babar physics highlights and ucsd contributions

BaBar Physics Highlights and UCSD ContributionsVivek Sharma University of California, San Diego October 2nd, 2001

V.Sharma DOE Review 2001

Outline of This Talk BaBar Physics Highlights : A Short summaryTime-dependent B physics measurementsSin2B Mixing and Lifetimes UCSD contributions to BaBar PhysicsLeadership roles in Time-dependent B physics measurementsLeadership roles in BaBar Physics InfrastructureProlific B meson reconstruction (if time permits)Physics plans for coming year(s)


Over-Constraining the Unitarity TriangleMajor goal of BaBar experiment : Precisely determine the sides and the angles of the Unitarity Triangle : A terrific start already !


BaBar Physics Highlights : 2001Observation 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 Worlds 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 DecaysRare Hadronic B Decays => Future CPV studies Worlds largest sample of fully reconstructed B Mesons and the beginning of a new paradigm: Recoil Side B physics Diverse Program in B Physics : See DMs talk for publications so far


Major Emphasis of These Past Years : Sin2 and associated Time-dependent B Decay Measurements

Focus of UCSD Groups Physics Effort in BaBar


Data Sample : Available and Analyzed30/fb analyzedfor CPV related Studies (summer)October 99September 25, 2001PEP-II & BaBar establishing world records in delivering and recording High Luminosity data


CPV in Interference Between B Mixing and DecayTime evolution of initial pure B0/B0 states: MixingMass eigenstates:


Time evolution of B0 mesons into a final CP eigenstateThe decay distribution for events with a B0 (f+) and B0bar tags (f-)


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 :


Golden Decay Mode: B0 J/y K0Theoretically clean mode to measure the phase of l (sin2b)Clean experimental signatureLarge branching fraction compared to other CP eigenstatesK0 mixinghCP = +1 B0 J/ K0L hCP = -1 B0 J/ K0S B0 (2s) K0SGolden Modes


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 B0 and B0 decay rates In this ideal case, the amplitude of the oscillation is the CP Asymmetry time-integrated asymmetry is 0t


B Decay Topology in the Boosted (4S) EnvironmentAll the action is along the beam (Z) axis


Sin2 Analysis ApproachMeasurementsB/B0 Lifetimes

B0 B0-Mixing

CP AsymmetryAnalysis Ingredient(a) Reconstruction of B mesons in flavor eigenstates(b) B decay time reconstruction

(c) B Flavor Tagging + a + b

Reconstruction of neutral B mesons in CP eigenstates + a + b + cFactorize the analysis into three conceptual building blocksWalk thru each analysis step


Calibrating the t Clock : B Lifetime Measurement3. Reconstruct Inclusively the vertex of the recoil B meson (BTAG)4. compute the proper time difference Dt5. Fit the Dt spectraFully reconstruct one B meson in flavor eigenstate (BREC)Reconstruct the B decay vertex


Fully-Reconstructed Hadronic B Decay SampleCabibbo-favored hadronic decays Open Charm decaysNeutral B MesonsCharged B MesonsFlavor Eigenstates Bflav : for lifetime and B mixing measurements[GeV]30 fb-1Hadronic decays into final stateswith Charmonium


B Lifetime ResultsPrecision measurements2 % statistical error1.5% systematic errorMain source of systematic errorParameterization of the Dt resolution functionDescription of events with large measured Dt (outliers)B0/ B0BDt (ps)t0 = 1.546 0.032 0.022 ps PDG: 1.548 0.032 pst = 1.673 0.032 0.022 psPDG: 1.653 0.028 pst/t0 = 1.082 0.026 0.011PDG: 1.062 0.02920 fb-1backgroundsignal + bkg To be published in PRL


B0B0 Mixing with Fully Reconstructed B Mesons3. Reconstruct Inclusively the vertex of the other B meson (BTAG)4. Determine the flavor of BTAG to separate Mixed and Unmixed events5. compute the proper time difference Dt 6. Fit the Dt spectra of mixed and unmixed events1. Fully reconstruct one B meson in flavor eigenstate (BREC)2. Reconstruct the decay vertex


Dt Spectrum of Mixed and Unmixed B Eventsw: the fraction of wrongly tagged eventsDmd: oscillation frequency_+


B Meson Flavor TaggingFor 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) Hierarchical Tagging Categories


B Flavor Tagging PerformanceSmallest mistag fractionHighest tag efficiencyThe error on sin2b related to the quality factor QThe large sample of fully reconstructed B decays provides the precise determination of the B flavor tagging parameters required in the Mixing/ CP Asymmetry analysis

Tagging categoryFraction of tagged events e (%)Wrong tag fraction w (%)Q = e (1-2w)2 (%)Lepton10.9 0.38.9 1.3 7.4 0.5Kaon35.8 0.517.6 1.015.0 0.9NT1 7.8 0.322.0 2.1 2.5 0.4NT2 13.8 0.335.1 1.9 1.2 0.3ALL68.4 0.726.1 1.2


B0B0 Mixing Measurement Dmd = 0.519 0.020 (stat) 0.016 (syst) h ps-120 fb-1C.L. 28 %Preliminary


Dmd Measurement Precision preliminaryPrecision Dmd measurement

4% statistical error

3% systematic error dominated by MC correction


Measurement of CP Asymmetry : Sin2 3. Reconstruct Inclusively the vertex of the other B meson (BTAG)4. Determine the flavor of BTAG to separate Mixed and Unmixed events 5. compute the proper time difference Dt 6. Fit the Dt spectra of B0 and B0 tagged events1. Fully reconstruct one B meson in CP eigenstate (BCP)2. Reconstruct the decay vertex


Back to Sin2 : Dt Spectrum of CP Events


The fully Reconstructed CP Eigenstate SampleAfter taggingBefore tagging requirement

Sampletagged eventsPurityCP[J/, (2S), cc1] KS48096%-1J/ KL27351%+1J/ K*0(KSp0)5074%mixedFull CP sample80380%


Raw Time-Dependent CP Asymmetry sin2b=0.56 0.15sin2b=0.59 0.20Kaon tagsAll tagsRaw ACPf = -1 events


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


Consistency Checkssin2b measured in several Dt binssin2b vs. J/ decay mode and tagging category and flavor for = -1 eventsCombined CP=-1


The Unitarity Triangle NowMethod as in Hcker et al, hep-ph/0104062(also other recent global CKM matrix analyses)BaBar sin2b (with 30/fb)Error on sin2b is dominatedby statistics will decrease asOne solution for b is consistent with measurements of sides of Unitarity Triangle


UCSD Contributions to Sin2b And Related Time Dependent Measurements


Riccardo Faccini : Sin2b Technical CoordinatorResponsible for integrating all aspects of physics necessary for CP Asymmetry measurement Co-Convener, Charmonium Group : Reconstruction of CP sampleGerhard RavenCo-Convener B Mixing and Lifetime group,Principal analysis on B Mixing ( with Prell, Rahatlou) Soeren PrellFitting algorithm (tFit) for Sin2b, time-dependent mixing and Lifetime (BaBar Standard) Shahram RahatlouAuthor of analysis packages for prolific B meson Reconstruction Ph.D Thesis on Sin2b MeasurementDavid MacFarlaneB Mixing and Sin2b, Vivek Sharma Co- Convener, B Reconstruction (Breco) Group (B Mixing) and Sin2b : Editor of July CPV Observation paper


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 analysesCompositionTools : 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 PhysicsCopied for other analyses with our technical assistancetFIT: 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


Recoil Side B Physics With Fully Reconstructed B SampleA new B-factory era idea (whose time has come): to alleviate model dependence in key measurementsFully reconstructed, flavor specific sample of B mesons provide a very clean sample of B tagsFull B reconstruction of 1 B in (4S) provides:Information about flavor of the other ( Recoil side) B => charge correlationProvides 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


A Completely Reconstructed (4S) Event All particles accounted forNothing Missing !Example of Recoil Side Physics


Possible Recoil Side MeasurementsBread and Butter Physics examplesInclusive Semileptonic decay rate for B0 and B- (LP01)Particle spectra (K, , ..) Right and Wrong Sign (upper vertex ) Charm productionCharm species, Rate and spectrum trivially obtainedMore 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 dependenceAdd your favorite physics


Exclusive B Semileptonic Samples: 2000 Data KpppKSpp5.0kKpp05.0kKp6.1k

~ 1K reconstructed per fb-1 Very High Purity ~80% => 500K fully recoed B in 500 fb-1


Fully Reconstructed Hadronic B Decay SampleRun I with D0 p-, D*0 p-, D*0 r-, D*0 a1-, J/y K-, y(2S) K-, cc K- and J/y K*-.B- Sample: 20K in 20 fb-1500K Clean in 500 fb-1 This is just a proof of principle!Expect to increase the reconstruction rate by ~2-3Expect 1-1.5 M Hadronic B of each species by 2005

Sample with the largest Set of Constraints for Recoil side studies


Example of Recoil Side B Physics : Precision Vub Measurement To distinguish bu from bc theoretically: better betterq2 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 Reco this Study this


Inclusive Hadronic Mass Spectrum 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 Jik Lee@Snowmass


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 # bul #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%


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 issuesTransversity (angular) analysis for PsiK*, D*D* Sin2aContinue 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


firts q^2 plot shows end pointregions, at high q^2 the range of lepton energies is onbly about twice as great asthe endpoint cut the second ploitis after data have been extrapolated to full q2 rangethis means that allowance is amde for the fraction of leptons in each q^2 bin that fail the endpoint lepton cutthe error bar ijs larger at lower q^2 becasue more of the leptons failed the endpoint cut there

could add the plot from lep tha shows the benefits of working in the m_x, mDfirts q^2 plot shows end pointregions, at high q^2 the range of lepton energies is onbly about twice as great asthe endpoint cut the second ploitis after data have been extrapolated to full q2 rangethis means that allowance is amde for the fraction of leptons in each q^2 bin that fail the endpoint lepton cutthe error bar ijs larger at lower q^2 becasue more of the leptons failed the endpoint cut there

could add the plot from lep tha shows the benefits of working in the m_x, mD

babar physics highlights and ucsd contributions

Documents

b0 decays

timedependent cp asymmetry

b decay topology

b0 j k0s b0

b0 decay rates

time evolution of b0

timedependent asymmetry

b meson lifetimes