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Search for the decay with the BaBar detector at SLAC

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

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Search for the decay with the BaBar detector at SLAC

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

  2. 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(2β+γ) possible by time-dependent analysis NIKHEF

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

  4. A test of factorization If decay is factorizable one is not sensitive for the factorization breaking part A Anon Afac A Anon Afac By suppressing the factorization part the factorization breaking part becomes visible A Anon Afac A Anon Afac X X A A Y Y 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=Afac + Anon. Factorization works well if Afac>>|Anon| 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. Designer mesons Some mesons are almost designed to ‘switch off’ the factorizing part of the decay amplitude. The a0 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. 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. NIKHEF hier nog de klassieke test

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

  7. Part II: The analysis • SKIM selection • Selection optimization NIKHEF

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

  9. Optimization of selection • Signal MC: BtoDstarA0 16000 events • Generic MC: BBbar 160 mil events • BpBm 168 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. NIKHEF

  10. 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 χ2 that uses the mass of the eta and the mass difference of the D* and the daughter D0. 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 NIKHEF

  11. 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 list eta list Reject eta’s with |MPi0-0.135| < cut A cut at 13 MeV cuts out 20% signal and 75% of the background events. NIKHEF mpion -134 MeV

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

  13. 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 plaatje abs maken B event Jet Like event NIKHEF

  14. Event shape variables r2 L2/L0 p_B NIKHEF

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

  16. Momentum Variables pD0Cms pDstCms NIKHEF pEtaCms pPiCms

  17. NIKHEF

  18. Preliminary results • Signal efficiency: 4.7% • Significance: 0.25 NIKHEF

  19. mES vs dE after optimized cuts B0B0bar BpBm Continuum Signal NIKHEF

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