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Radiative and Electroweak Penguin Decays of B Mesons

Jeffrey D. Richman University of California, Santa Barbara B A B AR Collaboration. Radiative and Electroweak Penguin Decays of B Mesons. 11 th International Conference on B Physics at Hadron Machines Oxford, Sept. 28, 2006. Outline.

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Radiative and Electroweak Penguin Decays of B Mesons

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  1. Jeffrey D. Richman University of California, Santa Barbara BABAR Collaboration Radiative and Electroweak Penguin Decays of B Mesons 11th International Conference on B Physics at Hadron Machines Oxford, Sept. 28, 2006

  2. Outline • Overview: a little history, physics goals, and challenges • B+r+g, B0r0g, B0wg and theextraction of |Vtd/Vts| • BKl+l- and BK*l+l-: search for new physics using the lepton forward-backward asymmetry • Inclusive BXs g: branching fraction measurements and extraction of heavy-quark-expansion parameters (including mb) using the Eg spectrum • Conclusions Apologies for not covering all results on radiative/electroweak penguin decays in this talk!

  3. Radiative penguin decays of B mesons Now it’s a physics program! Observation of BK* g CLEO II (1993): Loops in B decays! PRL 71, 674 (1993): cited >500 times! Rare, but not all that rare!

  4. What can we learn from bs, d transitions? • Probe SM at 1-loop level (flavor-changing neutral currents) • Search for new physics: can affect amplitudes at leading order • As for semileptonic decays, the amplitude in EM/EW penguins involves only one hadronic current  factorizes. (+ W+W-box diagram) (dominated by t quark)

  5. What can we learn from bs,d transitions? • Understand QCD dynamics: single hadronic current allows us to isolate non-perturbative parameters in well-defined way. Can be related to same/similar parameters for other decays. • Exclusive decays: decay form factors fi(q2). bs transition is similar to bu (heavy-to-light decays) • Inclusive decays: parameters of heavy-quark expansion (mb, mp2,…); important input for |Vub|, |Vcb| extractions. • Measure/constrain CKM elements (|Vtd/Vts|): if info on hadronic parameters is available from data, theory, or both.

  6. Observation of bdg and Measurement of |Vtd/Vts| + W annihilation diagram (small) Ali, Lunghi, Parkhomenko, PLB 595, 323 (2004) [for I-spin avg.] Ball and Zwicky, JHEP 0604, 046 (2006) Ball and Zwicky, hep-ph/0603232 I-spin (r), quark model (w). Expect small I-spin violation: (1.1+/-3.9)%.

  7. Measurement of bdg Decays (Belle) Belle, PRL 96, 221601 (2006); 386 M BB. Signal continuum background BK*g Good particle ID is critical in this measurement to suppress BK* g feed-down.

  8. Measurement of bdg Decays (BABAR) BABAR, hep-ex/0607099, 347 M BB projections of 4-D fit signal + bkgnd B+r+g bkgnd B+r+g signal B0r0g B0 r0g

  9. Comparison of bdg Branching Fractions CKM fitter includes CDF Bs mixing result. Error on CKM Fitter prediction includes uncert. on BVg form-factor ratio. I-spin consistency? preliminary;hep-ex/0607099 PRL 96, 221601 (2006).

  10. Extracting |Vtd /Vts| from bdg Decays Belle, PRL 96, 221601 (2006). courtesy M. Bona (UTfit collab.) expt thy BABAR, hep-ex/0607099 (preliminary) thy expt CDF, hep-ex/0609040 (preliminary) expt thy Consistent within errors! (used CDF hep-ex/0606027) Theoretical uncertainties already or soon limiting both approaches.

  11. BKl+l- and BK*l+l- in the SM and Beyond Photon penguin Z penguin W+W- box • 3-body decays  dependence of rate on kinematic variables can be used to study the different amplitudes and their interference effects. • The mode BKl+l- is allowed as well as BK*l+l- (BKg forbidden by conservation of angular momentum).

  12. BK*l+l- Dalitz plot Can see AFB behavior and q2 dependence from the Dalitz plot Standard Model Prediction effect of g pole Note: BKl+l- is expected to have very small AFB, even in presence of new physics; effectively provides a crosscheck.

  13. Amplitude for BK*l+l- photon penguin dom. at v. low q2 mix of Z-penguin, W+W- box Kruger and Matias; PRD 71, 094009 (2005) • Short-distance physics encoded in Ci’s (Wilson coefficients); calculated at NNLO in SM: • Interference termsgenerate asymmetries in lepton angular distribution over most of q2range. • Ci’scan be affected by new physics; enters at same order as SM amp. Ali et al., PRD 61, 074024 (2000)

  14. Form Factors and Observables • Long distance QCD physics is mainly described in terms of form • factors, which are functions of • 4 semileptonic form factors: A1, A2, V, A0 (similar to BD*ln, Brln) • 3 penguin form factors: T1, T2, T3 • Form factor uncertainies  35% uncertainty in rate predictions. large s

  15. Predictions for AFB in BK*l+l-: SM and beyond Standard Model s0: Ali, Kramer, Zhu, hep-ph/0601034

  16. BKl+l- and BK*l+l- Signals from BABAR BABAR, PRD 73, 092001 (2006) 229 M BB (6.6 s, rarest observed B decay) (5.7 s)

  17. BK(*)l+l- Signals from Belle Belle, PRL 96, 251801 (2006) 386 M BB (Data sample used for study of Wilson coefficients)

  18. BKl+l- and BK*l+l- branching fractions PRD 73, 092001 (2006) preliminary, hep-ex/0410006 HFAG avg. Inclusive:

  19. BK*l+l-: BABAR results on K* polarization apply in 2 bins of q2 BABAR, PRD 73, 092001 (2006) J/y (vetoed) K* polarization SM Data SM low q2 high q2 Polarization consistent with SM, but doesn’t discriminate against new physics scenarios with current data sample. Theory predictions in graphs: Ali et al., PRD 66, 034002 (2002); Ball and Zwicky, PRD 71, 014029 (2005).

  20. BK*l+l-: BABAR results on AFB and GL use in 2 bins of q2 Data SM excluded at 3.6s! Any AFB<0 excluded at >2.7s (AFB=0 in SM and many BSM)

  21. BK*l+l-: Belle results on AFB Belle, PRL 96, 251801 (2006) best fit with A7 fixed to SM for reference:

  22. BK*l+l-: Belle results on Wilson coefficients Fit q2 and cosql for allowed excluded (Ai are real and constant; q2 dep. corrections fixed to theory) SM fit • fix |A7| to SM (BXsg) • fit for A9/A7 and A10/A7 • data consistent with SM • quadrants I, III excluded at 98.2% C.L. allowed excluded A10>0 need A9A10<0 to get AFB>0 in upper q2 region

  23. Inclusive B Xsg • Canonical process for studying bs transition. Theory uncertainties currently at 10% level (NLO); pushing toward 5% (NNLO). • Huge theoretical effort to predict branching fraction & photon energy spectrum. Also predictions for CP and I-spin violation. • Spectrum is insensitive to new physics but is sensitive to mb and Fermi motion of b-quark (“shape function”). T. Hurth, E. Lunghi, W. Porod, Nucl. Phys. B 704, 56 (2005). M. Neubert, Eur. Phys. J. C 40, 165 (2005). all for M. Misiak and M. Steinhauser, hep-ph/0609241 NNLO New!

  24. Challenges of measuring inclusive B Xsg • Weak experimental signature: single high-energy photon + event-shape cuts. Huge background from p0’s and h’s! • Difficult to carry analysis down to Eg < 2.0 GeV. • Want to push toward 5% precision to match the expected precision of NNLO calculations.

  25. Fully inclusive B Xsg Belle, PRL 93, 061803 (2004), 140 fb-1 Belle, hep-ex/0508005 (moments) CLEO, PRL 87, 215807 (2001), 9.1 fb-1 background subtracted efficiency corrected background subtracted not efficiency corrected Measure for Eg>2.0; extrap. to Eg>0.25 GeV Measure for Eg>1.8 GeV; extrap. to full

  26. qq + ττ BB XSγ Fully inclusive, lepton-tagged B Xsg(BABAR) hep-ex/0607071 (preliminary, submitted to PRL) • Suppress large continuum background using • Event-shape cuts (continuum has jet topology) • Lepton tag: high energy lepton from 2nd B in event (BXcln) BB dominated (blinded) continuum dominated lepton tag

  27. BABAR Fully Inclusive B Xsg, w/lepton tag hep-ex/0607071 (preliminary, sub. to PRL) spectrum not efficiency corrected Spectrum from best fit to kinetic scheme. Spectrum from best fit to shape function scheme. (measured) model sys stat (extrapolated, kinetic scheme)

  28. BABARB Xsg with Sum of Exclusive Final States BABAR, PRD 72, 052004 (2005) for BF, sum over all m(Xs): comb. BB signal continuum peaking bknd • averages over two shape-function schemes • errors: stat, sys, variation of shape fcn params BF/10-3 for spectrum, fit mES in bins of m(Xs) K*(890) • Eg (min) = 1.897 GeV

  29. Summary: B Xsg Branching Fraction & Moments Buchmüller and Flächer, PRD 73, 073008 (2006) HFAG 2006: common corrections to for BFs for extrapolations to Eg=1.6GeV. Gambino and Uraltsev, Eur. Phys. J C34, 181 (2004) green band expt uncert. average stat+sys shape fcn bdg frac

  30. Fits to moments of inclusive BXcln and BXsg distributions Buchmüller and Flächer, PRD 73, 073008 (2006) Data from BaBar, Belle, CDF, CLEO, & DELPHI all moments all moments kinetic mass scheme mb used for |Vub| (7.5% error!)

  31. Conclusions Studies of radiative/electroweak penguins have moved far beyond BK*g. • Observation of exclusive bd g decays: B(r0, r+, w) g • Use to extract |Vtd/Vts|; consistent with value from Bs mixing. Precision soon to be limited by theoretical uncertainties. • Electroweak penguins decays BKl+l-, BK* l+l-, and BXsl+l-have been measured. First studies of decay distributions have been performed and exclude some non-SM scenarios. More data needed to exploit full potential. • Inclusive BXsg measurements provide information on mb and non-pert. QCD parameters and help improve precision on |Vcb| and |Vub|. Difficult issues with systematic errors, but goal is to achieve 5% uncertainty on branching fraction. • We will study radiative/EW penguins for many years to come at BaBar, Belle, and LHC-b!

  32. BABAR

  33. Backup slides

  34. BR(B→(ρ/ω)γ)/BR(B→K*γ) BaBar ICHEP 2006 Belle 2005 B-Factories average CDF measurement (mS) CKM fitter code w/o Δms Extracting |Vtd /Vts| from bdg Decays Belle, PRL 96, 221601 (2006). BABAR, hep-ex/0607099 (preliminary) CDF, hep-ex/0606027 (preliminary) Consistent within errors. Theoretical uncertainties limiting both approaches.

  35. B0 wg BABAR, hep-ex/0607099, 347 M BB

  36. BKl+l- and BK*l+l- : q2 distributions J/yK Pole from K*g, even in m+m- SUSY models y(2S)K SM nonres SM nonres q2 q2 constructive interf. destructive

  37. BKl+l- and BK*l+l-: the J/y veto • The decays BJ/yK and BJ/yK* are huge backgrounds and must be carefully removed (also By(2S)K, y(2S)K*). • These backgrounds are restricted in q2, but there is a tail due to bremsstrahlung in the electron modes. • But BJ/yK and BJ/yK* are valuable control samples; use them to study efficiency of almost any analysis cut. • Ali, Kramer, Zhu: m(e+e-) projection: MC BKe+e- J/y and y(2S) veto: MC BKe+e-

  38. M(l+l-) distributions from BJ/yK+ control samples: data vs. Monte Carlo BABAR points: data histogram: MC Bremsstrahlung tails well described by MC. absolute normalization

  39. BKl+l- Signal from BABAR BABAR, PRD 73, 092001 (2006) 229 M BB • summed over all K l+l- modes (K+e+e-, K+m+m-, KS e+e-, KS m+m-) • significance=6.6 s; rarest observed B decay (averaged)

  40. BK*l+l- Signal from BABAR BABAR, PRD 73, 092001 (2006) 229 M BB

  41. BK*l+l- Dalitz plot Can see AFB behavior and q2 dependence from the Dalitz plot Standard Model Prediction effect of g pole Note: BKl+l- is expected to have very small AFB, even in presence of new physics; effectively provides a crosscheck.

  42. BK*l+l- Dalitz plot Can see AFB behavior and q2 dependence from the Dalitz plot Maximal new physics effect: effect of g pole

  43. BK*l+l-: BABAR results on q2distribution BABAR, PRD 73, 092001 (2006)

  44. Lepton angular distribution in l+ l- rest frame use l- if B use l+ if B Ali, Kramer, Zhu, hep-ph/0601034

  45. Extracting AFB and FL in bins of q2 BABAR, PRD 73, 092001 (2006)

  46. Belle, hep-ex/041006

  47. Inclusive B Xsg: some history CLEO, PRL 74, 2885 (1995); 2.01 fb-1 on Y(4S), 0.96 fb-1 below Y(4S) Backgrounds: B decays, continuum, e+e-qqg (ISR), e+e-qqp0X “Event-shape analysis” “B-reconstruction analysis” total background (points w/error bars) scaled off resonance

  48. BABARB Xsg with Sum of Exclusive Final States Reconstruct 38 exclusive modes • |DE|<40 MeV • For Eg spectrum, fit mES distrib. in bins of m(Xs) • Correct for efficiency of each mode and missing modes fraction (model dependence) for BF, sum over all m(Xs): comb. BB signal continuum peaking bknd

  49. Systematic Errors on BXsg Belle, PRL 93, 061803 (2004)

  50. Belle: BXsl+l- Belle, PRL 72, 092005 (2006) 5.4s

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