1 Gerhard Raven Measurement of CP Violation in B Decays with the BaBar detector Nikhef Colloquium December 7 th 2001 Gerhard Raven University of California, San Diego

2 Gerhard RavenOutline What is CP (a)symmetry? B mesons and CP violation in the Standard Model How can we measure CP Violation? Brief introduction to PEP-II and the BaBar detector Overview of the measurement technique –B reconstruction –B 0, B + Lifetime measurement –Measurement of B 0 B 0 Mixing Frequency –Time Dependent CP Asymmetries sin(2  ) sin(2  eff ) Summary and Outlook

3 Gerhard Raven Discrete Symmetries In general if a physical law is symmetric under a transformation, then there is a conserved quantity 3 important discrete symmetries in Particle Physics Parity, P –Parity reflects a system through the origin. Converts right-handed coordinate systems to left-handed ones. –Vectors (momentum) change sign but axial vectors (spin) remain unchanged x   xL  L Charge Conjugation, C –turns a particle into its anti-particle e   e   Time Reversal, T –Changes, the sign of the time; t  t all time dependent quantities, e.g. momentum, change sign  

4 Gerhard Raven Why is CP Violation interesting? Universe is matter dominated –Where has the anti-matter gone? In 1967, Sakharov showed that the generation of a net baryon number requires: 1.Baryon number violating processes (e.g. proton decay) 2.Non-equilibrium state during the expansion, therefore unequal number of particles and anti-particles 3.C and CP symmetry Violation Standard Model CP-violation is unlikely to be sufficient to explain matter asymmetry in the universe –It means there is something beyond SM in CP violation somewhere, so a good place to work

5 Gerhard Raven Weak Interactions and Symmetry Violation In 1957 violation of parity was observed –Asymmetry in  decays of 60 Co  60 Ni  e   –Electrons produced mostly in one hemisphere C is violated too! –only left-handed neutrinos and right-handed anti-neutrinos (assuming massless neutrinos ) In 1964 CP violation was observed in the weak decay of neutral K mesons –K s      (CP = 1) –K l        (CP = -1) –Observed K l      (0.2%)  CP violation! Theoretically difficult to precisely interpret CP violation results in neutral K systems B Mesons expected to show CP violation –good testing ground for possible sources of CP violation

6 Gerhard Raven The Weak Interactions of Quarks The coupling strength at the vertex is given by g V ij –g is the universal Fermi weak coupling –V ij depends on which quarks are involved –For leptons, the coupling is just g For 3 generations, the V ij can be written as a 3x3 matrix –This matrix is referred to as the CKM matrix We can view this matrix as rotating the quark states from a basis in which they are Mass eigenstates to one in which they are Weak eigenstates b WW c gV cb

7 Gerhard Raven CP Violation via the CKM matrix The CKM matrix is a 3  3 complex unitary matrix Requires 4 independent, physical parameters to describe it: –3 real numbers & 1 complex non-trivial phase The existence of the complex coupling (phase) gives rise to CP violation – All CP violating observables are possible due to interference between different decay amplitudes involving a weak phase If there were only 2 quark generations, the corresponding 2  2 matrix would be all real  No CP violation –CP violation is possible in the Standard Model with at least 3 generations

8 Gerhard Raven The CKM Matrix: Wolfenstein parameterization Complex phase λ =V us = sin(  cabbibo ) = ± A =V cb / λ 2 = 0.83±0.06 Out of 6 triangles, this one (together with the “tu” one) is “special”: It has all sides O( 3 ) Large phases  potentially large CP asymmetries = Wolfenstein parameterization uses the observed hierarchy of the CKM elements and pushes the complex phase to the smallest elements Unitarity

9 Gerhard Raven Unitarity of the CKM Matrix The sides and the angles of this triangle can be determined experimentally in B decays Also see Peter Kluits colloquium last month for measurements of the magnitude of the sides

10 Gerhard Raven CP violating observables for B mesons As mentioned, need at least two amplitudes with different phases In B decays, we can consider two different types of amplitudes: –Those responsible for decay –Those responsible for mixing This gives rise to three possible manifestations of CP violation: –Direct CP violation (interference between two decay amplitudes) –Indirect CP violation (interference between two mixing amplitudes) –CP violation in the interference between mixed and unmixed decays d b WW d u u d   B0B0 B0B0 B0B0 b bd d u,c,tu,c,t u,c,tu,c,t WW WW

11 Gerhard Raven CP violation in decay Requires two decay amplitudes –Eg. K +  - : “easy” to measure –A CP = N(K +  - ) – N(K -  + ) / N(K +  - ) + N(K -  + ) –Asymmetry expected to be small Large asymmetry requires ~equal amplitudes… –But difficult to interpret: How large is the penguin contribution? What is the relative phase? –Difficult to disentangle contributions… To get a feeling for the relative weight, compare  +  - and K +  - : Br(K +  - ) >> Br(     )! : :

12 Gerhard Raven B 0 B 0 mixing: ARGUS, 1987 Fully reconstructed mixed event and dilepton studies demonstrate mixing Integrated luminosity : –103 pb -1

13 Gerhard Raven CP violation in mixing Mixing between B 0 and B 0 can be described can by effective Hamiltonian:  12 describes B 0  f  B 0 via on-shell states This is rare: the branching ratios of CP states is very small M 12 describes B 0  f  B 0 via off-shell states CP violation can occur in the interference between the on-shell and off- shell amplitudes, and leads to However, for B 0 mesons,  12 is very small: mixing is dominated by  m=2M 12 Little CP sensitivity…  Prob(B 0  B 0 )  Prob(B 0  B 0 )  |q/p|  1 Time evolution of a state produced as a pure B 0 : In the SM:

14 Gerhard Raven CP violation in the inference between mixing and decay Amplitude ratio Mixing Phase In order to have CP Violation Time evolution of initial B 0 (or B 0 ) mesons into a final CP eigenstate A single decay amplitude is sufficient Mixed decay has taken the role of the 2 nd amplitude Thus interfering amplitudes are comparable by construction and large CP asymmetries are possible!!!

15 Gerhard Raven Time Dependent CP Asymmetry From the time evolution of the B 0 and B 0 states we can define the time- dependent asymmetry to be Probe of direct CP violation since it requires Sensitive to the phase of even without direct CP Violation Im = 0.75 | |=1

16 Gerhard Raven Golden Decay Mode: B 0  J/  K 0 S Theoretically clean way to measure the phase of (i.e. sin2  ) Clean experimental signature Branching fraction: O(10 -4 ) “Large” compared to other CP modes! Time-dependent CP asymmetry u,c,tu,c,t u,c,tu,c,t WW WW K 0 mixing   CP = +1 B 0  J/  K 0 L   CP = -1 B 0  J/  K 0 S B 0   (2s) K 0 S B 0   c1 K 0 S “Golden Modes”

17 Gerhard Raven B meson production Electron-Positron collider: e + e -   (4s)  B 0 B 0 –Only 4s resonance can produce B meson pair –Low B 0 production cross-section: ~1 nb –Clean environment, coherent B 0 B 0 production B-Factory approach B 0 B 0 threshold Off On PEP-II B A B A R BB threshold

18 Gerhard Raven  (4S): Coherent B 0 B 0 production B 0 B 0 system evolves coherently until one of them decays –CP/Mixing oscillation clock only starts ticking at the time of the first decay, relevant time parameter  t: –B mesons have opposite flavour at time  t=0 –Half of the time CP B decays first (  t<0) Integrated CP asymmetry is 0: Coherent production requires time dependent analysis At t cp =0 B0B0 B0B0 At t=0 B0B0 B0B0 t = t CP - t OtherB Coherent Incoherent -- ++ ++ --  t(ps) t(ps)

19 Gerhard Raven A Symmetric Collider won’t work… CP asymmetry is a time-dependent process –A CP   t between two B decays,  t ~ ps –In reality one measures decay distance between two B decays In symmetric energy e + e - collider, where  (4S) produced at rest, daughter B’s travel ~ 20  m –Too small a distance to discern with today’s detector technology  l  40  m B tag B CP 5.3 GeV e+e+

20 Gerhard Raven Solution: Boost the CMS! Coherent BB pair z Start the Clock This can be measured using a silicon vertex detector! (  )  (4S) = 0.56

21 Gerhard Raven Asymmetric B Factories  = 0.56,  s = M  (4S) Collisions every 4.2 ns Large currents! HERLER Energy (GeV) Number of bunches1658 Beam Current (A)1.02.1

22 Gerhard RavenPEP-II PEP-II delivered : 63 fb -1 B A B AR recorded : 60 fb -1 (incl. 6.5 fb -1 off peak) 60 Million B meson pairs “on tape”! PEP-II top luminosity: 4.3 x cm -2 s -1 (design 3.0 x ) Best shift: 102 pb -1 Best day: 282 pb -1 Best month: 6 fb -1 Average logging efficiency: > 96% October 99 December 5, /fb used for CP and mixing 20/fb used for lifetime off-peak

23 Gerhard Raven KEK-B has reached cm -2 s -1 ! (design ) Extrapolation suggest both machines will have delivered ~100 fb -1 by the time of ICHEP 2002 – we live in interesting times! KEK-B performance peak luminosity = × /cm 2 /sec integrated luminosity : shift = /pb day = /pb 24h = /pb 7days = /pb month = /pb

24 Gerhard Raven The BaBar Detector Cerenkov Detector (DIRC) 144 quartz bars PMs 1.5 T solenoid Electromagnetic Calorimeter 6580 CsI(Tl) crystals Drift Chamber 40 stereo layers Instrumented Flux Return iron / RPCs (muon / neutral hadrons) Silicon Vertex Tracker 5 layers, double sided strips e + (3.1 GeV) e - (9 GeV) SVT: 97% efficiency, 15  m z hit resolution (inner layers, perp. tracks) SVT+DCH:  (p T )/p T = 0.13 %  p T % DIRC: K-  separation GeV/c  GeV/c EMC:  E /E = 2.3 %  E -1/4  1.9 %

25 Gerhard Raven Silicon Vertex Detector 5 Layer AC-coupled double sided silicon detector SVT Located in high radiation area Radiation hard readout electronics (2Mrad) 97% hit reconstruction efficiency Hit resolution ~15 μm at 0 0 e - beame + beam

26 Gerhard Raven Silicon Vertex Detector Beam pipe Layer 1,2 Layer 3 Layer 4 Layer 5 Beam bending magnets Readout chips

27 Gerhard Raven Drift Chamber 40 layers of wires inside 1.5 Tesla magnetic field Measurement of charged particle momentum Limited particle identification from ionization loss

28 Gerhard Raven Cerenkov Particle Identification System Čerenkov light in quartz –Transmitted by internal reflection –Rings projected in standoff box –Detected by PMTs –Essential for Kaon ID >2 GeV

29 Gerhard Raven ElectroMagnetic Calorimeter 6580 CsI(Tl) crystals with photodiode readout About 18 X 0, inside solenoid Excellent energy resolution, essential for  0    = 5.0% 00

30 Gerhard Raven Instrumented Flux Return Up to 21 layers of RPCs sandwiched between iron plates Muons identified above 500 MeV Neutral Hadrons (K L ) detected

31 Gerhard Raven Event Topology and Analysis Strategy z Exclusive B Meson and Vertex Reconstruction Tag vertex reconstruction Flavor Tagging e+e+ K-K-

32 Gerhard Raven Analysis Strategy Measurements B ± /B 0 Lifetimes B 0 B 0 -Mixing CP-Asymmetries sin(2  ) sin(2  eff ) Analysis Ingredient Reconstruction of B mesons in flavor eigenstates B vertex reconstruction Flavor Tagging + a + b Reconstruction of neutral B mesons in CP eigenstates + a + b + c Higher precision Increasing complexity Factorize the analysis in building blocks

33 Gerhard Raven Blind Analysis All analysis were done “blind” to eliminate possible experimenters’ bias –In general, measurements of a quantity “X” are done with likelihood fits – blinding done by replacing “X” with “X+R” in likelihood fits –R is draw from a Gaussian with a width a few times the expected error –Random number sequence is “seeded” with a “blinding string” –The reported statistical error is unaffected –It allows all systematic studies to be done while still blind –The sin(2b) result was “unblinded” 1 week before public announcement this summer!

34 Gerhard Raven Measurement of B 0 and B + Lifetime 3. Reconstruct Inclusively the vertex of the “other” B meson (B TAG ) 4. compute the proper time difference  t 5. Fit the  t spectra (4s)  = 0.56 Tag B  z ~ 110 m Reco B  z ~ 65 m ++ zz t  z/c K0K0  D-D- -- -- K+K+ 1.Fully reconstruct one B meson in flavor eigenstate (B REC ) 2.Reconstruct the decay vertex

35 Gerhard Raven Fully-Reconstucted B sample Cabibbo -favored hadronic decays “Open Charm” decays Neutral B Mesons Charged B Mesons Flavor eigenstates B flav : for lifetime and mixing measurements [GeV] 30 fb -1 Hadronic decays into final states with Charmonium

36 Gerhard Raven Vertex and  t Reconstruction Reconstruct B rec vertex from charged B rec daughters Determine B Tag vertex from charged tracks not belonging to B rec B rec vertex and momentum beam spot and  (4S) momentum High efficiency (97%) Average  z resolution is 180  m ( ~  ct = 260  m) Conversion of  z to  t takes into account the (small) B momentum in  ( 4S) frame  t resolution function measured directly from data Beam spot Interaction Point B REC Vertex B REC daughters B REC direction B TAG direction TAG Vertex TAG tracks, V 0 s z

37 Gerhard Raven Vertex and Dt reconstruction: Belle

38 Gerhard Raven  B Measurements in BaBar e -|  t|/  Either B rec or B tag can decay first (this analysis) BaBar  t resolution e -t/  true  t B production point known eg. from beam spot LEP/SLD/C DF/D0/ LHC-B/… Need to disentangle resolution function from physics ! measured  t Resolution function Resolution fcn + lifetime Resolution Function + Lifetime  = = 

39 Gerhard Raven  t Signal Resolution high flexibility small correlation with  B) zz Signal MC (B 0 )  t  (meas-true)   t tracks from long-lived D’s in tag vertex  asymmetric RF event-by-event  (  t) from vertex errors Resolution Function (RF) – 2 models: –Sum of 3 Gaussians (mixing + CP analyses) –Lifetime-like bias (lifetime analysis) ~0.6 ps

40 Gerhard Raven Lifetime Likelihood Fit Simultaneous unbinned maximum likelihood fit to B 0 /B + samples 19 free parameters –  (B + ) and  (B 0 )2 –  t signal resolution 5 – empirical background12 description Background parameters determined from m ES sideband B 0 m ES B 0 Bkg  t m ES <5.27 GeV/c 2  t characteristics determined from data

41 Gerhard Raven Neutral and Charged B meson Lifetimes Precision measurements:  t (ps)  0 =   ps   =   ps   /  0 =    t RF parameterization,  t outlier description Common resolution function for B + and B 0 20 fb -1 PRL 87 (2001) 2 % statistical error 1.5 % systematic error  t distribution well described! bkgd signal +bkgd outliers

42 Gerhard Raven Comparison of Lifetime Ratio Measurements Single most precise measurement Systematic error 1% in B + /B 0 lifetime ratio

43 Gerhard Raven Belle result from 5 th KEK conference (end Nov)

44 Gerhard Raven Belle result from 5 th KEK conference (end Nov)

45 Gerhard Raven Analysis Strategy (II) Measurements B ± /B 0 Lifetimes B 0 B 0 -Mixing CP-Asymmetries Analysis Ingredient Reconstruction of B mesons in flavor eigenstates B vertex reconstruction Flavor Tagging + a + b Reconstruction of neutral B mesons in CP eigenstates + a + b + c

46 Gerhard Raven Measurement of B 0 B 0 Mixing 3. Reconstruct Inclusively the vertex of the “other” B meson (B TAG ) 4. Determine the flavor of B TAG to separate Mixed and Unmixed events 5. compute the proper time difference  t 6. Fit the  t spectra of mixed and unmixed events (4s)  = 0.56 Tag B  z ~ 110 m Reco B  z ~ 65 m ++ zz t  z/c K0K0  D-D- -- -- K+K+ 1. Fully reconstruct one B meson in flavor eigenstate (B REC ) 2. Reconstruct the decay vertex

47 Gerhard Raven  t distribution of mixed and unmixed events perfect flavor tagging & time resolution realistic mis-tagging & finite time resolution w: the fraction of wrongly tagged events  m d : oscillation frequency

48 Gerhard Raven Extraction of  m d and Flavour Mistag Fractions Fraction of Mixed Events as Function of time Sensitive to mistag fraction measurement because the mixing has not started yet At t=0 the observed ‘mixed’ events are only due to wrongly tagged events Sensitive to  m d when the rate of change of the amplitude is at its maximum

49 Gerhard Raven B Flavour tagging methods NN output Not Used For electrons, muons and Kaons use the charge correlation b c dd l-l- B0B0 D, D* W- Lepton Tag b d B0B0 W- W+ cs K *0 d Kaon Tag Each category is characterized by the probability of giving the wrong answer (mistag fraction w) Multivariate analysis exploiting the other kinematic information of the event, e.g.,  Momentum spectrum of the charged particles  Information from non-identified leptons and kaons  Soft  from D* decay Neural Network Hierarchical Tagging Categories

50 Gerhard Raven Flavour Tagging Performance Tagging category Fraction of tagged events  (%) Wrong tag fraction w (%) Q =  (1-2w) 2 (%) Lepton10.9    0.5 Kaon35.8    0.9 NT1 7.8    0.4 NT    0.3 ALL68.4   1.2 Smallest mistag fractionHighest “efficiency” The error on sin2  and  m depend on “the quality factor” Q: The large sample of fully reconstructed events provides the precise determination of the tagging parameters required in the CP fit

51 Gerhard Raven Belle Flavour Tagging

52 Gerhard Raven Belle Flavour Tagging

53 Gerhard Raven Mixing Likelihood Fit Fit Parameters  m d 1 Mistag fractions for B 0 and B 0 tags8 Signal resolution function(scale factor,bias,fractions)8+8=16 Empirical description of background  t19 B lifetime fixed to the PDG value  B = ps Unbinned maximum likelihood fit to flavor-tagged neutral B sample 44 total free parameters All  t parameters extracted from data

54 Gerhard Raven Beware of Correlations! Difficult part of the  m d analysis are correlations For this result, 2 correlation are not modeled in the likelihood function –Between m ES and  t For m ES close to m B, more background due to (incorrectly reconstructed) real B mesons For smaller m ES, more continuum background Leads to a ps -1 correction determined from data –Between mistag rate and resolution Eg. “wrong” sign K ± are mainly produced by D ( * ) D ( * ) decays Higher charged multiplicity, no (or only low momentum) tracks from B decay vertex  different  t resolution Leads to a ps -1 correction determined from MC Next generation of this measurement should / will have to model this in the likelihood…

55 Gerhard Raven Mixing Likelihood Fit Result  m d =0.516±0.016±0.010 ps -1 BaBar internal review passed currently in “final circulation” Numbers are final To be submitted to PRL in the very near future (please don’t tell your friends on Belle just yet!) CL=44%

56 Gerhard Raven Cross Checks and Systematic Errors

57 Gerhard Raven  m d Measurement in Comparison Precision  m d measurement (3%) with B flav sample is still statistically limited Systematic error under control (2%) –Dominated by uncertainty on  B –Followed by resolution fcn and tagging-vertexing correlations. Theoretical hadronic uncertainties limit extraction of |V td | My Average, using COMBOS (PDG 2000)

58 Gerhard Raven Recent Belle Result (5 th KEK topical conference)

59 Gerhard Raven Recent Belle Results (5 th KEK topical conference)

60 Gerhard Raven Analysis Strategy (III) Measurements B ± /B 0 Lifetimes B 0 B 0 -Mixing CP- Asymmetries Analysis Ingredient Reconstruction of B mesons in flavor eigenstates B vertex reconstruction Flavor Tagging + a + b Reconstruction of neutral B mesons in CP eigenstates + a + b + c

61 Gerhard Raven Measurement of sin(2  ) 3. Reconstruct Inclusively the vertex of the “other” B meson (B TAG ) 4. Determine the flavor of B TAG to separate B 0 and B 0 5. compute the proper time difference  t 6. Fit the  t spectra of B 0 and B 0 tagged events (4s)  = 0.56 Tag B  z ~ 110 m Reco B  z ~ 65 m -- zz t  z/c K0K0  KS0KS0 -- ++ 1. Fully reconstruct one B meson in CP eigenstate (B REC ) 2. Reconstruct the decay vertex ++

62 Gerhard Raven The CP Sample  c1 K s J/  K s K s (  0  0 ) J/  K* 0  (2S)K s J/  K s K s (  +  - ) After tagging: Sampletagged events PurityCP [J/ ,  (2S),  c1 ] K S 48096% J/  K L 27351%+1 J/  K* 0 (K S  0 )5074%mixe d Full CP sample 80380% data 32 x 10 6 BB pairs 29 fb -1 on peak Before tagging requirement m ES (GeV/c 2 )  E=E B * -  s/2 (GeV) J/  K L

63 Gerhard Raven Example of a Fully Reconstructed Event  (2S) K s   +  -   +  - D* +  -  D  +  K -  + Exercise for the viewer/reader/liste ner: how many ways are there to flavour tag this event? –Bonus points: which tag was actually used?

64 Gerhard Raven A few words about J/  K* 0 (K S  0 ) J/  K* 0 (K S  0 ) angular components: A || : CP = +1 A 0 : CP = +1 A  : CP = -1 (define R  = |A  | 2 )  CP asymmetry diluted by D  = (1 - 2R  )  R  = (16.0 ± 3.2 ± 1.4) % (B A B AR, to appear in PRL) => Effective  f = 0.65  0.07 (includes acceptance corrections) Sample used in R  measurement (20.7fb -1 ) and the angular fit

65 Gerhard Raven  t Spectrum of CP events perfect flavor tagging & time resolution Mistag fractions w And resolution function R CP PDF realistic mis-tagging & finite time resolution Mixing PDF determined by the flavor sample

66 Gerhard Raven Sin(2  ) likelihood fit Combined unbinned maximum likelihood fit to  t spectra of flavor and CP sample 45 total free parameters All  t parameters extracted from data Correct estimate of the error and correlations Fit Parameters sin2  1 Mistag fractions for B 0 and B 0 tags8 Signal resolution function16 Empirical description of background  t20 B lifetime fixed to the PDG value  B = ps Mixing Frequency fixed to the PDG value  m d = ps -1 Global correlation coefficient for sin2b: 13% Different  t resolution function parameters for Run1 and Run2 tagged flavor sample tagged CP samples Driven by

67 Gerhard Raven Sin(2b) Fit Results Consistency of CP channels P(  2 ) = 8% sin2  = 0.59 ± 0.14 Cross-checks: Null result in flavor samples Goodness of fit(CP Sample): P(L max >L obs ) > 27% Phys. Rev. Lett (2001) Combined fit to all modes

68 Gerhard Raven Raw CP Asymmetry sin2  =0.56 ± 0.15 sin2  =0.59 ± 0.20 Kaon tags All tags Raw A CP  f = -1 events

69 Gerhard Raven Raw CP Asymmetry for J/  K L sin2  =0.70±0.34 Background contribution

70 Gerhard Raven Check “null” control sample Treat B flav sample as CP No asymmetry seen Analysis doesn’t create artificial asymmetries

71 Gerhard Raven Consistency checks sin2  measured in several  t bins sin2  vs. J/  decay mode and tagging category and flavor for  = -1 events Combined CP=-1

72 Gerhard Raven Is it possible to measure a very large asymmetry? The answer is… yes! Suppose at a given time t’ you have N events < 0 is possible in the likelihood fit –The signal PDF can be negative in some regions –Requires having NO OBSERVED event in those regions –The only constraint on the PDF is the normalization

73 Gerhard Raven Large sin2  in B 0   C1 K S fit for B 0 /B 0  t PDFs, not for A CP Large sin2  possible, because –No events where PDF<0 (eg. lepton tags) –Sum of signal + background PDFs positive (eg. Kaon tags) Note: a single lepton B 0 -tag at  t = -  /2  m  would bring sin2  from 2.6 to ~1/(1-2w lep )  1.1 Measure sin2  unbiased for low stat. samples and probability to obtain sin2   2.6 when true value 0.7 is 1~2% Lepton tags Kaon tags  t [ps] B 0 tags  t [ps]

74 Gerhard Raven Systematic Errors Signal resolution and vertex reconstruction 0.03 Resolution model, outliers, residual misalignment of the Silicon Vertex Detector  Tagging 0.03  possible differences between B CP and B flavor samples Backgrounds 0.02 (overall) Signal probability, fraction of B + background in the signal region, CP content of background Total 0.09 for J/  K L channel; 0.11 for J/  K *0 Total = 0.05 for total sample Error/SampleKSKS KLKL K *0 Total Statistical Systematic

75 Gerhard Raven Belle sin(2  1 ) result

76 Gerhard Raven Belle sin(2  1 ) result

77 Gerhard Raven Belle sin(2  1 ) result

78 Gerhard Raven The New World Average Measurements assumed to be uncorrelated New sin2  world average is 8  significant!

79 Gerhard Raven Interpretation of the result One solution for  is consistent with measurements of sides of the unitarity triangle Method as in Höcker et al, hepex/ (see also many other recent global CKM analyses) Error on sin2  is dominated by statistics and will decrease ~1/ for the forseeable future…

80 Gerhard Raven Search for Direct CP To probe new physics (only use  CP =-1 sample that contains no CP background) | | = 0.93 ± 0.09 (stat) ± 0.03 (syst) No evidence of direct CP violation due to decay amplitude interference (S CP unchanged in Value) Without SM Prejudice : If more than one amplitude present then | | might be different from 1

81 Gerhard Raven CP Violation in B 0  +  - decays u u d b d u b u | |  1  must fit for direct CP Im ( )  sin2   need to relate asymmetry to  Decay distributions f + (f - ) when tag = B 0 (B 0 ) C   0, S  = sin2  C   0, S  = sin2  eff Weak phase (only tree diagram) Additional phase from penguin diagram penguin diagramtree diagram

82 Gerhard Raven B     ,K   ,K  K  Data Sample Lepton Kaon NT1 NT2 Likelihood Analyis with high reconstruction efficiency: Loose selection criteria yield 9741 two-prong candidates in 30.4 fb -1 (includes 97% background, almost entirely from continuum) sum of  +  - /K +  - m ES distributions by tagging category particle ID used in likelihood fit for  /K  separation

83 Gerhard Raven B        K    Likelihood Fit –8 event types –Sig and Bkg:  +  -, K +  , K -  +, K + K -  measure also direct CP violation in charge asymmetry –Discriminating variables –m ES,  E, Fisher (Event shapes), Cerenkov angles,  t –Mistag rates and  t signal resolution function same as in sin2  fit (uses also untagged events to improve BR measurements) –Empirical background parameters determined from m ES sidebands –  m d, B 0 lifetime fixed to PDG values A = N(K -  + )-N(K +   ) / N(K -  + )+N(K +   ) Simultaneous extended unbinned ML fit to the yields and CP asymmetries:

84 Gerhard Raven CP Sample:     /K    Candidates L = 30.4 fb -1 Events after likelihood ratio cuts Total Yields from fit: Measured Branching Ratios (using 20 fb -1 ):  +  - : ( )10 -6 K +  - : ( )10 -6 K + K - : < (90%CL)   K+K-K+K- K+K-K+K- Background (incl. crossfeed) Tagged events

85 Gerhard Raven B 0      Asymmetry Result Measurement compatible with no CP in B 0      Statistically limited due to small branching fraction Need ~500fb -1 for  (S  ) ~ To appear in PRD Rapid Communications

86 Gerhard Raven Summary and Outlook New precision measurements of B 0 /B + lifetimes and B 0 B 0 mixing frequency  m d Measurement of flavor-tagged, time-dependent B decays at asymmetric B factory has become established technique BaBar observes CP violation in the B 0 system at 4  level –Probability is < 3 x to observe an equal or larger value if no CP violation exists –Corresponding probability for only the  CP = -1 modes is 2 x sin(2  ) = 0.59 ± 0.14 ± 0.05  0 =   ps   =   ps  0 /   =    m d = ± ± ps -1

87 Gerhard Raven Summary and Outlook (II) First measurement of time-dependent CP asymmetry in rare B decay mode B      The study of CP violation in the B system has started: –sin(2  ) will very soon become precision measurement (  unitarity triangle constraints will be limited by other CKM parameters) –Need to compare sin(2  ) from different decay modes to test standard model With anticipated 100 fb -1 by summer, error in sin(2  ) will be 0.08 and for the asymmetry in B      error will be ~0.3

88 Gerhard Raven Summary and Outlook (III) 37 years after the discovery of CP violation in Kaon decays, a 2 nd system with CP violation is found – and its study is just beginning… The Standard Model prediction of a single phase as the source of CP violation seems right (sofar -- given the current experimental data…) New physics and its contribution to CP violation in B decays are possible, but remain to be discovered… Current experimental measurements of CP violation in weak interactions are very unlikely to explain the CP asymmetry observed in the universe…

89 Gerhard Raven Luminosity Outlook of PEP-II & BaBar Expect >500 fb -1 by 2007

90 Gerhard Raven Changes between Run1 and Run2 First publication in March 2001 Changes since then: –More data (run 2): 23  32 BB pairs –Improved reconstruction efficiency –Optimized selection criteria takes into account CP asymmetry of background in J/  K L –Additional decay modes  C1 K S and J/  K *0 –Improved vertex resolution for reconstructed and tag B sin(2  ) = 0.34 ± 0.20 (stat) ± 0.05 (syst) PRL 86 (2001) 2515