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New Results on |V td /V ts | from Radiative Decays

CKM 2008: 5 th International Workshop on the CKM Unitarity Triangle Rome, Italy, September 9-13, 2008. BaBar. New Results on |V td /V ts | from Radiative Decays. for the BaBar and Belle Collaborations. Bruce A. Schumm Santa Cruz Institute for Particle Physics

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New Results on |V td /V ts | from Radiative Decays

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  1. CKM 2008: 5th International Workshop on the CKM Unitarity Triangle Rome, Italy, September 9-13, 2008 BaBar New Results on |Vtd/Vts| from Radiative Decays for the BaBar and Belle Collaborations Bruce A. Schumm Santa Cruz Institute for Particle Physics University of California, Santa Cruz BaBar TALK-08/121

  2. Introduction • Motivation • B →(ρ,ω)g (“Standard” Approach) • B→Xd (“Semi-Inclusive” Approach) • Status of |Vtd/Vts| and Conclusions CKM 2008: Vtd/Vts from Radiative Decays

  3. (d) (d) (d) (d) Vt(s,d) (d) (d) Measuring |Vtd/Vts| Two independent diagrams provide sensitivity to CKM parameter Vtd B Mixing Note: In both cases, hadronic uncertainties minimized by comparing to corresponding Vts process (Bs mixing, b  s)  Observable is | Vtd / Vts | Radiative Penguins CKM 2008: Vtd/Vts from Radiative Decays

  4. |Vtd/Vts| from Penguins: Motivation ICHEP ’08 B Mixing Results [Farrington(CDF), Moulik(D0), averaged by DeLodovico(BaBar)]: How do penguins fit into the picture? SM effects suppressed by 10-5 relative to mixing Mixing: xd = mB/B ~ 1  mB ~ B Penguins: Br(bd) ~ 10-5 d~ 10-5B Furthermore (Ali, Asatrian, Greub, Phys. Lett B 429, 87): “These [b  d] vertices are CKM-suppressed in the standard model, but new physics contributions may not follow the CKM pattern in flavor-changing-neutral-current transitions and hence new physics effects may become more easily discernible in B  Xd +  (and its charge conjugate) than in the corresponding CKM-allowed vertices b  s and b  sg” With |Vtd/Vts| precisely constrained by mixing, b  d is a compelling testbed for new physics. CKM 2008: Vtd/Vts from Radiative Decays

  5. (and ) Exclusive Approach: B  ()  “Traditional” Approach: measure exclusive rate Br(B  () ); normalize with Br(B  K* ) Annihilation Diagram Values of 2 and R are state (+,0,) dependent and are available from Ali, Parkhomenko, arXiv:hep-ph/0610149 Ball, Zwicky, J. High. Energy Phys. 0604, 046 (2006); Ball, Jones, Zwicky, Phys. Rev. D 75 054004 (2007) at approximately 8% overall accuracy. CKM 2008: Vtd/Vts from Radiative Decays

  6. Measurement of B(B  ()  ) Belle: New result this Spring 351 fb-1 (2006)  598 fb-1 (April 2008) BaBar: New result this Summer 316 fb-1 (April 2007)  423 fb-1 (July 2008) • Challenge: BRs are small (<10-6); backgrounds are high • continuum [Neural Net with event shape, B tagging information, …] • B → K*; K* K [particle ID] • B → ( [veto if  found such that M~ M(,)] CKM 2008: Vtd/Vts from Radiative Decays

  7. Measurement of B(B  ()  ) (continued) Remaining separation achieved by two-dimensional fit to the largely independent kinematic variables “Energy-substituted mass”; since Ebeam ~ MB, largely a measurement of momentum balance EB = Ebeam for properly reconstructed candidate; total energy measurement *In e+e- CMS frame Example: BaBar B0 0  • “self-calibrating” continuum background subtraction • efficiencies (~5-15%) estimated with control samples CKM 2008: Vtd/Vts from Radiative Decays

  8. Belle’s April Update of B  ()  • Increase sample from 351 fb-1 to 598 fb-1 • Continuum: Fischer Discriminant with Fox-Wolfram moments, B flight information, vertex information • Include photons from endcap calorimeter Ji Lin, ICHEP ‘08 CKM 2008: Vtd/Vts from Radiative Decays

  9. BaBar’s July Update of B  ()  • Increase sample from 316 fb-1 to 423 fb-1 (final data set) • Strategy: Focus on unconfirmed B   mode • Continuum suppression: “Bagged Decision Tree” with 60 input event variables  Relatively good signal-to-noise + CKM 2008: Vtd/Vts from Radiative Decays

  10. BaBar’s July Update of B  ()  continued 0  CKM 2008: Vtd/Vts from Radiative Decays

  11. SU3(F)-Averaged Branching Fractions Assuming SU3(F) symmetry [B(B0) ~ B(B)] and (approximately true by static quark model) we can write from which it follows  Can combine +, 0,  results to derive |Vtd/Vts| from CKM 2008: Vtd/Vts from Radiative Decays

  12. |Vtd/Vts| from Exclusive (,) Decays BELLE: yielding BaBar: yielding assuming the world-average Combining, for exclusive radiative decay overall: CKM 2008: Vtd/Vts from Radiative Decays

  13. Semi-Inclusive Approach: B  Xd  “New” Approach (BaBar): Reconstruct seven exclusive final states Xd in range 0.6 GeV/c2 < MXd < 1.8 GeV/c2 • |Vtd/Vts|2 related to (bd)/(bs) with ~1% theoretical uncertainty [Ali, Asatrian, Greub, Phys. Lett. B 429, 87 (1998)] • However, must correct for unmeasured regions: • Higher-multiplicity final states • Higher-mass hadronic component (i.e. MXd > 1.8 GeV/c2) CKM 2008: Vtd/Vts from Radiative Decays

  14. # bodies # 0 Measured Regions for B  Xd(s)  UNMEASURED XS MEASURED (,,K*) 1.0 < Mhad < 1.8 1.8 < Mhad Xd Xd analysis only  and Xd analyses Mhad (MXd) CKM 2008: Vtd/Vts from Radiative Decays

  15. Continuum background Xs, MisID background B  X(s,d)  Partial Branching Fraction Results Fit in high-mass Xd region (first time measured): BABAR BABAR Yields and partial branching fractions: High-mass b  Xd  CKM 2008: Vtd/Vts from Radiative Decays

  16. Errors: Statistical  Experimental Systematic Correction for Missing Modes • Dominant systematic error for 1.0 < MX < 1.8 GeV/c2 • Most difficult for B  Xd  (not constrained by data) • Can improve with statistics (internal constraints) • Try several models: • MX given by “KN Model” Kagan & Neubert, Phys. Rev. D 58, 094012 (1998), with phase-space fragmentation • As above, but with 50% replaced by mix of resonances • Fix to measured b  s fragmentation BABAR Primary experimental result CKM 2008: Vtd/Vts from Radiative Decays

  17. Ratio of Total Widths and |Vtd/Vts| Precise (~1%) expression for |Vtd/Vts|[Ali, Asatrian, Greub] is based on ratio of full widths(bd)/(bs) Measured region 0.6 < MX < 1.8 is ~50% of width Extrapolate to full mass region via “KN Model”; KN calculation suggests negligible difference and uncertainty in extrapolation of the ratio (because ms,md << 1.8 GeV/c2?) This remains a bit of a caveat… BABAR BABAR Ali Asatrian Greub Expt. Theory arXiv:0807.4975 [hep-ex]; submitted to PRL CKM 2008: Vtd/Vts from Radiative Decays

  18. Global Status of |Vtd/Vts| No evidence for non-Standard Model contribution to the decay width. CKM 2008: Vtd/Vts from Radiative Decays

  19. Concluding Remarks • Radiative measurements of |Vtd/Vts| are becoming precise: | Vtd/Vts|rad = 0.203  0.020 • Semi-inclusive approach works, and is independent of exclusive approach, with small theoretical uncertainty • Agreement with SM (as constrained by B mixing) is good In principle, the severe SM suppression of this radiative processes (x10-6 of B mixing) should make it very sensitive to new physics contributions. Have we fully thought through the meaning of this constraint? CKM 2008: Vtd/Vts from Radiative Decays

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