1. CP Asymmetry in B 0 ->π + π – at Belle Kay Kinoshita University of Cincinnati Belle Collaboration B 0 ->π + π – and CP asymmetry in CKMB 0 ->π + π – and CP asymmetry in CKM e + e – ->  (4S) at KEKB and Belle e + e – ->  (4S) at KEKB and Belle Belle data Belle data Measurement of CP asymmetry in B 0 ->π + π – Measurement of CP asymmetry in B 0 ->π + π – Interpretation vis-a-vis CKM Interpretation vis-a-vis CKMFuture

2. DPF, April 5, 2003 2 Represented in complex plane as "unitarity triangle" B 0 ->π + π – involves  2 (  ) of CKM: V ub *V ud V cb *V cd V tb *V td V cb *V cd + 1 += 0  CKM: matrix of W-quark couplings - 3x3, unitary One condition of unitarity:  

3. DPF, April 5, 2003 3  V tb *2 V td 2 V ub V ud *  V ub * V ud B 0 ->π + π –  2 =arg 2 paths, each w/wo mixing: Tree Penguin  V tb * V td  V tb *2 V td 2 V tb V td * "direct" asym V td V tb * –V ud V ub * mixing+ " Bottom line: CP-asymmetric time-dependent rate from x-terms

4. DPF, April 5, 2003 4 Uncertainty: relative amplitudes of Tree, Penguin if T dominates, A ππ =0, S ππ =sin2  2 if T dominates, A ππ =0, S ππ =sin2  2 if P, T comparable, A ππ ≠0, S ππ ~sin(2  2 +2  )2/(| | 2 +1) if P, T comparable, A ππ ≠0, S ππ ~sin(2  2 +2  )2/(| | 2 +1) Direct CP violation Now: more data - 78 fb –1 more data - 78 fb –1 improved analysis - tracking, improved analysis - tracking,  t resolution, event selection  t resolution, event selection statistical analysis statistical analysis (total 126 fb –1, ~1.3x10 8 B events) Each 2.9  from zero; note physical region is difference of strong phase ≠1 if direct CP violation+0.38+0.16–0.27–0.13+0.25+0.09 –0.31 –0.09 S ππ = –1.21 A ππ = +0.94 Previous Belle result {PRL 89, 071801 (2002)} (42 fb –1 ~45M B pairs)

5. DPF, April 5, 2003 5 B production: } B BB threshold e-e-e-e- e+e+e+e+   CP=–1,conserved   + e - ->  (4S) {  = 0.425}  z≈  t  c ~200 µm CP mode @ t=  t flavor tag @t=  : e, µ, K ±,... As with sin2  1 via J/  K: reconstruct CP mode reconstruct CP mode tag flavor tag flavor reconstruct vertices reconstruct vertices unbinned max. unbinned max. likelihood fit to  t likelihood fit to  t B2B2B2B2t=0 B1B1B1B1 first B decay (t=0), break CP

6. DPF, April 5, 2003 6 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

7. DPF, April 5, 2003 7 …the people 274 authors, 45 institutions many nations many nations

8. DPF, April 5, 2003 8 B 0 ->π + π – reconstruction final selection:  E  E* cand –E* beam : 0±0.057 GeV(E* beam  s 1/2 /2) {Kπ shift –45 MeV}  E  E* cand –E* beam : 0±0.057 GeV(E* beam  s 1/2 /2) {Kπ shift –45 MeV} M bc  (E* beam 2 -p* cand 2 ) 1/2 : 5.271 –5.287 GeV/c 2 (Beam-constrained) M bc  (E* beam 2 -p* cand 2 ) 1/2 : 5.271 –5.287 GeV/c 2 (Beam-constrained) … but less clean than B 0 ->J/  K s : "physics bg" B 0 ->K + π – "physics bg" B 0 ->K + π – => hadron ID, kinematics dE/dx, TOF, Aerogel – “ positive ID ”  π =91%,  K =10% continuum => event shape {qq “jet-like” vs BB “spherical”) continuum => event shape {qq “jet-like” vs BB “spherical”) Fisher discriminant from modified Fox-Wolfram moments Fisher discriminant from modified Fox-Wolfram moments B candidate direction relative to beam axis B candidate direction relative to beam axis Construct Likelihood ratio LR=L BB /[L BB +L qq ], 2 selections: Construct Likelihood ratio LR=L BB /[L BB +L qq ], 2 selections: LR > 0.825 {} LR > 0.825 {  BB =53%,  qq =5%} 0.825 > LR > LR min (cut depends on flavor tag classification)

9. DPF, April 5, 2003 9 B 0 ->π + π – Candidates LR>0.825 0.825>LR>LR min ππ ππππ:106±16Kπ:41±10qq:128±6ππ:57±8Kπ:22±6qq:406±17 Total signal 163±24 760 in signal box - 391 B 0, 369 B 0

10. DPF, April 5, 2003 10 Flavor tagging: same as for sin2  1 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 + } hard π b->{c}π – X * multidimensional likelihood,  >99% or π – wrong-tag fraction w classify events based on expected w (MC) - 6 bins. (B 0 mixing amplitude in data) => effective efficiency =  (1-2w): net (28.8±0.5)% mixing amplitude w

11. DPF, April 5, 2003 11  K-K- K-K- sin2  1  z vertex reconstruction: same as for sin2  1    t ~1.43 ps (rms) zz B 0  D   , D*   , D*   , J/  K S, J/  K* 0 Resolution function: validate via lifetime <=  B0 = 1.551±0.018 ps (PDG02: 1.542±0.016) z

12. DPF, April 5, 2003 12 More checks of  t resolution+flavor tag  B0 = 1.42±0.14 ps (PDG02: 1.542±0.016)  B0 = 1.46±0.08 ps B 0 ->K + π – mixing  m d = 0.55±0.07 ps –1 (PDG02: 0.489±0.008) Fitted bg agrees w sideband

13. DPF, April 5, 2003 13 Check for flavor bias Look where zero asymmetry expected: "S ππ "= –0.045±0.033 "A ππ "= -0.015±0.022 S Kπ = –0.03±0.11 A Kπ = +0.08±0.16

14. DPF, April 5, 2003 14 Fitting for CP asymmetry Same technique as with sin2  1 unbinned maximum likelihood fit unbinned maximum likelihood fit resolution function event-by-event: tracking, misreconstruction, resolution function event-by-event: tracking, misreconstruction, physics, approximation of  t=  z/  c physics, approximation of  t=  z/  c wrong tag fraction w, backgrounds wrong tag fraction w, backgrounds Fit for A ππ, S ππ : rootDiluted +Kπ (set A Kπ = 0) +resolution + bg

15. DPF, April 5, 2003 15 5-5 0 5 0 Backgroundsubtracted rawasymmetry LR>0.825 Fit Results display  t projection (78 fb –1 ~85M B pairs) display  t projection (78 fb –1 ~85M B pairs) Likelihood not parabolic -> statistical errors estimated numerically via MC ensemble S ππ = –1.23±0.41 A ππ = +0.77±0.27±0.08 (stat) (sys) (stat) (sys)+0.08–0.07 still outside physical region => investigate …

16. DPF, April 5, 2003 16 Fit Results: statistical analysis MC ensemble - 30k expts, 760 events ea, A ππ =0.569, S ππ =–0.822 MC ensemble - 30k expts, 760 events ea, A ππ =0.569, S ππ =–0.822 probability of being outside physical boundary =60.1% probability of being outside physical boundary =60.1% " further (in  ) from (0,0)=16.6% " further (in  ) from (0,0)=16.6% S ππ A ππ x data physical boundary check linearity: generated vs fitted A ππ, S ππ

17. DPF, April 5, 2003 17 Feldman-Cousins frequentist approach. Acceptance regions from MC ensembles. Systematic errors included. Confidence Level (CL) calculated at each point. Confidence regions (2.2  ) hint of direct CP non-conservation } interpret as evidence for CP non-conservation in B 0 ->π + π – (3.4  ) }

18. DPF, April 5, 2003 18 Constraints on the CKM angle  2 S ππ, A ππ depend on 4 parameters: S ππ, A ππ depend on 4 parameters:  2,  1 [21.3°-25.9°], |P/T| [0.15-0.45],  -> plot confidence contours in (  2,  )for various |P/T| -> plot confidence contours in (  2,  )for various |P/T| e.g. e.g. |P/T|=0.3  1 =23.5°  2222 From other CKM (CKM fitter group, 2002) : 78.3°≤  2 ≤ 121.6° 78.3°≤  2 ≤ 121.6° (95% C.L.) => consistent Find: 78°≤  2 ≤ 152° (95% C.L.)  insensitive to 

19. DPF, April 5, 2003 19 Summary Belle, 2000-2: peak L= 9.5x10 33 cm –2 s –1 - nearly at design (1x10 34 cm –2 s –1 ) peak L= 9.5x10 33 cm –2 s –1 - nearly at design (1x10 34 cm –2 s –1 ) passed 100 fb -1 in Oct. 2002 passed 100 fb -1 in Oct. 2002 with 78 fb –1 on  (4S), sensitive to large values of sin2  2 with 78 fb –1 on  (4S), sensitive to large values of sin2  2 measure CP asym in B 0 ->π + π – measure CP asym in B 0 ->π + π – constraints on  2, consistent with other CKM constraints. hint of direct CP non-conservation result submitted to PRD. Next ->150 fb –1 by summer, 500 fb –1 by 2005 ->150 fb –1 by summer, 500 fb –1 by 2005 Luminosity >@ design Luminosity >@ design the CP challenge: stay tuned on  2 the CP challenge: stay tuned on  2

20. DPF, April 5, 2003 20 additional slides

21. DPF, April 5, 2003 21 Systematic uncertainties* source A ππ S ππ +error  error+error  error Background fractions+0.058  0.048+0.044  0.055 Vertexing+0.044  0.054+0.038  0.012 Fit bias+0.016  0.021+0.052  0.020 Wrong tag fraction+0.026  0.021+0.015  0.016  B,  m d, A Kπ +0.021  0.014+0.022  0.022 Resolution function+0.019  0.020+0.010  0.013 Background shape+0.003  0.015+0.007  0.002 Total+0.08  0.08+0.08  0.07 * blind analysis: actual estimations done before seeing fit result.

22. DPF, April 5, 2003 22 convention taken from M.Gronau & J.L.Rosner Phys Rev D65, 093012 (2002) Constraints on the CKM angle  2 4 parameters |P/T| 0.15-0.45 (representative) Theory ~0.3  1 21.3 - 25.9deg (Belle & BaBar combined)