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Atsushi Tokiyasu (for LEPS collaboration)

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  1. Search for Kaonic nuclei at SPring8/LEPS Atsushi Tokiyasu (for LEPS collaboration) Experimental Nuclear and Hadronic Physics Laboratry, Department of Physics, Kyoto University GCOE Symposium 12th – 14th .Feb.2013 @ Kyoto University

  2. strangeness in nuclei SU(3) octet baryon SU(3) nonet meson dsus, uds kaon Kaonic nuclei new form of the nuclei whether exist or not? What happens in nuclei? hyperon L Hyper nuclei Shrinkage  impurity effect. nuclear force in SU(3) ? K GCOE Symposium @ Kyoto University

  3. Kaonic nuclei • K can be bound in the nuclei by strong interaction. • K N interaction (I=0) is strongly attractive ! • X-ray shift of Kaonic Hydrogen • K- p scattering data • 2-body: KN : L(1405) ? • 3-body: KNN : lightest nucleus. K-pp the strongest bound state in 3-body systems • Theoretical prediction (All theory support the existence) • B.E. = 20-100 MeV • G = 40- 110 MeV • If G > B.E, it is difficult to observe experimentally. Formation of Cold (T=0) and Dense (r > 2r0) nuclei. dependent on the models of KN interaction the calculation methods. Ref: Particle Data Group GCOE Symposium @ Kyoto University

  4. Experiments K-pp  L p , S0 p, S+ n (non-mesonic decay)  easy to identify experimentally  S p p(mesonic decay) M.Agnello, Nagae and Fujokaet al., PRL 94, 212303 (2005) T.Yamazakiet al., PRL 104, 132502 (2010) FINUDA @ DAFNE (2005) DISTO@ SATURNE(2010) stropped K- on (6Li, 7Li, 12C, 27Al and 51V) • p p L p K+ invariant mass (L + p) Missing mass (K+) MeV B.E. = B.E. = MeV MeV G = G = MeV GCOE Symposium @ Kyoto University

  5. Summary of the introduction • K-pp is the lightestkaonic nuclei. • Existence of K-pp is not established. • Experimental search using different reactions are awaited! • Forthcoming experiments • 3He(K-, n)X  E15 @ J-PARC • D(p+, K+)X  E27 @ J-PARC • g D K+ p- X  LEPS @ SPring-8  Prof.Nagae’s talk GCOE Symposium @ Kyoto University

  6. g D  K+p - X reaction • “K” exchanged in t-chanel •  unique for g-induced reaction • ( J = 1) • polarization observables are available. • K-pp is “soft” object. •  small momentum transfer •  detect K+ and p- at forward angle • Search for a bump structure • in the missing mass spectrum • Mx2 =(Eg + MD – EK- Ep)2 • - (pg – pK - pp)2 •  independent of decay chanel. (Eg, pg) (EK, pK) K+ g p- (Ep, pp) K, K* Y* Y* n K- p p p (MD,0) Y* door-way. GCOE Symposium @ Kyoto University

  7. SPring-8 “Super Photon ring-8GeV” SPring-8: 8 GeV electron storage-ring LEPS : hadron physics using g beam Back-word Compton Scattering DEg=12 MeV Detect with Tagging counter e e 8 GeV 355nm laser Eg=1.5 - 2.4 GeV experimental hatch  Data take: 2002/2003, 2006/2007 7.6 x 1012 photons on LD2 target LEPS GCOE Symposium @ Kyoto University

  8. LEPS spectrometer position TOF SVTX DC1 SSD (SVTX) Drift Chamber (DC 1~3) p- AC(n=1.03) time Start Counter (SC) Time of flight wall (TOF) K+ g (1.5-2.4 GeV) trigger AerogelCherencov counter (AC) Start Counter (SC) Target Dipole Magnet 0.7[Tesla] DC2 DC3 Start Counter GCOE Symposium @ Kyoto University

  9. particle identification TOF (Time of flight) p m2 = p2(1/β2 - 1) K+ line tracking + Runge-Kutta method. p+ 0 Dp/p ~ 6 MeV/c @ 1 GeV/c p- K- c.f. mass p = 938.3 MeV mass K+ = 493.7 MeV mass p- = 139.6 MeV GCOE Symposium @ Kyoto University

  10. Missing Mass Spectrum acceptance was corrected with Monte-Carlo simulation preliminary L S Error Bar : statistical uncertainty (~5%) Red Box : systematic uncertainty (~20%) Hatched : discrepancy between datasets (~12%) expected signal n No bump structure was observed! upper limit of cross section search region: Mass = 2.22 - 2.36 GeV/c2 B.E. = 150 - 10 MeV GCOE Symposium @ Kyoto University

  11. Upper Limits of differential cross section upper limits of cross section were determined log likelihood ratio method B.E. 15 points (10-150 MeV) G3 points -G= 20 MeV 0.05 - 0.25 mb -G = 60 MeV 0.15 - 0.6 mb -G =100 MeV 0.15 - 0.7 mb a few % of typical hadron production cross section. g N L K p (~8 mb ) g N S K p (~4 mb) preliminary GCOE Symposium @ Kyoto University

  12. Conclusion and future prospect • The existence of Kaonic nuclei is not established. • K-pp was searched for using g D  K+p - X reaction • No bump structures were found, and the upper limits of differential cross section were determined to be a few % of typical hadron production cross section. • Future prospect • detect the decay products from K-pp.  increase S/N • search for other charge states using gDK+ K-pn , gDK+p+ K-nn GCOE Symposium @ Kyoto University

  13. Collaborators GCOE Symposium @ Kyoto University

  14. Appendix GCOE Symposium @ Kyoto University

  15. Appendix • Merit • deuteron small nuclear effect(FSI). • additional p- emission reduce the momentum transfer. • K can be exchanged. • polarization observable is available. • Demerit • small cross section (~nbarn). • many background source • limited information on hadron resonance. • necessary to detect the decay product. GCOE Symposium @ Kyoto University

  16. Calculation of Upper Limits Upper Limit was calculated with log Likelihood ratio method preliminary Background proces - g p  K+ p- L - g p  K+ p-S - g p  K+ p- S(1385) - g p  K+ p- S(1385)- - g p  K+ p-p L constant offset Signal Breit Wigner distribution preliminary -2DlnL = 3.841  upper limit (95% C.L.) Signal Yield GCOE Symposium @ Kyoto University

  17. Theoretical calculation All calculations predict that K-pp can exist!! However… B.E. = 20 – 100 MeV G = 40 – 110 MeVDepending on the K N interaction model and Calculation Method. GCOE Symposium @ Kyoto University

  18. Background processes MM(K+,p-) g N  K+p- X MM(K+,p-) • 15 quasi- free processes were considered for fitting. • N  • Y K+ • Y K+ p- • Y* K+ p- • Y K+ p- p • The main background (~20 %) • n  K+L(1520) •  Sp • Lpp MM(K+) c2/ndf ~ 1.3 MM(K+) Y hyperon (L,S) Y* hyperon resonance (L(1405),S(1385)…) preliminary GCOE Symposium @ Kyoto University