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Recent Results on Charm Decays

Recent Results on Charm Decays. Lifetimes mesons baryons “Wrong” sign D 0 decays Mixing Doubly suppressed cabibbo decays CP violation searches Semileptonic charm decay Summary/Outlook. weak. Results from: BABAR BELLE CLEO FOCUS SELEX. Charm Particle Lifetimes.

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Recent Results on Charm Decays

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  1. Recent Results on Charm Decays • Lifetimes • mesons • baryons • “Wrong” sign D0 decays • Mixing • Doubly suppressed cabibbo decays • CP violation searches • Semileptonic charm decay • Summary/Outlook weak Results from: BABAR BELLE CLEO FOCUS SELEX Richard Kass

  2. Charm Particle Lifetimes Lifetime is a defining property of a “particle”. necessary to convert BR’s to decay rates Þ theoretical comparisons Weak interaction lifetime modified by strong interaction effects Þ non-perturbative QCD spectator exchange annihilation color suppressed internal spectator Charmed mesons and baryons provide a rich testing ground: 3 mesons (D+, D0, Ds) 4 baryons (Lc, Xc+, Xc0, W0c) doubly charmed baryons Interference effects are important: Pattern of lifetimes “predicted” but not exact lifetime values Richard Kass

  3. Colliding Beam vs Fixed Target Silicon detectors Beampipe Silicon detectors K g D0 p Colliding Beam Fixed target Better acceptance for short lifetimes Better L/s separation Cleaner environment Large data samples Unbinned ML fit Binned ML fit 1d or 2d vertex 3d vertex Neither actually “see” the decay as in emulsion and/or bubble chamber Richard Kass

  4. Charmed meson lifetimes Fixed target: exponential decay D0®K+p- signal Colliding beam: exponential decay smeared by resolution D0®K+p- sideband Richard Kass

  5. 1100 1080 1060 1040 1020 1000 E691 E687 CLEOII BELLE Lifetime results for Charmed Mesons ±1s PDG2001 lifetime (fs) + D preliminary Annihilation and exchange diagrams are important for mesons. Expect <1.07 without annihilation and exchange. Bigi & Uraltsev, Z.Phys. C.62, 623, 1994 Richard Kass

  6. Charmed Baryon Lifetimes Baryon lifetimes not measured as precisely as mesons: 5-30% vs 1-2% Baryon lifetimes shorter than mesons (e.g. tWc= 60 fs vs tD0= 410 fs ) Baryon cross sections are low Þsamples smaller than mesons Lifetime calculations more complicated than mesons New results for Lc+, Xc+, Xc0 not in PDG2001 preliminary preliminary ±1s PDG2001 Lc+ Richard Kass

  7. Recent Xc+lifetime Results t=503±47±18fs Xc+®X-p+p- 250±18 not in PDG2001 ±1s PDG2001 Xc+®X-p+p- Xc+®S+p+K- Xc+®pp+K- Xc+®Lp+p- K- 581±32 Richard Kass

  8. Charmed Baryons Lifetimes -9 -15 Preliminary Xc0result from FOCUS: t=109+10 fs (PDG2001: t=98+23 fs) Based on a total of 137±19 events (Xc0®W-K+, X-p+ ) Comments: Measured lifetime ratio for Xc+ / Lc+ larger than theory: Theory ranges from: 1.3 Blok and Shifman, proceedings of 3rd workshop on physics of a tau charm factory, (1993) 1.2-1.7 Guberina and Melic, Eur. Phys. J. C2, 697 (1998) At some point in the future lifetime analyses may have to correct for: Wc0® Xc+p-contamination of Xc+ sample Xc0® Lc+p-contamination of Lc+ in sample Doubly charmed baryons No Calculations available Cabibbo suppressed s ® u instead of c ® s Richard Kass

  9. - Why is D0-D0 mixing interesting? Only meson system where mixing has not been observed Only meson system where mixing is generated by down quarks Mixing in D sector expected to be small in Standard Model doubly Cabibbo Suppressed (DCS) vanishes the limit of SU(3) flavor symmetry If D mixing is large: DG ³ DM: large flavor SU(3) breaking ? DM >> DG: new physics ? D mixing only involves the first two generations: CPV >> 10-3Þ New Physics Can make measurements to look for mixing ! Richard Kass

  10. D mixing Phenomenology Usual definitions: Phases: d is the strong phase between Cabibbo allowed and doubly Cabibbo suppressed amplitudes f is the CP violating phase in mixing (very small in SM) CP Violation: CPV in mixing due to |p/q|¹1 CPV in interference between decay with and without mixing µsinf¹0 Assume no direct CPV Richard Kass

  11. Ways to Observe D mixing Measure lifetime difference between CP+ and/or CP- states and with flavor specific (CP mixed) states. CP+: D0®K+K-, p+p- CP-: D0®Ks0r0, Ks0w Mixed: D0®K-p+ Gives info on y: ycp» y if no CPV Requires good time (vertex) resolution Measure “Wrong” sign Decays. hadronic decays: D0®K+p- semi-leptonic decays: D0®K+l-v Don’t have to measure time dependence - Richard Kass

  12. “Wrong” sign D0 decays These decays can originate from: • Double Cabibbo suppression (DCS) (hadronic decays only) • Mixing Wrong sign rate (RWS) has interesting time dependence due to mixing+decay: Usual assumptions: CP conserved Þ|p/q|=1 |x|, |y|, RDCS<<1 d=strong phase difference between CF and DCS decays Convenient to rotate away d: x¢=xcosd+ysind, y¢=ycosd-xsind NO DCS for semi-leptonic decays: Richard Kass

  13. Some Recent ycp Lifetime Results CLEO: sub. PRD Not a full blown lifetime analysis Looking for lifetime differences KK: ycp =-1.9 ±2.9 ±1.6 pp: ycp = 0.5 ±4.3 ±1.8 FOCUS: PLB485, 62 (2000) ycp =3.4 ±1.4 ±0.7 BABAR: preliminary ycp =-1.0 ±2.2 ±1.7 Richard Kass

  14. Recent Mixing Results via ycp preliminary +0.7 -0.8 Richard Kass

  15. Mixing Limits using “wrong” sign and ycp measurements ¨CLEO’sTime dependence of G(D0®K+p- )/ G(D0®K-p+) Published Data ¨E791 Semi-leptonic G(D0®K+l-v)/ G(D0®K-l+v) limit: G(D0®K+l-v)/ G(D0®K-l+v)<0.5%@ 90%CL ¨ ycp measurements (FOCUS, E791) Richard Kass

  16. Mixing Limits using “wrong” sign and ycp measurements What will this plot look like in the near future? New results expected soon from CLEO, FOCUS, BABAR, BELLE FOCUS, CLEO SL sensitivity average ycp FOCUS preliminary Kp Richard Kass

  17. “Wrong” sign D0 Decay rates RWS=G(D0®K+p- )/ G(D0®K-p+) (%) Improved measurements of G(D0®K+p- )/ G(D0®K-p+): preliminary 10X data soon preliminary Preliminary D*+ D0p+ D0 K+p- Richard Kass

  18. CLEO II.V result for D0®K+p-p+p- More “wrong” sign D0 Decay rates 9fb-1 of data used in analysis 54 ± 14 WS events from 2D binned ML fit +0.12 (stat) ±0.04(sys)] ´(1.07±0.10)(phase space)(%) [0.41 -0.11 CLEO II.V result consistent with previous E791 result: +0.36 (stat) ±0.03 (sys) (%) (phase space=1) RWS=0.25 -0.34 But cannot tell if this result is from DSC or mixing since: Only other WS D0 result: CLEO’s Richard Kass

  19. D0®K0p0 and K0p0 L S - Interference between the Cabibbo allowed decay D0®K0p0 and the DCS decay D0®K0p0 can lead to a rate difference between D0®KLp0 and KSp0. Preliminary result from BELLE Expect a 5% (»tan2qc) asymmetry in: The magnitude and sign of A provides info the strong phase difference (d) between D0®K+p- and D0®K-p+ . Experimentally very challenging ! Difficult to reconstruct KL’s in an e+e- experiment BELLE calibrates KL efficiency using D0®K*-p+ , with K*-®KLp- . Richard Kass

  20. L S D0®K0p0 and K0p0 D0®KLp0 D0®KSp0 Preliminary First reconstruction of D’s using KL’s! D0®K*-p+ ®KLp-p+ D0®K*-p+ ®KSp-p+ Using 23 fb-1 of data BELLE measures: Richard Kass

  21. CP Violation in D0 Decay CPV expected to be small in the charm sector SM predictions O(0.1%) CPV > 1% evidence for non-SM processes Look for particle Û anti-particle rate differences - Use D* tag to distinguish D0 from D0. Measure: Where f is: K+K-, p+p-, Ksf, Ksp0, p0p0, and KsKs Richard Kass

  22. CP Violation in D0 Decay K+K- p+ p- CLEO also has the following results: ACP(Ksf)=-2.8±9.4% ACP(p0p0)=0.1±4.8% ACP(Ksp0)=0.1±1.3% ACP(KsKs)=23±19% CLEO “wrong” sign D0®K+p- analysis yields: No mixing in fit ACP(K+p-)=2+19±1.0 % -20 No evidence for CP violation in D0 decay Richard Kass

  23. CP Violation in D+ Decay For charged D’s measure the following: Look for direct CP violation, no mixing. Not much new since 2000 All results are from fixed target experiments. K ±K*0 fp ± p+p-p± K+K-p± No evidence for CPV Richard Kass

  24. CLEO Measurement of B(D+®K*0l+nl) CLEO Method: Use D* tag, reconstruct n using jet direction for D+ direction 2-fold ambiguity, choose solution closest to dm=MD*-MD=140.6 MeV fit K* mass in bins for dm then fit resulting dm with K*+data to extract signal This decay is sensitive to P ®V form factor These form factors are related to ff’s in b®ulv and b®sll. Can help reduce uncertainty in extraction of |Vub| preliminary Re=0.74 ± 0.04 ± 0.06 Rm=0.72 ± 0.104 ± 0.06 R=0.73 ± 0.04 ± 0.05 PDG: B(D+®K-p+p+) =(9.0 ± 0.6)% BRe =(6.7 ± 0.4 ± 0.5 ± 0.4)% BRm =(6.5 ± 0.9 ± 0.5 ± 0.4)% BR =(6.6 ± 0.4 ± 0.5 ± 0.4)% Richard Kass

  25. Motivation: Alternative method for extracting |Vub| and |Vcb| CLEO’s form factor ratio measurement in Lc®Le+n Same set of form factors in both decays: f1(q2), f2(q2) Korner&Kramer predict: R= f2(q2)/f1(q2)=-0.25 (PL B275,495 (1992)) right sign Le+, Le- wrong sign Le-, Le+ Extract R using ML fit to 3 variables: t=(q/qmax)2 cosqW= angle between e and W in cm of W cosqL= angle between p and L in cm of L Preliminary Result: R= -0.31±0.06±0.06 Improvement over previous CLEO result: R= -0.25±0.14±0.08, (PRL 75,624 (1995)) Consistent with Korner&Kramer Richard Kass

  26. Wc0®W-e+n preliminary Search for Wc0®W-e+n by comparing “right” (W-e+) sign and “wrong” sign (W-e-) event yields. (W-e-) (W-e+) 10X smaller than ARGUS result 520±230±130 fb Probability of background fluctuation < 9x10-4 B(Wc0®W-e+n )s(e+e-®Wc X)=42.2±14.1±11.9 fb First observation of baryon b decay with no u or d in parent particle Richard Kass

  27. Charm Review Summary + + c c c c Lifetimes: mesons: lifetimes measured to 1- 2% baryons: lifetimes measured ~2 - 30% theory may need a tune up: tX /tL|exp>2 vstX /tL|th< 1.7 D Mixing: Exciting times ahead new results expected from BELLE & BABAR soon CP Violation: Keep looking ! Semileptonic Decays: Progress measuring rates and form factors “The future of charm physics lies ahead of us !” Yogi Berra? George W.? b-factories are charm factories too CLEO-c Richard Kass

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