1. Wouter Verkerke, UCSB CP Violation Measuring matter/anti-matter asymmetry with BaBar Wouter Verkerke University of California, Santa Barbara

2. Wouter Verkerke, UCSB Outline of this talk Introduction to CP violation –A quick review of the fundamentals. –CP-violating observables Experiment and analysis techniques –Accelerator and detector (PEP-II and BaBar) –Event selection, measuring time dependent CP asymmetries Selection of (recent) BaBar CP violation results –The angle  –The angle  –The angle 

3. Wouter Verkerke, UCSB Why is CP violation interesting? It is of fundamental importance –Needed for matter/anti-matter asymmetry in the universe –Standard Model CP-violation in quark sector is far too small to explain matter asymmetry in the universe History tells us that studying symmetry violation can be very fruitful CP violating processes sensitive to phases from New Physics Can CP-violation measurements at the B factories break the Standard Model in this decade? –Measure phases of CKM elements in as many ways as possible

4. Wouter Verkerke, UCSB In the Standard Model, the CKM matrix elements V ij describe the electroweak coupling strength of the W to quarks –CKM mechanism introduces quark flavor mixing –Complex phases in V ij are the origin of SM CP violation The Cabibbo-Kobayashi-Maskawa matrix u d t c bs CP The phase changes sign under CP. Transition amplitude violates CP if V ub ≠ V ub *, i.e. if V ub has a non-zero phase Mixes the left-handed charge –1/3 quark mass eigenstates d,s,b to give the weak eigenstates d’,s,b’. 3 2 2 3 =cos( c )=0.22

5. Wouter Verkerke, UCSB The Unitarity Triangle – Visualizing CKM information from B d decays The CKM matrix V ij is unitary with 4 independent fundamental parameters Unitarity constraint from 1st and 3rd columns:  i V * i3 V i1 =0 Testing the Standard Model –Measure angles, sides in as many ways possible –SM predicts all angles are large CKM phases ( in Wolfenstein convention ) u d t c bs

6. Wouter Verkerke, UCSB Observing CP violation So far talking about amplitudes, but Amplitudes ≠ Observables. CP-violating asymmetries can be observed from interference of two amplitudes with relative CP-violating phase –But additional requirements exist to observe a CP asymmetry! Example: process B  f via two amplitudes a 1 + a 2 = A. weak phase diff.   0, no CP-invariant phase diff. BfBf A A BfBf a1a1 a1a1 a2a2 a2a2 A=a 1 +a 2 ++ -- |A|=|A|  No observable CP asymmetry

7. Wouter Verkerke, UCSB Observing CP violation Example: process B  f via two amplitudes a 1 + a 2 = A. weak phase diff.   0, CP-invariant phase diff.   0 BfBfBfBf A=a 1 +a 2   ++ -- |A||A|  Need also CP-invariant phase for observable CP violation a1a1 a1a1 a2a2 a2a2 A A

8. Wouter Verkerke, UCSB  CP violation: decay amplitudes vs. mixing amplitudes Interference between two decay amplitudes gives two decay time independent observables –CP violated if BF(B  f) ≠ BF(B  f) –CP-invariant phases provided by strong interaction part. –Strong phases usually unknown  this can complicate things… Interference between mixing and decay amplitudes introduces decay-time dependent CP violating observables –B d mixing experimentally very accessible: Mixing freq m d 0.5 ps -1, =1.5 ps –Interfere ‘B  B  f’ with ‘B  f’ –Mixing mechanism introduces weak phase of 2 and a CP-invariant phase of /2, so no large strong phases in decay required 2  m d  2 B N(B 0 )-N(B 0 ) N(B 0 )+N(B 0 )

9. Wouter Verkerke, UCSB A CP (t) from interference between mixing+decay and decay Time dependent CP asymmetry takes Ssin(m d t)+Ccos(m d t) form C=0 means no CP violation in decay process If C=0, coefficient S measures sine of mixing phase mixingdecay If only single real decay amplitude contributes 

10. Wouter Verkerke, UCSB CKM Angle measurements from B d decays Sources of phases in B d amplitudes* The standard techniques for the angles: *In Wolfenstein phase convention. AmplitudeRel. MagnitudeWeak phase ‘b  c’Dominant0 ‘b  u’Suppressed  B=2 (mixing) Time dependent  B 0 mixing + single b  c decay B 0 mixing + single b  u decay Interfere b  c and b  u in B ± decay. The distinction between  and  measurements is in the technique. bubu tdtd

11. Wouter Verkerke, UCSB The PEP-II B factory – specifications Produces B 0 B 0 and B + B - pairs via Y(4s) resonance (10.58 GeV) Asymmetric beam energies –Low energy beam 3.1 GeV –High energy beam 9.0 GeV Boost separates B and B and allows measurement of B 0 life times Clean environment –~28% of all hadronic interactions is BB BB threshold  (4S)

12. Wouter Verkerke, UCSB The PEP-II B factory – performance Operates with 1600 bunches –Beam currents of 1-2 amps! Continuous ‘trickle’ injection –Reduces data taking interruption for ‘top offs’ High luminosity –6.6x10 33 cm -2 s -1 –~7 BB pairs per second –~135 M BB pairs since day 1. Daily delivered luminosity still increasing Projected luminosity milestone – 500M BB pairs by fall 2006.

13. Wouter Verkerke, UCSB Silicon Vertex Detector (SVT) Drift chamber (DCH) Electromagnetic Calorimeter (EMC) 1.5 T Solenoid Instrumented Flux Return (IFR) SVT: 5 layers double-sided Si. DCH: 40 layers in 10 super- layers, axial and stereo. DIRC: Array of precisely machined quartz bars.. EMC: Crystal calorimeter (CsI(Tl)) Very good energy resolution. Electron ID,  0 and  reco. IFR: Layers of RPCs within iron. Muon and neutral hadron (K L ) The BaBar experiment Outstanding K  ID Precision tracking (t measurement) High resolution calorimeter Data collection efficiency >95% Detector for Internally reflected Cherenkov radiation (DIRC)

14. Wouter Verkerke, UCSB Silicon Vertex Detector Beam pipe Layer 1,2 Layer 3 Layer 4 Layer 5 Beam bending magnets Readout chips

15. Wouter Verkerke, UCSB Čerenkov Particle Identification system Čerenkov light in quartz –Transmitted by internal reflection –Rings projected in standoff box –Thin (in X 0 ) in detection volume, yet precise…

16. Wouter Verkerke, UCSB Selecting B decays for CP analysis Exploit kinematic constraints from beam energies –Beam energy substituted mass has better resolution than invariant mass –Sufficient for relatively abundant & clean modes  ( m ES )  3 MeV  (E)  15 MeV m es >5.27 GeV N = 1506 Purity = 92% m es (GeV) m es EE 2

17. Wouter Verkerke, UCSB Measuring (time dependent) CP asymmetries B 0 B 0 system from Y(4s) evolves as coherent system –All time dependent asymmetries integrate to zero! Need to explicitly measure time dependence –B 0 mesons guaranteed to have opposite flavor at time of 1 st decay Can use ‘other B 0 ’ to tag flavor of B 0 CP at t=0 B-Flavor Tagging Vertexing t=1.6 ps  z 250 m  z  170 m  z  70 m  z/c Tag-side vertexing ~95% efficient Exclusive B Meson Reconstruction

18. Wouter Verkerke, UCSB Flavor tagging Leptons : Cleanest tag. Correct >95% Kaons : Second best. Correct 80-90% b c ee WW b c e+e+ W+W+ b WW c s u d KK W+W+ b W+W+ c s u d K+K+ WW Full tagging algorithm combines all in neural network Four categories based on particle content and NN output. Tagging performance = 28% Determine flavor of B tag  B CP (t=0) from partial decay products efficiencymistake rate

19. Wouter Verkerke, UCSB B 0 (t) A CP (t) = Ssin(m d t)+C  cos(m d t) sin2 Dsin2 Putting it all together: sin(2) from B 0  J/ K S Effect of detector imperfections –Dilution of A CP amplitude due imperfect tagging –Blurring of A CP sine wave due to finite t resolution Measured & Accounted for in simultaneously unbinned maximum likelihood fit to control samples –measures t resolution and mistag rates. –Propagates errors  Actual sin2 result on 88 fb -1 Imperfect flavor tagging Finite t resolution tt tt

20. Wouter Verkerke, UCSB Interference between mixing and single real decay –Interfering amplitudes of comparable magnitude  the observable asymmetry is large (A CP of order 1) Extraordinarily clean theory prediction (~1% level) –Single real decay amplitude  all hadronic uncertainty cancel –A CP (t) = sin(2) sin(m d t) Experimentally easy –‘Large’ branching fraction O(10 -4 ) –Clear signature (J/  l + l - and K S   +  - ) B-factory ‘flagship’ measurement: sin2 from J/ K S  B 0 Mixing……followed by………Decay Decay B0B0 b d d s c c W+W+ V cb V cs J/ KsKs *  c c d s W+W+ V cb V cs J/ KsKs * 

21. Wouter Verkerke, UCSB ‘Golden’ measurement of sin2 sin2 = 0.76  0.074 Combined result (88 fb -1, 2001) sin2 = 0.741  0.067  0.034 || = 0.948  0.051  0.030 (stat)(syst) B 0  (cc) K S (CP=-1) B 0  (cc) K L (CP=+1) sin2 = 0.72  0.16 No evidence for cos(mt) term

22. Wouter Verkerke, UCSB Constraints on the apex of the Unitarity Triangle. Standard Model interpretation   Method as in Höcker et al, Eur.Phys.J.C21:225-259,2001  = (1- 2 /2)  = (1- 2 /2)

23. Wouter Verkerke, UCSB Standard Model interpretation   Method as in Höcker et al, Eur.Phys.J.C21:225-259,2001 Latest results including the Belle experiment. One solution for  is very consistent with the other constraints. 4-fold ambiguity because we measure sin(2), not  1 2 4 3 The CKM model for CP violation has passed its first precision test! There is still room for improvement: measurement is statistics dominated Summer ’04 data  2-3 x 88fb -1

24. Wouter Verkerke, UCSB B-factory measurements of sin2 Going beyond the ‘golden’ modes –Consistency requires S=sin2, C=0 for all B 0 decay modes for which the weak phase is zero. –Decay modes dominated by the b  s penguin may meet these criteria –Measure A CP (t) from interference between mixing + b  s decay and b  s decay Loop diagrams are sensitive to contributions from new physics –Look for deviations of S=sin2  

25. Standard model expectation for sin(2) from b  s penguins B0K0B0K0 B 0  ’K 0 B00K0B00K0 Experimentally best modes: SM contributions that spoil S = sin2 u-quark penguin (weak phase = !) but relative CKM factor of ~0.02 u-quark tree (different phase) u /u / u /u / *Grossman, Ligeti, Nir, Quinn. PRD 68, 015004 (2003) and Gronau, Grossman, Rosner hep-ph/0310020 I II III (I) (I, II & III)(II & III) SM sin2 from SU(3) B0K0B0K0 <0.25 B 0  ’K 0 <0.35 B00K0B00K0 <0.20 these limits will improve with additional data  

26. Wouter Verkerke, UCSB b  s penguin measurements ModeBF(B  f) x10 -6  i BF i x10 -6 Reco. Efficiency Purity Tagged signal Events 81fb -1 115fb -1 J/K s 44036.044%97%940 ’K s 3310.623%~60%110 KsKs 41.442%~80%~34~48 0Ks0Ks 64.117%~50%~83 Experimentally more difficult Branching fractions smaller, more irreducible background B 0  ’K S B0  KSB0  KS B 0  K S  0

27. Wouter Verkerke, UCSB sin2 from b  s penguin measurements ’ ’K s BaBar 0.02  0.34  0.03 K s BaBar 0.45  0.43  0.07 b  s penguin average Babar 0.27  0.22  0 K s BaBar 0.48 ( +0.38 )  0.11 –0.47 sin2 from B 0  (cc) K S

28. Wouter Verkerke, UCSB sin2 from b  s penguin measurements ’ ’K s BaBar 0.02  0.34  0.03 Belle0.43  0.27  0.05 Ave0.27  0.21 K s BaBar 0.45  0.43  0.07 Belle –0.96  0.50 ( +0.09 ) Ave–0.14  0.33 K + K - K s non-resonant Belle 0.51  0.26  0.05 ( +0.18 ) b  s penguin average Babar and Belle 0.27  0.15 –0.00 –0.11  0 K s Babar 0.48 ( +0.38 )  0.11 –0.47 sin2 from B 0  (cc) K S (My naïve averages)

29. Wouter Verkerke, UCSB sin2 : b  s penguin modes Current naïve world averages S = 0.27 ± 0.15 (~3  below J/K s S = 0.74 ± 0.05). C = 0.10 ± 0.09 Still very early in the game –Measurements are statistics limited. Errors smaller by factor 2 in 2-3 years. –Standard Model pollution limits from SU(3) analysis will also improve with more data.

30. Wouter Verkerke, UCSB The angle  from B   Determination of : Observe A CP (t) of B 0  CP eigenstate decay dominated by b  u –Interference between mixing+b  u decay and b  u decay –Textbook example is B 0   +  . If the above b  u tree diagram dominates the decay A CP (t)=sin(2)sin(m d t). b  u decay V ub  B 0 Mixing  sin2

31. Wouter Verkerke, UCSB The angle  - the penguin problem Turns out the dominant tree assumption for     is bad. –There exists a penguin diagram for the decay as well –Magnitude of penguin can be estimated from B  K +  - (dominated by SU(3) variation of this penguin) –Penguin amplitude is large, contribution to B      could be ~30%! Including the penguin component (P) in Coefficients from time-dependent analysis penguin decay tree decay V ub V td /V ts   s Ratio of amplitudes |P/T| and strong phase difference  can not be reliably calculated Unknown phase shift  

32. Wouter Verkerke, UCSB Disentangling the penguin: determining 2 Gronau & London: Use isospin relations –Measure all isospin variations of B   – B 0   +  -, B 0   +  -, B 0   0  0, B 0   0  0 B -   -  0 = B +   +  0 –Weak phase offset 2 can be derived from isospin triangles Complicated… - 

33. Wouter Verkerke, UCSB Disentangling the penguin: the Grossman-Quinn bound Easy alternative to isospin: Grossman-Quinn bound –Look at isospin triangles and construct upper limit on  –Minimum required input: BF(B      0 ) and limit on BF(B 0   0  0 ) –Works best if B 0   0  0 is small –Experimental advantage: no flavor tagging in B   0  0 Measure B 0   0  0 ! ‘~10 -5 ’ ‘~10 -6 ’

34. Wouter Verkerke, UCSB the Grossman-Quinn bound on  for B 0   B 0   0  0 is observed! (4.2) GQ Bound using world averages –  0  0 : (1.9±0.5)x10 -6 –  ±  0 : (5.3±0.8)x10 -6  0  0 large, thus GQ bound not very constraining –Isospin analysis required for  0  0 ! Plots are after cut on signal probability ratio not including variable shown, optimized with S/sqrt(S+B). [BELLE: (1.7±0.6±0.2)x10 -6, 3.4]

35. Wouter Verkerke, UCSB Alternatives to B   for determination of  There are other final states of b  u tree diagram, e.g. –B    (Dalitz analysis required) –B    (Vector-vector  multiple amplitudes) B   +  - analysis –3 helicity amplitudes: Longitudinal (CP-even), 2 transverse (mixed CP) –Looks intractable, but entirely longitudinally polarized*! –  +   is basically a CP-even state with same formalism as  +  . *As predicted by G.Kramer, W.F.Palmer, PRD 45, 193 (1992). R.Aleksan et al., PLB 356, 95 (1995).

36. Wouter Verkerke, UCSB the Grossman-Quinn bound for B 0   The Grossman-Quinn bound for B 0   (assuming full longitudinal polarization) (BaBar) (Belle)

37. Wouter Verkerke, UCSB Alpha summary The  system: large penguin pollution –We have seen B 0   0  0 ! –Current GQ bound: –Full isospin analysis required! The  system: small penguin pollution –Polarization is fully longitudinal (as predicted). –Current GQ bound: –Bound may improve as additional data becomes available –Time-dependent  +   results (measures sin(2+2)) coming soon. There are more techniques than  and  –e.g. Dalitz analysis of 

38. Wouter Verkerke, UCSB The angle  Measuring  = Measuring the phase of the V ub –Main problem: V ub is very small: O( 3 ) –Either decay rate or observable asymmetry is always very small. Conventional wisdom: measuring  at B factories is difficult/impossible. –Gamma is the least constrained angle of the Unitarity Triangle Current attitude: we should try. –There are new ideas to measure Dalitz decays, 3-body decays,…) –New experimental data suggest color suppression is less severe, which eases small rate/asymmetry problem somewhat –B-Factories produce more luminosity than expected (BaBar & Belle approaching O(200) fb -1 by Summer ’04 time )

39. Wouter Verkerke, UCSB The angle : B  DK Strategy I: interfere b  u and b  c decay amplitudes –D 0 /D 0 must decay to common final state to interfere Ratio of decay B amplitudes  r b is small: O(10 -1 ) r b is not well measured, but important –r b large  more interference  more sensitivity to   color suppression  R u is the left side of the Unitarity Triangle (~0.4). F CS is (color) suppression factor ([0.2-0.5], naively1/3)

40. Wouter Verkerke, UCSB  from B  DK – Two approaches Approach I: D 0 /D 0 decay to common CP eigenstate –‘Gronau, London & Wyler’ –D 0 /D0 decay rate same Approach II: D 0 /D 0 decay to common flavor eigenstate –‘Atwood, Dunietz & Soni’ –Use D 0 /D 0 decay rate asymmetry to compensate B decay asymmetry ` Complementary in sensitivity –GLW: large BF: O(1±r b ), small A CP : O(r b ) –ADS: small BF: O(r b 2 ), large A CP : O(1) Branching fractions small (0.1%-1%) CKM favored Doubly Cabibbo suppressed (by factor O(100))

41. Wouter Verkerke, UCSB B  DK Observables – Gronau-London-Wyler There are more observables sensitive to  than A CP –Absolute decay rate also sensitive to , but hard to calculate due to hadronic uncertainties –GLW: measure ratio of branching fractions: hadronic uncertainties cancel! –Experimental bonus: many systematic uncertainties cancel as well –Bottom line: 2 observables each for CP+ and CP- decays 3 independent observables (R +, R -, A + =-A - ), 3 unknowns (r b,  b, )

42. Wouter Verkerke, UCSB B  DK : GLW results Result for B-  D 0 K - in 115 fb-1 Results for CP-odd modes in progress (R -, A - ) D 0   background GLW method: large BF, small A CP

43. Wouter Verkerke, UCSB B  DK : The Atwood-Dunietz-Soni method Two observables, similar to GLW technique –Ratio of branching fractions and A CP D 0  K +  - : 2 observables (A, R), 3 unknowns (r b,  b + d, ) –Insufficient information to solve for  –Can add other D 0 decay modes, e.g. D 0  K +  -  0  4 observables (2xA, 2xR), 4 unknowns (r b,  b + DKp,  b + DKpp0, ) Expected BF is ~510 -7 – very hard! –Expect observable O(10) events in 100M BB events –Unknown values of , r b,  b add O(10) uncertainty of BF estimate –Measurement not attempted until now

44. Wouter Verkerke, UCSB  from Atwood-Dunietz-Soni method: B -  [K +  - ] D0 K - : results Newly developed background suppression techniques give us sensitivity in BF = O(10 -7 ) range BF 5x10 -7  ~10 events But we don’t see a signal! –Destructive interference, r b is small, or just unlucky? Cannot constrain  with this measurement… –But BF proportional to r b 2  results sets upper limit on r b MC yield prediction with BF=7x10 -5 : 12 evts Yield in 115 fb-1 of data: 1.1  3.0 evts No assumptions: r b < 0.22 (90% C.L.)  from CKM fit : r b < 0.19 (90% C.L.) (95% C.I. region) ADS method: small BF, large A CP

45. Wouter Verkerke, UCSB B  DK : prospects for B-factories at 500 fb -1 Combine information on  from various sources Example study –Assume =75 o,  b =30 o,  d =15 o –Consider various scenarios GLW alone  r b =0.3 =75 o,  b =30 o,  d =15 o 33 22 11 GLW  2

46. Wouter Verkerke, UCSB  2 B  DK : prospects for B-factories at 500 fb -1 Combine information on  from various sources Scenarios –GLW alone –GLW+ADS(K) –GLW+ADS(K) + d from CLEO-c ADS/GLW combination powerful There are additional information not used in this study, e.g. –GLW: D*0K,D0K*,D*0K* –ADS: K 0,K3 –sin() from D*, D 0 K 0, DK,…  r b =0.3 =75 o,  b =30 o,  d =15 o 33 22 11 11 o GLW GLW +ADS GLW+ADS +CLEO-c

47. Wouter Verkerke, UCSB B  DK : prospects for B-factories at 500 fb -1 Combine information on  from various sources r b is critical parameter  22 r b =0.1 r b =0.2 r b =0.3 =75 o,  b =30 o,  d =15 o 11 22 33 33 33 22 22 11 11 11 o 23 o 67 o

48. Wouter Verkerke, UCSB Gamma summary The B  DK program is underway –Measurements for GLW methods in progress (B  D(*)0 K(*)-) –First measurement of ADS method (B  [K +  - ]K - ) –ADS and GLW techniques powerful when combined –Final results depends strongly on r b Other  methods in progress as well –Dalitz analyses of B -  D 0 (K S     )K -, B  DK –Time dependent analysis of B  D* - (mixing + V ub decay) |sin(2+)|>0.57 (95% C.L.)) –Analysis of B 0  D (*)0 K (*)0 There is no ‘golden’ mode to measure  –All techniques are difficult and to 1 st order equally sensitive. –Combine all the measurements and hope for the best

49. Wouter Verkerke, UCSB Concluding remarks The CKM model for CP violation passed it’s first test (sin2). –Future measurements of sin2 from B0  (cc)K S will continue improve constraints on apex of unitarity triangle The b  s penguin measurement of sin2 offers a window to new physics. –Another 2-3 years worth of data will clarify current 3 discrepancy We are cautiously optimistic that we can measure  now that B   decay turns out have little penguin pollution Measurement of  just starting. Success depends on many unknowns… BaBar is projected to double its current dataset by 2006