Measurements of the angle  : ,  (BaBar & Belle results) Georges Vasseur WIN`05, Delphi June 8, 2005

Georges Vasseur2 Outline Physics motivation Measurement of  in B→  Measurement of  in B→  Dalitz. Summary on .

June 8, 2005Georges Vasseur3 CP violation CP violation is explained in the Standard Model by a phase in the CKM unitary matrix. In the Wolfenstein parameterization:   with  0.22, A  0.83 CP violation if  ≠ 0.

June 8, 2005Georges Vasseur4 The unitarity triangle  = process involving both B 0 mixing and b→u transition (0,0)(0,1) V ub V ud * V td V tb * V cd V* cb V cd V cb *     = phase of V td (B 0 mixing)  = phase of V ub (b→u transition)

June 8, 2005Georges Vasseur5 CP violation in the interference between mixing and decay For a CP final state f CP, time-dependent asymmetry is: With C  0 : Direct CP violationS  0 : Indirect CP violation Final State Amplitudes from mixing B0B0 B0B0 f CP Mixing (q/p)

June 8, 2005Georges Vasseur6 CP violation in B 0 →ρ + ρ - I Access to  from the interference of a b→u decay (  ) with B 0 B 0 mixing (  ). B 0 B 0 mixing Tree decayPenguin decay  Inc. penguin contribution How can we obtain α from α eff ?  T = tree amplitude P = penguin amplitude  = strong phase difference between penguin and tree Tree onlyTree + Penguin

June 8, 2005Georges Vasseur7 Isospin analysis Use SU(2) to relate amplitudes of all  modes. Gronau, London : PRL65, 3381 (1990) Small amplitudes 2|  eff |

June 8, 2005Georges Vasseur8 Asymmetry measurement Exclusive B meson reconstruction. Time measurement:  z ≈ 250  m,   z ≈ 170  m. B-flavor tagging: Q =   (1-2  ) 2 ≈ 30%. –with  efficiency and  mistag rate. t =0  (4S) tag B 0 l  (e-,  -)  z =  t  c fully reconstructed B B 0 Coherent B 0 B 0 production

June 8, 2005Georges Vasseur9 Common features of the analyses Kinematical signal identification with –Beam energy substituted mass –Energy difference Hadron ID (separation  /K). Event-shape variables combined in a neural network (NN) or Fisher discriminant to suppress jet-like continuum event.

June 8, 2005Georges Vasseur10 B 0 →ρ + ρ - analysis B→ρ + ρ - B→ρ + ρ - not historically favored for measuring α:  2 π 0 s in the final state.  3 amplitudes (VV decay): A 0 (CP-even longitudinal), A || (CP-even transverse), A ┴ (CP-odd transverse). But turned out to be the best mode:  Large branching fraction.  Penguin pollution much smaller than in B→ππ.  ~100% longitudinally polarized! Pure CP-even state. BaBarPreliminary signal bkgd BaBar, hep-ex/050349, submitted to PRL BaBar, Phys.Rev.Lett 93, (2004) 232 M BB

June 8, 2005Georges Vasseur11 Details of the B 0 →ρ + ρ - analysis Unbinned extended maximum likelihood fit on a data sample of events. Efficiency on signal: 7.7%. 8 observables: m ES,  E,  t, NN, m  (x2), cos   hel (x2). Modelisation of signal (1% of fit sample), continuum (92% of fit sample), and 38 different modes of B-background (7% of fit sample). Extract signal yield, longitudinal polarization fraction, cosine and sine coefficients. 232 M BB

June 8, 2005Georges Vasseur12 A CP (t) in B 0     decays Preliminary BaBar, hep-ex/ , submitted to PRL signal bkgd 232 M BB

June 8, 2005Georges Vasseur13 B + →ρ + ρ 0 analysis For isospin analysis, need other B→  rates. B + →ρ + ρ 0 was measured two years ago by both BaBar and Belle. Phys.Rev.Lett 91, (2003)Phys.Rev.Lett 91, (2003) 89 M BB 85 M BB

June 8, 2005Georges Vasseur14 B 0 →ρ 0 ρ 0 analysis Limiting factor in the isospin analysis. Tree is color suppressed. No significant signal: –Penguin are smalls. Dominant systematic comes from the potential interference from B→a 1 ±  ± (~22%). BaBar, Phys.Rev.Lett 94, (2005)

June 8, 2005Georges Vasseur15 Isospin analysis with B →ρρ Phys.Rev.Lett 94, (2005) Phys.Rev.Lett 91, (2003) Phys.Rev.Lett 91, (2003) Phys.Rev.Lett 93, (2004) |  eff |< 11° BaBar, hep-ex/050349, submitted to PRL Error dominated by     measurement

June 8, 2005Georges Vasseur16 B 0 →(ρ  ) 0 analysis Unlike    ,     is not a CP eigenstate –Must consider 4 configurations –Equivalent "isospin analysis" not viable. However, a full time-dependent Dalitz plot analysis can constrain  –+–+ +–+– 0000 Snyder, Quinn : PRD 48, 2139 (1993) Interference at equal masses- squared gives information on strong phases between resonances         

June 8, 2005Georges Vasseur17 Time-dependent Dalitz analysis Extract  and strong phases using interferences between amplitudes of decay. Assuming amplitude is dominated by  ,   and   resonances –The "f"s are functions of the Dalitz-plot and describe the kinematics of B→  (S→VS). –The "A"s are the complex amplitudes containing weak and strong phases. They are independent of the Dalitz variables. script {  } refers to {       }

June 8, 2005Georges Vasseur18 Result with B→       Hint of direct CP-violation Mirror solution not shown Weak constraint at C.L.<5% 2.9  Likelihood scan of  using:  {  } T =tree amp. P =penguin   213 M BB

June 8, 2005Georges Vasseur19 Combined α measurement The best individual measurement comes from . Mirror solution are disfavored, thanks to . Good agreement with global CKM fit. Combined value:

June 8, 2005Georges Vasseur20 Summary CP violation has entered a phase of precision measurements thanks to the B-factories. The angle  of the unitarity triangle has been measured with an uncertainty of ~10°. Will still improve.