1 Daniela Bortoletto Purdue University Introduction  SM expectations  Previous measurements The measurement of sin 2  at CDF  Signal reconstruction  Flavor tagging methods  Fit results and cross checks Future prospects The measurement of sin(2  ) University of Southampton July 199

2 SM with 3 generations and the CKM ansatz can accomodate CP if the complex phase  is  0  CP. Only =  0.023, A=0.819  are measured precisely. CP is one of the less well-tested parts of SM ( ,  /  in the Kaon system) CP asymmetries in the B system are expected to be large. Independent observations of CP in the B system can:  test the SM Introduction  lead to the discovery of new physics

3 The goal of B-physics is to over-constrain the unitarity triangle to test the CKM ansatz or to expose new physics B Physics and CKM matrix Unitarity triangle B  B  J/  K 0 s BKBK    (,)(,) (1,0)   (1-  -i  )(  +i  ) (0,0) B  /   B 0 -B 0 mixing V ud V ub * +V cd V cb * +V td +V tb * =0

4 Possible manifestations of CP violation can be classified as:  CP violation in the decay: It occurs in B 0 /B + decays if |A(f)/|A(f)|  1  CP violation in mixing: It occurs when the neutral mass eigenstates are not CP eigenstates (|q/p|  1)  CP violation in the interference between decays with and without mixing Mixing: V td introduces a complex phase in the box diagram Interfering amplitudes:  direct decay B 0  f  B 0  B 0 mixing followed by B 0  f CP violation in B decays B0B0 B0B0 f B0B0 B0B0 f V td V * td b b d d t t B0B0 B0B0 W W Box Diagram

5 Determination of sin(2  ) Color suppressed modes b  ccs. Dominant penguin contribution has the same weak phase  Negligible theoretical uncertainty Cabibbo suppressed modes b  ccd such as B 0 /B 0  DD,D * D *.  Large theoretical uncertainties due to the penguin contribution Penguin only or penguin dominated modes b  sss or dds. Tree contributions absent or Cabbibbo and color suppressed  penguin diagrams dominate  even larger theoretical uncertainties

6 B-factories at the  (4S) :  B 0 and B 0 mesons are produced in a coherent C=-1 state  time integrated CP asymmetry = 0.  Determination of CP needs A(  t ) where  t =t(CP)-t(tag) or  z =  c  t  Need good  z resolution pp and pp colliders: time integrated asymmetry does not vanish Since x d =0.732  (PDG98) Experimental considerations A CP is Maximum at t=2.2 lifetimes A CP (t) t Measurement of the asymmetry as a function of proper time A CP (t) is more powerful  Combinatoric background dominates small ct region

7 B 0 /B 0  J/  K 0 s For B 0 /B 0  J/  K 0 S we have CP(K 0 s )=1 and CP(J/  K 0 S )= -1. To reach a common final state the K 0 must mix  additional phase Asymmetry is directly related to sin2 . A CP (t)=sin[2(  M -  D )]sin  m d t =sin2  sin  m d t and sin2  = B 0 B 0 Mixing Ratio of K 0 -K 0 mixing

8  V ub /V cb =0.093 from semileptonic decays   K =2.28   B 0 -B 0 mixing  m d =0.472 ps -1  Limit on B s -B s mixing  m s >12.4 ps -1 Indirect determination of sin2  In SM the asymmetries in the B system are expected to be large S. Mele CERN-EP , 1998 finds sin2  =0.75  0.09 Parodi et al. sin2  =0.725  0.06 Ali et al. 0.52<sin2  <0.94

9 Measurement of A CP (t) requires:  Reconstruct the signal B 0 /B 0  J/  K 0 S  Measure proper decay time (not critical in pp colliders but useful)  Flavor tagging to determine if we have a B 0 (bd) or B 0 (bd) at production Tagging algorithms are characterized by an efficiency  and a dilution D. The measured asymmetry is A obs CP =D A CP  N tot = total number of events  N W = number of wrong tags  N R =number of right tags  D=2P-1 (P=prob. of correct tag) and D=1 if N W =0 D=0 if N W =N R  Best tagging methods has highest  D 2 Measurement accuracy Crucial factor

10 Assume you have 200 events  N=200  100 are tagged  N tag =100  tagging efficiency  =N tag /N tot =50% Of those 100 events  60 are right sign  N R =60  40 are wrong sign  N W =40 Dilution  D=(N R -N W )/(N R +N W )=(60-40)/100=20% Effective tagging efficiency   D 2 =( 0.5)(0.2) 2 =2% Statistical power of this sample  N  D 2 =200*0.02=4 events Tagging

11 Previous Measurements sin2  =3.2   0.5 Opal Z  bb D. Ackerstaff et al. Euro. Phys. Jour. C5, 379 (1998) (Jan-1998) Flavor tagging techniques:  Jet charge on opposite side jet  Jet charge on same side B  Vertex charge of a significantly separated vertex in the opposite hemisphere 24 J/  K 0 S candidates Purity  60 %

12 Previous Measurements sin2  =1.8  1.1  0.3 CDF pp  bb Abe et al. PRL. 81, 5513 (1998) (June 1998) 198  17 B 0 /B 0  J/  K 0 S candidates with both muons in the SVX ( S/B  1.2). Measure asymmetry with Same side tagging Dsin2  =0.31  1.1  0.3. Using D=0.166  (data)  (MC) from mixing measurement + MC

13 Run I CDF detector Crucial components for B physics:  Silicon vertex detector  proper time measurements  impact parameter resolution:  d =(13+40/p T )  m  typical 2D vertex error  (r-  )  60  m  Central tracking chamber  mass resolution. B=1.4T, R=1.4m (  p T /p T )2=(0.0066) 2  (0.0009p T ) 2 typical J/  K 0 S mass resolution  10 MeV/c 2  Lepton detection (triggering and tagging)

14 CDF updated measurement Add candidate events not fully reconstructed in the SVX  Double the signal to 400 events but additional signal has larger  (ct) Use more flavor tag methods to establish b flavor at production Check  D 2 with mixing analysis Use a maximum likelihood method to combine the tags. Weight the events:  in mass (B peak versus sidebands)  in lifetime (more analyzing power at longer lifetimes)  in tagging probability  Account for detector biases B background  c   (B 0 )=1.56  s

15 Signal  J/    -  + require two central tracks with matching hits in the muon chambers  K 0 S   -  + use long lifetime c  (K 0 S )=2.7 cm to reject background by requiring L xy /  (L xy )>5  Perform 4-track fit assuming B  J/  K 0 S  Constrain  -  + and  -  + to m(K 0 S ) and m(J/  ) world average respectively  K 0 S points to B vertex and B points to primary vertex Background  cc production  prompt J/  ( not from b decays) + random K 0 S or fake  bb production  J/  +X, random K 0 S or fake J/  K 0 S Event selection B decay ++ -- ++ -- primary

16 J/  K 0 S Signal sample CDF run1, L=110 pb -1  202 events with both muons in SVX   (ct)  60  m.  193 with one or both muons NOT in SVX   (ct)   m Plot normalized mass M  -M B / error on M Both  in SVX One or Both  not in SVX 395  31 events S/B=0.7 S/B=0.9 S/B=  18 events 193  26

17 We must determine if we had a B 0 or a B 0 at the time of production. Opposite-side flavor tagging (OST)  bb produced by QCD  Identify the flavor of the other b in the event to infer the flavor of the B 0 /B 0  J/  K 0 S. At CDF  60% loss in efficiency due the acceptance of the other B 0.  Lepton tagging :  b  + X  b  b  - X  b  Jet charge tag :  Q(b-jet) > 0.2  b  Q(b-jet) <- 0.2  b Flavor tagging methods B 0 (bd)  J/  K 0 S ++ -- ++ -- Opposite side b + Q(b-jet)>0.2 K0SK0S

18 Identify the flavor of the B 0 /B 0  J/  K 0 S through the charge of the opposite b-jet Jet definition allows for wide low P T jets:  Cluster tracks by invariant mass ( Invariant mass cutoff  5 GeV/c 2 )  remove track close to primary B Weight tracks by momentum and impact parameter  p T = track momentum  T P = probability track comes from primary vertex (low T p more likely track comes from B ) Jet Charge Flavor tagging Q jet >0.2  b Q jet <-0.2  b |Q jet |<0.2  no tag  =(40.2  3.9)% Q jet in B   J/  K  -Q K *Q Jet

19 Soft Lepton Flavor tagging Identify the flavor of the B 0 /B 0  J/  K 0 S through the semileptonic decay of the opposite B.  b  - X b  + X Electron: central track (P T >1 GeV/c) matched to EM cluster Muon: central track (P T >2 GeV/c) matched to muon stub Efficiency  6% Source of mistags:  Sequential decay b  c  X  Mixing  Fake leptons Opposite side tagging was used at CDF to study B 0 B 0 mixing Ph. D. Thesis O. Long and M. Peters  m d =0.50  0.05(stat)+0.05(sys)  ps -1  m d =0.464   ps -1 (PDG)

20 Same side tagging d u b B0B0 -- s u b BSBS K-K- d s b B0B0 K0K0 u s b B-B- K+K+ u d b B-B- ++ No K/  separation  higher correlation for charged B Problems with opposite side tagging  Opposite b-hadron is central only  40 % of the time  If opposite b-hadron is B 0 d or B 0 s mixing degrades tagging Same side flavor tagging (SST). Exploits the correlation between the charge of nearby  and the b quark charge due to fragmentation or B** production (Gronau,Nippe,Rosner)

21 Correlation due to excited B** production B** + (I=1/2) resonance B** -  B 0  - Implementation of SST: Search for track with minimum P t rel in b-jet cone SST has higher efficiency (  70 %) than OST Same side tagging Candidate track P t >400 MeV/c d/  <3 wrt primary vertex PBPB B 0  J/  K 0 S ++ -- ++ -- Same side pion negative charge d bb d u B0B0 -- B **- P tr rel P B + P tr P tr Cone  R=0.7 B direction

22 Tagger calibration Use B   J/  K  sample to determine the efficiency  and the dilution D of the sample:  Charge of the K   b or b  Decay mode and trigger analogous to B  J/  K 0 S  B + /B - does not mix

23 Calibration Jet Charge Tagging Sample of 988 J/  K  events  273 right-sign events  175 wrong-sign events Tagging efficiency:  =N tag /N tot =(44.9  2.2)% Tagging dilution: D=N R -N W /N R +N W = (21.5  6.6)% Mistag fraction: w=(39.2  3.3)%

24 Calibration of Soft Lepton Tagging Sample of 988 J/  K  events  54 right-sign events  12 wrong-sign events Tagging efficiency:  =N tag /N tot =(6.5  1.0)% Tagging dilution: D=N R -N W /N R +N W =(62.5  14.6)% Mistag fraction: w=(18.8  7.3)%

25 Same Side Tagging Calibration D + =0.27  0.03(stat)+0.02(syst) D 0 =0.18  0.03(stat)+0.02(syst) D=0.166  both muons in SVX D=0.174  one/both muons NOT in SVX Use inclusive + D* sample. This sample was used for the determination of B0/B0 mixing in F. Abe at al Phys. Rev. Lett. 80, 2057(1998) and Phys. Rev. D 59 (1999) Use MC to scale for different P T spectrum in J/ K 0 S wrt + D/D* sample

26 Combining Dilution: Define D=qD where q=-1 (b-quark), q=+1 (b-quark) and q=0 (no tagging) then D eff =(D 1 +D 2 )/(1+D 1 D 2 )  Tags agree D eff =(D 1 +D 2 )/(1+D 1 D 2 ) Example SST and JCT D=36.8%  Tags disagree D eff =(D 1 -D 2 )/(1-D 1 D 2 ) Example SST and JCT D=5.1%  Each event is weighted by the dilution in the fit  Same side SVX  =(35.5  3.7)%D= (16.6  2.2 )%  Same side non-SVX  =(38.1  3.9)% D= (17.4  3.6 )%  Soft lepton all  = (5.6  1.8)% D= (62.5  14.6)%  D 2 = (2.2  1.0)%  Jet charge all  = (40.2  3.9)% D= (23.5  6.9 )%  D 2 = (2.2  1.3)% (if SLT do not use Jet charge)  D 2 = (6.3  1.7)% Flavor Tagging Summary Combined flavor tagging power including correlations and multiple tags: A sample of 400 events has the statistical power of 25 perfectly tagged events  D 2 = (2.1  0.5)%

27 Results Muons from J/  decay in Silicon vertex detector  High resolution ct  Asymmetry vs ct Data with low resolution ct measurement  Time integrated A CP A CP =0.47 sin2  If  m d is fixed to the PDG world average (  m d =0.464  ps -1 ), the minimization of the likelihood function yields: sin2  =0.79  0.39(stat)  0.16(syst) Statistical error >systematics. Float  m d sin2  = (stat.+sys.)

28 Systematic errors :  Dilution 0.16 (limited by the statistics of the calibration sample)  Other sources  0.02 Cross checks:  Float  m d :  Measure time integrated asymmetry: sin2  =0.71  0.63  Only SVX events and SST: sin2  =1.77  1.02  Verify errors and pulls with toy MC Systematic errors and cross checks 1  contours Mean:0.44  =1.01 error Pull

29 As a check we can apply the multiple flavor tagging algorithm to the measurement of mixing in B 0  J/  K 0* decays. The data is consistent with the expected oscillations Measurements:   m d =(0.40  0.18) ps -1  D K =0.96  0.38 dilution due to incorrect K-  assignments Expectation:   m d =(0.464  0.018) ps -1  D K =0.8  0.3 Cross checks

30 Measurement  Feldman-Cousin frequentist (PRD 57, 3873, 1998) 0<sin2  <1 at 93 % CL  Bayesian (assuming flat prior probability in sin2  ) 0<sin2  <1 at 95 % CL  Assume true value sin2  =0. Probability of observing sin 2  >0.79 =3.6 %. Confidence Limits on sin(2  ) Scan of the likelihood function sin2  sin2  = (stat.+sys.)

31 Results in  and  plane CDF sin2  measurements  fourfold ambiguity { ,  /2- ,  + , 3  /2-  }  Solid lines are the 1  bounds, dashed lines two solutions for  for  0 (shown)  two solutions for  >1,  <0 (not-shown) 1  bounds

32 B-factories at  (4S) pp colliders: BABAR estimates J/  K 0 S  (bb )  50  b but  (bb)/  (total)  Tagging factor (Run1)  (Run II-with Kaon tagging) N(B 0 /B 0  J/  K 0 S ) =400 /100 pb -1 (Run 1)  /2 fb -1 (run II  +e triggers) S/B =0.9 in B 0 /B 0  J/  K 0 S  ( sin2  )=0.4  0.08 in Run II  (bb )  1.05 nb but  (bb)/  (total)  0.26 Tagging factor (MC) N(B 0 / B 0  J/  K 0 S ) =660 / 30fb -1 S/B=16 in B 0 /B 0  J/  K 0 S  (sin2  )=0.12

33 CDF reach in run II for sin2  Run I value with Run II projected error sin2  =0.79  0.084

34 Summary CDF measures: Mixing mediated CP will be measured precisely by CDF/D0 /BaBar/Belle/HeraB by the beginning of the new century Precise determination of sin2  is a key step towards understanding quark mixing and CP sin2  =