Y. Matsuyama

The superconducting kaon spectrometer — SKS

A superconducting kaon spectrometer has been installed in the north experimental hall of the KEK 12-GeV proton synchrotron. The spectrometer was designed to serve for nuclear physics experiments with meson beams in the 1 GeV/c region, particular emphasis being laid on study of Λ-hypernuclei via (π+, K+) reactions. In order to obtain Λ-hypernuclear data with better statistics and energy resolution, it was designed to have a good momentum resolution of 0.1% FWHM and a large acceptance of 100 msr. It consists of a large superconducting dipole magnet, tracking chambers, and trigger counters that can efficiently select kaons from large background of pions and protons. The overall energy resolution for scattering is realized together with a beam-line spectrometer in the K6 beam line, the momentum resolution of which was also designed to be better than 0.1% FWHM. A good energy resolution of better than 2 MeV FWHM has been confirmed in π−-12C elastic scattering and in the (π+,K+) reaction on 12C.

Multiple-sampling and tracking proportional chamber for nuclear reactions with low-energy radioactive isotope beams

Abstract Nuclear reactions with radioactive isotope beams at low energy near to the Coulomb barrier are very important for studying nuclear astrophysics, nuclear structure and the reaction mechanism involving unstable nuclei. Due to the limited intensity of low-energy radioactive isotope beams, a new device is required to carry out experiments with reasonable statistics. A multiple-sampling and tracking proportional chamber was constructed for measuring these reactions and tested with radioactive isotope beams. In addition, read-out electronics and a data-acquisition system were developed and tested along with the detector. It was proved that they are useful for detecting nuclear reactions in the low-energy region, like a fusion reaction and astrophysical nuclear reactions.

Enhanced ΛΛ production near threshold in the 12C(K−,K+) reaction

Abstract Enhanced production of ΛΛ pairs, above levels predicted by a two-step process model, has been observed near threshold (in the mass range 2.23-2.26 GeV/c2) in the 12C(K−,K+) reaction at 1.66 GeV/c using a scintillating fiber target. The differential cross section for ΛΛ production in the momentum region 0.95≤pK+≤1.3 GeV/c averaged over the range 2.3o≤θK+≤14.7o was found to be 7.6±1.3 ±0.9 μ b/sr, and that for the enhancement was found to be approximately 3 μ b/sr.

Scalar and vector meson production and two-step processes in the (K-, K+) reaction on 12C

Abstract The double strangeness exchange reaction ( K − , K + ) is investigated with respect to the sub-threshold production of scalar and vector mesons ( f 0 / a 0 / φ ) decaying into K + K − and the two-step processes induced by intermediate mesons and Ξ − hyperons at p k − = 1.66 GeV/ c using a scintillating fiber active target. The differential cross section ( 〈 dσ dΩ L 〉) averaged over the angular interval (2.3° ⩽ θ K + L ⩽ 14.7°) for the sub-threshold f 0 / a 0 / φ meson production with the K + K − decay is 11 ± 6 μ b/sr at 0.6 ⩽ p K 1 c . The present result differs significantly from the theoretical calculation which predicts the contribution of the f 0 / a 0 / φ meson production to be predominant in the ( K − , K + ) reaction below p K + = 0.95 GeV/ c . We found a sizable contribution from two-step ( K − , K + processes, characterized by production of two S = −1 hyperons, consistent with the result of the intra-nuclear cascade (INC) model calculation with respect to the meson-induced hyperon (or hyperon resonance) pair production in the momentum region 0.6 ⩽ p K + c . The observed enhancement of the cross section for the two-step ΛΛ production beyond the prediction of the INC model at p K + ⋍ 1.1 GeV /c could be due to the Ξ − p → ΛΛ reaction in 12 C.

A broad range spectrometer PIK for medium-energy meson spectroscopy

Abstract A broad range spectrometer, PIK, has been constructed for the study of Λ hypernuclei via the ( π + , K + ) reaction. The spectrometer can also be used for nuclear spectroscopy with medium-energy meson beams. It consists of two independent spectrometers: one analyzes the incident beam momentum, and the other determines the momentum of the scattered particle. The latter spectrometer is characterized by a large solid angle of 15–22 msr, a broad range momentum acceptance of 0.55–1.1 GeV/ c , a wide angular acceptance of 11°, and a short flight path length of 4.5 m. The scattered particle is identified by the use of silica aerogel Cherenkov counters and Lucite Cherenkov counters and by measuring its time-of-flight. The performance of the spectrometer is examined by the ( π + , K + ) reaction on a 12 C target at P π = 1.05 GeV/ c and by the ( π + , p) reaction on a CH 2 target.

Enhanced production of ΛΛ pairs near threshold in the (K-,K+) reaction on 12C

Abstract Enhanced production of ΛΛ pairs, above the prediction of a two-step process model, is observed near threshold (around the masses of 2.23 – 2.26 GeV/c2) in the12C(K−,K+) reaction at PK− = 1.66GeV/c using a scintillating fiber target. The differential cross section for the ΛΛ production averaged over 2.3° ≤

Study of Λ 12 C and Λ 56 Fe hypernuclei by (π + , K + ) reactions at the KEK 12GeV PShypernuclei by (π + , K + ) reactions at the KEK 12GeV PS

K + ≤ 14.7° in the momentum region 0.95 ≤ pK + ≤ 1.3GeV/c was found to be 7.6 ± 1.3 μb/sr, and that for the enhancement approximately 3 μb/sr.

Measurement of the 8 Li( α, n ) 11 B Reaction with the Multiple-Sampling and Tracking Proportional Chamber (MSTPC) for Astrophysical Interest

SummaryEnergy spectra ofΛ12C andΛ56Fe have been measured by means of (π+, K+) reactions at the KEK 12 GeV PS. The spectrometer PIK, which has large angular and momentum acceptance and medium energy resolution, has been constructed to study the reaction. The differential cross-section of the (π+, K+) reaction at forward angles θK∼(0÷6)o for the ground state ofΛ12C and that for the effectively Λ-bound region ofΛ56Fe agree well with the DWIA calculation using single-particle Λ wave functions obtained from a Woods-Saxon potential. The spectrum ofΛ56Fe is consistent with the DWIA calculation using the realistic distribution of the hole-state strengths in55Fe.RiassuntoSono stati misurati gli spettri d’energia diΛ12C eΛ56Fe per mezzo delle reazioni (π+, K+) al KEK 12 GeV PS. Lo spettrometro PIK, che ha grande accettazione angolare e d’impulso e risoluzione ad energie medie, è stato costruito per studiare la reazione. La sezione d’urto differenziale della reazione (π+, K+) per angoli in avanti θK∼(0÷6)o per lo stato fondamentale diΛ12C e quella per la regione diΛ56Fe efficacemente limitata da Λ sono in buon accordo con il calcolo DWIA che utilizza funzioni d’onda di Λ ad una sola particella ottenuta da un potenziale di Woods-Saxon. Lo spettro diΛ56Fe è consistente con il calcolo DWIA che utilizza la distribuzione realistica delle forze dello stato di buco in55Fe.РеэюмеБыли иэмерены знергетические спектрыΛ12C иΛ56Fe с помошью (π+, K+) реакций в KEK 12 ГзB PS. Для исследования реакции был сконструирован спектрометр PIK, который имеет высокие угловой акцептанс и импульсное раэрещение, но среднее раэрещение по знергии. Дифференциальное поперечное сечение для (π+, K+) реакции при углахθK ∼ (0÷6)° для основного состоянияΛ12C и дифференциальное поперечное сечение для зффективно ограниченной области Λ дляΛ56Fe хорощо согласуются с вычислением DWIA, в котором испольэуются одночастичные волновые функции для Л, полученные иэ потенциала Вудса-Саксона. СпектрΛ56Fe согласуется с вычислением DWIA, в котором испольэуются реалистическое распределение сил дырочных состояний в55Fe.

H-dibaryon search with a scintillating fiber live target

SummaryEnergy spectra ofΛ12C andΛ56Fe have been measured by means of (π+, K+) reactions at the KEK 12 GeV PS. The spectrometer PIK, which has large angular and momentum acceptance and medium energy resolution, has been constructed to study the reaction. The differential cross-section of the (π+, K+) reaction at forward angles θK∼(0÷6)o for the ground state ofΛ12C and that for the effectively Λ-bound region ofΛ56Fe agree well with the DWIA calculation using single-particle Λ wave functions obtained from a Woods-Saxon potential. The spectrum ofΛ56Fe is consistent with the DWIA calculation using the realistic distribution of the hole-state strengths in55Fe.RiassuntoSono stati misurati gli spettri d’energia diΛ12C eΛ56Fe per mezzo delle reazioni (π+, K+) al KEK 12 GeV PS. Lo spettrometro PIK, che ha grande accettazione angolare e d’impulso e risoluzione ad energie medie, è stato costruito per studiare la reazione. La sezione d’urto differenziale della reazione (π+, K+) per angoli in avanti θK∼(0÷6)o per lo stato fondamentale diΛ12C e quella per la regione diΛ56Fe efficacemente limitata da Λ sono in buon accordo con il calcolo DWIA che utilizza funzioni d’onda di Λ ad una sola particella ottenuta da un potenziale di Woods-Saxon. Lo spettro diΛ56Fe è consistente con il calcolo DWIA che utilizza la distribuzione realistica delle forze dello stato di buco in55Fe.РеэюмеБыли иэмерены знергетические спектрыΛ12C иΛ56Fe с помошью (π+, K+) реакций в KEK 12 ГзB PS. Для исследования реакции был сконструирован спектрометр PIK, который имеет высокие угловой акцептанс и импульсное раэрещение, но среднее раэрещение по знергии. Дифференциальное поперечное сечение для (π+, K+) реакции при углахθK ∼ (0÷6)° для основного состоянияΛ12C и дифференциальное поперечное сечение для зффективно ограниченной области Λ дляΛ56Fe хорощо согласуются с вычислением DWIA, в котором испольэуются одночастичные волновые функции для Л, полученные иэ потенциала Вудса-Саксона. СпектрΛ56Fe согласуется с вычислением DWIA, в котором испольэуются реалистическое распределение сил дырочных состояний в55Fe.