Y. C. Han

Searching for the H-Dibaryon in J-PARC with a Large Acceptance Hyperon Spectrometer

Understanding of the hadron-hadron interactions and searching for exotic quark states remain important topics in contemporary hadron physics. The interactions of hyperon-nucleon and hyperon-hyperon systems are important extensions of what we understand about the nucleon-nucleon interaction. The famed yet elusive H-dibaryon, an exotic quark state (uuddss), was predicted several decades ago [1] and also supported by recently Lattice QCD calculations [2]. The E42 experiment has been approved at J-PARC to search for the Hdibaryon with high statistics [3]. The E42 collaboration designed a large acceptance hyperon spectrometer with a time projection chamber for searching the H-dibaryon resonance in ΛΛ production from (K, K) reaction off nuclei via its following decays. The E42 experiment has high sensitivity both above and below threshold and will be the definitive experiment on the existence of the Hdibaryon, once and for all. A prototype TPC was built for testing and optimization of various configurations. Simulations on estimation of TPC performance in the electric field and the magnetic field were performed with the Elmer and Garfield++ programs, and are still in progress. A dedicated experiment, scheduled at the Research Center for Electron Photon Science of Tohoku University in June 2014, will be executed for testing of various detectors and design used in the E42 experiment. Recent progress and achievements of the E42 collaboration will be presented.

Study of Double Delta Photoproduction on the Deuteron in the Energy Region of Eγ = 0.65–1.1 GeV

We studied the reaction d(γ, π+π−p)n with the Neutral Kaon Spectrometer 2 (NKS2) in a photon energy region of Eγ = 0.65-1.1 GeV at Research Center for Electron Photon Science (ELPH), Tohoku University. In this reaction, existence of the process where two nucleons are excited to Delta particles in the intermediate state was found. It is suggested that the nuclear effects cannot be ignored. By exploring the double Delta photoproduction, we investigated the double pion photoproduction on the deuteron, and the N∗-N interaction which contributes to the intermediate state of this reaction. The cross section of double Delta photoproduction was measured by the TAGX[1] and the NKS[2] in the photon energy region of Eγ = 0.57-0.85 GeV and 0.8-1.1 GeV, respectively. The reported cross sections are not consisted at 0.8 GeV. The theoretical calculation[3] does not reproduce the data above 0.8 GeV. We aim to precise measure the double Delta photoproduction in the photon energy region of Eγ = 0.65-1.1 GeV. Charged particles were detected using the NKS2 which has the large acceptance. The mass of the charged particles was calculated from measurements of the β and their respective momentum, allowing for the identification of π, π− and proton events. The d(γ, π+π−p)n events were extracted with a kinematical cut on the missing momentum. Double Delta excitation in the intermediate state was shown using the invariant mass distributions for πp and π−n. In this presentation, I will report on the invariant mass distributions for πN and the cross section of the double Delta photoproduction.

Measurement of Charged Pion Photoproduction at ELPH

We investigated the charged pion photoproduction on the deuteron in the energy region Eγ = 0.65− 1.1 GeV at Research Center for Electron Photon Science (ELPH), Tohoku University. The photon absorption by a nucleus mainly takes place on a single nucleon at energies above the first resonance region. The rest nucleons are called as the spectator and this process is called as the quasi-free process. The pion is emitted in the subsequent de-excitation process of the nucleon resonance excited through the absorption of the photon. The deuteron is the loosely bound system of the proton and the neutron and the photoreaction on it is considered to be dominated by the quasi-free process. However, significant contribution of the two nucleon absorption process in the π+π− photoproduction on the deuteron was measured in the energy region from 0.6 to 1.1 GeV[1, 2]. The importance of the nucleon resonances and the intermediate and final state interaction was suggested by the theoretical studies[3, 4]. For the detailed study of the intermediate states, precise experimental data, not only the total cross section but also the differential cross sections are required. The ABC effect [5] is a nuclear fusion reaction which is known to be related to the excitation of the two nucleon resonances (ΔΔ) in the intermediate state and their interaction. It is distinguished by a structure in the mass distribution of isoscalar pion pair[6, 7, 8]. One of our aim is the search for the ABC like effect in the photon induced double pion production reaction on the deuteron in the analysis of the similar final state with ABC effect (γd → π+π−d) and the explicit ΔΔ excitation (γd → ΔΔ → π+π−pn). The reactions d(γ, π+π−d) and d(γ, π+π−p)n were measured using the Neutral Kaon Spectrometer 2 (NKS2) at ELPH. The NKS2 is the magnetic spectrometer with the geometrical acceptance roughly 1/4 of the whole solid angle, dedicated for the multi-particle tracking. By refining the calibration of the detectors and the tracking procedures, the increased mass reconstruction resolution enabled us the efficient identification of these reactions with three charged particles in the final state. Simulation studies have been carried out for the extraction of the contributions of the intermediate states. We report on the current status of the analysis for the derivation of the cross sections of these reactions with the extraction of the intermediate states.

Investigation of Strangeness Photoproduction near the Threshold at ELPH, Tohoku University

Masashi Kaneta1, Brian Beckford1, Petr Bydžovský2, Takeshi Fujibayashi1, Takao Fujii1, Yu Fujii1, Kenta Futatsukawa1, Toshiyuki Gogami1, Yuncheng Han3, Osamu Hashimoto1 ∗, Kentaro Hirose4, Kenji Hosomi1, Ryotarou Honda1, Aran Iguchi1, Takatsugu Ishikawa4, Hiroki Kanda1, Yusuke Kaneko1, Yuma Kasai1, Taito Kawasaki1, Chigusa Kimura1, Shogo Kiyokawa1, Takeshi Koike1, Kazushige Maeda1, Nayuta Maruyama1, Masao Matsubara1, Koji Miwa1, Yohei Miyagi1, Sho Nagao1, Satoshi N. Nakamura1, Takashi Nishizawa1, Akira Okuyama1, Miloslav Sotona2,∗, Tadaaki Tamae4, Hirokazu Tamura1, Kyo Tsukada1, Nobu Terada1, Tieshan Wang3, Fumiya Yamamoto1, Takeshi O. Yamamoto1, and Hirohito Yamazaki4 (the NKS2 collaboration)