Y. Iseki

Polarization and weak decays of Λ hypernuclei produced by the (π+, K+) reaction on 12C

Abstract Non-mesonic weak-decay protons (NM-p) and mesonic weak-decay pions (M-π) from Λ produced by the (π+, K+) reaction on 12C have been measured. NM-p from the 11 Λ B ( 5 2 + ) produced through the proton-unbound states in 12ΛC and NM-p and M-π associated with the quasi-bound region (Ex ≈ 20 MeV) in 12ΛC show finite asymmetries of A1 = − 0.20 to − 0.35 with respect to the reaction plane. These results indicate finite polarizations of the relevant Λ-hypernuclei and asymmetric NM weak decays.

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.

Polarization and weak decay of Λ hypernuclei

Abstract The 12 C( π + , K + ) reaction was used to produce polarized. A hypernuclei for the first time. Asymmetries of weak decay particles were measured. In the high excitation region, where quasifree production of Λ hypersons is dominant, the polarization of Λ was derived. It is found to be consistent with that for the elementary n ( π + , K + ) Λ reaction which demonstrates that the spin characteristics of the elementary reaction is not modified by the nuclear medium. In the low excitation region, where hypernuclei are dominantly produced, asymmetries of the non-mesonic decay protons were measured. The measurement and calculated polarization gave large asymmetry parameter (−1). It will elucidate the non-mesonic decay mechanism and open a new field of hypernuclear physics.

Study ofΛ12C andΛ56Fe hypernuclei by (π+, K+) reactions at the KEK 12GeV PShypernuclei by (π+, K+) reactions at the KEK 12GeV PS

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.

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

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.

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@@@Исследование rиперядер Λ 12 C и Λ 56 Fe с помошью (π+, K+) реакций в KEK 12 ГзB PSс помошью (π+, K+) реакций в KEK 12 ГзB PS

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.