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Radiative B meson Decays at BaBar

Radiative B meson Decays at BaBar. Colin Jessop University of Notre Dame. Motivations. Window to new Physics Help measure the unitarity triangle Test QCD technology. Radiative Penguin Decays. The Penguin Zoo. Several different types of penguins (not including gluonic penguins).

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Radiative B meson Decays at BaBar

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  1. Radiative B meson Decays at BaBar Colin Jessop University of Notre Dame

  2. Motivations • Window to new Physics • Help measure the unitarity triangle • Test QCD technology Radiative Penguin Decays

  3. The Penguin Zoo Several different types of penguins (not including gluonic penguins) Electro-Magnetic Electroweak Vertical Electromagnetic Vertical electroweak I will focus today mostly on electromagnetic penguins. BaBar has results on all these processes

  4. Sensitivity to New Physics Example: If SUSY exact B(b->sg) = 0 SUSY g g W+ H+ + + .. b S/d b S/d t t New Physics enters at same order (1-loop) as Standard Model Sensitive to many models – very extensive literature

  5. g W+ b S/d t Penguin Theory – A brief Overview B mesons are low energy decays at scale m = mb ~ 5 GeV Formulate a low energy effective theory : g b S/d Generalization of Fermi Theory of b-decay.

  6. g b S/d Operator Product Expansion Ci : Wilson Coefficients – contains short distance (high energy) perturbative component Qi : Local Operators – contains long distance (low energy) non-perturbative component m(renormalization) scale dependence cancels in C and Q

  7. g b S/d Wilson Coefficients Ci i=1,2 current-current, i=3-6 gluonic penguins i=7-10 Electroweak Penguins Cicalculated at m=Mw and evolved down to m=mb. Effects of new high mass physics appear in C DC8 e.g constraints on C7 and C8 from B(B->Xsg) DC7

  8. g b S/d Matrix Elements <X|Q|B> are long distance (low-energy ) non-perturbative component • If X is exclusive state e.g | K*g > two possibilities • Lattice QCD : Lattice spacing >> compton wavelength of b -> Large errors • QCD sum rules: Relates resonances to vacuum structure of QCD Neither approach gives precise estimates – limits exclusive physics. Uncertainties cancel in ratios of modes or asymmetries.

  9. g b S/d Inclusive Matrix Elements If X is an inclusive state 0 Leading term is short distance quark contribution and non- perturbative effects appears at 1/mb2 –i.e (O(1%)) corrections Inclusive measurements are much more sensitive to new physics

  10. General Considerations

  11. B factories: e+e-  Y(4S)  BB • B factories operate at the Y(4S) resonance (10.58 GeV) • hadronic cross-sections: • udsc:bb = 3.4:1.1 nb • in the Y(4S) frame the B mesons are practically at rest •  PEP-II is an asymmetric collider • 9.0 GeV electrons vs • 3.1 GeV positrons

  12. PEP-II and BaBar at SLAC linac PEP-II storage ring SLD BaBar

  13. off-resonance data on-resonance data Integrated luminosity Currently 10 BB event per second. since 2000 BaBar has recorded 430M BB events about 8% of data is taken below the Y(4S) resonance results presented here are based on 90 fb-1 - 340 fb-1 on-resonance data Shutdown due to accident

  14. Other B meson experiments CLEO did much of the pioneering work. Stopped in 2001 BaBar forced to shut down for a year in 2004-2005 by DOE safety after accident Though BELLE has larger datasets BaBar remains competitive BaBar will stop running in 2008. Hope for 1000 fb-1 at that time.

  15. The BaBar detector Instrumented Flux Return 19 layers of RPCs μ and KL ID Electromagnetic Calorimeter 6580 CsI crystals e+ ID, π0 and γ reco Cherenkov Detector (DIRC) 144 quartz bars K, π, p separation 3 GeV positrons Drift Chamber 40 layers, tracking + dE/dx 9 GeV electrons Silicon Vertex Tracker 5 layers of double-sided silicon strips 1.5 T magnet

  16. Radiative penguin decays of B mesons CLEO Observation of BK* g 1993 BaBar BK* g 2006 First observation of penguins by CLEO. Now it’s a background !

  17. Radiative penguin portrait B+→ K*+γ (K*+->Ksπ+) candidate Muon from other B decay Detached vertex from Ks → ππ High energy photon in EMC Note Event tends To be isotropic In center of mass frame π+ from K*+

  18. Continuum Backgrounds Production of u,d,s,c quark and t pairs underneath U(4s) Lorentz boost makes a jet-like topology

  19. Event Shape Variables Construct “Shape” variables to distinguish between isotropy and jets Neural net combination of suite of topology variables effective with multicomponent background cos T* Angle between thrust and photon

  20. Additional Continuum separation Variables g B K* B Net Flavor = 0 DZvertex B’s have lifetime and decay weakly. uds decays promptly and strongly Net Flavor = (N(e+) – N(e-)) +(N(m+)-N(m-)) + (N(k+)-N(k-))

  21. Signal Variables for Exclusive Reconstruction analyses Beam Constrained Mass Reconstructed Energy - beam Energy Sensitivity can be enhanced by performing two dimensional likelihood fits to signal and background.

  22. A Colony of Penguins r,w dd (Vtd) (Vts) sd K*(892) K1(1270) K2(1430) …

  23. νe d g Vud g e+ u W+ W+ 1 λ λ3 λ 1 λ2 λ3 λ2 1 The CKM matrix leptons quarks Standard model explanation of CP violation is a single phase in the CKM matrix V.

  24. The unitarity triangle Photon spectrum in B->Xsg helps reduce error on Vub Photon spectrum in B->Xsg helps reduce error on Vbc Overconstraining the triangle may reveal new sources of CP violation.

  25. Matter-Antimatter Asymmetry in Universe CP violation is an essential component of the presumed mechanism for generating this asymmetry But: The Standard model has insufficient CP violation to account for the observed asym. Presumably extra CP violation comes from new physics that couples to quarks or leptons

  26. Measurement of bdg Decays B0r0g B+r+g signal + bkgnd bkgnd signal Mass projections from 4d fit 6.3 sigma observation BABAR, hep-ex/0607099, 347 M BB

  27. 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.

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

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

  30. Inclusive Penguins: G(B->Xsg) Quark-hadron duality The non-perturbative corrections are a few percent. Recently a new NNLO calculation for B(B->Xsg ) has been completed (Misiak,Asatrian,Bieri,Czakon,Czarnecki,Ewerth,Ferroglia,Gambino Gorbahn,Greub,Haisch,Hovhannisyan,Hurth,Mitov,Poghosyan,Slusarczyh) Major undertaking involving thousands of diagrams. New precise Calculation has renewed interest in the field Compare to NLO:

  31. Theory Errors on B(B->Xsg) Scale dependence onmb Theory errors from choice of Renormalization scales LO As go to higher orders this is reduced as expected. NLO NLO NNLO Scale dependence onmc mb (GeV) NLO At NLO the choice of charm quark renormalization scale had been a Problem. New calculation resolves this issue and errors are now understood LO NNLO mc (GeV)

  32. B g g b b s Xs Quark-Hadron duality Hadrons Quarks B(b -> sg) = B(B -> Xsg) A fully inclusive measurement can be related directly to quark calculation

  33. B g g b b s Xs Inclusive Photon Spectrum Confinement To be fully inclusive must measure all the photon spectrum

  34. B g b Xs Inclusive Photon Spectrum FirstMoment: Second Moment: (Kinetic energy of b)2 Information about motion of b-quark should be universal – i.e like a structure function and so can be applied to other inclusive processes

  35. Experimental Challenge g Model Dependence Monte Carlo : Just require g qq BB B -> Xsg Note additional BB background To reduce large backgrounds without cutting on g or Xs i.e a fully inclusive measurement

  36. g B Xs Two Methods for inclusive B Xsg Differ in treatment of Xs

  37. B KKK(p(0)) Baryons Kh(gg)pp(0) ISR Rare Decays KKK+nK+np(0) Kp(0)p(0)pp K+h(gg)np(0) Kp(0) KL+... KL+... K+>4 p(0) Kp(0)p(0)p Kp(0)p(0) Kp0p0p0(p0) Technique 1 – Semi-Inclusive g Exclusively Reconstruct as many of the final states of Xs as possible: Fundamental problem is that composition of final states must be guessed - large systematic Xs ~55% ~45% Missing Final States Reconstructed Final States K = K±, Ks

  38. g lepton B B Xc Xs Technique II “Fully Inclusive”: B -> Xsg Suppress continuum background by requiring a “lepton tag” from recoiling B (5% Efficiency for x1200 reduction in background) BB B->Xsg Remaining continuum subtracted with off-resonance data -> statistical uncertainty Multi-component BB background

  39. Fully Inclusive BB background BB B->Xsg Each BB component measured independently in data. Precision of these measurements is dominant systematic.

  40. BABAR Fully Inclusive B Xsg, w/lepton tag (PRL Oct 23 2006) Spectrum from best fit to kinetic scheme. Spectrum from best fit to shape function scheme. (measured) (extrapolated, kinetic scheme)

  41. Summary of B Xs g Branching Fraction Measurements Theory is NNLO prediction (2006)

  42. B(B-Xsg) constraints many models Error x 10-4 World Av3.55+-0.26 x 10-4 B(B->Xsg) x 10-4 Example: Two Higgs doublet model MH+>300 GeV cf. direct search > 79.3 GeV

  43. Future Precision of B(B->Xsg) Expect 5% precision from full dataset

  44. Direct CP asymmetry is sensitive to non MFV SUSY Fully-Inclusive: Lepton charge tags flavor. Dilution from mixing. Asymmetry consistent with Standard Model and previous measurements

  45. Hadron level Parton level Extracting Vbc and Vbu Use inclusive measurements of lepton spectra Motion of b quark is dominant theoretical Uncertainty Use B->Xsg to significantly increase precision decay rate El= lepton energy

  46. Moments • Fit predicted moments of inclusive processes bclv and bsgfor various cuts on kinematic variables in HQE: • Calculations available in “kinetic” and “1S” renormalization schemes • 47 measured moments used from DELPHI, CLEO, BABAR, BELLE, CDF (and, of course, the B lifetime) Matrix elements appearing at order 1/mb2 and 1/mb3 e or l energy cut c-quark mass b-quark mass Bauer, Ligeti, Luke, Manohar, TrottPRD 70:094017 (2004) Benson, Bigi, Gambino, Mannel, Uraltsev(several papers)

  47. Results: Spectrum Moments vs Eg most precise moments from BaBar fully inclusive Curves are theory prediction using measured b->Xclv moments Demonstrates assertion that b quark motion is universal

  48. kinetic scheme μπ2 (GeV2) combined mb (GeV) χ2 / Ndof = 19.3/44 Extraction of Vbc,mb,mp |Vcb| determined to <2% b->sg B->clv Buchmüller and Flächer,PRD 73: 073008 (2006) mb to 1%; crucial for |Vub| [kin]/[1S] values agree after scheme translation

  49. Extracting Vub Inclusive B->Xuln n mb enters as mb5 so 1% error in mb gives 2.5% error in Vub Other HQE parameters estimated from B->Xsg enter into non-perturbative terms

  50. World Average 4.49 ± 0.33 |Vub| from B->Xln Error dominated by theory (mb and HQE parameter estimation) χ2/dof = 6.1/6 7.2% error down from 15% in 2003. 5% ultimately

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