平岩聡彦 京都大学 On behalf of the J-PARC E15 collaboration

Outline Introduction J-PARC E15 experiment experiment & theory of K-pp J-PARC E15 experiment method setup background Possibility of E15 exp. @ 30kW Summary & outlook 2010/12/2-4 ストレンジネス研究会2010

Introduction 2010/12/2-4 ストレンジネス研究会2010

Low-energy KN interaction K-nucleon interaction Low energy Kp scattering Kaonic hydrogen level shift (KEK-PS E228) Kaonic nuclei Kaon bound states with a few nucleons Extract the information about KN interaction below KN threshold M.Iwasaki et al. , PRL 78, 3067(1997) Attractive (I=0) How strong? 2010/12/2-4 ストレンジネス研究会2010

Experimental results on K-pp FINUDA Invariant mass of back-to-back Lp pairs in K- absorptions B = 115±6(stat)±4(syst) MeV G = 67±14(stat)±3(syst) MeV DISTO pp  K+X+, X+ pL B = 105±2(stat)±5(syst) MeV G = 118±8(stat)±10(syst )MeV Several experimental searches for K-pp bound states have been done so far. FINUDA group reported the indication of K-pp bound states in the invariant mass spectra of back-to-back Lambda p pairs from Kaon absorption They claimed that the binding energy and the width are 115 MeV and 67 MeV, respectively. Very recently, DISTO collaboration re-analysised the old data and found the broad structure in the lambda p invariant mass spectra, which corresponds to the biding energy of 105 MeV and the width of 118 MeV. T.Yamazaki et al. , PRL 104, 132502 (2010)　 M.Agnello et al. , PRL 94, 212303 (2005) 2010/12/2-4 ストレンジネス研究会2010

Theoretical study on K-pp B.E [MeV] G [MeV] Method Yamazaki and Akaishi 48 61 (mesonic) Variational Method (ATMS) Shevchenko, Gal, and Mares 55-70 90-110 (mesonic) Coupled Channel Faddeev Calculation Ikeda and Sato 60-95 45-80 (mesonic) Nishikawa and Kondo ~126 Skyrme Model Dote, Hyodo, and Weise 20±3 (s-wave) 40-70 (mesonic) Chiral SU(3) Variational Method Arai, Oka, and Yasui depend on gΛ*Λ*σ Variational Method (as Λ*p state) Theoretical studies on K-pp are also advancing. Here we listed the recent results. All calculation support the existence of K-pp bound states. But we don’t know whether it is a deep state or shallow states and the decay width is sufficiently narrow or not. K-pp bound states should exist! A deep state or shallow state? Decay width is sufficiently narrow? 2010/12/2-4 ストレンジネス研究会2010

Formation spectra : in-flight 3He(K-,n) K- + 3He  “K-pp” + n @ PK=1GeV/c, q=0º YA potential quasi-free Signal can be clearly seen! bound K- conversion K- escape Integrated production cross section amounts to 3.5 mb/sr. 2010/12/2-4 ストレンジネス研究会2010 T.Koike and T.Harada. , PLB652 (2007) 262

Search for K-pp bound states at J-PARC E15 experiment via in-flight (K-, n) reaction 　on 3He. E27 experiment via d(p+, K+) reaction. 2010/12/2-4 ストレンジネス研究会2010

J-PARC E15 collaboration 2010/12/2-4 ストレンジネス研究会2010

J-PARC E15 experiment L neutron 3He K- p p- We can observe both the Experimental search for K-pp bound states using in-flight (K-, n) reaction on 3He K-pp cluster neutron K- 3He Formation 1 GeV/c Missing mass Spectroscopy via neutron Decay L p p- Mode to decay charged particles We can observe both the “Formation” and “Decay” of K-pp bound state Invariant mass reconstruction 2010/12/2-4 ストレンジネス研究会2010

Experimental Setup J-PARC K1.8BR Neutron 1.0 GeV/c K- TOF length 15m Invariant mass resolution for K-pp (B.E. 100 MeV) s ~ 13 MeV/c2 (sCDC=200mm, B=0.7T) Neutron counter Beam sweep magnet Cylindrical Detector System Neutron 1.0 GeV/c K- TOF length 15m Missing mass resolusion for K-pp (B.E. 100 MeV ) s ~ 9.2 MeV/c2 (Pn~1.3GeV/c, sTOF=150ps) Beamline Spectrometer 2010/12/2-4 ストレンジネス研究会2010

Identification of Lpn final state by CDS & NC Possible background - S0pn final state + g missing - QF-L + p missing - QF-S, SL conv. + p missing Other processes can be clearly separated!! 2010/12/2-4 ストレンジネス研究会2010

Background?? : two nucleon absorption 2NA + LN rescattering / SL conversion looks like a “signal” ?? (2NA itself is not a problem.) 12C(K-,n) @ 1GeV/c De Broglie wave length @ 1 GeV/c ~ 1.2 fm NN distance in 3He ~ 2.25 fm Proc. Jpn. Academy, Series B83 (2007) 144. 12C(K-,p) These probabilities are expected to be very small ... Anyway, let’s see how they look like! 2NA is very small 2010/12/2-4 ストレンジネス研究会2010 T. Kishimoto et al., Prog.Theor.Phys. 118(2007)181.

Signal(DISTO) vs Background(2NA+SL conv.) 2NA and S-L conversion (B.E.=100MeV G=100MeV) 2NA and S-L conversion 2010/12/2-4 ストレンジネス研究会2010

Signal(DISTO) vs Background(2NA+rescattering) 2NA and s-wave scattering 2NA and s-wave scattering 2010/12/2-4 ストレンジネス研究会2010

Possibility of the E15 experiment with 30kW PS operation 2010/12/2-4 ストレンジネス研究会2010

Yield estimation (1week run @30kW) Yield = NKaon x t x (ds/dW)q=0º x R x r x A x e x e Nkaon : kaons per spill (@30kW)  300k /spill t : target  0.08 [g/cm3] / 3 [g/mol] x 6.02x1023 [mol-1] x 9.3 [cm] ~ 1.4 x 1023 [cm-2] (ds/dW)q=0º : differential cross section @ q=0º  3 [mb/sr] R : Kpp decay branch (Lp)  0.5 r : branching ratio (L  p-p)  0.63 A : acceptance (NC + CDS)  5.3 [msr] e : NC efficiency  0.3 e : overall efficiency (trigger, detector, ana etc...)  0.7 PLB 652 (2007) 262. PRC80 (2009) 055208 4.5 x103 signals can be collected in 1 week run with 30kW operation. 2010/12/2-4 ストレンジネス研究会2010

Missing mass of 3He(K-, n) Lp / S0p decay branches stand on same mass! 4,500 signals (Lp) + 4,500 signals (S0p) ~ Total 9,000 signals ( [Lp] : [S0p] = 0.5 : 0.5 ) 2010/12/2-4 ストレンジネス研究会2010

Improvement of statistics Statistical improvement can be achieved by “one proton missing”. Missing proton resolution: 28  0.3 MeV/c2 (s) Acceptance (NC+CDS) 3body phase space  0.079% (all detected)  0.12% (one proton missing) K-pp (B=100MeV, G=100MeV)  0.042%(all detected)  0.098% (one proton missing) x2 Lpn final state still can be identified! 2010/12/2-4 ストレンジネス研究会2010

Summary & outlook J-PARC E15 experiment search for a K-pp bound state using in-flight (K- n) reaction on 3He measure the missing mass in (K-, n) reaction and the invariant mass via the decay of K-pp, simultaneously. E15 experiment @ 30kW operation Enough statistics for the first physics data can be collected within a week if the cross section is ~ 3 mb/sr. (2% of the requested beam time) We wish to start E15 exp. as soon as possible . (after E17) 2010/12/2-4 ストレンジネス研究会2010