Alexis POMPILI ( University & I.N.F.N. of Bari ) [representing the Collaboration]

1. CHARM PHYSICS in Alexis POMPILI (University &I.N.F.N. of Bari) [representing the Collaboration] Les Rencontres de Physique de la Vallee d’Aoste La Thuile – March 3, 2004

2. Charm Physics @ BaBar -Outline Analyses results reviewed here: D0 mixing with 2-body hadronic decays (wrong sign & CP final states) states spectroscopy Other Studies in progress: D0 mixing with semi-leptonic decays 3-body decays of D0, D+, Ds+( B. R., Light Meson Spectroscopy, CP, mixing ) charmed baryons ISR processes 2 La Thuile - 2004 Alexis Pompili(U. of Bari & I.N.F.N.)

3. Charm Physics @ PEP-II B-factory PEP-II (SLAC):asymmetric e+e- collider @ Y(4S) Integrated luminosity delivered : ~178fb-1 Effective qq cross sections at the energy of the Y(4S) Powerful tool for charm physics BABAR (90fb-1): ~220K Focus : 120K E791 : ~36K 3 La Thuile - 2004 Alexis Pompili(U. of Bari & I.N.F.N.)

4. The detector Crucial for charm physics PID CERENKOV DETECTOR e+ DRIFT CHAMBER TRACKING VERTEXING SILICON VERTEX e- KAON EFFICIENCY K-Id CHERENKOV PION CONTAMINATION Reconstructed K-K+ Mass (GeV/c2) 4 La Thuile - 2004 Alexis Pompili(U. of Bari & I.N.F.N.)

5. Selecting charm decays from continuum Kinematical selection: require cut on CMS momentum of charmed meson : combinatorial background strongly reduced D(*) from B-decays rejected D*-TAG withpS allows flavor-tagging reduces BKGD through dm = [m(K-p+ps) - m(K-p+)] D0 Refitting technique with beamspot - constraint pS D* improves dm resolution Beamspot 5 La Thuile - 2004 Alexis Pompili(U. of Bari & I.N.F.N.)

6. D-mixing: parameters & search methods Mass eigenstates: ( flavour eigenstates) masses: M1 , M2 widths: G1 , G2 MIXING PARAMETERS: beyond the reach of current experimental sensitivity SM : NEW PHYSICSmay enhancex …but FSI & SU(3)-breaking can enhance y Experimental goal : to put limits on the transition D0-D0 1) LIFETIME DIFFERENCE searches y [if CP conserved] 2) WRONG-SIGNsearches in hadronic decays x2, y ;d: unknown strong phase difference NP may not conserve CP consider CP when measuring mixing CP in mixing ( sure sign of NP ) CP in interference mixing–decay 6

7. Lifetime difference searches Mixing would alter the decay-time distributions of D0 and D0 that decay into CP eigenstates. They can be considered to a good approx. as pure exponential with effective lifetimes: for CSD of D0 (D0) into CP-even final states (such as K+K-,p+p-) for CFD LIFETIME RATIO These effective lifetimes can be combined into: where IF NO MIXING:x = y = 0 IF CP-CONSERVATION IN MIXING :rm=1 IFALSO … CP-CONSERVATION IN INTERFERENCE MIXING -DECAY: Systematics effects on lifetime tend to cancel in the lifetime RATIO 7 La Thuile - 2004Alexis Pompili(U. of Bari & I.N.F.N.)

8. Massfits DATA FIT RESULT ~265K ~26K SIGNAL (S) 99.4% 97.0% yield FROM THE FITS : BKGD (B) S/S+B mass window ~145K ~13K 68.1% Mass fits determine event-by-event signal probability 87.9% BKGD constrained in data “sidebands”candidates included as part of proper time fit 8 La Thuile - 2004 Alexis Pompili(U. of Bari & I.N.F.N.)

9. Decay-timedistributions fit within mass signal window: SIGNAL FROM THE FITS : BKGD DATA UNBINNED MAXIMUM LIKELIHOOD FIT RESULT 9 La Thuile - 2004 Alexis Pompili(U. of Bari & I.N.F.N.)

10. Summary oflifetime ratio results [Phys.Rev.Lett.91,12(2003)] hep-ex/0308034 BaBar has the most stringent limits on y BaBar has the firstmeasurement of a CP parameter with the method of lifetime ratio 10 La Thuile - 2004 Alexis Pompili(U. of Bari & I.N.F.N.)

11. Wrong-sign searchesin hadronic decays Study time-evolution of looking for a signal dKp: unknown relative strong phase (not measurable in a mixing analysis): rotation ofdKp in the x-y plane : DCSD & CFD may have different FSI Assuming and CP conservation : where deviation from pure exponential DCSD MIXING INTERFERENCE enhances mixing signal Integrating : mixing rate : Additional CP effects are included by measuring this distribution for D0 and D0 separately: 11 CPin their INTERFERENCE CPin DCSD CPin MIXING

12. Mass-mass differenceFit Assign each candidate to one of 4 categories: D0(RS,WS),D0(RS,WS) Unbinned extended max-likelihood fit to RS and WS samples simultaneously in 4D variable space performed in steps : proper time error 1st step fit m(Kp) d m Number of SIGNAL and BKGD candidates from a fit to m-dm plane (both RS and WS) by modelling BKGD categories Signal region Signal WS Wrong slow pion Combinatorial Sideband Double mis-id With 57fb-1: ~120,000 RS ~ 440 WS 12 La Thuile - 2004 Alexis Pompili(U. of Bari & I.N.F.N.)

13. Decay timeFit 2nd step fit Simultaneous fit time-distribution to RS and WS (include mixing parameters). The larger/clean RS sample fixes D0 lifetime and resolution model parameters for unmixed decays. BKGD time distributions determined from m,dm sidebands in data. WS Signal Wrong slow pion Combinatorial Double mis-id 13 La Thuile - 2004 Alexis Pompili(U. of Bari & I.N.F.N.)

14. Summary ofwrong-sign results [Phys.Rev.Lett.91,17(2003)] Results presented in 4 cases : 95% C.L. contours by a frequentistic approach (based on toy Monte Carlo experiments) : BEST FIT (x’2 free) NO CP BEST FIT (x’2=0) (stat.+syst.) (stat.) (Prelim.) CP allowed 14 La Thuile - 2004 Alexis Pompili(U. of Bari & I.N.F.N.)

15. Two surprising new Charmed Mesons : & [Phys.Rev.Lett. 90,24(2003)] BaBar discovered a new narrow state in the Ds+ p0 invariant mass distribution near 2.32GeV/c2 ! ! [Accepted by P.R.L. ; hep/ex-0310050] BaBar observed a second new narrow state in the Ds*+ p0 invariant mass distribution near 2.46GeV/c2 sidebands subtraction 15 La Thuile - 2004 Alexis Pompili(U. of Bari & I.N.F.N.)

16. Channel LikelihoodFit To disentangle these 2 possible DsJ(2458) decay modes & extract signal parameters: unbinned maximum likelihood fit using the channel likelihood method contribution from DsJ(2458) decays combinatorial background BELLE CLEO observed them in continuum and… Belle both in continuum and in B decays [] CLEO 16

17. SPIN-PARITY Decay to JP=0- mesons only natural spin-parity allowed [0+,1-,2+,…] JP=0+ suggested by: 1) low mass compared to Ds1(2535) & DsJ*(2573) 2) absence of decay to Ds+g (not allowed if JP=0+) 3) absence of decay to Ds+p+p- (not allowed if JP=0+) Un-natural spin-parity more likely (lack of decays to DK) Belle helicity analysis from B-decays favours J=1 Decay to Dsp+p- (by Belle) allowed by JP=1+ Two narrow states observed, in the inclusiveDsp0&Ds*p0 invariant mass distributions, near 2.317GeV/c2& 2.458GeV/c2. The widths [G<10MeV]are consistent with experimental resolution. The most likely assignment for their spin-parity is 0+& 1+. EXPERIMENTAL SUMMARY 17 La Thuile - 2004 Alexis Pompili(U. of Bari & I.N.F.N.)

18. Spectroscopy of states (before & after) Potential models of [heavy-quark | light-quark] mesons: so far reasonable success for spectroscopy of D, Ds, B, Bs systems New states do not fit well : masses below the DK[D*K] threshold. IF interpreted as ordinary states, they decay mainly by isospin-violating p-emission thus having widths quite narrow. ? A possibledecay mechanism is through a virtual h followed by h-p0 mixing[Cho-Wise,PRD49]. ? D*K p DK p g …as predicted by models based on HQET & chiral symmetry [Bardeen et al.,…] if new states are 0+ & 1+ p NEW STATES 40(!) papers by theorists: Exotic (4-quark, molecule, …) VS Ordinary explanations (HQET+chiral symmetry, …) S-wave P-wave [j=3/2; NARROW by K-emission] Crucial to measure radiative decays & di-pion emission 18

19. SUMMARY Competitive D0 mixing results obtained with 2 different experimental methods are consistent with no mixing and no CP. wrong-sign D0 mixing limits (95% CL,57fb-1;CP-allowed): D0 lifetime ratio (91fb-1): Wrong-sign D0 mixing limits from semileptonic decays coming soon Charmed mesons are a rich laboratory for Heavy Quark studies. After the discovery of D*sJ(2317) and the observation of DsJ(2458)… … further Ds mesons (spectroscopic) studies are ongoing. BaBar is a promising place to study charm physics … studies have just began ! 19 La Thuile - 2004 Alexis Pompili(U. of Bari & I.N.F.N.)

20. Backup Slides

21. Unbinned maximum likelihood fit S1 S2 s3 tD (1-f2)(1-f3) + f2(1-f3) + f3 Psig(mi) SIGNAL proper-time RESOLUTION tBKG e BUT with ... SBKG S1 + f0(1-f4) (1-f0) SBKG S2 NO-flying BKG [1-Psig(mi)] flying BKG s3 s4 fixed BKG f0f4 for tails BACKUP-1 La Thuile - 2004 A.Pompili(U. of Bari & I.N.F.N.)

22. Statistical error on lifetime extracted from the fit BACKUP-2 La Thuile - 2004 A.Pompili(U. of Bari & I.N.F.N.)

23. Fit allowed x’2<0. Central values for fits of both separate samples gave x’2<0. Due to allowing x’2<0 in the fits it is not clear how to apply a Bayesian ansatz to derive an error estimate from the 2D likelihood distributions. Moreover these ones depend strongly on the most likely fitted values of x’2 and y. 95% C.L. limits are determined using toy Monte Carlo samples at each point on the contour (frequentistic approach). (x’2,y) points on separate contours are combined in pairs to determine (x’2,y) on 95% CP contours. Systematic uncertainties included by calculating equivalent statistical deviation for each systematic check and expanding the 95% C.L. contour appropriately. BACKUP-3 La Thuile - 2004 A.Pompili(U. of Bari & I.N.F.N.)

24. BACKUP-4 La Thuile - 2004 A.Pompili(U. of Bari & I.N.F.N.)

25. Unbinned maximum likelihood fit Assign likelihood to each event for: • DsJ(2458)+  Ds*(2112)+ 0 • DsJ(2458)+  DsJ*(2317)+  • Combinatorial Ds+ 0  bkgd • Ds*(2112)++ random 0 • DsJ*(2317)++ random  • DsJ(2458)+  Ds*(2112)+ 0 … using wrong  The DsJ(2458) signal for a particular decay mode can be isolated by calculating a weight for each Dsp0g combination proportional to the relative likelihood contributed by the decay mode of interest BACKUP-5 La Thuile - 2004 A.Pompili(U. of Bari & I.N.F.N.)