Recent Results on Charm Decays Lifetimes mesons baryons

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 WIN 02 Jan 24, 2002 Results from: BABAR BELLE CLEO FOCUS SELEX Richard Kass

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 color suppressed internal spectator exchange annihilation Charmed mesons and baryons provide a rich testing ground: 3 mesons (D+, D 0, Ds) 4 baryons (Lc, Xc+, Xc 0, W 0 c) doubly charmed baryons Interference effects are important: Pattern of lifetimes “predicted” but not exact lifetime values WIN 02 Jan 24, 2002 Richard Kass

Colliding Beam vs Fixed Target Silicon detectors Beampipe Silicon detectors g K D 0 p Colliding Beam Fixed target Better acceptance for short lifetimes Cleaner environment Unbinned ML fit 1 d or 2 d vertex Better L/s separation Large data samples Binned ML fit 3 d vertex Neither actually “see” the decay as in emulsion and/or bubble chamber WIN 02 Jan 24, 2002 Richard Kass

Charmed meson lifetimes Fixed target: exponential decay D 0®K+psignal Colliding beam: exponential decay smeared by resolution D 0®K+psideband WIN 02 Jan 24, 2002 Richard Kass

Lifetime results for Charmed Mesons ± 1 s PDG 2001 1100 D+ lifetime (fs) 1080 1060 1040 1020 1000 E 691 E 687 CLEOII BELLE preliminary Annihilation and exchange diagrams are important for mesons. Expect <1. 07 without annihilation and exchange. Bigi & Uraltsev, Z. Phys. C. 62, 623, 1994 WIN 02 Jan 24, 2002 Richard Kass

Charmed Baryon Lifetimes Baryon lifetimes not measured as precisely as mesons: 5 -30% vs 1 -2% Baryon lifetimes shorter than mesons (e. g. t. Wc= 60 fs vs t. D 0= 410 fs ) Baryon cross sections are low Þ samples smaller than mesons Lifetime calculations more complicated than mesons New results for Lc+, Xc 0 not in PDG 2001 preliminary ± 1 s PDG 2001 Lc + WIN 02 Jan 24, 2002 Richard Kass preliminary

Recent Xc+ lifetime Results Xc+®X-p+p- t=503± 47± 18 fs 250± 18 not in PDG 2001 ± 1 s PDG 2001 581± 32 Xc+®X-p+p. Xc+®S+p+KXc+®pp+KXc+®Lp+p- K- WIN 02 Jan 24, 2002 Richard Kass

Charmed Baryons Lifetimes Preliminary Xc 0 result from FOCUS: +23 t=109+10 -9 fs (PDG 2001: t=98 -15 fs) Based on a total of 137± 19 events (Xc 0®W-K+, X-p+ ) Comments: Measured lifetime ratio for Xc+ / Lc+ larger than theory: Theory ranges from: 1. 3 Blok and Shifman, proceedings of 3 rd workshop on physics of a tau charm factory, (1993) 1. 2 -1. 7 Guberina and Melic, Eur. Phys. J. C 2, 697 (1998) At some point in the future lifetime analyses may have to correct for: Wc 0® Xc+p- contamination of Xc+ sample Cabibbo suppressed s ® u Xc 0® Lc+p- contamination of Lc+ in sample instead of c ® s Doubly charmed baryons WIN 02 Jan 24, 2002 No Calculations available Richard Kass

Why is - D 0 -D 0 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 -3 Þ New Physics Can make measurements to look for mixing ! WIN 02 Jan 24, 2002 Richard Kass

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|¹ 1 CPV in interference between decay with and without mixing µ sinf ¹ 0 Assume no direct CPV WIN 02 Jan 24, 2002 Richard Kass

Ways to Observe D mixing Measure lifetime difference between CP+ and/or CP- states and with flavor specific (CP mixed) states. CP+: D 0®K+K-, p+p. CP-: D 0®Ks 0 r 0, Ks 0 w Mixed: D 0®K-p+ Gives info on y: ycp» y if no CPV Measure “Wrong” sign Decays. hadronic decays: D 0®K+psemi-leptonic decays: D 0®K+l--v WIN 02 Jan 24, 2002 Requires good time (vertex) resolution Don’t have to measure time dependence Richard Kass

“Wrong” sign D 0 decays These decays can originate from: a) Double Cabibbo suppression (DCS) (hadronic decays only) b) 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: WIN 02 Jan 24, 2002 Richard Kass

Some Recent ycp Lifetime Results CLEO: sub. PRD KK: ycp =-1. 9 ± 2. 9 ± 1. 6 pp: ycp = 0. 5 ± 4. 3 ± 1. 8 Not a full blown lifetime analysis Looking for lifetime differences FOCUS: PLB 485, 62 (2000) ycp =3. 4 ± 1. 4 ± 0. 7 BABAR: preliminary ycp =-1. 0 ± 2. 2 ± 1. 7 WIN 02 Jan 24, 2002 Richard Kass

Recent Mixing Results via ycp preliminary experiment ycp(%) comments FOCUS 3. 4 ± 1. 4 ± 0. 7 Fixed target, K+K- E 791 0. 8 ± 2. 8 ± 1. 0 Fixed target, K+K- CLEO -1. 2 ± 2. 5 ± 1. 4 e+e-, K+K-, p+p- BELLE -0. 5± 1. 0 +0. 7 -0. 8 e+e-, K+K- BABAR -1. 0 ± 2. 2 ± 1. 7 e+e-, K+K- WIN 02 Jan 24, 2002 Richard Kass

Mixing Limits using “wrong” sign and ycp measurements ¨CLEO’s Time dependence of G(D 0®K+p- )/ G(D 0®K-p+) Published Data ¨E 791 Semi-leptonic G(D 0®K+l-v)/ G(D 0®K-l+v) limit: 0®K+l-v)/ G(D 0®K-l+v)<0. 5%@ 90%CL G(D ¨ y measurements (FOCUS, E 791) cp WIN 02 Jan 24, 2002 Richard Kass

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 WIN 02 Jan 24, 2002 Richard Kass

“Wrong” sign D 0 Decay rates Improved measurements of G(D 0®K+p- )/ G(D 0®K-p+): preliminary RWS=G(D 0®K+p- )/ G(D 0®K-p+) (%) CLEO II 0. 77 ± 0. 25 ALEPH 1. 84 ± 0. 59 ± 0. 34 E 791 0. 68 ± 0. 34 ± 0. 07 CLEO II. V 0. 33 ± 0. 06 ± 0. 04 FOCUS 0. 40 ± 0. 09 ± 0. 03 BABAR 0. 38 ± 0. 04 ± 0. 02 BELLE 0. 30 ± 0. 06 ± 0. 08 preliminary 10 X data soon D*+ D 0 p+ D 0 K + p - WIN 02 Jan 24, 2002 Richard Kass

More “wrong” sign D 0 Decay rates CLEO II. V result for D 0 ®K+p-p+p 9 fb-1 of data used in analysis 54 ± 14 WS events from 2 D binned ML fit +0. 12 (stat) -0. 11 [0. 41 ± 0. 04(sys)] ´(1. 07± 0. 10)(phase space)(%) CLEO II. V result consistent with previous E 791 result: RWS=0. 25 +0. 36 -0. 34 (stat) ± 0. 03 (sys) (%) (phase space=1) But cannot tell if this result is from DSC or mixing since: Only other WS D 0 result: CLEO’s WIN 02 Jan 24, 2002 Richard Kass

D 0®KL 0 p 0 and KS 0 p 0 Preliminary result from BELLE - Interference between the Cabibbo allowed decay D 0®K 0 p 0 and the DCS decay D 0®K 0 p 0 can lead to a rate difference between D 0®KLp 0 and KSp 0. Expect a 5% (» tan 2 qc) asymmetry in: The magnitude and sign of A provides info the strong phase difference (d) between D 0®K+p- and D 0®K-p+. Experimentally very challenging ! Difficult to reconstruct KL’s in an e+e- experiment BELLE calibrates KL efficiency using D 0®K*-p+ , with K*-®KLp-. WIN 02 Jan 24, 2002 Richard Kass

D 0®KL 0 p 0 and KS 0 p 0 D 0®KSp 0 D 0®KLp 0 First reconstruction of D’s using KL’s! D 0®K*-p+ ®KSp-p+ D 0®K*-p+ ®KLp-p+ Using 23 fb-1 of data BELLE measures: WIN 02 Jan 24, 2002 Richard Kass

CP Violation in D 0 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 D 0 -0 from D. Measure: Where f is: K+K-, p+p-, Ksf, Ksp 0, p 0 p 0, and Ks. Ks WIN 02 Jan 24, 2002 Richard Kass

CP Violation in D 0 Decay K+ K- p+ p- CLEO also has the following results: ACP(Ksf)=-2. 8± 9. 4% ACP(Ksp 0)=0. 1± 1. 3% ACP(p 0 p 0)=0. 1± 4. 8% ACP(Ks. Ks)=23± 19% CLEO “wrong” sign D 0®K+p- analysis yields: ACP(K+p-)=2+19 ± 1. 0 % -20 No mixing in fit No evidence for CP violation in D 0 decay WIN 02 Jan 24, 2002 Richard Kass

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- p ± K*0 fp ± p+p-p± No evidence for CPV WIN 02 Jan 24, 2002 Richard Kass

CLEO Measurement of B(D+®K*0 l+nl) 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| 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 Me. V fit K* mass in bins for dm then fit resulting dm with K*+data to extract signal preliminary Re=0. 74 ± 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)% WIN 02 Jan 24, 2002 Richard Kass

CLEO’s form factor ratio measurement in Lc®Le+n Motivation: Alternative method for extracting |Vub| and |Vcb| Same set of form factors in both decays: f 1(q 2), f 2(q 2) Korner&Kramer predict: R= f 2(q 2)/f 1(q 2)=-0. 25 (PL B 275, 495 (1992)) right sign Le+, Le- wrong sign Le-, Le+ Extract R using ML fit to 3 variables: t=(q/qmax)2 cosq. W= angle between e and W in cm of W cosq. L= angle between p and L in cm of L Preliminary Result: R= -0. 31± 0. 06 Improvement over previous CLEO result: R= -0. 25± 0. 14± 0. 08, (PRL 75, 624 (1995)) Consistent with Korner&Kramer WIN 02 Jan 24, 2002 Richard Kass

Wc 0®W-e+n Search for Wc 0®W-e+n by comparing “right” (W-e+) sign and “wrong” sign (W-e-) event yields. preliminary (W-e+) (W-e-) Probability of background fluctuation < 9 x 10 -4 10 X smaller than ARGUS result B(Wc 0®W-e+n )s(e+e- ®Wc X)=42. 2± 14. 1± 11. 9 fb 520± 230± 130 fb First observation of baryon b decay with no u or d in parent particle WIN 02 Jan 24, 2002 Richard Kass

Charm Review Summary Lifetimes: mesons: lifetimes measured to 1 - 2% baryons: lifetimes measured ~2 - 30% theory may need a tune up: +c t. X /t. L|exp>2 vs+c t. Xc/t. L|th< c 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 WIN 02 Jan 24, 2002 Richard Kass