Takatoshi Suzuki (RIKEN Nishina Center)

1. YN correlations from stopped K- reaction on 4He 1. Introduction 2. Experiment 3. N correlation analysis 4. Discussion and conclusion Takatoshi Suzuki (RIKEN Nishina Center) for KEK-PS E549 collaboration

2. KEK-PS E549 collaboration H. Bhang, J. Chiba, S. Choi, Y. Fukuda, T. Hanaki, R. S. Hayano, M. Iio, T. Ishikawa, S. Ishimoto, T. Ishiwatari, K. Itahashi, M. Iwai, M. Iwasaki, P. Kienle, J. H. Kim, Y. Matsuda, H. Ohnishi, S. Okada, H. Outa, M. Sato, S. Suzuki, T. Suzuki, D. Tomono, E. Widmann, T. Yamazaki, H. Yim

3. Original aim of the Experiment (semi-)Inclusive missing mass spectroscopy via K-stopped + 4He -> p + S0(T=1) -> n + S+(T=0,1) S+(T=0,1) -> Y()NN Y -> N ->M. Sato, nucl-ex/0708.2968 ->H. Yim Very strict upper limits for narrow(< ~40 MeV/c2)states Insensitive to broad (> ~40 MeV/c2) states covered in the previous talk by Prof. Iwasaki.

4. Recent Advanced Analysis Semi-exclusive missing mass spectroscopy via K-stopped + 4He -> N + 3S0/+ 3S0/+ -> Y()NN Small statistics, but well resolved final states. Dibaryon? K-stopped + 4He -> 2S0/+ + N + N 2S0/+ -> YN This talk. Inclusive measurement for K-stopped + 4He -> 2S0 + d Semi-exclusive measurement for K-stopped + 4He -> 2S0 + d 2S0 -> n -> 3S+ + n 3S+ ->d nucl-ex/0709.0996

5. Only total capture Rate is known. Dynamical nature is speculative Stopped K-Reaction on 4He

6. p/n/ p/n  p/n K-  E549 June 2005 ~100M stopped K- E570-1 October 2005 ~100M stopped K- E570-2 December 2005 ~ 40M stopped K- Measurement 4(5)-fold coincidence measurement of incident K- (+X)+back-to-back 2 nucleons+charged  Momentum decision by track detection+TOF method for pn

7. pinvariant massspectra and identification

8. Uncorrected opening angle distributions

9. 4He(stopped K-, N) missing mass Regardless of the medium states, K-stopped + 4He -> N+ N + N +  K-stopped + 4He -> N+ N + N K-stopped + 4He -> n+ d final states can be separated by 4He(K-stopped, N ) missing mass, which is actually internal energy of nuclear residual. Internal energycan give important information to interpret observed strength.

10. N invariant mass VS missing mass (cp/n):quasi-free hyperon production(+conversion for ) K- ‘N’ ->  (+‘N’ -> )  (ap/n):two-nucleon absorption K- ‘NN’ ->  (bp/n):non-mesonic. But ??

11. N invariant mass VS N total momentum Low-energy tail of (ap/n) originates from motion of residual nucleus -> “physically” broaden. ~0.2%/K-stopped ~2%/K-stopped

12.  momentum VS N momentum Comments on the nucleon momentum spectra…… (ap/n) -> Purified two-nucleon process, having ~100 MeV/c FWHM. (ap/n) + (cp/n) -> Expected contribution for background spectrum(M. Iwasaki, et.al., NIM A 473 286 ). (bp/n) -> Unresolved broad strength peaked at E471 S0/+ regionon nucleon momentum spectra.

13. Discussion of ap/an components Clear observation of“two”-nucleon absorption, K- ‘pp’ -> p (ap~0.2%/K-stopped) K-‘pn’ -> n(an ~2%/K-stopped) Production rate is significantly small on p(I=0 dominance), to which the peak is broaden and shifted to low-energy side. Observed nucleon momentum distribution is very broad as expected reflecting the Fermi-motion of nucleons in 4He(cf. NIM A 473 286 (2001)), contradicting the mono-energetic emission of Y and N (PRC 74 015207 (2006)). It accounts for only ~20% of known (pnn)(11.7 +-2.4)% (PRD 1 1267 (1970)) final states!

14. Discussion of bp/bn components (1) On the both of p/n, there exist non-mesonic strength (bp)/(bn) cannot be explained well by ”two”-nucleon absorption alone. Much different (ap):(bp),(an):(bn) intensity ratio. (bp) is not likely to be explained by the re-scattering effect which Magas et. al. suggested for FINUDA p spectrum (PRC 74 025206) because both of and p momenta are shifted to lower side, while (bn) could be partly explained by the mechanism. Component (bp) is extremely peculiar.

15. N invariant mass under coincidence conditions Electro-magnetic decay of , K-stopped + 4He -> +p+ n + n -> K-stopped + 4He -> +n+ p + n -> is estimated by additional γcoincidence events (+γe+e- cross section +geometrical coverage). Its contributions to BN components are Bp:(12/Eff=0.014)/1683~0.5 Bn:(21/Eff=0.019)/3521~0.3 30~50%, (very preliminary).

16. Discussion of bp/bn components (2) Possible contributions to component (bp(/n))… 1. branch of“two”-nucleon absorption and successive  conversion process K-‘NN’ -> N  ‘N’ -> N Non-negligible contribution from K-‘pp’ -> p ->  2. “three”-nucleon absorption cf. nucl-ex/0709.0996 K-‘NNN’ -> NN 3. 2S+ dibaryon production and its p decay (for 6Li + 7Li + 12C, FINUDA collaboration, PRL 94 (2005) 212303) K-stopped + 4He -> 2S+ + n + n 2S+ ->+p 4. Broad 3S0 tribaryon production and its nn decay K-stopped + 4He -> 3S0 + p 3S0 ->+ n + n

17. Conclusion 1. Clear observation of“two”-nucleon absorption, K- ‘pp’(nn) -> p (nn)K-‘pn’(pn) -> n(pn) on 4He(stopped K-,p/n)spectra.The dynamical property of the process is now well investigated. It accounts for only ~20% of non-mesonic  branch. 2. Presence of mysterous non-mesonic contributions on both spectra. Only a few possibilities remain to interpret them. 3. Quantitative estimation of K- ‘NN’ -> N followed by  conversion will be the final task of the work.