A High Statistics Study of the Decay

1. A High Statistics Study of the Decay Outline 1.Introduction 2.Experiment Belle detector 3.Analysis Event selection Mass spectrum Muon anomalous magnetic moment 4.Summary M. Fujikawa for the Belle Collaboration

2. hadron Introduction • The hadronic vacuum polarization term plays an important role in the theoretical calculation of the muon anomalous magnetic moment. • The dominant part of the hadronic vacuum polarization term can be calculated from the 2p Spectral function measured with e+e－ or t data. • Recent data indicate that there is a systematic difference between the 2p system in e+e－reaction and t-decays, which needs to be understood. +CVC • In this talk, results from Belle experiment are presented. • Results are based on 72.2/fb data taken in 2000-2002 period. • One order of magnitude more data than preceding experiments.

3. spectral function fine structure constant What should be measured • Branching Fraction • Mass Spectrum

4. Experiment Apparatus : 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. 4 lyr. DSSD • / KL detection 14/15lyr. RPC+Fe Good tracking and particle identification

5. Low multiplicity: Number of charged tracks：2 or 4, net charge=0 Beam background rejection: Event Vertex Position 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 charged track t-p-p0nt Selection p0 • one charged track in the event hemisphere. • one p0 in the event hemisphere. • veto any additional gammaswith

6. Mass invariant mass distribution resolution of p0Signal Sideband region Signal region right： left： Sideband region is used to estimate the non-p0 background t-p-p0nt 5.55×106 event

7. m2ppdistribution • B.G. estimated by MC • non-t B.G. Checked above kinematical limit of tau decay • feed across B.G. • t-→p-p0ntMC(TAUOLA) Includes r(770),r’(1400) Does not include r”(1700)

8. Mpp0(generated) ２ ２ Mpp0(observed) Acceptance correction After background subtraction, data are Unfolded with the SVDmethod. Singular Value Decompositionmethod Ref.Nucl.Instr.Math.,A372,469(1996) Acceptance (GeV)2 (GeV)2

9. Fit with BW Forms. Next slide Number of entries /0.05 (GeV/c2)2 2 2 F F p p Mass spectrum after Unfolding Pion Form Factor|Fπ|2 Mass spectrum phase space Form Factor r Interference between r’andr” r” r’ Dip at s=2.5 GeV2 Agrees with ALEPH data. Our result is more precise especially in the high mass region.

10. fit parameter Parameterization of resonances r(770), r’(1400), r’’(1700) Gounaris-Sakurai(GS) parameterization Normalization: BW=1 at s=0 GeV

11. Fit result • 1st Errors: Statistical • 2nd Errors: Systematics. • Sources: • 1. Photon energy scale • 2. Unfolding Procedure • (DRank = +/- 3) • 3. Background Subtraction.

12. Stat. error only Comparison with preceding experiments strong correlation between Mr” and fg

13. Hadronic vacuum polarization am • Threshold region(0.25GeV2<Mpp2) is not included because the experimental uncertainty is large.

14. Internal Systematic Error

15. External parameters World average is calculated combining our new result and the preceding measurements of other experiments.

16. am(2p) after SU(2) correction • Isospin breaking correction in this mass region. • (-1.8 ± 2.3)x10-10 r-w interference effects in the phase space in the width Ref.Phys.Lett.B513,361(2001) • Consistent with other tdata c.f. Ref. Eur.Phys.C27,497(2003) Ref. Eur.Phys.C31,503(2003)

17. e+e－ - base : 2.7s • t - base : 1.4s not yet published Belle not yet published preliminary recent summery of a status Direct measurement BNL(2004):aexp = (11 659 208.0  5.8)×1010 Theoretical calculation (using e+e－ortmeasurement) Exp. e+e－p+p－ t－p－p0nt Ref. hep-ph/0507078(2005)

18. Summary • We measure p-p0mass spectrum with 72.2/fb data collected with the Belle detector at KEKB. • In addition to the r(770) and r’(1400) , the production of the r”(1700)in t decays is observed and its parameters are determined. • We evaluate the 2p contribution to the muon anomalous magnetic moment am using mass spectrum. • Our result agrees well with the preceding t-based results but is higher than the e+e- results.

19. Backup slides

20. 2nd iteration • r’,r” resonance parameter obtained in the fit are used input signal MC generation in the TAUOLA program.

21. m2ppdistribution Original 2nd iteration

22. Measurement of Branching Fraction Method: From the ratio →Many systematics cancel in the ratio. 72.2/fb Data No. of tau-pairs 22.71x106 events No. pp0 5.55x105 events Use for p0 efficiency calibration:

23. Br: Systematics

24. Br hpi0 result: Preceding Exp. • Consistent with preceding results. • The systematics is the same level as CLEO/OPAL • World average is used for am evaluation.

25. Br pipi0 result: Subtract kaon branching fraction Br(Kpi0)=(0.45±0.03)%

26. Number of entries /0.05 (GeV/c2)2 Mass spectrum after Unfolding Mass spectra ＝ Phase space × Form Factor

27. Fit with BW Forms. →Next slide 2 F p Pion Form Factor|Fπ|2 r Interference between r’andr” r” r’ Dip at s=2.5 GeV2

28. Fit with BW Forms. →Next slide 2 F p Pion Form Factor|Fπ|2 r Interference between r’andr” r” r’ Dip at s=2.5 GeV2 Agrees with ALEPH data. But our results are more precise in particular in high mass region.

29. 2 F p Pion Form Factor|Fπ|2 Comparison with CLEO.

30. Comparison of t data • (Data-Fitted curve)/Fit • This fitted curve is the fit of the Belle 2p data to the GS model.

31. 2 F p Pion Form Factor|Fπ|2-r mass region- ALEPH CLEO

32. Experiment apparatus : KEKBCollider Belle detector KEKB • KEKB Collider • High Luminosity • Asymmetric energy collider 8GeV :e- + 3.5GeV:e+ • s = 10.58GeV (U(4S)) e+e-U(4S)BB • Integrated Luminosity: ~ 550 fb-1 ~ 30fb-1 => off-resonance L>1.6x1034cm-2s-1 !!