1 / 37

t -  p - p 0 n t decay at Belle

t -  p - p 0 n t decay at Belle. Tau08; Novosibirsk, 22-25, September, 2008 Hisaki Hayashii Nara women’s University. hadron. +CVC. Introduction. Hadronic decays of tau lepton provide clean environment for studying the dynamics of hadronic states. a s (s), a m , V us , m s

aislin
Download Presentation

t -  p - p 0 n t decay 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. t-p-p0nt decay at Belle Tau08; Novosibirsk, 22-25, September, 2008 Hisaki Hayashii Nara women’s University Tau08

  2. hadron +CVC Introduction • Hadronic decays of tau lepton provide clean environment for studying the dynamics of hadronic states. as(s), am, Vus, ms • t-p-p0nt • has the largest Br • CVCrelation with e+e-→p+ p- • Plays an important role for the h. v. p. term in the muon anomalous magnetic moment. am=(gm-2)/2

  3. not yet published not yet published preliminary Introduction（cont.） • Recent data indicate that there is a systematic difference between the 2psystem in e+e－reaction and t-decays, even after applying knowniso-spin violation correction. Main difference btw and is from 2p mode. ICHEP-2006(M.Davier et al.): am(exp)-am(th) is Ahint to New Physics beyond the SM!

  4. What should be measured • In this talk, We present update results from Belle experiment based on 5.6x 106t-p-p0ntdecays (72.2/fb). • Branching Fraction • Mass Spectrum spectral function B-factory exp. : final state particles are separated well. c.f. LEP exp.

  5. DATA unfolding（correct the detector effect） Unfolded p+p- distribution Extract pion form factor evaluation of the Analysis Procedure 72.2/fb event selection • e+e-t+t- selection • t-p-p0nt selection • Background subtraction • Unfolding • Br measurement • Extract pion form factor |Fp(s)|2 • Fit with Breit-Wigner Form • Evaluation of am event selection distribution unfolded distribution

  6. Low multiplicity: Number of charged tracks：2 or 4, net charge=0 Rejection of Bhabha and m+m-; S|P|*< 9 GeV Physics background rejection: Use Missing Mass and Missing Angle information.(Bhabha,2photon) Low track and gamma multiplicity. (qq continuum) Event Selection e+e-t+t- Selection t-p-p0ntSelection charged track • one charged track in the event hemisphere. • one p0 in the event hemisphere. • No additional g with Eg≥200MeV • Tag-side condition: 1, 3 prong+ any g : For Br measurement 1 prong + no g : For mass spectrum p0

  7. e+e-t+t- Selection Two photon Bhabham+m- Particle multiplicity

  8. t-p-p0nt p0Signal Sideband region Signal region right： left： • Sideband region is used to estimate the non-p0 background Generally background free, but non-negligible BK In the low Mpp0 region. 5.6M events -Ｓｉｄｅ　ｂａｎｄ　ｒｅｇｉｏｎ：　Ｄｏｍｉｎａｔｅｄ　ｂｙ　ｔｈｅ　ｔａｉｌ　from　ｔｒｕｅ　“p0” -Reproducing the signal shape by MC is important.

  9. t-p-wnt(wp0g) m2ppdistribution • Thesignal level is different more than 4th order of magnitude betweenr(770) and r’’(1700). • Background • non-t B.G. • feed down B.G. Tau mass limit BG is important at threshold and r’’ region.

  10. Some important features • New MC set • New t MC (include r” to TAUOLA MC) • More reliable estimate of continuum BG • Estimate continuum using BG enriched sample. • Require stronger cut for tag side • 1 charged track + no g • More reliable estimate of feed-down BG. some modes have small Br but dominate in the special region. i.e. threshold region • t-p-wnt(wp0g) • t-p-p0KLnt etc. • Systematic study • p0 side band, efficiency check

  11. Acceptance Data are Unfolded with the Singular Value Decomposition (SVD) method. Acceptance (including tagging eff.)

  12. Results • Br • Mass Spectrum • Pion form factor • Extract resonance Parameters • Comparison with previous exp. • Evaluation of am and iso-spin violation correction.

  13. Belle 25.24 0.04 0.39 Result (1) Branching Fraction • Normalized to the number of t-pairs • Tau-pair selection acceptance : 32.6 0.05% : 1.1120.003 background : 7.8 0.03% • pp0 selection Acceptance: 41.0 0.1 % Background feed down: 7.02 0.08 % qq-conti. : 2.22 0.05 % • Br2p= (25.24 0.01（stat) 0.39(sys))%

  14. Systematic on Br Measurement • Source Tracking efficiency 0.47 p0 efficiency 1.3 Background in t-pair 0.59 Feed down background 0.16 Continuum background 0.20 g veto 0.20 Trigger 0.32 MC statistics 0.08 Total 1.52 • Systematic is dominated by the uncertainty of the p0 efficiency and the BG in t-pair p0 • Calibrated by h signals ( ). • Checked by using electron tracks.

  15. Number of entries /0.05 (GeV/c2)2 Result (2): Mass spectrum Unfolded Results Mass spectra ＝ Phase space × Form Factor

  16. 2 F p Result (3) Pion Form Factor |Fπ|2 From 64M t+t-pairs, Belle selects 5.5M t-p-p0nt events! |Fπ|2 • Error bars include both statistical and systematic • Interference between r’ and r” • Fit with BW

  17. Systematic on the mass distribution (1) • Unfolding procedure • Reproducibility of the signal. （UNF ①） • Unfolding condition : value±5　（UNF ②） • Acceptance (Accept.) • p0 efficiency uncertainty • Effect of g-track isolation • Change a cut on the cluster-track distance （default and tighter one(30cm）) • Momentum or energy scale (ENS) • Change Eg by it’s uncertainty estimated from the p0 mass peak position.(±0.2％)

  18. Systematic on the mass distribution (2) • Background • Continuum BG (BKG ①) • estimate at the mass region higher than mt • uncertainty  is estimated to be 10% • Feed down BG (BKG ②) • dominated by t-p-2p0nt • systematic is estimated by changing the Br in PDG by 1s • non-p0 BG (BKG ③) • dominated in the low (Mpp0)2region. • In this region, the size of the non-p0 background in the lower Mgg side is different between data and MC. This differences is corrected and the difference is included as a systematic.

  19. 0.10<(Mpp0)2<0.15 0.55<(Mpp0)2<0.60 Non-p0 background( details). p- p0 F=1 F=1.375 Mgg Mgg

  20. Systematic on the Mass Spectrum/Form Factor ( %) by Toy MC Systematic Region Dominant Factor 0.7-1.8% r,r’ Energy scale/Unfolding 5% threshold Background (p0, feed down) 10% r’’ Continuum BG

  21. Result(4)Resonance parameters • Fit with BW form r(770), r’(1400), r’’(1700) • Gounaris-Sakurai (GS) parameterization • 10 fit parameters • The normalization of the GS form is given by

  22. Fit Results PDG2006 Hadron reaction t, e+e- 775.4 0.4 ± 766.5 1.1 ± 150.2 2.4 ± 146.4 1.1 ± fit with r’’ x2/ndf=80/(90-10) fit w/o r’’ x2/ndf=135/(90-6) Significance of r’’ : 6.5 s • All r, r’, r’’ resonance parameters are determined at the same time! Most precise

  23. 2 2 F F p p Comparison with previous exp. BELLE & ALEPH BELLE & CLEO Ref: Phys. Rep.421 (2005) 191 Ref: Phys. Rev. D61, 112002(2000) 1 • Agree with previous exp. of data. • Our result is more precise especially in high mass region.

  24. Detailed Comparison:r, r’ region Fit: Fit to Belle Data • Belle-CLEO consistent, • ALEPH is higher at (Mpp)2 > 0.8 GeV2; Effect on am2p? i

  25. Evaluation of am(2p) World average is calculated combining our new result

  26. am （２p）: contribution from each mass range X 10 -10 Belle> ALEPH Belle<ALEPH No iso-spin violation correction is applied Total

  27. Iso-spin Violation Correction • Ref. V. Cirgliano et al., J. High Energy Phys. 08, 002(2002) A.Flores-Tlalpa et al., Phys. Rev. D 74, 071301 (2006) Source Correction Uncertainty Short distance rad. Cor (SEW) - 12.0 ± 0.2 Long distance rad. Cor.(GEM) - 1.0 mp- = mp0(in phase space) - 7.0 r-w interference + 3.5 ±0.6 mp- = mp0(in decay width) +4.2 Electromagnetic decays -1.4 ± 1.4 mr0 = mr– - ± 2.0 Total -13.7 ± 2.5 X10-10 FSR correction in e+e-Vg->p+p-g: +4.2  Total+FSR = -9.5 2.5 ±

  28. Results (5) am （２p） • Integrated region: • After applying the known iso-spin violation correction. • Belle(t) • ALEPH, CLEO, OPAL (t) Ref. Eur. Phys. J. C27, 497 (2003) • CMD2,SND (e+e-) Ref. Nucl. Phys. Proc. Suppl. 169, 288 (2007) t results are higher than those from e+ e-.

  29. Summary • We have studied t-p-p0ntusing high statistics Belle data • Br measurement: (1.6% accuracy) • Precise 2p mass spectrum and the pion form factor are determined. Wecan provide them by a table. • Inaddition to r(700), r’(1400),the production of r’’(1700) is unambiguously identified and its parameters are determined. • Our results for agree with the previous t based results but are higherthan those from e+ e-. The paper is accepted by PRD and will appear in Oct. issue. The results are accepted by PRD, will appear in Oct. issue.

  30. Backup Slide

  31. Comparison :t-->p-p0nt and e+e-->p+p- • by F. Jegerlehner (private commun.)

  32. Internal Systematic Error

  33. r-w interference • r-w interference effects are estimated using following form for the amplitude.

  34. Pion Form Factor |Fπ|2 (linear scale) Low mass region r mass region Error bars include both statistical and systematic

  35. Systematic of resonance parameters (MeV) (MeV) (MeV)(MeV) (deg.) (MeV) (MeV) (deg.)

  36. Belle detector Mt. Tsukuba Ares RF cavity KEKB Belle e+ source ~1 km in diameter The KEKB Collider SCC RF(HER) World record: L = 1.7118 x 1034/cm2/sec First successful op. of Crab cavities ARES(LER) 8 x 3.5 GeV 22 mrad crossing since 1999

  37. Belle detector SC solenoid 1.5T Aerogel Cherenkov cnt. n=1.015~1.030 CsI(Tl)16X0 p0 mass resolution; sp 0 ~ 5 -8MeV 3.5 GeVe+ TOF counter Central Drift Chamber Tracking +dE/dx Small cell +He/C2H６ 8 GeVe- Si vtx. det. 3 lyr. DSSD • / KL detection 14/15lyr. RPC+Fe Good tracking and particle identification

More Related