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B Physics and CP Violation Jeffrey D. Richman UC Santa Barbara CTEQ Summer School Madison, June 7-8, 2002.

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Presentation on theme: "B Physics and CP Violation Jeffrey D. Richman UC Santa Barbara CTEQ Summer School Madison, June 7-8, 2002."— Presentation transcript:

1 B Physics and CP Violation Jeffrey D. Richman UC Santa Barbara CTEQ Summer School Madison, June 7-8, 2002

2 Outline (Lecture 1) Overview of B decays Overview of B decays  Why B physics is interesting; overview of decay diagrams; introductory discussion of CP violation. Accelerators and b-quark production Accelerators and b-quark production The BaBar Detector The BaBar Detector Identifying B decays Identifying B decays B-meson lifetimes and mixing B-meson lifetimes and mixing CP Violation (CPv) and the CKM matrix CP Violation (CPv) and the CKM matrix  the CKM hierarchy and the prediction of large CP asymmetries in B decays

3 Outline (Lecture 2) CP Asymmetries: CP Asymmetries:  sin(2  ): the golden measurement  the struggle for the other angles Rare decays Rare decays  Penguins are everywhere! Semileptonic decays, decay dynamics, and the magnitudes of CKM elements. Semileptonic decays, decay dynamics, and the magnitudes of CKM elements.  Heavy-quark symmetry and V cb Prospects and future directions Prospects and future directions A reference: J. Richman, Les Houches lectures, (or send asking for a copy:

4 I will be unashamedly pedagogical, and I will not aim for the level of impartiality that is customary in a review talk or article. I will be unashamedly pedagogical, and I will not aim for the level of impartiality that is customary in a review talk or article. I will be unashamedly selective: many important topics have been left out. I will be unashamedly selective: many important topics have been left out. There will be a strong bias towards recent results from e + e - colliders at the Y(4S). This is probably not too misleading for now, since BaBar, Belle, and CLEO have to some extent defined the state of the art, especially in CPv and rare decays. However, soon-to-come measurements from the Fermilab Tevatron (CDF, D0) will be of major importance. There will be a strong bias towards recent results from e + e - colliders at the Y(4S). This is probably not too misleading for now, since BaBar, Belle, and CLEO have to some extent defined the state of the art, especially in CPv and rare decays. However, soon-to-come measurements from the Fermilab Tevatron (CDF, D0) will be of major importance. My own background in b physics: BaBar, CLEO My own background in b physics: BaBar, CLEO I strongly encourage you to ask questions! I strongly encourage you to ask questions! Remarks/disclaimers

5 Goals of B (and B s ) Physics 1. Can CP violation be understood quantitatively within the Standard Model, or is new physics needed? Perform a comprehensive set of measurements to check for the presence non-SM CP-violating phases. 2. Make precise measurements of the Standard Model CKM parameters: | V cb |, | V ub |, | V td |, | V ts |,  3. Map out and understand rare B decays, especially processes with loops that can be very sensitive to particles outside the Standard Model. 4. Understand the dynamics of B decays: underlying weak interaction process with overlay of complex strong interaction effects. Progress: HQET, lattice QCD, many measurements to test predictions.

6 Overview of B Decays b is the heaviest quark that forms bound states with other quarks (t-quark decays too rapidly). b is the heaviest quark that forms bound states with other quarks (t-quark decays too rapidly). m(b) the b-quark is forced to decay outside of its own generation m(b) the b-quark is forced to decay outside of its own generation  Dominant decays are CKM suppressed:  Relatively long B lifetime: Silicon tracking systems have been essential tools.  Largest single branching fraction:  Many interesting rare decay processes are experimentally accessible (b->uW, gluonic penguins, electroweak penguins).

7 Leptonic and Semileptonic Decays Leptonic B + decay not yet observed! Leptonic B + decay not yet observed! Largest expected mode is: Largest expected mode is: Ignoring photon radiation: Ignoring photon radiation: Used to measure magnitudes of CKM elements: V cb and V ub Used to measure magnitudes of CKM elements: V cb and V ub Amplitude can be rigorously parametrized in terms of form factors. Amplitude can be rigorously parametrized in terms of form factors.

8 Hadronic Decays: Tree Diagrams Theoretical predictions very difficult. Theoretical predictions very difficult. Naïve factorization model works reasonably well in predicting pattern of decays. Naïve factorization model works reasonably well in predicting pattern of decays. “Color suppressed” “Color suppressed” Naïve factorization model probably breaks down. (New data on B->D 0   and B->D* 0    Naïve factorization model probably breaks down. (New data on B->D 0   and B->D* 0    The color allowed and color suppressed amplitudes interfere constructively in charged B decays. (Opp. effect for D +.) The color allowed and color suppressed amplitudes interfere constructively in charged B decays. (Opp. effect for D +.)

9 Processes with loops: sensitivity to new particles Both gluonic and electoweak penguins have been observed! Both gluonic and electoweak penguins have been observed! The SM mixing rate is dominated by tt (off-shell) intermediate states. The SM mixing rate is dominated by tt (off-shell) intermediate states.

10 Processes used for sin2  measurement b d d s c c W+W+ A color suppressed decay! However, in this case, the rate is enhanced by the relatively large decay constant of the J/ 

11 Decay modes for sin2  measurement Decay modes for sin2  measurement

12 The C, P, and T Transformations C, P, and T are discrete transformations: there is no continuously varying parameter, and these operations cannot be constructed from successive infinitesimal transformations. In all well-behaved quantum field theories, CPT is conserved. A particle and its antiparticle must have equal mass and mean lifetime.

13 P and C violation in Weak Interactions is Maximal (V-A) P C Allowed Not Allowed

14 A First Look at CP violation The discovery of CP violation in 1964 was based on the demonstration that the mass eigenstate K L is not an eigenstate of CP, so. The discovery of CP violation in 1964 was based on the demonstration that the mass eigenstate K L is not an eigenstate of CP, so. The lifetime separation between B H and B L is tiny, so we must use a different method, in which we compare the rates for CP-conjugate processes. The lifetime separation between B H and B L is tiny, so we must use a different method, in which we compare the rates for CP-conjugate processes. Remove K s from beam using lifetime difference. CPv small in kaon system!

15 Cronin, Nobel Prize lecture*. “...the effect is telling us that at some tiny level there is a fundamental asymmetry between matter and antimatter, and it is telling us that at some tiny level interactions will show an asymmetry under the reversal of time. We know that improvements in detector technology and quality of accelerators will permit even more sensitive experiments in coming decades. We are hopeful then, that at some epoch, perhaps distant, this cryptic message from nature will be deciphered.”...J.W. Cronin, Nobel Prize lecture*. J.W. Cronin and V.L. Fitch, Nobel Prize *J.W. Cronin, Rev. Mod. Phys. 53, 373 (1981). J.H. Christenson, J.W. Cronin, V.L. Fitch, and R. Turlay, Phys. Rev. Lett. 13, 138 (1964). The Legacy of Kaon Physics

16 CP violation and alien civilizations We can use our knowledge of CP violation to determine whether alien civilizations are made of matter or antimatter, without having to touch them. Long-lived neutral kaon We have these inside of us

17 CP Violation and Cosmology A. Sakharov noted (1967) that CP violation has an important connection to cosmology. 3 conditions for an asymmetry between N(baryons) and N(anti-baryons) in the universe (assuming equal numbers initially due to thermal equilibrium).  baryon-number-violating process  both C and CP violation (helicities not relevant to particle populations)  departure from thermal equilibrium

18 How can CP asymmetries arise? (I) When we talk about CP violation, we need to talk about the phases of QM amplitudes. This is usually very confusing.  some phases are physical; others are not.  many treatments invoke specific phase conventions, which acquire a magical aura. Need to consider two types of phases  CP-conserving phases: don’t change sign under CP. (Sometimes called strong phases since they can arise from strong, final-state interactions.)  CP-violating phases: these do change sign under CP.

19 How can CP asymmetries arise? (II) Suppose a decay can occur through two different processes, with amplitudes A 1 and A 2. First, consider the case in which there is a (relative) CP-violating phase between A 1 and A 2 only. No CP asymmetry! (Decay rate is different from what is would be without the phase.)

20 How can CP asymmetries arise? (III) Next, introduce a CP-conserving phase in addition to the CP-violating phase. Now have a CP asymmetry

21 Measuring a CP-violating phase To extract the CP-violating phase from an observed CP asymmetry, we need to know the value of the CP- conserving phase. To extract the CP-violating phase from an observed CP asymmetry, we need to know the value of the CP- conserving phase. In direct CP-violating processes we usually do not know the relative CP-conserving phase because it is produced by strong-interaction dynamics that we do not understand. In direct CP-violating processes we usually do not know the relative CP-conserving phase because it is produced by strong-interaction dynamics that we do not understand.

22 B production at the Y(4S) Rate of events vs. total energy in e + e - CM frame: TM No accompanying pions! The B-meson energy is known from the beam energy. (CLEO, CLNS 02/1775)

23 The New e + e - B factories The machines have unequal (“asymmetric”) energy e + and e - beams, so two separate storage rings are required. The machines have unequal (“asymmetric”) energy e + and e - beams, so two separate storage rings are required. PEP-II: E(e - )=8.992 GeV E(e + )=3.120 GeV  =0.55 The machines must bring the beams from the separate rings into collision. The machines must bring the beams from the separate rings into collision.  KEK-B: +-11 mrad crossing angle  PEP-II: magnetic separation With two separate rings, the machines can store huge numbers of beam bunches without parasitic collisions. With two separate rings, the machines can store huge numbers of beam bunches without parasitic collisions.  KEK-B: 1224 bunches/beam; I(e + )=716 mA; I(e - )=895 mA  PEP-II: 831 bunches/beam; I(e + )=418 mA; I(e - )=688 mA  CESR (single ring): 36 bunches/beam; I(e + )=I(e - )=365 mA

24 PEP-II e + e - Ring and BaBar Detector Linac PEP-II ring: C=2.2 km BaBar LER (e +, 3.1 GeV) HER (e -, 9.0 GeV) BaBar May 26, 1999: 1st events recorded by BaBar

25 The Y(4S) Boost The purpose of asymmetric beam energies is to boost the B 0 B 0 system relative to the lab frame. The purpose of asymmetric beam energies is to boost the B 0 B 0 system relative to the lab frame. By measuring  z, we can follow time-dependent effects in B decays. By measuring  z, we can follow time-dependent effects in B decays. The distance scale is much smaller than in the kaon decay experiments that first discovered CP violation! The distance scale is much smaller than in the kaon decay experiments that first discovered CP violation!

26 From CESR (1 ring, E symmetric) to PEP-II (2 rings, E asymmetric) From CESR (1 ring, E symmetric) to PEP-II (2 rings, E asymmetric) Pretzel orbits in CESR (36 bunches, 20 mm excursions) Top view of PEP-II interaction region showing beam trajectories. (10X expansion of vertical scale)

27 The race between BaBar/PEP-II and Belle/KEK-B Belle Exceeds design luminosity!

28 e + e - vs. pp and pp Production cross sections Production cross sections  Y(4S):  pp at Tevatron:  pp at LHC: b fraction (ratio of b cross section to total hadronic cross section) b fraction (ratio of b cross section to total hadronic cross section)  Y(4S): 0.25  pp at Tevatron:  pp at LHC: Comments Comments  Triggering: so far, most B branching fractions have been measured at e + e - machines, because CDF, D0 triggers were very selective in Run 1. Also, PID &  detection are  better at Y(4S) experiments so far.)  Hadron colliders produce B s and b-baryons. (LEP also.)  New displaced-vertex triggers at hadron-collider experiments should make a dramatic improvement.

29 The B A B AR Detector DIRC (particle ID) 1.5 T solenoid CsI (Tl) Electromagnetic Calorimeter Drift Chamber Instrumented Flux Return Silicon Vertex Tracker e + (3.1GeV) e - (9 GeV) SVT: 97% efficiency, 15  m z resol. (inner layers, perpendicular tracks) Tracking :  p T )/p T = 0.13% P T  0.45% DIRC : K-  separation >3.4  for P<3.5GeV/c EMC:  E /E = 1.33% E -1/4  2.1%

30 BaBar Detector e-e- e+e+ center line CsI crystals Drift chamber Superconducting magnet (1.5 T) Muon detector & B-flux return Silicon Vertex Tracker DIRC: quartz bars standoff box PM tubes

31 BaBar Event Display (view normal to beams) R drift chamber =80.9 cm (40 measurement points, each with  m res. on charged tracks) EM Calorimeter: 6580 CsI(Tl) crystals (5%  energy res.) Silicon Vertex Tracker 5 layers:  m res. Cerenkov ring imaging detectors: 144 quartz bars (measure velocity) Tracking volume: B=1.5 T

32 Innermost Detector Subsystem: Silicon Vertex Tracker Be beam pipe: R=2.79 cm Installed SVT Modules (B mesons move 0.25 mm along beam direction.)

33 BaBar Silicon Vertex Tracker BaBar Silicon Vertex Tracker 5 layers of double-sided silicon-strip detectors (340) 300  m 50  m 80 e-/hole pairs/  m

34 Measure angle of Cherenkov cone –Transmitted by internal reflection –Detected by PMTs Particle Identification (DIRC) (Detector of Internally Reflected Cherenkov Light) Particle Quartz bar Cherenkov light Active Detector Surface No. light bounces (typical)=300

35 DIRC  c resolution and K-  separation measured in data  D *+  D 0  +  (K -  + )  + decays DIRC  c resolution and K-  separation measured in data  D *+  D 0  +  (K -  + )  + decays Particle Identification with the DIRC.  (  c )  2.2 mrad >9>9 2.5  K/  Separation

36 Particle Identification Electrons – p* > 0.5 GeV shower shapes in EMC E/p match Muons – p* > 1 GeV Penetration in iron of IFR Kaons dE/dx in SVT, DCH  C in DRC E/p from E.M.Calorimeter Shower Shape e e   1 < p < 2 GeV/c 0.8 < p < 1.2 GeV/c E/p > 0.5 e  e   c from Cerenkov Detector e  0.5 < p < 0.55 GeV/c dE/dx from Dch 0.8 < p < 1.2 GeV/c

37 m es EE  m es  3 MeV  E  15 MeV All K s CP modes N sig  750 Purity 95% Identifying B Decays in BaBar Select “candidate daughter particles” using particle ID, etc. Compute the total 4-momentum: (E, p)=(E 1 +E 2 +E 3, p 1 + p 2 +p 3 ) Compute invariant mass: m 2 =E 2 -|p| 2 Gives 10x improvement in mass resolution.

38 sin2  Signal and Control Samples J/ K s (K s   +  - ) J/ K s (K s   0  0 ) J/ K *0 (K *0  K s  0 )  c1 K s (2s) K s J/  K L B flav mixing sample J/ K s (K s   0  0 ) J/  K s (K s      ) J/ K *0 (K *0  K s  0 ) CP=-1 CP=+1

39 The Lorentz Boost The asymmetric beam energies of PEP-II allow us to measure quantities that depend on decay time. (4s)  = 0.56 Tag B  z ~ 170 m CP B  z ~ 70 m J/ K0K0 zz t  z/cc B  250 m e-e- 9.0 GeV e+e+ 3.1 GeV

40 Measurement of Decay Time Distributions B 0 decay time distribution background (linear scale)

41 B 0 and anti-B 0 mesons spontaneously oscillate into one another! (Mixing also occurs with neutral kaons.) Neutral B mesons can be regarded as a coupled, two- state system. To find the mass eigenstates we must find the linear combinations of these states that diagonalize the effective Hamiltonian.

42 Interpretation of the Effective Hamiltonian The effective Hamiltonian for the two-state system is not Hermitian since the mesons decay. Quark masses, strong, and EM interactions Decays

43 CP Violation in Mixing CP Violation in Mixing Compare mixing for particle and antiparticle Compare mixing for particle and antiparticle off-shell on-shell CP-conserving phase

44 CP violation in mixing, continued To produce a CP asymmetry in mixing, M 12 and  12 must not be collinear and both must be nonzero: To produce a CP asymmetry in mixing, M 12 and  12 must not be collinear and both must be nonzero: No CP violation in mixingCP violation in mixing

45 Time evolution of states that are initially flavor eigenstates General case; allows CP violation.

46 CP Violation in B Mixing is Small When CP violation in mixing is absent (or very small), we have When CP violation in mixing is absent (or very small), we have In the neutral B-meson system, the states that both B 0 and B 0 can decay into have small branching fractions, since In the neutral B-meson system, the states that both B 0 and B 0 can decay into have small branching fractions, since normally lead to different final states. Can have (Cabibbo suppressed) and (b->u is CKM suppressed). So the SM predicts normally lead to different final states. Can have (Cabibbo suppressed) and (b->u is CKM suppressed). So the SM predicts not yet observed

47 Time evolution of states that are initially flavor eigenstates In these formulas, we have assumed that  /  and have set

48 The Oscillation Frequency (  m) In the neutral B-meson system, the mixing amplitude is completely dominated by off-shell intermediate states (  m) [contrast with the neutral kaon system]. Calculation of the mixing frequency Time-dependent mixing probabilities and asymmetry

49 Tagging Tagging CP asymmetry is between B 0  f cp and B 0  f cp Must tag flavor at  t=0 (when flavor of two Bs is opposite). Use decay products of other (tag) B. Leptons : Cleanest tag. Correct 91% b c e-e- W-W- b c e+e+ W+W+ Kaons : Second best. Correct 82% b W-W- c s u d K-K- W+W+ b W+W+ c s u d K+K+ W-W-

50 Effect of Mistagging and  t Resolution No mistagging and perfect  t Nomix Mix tt tt D=1-2w=0.5  t res: 99% at 1 ps; 1% at 8 ps w=Prob. for wrong tag tt tt

51 NoMix(t)-Mix(t) NoMix(t)+Mix(t ) T=2  m ~D~D  m = (0.516   0.010) ps -1 Measure mixing on control sample: constrain model of  t resolution measure dilution D = (1-2w)

52 CP violation in the Standard Model In the SM, the couplings of quarks to the W are universal up to factors that are elements of a unitary, 3x3 rotation matrix V ij of the quark fields. This matrix originates in the Higgs sector (mass generation of quarks). W-W- e-e- e b u W-W- W+W+

53 The Standard Model “Unitarity Triangle” Weak interaction eigenstates Quark mass eigenstates Cabibbo-Kobayashi-Maskawa (CKM) matrix [Col 1][Col 3]*=0 V has only 4 real parameters, including 1 CP-violating phase. If just 2 quark generations: no CP phase allowed! CPv 1 of 6 equal-area triangles: orientation is just an unphysical phase

54 The Structure of the CKM Matrix The CKM matrix exhibits a simple, hierarchical structure (which we do not understand) with 4 real parameters (All unitarity triangles have same area, corresponding to the sizes of interference terms between 1 st order weak amps. But we care about CP asymmetries, so the angles of the triangles also matter.)

55 End of Lecture 1

56 Outline (Lecture 2) CP Asymmetries: CP Asymmetries:  sin(2  ): the golden measurement  the struggle for the other angles Rare decays Rare decays  Penguins are everywhere! Semileptonic decays, decay dynamics, and the magnitudes of CKM elements. Semileptonic decays, decay dynamics, and the magnitudes of CKM elements.  Heavy-quark symmetry and V cb Prospects and future directions Prospects and future directions A reference: J. Richman, Les Houches lectures, (or send asking for a copy:

57 Decay rates for B 0 (t) and B 0 (t) to f CP

58 Calculating the CP Asymmetry If there is just one direct decay amplitude, we will see that If CP violation is due to interference between mixing and one direct decay amp: pure sin(  m t) time dependence.

59 Calculating Calculating if just one direct decay amplitude to f CP Piece from mixing (  ) Piece from mixing (  ) Piece from decay Piece from decay Hadronic physics divides out!

60 Calculating  for specific final states

61 Why it is magic CP conserving phase! CP violating phase

62 asdf Graphical Analysis

63 Analogy: “Double-Slit” Experiments with Matter and Antimatter source In the double-slit experiment, there are two paths to the same point on the screen. In the B experiment, we must choose final states that both a B 0 and a B 0 can decay into. We perform the B experiment twice (starting from B 0 and from B 0 ). We then compare the results.

64 CP violation due to interference between mixing and decay: non-exponential decay law

65 Ingredients of the CP Asymmetry Measurement Determine initial state: “tag” using other B. Measure  t dependence Reconstruct the final state system.

66 The Lorentz Boost The asymmetric beam energies of PEP-II allow us to measure quantities that depend on decay time. (4s)  = 0.56 Tag B  z ~ 170 m CP B  z ~ 70 m J/ K0K0 zz t  z/cc B  250 m e-e- 9.0 GeV e+e+ 3.1 GeV

67 Tagging Tagging Leptons : Cleanest tag. Correct 91%, Efficiency 11% b c e-e- W-W- b c e+e+ W+W+ Kaons : Second cleanest. Correct 82%, Efficiency 35% b W-W- c s u d K-K- W+W+ b W+W+ c s u d K+K+ W-W- We must classify each neutral B according to whether it “started” as a B 0 or a B 0. The start time is defined as the decay time of the accompanying B meson (“tag B”). We use flavor-specific final states of the tag B.

68 The Correlated State At the Y(4S), the two neutral B mesons evolve as a correlated quantum state until one of them decays. At the Y(4S), the two neutral B mesons evolve as a correlated quantum state until one of them decays. As a consequence, the asymmetry of time-integrated rates is identically zero! As a consequence, the asymmetry of time-integrated rates is identically zero! At the Y(4S), we must measure the CP asymmetry as a function of time. The experiment would not work with the silicon vertex detector. At the Y(4S), we must measure the CP asymmetry as a function of time. The experiment would not work with the silicon vertex detector.

69 A cp (t)F(t) t(ps) sin2 D sin2 Everything perfect  Add tag mistakes  Dilution: D=1-2w Add imperfect t resolution Must understand tagging/mistagging and  t resolution !! Experimental aspects of the sin2  measurement: 

70 Blind Analysis The whole analysis is performed blind. All studies are performed in such a way as to hide information on the value of the final answer. Avoids any subconscious experimenter bias Ø e.g. agreement with the Standard Model! When we are ready, we have an unblinding party…..

71 sin2 (cc) K s CP =  0.10  0.04 J/ K L CP =  0.19  0.07 All modes 0.75  0.09  0.04 sin2 (cc) K s CP =  0.10  0.04 J/ K L CP =  0.19  0.07 All modes 0.75  0.09  0.04 (stat)(syst) Fit results 56 fb -1 : 62 M BB pairs.

72 CP asymmetry in CP -1 and +1 modes J/ K L CP = +1 J/  K s CP = -1 Note: likelihood curves are normalized to the total number of tagged events, not B 0 and anti-B 0 separately.

73 Crosscheck: fit B flav events as a CP sample A CP =  Expect no CP asymmetry

74 sin2  fit results sin2 (cc) K s CP =  0.10  0.04 J/ K L CP =  0.19  0.07 All modes 0.75  0.09  0.04 sin2 (cc) K s CP =  0.10  0.04 J/ K L CP =  0.19  0.07 All modes 0.75  0.09  0.04 Systematic errors CP = -1 background0.019 t resolution and detector effects m d and  B (PDG 2000)0.014 Monte Carlo statistics0.014 J/ K L background0.013 Signal mistag fractions0.007 Total systematic error0.04 Systematic errors CP = -1 background0.019 t resolution and detector effects m d and  B (PDG 2000)0.014 Monte Carlo statistics0.014 J/ K L background0.013 Signal mistag fractions0.007 Total systematic error0.04 (stat)(syst) Fit without ||=1 constraint (CP=-1 only) || = 0.92  0.06 (stat)  0.03 (syst) Im/|| = 0.76  0.10 Fit without ||=1 constraint (CP=-1 only) || = 0.92  0.06 (stat)  0.03 (syst) Im/|| = 0.76  0.10

75 Cross checks sin2  by decay mode sin2  in sub-samples Individual modes and sub-samples are all consistent.

76 CKM interpretation   Our sin2 measurement is consistent with current Standard Model constraints from measurements of other parameters.  = (1- 2 /2)  = (1- 2 /2) Method as in Höcker et al, Eur.Phys.J.C21: ,2001 (also other recent global CKM matrix analyses)

77 Michael Peskin’s viewpoint

78 Conclusions so far... We have observed CP violation in the neutral-B meson system. We have observed CP violation in the neutral-B meson system. The asymmetry is large, unlike the O(10 -3 ) effects observed in the neutral-K system. The asymmetry is large, unlike the O(10 -3 ) effects observed in the neutral-K system. The asymmetry displays consistent behavior across all observed channels, including CP odd and CP even final states. The asymmetry displays consistent behavior across all observed channels, including CP odd and CP even final states. The time dependence of the asymmetry agrees with the expectation based on interfering amplitudes involving mixing and direct decay. The time dependence of the asymmetry agrees with the expectation based on interfering amplitudes involving mixing and direct decay.

79 Conclusions so far... With the present data sample, the region allowed by the measurement is consistent with the Standard Model CKM framework constrained by With the present data sample, the region allowed by the measurement is consistent with the Standard Model CKM framework constrained by  CP-violation measurements in K decay  non-CP-violating observables in B decay

80 Hadronic Rare B Decays: Towards sin(2  ) B->  would measure sin(2  )… B->  would measure sin(2  )… …except there is a second direct decay amplitude! …except there is a second direct decay amplitude!

81 Hadronic Rare B Decays: B->    , B->K +   B->     B->K +   m ES EE EE

82 Mixing and CP Asymmetry Measurement in B->  Mixing

83 Belle Mixing and Asymmetry Measurement in B-> 

84 B  K (*) l + l - in the SM and Beyond Flavor changing neutral current (b to s): proceeds via “penguin’’ or box diagrams in the SM. Flavor changing neutral current (b to s): proceeds via “penguin’’ or box diagrams in the SM. New physics at the EW scale (SUSY, technicolor, 4th generation quarks, etc.) can compete with small SM rate. New physics at the EW scale (SUSY, technicolor, 4th generation quarks, etc.) can compete with small SM rate. Complementary to studying b to s  due to presence of W and Z diagrams. Complementary to studying b to s  due to presence of W and Z diagrams.

85 Branching Fraction Predictions in the Standard Model New Ali et al. predictions lower by 30-40% long-distance contribution from  resonances excluded

86 Decay rate vs. q 2 in the SM and SUSY J/   (2S)K q2q2 q2q2 SM nonres SUSY models Pole from K*  even in  +  - constructive interf. destructive

87 Generator-level q 2 Distributions from Form- Factor Models Ali et al (solid line) Colangelo 1999 (dashed line) Melikhov 1997 (dotted line) Shapes are very similar!

88 J/  Sample: signal-like log L B off resonance J/  and Large Sideband Control Sample Study: B Likelihood Variable keep Large SB Sample: background- like log L B -10 4

89 K l + l - Fit Regions, Unblinded Run 1+2 data (56.4 fb-1) EE m ES

90 Fit Results (preliminary) B(B  K*ee)/B(B  K*  )=1.21 from Ali, et al, is used in combined K*ll fit.

91 Belle results (29.1 fb -1 ) Bkgd shape fixed from MC

92 Results We obtain the following preliminary results: We obtain the following preliminary results: The statistical significance for B  K l + l - is computed to be > 4  including systematic uncertainties. The statistical significance for B  K l + l - is computed to be > 4  including systematic uncertainties. BaBar and Belle results are both higher than typical theoretical predictions, but the uncertainties are still very large.

93 Measuring Magnitudes of CKM Elements with Semileptonic B Decays Expt. Need input from theory!

94 Kinematic Configurations in Semileptonic Decay b->cl processes are dominant and are much easier to understand than b->ul decays. b->cl processes are dominant and are much easier to understand than b->ul decays.  reliable theoretical predictions for b->cl at zero recoil (Heavy Quark Symmetry/HQET).  zero recoil: b->c without disturbing the light degrees of freedom  expansion in  QCD /m Q zero recoil

95 Semileptonic decays: Dalitz plot Effect of V-A coupling on lepton angular distribution and energy spectrum. Effect of V-A coupling on lepton angular distribution and energy spectrum. zero recoil

96 Contributions of different helicities to the rate Zero recoil Max recoil

97 New CLEO measurement of |V cb |

98 CLEO Measurement of |V cb | : w distribution and extrapolation to zero recoil

99 Systematic Errors on CLEO |V cb | Measurement

100 Recent |V cb | measurements Uncorrected for common inputs Uncorrected for common inputs Corrected for common inputs Corrected for common inputs (Compilation by Artuso and Barberio, hep-ph/ , May 2002.)

101 Recent |V cb | measurements

102 Form Factor at Zero Recoil and |V cb | The experimental extrapolation to zero recoil velocity of the daughter hadron provides the quantity The experimental extrapolation to zero recoil velocity of the daughter hadron provides the quantity Zero recoil form factor (“consensus value”) Zero recoil form factor (“consensus value”) World average |V cb | World average |V cb |

103 Bumps in the road: Crystal Ball observation of the  (8.3) (1984) Photon energy spectrum.

104 First observation of exclusive B decay CLEO I data (1983) CLEO I data (1983)

105 Some free advice Almost every measurement is very hard, even if it is of a quantity that no one cares about. So, try to find an important measurement that will have real scientific impact. Almost every measurement is very hard, even if it is of a quantity that no one cares about. So, try to find an important measurement that will have real scientific impact. Never determine your event-selection criteria using the same event sample that you will use to measure your signal. Never determine your event-selection criteria using the same event sample that you will use to measure your signal. Don’t use more cuts than you need. A simple analysis is easier to understand, check, duplicate, and present. Don’t use more cuts than you need. A simple analysis is easier to understand, check, duplicate, and present. Look at all the distributions you can think of for your signal and compare them with what you expect. Look at all the distributions you can think of for your signal and compare them with what you expect. Look at the distributions of events that you exclude. Do you understand the properties of your background? Look at the distributions of events that you exclude. Do you understand the properties of your background?

106 More free advice When possible, use data rather than Monte Carlo events to measure efficiencies and background levels. When possible, use data rather than Monte Carlo events to measure efficiencies and background levels. Do not use Monte Carlo samples blindly. Find out where the information came from that went into the MC. The MC may do well in someone else’s analysis, but in may never have been checked for the modes or region of phase space relevant to your analysis. Do not use Monte Carlo samples blindly. Find out where the information came from that went into the MC. The MC may do well in someone else’s analysis, but in may never have been checked for the modes or region of phase space relevant to your analysis. Be careful not to underestimate the systematic errors associated with ignorance of Be careful not to underestimate the systematic errors associated with ignorance of  signal efficiency  background shapes, composition, and normalization

107 Yet more advice Don’t be afraid to… Don’t be afraid to…  ask any question  pursue a crazy idea  jump into something you don’t already understand  question what people say is established fact  look into the details and assumptions

108 Conclusions We have two remarkable new facilities for B physics: We have two remarkable new facilities for B physics:  KEK-B/Belle  PEP-II/BaBar The performance of these accelerators is a major achievement for the laboratories. The performance of these accelerators is a major achievement for the laboratories. The clear observation of CP asymmetries in the B meson system is a milestone for particle physics. The clear observation of CP asymmetries in the B meson system is a milestone for particle physics. The measurement of sin(2  ) is very well accomodated by the SM. It suggests that the dominant source of CP violation in B decays is due to the CKM phase. In spite of this, we have a long way to go before we have fully tested the SM/CKM framework. The measurement of sin(2  ) is very well accomodated by the SM. It suggests that the dominant source of CP violation in B decays is due to the CKM phase. In spite of this, we have a long way to go before we have fully tested the SM/CKM framework.

109 Conclusions (continued) Hadron-collider experiments will soon start to play a major role: the observation and precise measurement of B s mixing is one of the next major goals. Hadron-collider experiments will soon start to play a major role: the observation and precise measurement of B s mixing is one of the next major goals. We are just beginning to scratch the surface of rare B decays. They have interesting sensitivity to new physics. We are just beginning to scratch the surface of rare B decays. They have interesting sensitivity to new physics. The next few years will be very exciting. The next few years will be very exciting.

110 Backup slides

111 PEP-II Very high current, multibunch operation 2 rings helps avoid beam instabilities and parasitic beam crossings (crossings not at the IP) I(e + )=1.3 A (LER), I(e - )=0.7 A (HER) Bunch spacing: ns Beam spot:   x =120  m  y =5.6  m  z =9 mm Number bunches/beam: (to 1658) High-quality vacuum to keep beam-related backgrounds tolerable for experiments

112 PEP-II/BaBar Construction 1993: Start of PEP-II construction 1993: Start of PEP-II construction 1994: Start of BaBar construction 1994: Start of BaBar construction Summer 1998: 1st e+e- collisions in PEP-II Summer 1998: 1st e+e- collisions in PEP-II Spring 1999: BaBar moves on beamline Spring 1999: BaBar moves on beamline May 26, 1999: 1st events recorded by BaBar May 26, 1999: 1st events recorded by BaBar Oct 29, 2000: PEP-II achieves design luminosity Oct 29, 2000: PEP-II achieves design luminosity Intense competition with KEK-B/Belle in Japan Intense competition with KEK-B/Belle in Japan

113 PEP-II/BaBar The Standard Model predicts O(1) CP asymmetries in B decays! However, these asymmetries occur in processes that are relatively rare, so a large data sample is required. To perform these measurements, a two-ring e + e - storage ring with unequal beam energies was built by SLAC/LBNL/LLNL with unprecedented luminosity. We now have >60 M  (4S) events.

114 The BaBar Collaboration (9 countries)

115

116 BaBar DIRC quartz bar 3.5 cm Overall length (4 bars): 4.9 m No. light bounces (typical)=300 Surface roughness (r.m.s.)= 0.5 nm (typical) = 400 nm

117 BaBar DIRC Principle Number of Cherenkov photons=20-60  (  C ) = 3 mrad

118 A cp (t)F(t) t(ps) sin2 D sin2 True t, Perfect tagging: True t, Imperfect tagging: Measured t, Imperfect tagging: Must measure flavor tag Dilution. D = (1-2) where w is mistag fraction. Must measure t resolution properties. Experimental aspects of CP measurement

119 A mix (t)F mix (t)F nomix (t) t(ps) D True t, Perfect tagging: True t, Imperfect tagging: Measured t, Imperfect tagging: B 0 mixing measurement: D and R(  t,  t’) Amplitude of mixing asymmetry is the dilution factor D. Mixing sample has 10x statistics of CP sample. Shape of t determines resolution function R(t,t’)

120 B->K* 


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