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Examining S bounds states with FINUDA

Examining S bounds states with FINUDA. FINUDA COLLABORATION Stefano Piano. S - Hypernuclei . 4 S He. Present knowledge:  Only one S -hyp. bound state found: 4 S He ( S  S 0 ,S + )  Pratically no data in heavier systems Possible explanations :

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Examining S bounds states with FINUDA

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  1. Examining S bounds stateswith FINUDA FINUDA COLLABORATION Stefano Piano

  2. S-Hypernuclei 4SHe Present knowledge:  Only one S-hyp. bound state found: 4SHe (SS0,S+)  Pratically no data in heavier systems Possible explanations : a) [S+A] SB: previous expt.’s were unable to detect SB b) SNLN previous expt.’s were unable to discriminate S/N c) no SB bound system nothing to be seen ! FINUDA can detect the formation and decay of S-hypernuclei in the (K-stop, ) reaction due to itstracking capabilities  A S-hyp. forms when a S substitutes a N into a nucleus (S=-1) R.S. Hayano et al., Phys. Lett. B 231 (1989) 355 T. Nagae et al., Phys. Rev. Lett. 80 (1998) 1605

  3. How to “dig-out” S-hypernuclei with FINUDA S-hyp simulated event Reaction steps K-stop+ A SB + prompt S + N  + N

  4. Silicon Vertex Detector PID Outer microstrip layer Inner microstrip layer

  5. +prompt + +prompt x - +prompt x - p +prompt x p +prompt x - x p p+prompt in coincidence with daughter particles K-stopped+ 12C 12S-Be + +prompt S + p  + n p + -

  6. K-stopped+ 12C 12S-Be + +prompt S + p  + n  p + - … due to 12S-Be ??? predicted G ~ 4-7 MeV(*) due to proton contamination (*) E.Oset et al, Phys. Rep. 188(1990)79

  7. Topology of a S-hyp event for 12C K- + 12C  12S-Be + +prompt 12S-Be  12Be + L + n L  - + p p ML [ p-] = 1114 MeV/c2 • K- vertex: • + 176 MeV/c • p 500 MeV/c • - 158 MeV/c +prompt -

  8. Topology of a S-hyp event for 12C Central region p p +prompt +prompt - L vertex - 12S-Be vertex Side view Front view

  9. K-stopped+ 12C 12S-Be + +prompt S + p  + n  p + -  [ - p] invariant mass distribution; (+, -,p) coincidence L needs to be improved !!! Entries / 4 MeV/c2 Invariant mass, MeV/c2

  10. Topology of a S-hyp event for 6Li p - + +prompt L p - L vertex +prompt + Central region front view

  11. Topology of a S-hyp event for 51V 49S-Sc vertex L vertex p + - +prompt - p Central region side view

  12. Summary • FINUDA/DAFNE a unique facility for S-hyp studies • Initial analysis yields positive expectations for bound SB beyond A=4 • Improve data analysis: • Better pattern recognition  increases a statistics: x3 • Better definition of   improves L (conversion reaction) invariant mass • Further improve p+to pPID • Strategy for future analysis: • tune-up analysis for the “reference nucleus” 12C • go for 6,7Li, 27Al and 51V • have a glance at S0/+-hyps • get theorists involved

  13. A first glance at 6Li

  14. p - + + Topology of a S-hyp event for 6Li • K- vertex: • + 151 MeV/c • p 271 MeV/c • - 127 MeV/c • K+ vertex: • + 236 MeV/c (p + -)Inv. Mass = 1116 MeV/c2 K- + 6Li  (5He+S-) + + (5He+S-)  3H + L + n +n

  15. Topology of a S-hyp event for 6Li p - + + L p - K- F K+ + +

  16. Topology of a S-hyp event for 6Li p - p L L - L K- + F K+ + + +

  17. 27Al target: typical event • K- vertex: • + 149 MeV/c • p 156 MeV/c • - 142 MeV/c p - (p + -)Inv. Mass = 1117 MeV/c2 + K- + 27Al (26Mg+S-) + + (26Mg+S-)25Na + L + n

  18. 27Al target: typical event K+ F K- L + p L - + p -

  19. 51V target: typical event • K- vertex: • + 163 MeV/c • p 248 MeV/c • - 124 MeV/c (p + -)Inv. Mass = 1110 MeV/c2 p + - K- + 51V  (50Ti+S-) + + (50Ti+S-)  49Sc + L + n

  20. 51V target: typical event K+ F K- L + L + - p p -

  21. Sigma Hypernuclei in FINUDA Kstopped+ A  B + prompt  + N   + N

  22. Monte Carlo simulations of S-hypernuclei 2p E.Oset, A.Ramos, I.Vidana, private communication • binding energies and width are • taken from: E.Oset et al., Phys. Rept. 188 (1990) 79 • bound nucleons have Fermi mom. • mom. distr. prob. dens. funct. final state particles tested for Pauli kinematics of f.s.p. feeds GEANT3 (geom., en. loss, trajectories) 1s tot

  23. Kstop + 12C  tot 2p 1s tot tot 2p 2p 1s 1s

  24. TOT K- p+ - K- p-+ -  n - K- n0 - p - K- n- K- (NN)- N -  n - Monte Carlo simulations of background reactions: p--spectra

  25. +,0-hyp region Monte Carlo simulations of background reactions: p--spectra

  26. --hyp region TOT K- p-+ K- p+- +  n + K- (NN)+ N +  n + Monte Carlo simulations of background reactions: p+-spectra

  27. Starting-line - Hypernuclei at 1.1 T  • trigger: + •  17% of K+K- • tagging with: • +prompt, -, p • two vertices • : invariant • mass

  28. Finishing-line - Hypernuclei at 0.6 T  • trigger: +prompt • 56% of 12-Be • improved tagging • better track and • vertex fitting

  29. - Hypernuclei in FINUDA at 0.6 Tvertex region

  30. +/o Hypernuclei in FINUDA • trigger: -prompt • tagging with: • -prompt, -, p • two vertices • : invariant • mass • background: o &  • quasi-free reactions

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