1. 27/September./2008Satellite Meeting on Super Tau-Charm Factory 1 Search for  ->  /e  at the Super-  -charm Factory [Comments from Belle experience] This talk is based on a study done for Super-B factory by T. Iijima, K. Hayasaka (Nagoya U.) H. Hayashii (Nara)

2. 27/September./2008Satellite Meeting on Super Tau- Charm Factory 2 Introduction Lepton flavor violation (LFV) in charged lepton ⇒ negligibly small probability in the Standard Model (SM) even including neutrino oscillation - Br(  →ℓ  ) <O(10 -54 ) Why SM + m  prediction is so small ?  (or e)   W-W- γ  : PMNS neutrino mixing matrix :Neutrino mass square difference -Lepton Flavor is conserved accidentally. -If O(1TeV) particles exit, Br is enhanced significantly, Theory needs some suppression mechanism. -Almost all Beyond Standard Model predict LFV

3. 27/September./2008Satellite Meeting on Super Tau- Charm Factory 3 Status of LFV  Decay Searches (Tau08) (based on data) B-factory CLEO ℓf 0 (980) ℓℓℓ ℓhh’ ℓV0ℓV0 ℓℓ ℓ//0ℓ//0 ℓKs 10 -7 10 -8 10 -6 10 -5 Upper limits for LFV  decay Improve by factor ~100 from CLEO update from TAU06

4. 27/September./2008Satellite Meeting on Super Tau- Charm Factory 4  →  e   (PLB666,16(2008)) Data: 535fb -1 Br(  →  )<4.5x10 -8 at 90%C.L. Br(  →e  )<1.2x10 -7 at 90%C.L. Results from Belle (1) signal data  →   →  (→  )  →e/  +(  ’   ) (PLB648, 341 (2007)) Data: 401fb -1 Expected BG : (0.0-0.6) events N obs : 1 event Br(  → ,  ’,  0 )<(6.5-13)x10 -8 Br(  →e ,e  ’,e  0 )<(8.0-16)x10 -8 signal region Final state: 1-prong decays and others Remaining many BG from e + e - →  +  -   sensitivity is limits by the background

5. 27/September./2008Satellite Meeting on Super Tau- Charm Factory 5 Super-B and Super  -c Factory B-factory (    nb, root(s)=10.6 GeV) L =10 36 cm -1 s -1    /year Super-B at Roma =3x10 35 cm -1 s -1 Super KEKB  -c factory (    nb, root(s)=4.25 GeV) L= 10 35 cm -1 s -1 3.5x10 9  /year -Final reach depends on, efficiency, background -Typical efficiency in B-factory exp.: 5-10%. -Background

6. 27/September./2008Satellite Meeting on Super Tau- Charm Factory 6 Super B-factory Expected sensitivity  →ℓ  Br~O(10 -8~9 )  →ℓℓℓ, l+meson Br~O(10 -9~10 ) ▲ Super (KEK)B-factory:(10~50) ab -1 Br(  →  )<3x10 -10 @50ab -1 Current UL@Belle Br(  →  ) <3.2x10 -8 @543fb -1 Super (KEK) B GOAL: Improve the sensitivity by additional factor of 100 and achieve 10 -10  and  >e  Background dominated

7. 27/September./2008Satellite Meeting on Super Tau- Charm Factory 7 Some detail of    search e + e    +   e e     generic  decay signal event  (signal side) 1 prong + missing ( tag side) for signal event signal MC 3  ellipse: blinded region signal extraction: M   E plane blind analysis -Tag side is not muon.

8. 27/September./2008Satellite Meeting on Super Tau- Charm Factory 8 Analysis of    search II Main BGs: –  +ISR  (    ) –  +ISR  Requirement on missing mass usefulto reduce     BG (signal: 1or2 ;  :>2 ) signal extraction: –Unbinned Extended Maximum Likelihood fit likelihood function: e e    ISR  BG:  +ISR  e e   ISR  BG:  +ISR  generic  decay signal data

9. 27/September./2008Satellite Meeting on Super Tau- Charm Factory 9 Result of    search Lum:535fb -1 (Belle) more tight requirements to reduce BG than the previous 86 fb-1. remaining events: 94ev./535fb -1 signal detection eff.: 11%  6.7% signal region: 5  box  2  ellipse signal extraction: UEML fit result:s=  3.9, b=13.9 (allow negative s and its prob. 25%) Br<4.5x10 -8 at 90%C.L. signal data 2D fit on M  E plane blinded region

10. 27/September./2008Satellite Meeting on Super Tau- Charm Factory 10  BG events in    analysis If we can remove BG events caused by ISR completely… When we run an accelerator with lower energy than  (4s), Can we reduce these ISR BG events? 1.5 ab -1 generic  MC sample removed by MC generator info. 90% events removed!

11. 27/September./2008Satellite Meeting on Super Tau- Charm Factory 11 ISR Spectrum At near threshold –E  for ee   background cannot be as high as E  for   . –Background from ee   will become more important.  good MUID is essential. E  (CMS) from    and ISR(  )  (4s) maximum 

12. 27/September./2008Satellite Meeting on Super Tau- Charm Factory 12 Summary    Background source: 1) ISR ee->  2) ee->  where tag-side muon is miss identified as pion. Achievable sensitivity in Super (KEK) B-factory sensitivity will be limited by ISR BG although there is a room to optimize selection criteria. High intensity  c factory running at root (s)= 4.25 GeV is ideal place for  as well as  ->e  searches. Very good  separation is essential to suppress ee->  background.

13. 27/September./2008Satellite Meeting on Super Tau- Charm Factory 13 Backup Slide

14. 27/September./2008Satellite Meeting on Super Tau- Charm Factory 14  pair production cross section Threshold at 3.55GeV Maximum at 4.25GeV (  (  (4s))x 4)  : velocity of  B-factory