Measurement of  2 /  using B   Decays at Belle and BaBar Alexander Somov CKM 06, Nagoya 2006 Introduction (CP violation in B 0   +   decays) Measurements in B 0   +   B      0 B 0   0  0  2 constraint from an Isospin analysis

CP Violation in B 0   +  decays CP Violation in B 0   +   decays d W + b u d u d B0B0 + (+)+ (+)  - (  - ) B0B0 b d d d u u + (+)+ (+) W + u,c,t TreePenguin direct CP violation determine  2 using isospin analysis Tree onlyTree + Penguin Direct CPVMixing induced CPV

B 0   +   relatively clean signal, large penguin contribution B 0     not a CP eigenstate, time-dependent Dalitz analysis B 0   +   Advantages of  +   :  small penguin contribution due to relatively small [Babar, hep-ex/ ]  relatively large measured branching fraction b  u for b  u process Three main decays used for the extraction of  2 (  )  2 /   2 /  measurement

  +   is a VV state 3 helicity states (three helicity amplitudes should be considered) ++    H0H0 H+H+ HH longitudinal polarization Fortunately, longitudinal polarization dominates Complications: BaBar: hep-ex/ PDG Belle: PRL96, CP analysis in B   +   decays

Complications (cont’d):  ‘Dirty’ final state  +     +  0    0 ;  (  ) = 150 MeV large backgrounds  I = 1 contribution due to finite width of  [A.F.Falk, Z.Ligeti, Y. Nir, H.Quinn PRD69, , 2004]  Contribution from EW penguin CP analysis in B   +   decays (cont’d)

Constraint on  2 /   Extract  2 using an Isospin analysis (similar to  +   analysis) - ‘model independent’ approach  The penguin contribution can also be bound using flavor SU(3) relations [ M.Beneke, M.Gronau, J.Rohrer, M.Spranger hep-ph/ ] [M.Gronau, O.F.Hernandez,D.London,J.L.Rosner, Phys.Rev.D50,4529,1994]

22  Measure A  and S  :  Use isospin relations [M.Gronau and D.London, Phys.Rev.Letter. 65, 1990] Two amplitude triangles:  Calculate confidence level applying R-fit method (see next talks) [J.Charles et. Al. Eur.Phys.J.C41:1-131, 2005 ] Isospin analysis in B   (  ) 6 unknowns, and 5 observables: Br’s, A , S  ( + 2, not yet measured CP asymmetries in  0  0 )

Common features of B   measurements  small branching fractions: –  Large background S/B ~ O(1%)  All types of background contribute: continuum, b  c and b  u continuum is a dominant background. Use Fisher or neural nets (BaBar) to discriminate  Multiple B candidates in the same event. Best candidates selection based on best  0 mass and best  2 of the vertex fit. Events with misreconstructed pions, SCF. Use separate PDFs.  Several variables used to separate signal from backgrounds: m bc,  E, m , cos , event topology, flavor,  t

Analysis strategy BaBar  Determine signal yield, polarization, CP parameters simultaneously using a multidimensional fit.  Loose cuts on kinematical variables  more signal events in the fit.  Use PDFs for ‘all’ variables to discriminate against background - PDF shapes, correlations among variables (sometimes fits exhibit small bias) Belle  Relatively stringent cuts on kinematical variables.  Separate fits for event yields, polarization, and CP parameters. - larger statistical errors

M bc -  E - LR fit results LR fit projection high quality tag high quality tag Fit results: N evt in the fit = Million BB pairs NEW Belle results (preliminary)

High quality tag Low quality tag 535 Million BB pairs Preliminary Signal true PDF fit for two parameters A , S  CP fit results

high-purity events 347 Million BB pairs Updated this summer hep-ex/ m ES EE cos  m(    0 ) Simultaneous fit for the yield, polarization, and CP parameters C and S Previous BaBar: Previous Belle: (PRL 96,171801, 2006) (PRL 95,041805, 2005) B 0   +   fit results

hep-ex/ Signal true PDF B 0 tags background CP Asymmetries

NEW measurements last summer, hep-ex/ Million BB pairs Extract signal yield, polarization and charge asymmetry using an extended unbinned (7-dimensional) ML fit to m ES,  E, m(  ) +0, cos  +0, x N N total = Simultaneous fit for the yield, polarization, and charge asymmetry Measurements in B      0 decays

 Determine signal yield from a fit to  E distribution  Obtain polarization from a simultaneous fit to background subtracted cos  + cos  0 distributions  Determine charge asymmetry from separate fits to  E distributions of B +   +  0 and B      0 candidates Background subtracted m(  +   ) and m(    0 ) Belle results (old), PRL 91, (2003) Background subtracted cos  +  cos  0 Measurements in B      0 decays (cont’d) 85 Million BB pairs

HFAG Previous BaBar measurement: Phys. Rev. Lett. 91, (2003) B      0 results 85 Million BB pairs232 Million BB pairs

Use an unbinned extended ML fit to extract signal yield and polarization  8 dimensional fit: m ES,  E, m(  ) 1,2, cos  1,2, event topology, flavor tags  total number of events in the fit 65180, N(  0  0 ) = Main components in the fit  signal,  = 24.2%  continuum background (use neural network and tagging information)  float parameter values  b  c background  b  u background - similar topology: B 0  a 1  (dominant peaking background),  0 f 0, f 0 f 0 - other modes:  0 K *0,  +  0, ,  +  , remaining  float normalization 348 Million BB pairs hep-ex/ Evidence for B   0  0

Evidence for B   0  0 (cont’d) m ES EE hep-ex/ background 0000 Results statistically consistent with previous BaBar measurements, PRL 94, (2005) Br < at 90% CL Sourses of dominant systematic errors: PDF shapes, interference with B 0  a 1 , fit bias

B   0  0 - last minute results! m ES EE hep-ex/ (12/11/2006) submitted to PRL background 0000 m  cos  384 Million BB pairs

Constraint on  2 /  Caveats  ignore interference with ,  +  0    0, a 1   ignore possible I = 1 contribution  neglect EW penguin (all believed to be small) Branching fractions and polarization fractions used in the calculations (HFAG, Aug. 2006) (26 ± 6) (25 ± 4) > The isospin triangle is ‘closed’ with new measurements of Br(  +   ), Br(  +  0 ), Br(  0  0 ), OLD

is not measured. We have 6 unknowns and 5 measurements.  leads to plateau on 1-CL plot  the plateau width depends on Br(  0  0 ) Constraint on  2 /  (cont’d) at 68% CL 1-CL B   (WA) B   (BABAR) B   (Belle) & B  0  0 (BABAR) (92  21)  Squashed Isospin triangles at Belle due to large Br(B      0 ) = 31.7  no ‘plateau’, 2-fold ambiguity Generally, Isospin analysis allows to extract  2 /  with 8-fold ambiguity If Br(  0  0 )  0, Isospin triangles squashes 0000

Several new results during this year:  Measurement of CP asymmetries in B   +   at Belle  Measurement of branching fractions, polarization fractions, and CP asymmetries in B   +   and B   +  0 decays at BaBar  First evidence for B   0  0 decays at BaBar From an Isospin analysis  2 /  is constrained as Summary at 68% CL New measurements are awaited to improve our knowledge on  2 /  (Belle first results on Br(B   0  0 ) will appear soon)

Backup slides

B0  00B0  00 B 0   +   B      0 Summary of systematic errors BB pairs 10 6 ValueBB pairs 10 6 Value Br fLfL A(C) S BB pairs 10 6 ValueBB pairs 10 6 Value Br fLfL A CP BB pairs 10 6 Value Br

Mixing induced CP violation (sin 2  2 /  ) B0B0 B0B0 Mixing b d d b t t WW d W + b u d u d B0B0 + (+)+ (+)  - (  - ) Tree 1()1() 3()3() 2()2() A CP = S  sin(  m  t) S  = sin 2  2 B0B0 B0B0 f CP