t-p-p0nt decay at Belle

Tau08; Novosibirsk, 22-25, September, 2008Hisaki HayashiiNara womens University

Tau08

IntroductionHadronic decays of tau lepton provide clean environment for studying the dynamics of hadronic states. as(s), am, Vus, mst-p-p0nthas 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

Introductioncont.

Recent data indicate that there is a systematic difference between the 2p system in e+e reaction and t-decays, even after applying known iso-spin violation correction. Main difference btw and is from 2p mode.am(exp)-am(th) is ICHEP-2006(M.Davier et al.):Ahint to New Physics beyond the SM!

What should be measuredBranching FractionMass Spectrum In this talk, We present update results from Belle experiment based on 5.6x 106 t-p-p0nt decays (72.2/fb).

spectral functionB-factory exp. : final state particles are separated well. c.f. LEP exp.

Analysis Procedure

e+e-t+t- selection t-p-p0nt selectionBackground subtractionUnfolding Br measurement Extract pion form factor |Fp(s)|2Fit with Breit-Wigner FormEvaluation of am distribution event selection event selectionunfolded distribution72.2/fb

Event Selection Low multiplicity: Number of charged tracks2 or 4, net charge=0Rejection 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) e+e-t+t- Selectionp0charged trackt-p-p0nt Selectionone charged track in the event hemisphere.one p0 in the event hemisphere.No additional g with Eg200MeVTag-side condition: 1, 3 prong+ any g : For Br measurement 1 prong + no g : For mass spectrum

e+e-t+t- SelectionParticle multiplicityBhabham+m-Two photon

p0 SignalSignal regionrightleftSideband regionSideband region is used to estimate the non-p0 background5.6M events Generally background free, but non-negligible BK In the low Mpp0 region.-fromp0-Reproducing the signal shape by MC is important.

m2pp distributionBackground non-t B.G.

feed down B.G.Tau mass limit Thesignal level is different more than 4th order of magnitude between r(770) and r(1700). BG is important at threshold and r region.

Some important features New MC set New t MC (include r to TAUOLA MC)More reliable estimate of continuum BGEstimate continuum using BG enriched sample.Require stronger cut for tag side1 charged track + no gMore reliable estimate of feed-down BG. some modes have small Br but dominate in the special region. i.e. threshold region t-p-wnt(wp0g) t-p-p0KLnt etc. Systematic study p0 side band, efficiency check

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

Results

BrMass SpectrumPion form factorExtract resonance ParametersComparison with previous exp.Evaluation of am and iso-spin violation correction.

Result (1) Branching FractionNormalized to the number of t-pairs

Tau-pair selection acceptance : 32.6 0.05% : 1.112 0.003 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 0.01stat) 0.39(sys))%

Systematic on Br MeasurementSource 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 1.52Systematic is dominated by the uncertainty of the p0 efficiency and the BG in t-pair p0Calibrated by h signals ( ).Checked by using electron tracks.

Result (2): Mass spectrumMass spectra Phase space Form FactorUnfolded Results

Result (3) Pion Form Factor |F|2From 64M t+t- pairs, Belle selects 5.5M t-p-p0nt events!Error bars include both statistical and systematicInterference between r and rFit with BW |F|2

Systematic on the mass distribution (1)Unfolding procedure Reproducibility of the signal. UNF Unfolding condition : value5UNF Acceptance (Accept.) p0 efficiency uncertaintyEffect of g-track isolationChange a cut on the cluster-track distance default and tighter one(30cm)Momentum or energy scale (ENS)Change Eg by its uncertainty estimated from the p0 mass peak position.(0.2)

Systematic on the mass distribution (2)Background Continuum BG (BKG ) estimate at the mass region higher than mtuncertainty is estimated to be 10%Feed down BG (BKG ) dominated by t-p-2p0ntsystematic is estimated by changing the Br in PDG by 1snon-p0 BG (BKG ) 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.

Non-p0 background( details).F=1.375F=1MggMggp-p0

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

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

Fit Results All r, r, r resonance parameters are determined at the same time!

PDG2006t, e+e-Hadron reaction775.4 0.4766.5 1.1146.4 1.1150.2 2.4 fit with r x2/ndf=80/(90-10) fit w/o r x2/ndf=135/(90-6) Significance of r : 6.5 s

Most precise

Fit parameter Norm fixedNorm [1.0 ]774.60.20.5148.10.41.714467284341660

17281789

80/52

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

Effect on am2p ?iDetailed Comparison: r, r regionFit: Fit to Belle Data

Belle-CLEO consistent, ALEPH is higher at (Mpp)2 > 0.8 GeV2;

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

ItemValue1.02350.0006 0.200.97340.0008 0.42(17.840.06)% 1.82(25.420.11)% 2.30 Total

am p: contribution from each mass range Belle> ALEPHBelle

Iso-spin Violation CorrectionRef. 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 0.2Long distance rad. Cor.(GEM) - 1.0mp- = mp0 (in phase space) - 7.0r-w interference + 3.5 0.6 mp- = mp0 (in decay width) +4.2Electromagnetic decays -1.4 1.4 mr0 = mr - 2.0

Total -13.7 2.5X10-10FSR correction in e+e-Vg->p+p-g: +4.2 Total+FSR = -9.5 2.5

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

SummaryWe have studied t-p-p0nt using 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 higher than those from e+ e-. The results are accepted by PRD, will appear in Oct. issue.The paper is accepted by PRD and will appear in Oct. issue.

Backup Slide

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

Internal Systematic Error

sourceBackground estimationnon- tee->hadronfeed-downh2p0nfeed-downKp0n0.110.090.15p0/g selection efficiency/shape cuts0.35Energy scale0.10Gamma veto0.93g/track overlap0.24Tagging Dependence

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

Pion Form Factor |F|2Low mass regionr mass region(linear scale)Error bars include both statistical and systematic

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

Source of systematicsMr Gr Mr Gr bfbMr Gr gfg

Fit bias0.31.625490.028475100.03813

Unfold0.30.34240.001411140.00212B.G.0.3--1125+0.14-0.03+41- 513+86-10+0.053-0.020+117- 22Acceptance--0.114---0.60.17---1Momentum scale0.30.621---24515---1total0.51.72860+0.15-0.04+41-889+89-26+0.065-0.009+118- 28

World record: L = 1.7118 x 1034/cm2/secSCC RF(HER)ARES(LER)8 x 3.5 GeV 22 mrad crossingsince 1999First successful op. of Crab cavities The KEKB Collider

/ KL detection 14/15lyr. RPC+Fe

Central Drift Chamber Tracking +dE/dxSmall cell +He/C2HCsI(Tl)16X0Si vtx. det. 3 lyr. DSSDTOF counterSC solenoid 1.5T8 GeV e-3.5 GeV e+Good tracking and particle identification Belle detector p0 mass resolution;sp 0 ~ 5 -8MeVAerogel Cherenkov cnt. n=1.015~1.030

1.tau MC is the result of the second iteration, where rho' signal is included.2. The continuum background is dominated at the high mass region. And it estimation is carried out by using the sample in the mass region higher than m_tau. 3. The tau->omega pi nu contribution is shown by green. That is dominated in the low-mass region.Include subtract B.R.(tau->Kpi0) stat err. 0.450.03