The Discovery and Study of B Mesons in the CLEO Experiment

Transcription

1 The Discovery and Study of B Mesons in the CLEO Experiment Jeffrey D. Richman University of California, Santa Barbara Symposium Celebrating CLEO and CESR, 31 May 2008

2 Outline Terra incognita: Mapping the unknown territory of B physics in the CLEO I era CLEO II & CLEO II.V: the right stuff The march of the penguins The elegant simplicity of semileptonic decays The triumph of hadronic decays The success of the CLEO program as a scientific enterprise My apologies for not covering all the important measurements and papers. I had to leave out a lot of them!

3 Terra Incognita: Mapping the New Territory of B Physics in the CLEO I Era [1977: discovery of Y states at FNAL] courtesy Karl Berkelman

4 Physics themes of the early CLEO I era Y(1S), Y(2S), Y(3S), and... discovery of the Y(4S)! (1980) large decay width σ(y(4s)) vs. σ(continuum) Evidence for New Flavor Production at the Y(4S) (1981) Y(4S) as a fountain of BB pairs can study weak decays! Inclusive single-lepton final state as signature of weak decay; issues of continuum background & event shape variables; off-resonance running Inclusive properties of B Decay Critical milestone: observation of fully reconstructed hadronic decays (1983)

5 1.09 pb -1 (scan) σ (nb) vs. E CM (GeV) R 2 <0.3 E CM Scan GeV Mass: M(1S)+(1112 +/- 5) MeV M(4S) = ( /- 5 MeV) PDG: M(4S) = ( / 1.2 MeV) Width: Γ = (19.9 +/ /- 5 ) MeV σ(res)/σ(non-res) = 1/3 Event shape: more spherical than jetlike; R 2 used from the beginning!

6 2.5 pb -1 (scan) BB ( Xeν ) = (13± 3± 3)% PDG: BB ( Xeν ) = (10.78 ± 0.18)% p e > 1 GeV/c 76 electron events total! Predicted spectrum assuming D*eν/Deν =1 E CM

7 Inclusive properties of B decays ( ) Decay of b-flavored b Hadrons to Single-Muon and Dimuon Final States (1981) Decay of B mesons into Charged and Neutral Kaons (1982) Charged-Particle Multiplicities in B-Meson B Decay (1982) Semileptonic Decay of B Mesons (1983) Ruling out Exotic Models of b Quark Decay (1983) Observation of Exclusive Decay Modes of b-b flavored Mesons (1983) D 0 spectrum from B-Meson B Decay (1983) Observation of Baryons in B-Meson B Decay (1983) PRL 51, 634 (1983) M ( φπ ± ) + ± M( K K π ) φ sideband

8 40.7 pb -1 Until now, the b-flavored mesons themselves had not been found. Here we report that discovery. 2 evts 5 evts 5 evts 6 evts Signal region D 0 sidebands M(B 0 ) wrong-sign combs /-1.9+/-2.0 MeV /-0.7 MeV PDG 06 M(B - ) /-2.3+/-2.0 MeV /-0.5 MeV PDG 06 Branching fractions a little high.

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10 Beyond the basics Limit on the b u coupling from Semileptonic B Decay (1984) Upper Limit on Flavor-Changing Neutral- Current Decays of the b Quark (1984) Two-Body Decays of B Mesons (1984) Inclusive Decay of B Mesons into Charged D* (1985) Observation of the Decay B 0 D* + ρ - (1985) Decay B ψ X (1985) Inclusive φ production in B-Meson B Decay (1986) Observation of the Decay B FX B (1986) Inclusive B-Meson B Decay to Charm (1987) Limits on Rare Exclusive Decays of B Mesons (1987) Observation of B FX PRL 56, 2781 (1986) M ( φπ ± ) on-res+off-res on-res, p<2.5 GeV off-res, p<2.5 GeV 10

11 on-resonance 117 pb -1 below-resonance subtracted Very relevant selection of modes!

12 Into the era of B 0 B 0 mixing Limits on B 0 -B 0 Mixing and τb 0 /τb + (1987) Branching Ratios of B Mesons to K +, K -, and K 0 /K 0 (1987) Improved Upper limit on Flavor-Changing Neutral-Current Decays of the b Quark (1987) Evidence for Charmed Baryons in B-Meson B Decay ((1987) Γ(b ulν)/ )/Γ(b clν)) from the End Point of the Lepton Momentum Spectrum in Semileptonic B Decay (1987) Exclusive Decays and Masses of the B Mesons (1987) B 0 - B 0 mixing at the Y(4S) (1989) 212 pb pb -1 Argus ARGUS 103 pb -1 ARGUS, Phys. Lett. B 192, 245 (1987) χ d = 0.17±0.05 Time-integrated mixing rate: 21%

13 212 pb -1 ; 240 K BB Big challenge: removing contribution from secondary leptons. r = = Nmix ( ) N( nomix) ( ) + N( B B ) 0 0 N B B N( B B ) = (0.19 ± 0.06 ± 0.06) ΔM = 0.69 ± 0.12 ± 0.12 Γ p PDG: ± 0.008

14 Observation of B 0 -B 0 Mixing in CLEO using Dileptons Unlike-sign dileptons Like-sign dileptons (For unlike sign, need to subtract contribution from B + B - events.)

15 BABARAR Mixing asymmetry data (raw) Δ m = ps (fixed to PDG'04) D<1 due to mistags T=2π/Δm τ Β =1.53 ps run out of events at long lifetimes A ( ) (, ) NoMix( t) Mix( t) N B B t N B B B B t () t = = NoMix( t) + Mix( t) N( B B t) + N( B B, B B t) mix

16 Searching for b u...and finding it! Search for Charmless Decays B pp π and B pp π π (1989) Search for b u Transitions in Exclusive Hadronic B-Meson Decays (1989) A Search for Exclusive Penguin Decays of B Mesons (1989) Study of the decay B D* B + l ν (1989) Observation of B-Meson B Semileptonic Decays to Noncharmed Final States (1990) Exclusive and Inclusive Decays of B Mesons into D s Mesons (1990) Exclusive and Inclusive Semileptonic Decays of B Mesons to D Mesons (1991) Inclusive and Exclusive Decays of B Mesons to Final States Including Charm and Charmonium Mesons (1992)

17 212 pb -1 scaled off res Vub 0 p Major 1 st step in the long struggle to measure V ub. Inclusive measurement...in very limited region of phase space. Continuum background suppression & determination crucial If V ub =0, SM would predict no CP violation.

18 CLEO II: The Right Stuff

19 How long to run below resonance?

20 20

21 several more pages of math...

22 March of the Penguins B * K γ B X γ s B Kπ (*) B K + B ργ

23 Loops in B decays: probe high mass scales! cited 560 times fb -1 b uct,, γ s 8 events 3 events 2 events d W d BB ( Kγ ) = (4.5 ± 1.5 ± 0.9) 10 * 5 0 *0 5 BB ( K γ ) = (4.01± 0.2) 10 HFAG

24 cited 768 times 2.01 fb -1 BB ( Xγ ) = (2.32 ± 0.57 ± 0.35) 10 s Event-shape analysis B-reconstruction analysis 4 not all that rare! Y(4S) data Y(4S) data scaled off-resonance backgroundsubtracted data scaled off-resonance E γ E γ

25 9.1 fb-1

26 Summary of B(B X s γ) CLEO Phys.Rev.Lett.87,251807(2001) BR(B Xsγ) = (3.29± 0.53) 10-4 (9.1 fb -1 ) Belle Semi Phys.Lett.B511:151(2001) BR(B Xsγ) = (3.29± 0.53) 10-4 (5.8 fb -1 ) BaBar Semi Phys.Rev.D72:052004(2005) BR(B Xsγ) = ( ) 10-4 (81.5 fb -1 ) Thanks to Henning Flaecher! HFAG average: 7% experimental uncertainty BaBar Incl Phys.Rev.Lett.97:171803(2006) BR(B Xsγ) = (3.92± 0.56) 10-4 (81.5 fb -1 ) BaBar Full Phys.Rev.D77:051103(2008) BR(B Xsγ) = (3.91± 1.11) 10-4 (210 fb -1 ) BELLE Incl (A. Limosani, Moriond EW08) BR(B Xsγ) = (3.37± 0.41) 10-4 (605 fb -1 ) HFAG Average 08 (preliminary) BR(B Xsγ) = (3.52± 0.25) 10-4 Very good agreement between experiments and analysis methods! BR(B X s γ) (10-4 ) huge theoretical effort: SM predictions: Misiak et al. (hep-ph/ ) ph/ ) Becher et. al. (hep-ph/ ) ph/ ) Andersen et al. (hep-ph/ ) ph/ )

27 Radiative penguins: The Next Generation! B /10 6 BABAR, PRL 98, (2007) B + ρ + γ signal + bkgnd bkgnd 42 evts signal B 0 ρ 0 γ 38.7 evts BB ( Xγ )/10 s

28 Yet another generation: electroweak penguins! Photon penguin b d γ uct,, W s d + Z penguin b d Z uct,, W d s + W + W - box ν + b d W W + uct,, d s BaBar, Belle, CDF have observed B Kl + l - and B K*l + l - Rarest observed B decay: BB ( K + ) = (3.9± 0.6) 10 Kinematic distributions sensitive to new physics (A FB vs. q 2 ) 7

29 + + * + B, B K, B K Branching Fraction/10-6

30 1.37 fb -1 b V ub V us u u s K 0 B d d π + 0 B b d V ts u s d u K π + 30

31 3.14 fb -1 /10 5

32 B K π: Direct CP Violation from Interference between Penguin and Tree Diagrams BaBar, PRL 93, , 2004 Bkgd symmetric! ( 0 + K π ) n B ( 0 K + π ) n B = = AK π = = A π = ± ± K 6 N( BB ) = penguin pollution in B π + π -

33 from Steve Olsen s talk at Aspen Winter Conf., 2008 Direct CPV in B Kπ decays World Averages: A cp (K + π - ) = ± σ difference! A cp (K + π 0 ) = ± Oct 30, 2000 HEPAP Meeting 33

34 Simple is beautiful: semileptonic B decays B b V cb, V ub c, u ν b c: D, D, D * ** q q b u: π, ρ, η, η, ω,... CKM matrix elements Understanding dynamics: form factors, HQE params, quark masses

35 924 pb -1 contin. B X c l ν + continuum strict contin suppression R 2 < 0.3 Quantitative statement about size of V ub Vub V = ± Altarelli model cb Model dependence studied; part of long, long struggle.

36 ...and with a factor of 10 more data 9.13 fb -1 Total background, including B decay (histogram) On-resonance data (points) Scaled off-res data (shaded region) Background-subtracted, efficiency corrected spectrum Histogram: B X u l ν spectrum predicted from measured B X s γ spectrum

37 V ub Inclusive Measurements: HFAG Averages Theory framework: BLNP - B.O. Lange, M. Neubert and G. Paz, Phys. Rev. D72: (2005) V ub = (3.99 ± 0.14 ) Good or Bad? The full breakdown of the uncertainties on the average V ub above is (all errors quoted in percent): positive errors: +2.0 stat +2.3 exp +1.3 b2c model +1.4 b2u model +7.0 HQE param +0.5 SF func +0.7 sub SF +3.6 matching +1.3 WA = +8.8 tot negative errors: -2.0 stat -2.2 exp -1.2 b2c model -1.4 b2u model -5.8 HQE param -0.5 SF func -0.7 sub SF -3.3 matching -1.3 WA = -7.7 tot

38 Lattice QCD input is essential to fully exploit...

39 The Heavy Quark Effective Theory Revolution TopCite (cited 1576 times) Weak Transition Form-Factors Factors Between Heavy Mesons, N. Isgur and M.B. Wise, Phys. Lett. B237, 527 (1990). Cited 1458 times. Semileptonic B and D Decays in the Quark Model, N. Isgur,, D. Scora,, G. Grinstein, and M. Wise, Phys. Rev. D39, 799, Cited 1114 times. 3 papers: 4000 citations

40 Find your favorite place in the Dalitz plot. * B D ν * D c q ν 2 2 q = q max final-state D* at rest V-A: more points on R- than L-side ν q c * D 2 2 q = q min 40

41 2.4 fb -1 Confirmed by BaBar, PRD 74, (2006)

42 soft π + gentle fall-off of form factor

43 The Triumph of Hadronic Decays Hadronic B decays have ultimately provided the most compelling test of the CKM framework through CP-violating effects. We need interfering amplitudes to do this. CLEO laid much of the foundation for this work. CKM fit using angles only

44 The Big B Paper 203 cites 0.89 fb -1 *0 D π *0 D ρ * D π D ρ + * + Huge number of branching fractions Color-suppressed decays Polarization & factorization studies Resonant substructure D D π λ = * D * 0 * D + ρ ρ 0 ππ λ ρ = 0

45 B decays involving charmonium golden mode for sin2β

46 3.1 fb -1 de / dx B DK ΔE contributing mode for constraining γ B DK

47 A B D K A 0 ( ) = B b u Vcb * Vus = A path to γ u = λ K s c 2 Aλ 0 D u AB ( DK ) = Are δ γ 0 i( ) B B b u Vub * cs i e γ V = 1 color suppressed u c s u How can we get interference? Need D 0 f and D 0 f. (For example, f =K S0 π + π -.) Some observations: 0 D 1. Uses charged B decays; method is based on a direct CP asymmetry. Issues: strong phase δ, r B = A(b u)/a(b c) = Uses tree diagrams: no loops/mixing diagrams, no penguin/new physics issues. Together with V ub, gives CKM test with trees only. K

48 9.13 fb -1 contributing mode for constraint on CKM angle α

49 9.13 fb -1 φk φk sin2β with penguins! φ *0 φk *0 φk 0 B K 0

50 9.15 fb -1 50

51 The full glory of the Cabibbo-Kobayashi Kobayashi-Maskawa framework We need to see if it all fits: B, B s, K, penguins, box, trees:

52 The Success of the CLEO Program as a Scientific Enterprise Many experiments have contributed to the huge project of understanding B physics. ALEPH, ARGUS, BaBar, Belle, CDF, CLEO, D0, DELPHI, L3, OPAL,... ARGUS contributed enormously, far more than the relative size of their data sample suggests. Still, I believe that CLEO, more than any other experiment, set the standard and created the foundation of this field. I would like to express my deep appreciation to Wilson Laboratory and to all the members of the collaboration for making CLEO such a great project to work on!

53 Backup Slides

54 720 BB events BB ( Xμν ) = (9.4 ± 3.6)% The nonobservation of t quarks has led to the introduction of several models in which the t quark does not appear. Some of these models require flavor-changing neutral weak currents... Dilepton search: No μμ, including J/ψ μ + μ - 1 μ e, 2 e + e - (1 J/ψ e + e - ) B(B X l + l - ) <1.3% (90% C.L.)

55 40.8 pb -1 (on res) M(K - π + ) vs. p B(B D 0 X) = (0.8+/-0.2 +/- 0.2) used B(D 0 K - π + )=(3.0 +/- 0.6)% update to B(D 0 K - π + )=(3.8+/-0.07)% B(B D 0 X)=(0.63+/-0.2+/-0.2) PDG 06 (0.64+/-0.03) on-res continuum M( K π + ) 0 p D

56 yes! 40.6 pb -1

57 78 pb -1 (doubled)

58 still < 15 events in each mode

59 Time-integrated integrated mixing probabilities B 0 B 0 oscillations were measured without explicitly measuring the time dependence. How was the mixing rate inferred? χ P 0 0 () t dt B B 0 Γ = = 2 B d system: B s system: P 0 0() t dt + P 0 0() t dt ΔM 21 + Γ B B B B 0 0 ΔM Γ d d ΔM Γ s s ( -1)( ) ΔM = 0.51 ps 1.53 ps 0.8 χ 0.2 ( -1)( ) > 14.5 ps 1.48 ps 21.5 χ d s

60 Measurements from B D* B + l ν: HFAG Averages

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62 γ (Dalitz plot): B - [ D 0 K s π + π - ; D 0 K s π + π - ]K -, m m ( K π ± ) ± S B Giri, Grossman, Soffer, & Zupan, PRD 68, (2003), Bondar (Belle), PRD 70, (2004) [ (, ) (, )] 2 2 iδ 2 2 f m m r e B iγ e f m M ( m, m+ ) = A( B D K ) + + B + m B + M m m = A B D K f m m + r e e f m m iδ B + iγ (, + ) ( ) ( +, ) B (, + ) 2 m + 0 D 2 m + 0 D 2 M 2 = B + re δ B i( γ ) 2 m 2 m Relatively large BFs; all charged tracks; only 2-fold γ ambiguity. 0 0 * Interference depends on Dalitz region: f = K ρ (CP), f = K π + (DCSD) S

63 γ (GLW method): B - D CP K -, D CP f CP D 0 (D 0 ) f CP = CP eigenstate from singly-cabibbo-suppressed decay. [Gronau & London, PLB 253, 483 (1991), Gronau & Wyler, PLB 265, 172 (1991)]. D c u 0 * V ud W + V cd d u d u π + π D c u 0 V ud W * V cd d u d u π π + CP =+ + 1 ππ, K + K CP = 1 K π, K φ, K ω, K η, K η S S S S S ( ± ) 0 η B Amp B, CP = D A B 1 D + ηdrbe δ γ i ( ± ) Large rate, but interference is small: r B << 1

64 γ (ADS method): B - [ D 0 K + π - ; D 0 K + π - ]K B D K ; D K + π B b u c u u s D K 0 Atwood, Dunietz, & Soni, PRL 78, 3257 (1997), PRD 63, (2001) c u DCSD s u d u K + π 0 0 B D K ; D K + π B b u Vub i e γ u c s u D 0 K D 0 c u CFD d u s u π K + ( ± ± ) D ( B ), i δ i δ ± γ π = B D D + B A B D K A A r e r e Interference is large: r B, r D comparable, but overall rate is small!

65 V V V V td ts td ts Extracting V td /V ts from b d γ Decays Belle, PRL 96, (2006). = = BABAR, hep-ex/ (preliminary) V V td ts expt expt CDF, hep-ex/ (preliminary) = ± expt thy thy thy Consistent within errors! courtesy M. Bona (UTfit collab.) (used CDF hep-ex/ ) Theoretical uncertainties already or soon limiting both approaches.

66 Amplitude for B K*l + l - { * + GFαEM * eff * M( B K ) = VtsV tb C9 K sγ μpb L B 2π mix of Z-penguin, W + W - box 2 mb eff * 2 C 7 K si q ν σμν P R b B q photon penguin dom. at v. low q 2 ( μ γ ) Kruger and Matias; PRD 71, (2005) + C K sγ Pb B ( μ γ γ )} * 10 μ L 5 Short-distance physics encoded in C i s (Wilson coefficients); calculated at NNLO in SM: eff C7 0.3 C C Ali et al., PRD 61, (2000) Interference terms generate asymmetries in lepton angular distribution over most of q 2 range. C i s can be affected by new physics; enters at same order as SM amp.

67 How are CP violating asymmetries produced? The Standard Model predicts that, if CP violation occurs, it must occur through specific kinds of quantum interference effects.. source A 1 a A 1 f i A 2 A 2 Double-slit experiment: if the final state does not distinguish between the paths, then the amplitudes A 1 and A 2 interfere! a A 1 A 2 f i

68 Three Kinds of CP Violation We have seen that CP violation arises as an interference effect. Need at least two interfering amplitudes Need relative CP-violating phase Need relative CP-conserving phase A single CP-violating amplitude will not produce observable CP violation! Classification of CP-violating effects in particle transitions (based on the sources of amplitudes that are present). 1. CP violation in oscillations ( indirect CP violation ) 2. CP violation in decay ( direct CP violation ) 3. CP violation in the interference between mixing and decay

69 Two amplitudes with a CP-violating relative phase Suppose a decay can occur through two processes, with amplitudes A 1 and A 2. Let A 2 have a CP-violating phase φ 2. A = A + a e 1 2 A = A + a e 1 2 iϕ 2 iϕ No CP asymmetry! (But the decay rate is different from what it would be without the phase.) 2 A= A1+ A2 A = A 1 1 A = A1+ A2 ϕ 2 A 2 A 2

70 Two amplitudes with CP-conserving & CP-violating phases Next, introduce a CP-conserving phase in addition to the CP-violating phase. A= A + a e 1 2 i( ϕ + δ ) 2 2 A= A + a e 1 2 i( ϕ + δ ) 2 2 Now have a CP asymmetry A A A A= A1+ A2 = A 1 1 A 2 ϕ 2 ϕ 2 δ 2 A= A1+ A2 A 2

71 Amplitude analysis for direct CP violation A= A e + A e i( ϕ1+ δ1) i( ϕ2+ δ2) 1 2 A= A e + A e e i( ϕ1+ δ1) i( ϕ2+ δ2) ( ) 1 2 [ θ( ) θ( )] i P f Asymmetry 2 2 A A 2sin( ϕ1 ϕ2)sin( δ1 δ2) = = A + A A2 A cos( ϕ1 ϕ2)cos( δ1 δ2) A A 1 1 Problems with interpreting measurements of direct CP asymmetries: 1. we often don t know the difference δ 1 -δ 2, so we cannot extract φ 1 -φ 2 from the asymmetry. 2. we often don t know the relative magnitude of the interfering amps.

72 Direct CP violation in B K - π + Interference between tree and penguin amplitudes produces a CP asymmetry in B K - π +. Both processes are suppressed! External spectator b d * V us W V ub u s u d K π + Gluonic penguin 0 B b d V tb W t In our Wolfenstein convention, the CP-violating phase factor comes i from V e γ. ub * V ts u s u d K π +

73 cos Δm t 2 0 B B 0 () t fcp How the magic works 0 B i( D ) ae δ + φ η CP ( f) cos B 0 () t Δm t 2 0 B 0 B D a e δ φ i( ) f CP Δm t D i ηcp( f)sin a e e 2 i( δ φ ) 2iφ M Δm t D i sin a e e 2 i( δ + φ ) 2iφ M 0 0 Amp( B fcp ) Amp( B ( t) fcp) In each case, the two interfering amplitudes have the same CP conserving phase from strong interactions, so it is irrelevant. At = Im( λ) sin Δmt ( ) ( )

74 Time-dependent CP asymmetries from the interference between mixing and decay amplitudes By modifying the mixing measurement, we can observe whole new class of CP-violating phenomena: pick final states that both B 0 and B 0 can decay into. (Often a CP eigenstate, but doesn t have to be.) B 0 ( bd) no net oscillation f CP B 0 ( bd ) CP no net oscillation f 0 B net oscillation net oscillation 0 B 0 B 0 B Γ 0 ( Bphys( t) fcp) Γ 0 ( Bphys( t) fcp)

75 Results on sin2β from charmonium modes (cc) K S (CP odd) modes J/ψ K L (CP even) mode asymmetry is opposite! sin2β = ± (stat) ± (sys) λ = / (stat) +/ (sys) 227 M BB events (raw asymmetry shown above must be corrected for the dilution)

76 from Steve Olsen talk at Aspen Winter Conference, 2008 φ 1 from the golden b ccs mode - 535MBB PRL 98, (2007) Oct 30, 2000 HEPAP Meeting 76

77