1. Search for a nuclear kaon bound state K - pp at the J-PARC K1.8 beam line. Dep. of physics, Kyoto University / JAEA Y. Ichikawa for E27 Collaboration Korea-Japan workshop on nuclear and hadron physics at J-PARC （ 2011 ）

2. 1 Contents Introduction E27 experiment –d （ π +,K + ） X reaction –Two proton tagging Goals of the next beam time –Check the feasibility of exclusive measurement –See the inclusive missing mass spectrum Summary Korea-Japan workshop on nuclear and hadron physics at J-PARC （ 2011 ）

3. Introduction Nuclear K bound state –The deeply bound state by strong interaction. –Strong attraction of the I =0 KN interaction （ KN I=0 ） plays an important role in nuclear K bound state. K - pp nuclear bound state –The simplest nuclear K bound state. –Theoretical prediction of B.E. and Γ depends on the KN interaction models and the calculation method. 2 Korea-Japan workshop on nuclear and hadron physics at J-PARC （ 2011 ） PRC76, 045201 (2002) arXiv:0512037v2[nucl-th] PRC76, 044004 (2007) PRC76, 035203 (2007) NPA804, 197 (2008) PRC80, 045207 (2009) Theoretical prediction B.E （ MeV ） Γ （ MeV ） T. Yamazaki and Y. Akaishi 4861 A. N. Ivanov, P. Kienle, J. Marton, E. Widman 11858 N. V. Shevchenko, A. Gal, J. Mares, J. Revai 50~70~100 Y. Ikeda and T. Sato 60~9545~80 A. Dote, T. Hyodo, W. Weise 20±340~70 S. Wycech and A. M. Green 56.5~7839~60 ‘

4. T.Yamazaki et al., PRL 104, 132502 (2010) M.Agnello et al., PRL 94, 212303 (2005) Experimental approach of K - pp 3 E27 and E15 experiments are proposed at J-PARC !! - FINUDADISTO reactionStopped K - absorption on 6,7 Li+ 12 C p + p @ Tp=2.85GeV methodInvariant mass of back to back Λp pairs p+p→X+K + （ missing mass ） X→Λ+p （ invariant mass ） B.E105 ± 5 MeV Width118 ± 8 MeV M.Agnello et al., PRL 94, 212303 (2005)T.Yamazaki et al., PRL 104, 132502 (2010) Korea-Japan workshop on nuclear and hadron physics at J-PARC （ 2011 ）

5. J-PARC E27 experiment 4 Korea-Japan workshop on nuclear and hadron physics at J-PARC （ 2011 ）, Y.Ichikawa

6. d （ π +,K + ） X reaction @ p π = 1.7 GeV/c 5 π + + n → Λ(1405) + K + Λ(1405) + p → bound K - pp （ 1 % ） → quasi free Λ* （ 99% ） n p d π+π+ K+K+ Missing mass π+π+ K+K+ Y.Akaishi, T.Yamazaki, Phys. Rev. C 76 045201 (2007) Λ* 1 % K - pp Λ* E27 experiment @ J-PARC K1.8 beam line Korea-Japan workshop on nuclear and hadron physics at J-PARC （ 2011 ）

7. Background of d(π +,K + ) reaction @ p π =1.7GeV/c 6 Inclusive missing mass Missing mass d(π +,K + ) [GeV/c 2 ] Korea-Japan workshop on nuclear and hadron physics at J-PARC （ 2011 ） counts (/5M beam ・ 1day ) MC Simulation Y. Akaishi, T. Yamazaki, Phys. Rev. C 76 045201 (2007) K - pp~600ev (Λ* trapping probability = 1%) counts (/5M beam ・ 1day ) Cannot observe K - pp signal.

8. K - pp Λ p1p1 Λ P２P２ π-π- Λ* π＋π＋ n d K - pp → Λ + p 1, K - pp → Σ 0 + p 1, p 2 + π - Λ + γ, p 2 + π - 7 π + + d → Λ * + K + + p 1s, Λ * → Σ + π, Σ + → p 2 + π 0 Background process P１P１ π＋π＋ n d Λ* P１P１ P 1s < 250MeV/c Background rejection by Two protons tag Korea-Japan workshop on nuclear and hadron physics at J-PARC （ 2011 ） P2P2

9. K - pp → Λ + p 1, → p 2 + π - proton2 theta_Lab proton1 theta_Lab angular distribution of 2protons （ >300MeV/c) from K - pp 8 Korea-Japan workshop on nuclear and hadron physics at J-PARC （ 2011 ） π + + d → Λ * + K + + p 1s, Λ * → Σ + π, Σ + → p 2 + π 0 Background process P 2 > 250MeV/c θ P2 < 30° Background rejection by Two protons tag

10. SKS 6 units of Range counter π+π+ p p 9 K+K+ 33° 93° p Target p π+π+ ＳＫ Ｓ BH2 K+K+ 500 Range counter for two protons tag 9 6units of Range counter arrays around the target (33°~93°) Yield Estimation –π + intensity = 5M/spill –dσ/dΩ = 60μb/sr, ΔΩ = 100 msr –Deuteron = 1.4 g/cm2 –η decay, η track = 0.5, 0.5 Λ(1405) production rate = 6.0x10 4 /day –Λ* trapping probability = 1.0 % –K - pp non-mesonic decay branch = 20% –Λ + Σ 0 decay modes = 2/3 –Λ to emit proton = 2/3 –Two-proton tagging efficiency = 14% K - pp event rate = 8.0/day 300 events/40days Korea-Japan workshop on nuclear and hadron physics at J-PARC （ 2011 ）

11. Goals of the next beam time as a first step data taking for E27 10 Because the present beam condition is not good, we can only use 1M beam. →Statistics of K - pp are insufficient. →It is very difficult to carry out two proton tagging as proposed. inclusive d(π +,K + )X spectrum @2.2 < Mx <2.5GeV/c 2. –To understand background shape. → The first measurement of this reaction and this missing mass region. –evaluate the upper limit of the cross section. Check the feasibility of exclusive measurement - two protons tag. - one proton tag. Korea-Japan workshop on nuclear and hadron physics at J-PARC （ 2011 ）

12. Yield estimate of inclusive measurement 11 Missing mass d(π +,K + ) [GeV/c 2 ] K+p+p~2.37[GeV/c 2 ] MC Simulation 20.6μb 76.7μb 124μb 13.7μb 40μb 28.9μb 40μb Full acceptance ~100msr FINUDA, DISTO counts (/1M beam ・ 1week ) evaluate the upper limit of the cross section.

13. Goals of the next beam time as a first step data taking for E27 12 Because the present beam condition is not good, we only use 1M beam / spill. →Statistics of K - pp are insufficient. →It is very difficult to carry out two proton tagging as proposed. inclusive d(π +,K + )X spectrum @2.2<Mx<2.5GeV/c 2. –To understand background shape. → The first measurement of this reaction and this missing mass region. –evaluate the upper limit of the cross section. Check the feasibility of exclusive measurement - two protons tag. - one proton tag. Korea-Japan workshop on nuclear and hadron physics at J-PARC （ 2011 ）

14. K - pp → Λ + p 1, p 2 + π - 13 π + + d → Λ * + K + + p 1s, Λ * → Σ + π, Σ + → p 2 + π 0 Background process Background suppression by one proton tag Korea-Japan workshop on nuclear and hadron physics at J-PARC （ 2011 ） But, it can suppress the BG ↓ cannot reject the Background by one proton tag.

15. Expected spectrum with one proton tag 14 MC Simulation Missing mass d(π +,K + ) [GeV/c 2 ] Mom proton >300MeV/c BG process (M.M.<2.37GeV/c 2 ) ~10nb/sr K - pp signal （ w 1proton_tag ） 60ub/sr × 0.01 × 0.2 × 0.3 ~4nb/sr counts (/1M beam ・ 1week ) Λ(1405) cross section (Lab) D.W. Thomas et al., Nucl. Phys. B56 (1973) 15. 1% trapping probability Non_mesonic decay Tagging efficiency Comparable Korea-Japan workshop on nuclear and hadron physics at J-PARC （ 2011 ） FINUDA, DISTO K+p+p~2.37[GeV/c 2 ]

16. One proton tag –S/N is worse.(S and N will be same order.) –Tagging efficiency is better. ( ~ 30% ) Two protons tag –S/N is better. (we assume B.G free) –Tagging efficiency is worse. ( ~ 14%) Check the feasibility of exclusive measurement by comparing data with MC simulation. Measure the cross section or upper limit. 15 Comparison of one proton tag and two protons tag Korea-Japan workshop on nuclear and hadron physics at J-PARC （ 2011 ）

17. Summary E27 experiment –Search for K - pp bound state via the d(π +,K + ) reaction. –Exclusive measurement by 6 units of range counter arrays. We request the first step data taking –Measure inclusive missing mass spectrum. –Check the feasibility of one proton / two protons tagging method. →We request the beam time in 2012. The preparation and repair is well under way 16 Korea-Japan workshop on nuclear and hadron physics at J-PARC （ 2011 ）

18. Back up 17 Korea-Japan workshop on nuclear and hadron physics at J-PARC （ 2011 ）

19. The differential cross section for π - p →Λ(1405)K 0 Λ （ 1405 ） production cross section in the very forward direction is 5μb/sr （ CM ）. 18 → 60μb/sr （ Lab ） Korea-Japan workshop on nuclear and hadron physics at J-PARC （ 2011 ） D.W. Thomas et al., Nucl. Phys. B56 (1973) 15.

20. 19 Elementary process Production of Λ(1405) – about 400 events clearly identified in theΣπ modes. D.W. Thomas et al., Nucl. Phys. B56 (1973) 15. Korea-Japan workshop on nuclear and hadron physics at J-PARC （ 2011 ）

21. K - pp → Λ + p 1, → p 2 + π - proton2 theta_Lab proton1 theta_Lab angular distribution of 2proton （ >300MeV/c) from K-pp 20 K - pp → Σ 0 + p 1 → Λ + γ, → p 2 + π - proton1 theta_Lab proton2 theta_Lab Background suppression （ 2proton tagging system ） Korea-Japan workshop on nuclear and hadron physics at J-PARC （ 2011 ）

22. Calculated spectrum of the d （ π +,K + ） K - pp reaction 21 Harada’s Calculation preliminary FINUDA; B = 115 MeV ， Γ = 67 MeV YA potential; B = 86 MeV ， Γ = 58 MeV Korea-Japan workshop on nuclear and hadron physics at J-PARC （ 2011 ）