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

1 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 2  Spectral function measured with e + e － or  data. Recent data indicate that there is a systematic difference between the 2  system in e + e － reaction and  -decays, which needs to be understood. +CVC hadron In this talk, results from Belle experiment are presented. –Results are based on 72.2/fb data taken in period. –One order of magnitude more data than preceding experiments.

2 spectral function fine structure constant What should be measured Branching Fraction Mass Spectrum

3  / K L detection 14/15lyr. RPC+Fe Central Drift Chamber Tracking +dE/dx Small cell +He/C 2 H 6 CsI(Tl) 16X 0 Si vtx. det. 4 lyr. DSSD TOF counter SC solenoid 1.5T 8 GeV e  3.5 GeV e  Good tracking and particle identification Belle detector Experiment Apparatus :  0 mass resolution ;   ~ 5 -8MeV Aerogel Cherenkov cnt. n=1.015~1.030

4 one charged track in the event hemisphere. one  0 in the event hemisphere. veto any additional gammas with Event Selection 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) e + e    +   Selection         Selection  charged track

5  0 Signal Mass invariant mass distribution resolution of Signal region right ： left ： Sideband region Sideband region is used to estimate the non-  0 background 5.55×10 6 event        

6 m 2  distribution Checked above kinematical limit of tau decay feed across B.G. non-  B.G.    →       MC(TAUOLA) Includes  (770),  ’(1400) Does not include  ”(1700)  B.G. estimated by MC

7 Acceptance After background subtraction, data are Unfolded with the SVD method. Acceptance correction M  0 (observed) ２ M  0 (generated) ２ (GeV) 2 Ref.Nucl.Instr.Math.,A372,469(1996) Singular Value Decomposition method

8  umber of entries /0.05 (GeV/c 2 ) 2 Mass spectrum  phase space  Form Factor Mass spectrum after Unfolding Pion Form Factor|F π | 2 Interference between  ’  and  ” Fit with BW Forms.  Next slide Dip at s=2.5 GeV2 Agrees with ALEPH data. Our result is more precise especially in the high mass region. 2  F 2  F  ’’ ””

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

10 Fit result  1 st Errors: Statistical  2 nd Errors: Systematics. Sources: 1. Photon energy scale 2. Unfolding Procedure (  Rank = +/- 3) 3. Background Subtraction.

11 strong correlation between M  ” and   Comparison with preceding experiments fit parameter Belle ALEPH(  ) CMD-2( ) 774.6± ± ± ± ± ± ± ± ±35 471±29 468±41 569± ± ± ± ± ± ± ± (fixed) 1713±15 255±19 235(fixed) 0.062± ± ± ±7.9 0 (fixed) 55/51 119/ Stat. error only

12 Hadronic vacuum polarization a  Threshold region(0.25GeV 2 <M  2 ) is not included because the experimental uncertainty is large.

13 Internal Systematic Error source Background estimation ・ non-  （ ee->hadron ） ・ feed-down h≥2  0 ・ feed-down K －  0 ±0.11 ±0.09 ±0.15  0 /  selection efficiency/shape cuts ±0.35 Energy scale ±0.10 Gamma veto ±0.93  /track overlap 0.24 Tagging Dependence <0.1 Smearing/Migration effect Total ±1.04

14 External parameters ItemValue ± ± ± ±0.42 (17.84±0.06)% ±1.82 (25.42±0.11)% ±2.30 Total ± ３．０ World average is calculated combining our new result and the preceding measurements of other experiments.

15 Isospin breaking correction in this mass region. (-1.8 ± 2.3)x a   after SU(2) correction  -  interference effects in the phase space in the width c.f. Ref. Eur.Phys.C27,497(2003) Ref. Eur.Phys.C31,503(2003) Consistent with other  data Ref.Phys.Lett.B513,361(2001)

16 BNL(2004):a  exp = (  5.8)×10  10 Ref. hep-ph/ (2005) Direct measurement Theoretical calculation e + e －  base : 2.7   base : 1.4  e+e－+－e+e－+－  －   －    not yet published preliminary Exp. Belle recent summery of a  status (using e + e － or  measurement)

17 Summary We measure  -  0 mass spectrum with 72.2/fb data collected with the Belle detector at KEKB. In addition to the  (770) and  ’(1400), the production of the  ”(1700) in  decays is observed and its parameters are determined. We evaluate the 2  contribution to the muon anomalous magnetic moment a  using mass spectrum. Our result agrees well with the preceding  -based results but is higher than the e + e - results.

18 Backup slides

19 2nd iteration  ’,  ” resonance parameter obtained in the fit are used input signal MC generation in the TAUOLA program.

20 m 2  distribution Original2 nd iteration

21 →Many systematics cancel in the ratio. Measurement of Branching Fraction No. of tau-pairs 22.71x10 6 events No.  x10 5 events Data 72.2/fb for  0 efficiency calibration: Use Method: From the ratio

22 Br: Systematics Source 1) Tracking efficiency 2)  0 efficiency 3)Background in  pair 4)Feed-down background 0.12% 0.25% 0.09% 0.04% 5)Non  background 6) Gamma veto 0.05% 7) Trigger 0.08% 8)MC Statistics 0.04% Total 0.31%

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

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

25  umber of entries /0.05 (GeV/c 2 ) 2 Mass spectrum after Unfolding Mass spectra  ＝  Phase space  Form Factor

26 Fit with BW Forms. →Next slide  ’’ ”” 2  F Pion Form Factor|F π | 2 Dip at s=2.5 GeV2 Interference between  ’  and  ”

27 Fit with BW Forms. →Next slide  ’’ ”” 2  F Pion Form Factor|F π | 2 Dip at s=2.5 GeV2 Agrees with ALEPH data. But our results are more precise in particular in high mass region. Interference between  ’  and  ”

28 2  F Pion Form Factor|F π | 2 Comparison with CLEO.

29 Comparison of  data (Data-Fitted curve)/Fit This fitted curve is the fit of the Belle 2  data to the GS model.

30 2  F Pion Form Factor|F π | 2 -  mass region- ALEPH CLEO

31 KEKB Collider –High Luminosity –Asymmetric energy collider 8GeV :e GeV:e + –  s = 10.58GeV (  (4S)) e + e -   S    –Integrated Luminosity: ~ 550 fb -1 ~ 30fb -1 => off-resonance L>1.6x10 34 cm -2 s -1 !! KEKB Collider Belle detector KEKB Experiment apparatus :