ± 0.16 +0.4

19. 9/15/2004Search for LFV tau decay involving neutral meson at Belle19 Result:   l  0, l , l  ’ 5 ev./2.7±0.7 1 ev./0.2±0.2 1 ev./3.1±1.0 0 ev./0.0 +0.4 0 ev./0.2±0.2 0 ev./0.6±0.4 0 ev./1.4±0.6 Preliminary  = 4.7%  = 6.8%  = 5.7%  = 8.5%  = 6.4%  = 7.2%  = 8.0%  = 8.4% -0.0 N obs /N exp

20. 9/15/2004Search for LFV tau decay involving neutral meson at Belle20 History of integrated luminosity Continuous injection 2003 Summer: SVD/CDC inner part replacement  L dt = 154fb -1  L dt = 288fb -1  L dt = 244fb -1

21. 9/15/2004Search for LFV tau decay involving neutral meson at Belle21 KEKB HER: 8.0 GeV e – LER: 3.5 GeV e + L peak = 13.9×10 33 /cm 2 /sec  Ldt = 287.85 fb -1 Cross section @ s =10.58GeV     : 0.9 nb BB : 1.0 nb performance snap shot (2004.3.1) Continuous injection mode LER 1.6A HER 1.1A L ~ 1.1×10 34 /cm 2 /sec KEKB is  Factory!!!.

22. 9/15/2004Search for LFV tau decay involving neutral meson at Belle22 Belle detector  / K L detection 14/15 lyr. RPC+Fe C entral D rift C hamber small cell +He/C 2 H 5 CsI(Tl) 16X 0 Aerogel Cherenkov cnt. n=1.015~1.030 Si vtx. det. 3 lyr. DSSD TOF conter Scinti + FM-PMT SC solenoid 1.5T 8 GeV e  3.5 GeV e   -ID eff. = 87.5% fake = 1.4 % e-ID eff. = 92.4% fake = 0.25 % proton ID eff. ~ 70 % fake ~ 1 % E  resol.  E /E = 1.8% @ E=1GeV Trk. resol.  pt /p t ~ 0.19p t  0.30/  %

23. 9/15/2004Search for LFV tau decay involving neutral meson at Belle23 Status of LFV search in Belle New result of this summer. CLEO Babar Belle Published Preliminary

24. 9/15/2004Search for LFV tau decay involving neutral meson at Belle24 Summary table of LFV search in Belle Preliminary result Published results New result in this summer. First search result. B < O(10 -7 ) are obtained

25. 9/15/2004Search for LFV tau decay involving neutral meson at Belle25 Systematic uncertainty Related sensitivity Related BG –Using statistical error as systematic error. (30~45%) –If b0 < 1, we set b0=0 in order to obtain conservative limit. In Total : 4.5 ~ 8.7 %  POLE program

26. 9/15/2004Search for LFV tau decay involving neutral meson at Belle26 2.1 Selection criteria ( 1-3 prong +  ’) –1-3 prong + n   2 E  > 0.1 GeV, barrel and endcap p trk >0.06GeV/c barrel. p trk >0.1GeV/c endcap. net charge=0. dz rms < 1cm, dr rms < 1cm  to reject junk track. signal side:  e  ID > 0.9 + 2trk(+,–). –Missing momentum towards tag side. –p miss vs. m miss 2 2-D cut. –0.5 < cos   ’ < 0.92 –-3  < M  < 3  using thrust axis, divide 2 hemisphere for tag side, m tag < 1.777 GeV/c 2  ’    e/ 

27. 9/15/2004Search for LFV tau decay involving neutral meson at Belle27 2.2 Selection criteria (1-1 prong +    ) –1-1 prong + n   2 signal side:  e  ID > 0.9 + 2 . P  e  >0.7GeV/c, E  > 0.22GeV –  0 veto for  ’s  tag side: –NOT  (e) –M tag < 1.777 GeV/c 2 Kinematical cut. –Missing momentum towards tag side. –p miss vs. m miss 2 2-D cut. –0.5 < cos   ’ < 0.92 –-5  < M  < 3  e/    