1. Search for the decay with the BaBar detector at SLAC Hella Snoek Bfys-meeting @ Nikhef Monday Dec 20 2004 Part I One way of measuring γ Part II Analysis

2. Hella SnoekNIKHEF2 Part I: One way of measuring γ 1 Two tree decay modes with phase difference of γ (no penguin decay possible due to c-quark) Measurement of sin(2 β+γ ) possible by time-dependent analysis

3. Hella SnoekNIKHEF3 Statistics versus sensibility The sensitivity to the CP asymmetry scales with Coupling to W 200 MeV 300 130 ~1.1 For we are more sensitive to the CP asymmetry however we also have less events! So how does a low Branching Fraction affect the error on the CP asymmetry A? error on measurement of A: A - CP asymmetry N – number events for : A ~ N = for : A ~ 1 N =

4. A test of factorization A X Y X Y A Factorizing part- the X meson is produced without further interaction with Y Non-factorizing part- the X meson is produced with a gluon interaction The total decay amplitude A has a factorizing and a non-factorizing part: A=A fac + A non. Factorization works well if A fac >>|A non | If decay is factorizable one is not sensitive for the factorization breaking part A fac A non A A fac A non A By suppressing the factorization part the factorization breaking part becomes visible A non A fac A A Theorists say: The non-factorizing part of the decay amplitude is not well calculable and not well known. A measurement of this part will be valuable for the understanding of QCD.

5. Hella SnoekNIKHEF5 Designer mesons Some mesons are almost designed to ‘switch off’ the factorizing part of the decay amplitude. The a 0 meson is an example of a designer meson. The coupling constant to the weak current is proportional to the mass difference between the u and d quark, and thus very small. The a0 is a scalar and couples to the axial term, the pion is a psuedoscalar and couples to the vector term. Predicted Branching Ratio Decay modeNaïve factorization QCD factorization hier nog de klassieke test Classically factorization tests are performed with decays like B->Dpi/a1. But these measurements need a high precision in the measurement and the theoretical prediction. Designer mesons can relax these requirements.

6. Hella SnoekNIKHEF6 Verifying the coupling constants 1 1 Analyzed by V. Eyges and S.Prell at BaBar Expected BF:7.3x10-5 BF will give the coupling to the weak current

7. Hella SnoekNIKHEF7 Part II: The analysis SKIM selection Selection optimization

8. Data selection Some of the SKIM (strip) selection cuts: 40% ~100% 4% 67%

9. Hella SnoekNIKHEF9 Optimization of selection Signal MC:BtoDstarA0 16000 events Generic MC: BBbar 160 mil events BpBm168 mil events Continuum Data:off peak run1-3 11.6 fb-1 All scaled to 210 fb-1 (the size of the current data set) Cut optimization assumes BF 1x10-5 Theory predicts (10-6 – 10-7) depending on the theorist. We optimize for the significance of the signal: We use the mES side band for estimating the background in the signal box.

10. Hella SnoekNIKHEF10 Multiple Candidate selection For every event there can be several candidates for my decay. The selection of the best candidate is based on a calculated χ 2 that uses the mass of the eta and the mass difference of the D* and the daughter D 0. The multiplicity of the events in the SKIM is 4-5 The multiplicity of the events in the final selection will depend on the selection parameters, typically this is ~1.1

11. Hella SnoekNIKHEF11 Overlapping photon veto Most of the photons originate from pions. For every eta-candidate the photons are compared to the photon-list that was used to reconstruct the pions. If the photon can be combined with another photon in the event to a pion the eta corresponding to photon will be ignored. pion listeta list Reject eta’s with |MPi0-0.135| < cut A cut at 13 MeV cuts out 20% signal and 75% of the background events. mpion -134 MeV

12. Hella SnoekNIKHEF12 Mass difference D* and D 0 daughter Mass difference between the D* and the D0 are very close to the mass of the pion. (MDst-MD-0.1454) MeV

13. Hella SnoekNIKHEF13 Event shape variables The thrust angle is defined as the angle between the thrust of the B meson and the thrust of the rest of the event. For BBbar events the distribution is flat, for qqbar the event is jet-like and peaks at =1 pla atje abs ma ken Jet Like event B event

14. Hella SnoekNIKHEF14 Event shape variables L2/L0 r2 p_B

15. Hella SnoekNIKHEF15 Mass/Energy plots EGamma1 EGamma2 && (Meta - 0.547)

16. Hella SnoekNIKHEF16 Momentum Variables pDstCms pD0Cms pPiCmspEtaCms

17. Hella SnoekNIKHEF17

18. Hella SnoekNIKHEF18 Preliminary results D0->KpiEvents before scalingScaling Factor Number of expected events Signal1020.01081.1 BBbar60.724.3 BpBm210.6814.4 Continuum1.018.1 Signal efficiency: 4.7% Significance: 0.25

19. Hella SnoekNIKHEF19 mES vs dE after optimized cuts Signal B0B0barBpBmContinuum