1 Koji Hara (KEK) For the Belle Collaboration Time Dependent CP Violation in B 0 →  +  - Decays [hep-ex/ ]

2 Time dependent CP-violating parameters in B 0 →  +  − decays S  : B 0 B 0 mixing induced CPV A  : direct CPV In B 0 →  +  - decays, S  is sensitive to   (  ): u W u d bd W g u u tree penguin can be determined with isospin relations Direct CP violation may occur.

3 Previous experimental situation CPV with 5.2 , 3.2  evidence for DCPV Belle 152 M BB with 372±32 B 0 →  +  − events B A B AR 227M BB hep-ex/  difference PRL 93, (2004) with 467±33 B 0 →  +  − events

4 New Belle measurement with 275M BB pairs additional data  152 → 275 M BB pairs  the inner tracker and interaction region was replaced in the summer layer SVD (152 M BB) to 4-layer SVD with small-cell drift chamber (123 M BB). Analysis procedure is basically same as before

5 Event Selection B 0 →  +  − selection corresponding ±3  Kinematical Selection Flavor Tagging q=+1 tagged as a B 0, q=−1 tagged as a B 0 Pion Identification using aerogel and dE/dx r=0 no flavor discrimination, r=1 unambiguous flavor assignment r: flavor tag quality 0<r≤1 q: flavor charge

6 Event Selection (continuum suppression) Event shape B flight direction LR (Likelihood Ratio) e+e+ e-e- Signal B Other B e+e+ e-e- qq Jet-like Spherical

7 LR (Likelihood Ratio) B 0 →  +  − signals r (flavor tag quality) (LR>0.86) (LR<0.86) 2,820 candidates containing (666      signal events

8  t (ps) Unbinned CP Fit Result Points  E-Mbc 2D fits to individual time intervals B 0 tagged  +  − A CP  +  − Yield B 0 tagged Background subtracted fit projection for all events

9 Consistency checks with Time-integrated fits consistent with time-dependent fit B 0 tagged  : 107± 13 K  : 42 ±9 cont: 38 ±1  : 69 ±11 K  : 43 ±9 cont: 38 ±1 Direct CP Violation is evident!  E (GeV) LR>0.86 & 0.5<r≤1.0

10  t distribution and raw asymmetry Raw asymmetry Events /(1.25ps) q=+1 q=−1 0.0<r≤ <r≤1.0  t (ps) LR>

11 (A,S)=(0,0) 1-C.L.=5.62x10 -8, 5.4  (A,S)=(0,−0.62) 1-C.L.=5.13x10 -5, 4.0  Significance calculation with Feldman-Cousins method Large CP Violation, Large Direct CP violation, confirmation of the previous Belle results C.L. = Confidence Level both statistical and systematic errors are taken into account. S  A 

12 New experimental situation Belle 275M B A B AR 227M A  ~2.3  difference between Belle and B A B AR S 

13  Interpretation:  2 constraint using isospin M. Gronau and D. London, PRL 65, 3381 (1990) We use the HFAG summer 2004 values for the branching ratios of B 0 →  +  −,  0  0, B + →  +  0 and direct CP asymmetry of B 0 →  0  0. We use the statistical treatment of J. Charles et al., hep-ph/ The cleanest method to extract  2

14  Interpretation :  2 constraint using isospin and 95.4% confidence interval  2 (degrees) 1−C.L. using HFAG summer 2004 J. Charles et al., hep-ph/

15 &  Summary of new Belle B 0 →  +  − CP results The fit yields Large direct CP violation with 4.0  significance is observed The results confirm the previous Belle results. Isospin analysis gives at 95.4% C.L. [hep-ex/ ]

16 backup slides

17 Probability Density Functions (PDFs) for the CP fit a likelihood function are event fractions as functions of  E and M bc is maximized. two free parameters: A  and S 

18 Probability Density Functions (PDFs) for the CP fit For  +  − wrong tag fraction obtained from data For  +  − HFAG2004 For qq is set to 0 in default backup

19 New experimental situation 140fb fb -1 combined BaBar 227M inside the physical boundary! A  ~2.3  difference between Belle and BaBar

20 ~10 10 BB/year !! & similar number of  +  - L peak = 1.4  cm -2 s -1 L tot = 350fb -1 (Feb.8, 2005) Crab cavities Major upgrade of KEKB & Belle detector (>1yr shutdown) world records ! 1.4x fb -1 5x10 34 ~1 ab -1 5x10 35 ~10 ab -1 L peak (cm -2 s - 1 ) L int Future prospect

21 Future prospect assuming the current measured values ~0.5ab -1 ~2ab -1 ~8ab -1 ~32ab -1 Super-B factories can pin down the  2 value. Current

22  Validity check with B 0 →  +  − We extract B 0 →K +  − events LR>0.86 (including 2,207 K +  − ) events in total 4,293 good control sample because of the similar topology to B 0 →  +  − Lifetime fit ps ps -1  t (ps) (OF-SF)/(OF+SF) consistent with the WA values

23  Background asymmetry  sideband  sideband B0:42467, B0b:42090 B0:43577, B0b:43308 No background asymmetry possible background asymmetries are included in the systematic error

24  Systematic errors S  A  wrong tag±0.01 physics param.<0.01±0.01 resolution func±0.04±0.01 bkg Dt shape<0.01 event fraction±0.02±0.04 fit bias±0.01 vertexing± −0.01 tag side interfere ± −0.04 total±0.06 including uncertainties in the b.k.g and Final State Radiation O. Long, M. Baak, R.N. Cahn, and D. Kirkby, PRD 68, (2003)

25  Validity check (lifetime fit with B 0 →  +  − ) 2820 events ps Lifetime fit good agreement with the World Average (W.A.) Value ps PDG2004 B0→+−B0→+− continuum

26  Validity check with B 0 →  +  − total 4293 events B0: 2106, B0b: 2187 CP fit results  t (ps) Raw A CP consistent with the WA value in agreement with null asymmetry