Measurements of the angle a : rr , rp (BaBar & Belle results)

WIN`05, Delphi June 8, 2005 Measurements of the angle a: rr, rp (BaBar & Belle results) Georges Vasseur

Outline • Physics motivation • Measurement of a in B→rr. • Measurement of a in B→rp Dalitz. • Summary on a. Georges Vasseur

CP violation • CP violation is explained in the Standard Model by a phase in the CKM unitary matrix. • In the Wolfenstein parameterization: with l  0.22 , A  0.83 • CP violation if h≠ 0. Georges Vasseur

* Vtd Vtb * Vub Vud * Vcd Vcb VcdV*cb The unitarity triangle a = p-b-g = process involving both B0 mixing and b→u transition g= phase of Vub (b→u transition) b = phase of Vtd (B0 mixing) a g b (0,0) (0,1) Georges Vasseur

Final State Amplitudes CP violation in the interference between mixing and decay • For a CP final state fCP, time-dependent asymmetry is: • With B0 Mixing (q/p) B0 fCP from mixing S 0 : Indirect CP violation C 0 : Direct CP violation Georges Vasseur

Tree decay B0B0mixing Penguin decay  CP violation in B0→ρ+ρ- • Access to a from the interference of a b→u decay (g) with B0B0 mixing (b). • I g Tree only Tree + Penguin T = tree amplitude P = penguin amplitude d = strong phase difference between penguin and tree Inc. penguin contribution How can we obtain α from αeff ? Georges Vasseur

Isospin analysis • Use SU(2) to relate amplitudes of all rr modes. 2|-eff| Small amplitudes Gronau, London : PRL65, 3381 (1990) Georges Vasseur

Dz = Dt gbc l - (e-, m -) (4S) Asymmetry measurement t =0 fully reconstructed B • Exclusive B meson reconstruction. • Time measurement: Dz ≈ 250 mm, s Dz ≈ 170 mm. • B-flavor tagging: Q = Se(1-2w)2≈ 30%. • with e efficiency and w mistag rate. Coherent B0B0production B 0 tag B 0 Georges Vasseur

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

B0→ρ+ρ- analysis B→ρ+ρ-not historically favored for measuring α: • 2 π0s in the final state. • 3 amplitudes (VV decay):A0 (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. BaBar, Phys.Rev.Lett 93, 231801 (2004) BaBar Preliminary signal 232 MBB bkgd BaBar, hep-ex/050349, submitted to PRL Georges Vasseur

Details of the B0→ρ+ρ- analysis • Unbinned extended maximum likelihood fit on a data sample of 68703 events. • Efficiency on signal: 7.7%. • 8 observables: mES, DE, Dt, NN, mpp (x2), cosQpphel (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 MBB Georges Vasseur

ACP(t) in B0r+r- decays BaBar, hep-ex/0503049, submitted to PRL Preliminary 232 MBB signal bkgd Georges Vasseur

B+→ρ+ρ0 analysis • For isospin analysis, need other B→rr rates. • B+→ρ+ρ0was measured two years ago by both BaBar and Belle. 89 MBB 85 MBB Phys.Rev.Lett 91, 171802 (2003) Phys.Rev.Lett 91, 221801 (2003) Georges Vasseur

B0→ρ0ρ0 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→a1±p± (~22%). BaBar, Phys.Rev.Lett 94, 131801 (2005) Georges Vasseur

Isospin analysis with B→ρρ Phys.Rev.Lett 93, 231801 (2004) |a-aeff |< 11° Phys.Rev.Lett 91, 171802 (2003) Phys.Rev.Lett 91, 221801 (2003) Phys.Rev.Lett 94, 131801 (2005) Error dominated by r0r0 measurement BaBar, hep-ex/050349, submitted to PRL Georges Vasseur

+– 00 –+ B0→(ρp)0 analysis • Unlike r+r-, r+p- is not a CP eigenstate • Must consider 4 configurations • Equivalent "isospin analysis" not viable. • However, a full time-dependent Dalitz plot analysis can constrain a. Snyder, Quinn : PRD 48, 2139 (1993) Interference at equal masses-squared gives information on strong phases between resonances r0 p- p0 p+  p- p0 r- p+ Georges Vasseur

Time-dependent Dalitz analysis • Extract  and strong phases using interferences between amplitudes of decay. • Assuming amplitude is dominated by r+,r-and r0 resonances script {+,-,0} refers to {r+,r-,r0} • The "f"sare functions of the Dalitz-plot and describe the kinematics of B→rp (S→VS). • The "A"s are the complex amplitudes containing weak and strong phases. They are independent of the Dalitz variables. Georges Vasseur

Result with B→p+p-p0 • Hint of direct CP-violation • Likelihood scan of a using: k {+,-,0} T =tree amp. P =penguin - - 213 MBB 2.9  Mirror solution not shown Weak constraint at C.L.<5% Georges Vasseur

Combined α measurement • The best individual measurement comes from rr. • Mirror solution are disfavored, thanks to rp. • Good agreement with global CKM fit. • Combined value: http://ckmfitter.in2p3.fr Georges Vasseur

Summary • CP violation has entered a phase of precision measurements thanks to the B-factories. • The angle a of the unitarity triangle has been measured with an uncertainty of ~10°. • Will still improve. Georges Vasseur http://ckmfitter.in2p3.fr

Measurements of the angle a : rr , rp (BaBar & Belle results)