1. FOCUS baryons and HQ spectroscopy Cristina Riccardi Dipartimento di Fisica Nucleare e Teorica & INFN-Pavia XXXI International Conference on High Energy Physics July 24-31, Amsterdam Outline Charm Baryon lifetimes Measurements of  c + decay modes Double Charm Baryon search Conclusions Charmed baryons and HQ spectroscopy results from

2. 24-31 July 2002 Amsterdam Charmed baryons and HQ spectroscopy from FOCUS 2 PWC Over 1 million reconstructed! Vertexing Cerenkov Spectrometer at FNAL Wide Band Photon Beam Member groups from USA, Italy, Brazil, Mexico, Korea. Successor to E687. Designed to study charm particles produced by ~180 GeV photons using a fixed target spectrometer with updated Vertexing, Cerenkov, EM Calorimeters, Hadron Calorimeter and Muon id capabilities.

3. 24-31 July 2002 Amsterdam Charmed baryons and HQ spectroscopy from FOCUS 3 Charm Baryon Lifetimes Expected hierarchy:  (  c + ) <  (  c + ) <  (  c 0 )  (  c 0 ) <<  Not universal semileptonic decay widths for charm baryons Lifetimes study provides:  Probe into the non-perturbative sector of heavy quark decay  Test of various quark models and Heavy Quark Expansion methods  Exp BR  calculated decay rates Needed  of  c +,  c 0,  c 0 to 10% to quantify contributions Improvement on the lifetimes understanding can be provide by:  measurement of the semileptonic BR of charm baryons to probe HQE  study of the exclusive modes of  c + ( in particular CS decays)  The hadronic partial width has contributions from mechanisms other than spectator quark decay (W exchange, destr. and constr. PI )  (  c + ) =  spec +  exc +    (  c + ) =  spec +    +    (  c 0 ) =  spec +  exc +    (  c 0 ) =  spec + (10/3)   Qualitatively ( neglecting mass difference and CS decays ):

4. 24-31 July 2002 Amsterdam Charmed baryons and HQ spectroscopy from FOCUS 4 Lifetime measurement technique Fit  Parameters are  B L = We maximize likelihood function: B-tie term. Proper time resolution: (   40fs) – No resolution convolution systematics/error inflation –Systematic test of the method validity for short lived decays Binned likelihood method The expected number of events in each t’ bin is:  Acceptance/efficiency/absorption f(t’) correction by MC  b i : background from the i th t’ bin of sidebands distributions reducedThe fit variable is the reduced proper time t´ = (L - N  L )/  c, N where N is the detachment cut  minimize acceptance corrections Vertex algorithm is driven by charm candidates (cut on L > N  L ) L  p K-K- ++ c+c+

5. 24-31 July 2002 Amsterdam Charmed baryons and HQ spectroscopy from FOCUS 5  c + lifetime measurement High statististics measurement with a  c +  pK -  + sample of 8034±122 events MC correction function Check MC simulation: momenta, primary vtx multiplicity, decay lengh, proper time resolutions Acceptance/efficiency corrections check using short-lived Ks (excellent agreement  upper limit error) Variation of production parameter and resonance substructures Proper time resolution comparing data-MC, bin size and fit range variations Absorption effects: cross sections variation, in-out target decays, different target Uncertainty of f(t’) correction: A detailed study of systematics sources has been performed sources has been performed Charm reflection backgrounds: no significant contribution Variation of sidebands location and size/ no B-tie term Background: Level and lifetime distribution Absolute time scale

6. 24-31 July 2002 Amsterdam Charmed baryons and HQ spectroscopy from FOCUS 6 Acceptance corrected sidebands Background subtracted + Acceptance corrected data  c + lifetime result Syst. Source  sys (%) Time scale0.11 Backgrounds0.77 Acceptance0.83 Production0.38 Resolution Absorption0.23 Total1.23 Significant improvement on the  (  c + ) accuracy Comparison with other measurements PDG 2002: 200±6fs PRL, 88:161801,2002

7. 24-31 July 2002 Amsterdam Charmed baryons and HQ spectroscopy from FOCUS 7 Yield=532±30 Total sample FOCUS reduces the previous world average error by a factor of 3  -  +  + (300 events)  +  -  + (130 events) 3. p  -  + (45 events)  0  -  +  + (58 events) Product of 8 Likelihoods to fit for a single  Systematic studies No contribution when split topologies/modes Main contribution from variation of the fit conditions ( 8fs ) PLB, 523:53-59,2001 4 decay modes in 8 different topologies:  c + lifetime measurement

8. 24-31 July 2002 Amsterdam Charmed baryons and HQ spectroscopy from FOCUS 8  c 0 lifetime measurement Total sample: 110±17 events M(     ) M(     ) Yield=97±17 Yield=21±8   MC correction functions  Binned Likelihood method  L (  c 0 )= L (     ) x L (     )  Systematic investigation of resolution effect (  t (     ) =40 fs,  t (     ) =80fs comparable to  )  Variation of the fit method ( resolution convolution)  Mini MC study with a wide range of input lifetimes

9. 24-31 July 2002 Amsterdam Charmed baryons and HQ spectroscopy from FOCUS 9  c 0 lifetime systematics and result Syst. Source  sys (fs ) Production3 Fit4 Method (miniMC)2 Total5 Reduced proper time Comparison with other measurements Comparison with other measurements FOCUS reduces the percentage error on the  (  c 0 ) from 20% to 10% (Ref:hep-ex/0206069)

10. 24-31 July 2002 Amsterdam Charmed baryons and HQ spectroscopy from FOCUS 10  c 0 samples Yield=38±9 Yield=23±17 M(         ) M(     ) Total sample Yield=64±14 Mass=2697.5 ± 2.2 MeV/c 2 PDG2002 =2697.5 ± 2.6 MeV/c 2 preliminary

11. 24-31 July 2002 Amsterdam Charmed baryons and HQ spectroscopy from FOCUS 11  c 0 lifetime measurement preliminary MC correction functions Large corrections because of loose detachement cut 3 fit parameters:  B    B  L (  c 0 )= L (         ) x L (     ) L/  >0 L/  >2 t’ for signal (ps) t’ for background (ps) B  =50±3   bg  = 52 ± 4 fs B  =21±2   bg = 35 ± 3 fs  = 79 ±12 fs S ALL =59±11

12. 24-31 July 2002 Amsterdam Charmed baryons and HQ spectroscopy from FOCUS 12  c 0 lifetime systematics and result preliminary Systematic studies:  No remarkable effects of production/absorption  proper time resolution (bin size-fit range dependency)  as for  c 0, study effects due to resolution comparable to the lifetime  Background studies: signal /sidebands region (location and widths) Comparison with other measurements Comparison with other measurements Accuracy improved by a factor of 2 Preliminary FOCUS measurement: PDG 2002: 64±20 fs

13. 24-31 July 2002 Amsterdam Charmed baryons and HQ spectroscopy from FOCUS 13 Lifetime (fs) Results for Charm Baryons Lifetimes PDG2002FOCUS FOCUS (not in PDG2002) FOCUS preliminary c+c+c+c+ c+c+c+c+ c0c0c0c0 c0c0c0c0 1.5 ± 0.3 = 1.5 ± 0.3 Theory predictions: >  1 From the FOCUS results: ( PDG 2002: 2.21 ± 0.15 ) 2.15 ± 0.13 = 2.15 ± 0.13 Theory predictions: 1.2-1.7 FOCUS significantly improved the accurancy of all charm baryons lifetimes.

14. 24-31 July 2002 Amsterdam Charmed baryons and HQ spectroscopy from FOCUS 14  c   BR measurement of   c  decays into states containing   Th: Complicated dynamics for charm baryon decays W-exchange - investigation of the W-exchange contribution  c  CS modes - inputs for  c  lifetime from CS modes  Exp: low accuracy for many BR Yield=523  35 Yield=1666  60   FOCUS reconstructs  candidates throught the modes:  c   +  +  -  c   -  +  +  Our largest samples:  c   +  +  - and  c   -  +  +  + p  0 n  +  +  p  0 /n  +  - n  -  -  n  - FOCUS preliminary: (stat error only ) Unique previous measurement by E687:

15. 24-31 July 2002 Amsterdam Charmed baryons and HQ spectroscopy from FOCUS 15  c   + K + K - Study of the   c   + K + K - decay 105±15 ev Systematic effects reduced by using the  c   +  +  -  c   +  +  - decay as normalization mode, with similar selections 1706±88 ev W+W+ d c u u s u W exchange decay W -exchange decay  Comparison of independent sub-samples : momentum, particle/antiparticle, run conditions,  modes  Fit procedure varying: bin size,fitting range, signal shape (check two-fold ambiguity effect) Systematic studies:

16. 24-31 July 2002 Amsterdam Charmed baryons and HQ spectroscopy from FOCUS 16  + K + K - Same selection as  + K + K -, but lower L/  Cut on  /  *  signal regions Suppression of non-resonant / other resonances contributions with SB subtraction/ resonances mass cut  detailed systematics investigation  c   +  Y=57±10 ev Y=34±8 ev  c   *0 (1690)K + Y=8±8 ev Non-resonant  + K + K -  + K + K - contribution

17. 24-31 July 2002 Amsterdam Charmed baryons and HQ spectroscopy from FOCUS 17 FOCUSBELLECLEO (7.1±1.1 ±1.1) %(7.6±0.7 ±0.9) %(9.5±1.7 ±1.9) % (8.7±1.6 ±0.6) %(8.5±1.2 ±1.2) %(9.3±3.2 ±2.4) % (2.2±0.6 ±0.6) %(2.3±0.5 ±0.5) %- <2.8 % @ 90%CL <1.8 % @ 90%CL -  c   + K + K - Results for  c    + K + K - decay non resonant  c   + K + K - Upper limit @90%CL for the non resonant  c   + K + K - decay  + K + K - Almost all  + K + K - throught resonant modes comparison with other measurements (Ref:hep-ex/0206013)

18. 24-31 July 2002 Amsterdam Charmed baryons and HQ spectroscopy from FOCUS 18  c   c  Cabibbo suppressed decays  c   + K * 0 (892) Y=49±10 ev c- K++c- K++ Y=10±11 ev @ 90% CL First measurement (Ref:hep-ex/0206013) Most,if not all, of the  + K +  - via  + K *0 For the non- resonant 3-body decays quark pairs need to be created s W+W+ d c u u d s u  K *0

19. 24-31 July 2002 Amsterdam Charmed baryons and HQ spectroscopy from FOCUS 19 Double charm baryon search :  + cc &  ++ cc An extensive search was conducted in 2000 using: ~20,000  + c  pK  + ~1.2 million D +,o ( K , K2 , K3  ) No evidence of  cc 14  cc (D o,± X) and 7  cc (  + c X) decay modes searched

20. 24-31 July 2002 Amsterdam Charmed baryons and HQ spectroscopy from FOCUS 20 Dc comparison-efficiency FOCUS data for SELEX decay modes

21. 24-31 July 2002 Amsterdam Charmed baryons and HQ spectroscopy from FOCUS 21 Conclusions With ~20,000 + ~1.2 million D +,o, we found no evidence With ~20,000  + c + ~1.2 million D +,o, we found no evidence for production of and for production of  + cc and  ++ cc double charm baryons seen by SELEX BR’s. of  + c decays containing  ’s has been presented. First measurement of the CS decay mode  +    and upper limit for the  -  +  + mode. All charm baryon lifetimes measured with improved accuracy. Published measurements for,, Published measurements for  + c,  + c,  0 c Preliminary results for should be published by year end. Preliminary results for  0 c should be published by year end.

22. 24-31 July 2002 Amsterdam Charmed baryons and HQ spectroscopy from FOCUS 22 recover decays with decay vertex close to the  – or  – one. Three tracks vertex downstream of silicon to recover decays with  0 decay vertex close to the  – or  – one. Reconstruction of  –  n  –,    n  +,  +  p  0 Recover of the decays  –   0  – or  –   0  – Recover of the decays  –   0  – or  –   0  – when  0 unreconstructed when  0 unreconstructed. Link SSD track and MPWC track. The neutral particle is undetected. (for  confirm n in HadCal )  –   0  –  –   0  –  0  p  - with  0  p  - reconstructed over large regions of the spectrometer Decays upstream of/in silicon Decays downstream of silicon If decay vertex upstream of magnet, twofold ambiguity for the parent’s momentum. FOCUS developed several techniques to reconstruct hyperons for an extensive search of charm baryon decays.