1. Strange tribaryon: Experiments H. Outa (RIKEN) for KEK-PS E471/E549/E570 1. 1.Summary of 4 He(stopped K －,p) / 4 He(stopped K －,n) experiment (E471) 2. 2.Status of on-going experiments at KEK E549: 4 He(stopped K －,N) w/ upgraded detectors E570: K － 4 He X-ray measurement 3. Experiments at J-PARC HS05, KEK, 2005/12/2

2. G. Beer, H. Bhang, M. Cargnelli, J. Chiba, S. Choi, G. Franklin, Y. Fukuda, K. Gomikawa, T. Hanaki, R.S. Hayano,T. Hayashi, M. Iio, K. Ishikawa, T. Ishikawa,S. Ishimoto, T. Ishiwatari, K. Itahashi, M. Iwasaki,B. Jihasz, T. Katayama, P. Kienle, Y. Kondo,J. Marton, Y. Matsuda, T. Nakamura, H. Ohnishi, S. Okada, H. Outa, C. Petrascu, B. Quinn, M. Sato, M. Shindo, H. So, P. Strasser, T. Sugimoto, K. Suzuki, T. Suzuki, H. Tatsuno, D. Tomono, A.M. Vinodkumar, E. Widmann, T. Yamazaki, H. Yim, T. Yoneyama, J. Zmeskal List of collaboration (E471/E549/E570)

3. Quark mass ~300MeV Baryon formation T Baryon mass ~0 Big bang Higgs condensation T ： ~ 100GeV T ： ~ 200MeV Present universe T ： ~ 0 eV Quark mass ~MeV r Baryon mass ~1000 MeV Quark-pair condensation Quark-pair condensation ？ 1

4. Embedding Ｋ in nucles ？ ・ Deep! ・ Narrow! ～ 100 MeV ～ 20 MeV = meta-stable ・ Shrink! cf: B N ～ 10 MeV K-nucleus bound state ☞ hadron mass ☞ astronomical study = high density? 2

5. 4 He  How to produce ？ p p n K-p p n K- n Z : +1 T : 0 or 1 p p n n K-p n n K- Z : 0 Ｔ ： １ predicted unpredicted Missing mass measurement 3

6. Experimental setup of E471 K beam & NC & TC LC : K/  separation DC : K - beam trajectory NC wall (TOF stop): left/right of He n, p detection TOF distance ～ 2m vertex ( ,p) detector (TC): above/below of He DC & TC (2layer) reaction vertex PID KEK PS-E471 experiment at KEK-PS M.Iwasaki : NIM A473(2001)286 TOF wall trigger condition 4

7. 4 He(stopped K-, p) spectrum Detection threshold （ due to Fe plate ） K - + 4 He  S 0 + p 5

8. Result of Proton ・ distinct in proton ・ very narrow width Strange tribaryon S 0 (3115) ・ semi-inclusive ! P3 BG + Gaussian χ2 /DOF = 8.76/12 Gaussian center: 3117.7 MeV/c 2 Gaussian sigma: 8.7 MeV/c 2 Statistical significance: S/ΔS = 2441/297= 8.2 σ 6

9. Y Motion (relative to proton) Hyp. decay = should be in HERE! Hyp. decay = NO! 7

10. proton data neutron data Mass spectra nucl-ex/0310018 χ2/DOF = 28.52/31 Gaussian center: 3140.5 MeV/c2 Gaussian sigma: 7.3 MeV/c2 Statistical significance: S/ΔS=120/32= 3.7 σ 8

11. Summary of E471 results ＊ S + (3140) not conclusive ＊ Only upper limits on widths ＊ Large error on formation rate / mass 9

12. What was observed ? - K bound nuclei ？ - nonaquark? - pionic  Hypernucleus ？ ・ We searched for this… ・ Much different energy from the initial prediction ・ Excited state? ・ High density? ・ H-dibaryon ？ ・ energy is close to π+Λ+nuclei … - Two-nucleon absorption ？ ・ K- + “d” → Σ - + p (back-to- back) ・ Stopped d in  ? ・ Too-high Σ energy (βγcτ ～ 2cm) Need further study !! Only the energy is known 11

13. K - 3 He atom ~ Σ π threshold theory (isospin singlet) E What is the situation ？ theory (isospin triplet) pn particle(other) observed (isospin triplet) ~ 200 MeV (isospin singlet) (theory) (experiment) Binding energy - one nucleon is in p-wave? A. Dote et al. : PLB590 (2004) 51 10

14. On-going experiments…. No new “results” now, sorry !!

15. Incoming K － proton 4 He target Neutron counters Iron plate Charged particle veto counter E471 Setup Upgrade in E549 Incoming K － proton Neutron counters 4 layers→7 layers neutron Proton TOF stop (σ ～ 70ps) Veto counter for neutron detection Smaller target TOF Start counter （ σ< 70ps) Proton chamber resolution improve 150ps→50ps Both proton/neutron σ ～ 300ps proton σ=100 ～ 150ps neutron σ=200ps 12 E549 run ( May.24th-Jul.1 st )

16. Goal of E549 run ① 4 He(K -, p) S 0 (3115) position/width Error of energy ～ 3MeV now → ～ 1 MeV Width Limit→ finite value (if Γ>10MeV) proton statistics >×30 times (inclusive) energy resolution ×2-3 times better ② 4 He(K -, n) Confirm S + (3140) Statistical significance ～ 10σ Contribution of T=0 states neutron statistics×8 times 1.5 times better energy resolution ③ 4 He(K -, p) Search for excited states Direct evidence of high density K - + 4 He → (K - + pnn)[T=1] + p | 1/2 -1/2 > |1 -1> + |1/2 1/2> K - + 4 He → (K - + ppn)[T=1] + n | 1/2 -1/2 > |1 0> + |1/2 -1/2> Formation ratio = 2:1 １1１1 13

17. Target Image(E549) – seen from SIDE chamber Calibration by (π,π’) scattering events Vertex Z (mm) 14

18. Current status of E549 data analysis 1/  (K + stop ) event  (K +  2 )  (K +  2 ) e (K + e3 )  K +     1.1  Mass resolution σ ～ 4 MeV for S 0 (3115) Mass resolution σ ～ 4 MeV for S 0 (3115) TOF resolution   ~ 0.02   (width of  peak  TOF parameter tuning K + decay  K +       1.21  K +  e   1  mode  1/  distribution from K + 15

19. 1/  Total Light Output (MeVee) p d  e  K - stop events Charged particle PID / Stop K selection Total light output VS 1/  Identification of charged particle Proton events are clearly separated K stopping time distribution K - Stopping time (nsec) K - stop events Stopped K selection In-flight decay/reaction events are rejected In-flight reaction Accepted as Stopped K Event Incoming K － proton neutron 16

20. E471 E549 Neutron detection…. Background suppressed very preliminary σ=0.039 Better S/N ratio Better resolution All the detectors are working well 17

21. Kaonic Atom?? K-He  anomalous shift ?? Kaonic Nuclei ? KN interaction ? Exp. = 40 eV !! (repulsive) cf. < 1 eV (potential) We are measuring 3d→2p X-ray energy with ～ a few eV accuracy (E570; from this Oct. ) 18

22. E570 experiment (1) (1)Use 8 SDDs (Silicon Drift Detector) - better resolution σ>300 ⇒ ～ 150eV - very thin ( ～ 300μm) (2) Clean stopped K- on helium events selection w/ chamber tracking ～ 10 times more peak statistics S/N ～ 1 → 10 ～ 2 times improved resolution SDD 19

23. Preliminary result of Oct. run3d→2p 4d→2p 20

24. Experiments at J-PARC and other Lab.

25. Kaonic nuclei experiments… (In - flight K-,N ) Kishimoto’s group @BNL/KEK Stopped K - Light target only = 4 He, 3 He Huge background especially from 2N-abs. K-Fragment method @ FINUDA K - pp Heavy nuclei? Background seems to be not so serious Stable? (especially in nucleon side) Nagae’s group Invariant-mass  -d invariant-mass d+p -> K + + K - ppn 21

26. Data MC-sig MC-bg GSI-FOPI inv. mass method preliminary, HPC2005 Λ+d(Kppn) Ni+Ni @ 1.93AGeV: Λ+d(Kppn) B=149MeV, M = (3159 ± 20)MeV POOR SIGNAL/NOISE RATIO Phys. Rev. Lett. 94 212303 (3 June 2005) Results of measurement on invariant mass FINUDA K-pp K  “ pp ”    p p   22

27. JPARC experiment In - flight reaction Easy to carry out….. stop K Formation cross section ?? on 23

28. ？ by Y. Akaisi 24

29. Complete measurement on few-body system Exclusive measurement of all the particles emitted in formation & decay = charged particles 3 He target Spectator? Related to FINUDA DATA 25

30. Dalitz Plot 26

31. J-PARC Setup ・ 1 GeV/c line Ｓ＝ - １ ・ Measure both of formation and decay ・ Both of (K-,p) and (K-,n) ・ Both of missing mass/ invariant mass method 27

32. 1. 1.We discovered strange tribaryon S 0 (3115) with total isospin T=1 in the 4 He(K - stopped, p) reaction. Summary 2. New experiments(E549/E570) are on-going at KEK-PS E549: 4 He(stopped K-,p/n) w/improved statistics/resolution E570: K -4 He 3d→2p X ray with a few eV accuracy 3. Experiments at J-PARC - Light 3 He target / exclusive measurement - Both of formation (missing mass)/ ｄｅｃａｙ ( ｉ ｎｖ.mass) study; detector to identify Σ/Λ