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

Transcription

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->s) = 0 SUSY W+ + H+ +.. b t S/d b t S/d New Physics enters at same order (1-loop) as Standard Model Sensitive to many models very extensive literature

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

6 Operator Product Expansion H eff = 4G F 2 V tb V ts 10 i= 1 C i ( μ) Q i ( μ) b S/d Ci : Wilson Coefficients contains short distance (high energy) perturbative component Qi : Local Operators contains long distance (low energy) non-perturbative component μ(renormalization) scale dependence cancels in C and Q

7 H eff = 4G F 2 V tb V ts Wilson Coefficients 10 i= 1 C i ( μ) Q i ( μ) b S/d Ci i=1,2 current-current, i=3-6 gluonic penguins i=7-10 Electroweak Penguins Ci calculated at μ=mw and evolved down to μ=mb. Effects of new high mass physics appear in C ΔC8 e.g constraints on C7 and C8 from B(B->X s ) ΔC7

8 H eff = 4G F 2 V tb V ts Matrix Elements 10 i= 1 C i ( μ) Q i ( μ) b S/d <X Q B> are long distance (low-energy ) non-perturbative component If X is exclusive state e.g K* > two possibilities 1. Lattice QCD : Lattice spacing >> compton wavelength of b -> Large errors 2. 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 Inclusive Matrix Elements H eff = 4G F 2 Inclusive Matrix Elements V tb V ts 10 i= 1 C i ( μ) Q i ( μ) b S/d If X is an inclusive state X Q B = Ο( ) + Ο( ) m b m b 0 Leading term is short distance quark contribution and nonperturbative effects appears at 1/mb 2 i.e (O(1%)) corrections Inclusive measurements are much more sensitive to new physics

10 General Considerations Exclusive Inclusive Mode B->K* >K* B->ρ/ω B->Xs (#Events in~400fb-1) O(500) O(50) O(5000) Backgrounds Small Large Large Theory Uncertainty Large Medium Small (in ratios) 30-50% 15% 7%

11 B factories: e+e- Y(4S) BB o B factories operate at the Y(4S) resonance (10.58 GeV) o hadronic cross-sections: udsc:bb = 3.4:1.1 nb o 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 Integrated luminosity off-resonance data on-resonance data Currently 10 BB event per second. since 2000 BaBar has recorded 430M BB events Shutdown due to accident about 8% of data is taken below the Y(4S) resonance results presented here are based on 90 fb fb -1 on-resonance data

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

15 The BaBar detector Electromagnetic Calorimeter 6580 CsI crystals e+ ID, π 0 and reco Instrumented Flux Return 19 layers of RPCs μ and K L ID Cherenkov Detector (DIRC) 144 quartz bars K, π, p separation 3 GeV positrons 9 GeV electrons Drift Chamber 40 layers, tracking + de/dx 1.5 T magnet Silicon Vertex Tracker 5 layers of double-sided silicon strips

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

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

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

19 Event Shape Variables Construct Shape variables to distinguish between isotropy and jets cos θ T * Angle between thrust and photon Frac. Events/0.04 Neural net combination of suite of topology variables effective with multicomponent background Continuum Monte Carlo Off-Resonance Data 0 - B D π + Monte Carlo B 0 D - π + Data Neural Network Output

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

21 Signal Variables for Exclusive Reconstruction analyses Beam Constrained Mass Reconstructed Energy - beam Energy 2 Events/2.5 MeV/c 50 BABAR Events/20 MeV BABAR M ES = M ES (GeV/c ) ( *2 *2 E p ) beam B ΔE * = * * E B E beam Delta E (GeV) Sensitivity can be enhanced by performing two dimensional likelihood fits to signal and background.

22 A Colony of Penguins ρ,ω b uct,, d W, sd d sd dd (V td ) (Vts) 6 B(10 ) K*(892) K 1 (1270) K 2 (1430)

23 The CKM matrix ν e d leptons e + g quarks u g V ud W + W + 1 λ λ 3 λ 1 λ 2 λ 3 λ 2 1 Standard model explanation of CP violation is a single phase in the CKM matrix V.

24 The unitarity triangle Γ( B ρ, ω ) Γ( B K * ) measures V td Photon spectrum in B->Xs helps reduce error on Vub Photon spectrum in B->Xs 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 d Decays B 0 ρ 0 B + ρ + signal + bkgnd bkgnd signal Mass projections from 4d fit 6.3 sigma observation BABAR, hep-ex/ , 347 M BB

27 Comparison of b d Branching Fractions CKM fitter includes CDF B s mixing result. Error on CKM Fitter prediction includes uncert. on B V form-factor ratio. 6 (10 ) B B 0 B Mode ρ + + ρ 0 0 ω B ρ ρ ω BABAR (10-6 ) (6.3 σ signif.) ± ± < 0.84 (90% C.L.) + 0 (,, ) I -avg 1.01± 0.21± 0.08 Belle (10-6 ) (5.1σ signif.)

28 B b uct,, u Observation of b d and Measurement of V td /V ts W d u ρ + W annihilation diagram (small) 0 B b uct,, W 2 ( 2 2) 3 2 mb m ρ ρ V td ρ T 1 ( 2 2 ) ts mb m * K 1 BB ( ) (0) * = 3 * 1 K +Δ R BB ( K ) V T (0) d ( ) d d ρ 0, ω * T (0) ξ = 1.17 ± 0.09 K 1 T ρ 1 (0) Ball and Zwicky, JHEP 0604, 046 (2006) + Γ( B ρ ) = τ 2 τ B B + 0 Γ( B ρ ) 2 1/ξ τ B = 2 τ Γ( B Δ R = 0.1± 0.1 Ali, Lunghi, Parkhomenko, PLB 595, 323 (2004) ω ) I-spin (ρ), quark model (ω). Expect small I-spin violation:(1.1+/-3.9)%. B + 0

29 V V V V td ts td ts = = Extracting V td /V ts from b d Decays Belle, PRL 96, (2006) BABAR, hep-ex/ (preliminary) CDF, hep-ex/ (preliminary) V V td ts = Consistent within errors. Theoretical uncertainties limiting both approaches. courtesy M. Bona (UTfit collab.)

30 Inclusive Penguins: Γ(B->Xs Xs) Γ ( B X ) = Γ( b s ) s + Δ non pert Quark-hadron duality The non-perturbative corrections are a few percent. Recently a new NNLO calculation for B(B->X s ) has been completed B( B X s ) = 3.15 ± (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: B( B X s ) = 3.61±

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

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

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

34 Inclusive Photon Spectrum b B Xs FirstMoment: E B m b 2 E E B2 B Second Moment: (Kinetic energy of b) 2 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 Monte Carlo : Just require Model Dependence BB qq B -> Xs Note additional BB background To reduce large backgrounds without cutting on or Xs i.e a fully inclusive measurement

36 Two Methods for inclusive B X s Differ in treatment of Xs B Xs Method Fully inclusive don t reconstruct X s Sum of exclusive B K n(π) Advantages Closest correspondence to inclusive B(B X s ). Less background due to additional kinematic constraints. Better E resolution. Disadvantages More Backgrounds More model dependence due to finite set of explicitly reconstructed B X s decays.

37 B Technique 1 Semi-Inclusive Exclusively Reconstruct as many of the final states of Xs as possible: Xs Fundamental problem is that composition of final states must be guessed - large systematic Reconstructed Final States Kπ (0) ~55% KKK(π (0) ) Kη()ππ (0) Kπ (0) π (0) Kπ (0) (0) π (0) ππ Kπ (0) π (0) π K = K ±, K s ~45% Missing Final States ISR Baryons Rare Decays KKK+nK+nπ (0) K+η( )n K L +... K+>4 π (0) Kπ 0 π 0 π 0 (π 0 ) )nπ (0)

38 Technique II Fully Inclusive : B -> Xs Events / 100 MeV Suppress continuum background by requiring a lepton tag from recoiling B (5% Efficiency for x1200 reduction in background) continuum expect BBbar expect signal expect BABAR Events / 50 MeV BABAR Reconstructed E* (GeV) qq + ττ MC BB MC Signal MC Xs B lepton BB B->Xs Xc B Reconstructed E* - Simulation Remaining continuum subtracted with off-resonance data -> statistical uncertainty Multi-component BB background

39 Fully Inclusive BB background Events / 100 MeV BB B->Xs continuum expect BBbar expect signal expect BABAR Reconstructed E* - Simulation Component π0 η0 n e ± ω & η Other % Each BB component measured independently in data. Precision of these measurements is dominant systematic.

40 (PRL Oct ) BABAR Fully Inclusive B X s, w/lepton tag BB events Spectrum from best fit to kinetic scheme. Spectrum from best fit to shape function scheme. BB ( ) ( ) 10 4 X s = ± ± ± E > 1.9 GeV 4 X s = ± ± ± E > 1.6 GeV BB ( ) ( ) 10 (measured) (extrapolated, kinetic scheme)

41 Summary of B Xs g Branching Fraction Measurements Theory is NNLO prediction (2006) B( B X s ) = 3.15 ±

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

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

44 Direct CP asymmetry is sensitive to non MFV SUSY Γ( B Xs+ d ) Γ( B Xs+ d ) Acp ( B Xs+ d ) = Γ ( B X ) +Γ ( B X ) cp s+ d s+ d Fully-Inclusive: Lepton charge tags flavor. Dilution from mixing. A B X stat sys ( ) = ± 0.115( ) ± 0.017( B ) s s+ d X Cleo 01 BaBar Fully Inclusive 05 Standard Model A cp (B X s+d ) -3 Asymmetry consistent with Standard Model and previous measurements

45 Extracting Vbc and Vbu Parton level ν Hadron level ν decay rate b c b u E l = lepton energy Use inclusive measurements of lepton spectra Motion of b quark is dominant theoretical Uncertainty Use B->Xs to significantly increase precision

46 Moments Fit predicted moments of inclusive processes b clv and b sb for various cuts on kinematic variables in HQE: M n x E l > E 0 = τ B E 0 M n X dγ = f x n ( E 0, m b, m c 2, μ G 2 3, μ, ρ π D 3, ρ LS ) e or l energy cut b-quark mass Matrix elements c-quark appearing at order mass 1/m b2 and 1/m 3 b Calculations available in kinetic and 1S renormalization schemes Benson, Bigi, Gambino, Mannel, Uraltsev (several papers) Bauer, Ligeti, Luke, Manohar, Trott PRD 70: (2004) 47 measured moments used from DELPHI, CLEO, BABAR, BELLE, CDF (and, of course, the B lifetime)

47 Results: Spectrum Moments vs E most precise moments from BaBar fully inclusive 1st Moment (GeV) E B m b Curves are theory prediction using measured b->xclv moments ) 2 2nd Moment (GeV CLEO inclusive Belle inclusive untagged BaBar inclusive tagged (prel.) BaBar sum-of-exclusive (prel.) Theory Central value Theory range Minimum Photon Energy (GeV) Demonstrates assertion that b quark motion is universal

48 Extraction of Vbc,m b,μ π V cb (10-3 ) ± 0.23 exp ± 0.35 HQE ± 0.59 ΓSL kinetic scheme b->s m b [kin] kin](gev) μ 2 π [kin] (GeV 2 ) V cb 4.59 ± exp ± HQE ± exp ± HQE cb determined to <2% μ π 2 (GeV 2 ) combined χ 2 / N dof = 19.3/44 B->clv m b (GeV) m b to 1%; crucial for V ub Buchmüller and Flächer, PRD 73: (2006) [kin]/[1s] values agree after scheme translation

49 Extracting Vub Inclusive B->Xulν ν B W - l - V ub Γ ( B X lν ) u = G F V ub π m 5 b 2 α Λ s 1 Ο Ο π m QCD 2 b +... X u mb enters as mb 5 so 1% error in mb gives 2.5% error in Vub Other HQE parameters estimated from B->Xs enter into non-perturbative terms

50 Vub from B->XlB Xlν Statistical ±2.2% Expt. syst. ±2.8% B->Xclν model ±1.9% B->Xulν model ±1.6% Theory ±5.9% World Average /dof = 6.1/6 Error dominated by theory (mb and HQE parameter estimation) 7.2% error down from 15% in % ultimately

51 Current status of Unitarity Triangle sin(2β) measured to 4.7% Vtd/Vts measured to 3.7% Vub/Vcb measured to 7.6% 2-σ bands All constraints consistent with Standard model

52 Summary Large datasets have allowed us to catalog the rare penguin decays Penguins contributing to precision measurement of the triangle precision measurements of b->s strongly constrains new physics

53 Backup Slides

54 Technique 1 Semi-Inclusive ) 2 Events / (0.003 GeV 1600 BABAR N = 1504 ± 85 sig qq ( fixed from MC) Non-peaking BB peaking BB (fixed from MC) preliminary mes (GeV/c ) Xs E = m B m 2 2 B Xs 2m B Reconstruct in bins of MXs and convert to E Multicomponent fit to extract signal Dominant systematic is modelling missing final states

55 BABAR B X s with Sum of Exclusive Final States BABAR, PRD 72, (2005) K*(890) E E Energy Range >1.9 GeV >1.6 GeV (extrapolated) Branching Fraction (10-4 ) 3.27 ± ± averages over two shape-function schemes errors: stat, sys, variation of shape fcn params K*(890) E Moments E Value (GeV or GeV 2 ) ± E 2 E ± E (min) = GeV

56 Other Results on Fully inclusive B X s CLEO, PRL 87, (2001), 9.1 fb-1 Belle, PRL 87, (2004), 140 fb -1 Belle, hep-ex/ BF = (3.21± 0.43 ± ) 10 Measure for E >2.0; extrap. to E >0.25 GeV BF = (3.55± ) 10 Measure for E >1.8 GeV; extrap. to full

57 Constraining SUSY MH + tan(β) Excludes MH+ < 300 GeV independent of coupling (4x range of direct searches)

58 mb and μ π from b->sb Kinetic Scheme (Benson,Bigi and Uraltsev) Fermi -momentum Fit to moments in kinetic scheme scheme to obtain μπ and mb Ellipse because of correlations between first and second moments Fit includes theory errors Mass of b quark (GeV)

59 Results: Moments E m B b 2 1st Moment (GeV) E B2 B 2 2 E μπ (kinetic energy of b) 2 Theory is Bigi,Benson and Uraltsev (Nucl Phys B ) using BaBar measured B->Xclν moments PRL ) 2 2nd Moment (GeV CLEO inclusive Belle inclusive untagged BaBar inclusive tagged (prel.) BaBar sum-of-exclusive (prel.) Theory Central value Theory range Minimum Photon Energy (GeV) m = 4.6 GeV, = 0.45GeV B 2 2 μ π Curves are theory prediction using measured b->xclv moments

60 b->s and Vub Vub is extracted from inclusive B->Xulv decays. Photon spectrum from b->s helps reduce the uncertainty in determination. e.g. BaBar result: PRL 96: (2006) Fully reconstruct recoiling B and Study semileptonic decay Mx in B->Xulv Relate m max Γ m / 2 Γ b u B b to s dmx E X de d dm 0 min d W ( E, E ) min de V ub =(4.43 ±0.38(stat.) ±0.25(sys.) ±0.29(theory) x 10-3