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Recent Results from the BaBar Experiment.

Recent Results from the BaBar Experiment. Brian Meadows University of Cincinnati. Outline. The BaBar Experiment CP Violation B 0 – B 0 Mixing, Lifetime and sin 2  Measurements Charm at B A B AR A New Particle D 0 – D 0 Mixing : Summary. The BaBar Detector at SLAC (PEP2).

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Recent Results from the BaBar Experiment.

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  1. Recent Results from the BaBar Experiment. Brian Meadows University of Cincinnati Brian Meadows, U. Cincinnati.

  2. Outline • The BaBar Experiment • CP Violation • B0 – B0 Mixing, Lifetime and sin 2 Measurements • Charm at BABAR A New Particle D0 – D0 Mixing: • Summary Brian Meadows, U. Cincinnati

  3. The BaBar Detector at SLAC (PEP2) • Asymmetric e+e- collisions at (4S). •  = 0.56 (3.1 GeV e+, 9.0 GeV e-) 1.5 T superconducting field. Instrumented Flux Return (IFR) Resistive Plate Chambers (RPC’s): Barrel: 19 layers in 65 cm steel Endcap: 18 “ “ 60 cm “ Brian Meadows, U. Cincinnati

  4. Silicon Vertex Tracker (SVT) • 5 Layers double sided AC-coupled Silicon • Rad-hard readout IC (2 MRad – replace ~2005) • Low mass design • Stand alone tracking for slow particles • Point resolution z » 20 m • Radius 32-140 mm Brian Meadows, U. Cincinnati

  5. Drift Chamber 40 layer small cell design 7104 cells He-Isobutane for low multiple scattering dE/dx Resolution »7.5% Mean position Resolution 125 m Brian Meadows, U. Cincinnati

  6. Particle ID - DIRC Detector of Internally Reflected Cherenkov light • Measures Cherenkov angle in quartz • Photons transported by internal refl. • Detected at end by » 10,000 PMT’s 144 quartz bars Brian Meadows, U. Cincinnati

  7. Particle ID - DIRC It Works Beautifully! Provides excellent K/ separation over the whole kinematic range Brian Meadows, U. Cincinnati

  8. Particle ID - DIRC D0 D0 Brian Meadows, U. Cincinnati

  9. Electromagnetic Calorimeter • CsI (doped with Tl) crystals • Arranged in 48()£120() • » 2.5% gaps in . • Forward endcap with 8 more  rings (820 crystals). Brian Meadows, U. Cincinnati

  10. Off • On PEP-II performances Peak Luminosity 4.9 £ 1033 cm-2¢ s-1 • 24 fb-1 in run 1 • 70 fb-1 in run2 • 10 fb-1 so far in run3 run3 Most analyses use ~88M BB decays (runs 1+2) run2 (~12% off peak) run1 Brian Meadows, U. Cincinnati

  11. CP Violation • CP violation is manifest when a process involving particles occurs at a different rate to that with anti particles: (B ! f)  (B ! f) • Under CP transformation, amplitudes A have weak phases  that reverse sign but strong ones  that do not A = a exp{i(+ )} ! A = a e{i(- )} • If two amplitudes A1 and A2 contribute to a process, the rates are:  = |A1+ A2|2 = a12+ a22+ 2a1a2 cos( + )  = |A1+ A2|2 = a12+ a22+ 2a1a2 cos( - ) •  (CP Violation)when  (´2-1)  0 and (´2-1) 0. CP CP violation is maximum when a1 = a2 ! Brian Meadows, U. Cincinnati

  12. J=Vqq’ q’  (1+5) q q’ q W CP Violation in the Standard Model • The phase in the CKM quark mixing matrix can give rise to CP Violation. • CKM imparts a phase to weak currents that cannot be removed by re phasing the quark fields. • Interference between a tree and a penguin process can give direct CP Violation but information on strong phases is required to interpret it. • Decays of B0 to CP eigenstates f accessible also to B0 can occur directly or through mixing. Allows interpretation without knowing strong phases Brian Meadows, U. Cincinnati

  13. f B0 Mixing B0 Mixing Induced CP Violation • If final state f is accessible for both B0 and B0 decay then mixing will interfere with direct decays • If f is a CP eigenstate, the decay amplitudes <f|T|B0> and <f|T|B0> have: • identicalstrong phases • identical weak phases, but with opposite signs • the same magnitudes. • So the CP violation is maximized. • CP violation has a time structure emanating from B0 mixing Brian Meadows, U. Cincinnati

  14. dN/dt/ e - |t|/£ [1 §Ccos(mt) ¨S sin(mt)] C = (1 - |f|2) / (1 + |f|2) S = Im{ f }/ (1 + |f|2) • In the SM for b!ccs decays: • f = exp{2i} • AND no Penguin contributes Mixing Decay Interference between two direct decay modes such as P and T Interference between mixing and decay.  is one of the angles in a unitarity triangle ! Brian Meadows, U. Cincinnati

  15. d s b u c t The Unitarity Triangles (K system) d•s* = 0 (Bs system) s•b* = 0 (Bd system) d•b* = 0 These three triangles (and the three triangles corresponding to the rows) all have the same area. A nonzero area is a measure of CP violation and is an invariant of the CKM matrix. apply unitarity constraint to pairs of columns Brian Meadows, U. Cincinnati

  16. d s b u c t The Usual Unitarity Triangle Vtb*Vtd Vub*Vud    Vcb*Vcd Orientation of triangle has no physical significance. Only relative angle between sides is significant. apply unitarity constraint to these two columns Brian Meadows, U. Cincinnati

  17. d s b u c t (, ) Vtb*Vtd Vcb*Vcd Vub*Vud Vcb*Vcd    (1, 0) (0, 0) The Usual Unitarity Triangle apply unitarity constraint to these two columns Brian Meadows, U. Cincinnati

  18. p+ B0 / B0 e+ e- — B0 / B0 e ±, m ±, K± tag Dz =c t Dz ~ 255 mm for PEP-II: 9.0 GeV on 3.1 GeV ~ 200 mm for KEKB: 8.0 GeV on 3.5 GeV The Asymmetric-Energy B Factories (4S) Brian Meadows, U. Cincinnati

  19. Dt distributions with NO experimental effects Flavor states sorted by mixing status CP states sorted by B tag flavor B0B0 or B0 B0 Btag= B0 Btag= B0 B0B0 or B0 B0 B Mixing dN exp(–|Dt|/tB) ( 1 ± cos(DmDt) ) CP violation dN exp(–|Dt|/tB) ( 1 ± sin2b sin(DmDt) ) Brian Meadows, U. Cincinnati

  20. unmixed – mixed unmixed + mixed Asymmetry = ~ (1 – 2w)  (1 – 2w) cos(DmdDt) ~ p / Dmd Perfect flavor tagging and time resolution Realistic mis-tag and finite time resolution - unmixed - unmixed - mixed - mixed Brian Meadows, U. Cincinnati

  21. B0 – B0 Mixing md , B andsin 2 Measurements Brian Meadows, U. Cincinnati

  22. Increase in precision of B lifetimes and mixing frequency B0 Lifetime (ps) 1.548  0.032 1.542  0.016 Ratio of B+ to B0 Lifetime 1.060  0.029 1.083  0.017 B0 Mixing Frequency ( x 1012 s-1) 0.472  0.017 0.489  0.009 PDG2000 18 measurements 12 measurements 10 measurements PDG2002 New measurements: 3 B Factory 2 LEP 2 B Factory 1 LEP 3 B Factory 1 LEP • Uncertainties limited by: • knowledge of t resolution function • B (for mixing). • BABARMeasured both together using the copious B0!D*lmode. Brian Meadows, U. Cincinnati

  23. hep-ex/0207071 (ICHEP) Dmd=0.492±0.018±0.013ps-1 +0.024-0.023 B0=1.523±0.022ps correlation coefficient (m, B0) = -0.22 • In a few years we might: • anticipate < 1% uncertainty in B0 mixing • possibly measure  • (test CPT limits directly). Brian Meadows, U. Cincinnati

  24. Sin 2 Primary result comes from charmonium decay modes. Simultaneously fit flavour specific modes to determine flavour tagging quality and  resolution. Additional information from modes which include penguin (P) in addition to tree (T) modes. Vtb*Vtd  Vcb*Vcd Brian Meadows, U. Cincinnati

  25. Charmonium Modes for sin 2 b c , c, c One dominant decay amplitude !theoretically clean. (Penguin has same phase!) c B0 s KS , L d d Both BABAR and Belle use six charmonium modes: BJ/Ks0, Ks0p+p-, p0p0 BJ/KL0 B(2S) Ks0 Bc1Ks0 BJ/K*0, K*0 Ks0 BcKs0 Simultaneously measure self tagging modes to determine  and (t). Brian Meadows, U. Cincinnati

  26. Sin2b Data Samples in BABAR Bflav Mixing sample ccKs modes B0D(*)-p+/ r+/ a1+ Ntagged= 23618 Purity= 84% • Data • Data Signal J/y KL J/y Bkg Fake J/y Bkg (MeV) Brian Meadows, U. Cincinnati

  27. hep-ex/ 0207042 (PRL) Ks modes KL modes 81 fb-1 (88 M BB) 2641 tagged events with Dt measured (78% purity; 66% tagging e) sin2b = 0.741  0.067  0.034 || = 0.948  0.051  0.030 effective tagging eff: e=(28.1  0.7)% Brian Meadows, U. Cincinnati

  28. Golden modes with a lepton tag The best of the best! Ntagged = 220 Purity = 98% Mis-tag fraction 3.3% sDt 20% better than other tag categories background sin2b = 0.79  0.11 Brian Meadows, U. Cincinnati

  29. sin2b measurement history • “Osaka 2000” measurement • (hep-ex/0008048) • Only J/y Ks and y(2s) Ks. • 1st Paper (PRL 86 2515, 2001) • Added J/y KL. • Simultaneous sin2b and mixing fit. • 2nd Paper (PRL 87 201803, 2001) • Added J/y K*0 and c Ks. • Better vertex reconstruction. • Better SVT alignment and higher Ks efficiency for new data. • Winter 2002 (hep-ex/0203007) • Improved event selection. • Reprocessed 1st 20 fb-1. • e) Current measurement (hep- ex/0207042, PRL) • Improved flavor tagging. • One more CP mode: hcKs. (compiled by Owen Long) d e c b a Brian Meadows, U. Cincinnati

  30. Decrease in Statistical Uncertainty • Curves represent 1/sLdt. • Improvements in statistical uncertainty due to • adding new B decay modes, • improved vertex reconstruction, • improved SVT alignment, • improved tagging performance. Brian Meadows, U. Cincinnati

  31. hep-ex/0208025, sub to PRD RC Belle 78 fb-1 (85 M BB) 2958 events (81% purity) effective tagging efficiency: e=(28.8  0.6)% sin2b = 0.719  0.074  0.035|| = 0.950  0.049  0.025 Brian Meadows, U. Cincinnati

  32. Constraints on upper vertex of Unitarity Triangle from all measurements EXCEPT sin2b b Regions of >5% CL A. Höcker, H. Lacker, S. Laplace, F. Le Diberder, Eur. Phys. Jour. C21 (2001) 225, [hep-ph/0104062] Brian Meadows, U. Cincinnati

  33. World Average sin2b = 0.78  0.08 The Standard Model (and the CKM paradigm, in particular) wins again … at least at the current level of experimental precision, in this decay mode. Brian Meadows, U. Cincinnati

  34. s s s t t d Other studies of sin2 B0Ks b s   s b s B0 s B0 K0 K0 d d d • Pure penguin ! • time-dependent asymmetry in B0Ks measures sin2. • direct charge asymmetry in B+K+ sensitive to new physics. Brian Meadows, U. Cincinnati

  35. B0Ks samples 51 signal events hep-ex/0207070 (ICHEP2002) +0.52 - 0.50 sin2b = -0.19  0.90 • c.f. world average: sin2 = 0.73 ± 0.06 • >2 difference. • (over) stimulating theoretical interest. Brian Meadows, U. Cincinnati

  36. Charm Physics Brian Meadows, U. Cincinnati

  37. Charm at the BABARB Factory? • Cross section is large Present sample of 91 fb-1 sample contains • Compare with earlier charm experiments: • E791 - 35,400 1 • FOCUS - 120,000 2 • CDF - 56,320 • Approximately 1.12 £ 106 untagged D0!K-+ events 1. E791 Collaboration, Phys.Rev.Lett. 83 (1999) 32. 2. Focus Collaboration, Phys.Lett. B485 (2000) 62. Brian Meadows, U. Cincinnati

  38. A New Ds State .. or? Brian Meadows, U. Cincinnati

  39. A New Narrow Resonance • A striking signal observed in the Ds+0 system. • Signal clearly associated with both Ds+ and 0 • Is not a reflection of any other known state (MC) D § Ds§ 0 Brian Meadows, U. Cincinnati

  40. There are over 1500 events in the signal. The resonance has width comparable with the mass resolution in this system. It is evident in two different topologies a)D§s!K§ K¨ § b) D§s!K§ K¨ §0 Within a) it is seen in both K*K and § channels consistently. Generic MC test shows it is not a reflection of any known state. A New Narrow Resonance “Ds(2317)” Ds1(2112) p* > 3.5 GeV/c p* > 3.5 GeV/c Ds1(2112) Brian Meadows, U. Cincinnati

  41. A New Narrow Resonance Ds1+(2112) • There is no significant decay of the Ds (2317) resonance to Ds+ at the present level of statistics. • Nor to Ds1+(2112) . • A kinematic enhancement at 2460 MeV/c2 results from overlap if Ds(2317) and Ds(2112). (However, Ds(2317) is not a kinematic reflection from effect at 2460 MeV/c2). Ds+ Ds+  Ds1(2112) Ds+ 0 Ds1(2112)0 Suggests a JP = 0+ assignment Brian Meadows, U. Cincinnati

  42. … so what is it? • Both the Godfrey-Isgur-Kokoski and Di Pierro-Eichten* models predict a JP = 0+Ds level at a mass of ~2.48 GeV, having width in the range 270 to 990 MeV and prominent decay to D 0K. • Since the state observed is below DK threshold, it decays in an I spin violating mode. • These and other theoretical models have made mass predictions correct to ~ 10 MeV/c2 in all other cases for B as well as D mesons. • Perhaps this is the charm analogue of the a0(980) instead !! *PRD 64, 114004 (2001) Brian Meadows, U. Cincinnati

  43. D0 – D0 Mixing Brian Meadows, U. Cincinnati

  44. D0 Mixing with CP Violation • Parameters used to describe mixing are x=(m1-m1)/ ; y=(1-2)/2 where  = (1+2)/2 m1,2 and 1,2 are mass and width of mass eigenstates. • Mass eigenstates D1,2 are related to flavour eigenstates • For decay D (D) !f (f) as in B decays: |f|  1 implies CP violation in mixing; Imf0implies CP violation in interference between mixing & decay Brian Meadows, U. Cincinnati

  45. D0 Mixing with CP Violation • Most standard model estimates for x and y are . 10-3. • So mixing rate RM = (x2+y2)/2» 10-6 • Beyond experimental observation • Observation of mixing, especially |x|>|y|, could be evidence for new physics • CP violation in mixing would be sure sign of new physics. • New particles could • increase mixing • introduce phase in • decays. Brian Meadows, U. Cincinnati

  46. Mixing Parameters from Ratio of Lifetimes • D0 decays are ~ exponential. Lifetimes () depend on CP of final state. Previous analyses have measured: . • If CP violation occurs ! Different lifetimes for D0 (+) and D0 (-) decays to CP even states. • We define and measure two NEW quantities (Y and Y): Y´0/<> - 1 Y´ A0 / <> [ <> = (+ + -) / 2 A = (+ - -) / (+ + -) ] If direct CP violation absent in decays, KK or  modes can be averaged. for D0! CPmixed(K-+) Useful if |f|=1 and Im f=0 for D0! CPeven(K-K+ or -+ ) Brian Meadows, U. Cincinnati

  47. Fit Results • The fit uses all the data - Events within 15 MeV/c2 of D0 mass shown here. • Background estimated from mass and lifetime fits. • Statistical uncertainty small, e.g. for K-+ it is »0.9 fsec (»0.5% in y). Brian Meadows, U. Cincinnati

  48. Comparison with Earlier Results Published (23.4 fb-1) Moriond 2002 This Analysis Also Y = - (8 § 6 stat. § 2 syst.) £ 10-3 Brian Meadows, U. Cincinnati

  49. D0 Mixing from Wrong Sign Decays • Wrong sign (WS) decays D0! K+- can occur directly DCS or through mixing followed by the right sign (RS) CF decay: • WS decays are not exponential: • To search for CP violation, this distribution is measured for D0 and D0 separately to determine all the three terms. DCS CF Mixing Mixing DCS Interference units of 0 Brian Meadows, U. Cincinnati

  50. Fits with Mixing • Fit allowed x’ 2<0. Central values for D0, D0 and joint sample fits gave x’ 2<0. • 95% contours are determined using toy MC samples at each point on the contour (frequentist approach). • (x’ 2§, y’§) points on separate D0 and D0 contours are combined in pairs to determine (x’ 2, y’) on 95% CPV contour. • Systematic uncertainties are added in quadrature to distance from best fit to data. Best fit (x’ 2=0) Best fit (x’ 2 free) no CPV Brian Meadows, U. Cincinnati

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