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

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Presentation on theme: "APR01 APS Recent results from Belle: Reflections on Beauty Kay Kinoshita University of Cincinnati Belle Collaboration."— Presentation transcript:

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

2 2K. Kinoshita APR01 APS Outline CP asymmetry in Standard ModelCP asymmetry in Standard Model B decays and CPB decays and CP Asymmetric e + e - collisions at  (4S)Asymmetric e + e - collisions at  (4S) KEKB and Belle:KEKB and Belle: time-dependent measurement time-dependent measurement Measurement of sin2  1Measurement of sin2  1 SummarySummary

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

4 4K. Kinoshita APR01 APS CP Asymmetry in Standard Model Weak interaction of quarks (u,c,t), (d,s,b) {mass weak} eigenstates CKM - 3x3, unitary by definition -> 4 free parameters 1  2 /2 3 A(  i  )  1  2 /2 2 A 3 A(1  i  )  2 A 1 V td V tb *+V cd V cb *+V ud V ub *=0 “unitarity triangle” irreducibly complex -> CP violation   

5 5K. Kinoshita APR01 APS CP phenomenology before 1998: seen only in K system predicted for b-hadrons in Standard Model, e.g.: B 0 ->ππ B 0 ->  π B 0 ->J/  K s B 0 ->D ( * ) D ( * ) B 0 -> D*π B 0 ->D*  first result

6 6K. Kinoshita APR01 APS CP Asymmetry of B -> J/  K s Decays to CP eigenstate: paths w/wo mixing interfere CP-dependent oscillation in decay time distributions No theoretical uncertainty {cc}+{K s,K L,π 0 } CP = ±1

7 7K. Kinoshita APR01 APS Time measurement at  (4S) e-e-e-e- e+e+e+e+   B2B2B2B2 t=0  z≈  t  c B1B1B1B1 ~200 µm J/  KsKsKsKs flavor tag: e, µ, K ±,...  (4S): CP=-1, conserved   + e - ->  (4S) identify b/b {flavor tag} until first B decay (t=0) Reconstruct CP=±1 t=  t “CP side”

8 8K. Kinoshita APR01 APS Experimental considerations multiply by  for lab length (decay in flight) } Kaonsleptons B 0 lifetime = 1.548±0.032 ps, c  =464±10 µ m mixing  m = 0.47±0.02 ps – 1 ; cT~4.0 mm need to distinguish B 0 vs  B 0 (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  (4S) {>10 7 B events}, hadron ID, lepton ID

9 9K. Kinoshita APR01 APS Beams: KEKB  E* beam ) = 2.6 MeV IP size = 77µm(x) x 2.0µm(y) x 4.0mm(z) L max = 3.4 X cm –2 s –1 (design: 1x10 34 ) Data (6/1999–12/2000)  L dt = 10.5 fb  (4S), 0.6 fb –1 off e – 8.0 GeV e GeV 22 mr  = 0.425

10 10K. Kinoshita APR01 APS 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

11 11K. Kinoshita APR01 APS B 0  J/  K s (  +   ) as an example 1lepton+1”not-hadron” K s  +    ~4MeV/c 2 K s mass  4  J/  l + l  ) CP mode reconstruction

12 12K. Kinoshita APR01 APS CP mode (continued)  ~3MeV/c 2  ~10MeV Kinematics for final selection:  E  E* cand –E* beam  0 (E* beam  s 0.5 /2) MeV res, depends on mode M bc (Beam-constrained mass) M bc  (E* beam 2 -p* cand 2 ) 0.5 Signal region

13 13K. Kinoshita APR01 APS  J/  K L J/  : {tight mass cut} 1.42

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 (p B *) (~0.3 GeV for signal) backgrounds: random (from data), “feeddown,” known modes - estimate via MC

14 14K. Kinoshita APR01 APS CP candidates J/  K L Fully reconstructed modes

15 15K. Kinoshita APR01 APS CP candidates - numbers

16 16K. Kinoshita APR01 APS Flavor tagging bcs l-l-l-l- l+l+l+l+ K–K–K–K– D0D0 π+π+ D *+ – 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 *+ ->D 0 π + } * all into multidimensional likelihood Significance of CP asymmetry depends on – tagging efficiency  – wrong-tag fraction w (measured w data) - effective efficiency =  (1-2w)

17 17K. Kinoshita APR01 APS  K-K- K-K-  z: vertex reconstruction  Constrained to measured IP in r-  B CP :  z ~88 µm (rms) use only tracks from J/     B tag :  z ~164 µm (rms) remaining tracks, excluding K s ; iterate, excluding tracks w. poor  2 /n resolution includes physics (e.g. charm) Overall eff. = 87%

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

19 19K. Kinoshita APR01 APS  t resolution function Double Gaussian, parameters calculated event- by-event, includes effects of - detector resolution - poorly measured tracks - bias from e.g. charm - approximation of  t=  z/  c form, params determined by - Monte Carlo - fits for D 0  K - π +, B  D * l lifetimes tail fraction: 1.8%

20 20K. Kinoshita APR01 APS Verifying  t resolution  t used in other measurements, serve as checks B 0 mixing w. dileptons  m d =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.  0 =1.56±0.04 ps (PDG2000: 1.548±0.032 ps)  + =1.66±0.04 ps (PDG2000: 1.653±0.028 ps)

21 21K. Kinoshita APR01 APS  t resolution B 0 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) N opp -N same N opp +N same bcs l-l-l-l- l+l+l+l+

22 22K. Kinoshita APR01 APS Fitting  t distribution distribution in  t~  z/  c 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)

23 23K. Kinoshita APR01 APS Results binned in  t All modes combined : sin2  1 =

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

25 25K. Kinoshita APR01 APS Flavor tagging– Physics parameters– Background Fraction except K L – Background Fraction for K L – Background Shape– Resolution Function– IP measurement– Total– Systematic errors

26 26K. Kinoshita APR01 APS Result in context sin2  1 = Feldman-Cousins confidence interval Probability of observing sin2  1 >0.58 if CP is conserved: 4.9% CKM, from rates {PRL 86, 2509 (2001)}

27 27K. Kinoshita APR01 APS Summary/Prospects Successful run of Belle in 2000 Results on sin 2  1 : 10.5 fb – 1 on  (4S), 282 tagged events sin 2  1 : 10.5 fb – 1 on  (4S), 282 tagged events + 17 papers at Osaka ICHEP papers at Osaka ICHEP publications, 4 submitted, more soon 2 publications, 4 submitted, more soon Next some improvements to analysis data as of 4/ fb – 1 ; anticipate 30 fb – 1 by summer Luminosity: peak 3.41x10 33 cm – 2 s – 1 ; 24 hrs 198 pb – 1 ; month 4047 pb – 1 KEKB continuing to improve performance


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