lazzaroICHEP

Measurements of the CP angle b in charmless B decays at BaBar: 

Measurements of the CP angle b in charmless B decays at BaBar Alfio Lazzaro Università and INFN, Milano On behalf of BaBar Collaboration XXXIII International Conference on High Energy Physics Moscow, July 26 – August 2, 2006 alfio.lazzaro@mi.infn.it

Introduction: 

Introduction b→c measured with high precision in B-factories  small theoretical uncertainties, in agreement with the Standard Model (SM) prediction We extract sin2b b→s transition with loop diagrams  possible contribution from New Physics (NP) In case of NP, the effect is seen as discrepancy from sin2b  we expect it to be different among the modes Definition of Time Dependent CP asymmetry observables: In the SM: Sf = −hCP sin2bfeff ~ −hCP sin2b Cf ~ 0

SM or NP?: 

SM or NP? DSf = sin2bfeff − sin2b ≠ 0 can be explained inside the SM QCDF (Beneke, PLB620 (2005) 143-150; Cheng, Chua, Soni, PRD72 (2005) 094003; …) and SCET (Williamson, Zupan, hep-ph/0601214) allows to estimate DS: expect positive deviation for almost all modes Flavor-SU(3) provides only unsigned bounds assuming worst case for strong phase (Grossman et al, PRD68 (2003) 015004; Gronau et al, PRD71 (2005) 074019; …). We use the BF of other two body modes with h, h', f, p0, w, K*0, K0, (see talk by M. Bona, Section 10) some of recent QCDF estimates sin2bfeff − sin2b

All Results arePreliminary!: 

All Results are Preliminary!

Common Analysis Techniques (1): 

Common Analysis Techniques (1) Main background from e+e−→qq, q= u,d,s,c continuum events Rejection based on: Event-shape variables combined in Multivariate Analyzer [MVA] (Neural Network (NN) or Fisher Discriminant) Kinematics variables: beam-energy-substituted B mass (mES) and B-energy difference (E) invariant mass of the reconstructed B meson (mB) and invariant mass of the other B (mmiss) using the knowledge of beam energy and a mass constraint to the reconstructed B

Common Analysis Techniques (2): 

Common Analysis Techniques (2) Particle ID to separate charged particles (kaons and pions) K0L candidates reconstructed in EMC or IFR B-flavor tagging: NN-based, output sorted in 6 independent categories (plus untagged events) Unbinned maximum-likelihood fit using mES (mB), E (mmiss), the resonance mass and decay angle, the MVA, and t Likelihood components are signal (corrected and misreconstructed), continuum background, charmed and charmless B-related backgrounds

Analysis of B0→K+K−K0 (1): 

Analysis of B0→K+K−K0 (1) Angular moment analysis to determine the fraction of P-wave: 0.29 ± 0.03 over whole DP 0.89 ± 0.01 in f(1020) region 347  106 BB pairs BaBar-CONF-06/040 Need Dalitz plot analysis to measure CP asymmetry 11% is not P-wave under f resonance!!! (opposite CP) From fK+ sPlot [Pivk, Le Diberder, NIMA 555, 356 (2005)] Novel technique: Time-Dependent Dalitz Plot analysis: account for varying CP content and interference naturally in the fit Isobar model (f(1020)K0, f0(980)K0, X0(1550)K0, Non-resonant, cc0K0, D+K−, DS+K−)

Analysis of B0→K+K−K0 (2): 

We reconstruct K0→K0S with K0S→p+p−, p0p0 and K0→K0L Analysis of B0→K+K−K0 (2) 347  106 BB pairs BaBar-CONF-06/040 Main Systematic Contribution Dalitz model Fit to low mass K+K− region (<1.1 GeV) to extract fK0 and f0(980)K0 CPV parameters Average ACP, beff across the Dalitz plot Resolve trigonometric ambiguity in beff at 4.6s beff Reminders: ACP = −C, bCharmonium = 0.379 ± 0.023 DP fK0 in agreement with Q2B results (slightly lower) f0K0 studied for the first time with f0→K+K−

Analysis of B0 → h'K0 (1): 

Analysis of B0 → h'K0 (1) Reconstructed 6 sub-decays: 5 with K0→K0S (hCP = −1) and 1 with K0→K0L (hCP = +1), with h→gg, p+p−p0, and h'→hp+p−,r0g, and K0S→p+p−,p0p0 347  106 BB pairs Samples after L(Sg)/[L(Sg)+L(Bg)] cut BaBar-CONF-06/041

Analysis of B0 → h'K0 (2): 

Analysis of B0 → h'K0 (2) 347  106 BB pairs Combined fit: Main Systematic Contribution Signal PDFs S is 4.9s from zero!!! New SU(3) bound |DS|<0.08 BaBar-CONF-06/041

Analysis of B0 → p0K0S: 

425 ± 28 signal events Analysis of B0 → p0K0S No primary tracks from B vertex decay: require at least 4 SVT hits for both K0S pions (~60% of events) for t measurement determine t from a geometric fit to the U(4S)→B0B0 system taking in account the Interaction Point and by imposing a Gaussian constrain on the sum of the two B decay times to be equal to 2B keep remaining “no-t ”events for direct CPV measurement 347  106 BB pairs Main Systematic Contributions Fit method (0.027) on S Signal PDFs (0.021) on C BaBar-CONF-06/030

Analysis of B0→K0SK0SK0S: 

Analysis of B0→K0SK0SK0S Even CP eigenvalue (+1) Same vertex technique used in B0 → p0K0S analysis (essentially all events have at least one K0S candidate with both pions have at least one hit in the inner three SVT layers) Reconstructed with all K0S in charged tracks and with two K0S in charged pions and one in neutral pions K0SK0SK0L do not see significant signal (see talk by T. Latham, Session 10) 347  106 BB pairs Combined fit: 176 ± 17 signal events Main Systematic Contributions CP content of BB background Signal PDFs BaBar-CONF-06/018

Analysis of B0→K0SK0S: 

Analysis of B0→K0SK0S b→d transition expect with S = C = 0 Same vertex technique used in B0 →p0K0S 347  106 BB pairs Physically allowed region 32 ± 8 signal events Main Systematic Contribution: Signal PDFs BaBar-PUB-06/058

Analysis of B0→r0K0S: 

Analysis of B0→r0K0S Quasi 2-body approach (restricting to the region dominated by r0) Effects of interference with other resonances are estimated and taken as systematic errors 227  106 BB pairs 111 ± 19 signal events Main Systematic Contribution: Quasi 2-body assumption BaBar-PUB-06/039

Analysis of B0→wK0S: 

Analysis of B0→wK0S 347  106 BB pairs 142 ± 17 signal events Main Systematic Contributions: Signal PDFs BB background BaBar-CONF-06/012

Summary: 

Summary Individual mode measurements are consistent with the charmonium value No evidence for direct CPV in these samples The naïve b→s average is still lower than charmonium sin2b value (~2s)

Conclusion: 

Conclusion Several measurements to determine b in charmless B decays with loop diagrams from BaBar For each mode we study several sub-modes to increase the statistics Big improvements in the analysis technique provide better measurements (Dalitz Plot analysis) The significant decrease in the statistical errors begins to provide precision measurements of CP violation in loop processes Individual mode measurements are consistent with the SM value inside experimental and theoretical errors (however, the naïve average of Sf is still lower than charmonium value)

Backup Slides: 

Backup Slides

Old vs New measurements: 

Old vs New measurements Previous BaBar results  blue dashed line New measurements  red solid line old measurement new measurement f0K0 f0 → p+p− f0→K+K− fK0 Q2B approximation analysis DP analysis K+K−K0 no fK0 DP analysis