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Search for the K - pp bound state via photon-induced reaction

Search for the K - pp bound state via photon-induced reaction. A. O. Tokiyasu (RCNP) for LEPS collaboration. “Hadron in nucleus” @ Kyoto University 1 st . Nov. 2013. Contents. What are Kaonic nuclei? LEPS experiment at SPring-8 Results Future work: search in LEPS2 experiment

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Search for the K - pp bound state via photon-induced reaction

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  1. Search for the K-ppbound state via photon-induced reaction A. O. Tokiyasu (RCNP) for LEPS collaboration “Hadron in nucleus” @ Kyoto University 1st. Nov. 2013

  2. Contents • What are Kaonic nuclei? • LEPS experiment at SPring-8 • Results • Future work: search in LEPS2 experiment • Conclusion ☆This presentation is based on arXiv.1306.5320 Hadron in nucleus @ Kyoto University

  3. What are Kaonic nuclei? Hadron in nucleus @ Kyoto University

  4. Kaonic nuclei • KN interaction is strongly attractive (I=0) • K bound state in nucleus → Kaonic nuclei • important to understand the sub-threshold KN interaction • KNN bound states are the simplest kaonic nuclei. • K-pp bound state: largest B.E. Hadron in nucleus @ Kyoto University

  5. K-ppbound state B.E = 10- 95 MeV G = 39 – 100 MeV depending on - KN interaction - calculation methods stopped K- Lp invariant mass Theoretical prediction pp→K+Lp MM(K+) Experiment ↓inconsistent↓ MeV B.E. = MeV B.E. = MeV G = MeV G = DISTO@ SATURNE PRL 104, 132502 (2010) FINUDA @ DAFNE PRL 94, 212303 (2005) search experiments via different reactions are awaited! → photon-induced reaction. Hadron in nucleus @ Kyoto University

  6. g-induced reaction d (g, K+p) X Eg=1.5- 2.4 GeV p- X=K-pp←This talk p0 X=K-pn p+ X=K-nn E, p measured K+ g p HADRON13 (g, K+) K-pn (g, K+p+) K-nn K-, K*- N n K p search for the peak structure in the inclusive missing mass spectrum MMd(K+p-) search region: 2.22 – 2.36 GeV/c2 B.E. = 10 – 150 MeV N detect K+ at very forward angle → t-channel reaction (on-shell meson exchange) → virtual K- or K* beam ( p = 06-1.0 GeV/c) g (J=1, I=0, 1 ) Hadron in nucleus @ Kyoto University

  7. LEPS experiment at SPring-8 Hadron in nucleus @ Kyoto University

  8. LEPS/SPring-8 SPring-8: 8 GeV electron storage ring LEPS : hadron physics using g beam Backword 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 photonssLD2 target (Total) LEPS Hadron in nucleus @ Kyoto University

  9. 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 K+ and p- are detected at very forward angle(< 15 degree) Hadron in nucleus @ Kyoto University

  10. particle identification TOF (Time of flight) p m2 = p2(1/β2 - 1) K+ Track reconstruction + Runge-Kutta method. p+ 0 Dp ~ 6 MeV/c @ 1 GeV/c DM ~ 10 MeV/c2 (2.22 - 2.36 GeV/c2 ) in MMd(K+p-) p- K- Hadron in nucleus @ Kyoto University

  11. Analysis and Results Hadron in nucleus @ Kyoto University

  12. missing mass spectrum cut condition -cosqlabK+>0.95 -cosqlabp->0.95 -0.25<pK+<2.5 -0.25<pp-<0.6 B expected signal C A A: g n → S- K+ S- → n p- B: g p → L K+p- C: g p/n → S-/0 K+p- B+ C : ~11 mb Peak structure was searched in 2.22 - 2.36 GeV/c2. →No peak structure was observed! Hadron in nucleus @ Kyoto University

  13. Determination of the upper limit of production cross section log Likelihood ratio method. DlnL = logL[Signal + BG] - logL[BG] Signal : Breit-Wigner (fixed B.E., G) BG : quasi-free processes (listed in Figure) The yields : -2DlnL=3.84 → upper limit at 95 % C.L. Hadron in nucleus @ Kyoto University

  14. upper limit of cross section B.E. 15 points (10-150 MeV) G3 points (20, 60 and 100MeV) -G= 20 MeV 0.17 - 0.55 mb -G = 60 MeV 0.55 - 1.7 mb -G =100 MeV 1.1 – 2.9 mb 1.5 - 26 % of YK+p- production cross section. Hadron in nucleus @ Kyoto University

  15. Background processes MMp(K+p-) and Mp(K) spectra were fitted simultaneously. Fitting function: quasi-free process MMp(K+p-) MMp(K+) • - gNYK+p- • gNY* K+ • - gNYpK+p- • Main component: • p  L(1520) K+(~20%) • → Sp • → Np- • g N Y pK+ p-(~20%) Hadron in nucleus @ Kyoto University

  16. Search in LEPS-2 experiment Hadron in nucleus @ Kyoto University

  17. LEP2 facility • beam intensity x10 of LEPS ( 107 cps) • 4 p detector • under construction for the 1st experiment acceptance: 5 -120 degree (charged particle) 30 - 100 degree (g) p/Dp ~ 1% Hadron in nucleus @ Kyoto University

  18. LEPS 2-1 Exclusive search by tagging two protons • Main Back ground process: • quasi-free process • (one nucleon is spectator) • To improvement of S/N: • Non-mesonic decay mode • two high momentum proton Tag Toy MC accepted in LEPS2 • g + d  K+ + p- + K-pp • K-pp  L + proton(p1) • L  proton (p2) + p- accepted in LEPS2 Toy MC Hadron in nucleus @ Kyoto University

  19. LEPS 2 – 2Search in the g+d→KsL p Dalitz plot in the Center Mass system g+d→ Ks + K-pp K-pp → L+ p Toy MC K-pp production (B.E. = 60 MeV = 80 MeV = 100 MeV = 120 MeV) ー　Ks (L) p ーKs L (p) ー(Ks) L p ーKs L p ( ) ← ID with missing mass • g + d → Ks + K-pp • K-pp → S0 + p • S0 → L + g (50-140 MeV) • ← detectable • We can measure the B.R. (Lp/S0p) Hadron in nucleus @ Kyoto University

  20. Conclusion Hadron in nucleus @ Kyoto University

  21. Conclusion • K-ppbound state give us rich information on the sub-threshold KN interaction. • K-pp bound state was searched for via the g d  K+p- X reaction at LEPS/SPring-8. • Significant peak structures were not found in MMd(K+p-) spectrum, and the upper limits of the production cross section were determined. • Main component of background processes were found to be quasi-free processes (g p→ L(1520) K+, g N→ L/S p K+p-). • LEPS2 has potential for more sensitive search experiments. Hadron in nucleus @ Kyoto University

  22. Collaborators Thank you for your attention! Hadron in nucleus @ Kyoto University

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