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Unlocking CKM Parameter with Radiative Decays - BaBar and Belle Collaboration Insights

Investigating |Vtd/Vts| from Radiative Decays, emphasizing Penguin contributions and exploring exclusive approaches for precise constraints. BaBar and Belle share new results, detailing challenges in small branching ratios and continuum suppression. The seminar delves into the significance of exclusive decay modes and the latest updates from both collaborations.

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Unlocking CKM Parameter with Radiative Decays - BaBar and Belle Collaboration Insights

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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

  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 (preliminary) 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  PRELIMINARY • “self-calibrating” continuum background subtraction • efficiencies (~5-15%) estimated with control samples Continuum Signal bs Feedthrough 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  ()  (Preliminary) • 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 PRELIMINARY  PRELIMINARY CKM 2008: Vtd/Vts from Radiative Decays

  11. Isopsin-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 PRELIMINARY assuming the world-average Combining, for exclusive radiative decay overall: CKM 2008: Vtd/Vts from Radiative Decays

  13. Semi-Inclusive Approach: B  Xd  (Preliminary) “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: PRELIMINARY 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 PRELIMINARY 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 PRELIMINARY Ali Asatrian Greub PRELIMINARY Expt. Theory arXiv:0807.4975 [hep-ex]; submitted to PRL CKM 2008: Vtd/Vts from Radiative Decays

  18. * PRELIMINARY 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 process (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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