Experimental Aspects of CP Violation in B Decays : Lecture III Vivek Sharma University of California, San Diego

2 Outline of Lecture II: Yesterday PEP-II and KEK-B Colliders : Notable features Detectors at the Asymmetric energy collider –General requirements for CPV measurements Implementation in BaBar & Belle (similar but different) General Data analysis methods –B Meson Reconstruction & Continuum background rejection –B meson flavor determination : B or a B ? ? –Blind analysis !

3 Outline of Lectures 3 & 4 Lecture 3 Three types of CP violation & SM expectations in B Decays –Decay amplitude Weak phase structure –Decay asymmetry prediction in SM General strategy for time-dependent CP asymmetry measurement –Observables that probe angle  Time dependent CP asymmetry in B -> Charmonium KS modes Step-by-Step Other modes with subdominant or dominant Penguin Lecture 4 –Observables that probe angle  –Observables that probe angle  –Summary of current measurements –Future prospects

CP Violation In B Decays: SM Expectations

5 Decay Amplitude Weak Phase Structure in CPV Most B decay final states have contributions from both “Tree” and 3 “Penguin” (P t,P c,P u ) diagrams. –All Tree diagrams (Spectator, W-exchange, W-Annihilation, rescattering) have same weak phase –The three P i can have different Weak and Strong phases –EW penguins “suppressed” due to EW coupling

6 B Decay Amplitude Weak Phase Structure

7 Decay Amplitude Weak Phase Structure in CPV

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9 Five “Classes” of B Decays For CPV

10 Five “Classes” of B Decays For CPV

11 Some Examples of Class I (b  c c s): B 0  K S

12 Another Example of Class I (b  u u d): B 0  +  - Neglecting Penguin diagram

13 An Example of Class II (b  c c d): B 0  D + D - Ignoring Penguin Diagram (?)

14 CPV in Decay aka Direct CP Violation 2 2  B f f B

15 Observation of Direct CPV in B 0  K -  + Loop diagrams from New Physics (e.g. SUSY) can modify SM asymmetry Clean mode with “large” rate : Measure charge asymmetry, reject B  background with Particle ID B background signal  E (GeV) K  separation K  separation(  )

16 B0K+B0K+ B0K+B0K+ BABAR BaBar: First Observation of Direct CPV in B decay ! 4.2 , syst. included BABAR signal enhanced background subtracted

17 Confirmation of Direct CPV by Belle at ICHEP04 A CP =   M BB 3.9  significance B 0  K    _ B 0  K    Signal= 2139  53 Combined BaBar & Belle significance = 5.7  Establishes CPV not just due to phase of B Mixing (M 12 ) Theoretical (npQCD) uncertainties insufficient to prove or rule out NP

18 Direct CPV in B -  K -  0 Belle A CP ( K    ) = 0.04  0.05  0.02 Belle A CP ( K    ) = 0.06  0.06  0.01 BaBar Not in B  K -  +

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20 CPV in B 0 Mixing Occurs when Mass eigenstates  CP eigenstates (|q/p|  1 and  0) The Box diagrams provide the required 2 phases Strong phases depend on quark masses and non-perturbative physics. Asymmetries are small and hard to calculate precisely 2  2 B0B0 B0B0 f f B0B0 B0B0

21 CPV in B 0 Mixing off-shell states f on-shell states f 2  2 B0B0 B0B0 f f B0B0 B0B0

22 CPV in B 0 Mixing Time-dependent CP Asymmetry: Babar  Search for asymmetry in same-sign dilepton sample containing events

23 CPV in B 0 Mixing B A B AR 20.7 fb  B A B AR 20.7 fb  Sample backgrounds B(  t): 4.3% continuum 24% direct+cascade 12% direct+fake Measurement region > 200  m

24 CPV in B 0 Mixing B A B AR 20.7 fb  B A B AR 20.7 fb  BABAR PRL 88, (2002) To a good approximation: So far, no experimental evidence of large CP violation in B 0 mixing

25 CPV In Interference Between Mixing and Decay  B0B0 B0B0 B0B0 f cp B0B0 B0B0 B0B0 CP asymm. can be very large and can be cleanly related to CKM angles

26 CPV In Interference Between Mixing and Decay Requires measurement of proper time difference t=  t between the decay of B tag and B CP. Time dependent rates for a SC

27 Time-Dependent CP Asymmetry with a Perfect Detector Perfect measurement of time interval t=  t Perfect tagging of B 0 and B 0 meson flavors For a B decay mode such as B 0  Ks with |  f |=1 sin 2  B0B0 B0B0 Asymmetry A CP

Time Dependent CPV Measurement Technique Since the techniques of time-dependent analysis is common to many modes, I will now describe this in detail using the “golden” mode B 0  (c c ) K 0 from which CP violation in B 0 decays was first established. The analysis (from 2002) based on 88 fb -1 is “old” but forms basis for all other new (2004) analysis results that I will present later

Vivek Sharma, UCSD29 B 0  J/  K s CP Violation in Picture z   (4S) = 0.55 Coherent BB pair B0B0 B0B0   Separate B 0 and B 0 Separate B 0 and B 0

Vivek Sharma, UCSD30 Sin2  Analysis Strategy 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 Higher precision Increasing complexity Factorize the Time Dependent analysis into building blocks Obtain All analysis ingredients from DATA

Calibrating The BaBar Clock With B Meson Lifetime Measurement

Vivek Sharma, UCSD32 Measurement of the 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)  = 0.55 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

Vivek Sharma, UCSD33 Cabibbo-favored hadronic decays “Open Charm” decays Fully-Reconstructed B sample Neutral B Mesons Flavor eigenstates B flav : for lifetime and mixing measurements Hadronic decays into final states with Charmonium Charged B Mesons [GeV] ~21000 signal Purity: 85% ~20000 signal Purity: 85%

Vivek Sharma, UCSD34 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 ( ~  c  = 260  m)  t resolution function measured 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

Vivek Sharma, UCSD35 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  B Measurement in BaBar Need to disentangle resolution function from physics ! measured  t Resolution function lifetime Resolution Function + Lifetime  = = 

Vivek Sharma, UCSD36 event-by-event  (  t) from vertex errors Lifetime-like bias to Small correlation between lifetime and Resolution Function parameters  t Resolution Function zz Signal MC (B 0 )  t (meas-true)/   t tracks from long-lived D’s in tag vertex asymmetric Resolution Function ~0.6 ps

Vivek Sharma, UCSD37 Lifetime Likelihood Fit Simultaneous unbinned maximum likelihood fit to B 0 /B + samples Use data to extract the properties of background events Mass distribution provides the signal probability Use the events in the sideband (m ES < 5.27) to determine the  t structure of the background events under the signal peak 19 free parameters  (B + ) and  (B 0 )2  t signal resolution 5 empirical background12 description B 0 m ES B 0 Bkg  t

Vivek Sharma, UCSD38 B Lifetime Fit Results World’s best measurement 2 % statistical error 1.5% systematic error Main source of systematic error Parameterization of the  t resolution function Description of events with large measured  t (outliers) B0/ B0B0/ B0 BB  t (ps)  0 =   ps PDG:  ps   =   ps PDG:  ps   /  0 =   PDG:  fb -1 background signal + bkg PRL 87, (2001)

B Flavor Mistag Knowledge From Data

40 sin2  results from charmonium modes Start with a B 0 beam, slowly (compared to the lifetime) a B 0 component builds up But no “Mixed” events at t=0. If the detector measures some “mixed” events, it must be because it has measured the flavor of the B incorrectly (  mistag) B0B0 B0 B0B0 B0 B Lifetime

Vivek Sharma, UCSD41 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

Vivek Sharma, UCSD42 Measurement of B 0 B 0 Mixing rate Vs  t 3. Reconstruct Inclusively the vertex of the “other” B meson (B TAG ) 4. Determine 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)  = 0.55 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

Vivek Sharma, UCSD43  t Spectrum of Mixed and Unmixed Events perfect flavor tagging & time resolution Decay time diff (  t) in ps _ + w: the fraction of wrongly tagged events  m d : oscillation frequency realistic mis-tagging & finite time resolution Decay time diff (  t) in ps

Vivek Sharma, UCSD44 NN output Not Used B Flavor Tagging Methods 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

Vivek Sharma, UCSD45 Flavor Tagging Performance in Data Tagging category Fraction of tagged events  (%) Wrong tag fraction w (%) Mistag fraction difference  w (%) Q =  (1-2w) 2 (%) Lepton 10.9     0.5 Kaon 35.8     0.9 NT1 7.7     0.4 NT     0.3 ALL 68.4   1.2 The large sample of fully reconstructed events provides the precise determination of the tagging parameters required in the CP fit Highest “efficiency” Smallest mistag fraction B A B AR 29.7 fb  B A B AR 29.7 fb  Error on sin2  and  m d depend on the “quality factor” Q approx. as:

Vivek Sharma, UCSD46 Flavor Tagged B Meson Sample For Mixing Studies Gaussian ARGUS function p sig,i ~ 0p sig,i ~ 0.96 Background properties from sideband events Lepton Kaon Lepton NT2NT1

Vivek Sharma, UCSD47  t Resolution Function TailCoreOutlier Use the event-by-event uncertainty on  t  t Residual (ps) R(  t) Different bias scale factor For each tagging category B 0 flavour sample CP sample   t (ps)

Vivek Sharma, UCSD48 Fit Parameters  m d 1 Mistag fractions for B 0 and B 0 tags8 Signal resolution function2 x 8 Empirical description of background  t16+3 B lifetime fixed to the PDG value  B = ps Mixing Likelihood Fit on Reconstructed B 0 Sample Unbinned maximum likelihood fit to flavor-tagged neutral B sample 44 total free parameters All  t parameters extracted from data

Vivek Sharma, UCSD49 BABAR PRL 88, (2002) Mixing with Hadronic Sample B A B AR 29.7 fb  B A B AR 29.7 fb  Precision measurement consistent with world average Signal: m ES >5.27 Bgnd: m ES <5.27

Vivek Sharma, UCSD50  m d Measurement in Comparison With World Precision  m d measurement  3% statistical error  2% systematic error dominated by MC correction BaBar Measurements World Average: ± ps -1

Vivek Sharma, UCSD51 Folded raw asymmetry |  t| [ps] Flavor mistag rate well calibrated from mixing measurement B 0 B 0 Mixing Asymmetry with Hadronic Sample Unfolded raw asymmetry  t [ps] B A B AR 29.7 fb  B A B AR 29.7 fb 

Vivek Sharma, UCSD52 Mixing Measurement at Belle (Hadronic Modes) BELLE 29.1 fb  BELLE Mistag rate

Vivek Sharma, UCSD53 CP Analysis Analysis Strategy (Step 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

Vivek Sharma, UCSD54 Measurement of CP Asymmetry 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 B 0 and B 0 tagged events 1. Fully reconstruct one B meson in CP eigenstate (B CP ) 2. Reconstruct the decay vertex (4s)  = 0.55 Tag B  z ~ 110 m CP B  z ~ 65 m ++ zz t  z/c K0K0  ++ -- Ks0Ks0 --

Vivek Sharma, UCSD55 Charmonium+K 0 CP Sample for BABAR (’02) (after tagging & vertexing) 988 signal candidates, purity 55% 1506 signal candidates, purity 94% B A B AR 81.3 fb  B A B AR 81.3 fb 

Vivek Sharma, UCSD56 perfect flavor tagging & time resolution  t Spectrum of CP Events Mistag fractions w And resolution function R CP PDF realistic mis-tagging & finite time resolution Mixing PDF determined by flavor sample

57 Sin2  Likelihood Fit Combined unbinned maximum likelihood fit to  t spectra of flavor and CP sample 35 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 tags 8 Signal resolution function 8 Empirical description of background  t17 B lifetime fixed (PDG value)  B = ps Mixing Frequency fixed (PDG value)  m d = ps -1 tagged flavor sample tagged CP samples

58 sin2  Likelihood Fit Description Combined unbinned maximum likelihood fit to  t spectra of B flav and CP samples All  t parameters extracted from data Correct estimate of the error and correlations Fit Parameters#Main Sample Sin2  1Tagged CP sample Mistag fractions for B 0 and B 0 tags8Tagged flavor sample Signal resolution function 8Tagged flavor sample Empirical description of background  t 17Sidebands B lifetime from PDG  B = ps Mixing frequency from PDG  m d = ps -1 Total parameters34 Global correlation coefficient for sin2  : 13%

59 Check “null” Control Sample at BABAR Input B flav sample to CP fit No asymmetry expected Sample “sin2  ” B flav 0.021±0.022 B+B ±0.025

60 BABAR Result for sin2  (July 2002) sin2 =   CP = -1  CP = +1

61 Pure Gold : Lepton Tags Alone B A B AR 81.3 fb  B A B AR 81.3 fb  98% purity 3.3% mistag rate 20% better  t resolution 220 lepton-tagged  f = -1 events CP asymmetry is obvious !

62 Systematic Errors on sin2  from BABAR  [sin2  ] Description of background events0.017 CP content of background components Background shape uncertainties, peaking component Composition and CP content of J/  K L background  t resolution and detector effects Silicon detector residual misalignment  t resolution model (Gexp vs 3G, B flav vs B CP ) Mistag differences between B CP and B flav samples (MC)0.012 Fit bias correction and MC statistics0.010 Fixed lifetime and oscillation frequency0.005 Total0.033

63 Updated (ICHEP04) sin2  results from Charmonium Modes Limit on direct CPV B A B AR

64 Belle Results on sin2  from Charmonium Modes B elle

65 Lessons From sin2  Measurement With B 0  K 0 In 2001, CP Violation in B system was discovered in this mode by BaBar and Belle. It was the first instance of CPV outside the Kaon system. It was also the first instance of a CPV effect which was O(1) in contrast with the Kaon system and confirms the conjecture of Kobayashi & Maskawa made in 1972 for CPV phenomenon. It excludes models with approximate CP symmetry (small CPV). In 2004 sin2  is a precision measurement (5%) and agrees well with the constraints in the  -  plane from measurements of the CKM magnitudes. Now it appears unlikely that one will find another O(1) source of CPV and the enterprise now moves towards looking for corrections rather than alternatives to the SM/CKM picture Focus now shifts to measurements of time-dependent asymmetries in rare B decays which are dominated by Penguin diagrams in the SM and where New Physics could contribute to the asymmetries

66 sin2  From Penguin Modes: B 0  K 0

67 CP Asymmetry In Penguin Modes: B 0  K 0 full background continuum bkg Analysis based on 227 Million B B pairs Sample orthogonal to the non-resonant B  KKK 0 data

68 CP Asymmetry In Penguin Modes: B 0  K 0 B 0  K S B 0  K L

69 CP Asymmetry In Penguin Modes: B 0  K 0 KSKS Nsig=139  14 purity 0.63 pB*pB* Nsig= 36  15 KLKL purity 0.17 Belle 274M BB

70 CP Asymmetry In Penguin Modes: B 0  K 0  K 0  K S +  K L : S (  K 0 ) = ±0.33 ±0.09 C (  K 0 ) = ±0.22 ±0.09 ~2.2  away from SM  K S +  K L : S (  K 0 ) = ±0.33 ±0.09 C (  K 0 ) = ±0.22 ±0.09 ~2.2  away from SM Good tags Poor tags S = fit Good tags Belle 274 M BB

71 CP Asymmetry In Penguin Modes: B 0  / K 0 N sig =512  27 Belle 274M BB BaBar 227 M B B

72 CP Asymmetry In Penguin Modes: B 0  / K 0 Raw Asymmetry Good tags S = fit Belle 274M B B sin2  3.0  S =  0.18  0.04 C =  0.11  0.05

73 Results on sin2  from s-penguin modes All new! 2.7  from s-penguin to sin2  (cc) 2.4  from s-penguin to sin2  (cc)

74 Summary of sin2  eff

75 World Averages for sin2  and s-penguin modes 3.6  from s-penguin to sin2  (cc) No sign of Direct CP in averages Beginning to look suspicious but must wait for 5  /expt to get exciting

76 Projections for Penguin Modes K*K* 5  discovery region if non-SM physics is 30% effect 2004=240 fb =1.5 ab -1 Similar projections for Belle as well Projections are statistical errors only; but systematic errors at few percent level Luminosity expectations : f 0 K S K S  0  K S  ’K S KKK S

77 PEP II Luminosity Projections x ab -1

78 CP Asymmetries in b  c c d Modes Statistics limited, may get interesting in about 2 years !