-
S N Nakamura,
A Matsumura,
Y Okayasu,
T Seva,
V M Rodriguez,
P Baturin,
L Yuan,
A Acha,
A Ahmidouch,
D Androic, [......],
V Tadevosyan,
T Takahashi,
L Tang, K Tsukada,
V Tvaskis,
W Vulcan,
S Wells,
S A Wood,
C Yan,
S Zhamkochyan
[show abstract]
[hide abstract]
ABSTRACT: An experiment with a newly developed high-resolution kaon spectrometer and a scattered electron spectrometer with a novel configuration was performed in Hall C at Jefferson Lab. The ground state of a neutron-rich hypernucleus, _{Λ}^{7}He, was observed for the first time with the (e, e^{'}K^{+}) reaction with an energy resolution of ∼0.6 MeV. This resolution is the best reported to date for hypernuclear reaction spectroscopy. The _{Λ}^{7}He binding energy supplies the last missing information of the A=7, T=1 hypernuclear isotriplet, providing a new input for the charge symmetry breaking effect of the ΛN potential.
Physical Review Letters 01/2013; 110(1):012502. · 7.37 Impact Factor
-
X. Qiu,
L. Tang,
A. Margaryan,
P. Achenbach,
A. Ahmidouch,
I. Albayrak,
D. Androic,
A. Asaturyan,
R. Asaturyan,
O. Ates, [......],
W. Vulcan,
F. R. Wesselmann,
S. A. Wood,
L. Ya,
T. Yamamoto,
Z. Ye,
K. Yokota,
L. Yuan,
S. Zhamkochyan,
L. Zhu
[show abstract]
[hide abstract]
ABSTRACT: The lifetime of a Lambda particle embedded in a nucleus (hypernucleus)
decreases from that of free Lambda decay due to the opening of the Lambda N to
NN weak decay channel. However, it is generally believed that the lifetime of a
hypernucleus attains a constant value (saturation) for medium to heavy
hypernuclear masses, yet this hypothesis has been difficult to verify. The
present paper reports a direct measurement of the lifetime of medium-heavy
hypernuclei produced with a photon-beam from Fe, Cu, Ag, and Bi targets. The
recoiling hypernuclei were detected by a fission fragment detector using
low-pressure multi-wire proportional chambers. The experiment agrees remarkably
well with the only previously-measured single-species heavy-hypernucleus
lifetime, that of Fe56_Lambda at KEK, and has significantly higher precision.
The experiment disagrees with the measured lifetime of an unknown combination
of heavy hypernuclei with 180<A<225 and, with a small statistical and
systematic uncertainty, strongly favors the expected saturation of the lifetime
decrease.
12/2012;
-
B. Beckford,
P. Bydzovsky,
A. Chiba,
D. Doi,
T. Fujii,
Y. Fujii,
K. Futatsukawa,
T. Gogami,
O. Hashimoto,
Y. C. Han, [......],
K. Sugihara,
K. Suzuki,
T. Tamae,
H. Tamura, K. Tsukada,
K. Yagi,
F. Yamamoto,
T. O. Yamamoto,
H. Yamazaki,
Y. Yonemoto
[show abstract]
[hide abstract]
ABSTRACT: An experiment was carried out with the NKS2+ in 2010 at the Research Center
for Electron Photon Science (ELPH), in which tagged photon beams in the range
of 0.8 $\le$ $E_{\gamma}$ $\le$ 1.1 GeV were impinged on a liquid $^2$H target
positioned at the center of the NKS2+. The produced $\Lambda$ was subsequently
detected by the $p{\pi^{-}}$ decay channel. Integrated cross sections of the
$^2$H$({\gamma},{\Lambda})$X in the angular region of 0.9 $\le$
$\cos{\theta}_{\Lambda}^{LAB}$ $\le$ 1.0 was derived and compared with
preceding experimental results of the NKS2 collaboration. In addition, the
momentum spectra for two photon energy regions were also procured. The
${\Lambda}$ angle dependent cross sections as a function of the scattering
angle in the laboratory system was additionally deduced. We present the latest
results on the excitation function of ${\Lambda}$ photoproduction, the momentum
distributions, angular distributions, and polarization.
10/2012;
-
S. N. Nakamura,
A. Matsumura,
Y. Okayasu,
T. Seva,
V. M. Rodriguez,
P. Baturin,
L. Yuan,
A. Acha,
A. Ahmidouch,
D. Androic, [......],
V. Tadevosyan,
T. Takahashi,
L. Tang, K. Tsukada,
V. Tvaskis,
W. Vulcan,
S. Wells,
S. A. Wood,
C. Yan,
S. Zhamkochyan
[show abstract]
[hide abstract]
ABSTRACT: An experiment with a newly developed high-resolution kaon spectrometer (HKS)
and a scattered electron spectrometer with a novel configuration was performed
in Hall C at Jefferson Lab (JLab). The ground state of a neutron-rich
hypernucleus, He 7 Lambda, was observed for the first time with the (e,e'K+)
reaction with an energy resolution of ~0.6 MeV. This resolution is the best
reported to date for hypernuclear reaction spectroscopy. The he 7 Lambda
binding energy supplies the last missing information of the A=7, T=1
hypernuclear iso-triplet, providing a new input for the charge symmetry
breaking (CSB) effect of \Lambda N potential.
07/2012;
-
B. Beckford,
A. Chiba,
D. Doi,
J. Fujibayashi,
T. Fujii,
Y. Fujii,
K. Futatsukawa,
T. Gogami,
O. Hashimoto,
Y. C. Han, [......],
K. Suzuki,
T. Tamae,
H. Tamura,
N. Terada, K. Tsukada,
K. Yagi,
F. Yamamoto,
T. O. Yamamoto,
H. Yamazaki,
Y. Yonemoto
[show abstract]
[hide abstract]
ABSTRACT: An experiment designed to investigate the strangeness photoproduction process
using a tagged photon beam in the energy range of 0.90 -1.08 GeV incident on a
liquid deuterium target was successfully performed. The purpose of the
experiment was to measure the production of neutral kaons and the lambda
particles on a deuteron. The generation of photo produced particles was
verified by the measurement of their decayed charged particles in the Neutral
Kaon Spectrometer 2. The reconstructed invariant mass distributions were
achieved by selecting events where two or more particles tracks were
identified. Preliminary results are presented here.
02/2012;
-
B. Beckford,
P. Bydzovsky,
J. Fujibayashi,
T. Fujii,
Y. Fujii,
K. Futatsukawa,
T. Gogami,
O. Hashimoto,
Y. C. Han,
K. Hirose, [......],
S. N. Nakamura,
A. Sasaki,
H. Shimizu,
K. Shirotori,
K. Suzuki,
T. Tamae,
H. Tamura,
N. Terada, K. Tsukada,
H. Yamazaki
[show abstract]
[hide abstract]
ABSTRACT: We have been conducting an experimental program to study strangeness photoproduc‐tions on the deuteron by measuring K0 and Λ in the threshold energy region. The π−π+ from K0 and π−p from Λ are detected by use of large acceptance magnetic spectrometers. At the first stage of the program, we started with Neutral Kaon Spectrometer (NKS), which consisted of timing counters and tracking devices in the magnetic field. The NKS spectrometer was employed to measure K0 photoproductions from deuteron and carbon target for the first time. A newly constructed spectrometer (NKS2) has been employed for the second stage experiment. It consists of a 110 ton dipole magnet and a combination of detectors. The momentum distributions of K0 and A from γ+d process were observed, and compared with the calculations based on the isobar models. The NKS2 spectrometer has been upgraded by installing a three dimensional tracking device in the central region. This improvement enables to explore the simultaneous measurement of the K0‐A with reasonable statistics.
AIP Conference Proceedings. 10/2011; 1388(1):280-283.
-
K. Tsukada,
T. Takahashi,
T. Watanabe,
Y. Fujii,
K. Futatsukawa,
O. Hashimoto,
K. Hirose,
K. Ito,
S. Kameoka,
H. Kanda, [......],
T. Kinoshita,
F. Miyahara,
T. Nakabayashi,
H. Shimizu,
T. Tamae,
H. Yamazaki,
A. Sasaki,
O. Konno,
P. Bydžovský,
M. Sotona
Physical Review C 02/2011; 83(3):39904. · 3.31 Impact Factor
-
B. Beckford,
L. Cole,
A. de la Puente,
Y. Fuji,
K. Futatsukawa,
O. Hashimoto,
M. Kaneta,
H. Kanda,
K. Maeda,
A. Matsumura,
S. N. Nakamura,
Y. Okayasu,
N. Perez,
J. Reinhold,
L. Tang, K. Tsukada
[show abstract]
[hide abstract]
ABSTRACT: The collection efficiency for Cherenkov light incident on a wavelength
shifting plate (WLS) has been determined during a beam test at the Proton
Synchrotron facility located in the National Laboratory for High Energy Physics
(KEK), Tsukuba, Japan. The experiment was conducted in order to determine the
detector's response to photoelectrons converted from photons produced by a
fused silica radiator; this allows for an approximation of the detector's
quality. The yield of the photoelectrons was measured as a function of the
momentum of the incident hadron beam. The yield is proportional to
sin2{\theta}c, where {\theta}c is the opening angle of the Cherenkov light
created. Based on estimations and results from similarly conducted tests, where
the collection efficiency was roughly 39%, the experimental result was expected
to be around 40% for internally produced light from the WLS. The results of the
experiment determined the photon collection response efficiency of the WLS to
be roughly 62% for photons created in a fused silica radiator and 41% for light
created in the wavelength shifter plastic.
07/2010;
-
S. Ajimura,
G Beer,
H. Bhang,
M. Bragadireanu,
P. Buehler,
L Busso,
M. Cargnelli,
S Choi,
C. Curceanu,
S Enomoto, [......],
T Suzuki,
H. Tatsuno,
M Tokuda,
D. Tomono,
A Toyoda, K Tsukada,
E. Widmann,
T Yamazaki,
H Yim,
J. Zmeskal
[show abstract]
[hide abstract]
ABSTRACT: The J-PARC E15 experiment will be performed to search for the simplest kaonic nuclear bound state, K− pp, by the in-flight 3He(K−,n) reaction. The exclusive measurement can be performed by a simultaneous measurement of the missing mass using the primary neutron and the invariant mass via the expected decay, K− pp → Λp → pπ− p. In this report, an overview of the experiment and the preparation status are presented.
EPJ Web of Conferences. 01/2010;
-
M Iio,
H. Bhang,
M. Cargnelli,
S Choi,
C. Curceanu,
O. V. Doce,
S Enomoto,
H Fujioka,
Y Fujiwara,
C Guaraldo, [......],
H. Tatsuno,
M Tokuda,
D. Tomono,
A Toyoda, K Tsukada,
A. R. Vidal,
E. Widmann,
B. Wunschek,
T Yamazaki,
J. Zmeskal
[show abstract]
[hide abstract]
ABSTRACT: We will measure the Balmer-series x-rays of kaonic-3He atoms using large-area high-resolution silicon drift x-rays detectors in order to provide the crucial information of K−-nucleus strong interaction at the low energy limit. The strong interaction 2p level shift will be determined with a precision of a few eV. At the present status, the construction of all detectors is in progress. In February, 2009, the first tuning of K1.8BR beamline was performed by the secondary beam generated in J-PARC hadron facility. The data taking will be started soon.
EPJ Web of Conferences. 01/2010;
-
H. Bhang,
S. Ajimura,
K Aoki,
A. Banu,
T Fukuda,
O Hashimoto,
J I Hwang,
S. Kameoka,
B H Kang,
E Kim, [......],
Y Sato,
M Sekimoto,
T Takahashi,
H Tamura,
K Tanida,
A Toyoda,
K. Tshoo, K Tsukada,
T Watanabe,
H. J. Yim
[show abstract]
[hide abstract]
ABSTRACT: The serious inconsistency problem between the values of experimental and theoretical Γn /Γp ratio of the nonmesonic weak decay of Λ hypernuclei has been resolved recently. We have shown that the reason behind the problem was the quenching of the nucleon yields which in turn was due to the contribution of the three-body process. We have measured that the branching ratio of the three-body process in nonmesonic weak decay, 0.29±0.13, is so large that the absolute values of Γn and Γp must be determined taking account of the contribution of the 3-body process. In this paper, the recent studies toward the finding of the 3-body process via the exclusive coincidence experiments are presented.
EPJ Web of Conferences. 01/2010;
-
M Kim,
S Ajimura,
K Aoki,
A Banu,
H Bhang,
T Fukuda,
O Hashimoto,
J I Hwang,
S Kameoka,
B H Kang, [......],
Y Sato,
M Sekimoto,
T Takahashi,
H Tamura,
K Tanida,
A Toyoda,
K Tshoo, K Tsukada,
T Watanabe,
H J Yim
[show abstract]
[hide abstract]
ABSTRACT: We have measured the branching ratio of the three-body process in the nonmesonic weak decay of Lambda12C to be 0.29+/-0.13. This result was obtained by reproducing the nucleon and the nucleon pair yields introducing a measured final state interaction. At the same time, we have determined the absolute decay widths, Gamma(n) and Gamma(p), along with Gamma2N, whose relative ratio has been a long-standing puzzle. Including the three-body process, we have successfully reproduced the nucleon energy distribution, the coincidence two-nucleon angular correlation, and the momentum sum distribution simultaneously.
Physical Review Letters 10/2009; 103(18):182502. · 7.37 Impact Factor
-
S. Okada,
S. Ajimura,
K. Aoki,
A. Banu,
H. C. Bhang,
T. Fukuda,
O. Hashimoto,
J. I. Hwang,
S. Kameoka,
B. H. Kang, [......],
Y. Sato,
M. Sekimoto,
S. Shin,
T. Takahashi,
H. Tamura,
K. Tanida,
A. Toyoda, K. Tsukada,
T. Watanabe,
H. J. Yim
[show abstract]
[hide abstract]
ABSTRACT: We have measured for the first time yields of both neutron‐proton and neutron‐neutron pairs emitted from the non‐mesonic weak decay of the Λ5He and Λ12C hypernuclei, produced via the (π+,K+) reaction. From the yields of both the back‐to‐back np‐pair events and nn‐pair events, we have directly determined the ratio of the neutron‐ and proton‐induced decay widths, Γn(Λn→nn)/Γp(Λp→np). Meanwhile, we have also determined the quenching of the observed numbers of single nucleons and coincident nucleon pairs compared with theoretical calculations. Our results suggest that contributions from the two‐nucleon‐induced three‐body process ΛNN→NNN are significant.
AIP Conference Proceedings. 04/2008; 1011(1):135-139.
-
K Tsukada,
T Takahashi,
T Watanabe,
Y Fujii,
K. Futatsukawa,
O Hashimoto,
K Hirose,
K Ito,
S. Kameoka,
H Kanda, [......],
T Kinoshita,
F. Miyahara,
T Nakabayashi,
H Shimizu,
T Tamae,
H Yamazaki,
A Sasaki,
O. Konno,
P. Bydzovsky,
M. Sotona
[show abstract]
[hide abstract]
ABSTRACT: The photoproduction process of neutral kaons on a liquid deuterium target is
investigated near the threshold region, Egamma = 0.8-1.1 GeV. K0 events are
reconstructed from positive and negative pions, and differential cross sections
are derived. Experimental momentum spectra are compared with those calculated
in the spectator model using a realistic deuteron wave function. Elementary
amplitudes as given by recent isobar models and a simple phenomenological model
are used to study the effect of the new data on the angular behavior of the
elementary cross section. The data favor a backward-peaked angular distribution
of the elementary n(gamma,K0)Lambda process, which provides additional
constraints on current models of kaon photoproduction. The present study
demonstrates that the n(gamma,K0)Lambda reaction can provide key information on
the mechanism of the photoproduction of strangeness.
12/2007;
-
Y. Ma,
S. Ajimura,
K. Aoki,
M. Dairaku,
Y. Y. Fu,
H. Fujioka,
T. Fukuda,
K. Futatsukawa,
K. Hosomi,
W. Imoto, [......],
T. Suzuki,
T. Takahashi,
T. N. Takahashi,
H. Tamura,
K. Tanida,
N. Terada,
A. Toyoda, K. Tsukada,
M. Ukai,
S. H. Zhou
[show abstract]
[hide abstract]
ABSTRACT: In this paper, a preliminary result from the latest hypernuclear γ -ray spectroscopy experiment (KEK-E566) is presented together
with a short discussion. The experiment was performed at the KEK-PS K6 beam line in 2005. In this experiment, the 12C(π+, K
+)12
ΛC reaction was employed to populate 12
ΛC/11
ΛB hypernuclei. A germanium detector array, Hyperball2, was constructed to detect γ -rays emitted from the hypernuclei produced.
Three hypernuclear γ -ray peaks were observed and assigned.
European Physical Journal A 08/2007; 33(3):243-246. · 2.19 Impact Factor
-
T. Maruta,
S. Ajimura,
K. Aoki,
A. Banu,
H. Bhang,
T. Fukuda,
O. Hashimoto,
I. Hwang,
S. Kameoka,
B. H. Kang, [......],
H. Park,
P. K. Saha,
Y. Sato,
M. Sekimoto,
T. Takahashi,
H. Tamura,
K. Tanida,
A. Toyoda, K. Tsukada,
T. Watanabe
[show abstract]
[hide abstract]
ABSTRACT: The proton decay asymmetry, αNM
p , of the polarized Λ -hypernuclei, 5
ΛHe , 12
ΛC and 11
ΛB , has been investigated to understand the reaction mechanism of the non-mesonic weak-decay process. These Λ -hypernuclei
were produced in the highest statistics ever via the (π+, K
+) reaction at 1.05GeV/c by using the SKS spectrometer at KEK 12GeV PS. The results show that the αNM
p are very small for these s -shell and p -shell hypernuclei.
European Physical Journal A 08/2007; 33(3):255-258. · 2.19 Impact Factor
-
H. Bhang,
S. Ajimura,
K. Aoki,
A. Banu,
T. Fukuda,
O. Hashimoto,
J. I. Hwang,
S. Kameoka,
B. H. Kang,
E. H. Kim, [......],
Y. Sato,
M. Sekimoto,
S. Shin,
T. Takahashi,
H. Tamura,
K. Tanida,
A. Toyota, K. Tsukada,
T. Watanabe,
H. J. Yim
[show abstract]
[hide abstract]
ABSTRACT: Recent exclusive coincidence measurements of non-mesonic weak decays (NMWD) reported for the ratio of the partial decay width
of neutron-induced-to-proton-induced NMWD, Γn/Γp , values of 0.45±0.11±0.03 and 0.51±0.13±0.04 for 5lam and 12
Λ
C , respectively. These observations agree well with the improved theoretical Γn/Γp ratios which are in the range of 0.3-0.7. It appears that the long-standing discrepancy between the experimental and theoretical
values of Γn/Γp has finally been solved. However, when compared to the results of intra-nuclear cascade (INC) calculations, the observed
numbers of both single nucleons and coincident nucleon pairs are strongly quenched. The quenching of the proton yield observed
previously has been interpreted as an increase of the Γn/Γp ratio. On the other hand, significant contributions from the two-nucleon-induced three-body process ΛNN → nNN are predicted. Indeed, the angular correlation of the emitted nucleon pairs in the NMWD of 12
Λ
C showed not only decay events in back-to-back kinematics, but also events with non-back-to-back kinematics. In this paper
we show that the difficulties to extract the correct Γn/Γp ratio from the proton spectra is related to the three-body weak-interaction process which strongly quenches the nucleon yields.
European Physical Journal A 01/2007; 33(3):259-263. · 2.19 Impact Factor
-
T. Watanabe,
P. Bydžovský,
K. Dobashi,
S. Endo,
Y. Fujii,
O. Hashimoto,
T. Ishikawa,
K. Itoh,
H. Kanda,
M. Katoh, [......],
T. Takahashi,
T. Tamae,
H. Tamura,
T. Terasawa,
H. Tsubota, K. Tsukada,
M. Ukai,
M. Wakamatsu,
H. Yamauchi,
H. Yamazaki
[show abstract]
[hide abstract]
ABSTRACT: The kaon photo-production process on 12C has been studied by measuring neutral kaons in the photon energy range of 0.8–1.1 GeV. Neutral kaons were identified by the invariant mass constructed from two charged pions emitted in the decay channel. The differential and integrated cross sections in the threshold photon energy region were obtained. The obtained momentum spectra were compared with a Spectator model calculation using elementary amplitudes of kaon photo-production given by recent isobar models. The present results provide the first information on the n(γ,K0)Λ reaction, which is expected to play an important role in constructing models of strangeness production by electromagnetic interactions. The experimental results show that the cross section of is of the same order as that of and suggest that a slightly backward K0 angular distribution is favored in the γn→K0Λ process.
Physics Letters B. 08/2006;
-
B H Kang,
H Bhang,
E H Kim,
J H Kim,
M J Kim,
H J Yim,
S Ajimura,
Y Miyake,
K Aoki,
T Nagae, [......],
T Takahashi,
H Tamura, K Tsukada,
T Watanabe,
J I Hwang,
T Maruta,
M Nakamura,
S Okada,
H Park,
K Tanida
[show abstract]
[hide abstract]
ABSTRACT: We performed a coincidence measurement of two nucleons emitted from the nonmesonic weak decay of lambda(5)He formed via the 6Li(pi+, K+) reaction. The energies of the two nucleons and the pair number distributions in the opening angle between them were measured. In both np and nn pairs, we observed a clean back-to-back correlation coming from the two-body weak reactions of lambda p --> np and lambda n --> nn, respectively. The ratio of the nucleon pair numbers was N(nn)/N(np) = 0.45 +/- 0.11(stat) +/- 0.03(syst) in the kinematic region of cos theta(NN) < -0.8. Since each decay mode was exclusively detected, the measured ratio should be close to the ratio of gamma(lambda p --> np)/gamma(lambda n --> nn). The ratio is consistent with recent theoretical calculations based on the heavy meson and/or direct-quark exchange picture.
Physical Review Letters 02/2006; 96(6):062301. · 7.37 Impact Factor
-
M J Kim,
S. Ajimura,
K Aoki,
A. Banu,
H. Bhang,
T Fukuda,
O Hashimoto,
J I Hwang,
S. Kameoka,
B H Kang, [......],
Y Sato,
M Sekimoto,
S Shin,
T Takahashi,
H Tamura,
K Tanida,
A Toyoda, K Tsukada,
T Watanabe,
H. J. Yim
[show abstract]
[hide abstract]
ABSTRACT: We have measured the angular correlation of the pair nucleons np and nn emitted from the nonmesonic weak decay (NMWD) of ^{12}_{Lambda}C produced via the (pi^+,K^+) reaction in coincidence measurement. The Lambda p -> np and Lambda n -> nn modes were clearly identified by measuring the back-to-back correlation of the emitted nucleon pairs which is the characteristic of two-body kinematics. From the measured nucleon pair numbers N_{nn} and N_{np}, the ratio Gamma_n/Gamma_p of the partial decay widths Gamma_n(Lambda n -> nn) and Gamma_p(Lambda p -> np) of ^{12}_{Lambda}C was extracted to be 0.51+-0.13(stat) +- 0.05(syst); this result is almost free from the ambiguity due to the nuclear final state interaction and 3-body decay process, which were inherent in the previous results. The obtained Gamma_n/Gamma_p ratio of ^{12}_{Lambda}C (p-shell) is close to that of ^5_{Lambda}He (s-shell). The results are consistent with those of recent theoretical calculations. Comment: 13 pages, 4figures, 1 table,re-submitted to Physics Letters B
01/2006;
