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BaBar Physics Highlights and UCSD Contributions

BaBar Physics Highlights and UCSD Contributions. Vivek Sharma University of California, San Diego October 2 nd , 2001 . Outline of This Talk . BaBar Physics Highlights : A Short summary Time-dependent B physics measurements Sin2  B Mixing and Lifetimes

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BaBar Physics Highlights and UCSD Contributions

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  1. BaBar Physics Highlights and UCSD Contributions Vivek Sharma University of California, San Diego October 2nd, 2001

  2. Outline of This Talk • BaBar Physics Highlights : A Short summary • Time-dependent B physics measurements • Sin2 • B Mixing and Lifetimes • UCSD contributions to BaBar Physics • Leadership roles in Time-dependent B physics measurements • Leadership roles in BaBar Physics Infrastructure • Prolific B meson reconstruction (if time permits) • Physics plans for coming year(s) V.Sharma DOE Review 2001

  3. Over-Constraining the Unitarity Triangle • Major goal of BaBar experiment : Precisely determine the sides and the angles of the Unitarity Triangle : A terrific start already ! V.Sharma DOE Review 2001

  4. BaBar Physics Highlights : 2001 • Observation of CP Violation in B Meson System (PRL, 7/5/2001) • Preceded by “Measurement of CP-violating asymmetries in B0 decays to CP eigenstates” ( PRL, Feb 2001) • Precise measurements of time-dependent B0 Oscillations with • Fully reconstructed B Samples & Dilepton samples • World’s best measurement of B0 and B- Meson lifetimes and ratio • Measurement of B0  +- and K+- Rates, searches for time-dependent (Sin2) and “ Direct” CP Violating rate asymmetries • Studies of Electroweak Penguins and precise searches for CP asymmetries in B meson Decays • Rare Hadronic B Decays => Future CPV studies • World’s largest sample of fully reconstructed B Mesons and the beginning of a new paradigm: “Recoil Side B physics” Diverse Program in B Physics : See DM’s talk for publications so far V.Sharma DOE Review 2001

  5. Major Emphasis of These Past Years : Sin2and associated Time-dependent B Decay MeasurementsFocus of UCSD Group’s Physics Effort in BaBar V.Sharma DOE Review 2001

  6. Data Sample : Available and Analyzed 30/fb analyzed for CPV related Studies (summer) September 25, 2001 October 99 PEP-II & BaBar establishing world records in delivering and recording High Luminosity data V.Sharma DOE Review 2001

  7. Flavor eigenstate Flavor eigenstate B0(t) B0(t) fCP fCP Initialstate Initialstate B0 B0 fCP is a CP eigenstate CPV in Interference Between B Mixing and Decay Time evolution of initial pure B0/B0 states: Mixing Mass eigenstates: V.Sharma DOE Review 2001

  8. Amplitude ratio Weak Phase In order to have CP Violation Time evolution of B0 mesons into a final CP eigenstate The decay distribution for events with a B0 (f+) and B0bar tags (f-) V.Sharma DOE Review 2001

  9. Sensitive to the phaseof l even without direct CP Violation Probe of direct CP violation since it requires Time-dependent CP Asymmetry In Mixing and Decay : Sin2 From the time evolution of the B0 and B0 states we can define the time-dependent asymmetry : V.Sharma DOE Review 2001

  10. u,c,t u,c,t W- W- Time-dependent CP asymmetry Is “Golden” Decay Mode: B0® J/y K0 • Theoretically clean mode to measure the phase of l (sin2b) • Clean experimental signature • Large branching fraction compared to other CP eigenstates K0mixing “Golden Modes” • hCP = -1 • B0  J/ K0S • B0  (2s) K0S • hCP = +1 • B0  J/ K0L V.Sharma DOE Review 2001

  11. sin 2b CP Asymmetry: What does one expect to see? • Dt spectrum and the observed asymmetry for a perfect detector(assuming sin2b = 0.6) • Visible difference between B0and B0decay rates • In this ideal case, the amplitude of the oscillation is the CP Asymmetry • time-integrated asymmetry is 0 t V.Sharma DOE Review 2001

  12. z FlavorTagging (bg)U(4S) = 0.56 Tag vertex reconstruction Coherent BB pair Exclusive B Meson and Vertex Reconstruction The Clock Starts B Decay Topology in the Boosted (4S) Environment All the action is along the beam (Z) axis V.Sharma DOE Review 2001

  13. Measurements B±/B0 Lifetimes B0B0-Mixing CP Asymmetry Analysis Ingredient (a) Reconstruction of B mesons in flavor eigenstates (b) B decay time reconstruction (c) B Flavor Tagging + a + b Reconstruction of neutralB mesons in CP eigenstates + a + b + c Increasing complexity Higher precision Sin2 Analysis Approach Factorize the analysis into three conceptual building blocks Walk thru each analysis step V.Sharma DOE Review 2001

  14. p- K0 K+ p- Tag B sz ~ 110 mm g Reco B sz ~ 65 mm D- U(4s) p+ Dz bg = 0.56 Dt @Dz/gbc Calibrating the t Clock : B Lifetime Measurement 3. Reconstruct Inclusively the vertex of the “recoil” B meson (BTAG) • Fully reconstruct one B mesonin flavor eigenstate (BREC) • Reconstruct the B decay vertex 4. compute the proper time difference Dt 5. Fit the Dt spectra V.Sharma DOE Review 2001

  15. Fully-Reconstructed Hadronic B Decay Sample Flavor Eigenstates Bflav : for lifetime and B mixing measurements • Cabibbo-favored hadronic decays • “Open Charm” decays 30 fb-1 Neutral B Mesons Hadronic decays into final states with Charmonium Charged B Mesons [GeV] V.Sharma DOE Review 2001

  16. B Lifetime Results • Precision measurements • 2 % statistical error • 1.5% systematic error • Main source of systematic error • Parameterization of the Dt resolution function • Description of events with large measured Dt (outliers) 20 fb-1 B0/B0 B signal + bkg To be published in PRL t0= 1.546  0.032  0.022 psPDG: 1.548  0.032 ps t= 1.673  0.032  0.022 ps PDG: 1.653  0.028 ps t/t0= 1.082  0.026  0.011 PDG: 1.062  0.029 background Dt (ps) V.Sharma DOE Review 2001

  17. p- K0 K+ p- Tag B sz ~ 110 mm g Reco B sz ~ 65 mm D- U(4s) p+ Dz bg = 0.56 Dt @Dz/gbc B0B0 Mixing with Fully Reconstructed B Mesons 3. Reconstruct Inclusively the vertex of the “other” B meson (BTAG) ü 4. Determine the flavor of BTAG to separate Mixed and Unmixed events 1. Fully reconstruct one B meson in flavor eigenstate (BREC) ü 2. Reconstruct the decay vertex ü 5. compute the proper time difference Dt ü 6. Fit the Dt spectra of mixed and unmixed events V.Sharma DOE Review 2001

  18. realistic mis-tagging & finite time resolution perfect flavor tagging & time resolution Dt Spectrum of Mixed and Unmixed B Events + _ w: the fraction of wrongly tagged events Dmd: oscillation frequency V.Sharma DOE Review 2001

  19. W+ W- b c s Lepton Tag Kaon Tag l- NN output Multivariate analysis exploiting the other kinematic information of the event, e.g., n W- • Momentum spectrum of the charged particles • Information from non-identified leptons and kaons • Soft p from D* decay c b D, D* Neural Network Not Used B0 B0 d d K*0 d d B Meson Flavor Tagging Hierarchical Tagging Categories For electrons, muons and Kaons use the charge correlation with decay daughters Each category is characterized by the probability of giving the wrong answer (mistag fraction w) V.Sharma DOE Review 2001

  20. B Flavor Tagging Performance The large sample of fully reconstructed B decays provides the precise determination of the B flavor tagging parameters required in the Mixing/ CP Asymmetry analysis The error on sin2b related to the quality factor Q Highest tag “efficiency” Smallest mistag fraction V.Sharma DOE Review 2001

  21. B0B0 Mixing Measurement 20 fb-1 C.L. 28 % Dmd = 0.519 ± 0.020 (stat) ± 0.016 (syst) h ps-1 Preliminary V.Sharma DOE Review 2001

  22. Dmd Measurement Precision preliminary • Precision Dmd measurement • 4% statistical error • 3% systematic error dominated by MC correction V.Sharma DOE Review 2001

  23. p- K0 p+ Tag B sz ~ 110 mm g CP B sz ~ 65 mm Ks0 m- U(4s) Dz m+ bg = 0.56 Dt @Dz/gbc Measurement of CP Asymmetry : Sin2 3. Reconstruct Inclusively the vertex of the “other” B meson (BTAG) ü 4. Determine the flavor of BTAG to separate Mixed and Unmixed events ü 1. Fully reconstruct one B meson in CP eigenstate (BCP) 2. Reconstruct the decay vertex ü 5. compute the proper time difference Dt ü 6. Fit the Dt spectra of B0 and B0 tagged events V.Sharma DOE Review 2001

  24. perfect flavor tagging & time resolution realistic mis-tagging & finite time resolution CP PDF Mistag fractions w And resolution function R Mixing PDF determined by theflavor sample Back to Sin2 : Dt Spectrum of CP Events V.Sharma DOE Review 2001

  25. J/y KS KS p0 p0 J/y KS KSp+ p- 1999-2001 data32 x 106 BB pairs29 fb-1 on peak y(2S) KS cc1 KS J/y K* J/y KL The fully Reconstructed CP Eigenstate Sample Before tagging requirement After tagging V.Sharma DOE Review 2001

  26. Raw Time-Dependent CP Asymmetry All tags Kaon tags f = -1events sin2b=0.56 ± 0.15 sin2b=0.59 ± 0.20 Raw ACP V.Sharma DOE Review 2001

  27. Observation of CP Violation in B Decays ! Phys. Rev. Lett. 87 091801 (2001) Crosscheck: Null result in flavor eigenstate samples Consistency of CP channels P(c2) = 8% Goodness of fit (CP Sample): P(Lmax>Lobs) > 27% Combined fit to all CP modes sin2b = 0.59 ± 0.14 ±0.05 V.Sharma DOE Review 2001

  28. Consistency Checks Combined CP=-1 sin2b measured in several Dt bins sin2b vs. J/ decay mode and tagging category and flavor for  = -1 events V.Sharma DOE Review 2001

  29. The Unitarity Triangle Now One solution for b is consistent with measurements of sides of Unitarity Triangle BaBar sin2b (with 30/fb) Error on sin2b is dominated by statistics  will decrease as Method as in Höcker et al, hep-ph/0104062 (also other recent global CKM matrix analyses) V.Sharma DOE Review 2001

  30. UCSD Contributions to Sin2b And Related Time Dependent Measurements V.Sharma DOE Review 2001

  31. Riccardo Faccini : • Sin2b Technical Coordinator • Responsible for integrating all aspects of physics necessary for CP Asymmetry measurement • Co-Convener, Charmonium Group : Reconstruction of CP sample • Gerhard Raven • Co-Convener B Mixing and Lifetime group, • Principal analysis on B Mixing ( with Prell, Rahatlou) • Soeren Prell • Fitting algorithm (tFit) for Sin2b, time-dependent mixing and Lifetime (BaBar Standard) • Shahram Rahatlou • Author of analysis packages for prolific B meson Reconstruction • Ph.D Thesis on Sin2b Measurement • David MacFarlane • B Mixing and Sin2b, • Vivek Sharma • Co- Convener, B Reconstruction (Breco) Group • (B Mixing) and Sin2b : Editor of July CPV “Observation” paper V.Sharma DOE Review 2001

  32. UCSD Role In Physics Analysis Infrastructure • Critical Role in facilitating BaBar physics, e.g : • Developed and maintained Micro-DST for physics analysis used in all BaBar analyses • CompositionTools : Infrastructure for construction of decay chains , vertex reco., kinematic fitting • Authors of copious B meson reconstruction and analysis packages: CharmUser,BrecoUser and DstarlnuUser • heavily used in BaBar for a variety of “Recoil Side Physics” • Copied for other analyses with our technical assistance • tFIT: Framework for time-dependent CP asymmetry, B mixing and lifetime analysis : a BaBar Standard • Author of CPFramework and C++ based “Post” CPFramework : • Software standard for Data-mining and delivery of Fully Recoed B Mesons to a generic BaBar physicist interested in “Recoil Side B Physics” V.Sharma DOE Review 2001

  33. Recoil Side B Physics With Fully Reconstructed B Sample • A new B-factory era idea (whose time has come): to alleviate model dependence in key measurements • Fully reconstructed, flavor specific sample of B mesons provide a very clean sample of B tags • Full B reconstruction of 1 B in (4S) provides: • Information about flavor of the other ( Recoil side) B => charge correlation • Provides precise P vector of the recoiling B ( e.g. B -> t n) • => daughter particles can be transformed to the B rest frame, not (4S) CMS • => Any two body decay produces sharp peaks in momentum spectrum of daughter particles. (think b -> s g or s g) • No udsc (continuum background to deal with ..or subtract) • Half of the event is accounted for => drastically reduced combinatorial background in studying recoil side B properties V.Sharma DOE Review 2001

  34. A Completely Reconstructed (4S) Event Example of Recoil Side Physics All particles accounted for Nothing Missing ! V.Sharma DOE Review 2001

  35. Possible Recoil Side Measurements • Bread and Butter Physics examples • Inclusive Semileptonic decay rate for B0 and B- (LP01) • Particle spectra (K, ,  …..) • Right and Wrong Sign (upper vertex ) Charm production • Charm species, Rate and spectrum trivially obtained • More Serious Stuff • B -> s g, and b -> s Glue (exclusive and inclusive with reduced modelling) • B -> t n and B -> s n n (The ONLY way to get to them!) • Inclusive b -> u l n => Minimal Model dependence • Add your favorite physics V.Sharma DOE Review 2001

  36. Exclusive B Semileptonic Samples: 2000 Data Kp 6.1k ~ 1K reconstructed per fb-1 Very High Purity ~80% => 500K fully recoed B in 500 fb-1 Kppp KSpp 5.0k Kpp0 5.0k V.Sharma DOE Review 2001

  37. Fully Reconstructed Hadronic B Decay Sample Run I with D0p-, D*0p-, D*0r-, D*0 a1-, J/yK-, y(2S) K-, cc K- and J/yK*-. B- Sample: 20K in 20 fb-1 500K Clean in 500 fb-1 This is just a proof of principle! Expect to increase the reconstruction rate by ~2-3 Expect 1-1.5 M Hadronic B of each species by 2005 Sample with the largest Set of Constraints for Recoil side studies V.Sharma DOE Review 2001

  38. Example of Recoil Side B Physics : Precision Vub Measurement To distinguish bu from bc theoretically: better better q2 spectrum > mhad spectrum > Elepton spectrum But experimental difficulty is in opposite order To make major experimental progress in Vub need powerful suppression of b cl provided by full reconstruction of companion B Study this Reco this V.Sharma DOE Review 2001

  39. Inclusive Hadronic Mass Spectrum Jik Lee@Snowmass • select b u with mx< mD(~90% acceptance for b u (model ???) • require: Q(event) =0, 1 lepton/event, missing mass consistent with neutrino • just look at mhad< 1.7 , cut with largest acceptance and hence least theoretical uncertainty, keep bkgd small with p(lepton)>1.4 GeV TRKSIM CLEO III FAST MC V.Sharma DOE Review 2001

  40. Snowmass Study: Inclusive Vub • ~100 b ulv events/30 fb-1 : Method attractive with large data samples • Systematic error dominated by charm leakage into signal region. Depends on S/B ratio & B. Assume B = 0.1 B @ 100 fb-1. • S/B can be improved by vertexing. • B can be reduced as Br(B [D*/D**/D/D ] l) and the form factors in these decays become better measured. B can also be reduced through better knowledge of D branching ratios. • Assume these improvements lead to B = 0.05 B @ 500 fb-1 or higher Ldt. • Recall theoretical error is alleast ~ 10% year Ldt # bul #b cl Vub Vub Vub (stat) (sys) (expt) 2002 100 fb-1 335 127 3.2% 2.2% 3.9% 2005 500 fb-1 1675 635 1.5% 1.5% 2.1% 2010 2000 fb-1 6700 2540 0.7% 1.5% 1.7% V.Sharma DOE Review 2001

  41. UCSD Physics Goals in the Short Term • Continue with successful & singular focus on Sin2b and B0 mixing measurements • Expect a precision of +- 0.08 by next summer • Continue to develop tFIT to include more decay modes with their specific physics issues • Transversity (angular) analysis for PsiK*, D*D* • Sin2a • Continue to help build large samples of fully reconstructed B Mesons for • B-    • Model independent B  Xu l  final states : Vub Measurements • In 2002 data and beyond V.Sharma DOE Review 2001

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