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1 Koji Hara (KEK) For the Belle Collaboration Time Dependent CP Violation in B 0 → + - Decays [hep-ex/0502035]
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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.
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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/0501071 3.2 difference PRL 93, 021601 (2004) with 467±33 B 0 → + − events
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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 2003 3-layer SVD (152 M BB) to 4-layer SVD with small-cell drift chamber (123 M BB). Analysis procedure is basically same as before
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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
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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
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7 LR (Likelihood Ratio) B 0 → + − signals r (flavor tag quality) (LR>0.86) (LR<0.86) 2,820 candidates containing (666 signal events
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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
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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
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10 t distribution and raw asymmetry Raw asymmetry Events /(1.25ps) q=+1 q=−1 0.0<r≤0.5 0.5<r≤1.0 t (ps) 0-5+5 LR>0.86 -5 0 +5
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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
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12 New experimental situation Belle 275M B A B AR 227M A ~2.3 difference between Belle and B A B AR S
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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/0406184 The cleanest method to extract 2
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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/0406184
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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/0502035]
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16 backup slides
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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
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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
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19 New experimental situation 140fb -1 113fb -1 combined BaBar 227M inside the physical boundary! A ~2.3 difference between Belle and BaBar
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20 ~10 10 BB/year !! & similar number of + - L peak = 1.4 10 34 cm -2 s -1 L tot = 350fb -1 (Feb.8, 2005) Crab cavities Major upgrade of KEKB & Belle detector (>1yr shutdown) world records ! 1.4x10 34 330 fb -1 5x10 34 ~1 ab -1 5x10 35 ~10 ab -1 L peak (cm -2 s - 1 ) L int Future prospect
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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
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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
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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
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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±0.04+0.03 −0.01 tag side interfere ±0.01+0.02 −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, 034010 (2003)
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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
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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
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