T. Kishimoto RCNP and Physics Dept. Osaka University Kaon-Nucleus Interaction Studied through the In-Flight (K-, N) Reaction T. Kishimoto RCNP and Physics Dept. Osaka University Panic08

K-nucleus interaction Kaon condensation in neutron stars Atomic X ray data: two solutions (Batty, Friedman, Gal) deep ~180 MeV K-con (mK~2.5 r U) shalow ~80 MeV no K-con K- production in HI reaction: attractive L(1405) K- p X ray data repulsive shift: (bound state L(1405)) strongly attractive phenomenological potential (Akaishi Yamazaki) Recent experiments: controversial Kaonic nuclei Panic08

in-flight (K-,N) reactions TK, PRL83,4701, ’99 Elementary s K- n K ds/dW(lab)= (Pl/Pcm)2ds/dW(CM) ~10mb/sr Initial and final wf, q ~ 0.3 GeV/c ~ pF ★Known mechanism (predictable cross section) ★Least background (pN~1.3GeV/c for pK~1 GeV/c) Panic08

Exploratory Experiment at BNL Bound region Appreciable strength unbound 16O(K-,n) missing mass @PK~0.93GeV/c water target Attractive K-nucleus interaction p(K-, n)K0 sum Hyperon production Potential depth ~200MeV Cross sections: consistent a KEKPS E548 - M(15O+K-) Panic08

KEK-PS E548 Study of Kaonic Nuclei by the (K- ,p) reaction (K-,p) and (K-,n) reactions on 16O (water target) 12C (graphite and CH2 targets) Improvements over BNL experiment Proton (KURAMA spectrometer): 12MeV(σ)@BE=150MeV Neutron counter: ~20msr, 10MeV(σ)@BE=150MeV Decay counter (NaI array): ~0.5 of 4π Panic08

Beam line and spectrometer K2 beam line pK=1 GeV/c (pN=1.2~1.3 GeV/c) 10k K- for 3Tp (~1/10 of BNL) Trigger rate a ～500/spill ~1GK- on Target Liquid scintillator for Neutron counter Panic08

Neuron counters Plastic scintillator array Conversion layer 2 layers of 5cm thick plastic 1.5m x 1.5m Conversion layer Liquid scintillator container 20cm thick 1.5m x 1.5m Efficiency and time resolution 9.8m from the target p n Panic08

Decay counter ・Charged particles ・Vertex points NaI 5x5 KURAMA NaI 3x4 Decay particle FAC VZH 20cm BAC 1 BAC 2 LC BS P or n Target(water) BQC K- Beam 1.0 GeV/c 10.5cm CV Panic08 VZH is to identify vertex to give neutron flight length

MM 12C(K-, n) Solid line: best fit Re(V)=-190MeV Im(V)=-40 MeV multi.(decay)>=1 Solid line: best fit Re(V)=-190MeV Im(V)=-40 MeV Dotted line: Re(V)=-60 MeV Im(V)=-60 MeV Bound region ds/dW mb/sr/10MeV Panic08 -BE (MeV)

MM 12C(K-, p) Solid line: best fit Re(V)=-160MeV Im(V)=-50 MeV multi.(decay)>=1 Solid line: best fit Re(V)=-160MeV Im(V)=-50 MeV Dotted line: Chiral Re(V)=-60 MeV Im(V)=-60 MeV Bound region ds/dW mb/sr/10MeV Panic08 -BE (MeV)

Potential depth by comparison with calculated spectra Green function method Consistent description of bound to unbound region with imaginary part (all final states) J. Yamagata, S. Hirenzaki et al., PRC74 T. Hayakawa (PhD) Quantitative comparison Potential Re(V) Im(V(Eex)) Spectrum shape Absolute cross section Pion emission energy dependence Two nucleon absorption Panic08

c2 contour plot (K-, n) (K-, p) 60 MeV × Fit 1. whole region 2. bound region Re(V)=-190 MeV Im(V)=-40 MeV (K-, n) Im(V) MeV Re(V)=-160 MeV Im(V)=-50 MeV (K-, p) 60 MeV　× Panic08 Re(V) MeV

Effective nucleon number Neff Neff= s(12C(K-, N))/ s(p(K-, N)) ~1.5 calculation (40 mb for s(KN) and s(NN) Neff(Eik)~1.27 Neff(Eik)~1.44 (with A-1 correction) Background process Fitting of -BE=100~200 MeV region quadratic function multi-step? s~20 mb/sr We are seeing (K-, N) reaction not backgrounds Panic08

16O(K-,p) and 16O(K-,n) Χ2(DOF=12) (-60,-60) O(K,n)X 束縛領域 Best fit (-180,-40) (-160,-40) O(K,p)X 12 束縛領域 W(MeV) ΔV≠0 Panic08 BG (multi-step…) V(MeV) -BE(MeV)

A and Isospin dependence Assumption: attraction is from NI=0: I=0 (K- p, K0n) pairs in kaonic nuclei. NI=0 16O(K-,N) 12C(K-, N) Isospin of kaonic nuclei I=0 (K-,n) 4.5 3.5 I=1 (K-,p) 3.5 2.5 (K-,n) 4 3 Potential depth ∝ NI=0/A cal(MeV) obs(MeV) 12C(K-, n) 190 12C(K-, p) 158 ~160 16O(K-, n) 190 ~180 16O(K-, p) 166 ~160 (K-, n)=((I=0)+(I=1))/2 Panic08

Summary Missing mass spectra of 12C(K-, N) indicate 12C (K-, n): Vr ~ 190MeV Vi ~ -40 MeV, 12C (K-, p): Vr ~ 160MeV Vi ~ -50 MeV, Vr ~ 200 MeV a Kaon condensation Isospin dependence may be consistent 12C results in PTP 118, 181 (2007) 16O(K-, N): same conclusion paper in preparation Future study at J-PARC Panic08