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Radiative Penguin Decays of B Mesons

W -. b. s,d. t. g ,g Z . Radiative Penguin Decays of B Mesons. Adapted from: CKM, Moriond & LP05 Talks. Sridhara Dasu University of Wisconsin - Madison. Flavor changing neutral currents (b s, b d) are suppressed in nature At tree level, FCNC are prohibited in the Standard Model

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Radiative Penguin Decays of B Mesons

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  1. W - b s,d t g,gZ Radiative Penguin Decays of B Mesons Adapted from: CKM, Moriond & LP05 Talks Sridhara DasuUniversity of Wisconsin - Madison • Flavor changing neutral currents (bs, bd) are suppressed in nature • At tree level, FCNC are prohibited in the Standard Model • Loop level contributions (Strong and Electro-weak Penguins) permit sensitive measurement of the Standard Model parameters • New Physics can affect the branching fractions, CP violating and isospin breaking asymmetries • Electro-weak radiative penguins are a good indirect probe of new physics as non-Standard Model contributions (H±, c± , ..) can appear in the loop • In this talk I report on EW penguin measurements Sridhara Dasu, BaBar Seminar

  2. a B  p p Clean experiment/theory B  D K B  y K g b Quark Mixing : Unitarity In Standard Model CP violation is due to single non-zero complex phase of this matrix Agreement amongst various measurements of angles and sides is crucial test of the Standard Model All but DMs (CDF/D0) are accessible to BaBar |Vtd / Vts| Bd,s mixing: DMd / DMs b  d g / b  s g |Vub / Vcb| b  u l n / b  c l n Sridhara Dasu, BaBar Seminar

  3. The SLAC B-Factory Design Luminosity: 3 x 1033 cm-2 s-1 (Reached in 2001) Peak Luminosity: 9 x 1033 cm-2 s-1 (Reached in 2004) Sridhara Dasu, BaBar Seminar

  4. SLAC B-Factory Performance 1 fb–1 ~ 1.1 M BB events Run4 Run2 Over half a billion B’s produced! KEK integrated 470 fb–1 (while SLAC is recovering from accident) - SLAC has concrete plans to catch up by the end of 2006. Sridhara Dasu, BaBar Seminar

  5. e+ e– b b Signal: Continuum background: cont : B ~ 4.3 : 1 Sridhara Dasu, BaBar Seminar

  6. Charged Particle Tracking, Vertex Reconstruction (Dt),Low momentum particle ID dE/dx BaBar g, p0 and e± ID p/K/p ID m and KL ID RPC problems overcome Forward RPCs replaced (2002) Barrel RPCs  LSTs (2004/6) Sridhara Dasu, BaBar Seminar

  7. Four Main Themes in B Physics • CP Violation in B decays • Due to interference of mixing and decay amplitudes (indirect) • Due to decay amplitude interference (direct) • Searches for and studies of rare decays • Sensitive to physics beyond the Standard Model • B decay rate to rare final states • CP violation of rare decays - can be very sensitive • Precision determination of CKM matrix elements • Need to significantly improve in order to determine whether observed CP violation is consistent with SM predictions • Improving our understanding of B decays • Feeds back into precision SM tests and measurements Sridhara Dasu, BaBar Seminar

  8. The Standard Model CKM Matrix CKM Matrix Complex matrix described by 3 real parameters + 1 complex phase Wolfenstein parameterization: Exploit hierarchy in magnitudes by using Cabibbo angle, l=sinqc A, r, h are O(1) CP Violation: Sridhara Dasu, BaBar Seminar

  9. Unitarity Triangle Choice of parameters: a Rt g Ru b Sridhara Dasu, BaBar Seminar

  10. W - b s,d t g Rare Effective FCNC Weak B Decays - Access to CKM Parameters Sridhara Dasu, BaBar Seminar

  11. u,d W - b s,d Vts,Vtd t B-quarkmass B-mesonmass g Penguins used for measuring Vtd b-quark Fermi momentum Electromagnetic Penguin Sridhara Dasu, BaBar Seminar

  12. u,d W - b s,d Vts,Vtd t g Measuring EW Penguins • Measuring bsg and bdg • Theorists ideal: inclusive measurements • Avoid hadronic uncertainty • However, large experimental backgrounds • Experimentally more accessible: exclusive measurements • Backgrounds much reduced • Must contend with large B-meson model dependence • Most theoretical and systematic effects cancel in the ratios Sridhara Dasu, BaBar Seminar

  13. Measuring all decay products • Primary photon, • 0/ veto: suppress photon from 0 or  decay. • 25 cm away from any neutral or charge candidates. • Shower shape consistent with photon. 0 candidate: • [0.115, 0.155] GeV, mass-constraint refit, daughters consistent with photon, etc. K* Mass (MC) Charged K/: • (85% kaon eff; <3% pion mid-id), excellent Kaon/Pion separation in BaBar. KS candidates: • 0.3cm away from interaction point. • daughters from same decay point. • [0.487, 0.508] GeV mass window. Sridhara Dasu, BaBar Seminar

  14. Exclusive K* Reconstruction B0Decay Modes BDecay Modes B0g K*0 K-p+ (0.666) KSp0 (0.111)(*) B+g K*+ K+p0 (0.333) KSp+ (0.333)(*) *: only KS+- used. Common Variables, Signal MC ( ~0 for signal) where (peak at ~5.28 GeV for signal) Sridhara Dasu, BaBar Seminar

  15. background Signal Continuum Background Suppression At BaBar & Belle Bs are boosted • Large Dz identifies B In CMS frame • Signal events are spherical • Continuum is jet like • Thrust, sphericity, angles about g direction, net flavor of the event Multivariate analysis • Individual variables offer limited separation Sridhara Dasu, BaBar Seminar

  16. B Background Suppression B g XS K  … • Significant B background present, • BXS decays dominate. (XS: K* resonance with m > 1.1 GeV.) Mimic signal decay. MC Signal peaks at zero • Include B background as a component in the likelihood fit. Sridhara Dasu, BaBar Seminar

  17. Extended maximum-likelihood Fit 2-dimension (mES, E*) with 3 components (signal, B background, continuum background), With, No CP-asymmetry! Here ni and Aiare the total yields and the CP-asymmetry.fis underlying b quark flavor. b quark flavor: charge of K* for charged B decay; kaon charge for neutral B mode (K+-). Almost all PDF parameters are floating except B background PDF. Validated on MC; able to extract signal yield and ACP without bias. Sridhara Dasu, BaBar Seminar

  18. Exclusive Decay: BK*g • High statistics result: BF results are systematics limited. • Study CP asymmetries and isospin asymmetry 82 fb-1 Sridhara Dasu, BaBar Seminar

  19. Is it really K*? 82 fb-1 Relativistic Breit-Wigner shape using PDG parameters Sridhara Dasu, BaBar Seminar

  20. BK*g branching fraction Assuming QCD factorizationBeneke et al. and Bosch & Buchala calculations with formfactors from Lattice or Sum rules Sridhara Dasu, BaBar Seminar

  21. B rg B w  Challenges : • Lower branching fraction and higher background than for BK*g. Multivariate analysis techniques used for background subtraction. • Feed-through from K*g reduced using strict particle identification(Kp fake rate to ~1%) - remainder separated in fit using E • Brp0 background separated in the fit using angular variables Simultaneous fit to B+r+g, B0r0g, B0wg hep-ex/0408034 Sridhara Dasu, BaBar Seminar

  22. Usage of  average Two diagrams contribute for charged B decay • Can the average be used? • Verify with B  D*(SM expectation < 10–6) BABAR-PUB-05/009 Sridhara Dasu, BaBar Seminar

  23. B rg B w  Issues to be resolved • Compatibility between experiments • Isospin relations consistency LP PAPER-155 Sridhara Dasu, BaBar Seminar

  24. CKM Parameters: |Vtd / Vts| • Theoretical errors on hadronic effects mostly cancel in the ratio of exclusive modes • Left with ~15% residual uncertainty: Ali and Parmachenko • Measurement complementary to Bd,s mixing DMd/DMs BaBar/Belle AverageFrom UT fit Sridhara Dasu, BaBar Seminar

  25. CKM Implications bd g decays begin to provide interesting constraints on CKM parameters • and maybe open a window on new vistas. Need more data… Fit to all other data Sridhara Dasu, BaBar Seminar

  26. KL Reconstructed States K = K± / KS  = ± / 0 K± K K±± K K 3K Sum of exclusive states: B  K n()  • Reconstruct 38 hadronic modes • Require K± or Ks and up to 3 pions (np0≤1) • Extract signal from mes, DE fits in bins of hadronic mass Mhad • Advantages • Mhad has better resolution than Eg • Difficulties • Multiple candidates (Selected best with least DE) • Larger background for high multiplicty states • Missing mode correction model • Fixed using fragmentation in MC Sridhara Dasu, BaBar Seminar

  27. Fits to extract B  K n() signal 82 fb-1 Separate fits by B flavor and in Mhad bins Used for measurements of direct CP & isospin asymmetries, inclusive branching fraction and characterizing the B meson models. Used for cross check Sridhara Dasu, BaBar Seminar

  28. Direct CP & Isospin Asymmetry 82 fb-1 D0– improvement determines sign of C7 Standard Model ACP prediction is accurate and smallMeasurements are consistent with zero, dominated by statistical errors Future measurements can point to new physics Sridhara Dasu, BaBar Seminar

  29. Lepton tag technique Lepton Tagged Fully Inclusive Photon Spectrum • Reconstruct only photon in B  Xs,d • Advantage: Not dependent on JETSET Xs,d fragmentation. • High momentum lepton from other B against backgrounds. • Disadvantage: Loss of statistics • Tradeoff high B-Factory statistics to reduce backgrounds Sridhara Dasu, BaBar Seminar

  30. qq + ττ BB XSγ Power of Lepton Tag Remaining continuum background • Event shape reduces continuum. • Lepton tag beats it! • High P* lepton • Photon-lepton not back to back • Missing energy (neutrino) Sridhara Dasu, BaBar Seminar

  31. B Background Reduction B background is subtracted using MC 97% of BB background simulation corrected using independent data samples Remaining continuum subtracted w/off-peak data B background  systematic error Continuum BG  statistical error Sridhara Dasu, BaBar Seminar

  32. Using lepton tag charge: ACP(b s g+ b d g) = (- 0.010 0.115 0.017 ) Expected 10-9 Photon Spectrum Lepton tagged inclusive Sum of exclusive method preliminary K* K* (4s) frame B rest frame Sridhara Dasu, BaBar Seminar

  33. Total Branching Fraction Consistent with SM hep-ex/0506043 hep-ex/0506043 hep-ex/0403004 Inclusive bs branching fraction provides one of the more stringent constraints on new physics parameter space Sridhara Dasu, BaBar Seminar

  34. SUSY (cMSSM) Exclusion 0.8 TeV Ellis, et al. hep-ph/0305212 • Green shaded region is due to bsg • Plots for selected values of other parameters: A and m Universal sScalar mass 1 TeV Universal sFermion Mass See Luca Silvestrini(Lepton-Photon 2005) for a more model-independent discussion Sridhara Dasu, BaBar Seminar

  35. B-quarkmass B-mesonmass First, Second moments of Eg hep-ex/0506043 b-quark Fermi momentum Moments of  Spectrum Firstand second moments of the photon spectrum are used in heavy quark effective theory models. Sridhara Dasu, BaBar Seminar

  36. |Vcb| : moments analyses have 1.5–2% precision! Fit to all moments Fit to bcln moments Fit to b—sg moments CKM-05 Belle b—sgspectrum fit Shape Function • Fit to the Eg spectrum in bsg – Belle+Babar • Fit to the Eg moments of Eg spectrum - Babar • Had and lept. moments in bcln – Babar+others HQ parametersdetermine shape function for Vub extraction Sridhara Dasu, BaBar Seminar

  37. Average of Inclusive Determinations of |Vub| nonperturbative corrections free quark decay |Vub | The extraction of |Vub|from the measured partial BFs is not trivial • Inclusive decays depend on measured shape function and OPE More work needed to resolve discrepancies Sridhara Dasu, BaBar Seminar

  38. Complimentary to Bsl+l– AFB=(NF-NB)/NF+NB) Y Y’ Forward: l+ along BBackward: l+ opp. B Zero x-ing point Mll2 Mll2 New physics sensitivity is higher for b  s l+l– Sridhara Dasu, BaBar Seminar

  39. Knn sensitivity now <10X SM rate BKl+l–, BK*l+l–, BKnn Clean probes of EW scale physics Branching fractions ~ 10-6 Well-established Kll, K*ll signals for B factories ( l = e,m) K l+l- Preliminary Preliminary K* l+l- Sridhara Dasu, BaBar Seminar

  40. BKl+l-, BK*l+l- Kll, K*ll branching fractions in range predicted by SM + form factors theory uncertainty > experimental uncertainty 10-6 Rarest B decay observed! Beyond branching fractions: Asymmetries ACPconsistent with zero Kmm/Kee ratio consistent with unity Forward-backward angular asymmetry of lepton pair vs. dilepton mass probes relative size, phase of penguin diagrams Raw AFB, K*ll Sridhara Dasu, BaBar Seminar

  41. We are beginning to see higher hadronic mass contribution Inclusive decay: b  s l+l- 82 fb-1 • Semi-inclusive • Use sum of exclusive modes techniques a la bs g analysis • Hadronic component, Xs, has one K± and up to 2 p s e+ e– s m+m– s e+m– Sridhara Dasu, BaBar Seminar

  42. The Golden Channel Sridhara Dasu, BaBar Seminar

  43. Time Dependent Measurements Sridhara Dasu, BaBar Seminar

  44. Sin2b Measurement BABAR BABAR Update for ICHEP04 BABAR PUB-04/038 Sridhara Dasu, BaBar Seminar

  45. sin2 Comparison CP violation in B system is almost consistent with Standard Model expectations • Comparison of Tree and Gluonic penguin dominated decays provide new physics sensitivity • Curiously gluonic penguin results are systematically low • More data is needed to resolve experimental discrepancies • Do electroweak penguin modes have anything to say? Sridhara Dasu, BaBar Seminar

  46. Helicity Flip Suppressed by ms/mb mixing Time Dependent CP Fit toBK*( KSp0)g • Because of the correlation of photon helicity, time dependent CPV suppressed • Sine coeficient: LP Paper-97 Sridhara Dasu, BaBar Seminar

  47. MES BABAR-PUB-05/31 State BF(10-5) g polarization • Up to ms/mb corrections • A different polarization is a marker of NP • It can be probed in • Need 2 interfering amplitudes related by isospin: (Kp+)p0g (Kp0)p+g • No results on polarization, yet.Started measuring BF PRL 88 051802 (2002) Sridhara Dasu, BaBar Seminar

  48. Standard Model Unitarity Tree Level sin2b • Consistent with SM Progress requires • Measurements of a, g • Penguin pollution Further checks of sin2b • Measure in penguins Measurement of sides • Vub, Vtd • Rare processes • Hadronic uncertainty • HeavyLight form factor calculation • Radiative penguins are beginning to play an important role in constraining SM unitarity Sridhara Dasu, BaBar Seminar

  49. PEP-II Integrated Luminosity Goals x4 by Sep 2008 Improvement Plan • New feedback, filters, controls (05) • Additional HER rf station (06) • Additional LER rf station (06) • Upgrade IR vacuum chambers for higher currents (06) • Upgrade HER lattice for shorter bunches (06) x2 by Jul 2006 Sridhara Dasu, BaBar Seminar

  50. Summary Electro-weak penguins (b sg) are sensitive to new physics • Branching Fractions (especially inclusive modes): • Consistent with Standard Model - stringent limits on FCNC • CP & isospin asymmetries and  polarization are good probes: • Are also consistent with SM but will remain interesting • Photon spectrum analysis is proving to be important for Vub Beginning to see evidence for b dg • Allows measurement of Vtd/Vts complementary to DMd/DMs Discovered b  s l+ l- (More data needed to test new physics) • Forward-backward asymmetry is sensitive to new physics CP Violation in B system is consistent with Standard Model • Measurements of Tree and Gluonic penguin dominated decays are converging leaving little room for new physics contributions • More data is needed to resolve experimental discrepancies Integrated Luminosity: ~ 500 fb-1 by summer 2006 Sridhara Dasu, BaBar Seminar

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