.. Gabriella Sciolla Massachusetts Institute of Technology On behalf of the BaBar Collaboration APS/DPF Meeting Philadelphia, April 5 - 8, 2003 Cracking the Unitarity Triangle: B physics at BaBar

April 5, 2003B physics at BaBar G. Sciolla – M.I.T. All sides are ~ O(1)  measure independently: 2 sides: B mixing, V ub, V cb,… 3 angles: CPV in B decays The Beauty of the Unitarity Triangle      This allows us to: test CP sector of SM quantitatively CPV as a probe for New Physics

April 5, 2003B physics at BaBar G. Sciolla – M.I.T. Outline Introduction The experimental apparatus: PEP-II and BaBar CP violation in the B system: theory and analysis technique The angles: sin2  : the golden mode, the penguin modes, D *+ D *- The angle  : B 0       B 0   The angle  : progress in B +  D 0 CP K + The sides: Inclusive measurement of V ub Prospects for V td from b  d  Summary and conclusion

April 5, 2003B physics at BaBar G. Sciolla – M.I.T. The PEP-II accelerator Asymmetric B factory 9.0 GeV e - beam 3.1 GeV e + beam Peak luminosity Design: 3 x cm -2 s -1 Achieved: 5 x cm -2 s -1 Integrated Luminosity Delivered: 118 fb -1 Recorded: 113 fb -1 As of April 3, 2003: Results based on 89 M BB pairs

April 5, 2003B physics at BaBar G. Sciolla – M.I.T. The B A B AR Detector ) DIRC (PID) 1.5 T solenoid CsI(Tl) EMC Drift Chamber Instrumented Flux Return Silicon Vertex Tracker e + (3.1GeV) e - (9GeV) Tracking:  p T )/p T = 0.13% p T  0.45% DIRC: K-  separation: > 3.5  for p<3.5 GeV/c EMC:  E /E = 2.3% E -1/4  1.9%

April 5, 2003B physics at BaBar G. Sciolla – M.I.T. CP violation in B 0 decays mixing decay Scenario 1 Only one diagram contributes:  A CP (t) = - Im sin(  mt) CPV in interference between mixing and decays Im =sin2  sin2  etc. Scenario 2 More than one diagram contributes  both sin and cos terms will survive - S f : depends on Im sensitive to UT angles - C f : depends on | |, direct CP (f)(f)

April 5, 2003B physics at BaBar G. Sciolla – M.I.T. How to measure CPV at BaBar. Ingredient #1: Exclusive reconstruction Ingredient #3: Flavor tagging (coherent state) Ingredient #2:  t determination e-e-  (4S) B0B0 B0B0 e-e- ++ -- B reco B tag e+e+  z~  c  t ++ --

April 5, 2003B physics at BaBar G. Sciolla – M.I.T. The measurement of     

April 5, 2003B physics at BaBar G. Sciolla – M.I.T. B 0  charmonium K 0 The “golden channels”: Theoretically well understood Experimentally clean Relatively large BF (~10 -4 ) A CP (t) = sin2  sin  mt CP sample: ModeCPN event s J/  K s,  (2s)K s,  c K s,  c K s 1506 J/  K L J/  K *0 (K s  0 ) mixed147 Full CP sample2641 

April 5, 2003B physics at BaBar G. Sciolla – M.I.T. B flavor tagging Tagging parameters measured from data using B 0  flavor eigenstates in time dependent B 0 mixing analysis. Category  tag (%) w (%)  eff (%) Lepton 9.1    0.3 Kaon    0.4 Kaon    0.4 Inclusive 20.0    0.3 ALL 65.6   0.7 B0B0 D *- D0D0 l +l +   (soft) K +  B0B0 D *-   (hard) W+W+ 

April 5, 2003B physics at BaBar G. Sciolla – M.I.T. sin2  CP fit CP=+1CP=-1 sin(2  ) = ± stat ± syst Unbinned maximum likelihood fit to  t distribution 

April 5, 2003B physics at BaBar G. Sciolla – M.I.T. Testing the “usual assumptions” Assumptions made in the sin2  measurement: Same lifetime for B H and B L No CP/T/CPT violation in the mixing CP/T CPT SM z=0 SM Very good approximation in SM But can we test them?

April 5, 2003B physics at BaBar G. Sciolla – M.I.T. Fit for the “usual assumptions” Fit B  CP and B 0  flavor eigenstates floating  / , q/p, z and CP : 90% C.L. The “usual assumptions” work!  Direct limit on   Test of CPT invariance  Indirect CP in mixing

April 5, 2003B physics at BaBar G. Sciolla – M.I.T. Unitarity Triangle constraints sin2  vs indirect UT constraints: Excellent agreement This means: New Physics contribution is small OR New Physics is not small but does not appear in this particular decay because of accidental cancellations. sin2  from BaBar vs. indirect constraints  Observed CP asymmetry consistent with CKM mechanism being the dominant source of CPV at low energies Can we test this hypothesis?

April 5, 2003B physics at BaBar G. Sciolla – M.I.T. More measurements of sin2  Why do we need them? measure sin2  in many modes characterized by: completely different Feynman diagrams theoretically clean and well understood and compare results. Significant differences will be indication of New Physics. Modes under study: B  charmonium K 0 B 0   K S B 0   ’K S B 0  D*D* B 0  D*D 

April 5, 2003B physics at BaBar G. Sciolla – M.I.T. B 0   K S : the theory Pure penguin modes: b  sss |A/A|=1 within 4% Another clean measurement of sin2  ! A CP (  K S )~A CP (J/  K S ) If difference > few%  Clear signal of New PhysicsNew Physics  A CP (t)= - sin2  sin  m  t sssdsssd KSKS sssdsssd Grossman,Worah PLB 395, 241 (1997) Grossman, Isidori, Worah PRD 58, (1998) 

April 5, 2003B physics at BaBar G. Sciolla – M.I.T. sin2  in B 0   K S : the results Results: Fit with both S and C terms: Assuming no direct CP (C=0): Hints of New Physics? Compare S  Ks with sin2  (J/  K S )=0.73±  effect. S  Ks =  0.18 ± 0.51 ± 0.07 C  Ks =  0.80 ± 0.38 ± 0.12 S  Ks =  0.26 ± signal events  Background B 0 tag --- C+S __ S only

April 5, 2003B physics at BaBar G. Sciolla – M.I.T. sin2  in B 0   ’K S Another penguin dominated mode Tree is Cabibbo and color suppressed Compared to B   K S Larger Branching Fraction: BF BaBar = (5.54  0.52) x More challenging final state:  ’     and     ~70 candidates ’KS’KS sssdsssd b d s W–W– u u d ’KS’KS 

April 5, 2003B physics at BaBar G. Sciolla – M.I.T. CP fit of B 0   ’K S Results of CP fit: Hints of New Physics? Compare S ’Ks with sin2  (J/  K S )=0.73±  effect S ’Ks = 0.02  0.34  0.03 C ’Ks = 0.10  0.22  0.03 BaBar  Background B 0 tag

April 5, 2003B physics at BaBar G. Sciolla – M.I.T. B 0  D *+ D *- Tree measures sin2  from b  ccd transitions Penguin expected to be small in SM (<10%) But could be enhanced by New Physics Transversity analysis used to measure CP odd component: R  =0.07  0.06 (stat)  0.03 (syst)  Mainly CP even! 

April 5, 2003B physics at BaBar G. Sciolla – M.I.T. B 0  D *+ D *- : the CP fit CP fit: Compare with sin2  (J/  K S )=0.73  0.05 Im( ) =-0.310.430.13 = 0.980.250.09 N signal = 126  12  Indication for large penguin contribution

April 5, 2003B physics at BaBar G. Sciolla – M.I.T. sin2  summary Statistical fluctuation or first signs New Physics? 

April 5, 2003B physics at BaBar G. Sciolla – M.I.T. The measurement of     

April 5, 2003B physics at BaBar G. Sciolla – M.I.T.  from        Significant contribution from both diagrams: P/T ~ 1/3 from Br(B  K  )/Br(B   ) S   sin2  eff related to angle  through isospin C   direct CP violation T = TreeP = Penguin 

April 5, 2003B physics at BaBar G. Sciolla – M.I.T. B 0      : analysis technique K-  separation is a must Br(B 0  K +  - ) ~ 4 x Br(B 0   +  - ) * * PID gives >3.5  up to 3.5 GeV Continuum background rejected by Fisher discriminant Low branching fraction BR(B 0   +  - ) ~ 5 x PID and Fisher included in maximum likelihood fit      MC D 0    data Bkg MC m ES data sideband

April 5, 2003B physics at BaBar G. Sciolla – M.I.T. B 0      : the CP fit  No asymmetry seen in     yet… N  =157  20 

April 5, 2003B physics at BaBar G. Sciolla – M.I.T. B 0       the validation Extensive cross-checks: Possible two-body vertexing systematics CP asymmetry in the background Fit method Likelihood function Some examples: Measure mixing in B 0  K +  –  m d = (0.52  0.05) ps -1  OK! Measure  B in B 0   +  –  B = (1.56  0.07) ps  OK!   B = (1.56  0.07) ps  m B = (0.52  0.05) ps -1

April 5, 2003B physics at BaBar G. Sciolla – M.I.T. B 0       and B 0      Similar to B 0      … Measures both mixing-induced CP(  ) and direct CP …just more challenging! Not a CP eigenstate 4 configurations: B 0     , B 0      3  final state  combinatorics Analysis strategy Pseudo two-body analysis avoid interference regions of Dalitz plot Continuum background suppressed by NN Simultaneous fit for     and             

April 5, 2003B physics at BaBar G. Sciolla – M.I.T. B 0       and B 0      Combined Maximum Likelihood fit measures: BF(B 0   )= (22.6  1.8  2.2) BF(B 0   )= (7.3  1.3  1.3) and 6 other parameters related to CP: Indication for small penguins   N(   = 428  34N(  ) = 120  20

April 5, 2003B physics at BaBar G. Sciolla – M.I.T. B 0        )  the CP fit Time integrated direct CP: Time dependent CP: Asymmetry between rates: -- B backg. -- all backg.  First step towards a measurement of  in B   decays. Full Dalitz analysis in progress.

April 5, 2003B physics at BaBar G. Sciolla – M.I.T. Prospects for  Clean measurement will eventually come from B S  D + K - In the mean time B factories can constrain  using:    D 0 CP K  Theoretically clean (Gronau & Wyler, Dunietz 1991) Interference between b  u (cs) and b   c (us) Small accessible Branching Fractions ~ B 0  D (*)+   Theoretically clean measurement of 2  Interference between b  u (cd) and b  c (ud) B  K  Interference between penguin and tree diagrams Take ratios of Br’s to eliminate dependence on strong phases Model dependent - relies on assumptions of factorizaton, SU(3) 

April 5, 2003B physics at BaBar G. Sciolla – M.I.T. Isospin analysis Measurements: Progress in B   D 0 CP K  

April 5, 2003B physics at BaBar G. Sciolla – M.I.T. The measurement of the sides * * cbcd tdtb VV VV       B 0  

April 5, 2003B physics at BaBar G. Sciolla – M.I.T. Why another measurement of V ub ? sin2  is now very well known  (sin2  ) ~5% (BaBar+Belle) Measurement of the “decay side” ~ |V ub /V cb | is not as well known  (V cb ) ~ 5%  (V ub ) ~16-20% Better measurement of V ub needed for a more stringent test of CP side of Standard Model Indirect constraints vs sin2  world average

April 5, 2003B physics at BaBar G. Sciolla – M.I.T. A new measurement of V ub The idea: One B exclusively reconstructed (4K/fb -1 ) Inclusively measure Br(b  ul ) on recoiling B Many kinematical variables: p* lepton, Q 2, M X Reduce systematics measuring: B(X u l )/B(Xl ) Better purity and smaller model dependence! V ub p l * >1 GeV/c

April 5, 2003B physics at BaBar G. Sciolla – M.I.T. The result S/B ~ 1.7! V ub

April 5, 2003B physics at BaBar G. Sciolla – M.I.T. V ub inclusive: summary V ub This measurement: total error 13%

April 5, 2003B physics at BaBar G. Sciolla – M.I.T. B 0  0  B +  +  B 0  B   and B      (    ) + high energy  Continuum suppressed by NN PID rejects B  K*  EW penguin dominated by top quark:  BF(b  d  ) ~ |V td | 2  constraints on UT Mode90% CL (10 -6 )SM Expectation (10  6 )       < ± 0.21       < ± 0.40     <1.0~ 0.5 d Ali and Parkhomenko (hep-th ) V td

April 5, 2003B physics at BaBar G. Sciolla – M.I.T. Summary BaBar is attacking the UT from all sides and angles: …and much more in parallel sessions!  sin2  is well established golden mode used as calibration new modes: B 0   K S,  ’K S, D * D *,…   is coming… CPV in B 0      and B 0   V td from EW penguins B   complements mixing New V ub measurement The power of statistics!   is tough! B  D CP K -

April 5, 2003B physics at BaBar G. Sciolla – M.I.T. Conclusion Although, some interesting shifts observed in sin2  from penguin modes and D*D*: Hints of New Physics??? Statistics will tell… Despite the fierce attack, the Standard Model is still holding remarkably well… And much more data is coming: Run-3 in progress (>24 fb -1 so far) >500 fb -1 by 2006 >1 at -1 by 2009 if physics case remains compelling