Yudai Ichikawa Kyoto University/JAEA Progress on J-PARC hadron physics in 2014 Experimental search for the kaonic nuclei using the d(π +, K + ) reaction

2 Inclusive analysis results Coincidence analysis results arXiv:

Introduction (K - pp bound state) Introduction (K - pp bound state)  Simplest kanoic nuclei, KNN (Total charge=+1, I=1/2) system  B.E. and Γ strongly depend on the KN interaction.  It is difficult to reproduce the experimental values. Theoretica l value K bar -N interactionCalculation method ●Chiral baseVariation ○Chiral baseFaddeev ▲PhenomenologicalVariation △ PhenomenologicalFaddeev T.Yamazaki et al., PRL 104, (2010) M.Agnello et al., PRL 94, (2005) K - + p + p ~ 2.37GeV/c 2 3

J-PARC E27 experiment ( π + d→ K + X reaction at 1.69GeV/c) 4 π + + n → Λ(1405) + K + Λ(1405) + p → K - pp ( →quasi free Λ* ） K - pp is produced via a Λ(1405) doorway. π+π+ K+K+ J-PARC K1.8 beam line π+π+ K+K+ Y.Akaishi, T.Yamazaki, Phys. Rev. C (2007) K1.8 beam line spectrometer Sks spectrometer

 There are a lot of B.G. of the quasi-free hyperon production.  It is difficult to discuss the K − pp in the inclusive spectrum.  Detect the proton(s) from the K − pp decay with Range Counter Array.  K − pp→Λ p→p π − p; K − pp→Σ 0 p→p π − γ p; K − pp→Y π p→p π p + (etc.).  We suppress the quasi-free B.G. by tagging a proton or 2 protons. 5 RCA for B.G. suppression QF(B.G.): π + “n”→ Λπ 0 K + → p π - π 0 K + (proton spectator) RC-Seg3, 6 RC-Seg2, 5 RC-Seg1, 4 K - pp→ Λp→p π - p RC-Seg3, 6 RC-Seg2, 5 RC-Seg1, 4 5 p p π+π+ K+K+ Simulation

Spectrometer performance (Calibration) p( π +, K + ) Σ + at 1.58 GeV/c ・ Missing mass resolution of Σ + ΔM = 2.8 ± 0.1 MeV/c 2 (FWHM) ・ Missing mass resolution of the d(π +, K + )X reaction ・ X = K - pp (B.E = 100MeV) ΔM = 2.7 ± 0.1 MeV/c 2 (FWHM) ・ X = ΣN cusp (2.13 GeV/c 2 ) ΔM = 3.2 ± 0.2 MeV/c 2 (FWHM) The K + momentum is same region of the d(π +,K + )K - pp reaction. 6 Σ+Σ+

MM p [GeV/c 2 ] 7 Zoom Σ+Σ+ p( π +, K + ) at 1.69 GeV/c Σ(1385) + M = ± 3.6 MeV/c 2 Γ = 42 ± 13 MeV PDG: M = ± 0.35 MeV/c 2, Γ = ± 0.7 MeV

d( π +, K + ) at 1.69 GeV/c (Inclusive spectrum) 8 Quasi-free B.G. - Λ, Σ +/0, - Y * : Λ(1405), Σ(1385) +/0, - Λπ, Σπ There are a lot of B.G (quasi-free hyperon production). →It is difficult to identify the K - pp from inclusive spectrum. The overall structure was understood with a simulation except for two peculiar deviations. ΣN cusp (~2.13 GeV/c 2 ) and Y* peak postion Y* peak; data = ± 0.5(stat.) ± 0.6(syst.) MeV/c 2 sim = (syst.) MeV/c 2 “shift” = － 32.4 ± 0.5(stat.) (syst.) MeV/c

d( π +, K + ) at 1.69 GeV/c (Inclusive spectrum) 9 M(Σ 0 )+M(p) = GeV/c 2 M(Σ + )+M(n) = GeV/c 2  Forward scattering angle (θ piK(Lab) = 2-8°) was selected.  A cusp at ΣN threshold is prominent in the figure.  This is the first observation in the inclusive measurement of this reaction. Further detailed studies including the present data would reveal the ΣN-ΛN coupling strength and pole position. M 0 = ± 0.4 (stat.) ± 0.9 (syst.) MeV/c 2 Γ = 5.3 (stat.) (syst.) MeV +1.4 − −0.3

1 proton coincidence analysis ΣN Cusp K - pp? 1p coin / Inclusive 10  RC Seg2, 5 are free from the QF backgrounds.  Excess due to ΣN cusp is clearly observed ~ 2.13GeV/c 2.  Broad Enhancement is observed around 2.3GeV/c 2.  A possible explanation of the observed structure is the K - pp.

Cusp region K - pp region Y* region 2 proton coincidence analysis 2p coin / Inclusive K - pp? ΣN Cusp ①② ③ 11  2 protons coincidence spectrums show the same tendency as 1proton coincidence spectrum.  We divided the 3 regions at the missing mass spectrum. ① MM 2.35GeV

＋ Data ー X = π (F.S.:Λp) ー X = πγ (F.S.:Σ 0 p) ー X = 2π (F.S.:Yπp) ー Sum d( π +,K + pp)X spectra (Final state determination) MM d [GeV/c 2 ] 12 Λp Σ0pΣ0p Yπp 2p coin events Final states are known from 2p coincidence events. Λp Σ0pΣ0p Σ0pΣ0p Yπp Λp Σ0pΣ0p Yπp

“K - pp”-like structure 13  The broad structure around 2.26 GeV/c 2 have been observed in the Σ 0 p final state events.  We fitted with a relativistic BW function smeared with the resolution.  Mass: (BE: )  Width:  This distribution can reproduce the 1p coincidence probability spectrum (pink). Blue and red lines show the flat component and summed one. 1p coincidence probability Differential cross section of π + d→K + W, W→Σ 0 p process

The inclusive missing-mass spectra of the d(π +, K + ) reaction at 1.69 GeV/c has been observed for the first time. The overall structure was understood with a simple quasi- free picture. However, there are two peculiar deviations. The centroid of the broad bump structure in Y * region was shifted to low mass side, by － 32.4 ± 0.5 (stat.) (syst.) MeV/c 2. We observed the ΣN cusp in the inclusive spectrum for the first time in this reaction. The double differential cross section of each final state was estimated from 2p coincidence events. We have observed a clear bump structure which corresponds to “K-pp”-like structure in Σ 0 p final state events.  Mass: (BE: )  Width:

J-PARC E27 Collaboration T. Nagae, H. C. Bhang, S. Bufalino, H. Ekawa, P. Evtoukhovitch, A. Feliciello, H. Fujioka, S. Hasegawa, S. Hayakawa, R. Honda, K. Hosomi, Y. Ichikawa, K. Imai, S. Ishimoto, C. W. Joo, S. Kanatsuki, R. Kiuchi, T. Koike, H. Kumawat, Y. Matsumoto, K. Miwa, M. Moritsu, M. Naruki, M. Niiyama, Y. Nozawa, R. Ota, A. Sakaguchi, H. Sako, V. Samoilov, S. Sato, K. Shirotori, H. Sugimura, S. Suzuki, T. Takahashi, T. N. Takahashi, H. Tamura, T. Tanaka, K. Tanida, A. O. Tokiyasu, Z. Tsamalaidze, B. J. Roy, M. Ukai, T. O. Yamamoto and S. B. Yang 15