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Recent results from Belle: Reflections on Beauty

Recent results from Belle: Reflections on Beauty. Kay Kinoshita University of Cincinnati Belle Collaboration. Outline. CP asymmetry in Standard Model B decays and CP Asymmetric e + e - collisions at  (4S) KEKB and Belle: time-dependent measurement Measurement of sin2 f 1 Summary.

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Recent results from Belle: Reflections on Beauty

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  1. Recent results from Belle:Reflections on Beauty Kay Kinoshita University of Cincinnati Belle Collaboration APR01 APS

  2. Outline • CP asymmetry in Standard Model • B decays and CP • Asymmetric e+e- collisions at (4S) • KEKB and Belle: • time-dependent measurement • Measurement of sin2f1 • Summary K. Kinoshita APR01 APS

  3. Belle Collaboration 274 authors, 45 institutions many nations K. Kinoshita APR01 APS

  4. CP Asymmetry in Standard Model • Weak interaction of quarks (u,c,t), (d,s,b) • {mass <- CKM matrix -> weak} eigenstates • CKM - 3x3, unitary by definition -> 4 free parameters 1-l2/2 ll3A(r-ih) -l 1-l2/2 l2A l3A(1-r-ih) -l2A 1 irreducibly complex -> CP violation a VtdVtb*+VcdVcb*+VudVub*=0 “unitarity triangle” g b K. Kinoshita APR01 APS

  5. CP phenomenology •before 1998: seen only in K system •predicted for b-hadrons in Standard Model, e.g.: B0->ππ B0->rπ first result B0->J/Ks B0->D(*) D(*) B0-> D*π B0->D*r K. Kinoshita APR01 APS

  6. CP Asymmetry of B -> J/y Ks {cc}+{Ks,KL,π0} CP = ±1 • Decays to CP eigenstate: • paths w/wo mixing interfere • CP-dependent oscillation in decay time distributions • No theoretical uncertainty K. Kinoshita APR01 APS

  7. Time measurement at (4S) (4S): CP=-1, conserved until first B decay (t=0) identify b/b {flavor tag} Reconstruct CP=±1 mode @ t=Dt +e- -> (4S) t=0 Dz≈Dtbgc J/y “CP side” ~200 µm  B1 Ks e- e+ B2 flavor tag: e, µ, K±, ... K. Kinoshita APR01 APS

  8. Experimental considerations • B0 lifetime = 1.548±0.032 ps, ct=464±10 µm mixing Dm = 0.47±0.02 ps–1; cT~4.0 mm need to distinguish B0 vs `B0 (flavor tag), high efficiency • True CP asymmetry is diluted: background to CP reconstruction incorrect flavor tag rate vertex resolution • Bottom line: need >few x 10 fb–1 @ (4S) {>107 B events}, vertexing@<40µm, hadron ID, lepton ID multiply by bg for lab length (decay in flight) } Kaons leptons K. Kinoshita APR01 APS

  9. Beams: KEKB bg = 0.425 • s(E*beam) = 2.6 MeV • IP size = 77µm(x) x 2.0µm(y) x 4.0mm(z) • Lmax = 3.4 X 1033 cm–2s–1 (design: 1x1034) • Data (6/1999–12/2000) • Ldt = 10.5 fb–1@(4S), 0.6 fb–1off e– 8.0 GeV 22 mr e+ 3.5 GeV K. Kinoshita APR01 APS

  10. Belle detector Charged tracking/vertexing - SVD: 3-layer DSSD Si µstrip – CDC: 50 layers (He-ethane) Hadron identification – CDC: dE/dx – TOF: time-of-flight – ACC: Threshold Cerenkov (aerogel) Electron/photon – ECL: CsI calorimeter Muon/KL – KLM: Resistive plate counter/iron K. Kinoshita APR01 APS

  11. CP mode reconstruction J/l + l ) B0 J/ Ks(+ )as an example Ks+ 1lepton+1”not-hadron” ~4MeV/c2 Ks mass4 K. Kinoshita APR01 APS

  12. CP mode (continued) • Kinematics for final selection: • DEE*cand–E*beam0 (E*beams0.5/2) • 10-50 MeV res, depends on mode • Mbc (Beam-constrained mass) • Mbc(E*beam2-p*cand2 )0.5 ~3MeV/c2 Signal region ~10MeV K. Kinoshita APR01 APS

  13. J/y KL • • J/y: {tight mass cut} • 1.42<py*<2.00 GeV/c • • KL: {KLM/ECL cluster w/o track, • >1 KLM superlayers (resolution~ 3° (1.5° if ECL)} within 45˚ of expected lab direction • • Require cand to have B mass, calculate momentum in CMS (pB*) (~0.3 GeV for signal) • • backgrounds: random (from data), “feeddown,” known • modes - estimate via MC K. Kinoshita APR01 APS

  14. CP candidates Fully reconstructed modes J/y KL K. Kinoshita APR01 APS

  15. CP candidates - numbers K. Kinoshita APR01 APS

  16. Flavor tagging l- l+ b c s K– D*+ D0 • – high-p lepton (p*>1.1 GeV): b->l- • – net K charge b->K– • – medium-p lepton, b->c-> l+ – soft π b->c{D*+->D0π+} * all into multidimensional likelihood • Significance of CP asymmetry depends on • – tagging efficiency e • – wrong-tag fraction w (measured w data) • - effective efficiency = e(1-2w) π+ K. Kinoshita APR01 APS

  17. Dz: vertex reconstruction • Constrained to measured IP in r-f • • BCP: sz~88 µm (rms) • use only tracks from J/y • • Btag: sz~164 µm (rms) • remaining tracks, excluding Ks; • iterate, excluding tracks w. poor c2/n • resolution includes physics (e.g. charm) • • Overall eff. = 87% m+ m- K- K- K. Kinoshita APR01 APS

  18. Prepare to fit: Wrong tag fraction Bins of dilution parameter (MC) • Same fit method, but • CP->flavor-specific • • BD*-l+n, D(*)-π+, D*-r++flavor tag • • separate same-, opp-flavor events • • fit to Dz: mixing asymmetry, w: • • "effective tagging efficiency" • eeff=S(1-2wl)2etag, l =(27.0±2.2)% • 99.4% of candidates tagged • (good agreement w MC) K. Kinoshita APR01 APS

  19. Dt resolution function • • Double Gaussian, parameters calculated event-by-event, includes effects of • - detector resolution • - poorly measured tracks • - bias from e.g. charm • - approximation of Dt=Dz/bgc • • form, params determined by • - Monte Carlo • - fits for D0K-π+, BD*ln lifetimes tail fraction: 1.8% K. Kinoshita APR01 APS

  20. Verifying Dt resolution • Dt used in other measurements, serve as checks • • B0 mixing w. dileptons • Dmd=0.463±0.008±0.016 ps-1 (5.9 fb–1) PRL86,3228 • (PDG2000: 0.472±0.017 ps-1) • • B lifetimes • Reconstructed B + flavor tag vertex • BDX semileptonic+hadronic modes. • t0=1.56±0.04 ps • (PDG2000: 1.548±0.032 ps) • t+=1.66±0.04 ps • (PDG2000: 1.653±0.028 ps) PRELIMINARY K. Kinoshita APR01 APS

  21. Dt resolution l- l+ b c s • B0 mixing w. dileptons • Same sign • - 2 primaries, mixed event • - Primary+2ndary, unmixed & B+B- • - Backgrounds • Opposite sign • - 2 primaries, unmixed & B+B- • - Primary+2ndary, mixed&unmixed • - Backgrounds • Asymmetry in signal (2 primaries) • Nopp-Nsame • Nopp+Nsame K. Kinoshita APR01 APS

  22. Fitting Dt distribution • • distribution in Dt~Dz/bgc • • unbinned max. likelihood fit, includes • - signal root distribution (analytic) • - wrong tag fraction (const) • - background: right & wrong tag (MC, parametrized) • - detector & tagging resolution • (parametrized,evt-by-evt) K. Kinoshita APR01 APS

  23. Results All modes combined : sin2f1=0.58 +0.32 -0.34 binned in Dt K. Kinoshita APR01 APS

  24. Results likelihood Uncombined results are consistent Fit (stat. err.) Mode Non-CP CP = -1 CP = +1 All CP K. Kinoshita APR01 APS

  25. Systematic errors K. Kinoshita APR01 APS

  26. Result in context sin2f1=0.58 +0.32+0.09 -0.34-0.10 {PRL 86, 2509 (2001)} •Probability of observing sin2f1>0.58 if CP is conserved: 4.9% •Feldman-Cousins confidence interval CKM, from rates K. Kinoshita APR01 APS

  27. Summary/Prospects Successful run of Belle in 2000 Results on • sin 2f1: 10.5 fb–1 on (4S), 282 tagged events • + 17 papers at Osaka ICHEP 2000 • 2 publications, 4 submitted, more soon Next • some improvements to analysis • data as of 4/01 - 20.5 fb–1; anticipate 30 fb–1 by summer • Luminosity: peak 3.41x1033cm–2s–1; 24 hrs 198 pb–1; month 4047 pb–1 • KEKB continuing to improve performance K. Kinoshita APR01 APS

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