B 0 r 0 K s ; Branching Fraction and Time Dependent CP Analysis at BaBar

1. B0r0Ks; Branching Fraction and Time Dependent CP Analysis at BaBar Ian Forster University of Liverpool Ian Forster - U. of Liverpool IoP 2005

2. Introduction and Overview • Working with David Payne (University of Liverpool) • CKM Matrix, CP violation and the Unitarity Triangle • Event selection • Maximum Likelihood fit • Branching fraction results • CP fit validation Ian Forster - U. of Liverpool IoP 2005

3. CKM Matrix and Unitarity Triangle Requirement of unitarity CKM matrix relates rotated quark states to physical states This relation is depicted as a triangle in the complex plane h a Angles related to CKM matrix elements g b 0 r 1 Ian Forster - U. of Liverpool IoP 2005

4. CP violation due to Interference between Mixing and Decay Ratio of CKM elements In Feynman diagrams Particular B decays have physically interesting values of Im(l) eg: B0 J/Y Ks and decay modes dominated by ‘b-s penguin’ diagrams BB Mixing (Equivalent factor for KK mixing if decay involves KS) Ian Forster - U. of Liverpool IoP 2005

5. Measuring Sin2b From b-s Penguins • b-s penguins showing signs of measuring a different value for b to cc decays (eg B0 J/y Ks) • Interesting area of research at the moment -hfS C= (1 - |l|2) / (1 + |l|2) 3.6s from s-penguin to sin2b (cc) No sign of direct CP asymmetry Ian Forster - U. of Liverpool IoP 2005

6. B0 r0Ks CKM suppressed Tree diagram Gluonic penguin dominates • The two leading order Feynman diagrams. • Penguin decay has weak phase able to measure b,the Unitarity Triangle angle. • We extract a measurement of b by performing a time dependent CP analysis using a maximum likelihood fit. Ian Forster - U. of Liverpool IoP 2005

7. Initial Event Selection • |DE| < 0.3 GeV • mES > 5.18 GeV • Cos(Thrust angle)<0.9 • DT < 20 ps, • sDT < 2.5 ps DE = EB - EBEAM Energy of the B Energy of the beam Center of mass Momentum of B q • BB pair hardly moving in CM frame • If something other than BB pair, decay • will form back to back jets • A cut on the thrust of the event selects • BB pairs Rest of event DT is the time between the decay of the B’s B Thrust (CM frame) Ian Forster - U. of Liverpool IoP 2005

8. Ntuple Level Selection • The 2 tracks from the r0are required to fail tight PID selections for e, p and K. • Invariant mass of these two tracks must be within 0.375GeV of the PDG r0mass (0.776GeV) • mES > 5.23GeV (on peak data), mES > 5.21GeV (off peak data) • Cosine of pointing angle < 0.997 • Ks vertex must be displaced from the r0 vertex by more than 3x the error on the distance. • Mass of Ks must be within 0.13GeV of the PDG value for the K0 (0.498GeV) • Veto against D+p- and K*+p- by ensuring mass of Ksp combination are more than 0.055GeV and 0.04GeV away from the PDG masses of D+ and K*+. • Efficiency ~ 25% Pointing angle is the Angle between the Displacement vector Between the r0 and The Ks and the Ks Momentum vector Ian Forster - U. of Liverpool IoP 2005

9. Split into two fundamental categories; Charmed and Charmless. Charmed Backgrounds Identified with MC. Split up into B+ and B0 with all sub-modes collected together into two non-parametric PDF’s Charmless modes contributing < 1 event included in the PDF’s Charmless Backgrounds Identified with Generic MC all modes contributing > 1 event. Modeled with non-parametric PDF. Backgrounds Continuum Background • Almost all of the events in our selection are continuum ~99%!! B Backgrounds Ian Forster - U. of Liverpool IoP 2005

10. mES DE Neural Net Output (NNO) Cos(qHELICITY) DT pp Mass Maximum Likelihood Fit Discriminating Variables • NNO: Inputs to the neural net are: • Fisher: combines neutral and charged, 0th and 2nd order Legendre monomials • Sum of the transverse momentum • Cosine of angle between direction of B and the thrust axis • Cosine of angle between direction of B and the z axis • Cosine of angle between thrust axis of B and the z axis Ian Forster - U. of Liverpool IoP 2005

11. BF(B0r0Ks) = (5.1 +/-1.0+/-1.2) x 10-6 Float a non-resonant B0 Kspp component with flat helicity distribution Evidence for B0r0Ks at the 3.6s level Presented at ICHEP 2004 Results of BF Fit (Dataset – 227 million BB pairs corresponding to 205 fb-1 int. luminosity) Ian Forster - U. of Liverpool IoP 2005

12. CP Fit Validations Validation fits use the nominal fit but selecting the mass of The J/y or D+ instead of the r0 Plots of variable Mes Total Continuum Continuum + BBkg B0 D+p- study Also fit CP parameters to values consistent with theory B0 J/y Ks study Fit CP parameters to values consistent with theory Ian Forster - U. of Liverpool IoP 2005

13. Summary • Have measured evidence for the decay B0r0Ks • Result went to ICHEP in the summer • PRL in pipeline • Time dependent CP analysis • Fit two control samples and appear to get expected CP result • Aim to have CP analysis for summer Ian Forster - U. of Liverpool IoP 2005

14. Types of CP violation • Direct CP Violation • CP violation in decay • Indirect CP Violation • CP violation in mixing – when CP is conserved the mass eigenstates are CP eigenstates. • CP Violation in the interference between mixing and decay – The one we are interested in for this analysis! Ratio of decay amplitudes Ian Forster - U. of Liverpool IoP 2005

15. Which BSM models could account for the difference in Sin(2b)? • Assume difference comes from New Physics • 3 quark SM naturally produces a CP odd phase in the CKM matrix • There is no reason to think only one CP violating phase exists outside the SM • 2 Higgs doublets – 1 new phase • SUSY – 10’s of new phases • LR symmetry – up to 6 new phases Browder and Soni: hep-ph/0410192 Ian Forster - U. of Liverpool IoP 2005

16. Vertexing • Reconstruct Brec vertex from • charged Brec daughters • Determine BTag vertex from • charged tracks not belonging to Brec • Brec vertex and momentum • beam spot • Y(4S) momentum • Average Dz resolution is 180 mm • From measurement of Dz we calculate DT, the time between the decay of the B’s This gives us the time dependent analysis BREC daughters BREC direction BREC Vertex Interaction Point Beam spot TAG Vertex BTAG direction TAG tracks z Ian Forster - U. of Liverpool IoP 2005

17. Lepton: Charge of fastest electron (muon) with p* > 1.0 (1.1) GeV/c Kaon : Net charge of identified kaons  0 (Also non-identified leptons and kaons, soft pions from D*’s, etc) e- , m- c s b K- B Flavour Tagging Overall 67.5 +/- 0.5 % efficient Ian Forster - U. of Liverpool IoP 2005

18. B Background modes Ian Forster - U. of Liverpool IoP 2005