1 / 51

Search for Lepton Flavor violating decays t -  l - p 0 , l - h , l - h ’ at Belle

筑波山. Search for Lepton Flavor violating decays t -  l - p 0 , l - h , l - h ’ at Belle. Yuji Enari Nagoya University. Mt. Tsukuba. KEKB. Belle collaboration. Contents KEKB-Belle experiment Lepton Flavor violation Analysis Discussion and conclusion. 1. KEKB-Belle experiment.

alicia
Download Presentation

Search for Lepton Flavor violating decays t -  l - p 0 , l - h , l - h ’ at Belle

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. 筑波山 Search for Lepton Flavor violating decays t-l -p0, l -h, l -h’ at Belle Yuji Enari Nagoya University Mt. Tsukuba KEKB Belle collaboration

  2. Contents • KEKB-Belle experiment • Lepton Flavor violation • Analysis • Discussion and conclusion Search for LFV decays at Belle, Y. Enari

  3. 1. KEKB-Belle experiment Continuous injection mode HER: 1.2A  s = 10.58 GeV LER: 1.7A KEKB : Asymmetric energy e+e- Collider ARGUS 0.4fb-1 → ～8時間 Lpeak = 1.58 1034cm-2s-1 Ldt = 450 fb-1 World Record バンチ数: ~1200個 バンチサイズ：３mm/100mm (長さ２cm) e- : 8GeV e+ : 3.5GeV Cross section tt：0.9 nb BB : 1.0 nb 約１5Hｚでtt対が生成される。 KEKB ist-Factory Search for LFV decays at Belle, Y. Enari

  4. History of integrated luminosity Ldt = 450fb-1 Continuous injection Ldt = 244fb-1 Ldt = 154fb-1 2003 Summer: SVD/CDC inner part replacement Search for LFV decays at Belle, Y. Enari

  5. 1.2 Belle detector KLM RPC+Fe, sandwich structure Cylindrical Coordinate： e- Beam axis as ｚ axis. ECL CsI(Tl)16X0 Eg resol. E /E = 1.8% @E=1GeV 3.5 GeVe+ SC solenoid 1.5T 8 GeVe- ACCn=1.015~1.030 Sp/K ~ 3 s @ p < 3.5GeV/c TOF Scinti + FM-PMT sTOF = 100ps, Sp/K ~ 2 s @ p<1.4GeV/c SVD 3 lyr. DSSD CDC small cell +He/C2H6 Size ： 7m×7m×7m、　Weight : 2000t Search for LFV decays at Belle, Y. Enari

  6. 1.2 Performance of Lepton ID Electron ID Muon ID KLM: (a) # of Hit layer (b) Shower Shape ECL : (a) E/p (b) XECL-Xtrk (c) E9/E25 CDC: (d) dE/dx ACC: (e) Nphoton Efficiency (%) ~90% ~92.5% Fake rate (%) ~1.5% ~0.25% Search for LFV decays at Belle, Y. Enari

  7. Small cell drift chamber installation (2003. Aug.) • SVD upgrade (3Layer 4 layer) • To fit CDC configuration for SVD upgrade. • To reduce hit rate of Cathode part. HER 1.1A LER 1.5A L=9.6x1033cm-1s-1 Hit rate/wire(kHz) Cathode Inner Main Partial cross section of CDC (50 layer.) Layer Search for LFV decays at Belle, Y. Enari

  8. Small cell drift chamber • Replace Cathode chamber (1cm-cell 3 layers w/ cathode r~8cm) to Small cell chamber (5mm-cell / 2 layers r~10cm). Small cell Installation Search for LFV decays at Belle, Y. Enari

  9. Alignment after installation • Measure following variable using cosmic track. • rotation angle Df • shift length Dx,Dy for both forward and backward in each layer. of endplate Result: Large Dy~200mm were observed in Inner layers at forward. Small cell Inner Main part Search for LFV decays at Belle, Y. Enari

  10. Tracking performance after installation (CDC) Make alignment and calibration constants. spatial resolution pt resolution di-muon data sample. Small cell s = 120 mm Dpt/pt = 1.5% Normal cell (@before) s = 100 mm CDC tracking system work well with having good resolution. Search for LFV decays at Belle, Y. Enari

  11. Search for Lepton Flavor Violating decays. Search for LFV decays at Belle, Y. Enari

  12. 2. Lepton Flavor Violation In Standard Model, there is no Lepton Flavor Violation. Each lepton number is strongly conserved. Recently neutrino oscillation has been observed. Although take into account neutrino oscillation, expected branching ratio of LFV in charged sector is B < 10-40. ダークマター？　 ダークエナジー？ レプトンフレーバー保存則 レプトンの世代を超える遷移を禁止 m→e, t→ e/m  How strong is Lepton number? (Simple motivation) If we find LFV,  Direct evidence of New physics. Search for LFV decays at Belle, Y. Enari

  13. LFV in BSM If mn ~ 1 eV： B(t→LFV)<10-40 B(t→LFV) If our sensitivity is O(10-7), reach MSSM level. Search for LFV decays at Belle, Y. Enari

  14. Minimal Super-symmetric Standard Model M. Sher, Phys.Rev.D66 05731(2002) K.S.Babu PRL,89,241802 (2002) A. Dedes, et.al. PLB 549,2442 (2002) • Higgs mediated process t- m-h t- m-m+m- A0:CP-odd neutral Higgs boson. （１）Phase space 　　 → 2 body decay is bigger. （２）Color effect. 　　 → 3 times bigger. （３）Mass difference. 　　 → Bmh / Bmmm （ms/mm）2 Bt → mhis 8 times bigger than Bt → mmm Search for LFV decays at Belle, Y. Enari

  15. Purpose of this analysis. We search for LFV tau decay using t pair events of e+e- annihilation process, as evidence beyond the Standard Model. Signal modes：t-l - + M0 lepton pseudo-scalar meson (1) t- m-h (2) t- m- p0 (3) t- m- h’ • (4) t-e- h • (5) t-e- p0 • (6) t-e- h’ Search for LFV decays at Belle, Y. Enari

  16. Previous experimental results s0 2(eeff Ntt) B = eeff : 検出効率 Ntt : t+t-対の数 s0 : 信号事象数 • Using e+e- → t+t- process MARKII ARGUS B(p0gg) = 98% B(hgg) = 39% = 2.5 CLEO 90% C.L. U. L. on Br hの再構成： 改善が可能 This analysis Ntt = 137 M ？ MSSM Number of t+t- events B(p0gg) = 99% B(hgg) = 39% Data ： 4.26106 events Efficiency ：t→mh: 2.9% t→mp0: 6.8% Background ： t→mh: 0ev. t→mp0: 0ev./0.5ev. (obs./exp.) Search for LFV decays at Belle, Y. Enari

  17. 3. Analysis Procedure 1．Selection criteria - High signal efficiency - BG suppression 2．Signal extraction - e/m and p0,h,h’ - set signal box - BG estimation 3．Determine branching ratio （→　add subdecay mode for M0．） 検出効率 背景事象 は密接に関係。 Blind Analysis method To avoid making vias into results, we shaded around signal region at very first level until end of BG estimation. Search for LFV decays at Belle, Y. Enari

  18. 3.1 Signal event reconstruction Type mode BM 1－1 h→gg 39.4% 1－3 h→ppp0 22.7% (e+) signal side ( e/m + p0, h, h’) + tag side (1 trk + ng+ missing.) signal side： 1or 3 prong Br(t1 prong) = 84 % ・ recon. modes for p0, h, h’ tag side: 1 prong t decay h  gg ppp0 p0 gg h’ pph 検出効率 背景事象 Additional mode. ・ p0,h’の再構成モード • は密接に関係。 • →　信頼度の高い測定を行うために　 • ブラインド・アナリシス　を適用した。 Search for LFV decays at Belle, Y. Enari

  19. 3.2 BG suppression Level-1 Bhabha, m+m-process These events account for 95%. 　　　　　　→Reject at first level. Total Energy see ~ 120 nb smm= 1 nb Feature：Huge Cross section No missing momentum 　 　　↓ Rejection: e/m veto in tag side signal :5% loss mm : →1/45 ee : →1/4900 2 photon process seexx ~ 20 nb Feature: Large Cross section Low Pt. particles escape to Beam pipe. Rejection: pt, missing momentum towards acceptance. → Rej. Factor : 1/10000 Search for LFV decays at Belle, Y. Enari

  20. 3.2 BG suppression Level-2 qq process sqq = 4.2 nb • Opening angle of land M0. Feature： Multi prong includep0,h,h’。 sig : 2 % loss tt : 67% rej. uds: 65% rej. p0veto for h’s g Mtag< 1.777 GeV/c2 →Rej. Factor :1/83000 t+t-pair process stt = 0.9 nb Feature: Similar topology with signal Includee ,m,p0,h． Having n, large missing p. Rej. factor : 1/2900． Search for LFV decays at Belle, Y. Enari

  21. 3.2 BG suppression • Hard to reject tt events : Main BG. ←No p0/h. :Can be reject. Need additional criterion to reject tt process Search for LFV decays at Belle, Y. Enari →tt対事象以外は10-6~7の除去率だが、 tt対事象は1/3000.

  22. 3.2 BG suppression －newly applying cut－ Signal event : n are only in tag side. tt process : n are in both tag and signal side.  Having effective missing mass:mmissing become large. 2 black: signal MC Blue: tt generic Signal ev. tt process 欠損運動量 : pmissは測定可能領域に向いていること. Apply this cut : Signal event : 17% loss tt process: 95% reject. Search for LFV decays at Belle, Y. Enari

  23. 3. Analysis Procedure 1．Selection criteria - High signal efficiency - BG suppression 2．Signal extraction - e/m and p0,h,h’ - set signal box - BG estimation 3．Determine branching ratio 検出効率 背景事象 は密接に関係。  Blind region also explained. Search for LFV decays at Belle, Y. Enari

  24. 3.3 Signal extraction – e/m and p0,h,h’ – Data: 57ev. MC : 48.1±4.0 77ev. 81.6 ± 8.4 p0 h’ gg gg -3s < M h’ < 3s -5s < Mp < 3s Lepton ID requirement for track. Invariant mass distribution. (mID; 1.3<Mmh<2.1; with Blind) 109ev. 100±5.9 Data: MC : h 背景事象の構成 　　レプトンの誤識別：　全体の80％ 　　（p,Kを mと間違える） gg -5s < M h < 3s p0 : p0を含む事象 h,h’ : 偶然入ってきた事象 Good agreement are seen for sideband events. Search for LFV decays at Belle, Y. Enari

  25. 3.3 Signal event extraction Blind region • Blind region: • -0.5< DE < 0.5(GeV), • -5s < MlM< 5s t- m-h Blind region 検出効率 背景事象 信号領域とブラインド領域の設定 shi=35±1 MeV は密接に関係。 →　信頼度の高い測定を行うため　　　　 ブラインド・アナリシスを適用． ±10s ±10s slow=57±4 MeV 選択条件、背景事象の見積もり終了まで 信号領域付近のデータを見ずに解析を行う． (a) Inv. mass MlM should be tau mass. MlM= E2l M- p2l M (b) energy ElM should have beam energy. DE = ElM – Ebeam ±5s ±5s ±10s ±10s slow=25±2 MeV/c2 shi=14±2 MeV/c2 Ml M * signal event： Ml M=mt, DE=0 signal region： Elliptical shape which having efficiency of 90%.  Shape is determined by minimize the area. S/N is improved 1.5 times than sqare shape (et→mh~8%)． Search for LFV decays at Belle, Y. Enari

  26. 3.4 Background property (153.8,428, 232fb-1) レプトンの誤認識率の違い　 e ID: 0.25%, mID: 1.4% (誤認識率の違い)e ID: 0.25% mID: 1.4% - BG of muon modes are larger than electron modes.  The fake rate of lepton ID. - There is no peaking BG around signal region. Search for LFV decays at Belle, Y. Enari

  27. 3.4 Background Estimation 一様 2.65  0.74 2.65  0.74 Flat b0= b0= 2.95  0.82 Func b0= Try two pattern for BG function. Using sideband events. - Projection in each axis. - Fit BG events by Gaussian and 3rd polynomial -Normarized by sideband events. S楕円 一様 b0= Nサイド Sサイド サイドバンド の事象数 Flat distribution. Difference ： 0.30  take account as systematic error Search for LFV decays at Belle, Y. Enari

  28. 3.5 Signal efficiency and BG events - S/N - 1.7 1.5  1/5 Open Blind. High signal efficiency High BG suppression IfB= 510-7 , S/N=3~12． 　　　　　　→　3s observation can be achieved. 過去の実験: 0.5 ev. @ 4.7fb-1 ↓ 16 ev. @ 154 fb-1 are obtained Search for LFV decays at Belle, Y. Enari

  29. 3.6 Results　－Observed eventsー BG expect 3.9±1.2 0.6±0.4 3.0±0.8 0.9±0.4 5 ev. 1 ev. 0 ev. 0 ev. BG expect 0.2±0.2 0.2±0.2 0.0±0.4 0.3±0.2 0 ev. 1 ev. 0 ev. 0 ev. # of observed events are consistent with estimation． →　Set upper limit on Branching ratio． Search for LFV decays at Belle, Y. Enari

  30. 3.7 Systematic uncertainty s0 2(eBX Ntt) B = s0 2 Ntt BM0eeff • Concerning to s0 　　　→BG estimation Difference of two pattern - If b0＜1, set b0=0 in order to obtain conservative limit. • Concerning to sensitivity B = M0 recon. 2.0~4.0% Tracking 2.0% p0 veto 0 or 5.5% e ID 1.0% m ID 2.0% Trigger 0.5~0.7% Beam BG 2.1~2.3% MC model 0.5% MC stat. 0.8~1.7% Ntt 1.4% BM0 0.7~3.4% Total: 4.2 ~ 8.6% Total: 30 ~ 66 % Search for LFV decays at Belle, Y. Enari

  31. Upper limit on branching ratio（90％C.L.) • Upper limit evaluation (POisson Limit Estimator program) • Frequentist approach. J. Conrad et al., PRD 012002 (2003) • Systematic uncertainty: using the Gaussian error. 崩壊分岐比の上限値 Search for LFV decays at Belle, Y. Enari

  32. 4. Discussion Ldt # of BG CLEO 4.7 0.5→16 Belle 154 3.0 ratio 32 1/5 CLEO Efficiency： Add M0 recon. mode 　　　→ Gain 1.5~1.7 MSSM Higgs mediated R-parity-V First search result! Improve in efficiency and BG suppression from previous result. 　　→ Reach 10-7 level which is expected from MSSM. Search for LFV decays at Belle, Y. Enari

  33. Constraint on tanb vs mA In tanb> 50, mA > 110GeV/c2 This limit is comparable with Energy frontier experiment, Tevatron Search for LFV decays at Belle, Y. Enari

  34. Summary • Search for LFV decays t-e-p0,m-p0,e-h,m-h,e-h’,m-h’ using 137106t+t- pair events which are accumulated at KEKB-Belle experiment. • Achievement ：　Improve sensitivity by 64 (max.) （１）# of tt : Using 32 times larger statistics. （２）Efficiency : Add recon. M0 mode． →Gain 1.5~1.7 → First search for h’ mode. （３）BG :Newly missing cut apply →~ 5 times improve. （４）Reliability: Blind analysis Apply two pattern in BG estimation. • Result： No excess in signal region. Set 90% C.L. upper limit on branching ratio． The limits reach 10-7 level, put constraint on MSSM． In tanb> 50, mA > 110GeV/c2 → Comparable sensitivity with Tevatron． Search for LFV decays at Belle, Y. Enari

  35. Backup Search for LFV decays at Belle, Y. Enari

  36. Remarkable points s0 2 Ntt・eeff・BM0 B = 検出感度を決める Event selection criteria is most important. Sensitivity: s0 : # of signal events 探索実験のポイント BM0 : Branching ratio of M0 → KEKB-Belle実験のデータを使用 (1) # of t+t-pair (Ntt) (2) Signal detection efficiency(eeff) (3) Background Suppression factor:1/108 BG estimation. 再構成モードを増やすこと で効率の向上を図る。 　→ Add reconstruction mode for M0 →s0の測定精度 →Reliability Search for LFV decays at Belle, Y. Enari

  37. For future, Super B-factory project. Search for LFV decays at Belle, Y. Enari

  38. Status of LFV search in Belle Belle Published Preliminary New result of this summer. CLEO Babar Search for LFV decays at Belle, Y. Enari

  39. Systematic uncertainty Search for LFV decays at Belle, Y. Enari

  40. Signal MC model dependence. Search for LFV decays at Belle, Y. Enari

  41. Status for mu to e transition m  e B(m  eX) < 10-11~12 Search for LFV decays at Belle, Y. Enari

  42. Belle collaboration. • ~ 400 physicists from 59 institutions, 13 regions. • ~ 100 scientific papers were published. Search for LFV decays at Belle, Y. Enari

  43. Belle detector. • General purpose detector. • Super conducting Magnet. (1.5T) Belle control room Search for LFV decays at Belle, Y. Enari

  44. XT Curve & Max. Drift Time Normal cell Small cell Search for LFV decays at Belle, Y. Enari

  45. rf平面 運動量測定: 軌跡測定から spt/pt ~ 0.19pt0.30/b % TOF ACC CDC ECL 光子: 軌跡を伴わないECLのヒット 　　E /E = 1.8%@E=1GeV • e+e- → t+ t- →p-n • r+n • p+p0 Search for LFV decays at Belle, Y. Enari

  46. Official Goal Installation of Crab Cavity We are here. • 550 /fb will be reached before the Crab Cavity. • The Official Goal (=1 /ab) will be achieved before Summer 2007. Search for LFV decays at Belle, Y. Enari

  47. Shutdown for 18-26 months in 2009-2010 for upgrade. • 0.6 /ab/month in 2020. SuperKEKB Installation of Crab Cavity Shutdown We are here. Search for LFV decays at Belle, Y. Enari

  48. Motivation - t  l p, l h, l h’ - • In MSSM at large tanb region, t  mhmay havelarge branching ratio by Higgs mediated process. • Correlation between other mode • Br(t 3l )/ Br(t mh) ~ 0.2 • Br(tmp0)/ Br(t mh) ~ 0.006 • Br(tmh’)/ Br(t mh) ~ 0.004 M. Sher, Phys.Rev.D66 05731(2002) K.S.Babu PRL,89,241802 (2002) A. Dedes, et.al. PLB 549,2442 (2002) A.Brignole and A Rossi, hep-ph/0404211 The ratio could be a few times larger or smaller. It depend on radiative correction.  backup Our sensitivity reach this level. We can put constraint on tanb and mA Search for LFV decays at Belle, Y. Enari

  49. 2.1 Selection criteria ( 1-3 prong + h/h’) • 1-3 prong + ng2 Eg > 0.1 GeV , barrel and endcap ptrk>0.06GeV/c barrel. ptrk >0.1GeV/c endcap. net charge=0. dzrms < 1cm, drrms < 1cm  to reject junk track. signal side: m(e)-ID > 0.9 + 2trk(+,–). • Missing momentum towards tag side. • pmiss vs. mmiss2 2-D cut. • 0.5 < cosqmh’ < 0.92 • -3 s < Mh < 3 s e/m h/h’ p0/h using thrust axis, divide 2 hemisphere for tag side, mtag < 1.777 GeV/c2 Search for LFV decays at Belle, Y. Enari

  50. 2.2 Selection criteria (1-1 prong + p0/h) • 1-1 prong + ng  2 signal side: m(e)-ID > 0.9 + 2 g. Pm(e)>0.7GeV/c, Eg > 0.22GeV • p0 veto for h’s g tag side: • NOT m(e) • Mtag < 1.777 GeV/c2 Kinematical cut. • Missing momentum towards tag side. • pmiss vs. mmiss2 2-D cut. • 0.5 < cosqmh’ < 0.92 • -5 s < Mh < 3 s e/m p0/h Search for LFV decays at Belle, Y. Enari

More Related