We measured a set of π±Σ∓, π0Σ0, and π−Σ0 invariant mass spectra below and above the K¯N mass threshold in K−-induced reactions on deuteron. The measured πΣ mass spectral shape is well reproduced via ...the two-step mechanism, i.e., a neutron knocked out at a forward angle from a deuteron by an incident K−, with the K¯ recoiled backward reacting with the residual nucleon to produce π and Σ. We deduced the S-wave K¯N→πΣ and K¯N→K¯N scattering amplitudes in the isospin 0 channel in the framework of a K¯N and πΣ coupled channel. We find that a resonance pole corresponding to Λ(1405) is located at 1417.7−7.4+6.0 (fitting errors)−1.0+1.1 (systematic errors) + −26.1−7.9+6.0 (fitting errors)−2.0+1.7 (systematic errors) i MeV/c2, closer to the K¯N mass threshold than the value determined by the Particle Data Group.
We present a new measurement of the Λ4H hypernuclear lifetime using in-flight K− + 4He → Λ4H + π0 reaction at the J-PARC hadron facility. We demonstrate, for the first time, the effective selection ...of the hypernuclear bound state using only the γ-ray energy decayed from π0. This opens the possibility for a systematic study of isospin partner hypernuclei through comparison with data from (K−, π−) reaction. As the first application of this method, our result for the Λ4H lifetime, τ(HΛ4)=206±8(stat.)±12(syst.)ps, is one of the most precise measurements to date. We are also preparing to measure the lifetime of the hypertriton (Λ3H) using the same setup in the near future.
We have measured the 3d→2p transition x rays of kaonic ^{3}He and ^{4}He atoms using superconducting transition-edge-sensor microcalorimeters with an energy resolution better than 6 eV (FWHM). We ...determined the energies to be 6224.5±0.4(stat)±0.2(syst) eV and 6463.7±0.3(stat)±0.1(syst) eV, and widths to be 2.5±1.0(stat)±0.4(syst) eV and 1.0±0.6(stat)±0.3(stat) eV, for kaonic ^{3}He and ^{4}He, respectively. These values are nearly 10 times more precise than in previous measurements. Our results exclude the large strong-interaction shifts and widths that are suggested by a coupled-channel approach and agree with calculations based on optical-potential models.
We have proposed an experiment for studying charmed baryons via the p( pi super(-),D super(*-))p( pi -,D*-) reaction at the J-PARC high-momentum beam line. Charmed baryons will be measured by a ...missing mass method. Scattered D super(*-)D*- will be reconstructed by detecting its decay chain of D*- arrow right Dmacr0 pi - arrow right K+ pi - pi -. We designed a Ring Imaging Cherenkov (RICH) counter with two radiators, aerogel and C sub(4)F sub(10)C4F10 of refractive indices 1.04 and 1.00137, respectively, in order to identify pions and kaons in a wide momentum range from 2 to 16 GeV/c . Spherical mirrors will be used to focus Cherenkov photons to the photon sensor alloys. The performance of the designed RICH counter is evaluated by a Monte-Carlo simulation based on GEANT4. Detection efficiency for scattered particles averaged over pi and K is found to be 99%. Wrong particle identification ratios of pions and protons to kaons are 0.1% and 0.14%, respectively. The background level in the inclusive p( pi super(-),D super(*-))p( pi -,D*-) spectrum increases only 5% due to the wrong identifications.
We observed a distinct peak in the Λp invariant mass spectrum of He3(K−,Λp)n, well below mK+2mp, i.e., the mass threshold of the K− to be bound to two protons. By selecting a relatively large ...momentum-transfer region q=350∼650 MeV/c, one can kinematically separate the peak from the quasi-free process, K‾N→K‾N followed by the non-resonant absorption by the two spectator-nucleons K‾NN→ΛN. We found that the simplest fit to the observed peak gives us a Breit–Wigner pole position at BKpp=47±3(stat.)−6+3(sys.) MeV having a width ΓKpp=115±7(stat.)−20+10(sys.) MeV, and the S-wave Gaussian reaction form-factor parameter QKpp=381±14(stat.)−0+57(sys.) MeV/c, as a new form of the nuclear bound system with strangeness – “K−pp”.
The kaonic deuterium measurement at J-PARC and DAΦNE will provide a piece of information still missing to the antikaon-nucleon interaction close to threshold, providing valuable information to answer ...one of the most fundamental problems in hadron physics today - to the yet unsolved puzzle of how the hadron mass is generated. For this a new X-ray detector system has been developed to measure the shift and width of the 2p → 1s transition of kaonic deuterium with a precision of 60 eV and 140 eV, respectively.
K
¯
-nuclear bound systems, kaonic nuclei, have been widely discussed as products of the strongly attractive
K
¯
N
interaction in
I
=
0
channels. Recently, we demonstrated that kaonic nuclei can be ...produced via in-flight
(
K
-
,
N
)
reactions using the low-momentum DC kaon beam at the J-PARC E15 experiment. We observed the simplest kaonic nuclei,
K
-
p
p
, having a much deeper binding energy than normal nuclei. For further studies, we have proposed a series of experimental programs for the systematic investigation of light kaonic nuclei, from
K
¯
N
(
Λ
(
1405
)
) to
K
¯
N
N
N
N
. In the new experiment approved as J-PARC E80, we will measure the
K
¯
N
N
N
(
A
=
3
) system as a first step toward a comprehensive study.
After the radioactive material leak accident at the J-PARC hadron experimental facility on May 23, 2013, we designed a new production target, which is capable of a primary proton beam with the energy ...of 30 GeV and power of 50 kW. It is made of gold and cooled by water through a copper block. For the countermeasures of the recurrence of the accident, the target is enclosed by an airtight chamber and helium gas is circulated to monitor the target soundness. In this paper, technical details of the new target design are presented.
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