Showing papers by "Yorihito Sugaya published in 2022"

Differential cross sections and photon beam asymmetries of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>η</mml:mi></mml:math> photoproduction on the proton at <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>E</mml:mi><mml:mi>γ</mml:mi></mml

Abstract: We have carried out exclusive measurements for the photoproduction of an $\eta$ meson from a proton target with an egg-shaped calorimeter made of BGO crystals (BGOegg) and forward charged-particle detectors at the SPring-8 LEPS2 beamline. The differential cross sections and photon beam asymmetries of the $\gamma p \to \eta p$ reaction are measured in a center-of-mass energy ($W$) range of $1.82$-$2.32$ GeV and a polar angle range of $-1.0 < \cos{\theta^{\eta}_{\mathrm{c.m.}}} < 0.6$. The reaction is identified by selecting a proton and two $\gamma$'s produced by an $\eta$-meson decay. The kinematic fit method was employed to select the reaction candidate with the confidence level larger than $1$\%. A bump structure at $W$ = $2.0$-$2.3$ GeV in the differential cross section is confirmed at extremely backward $\eta$ polar angles, where the existing data are inconsistent with each other. This bump structure is likely associated with high-spin resonances that couple with $s\bar{s}$ quarks. The results of the photon beam asymmetries in a wide $\eta$ polar angle range are new for the photon beam energies exceeding $2.1$ GeV. These results are not reproduced by the existing partial wave analyses. They provide an additional constraint to nucleon resonance studies at high energies.

Conceptual Design Report of DaRveX: Decay at Rest $\nu_e$ + Lead Cross Section Measurement at J-PARC MLF

Abstract: DaRveX stands for “Decay at Rest ν e -Pb cross (X) section measure-ment,,. This report explains a conceptual design of DaRveX, an experiment that measures differential cross section of low energy ν e +Pb charged current interaction, for the first time using ν e from µ + decay at rest at J-PARC MLF. So far, there has not been good ν e target to detect low energy ν e . Lead is expected to be an excellent ν e target because the cross section is expected to be very large and the delayed coincidence technique can be used using final state neutron(s) to reduce backgrounds. However, the cross section have not been measured yet. If it is measured, it opens a new window to the future neutrino research field, such as low energy ν e oscillation measurements, flavor specific detection of the supernova explosion ν e and understanding of ν e -nucleus interactions. The DaRveX ν e detector is a remodeling of existing reactor neutrino detector PANDA (Plastic scintillator AntiNeutrino Detector Array). A thin lead sheet is sandwiched between two double-layer thin plastic scintillator strips. This thin lead-scintillators unit is sandwiched between PANDA scintillator modules and e − energy and direction will be measured. Backgrounds can be reduced by making use of very narrow pulsed beam of MLF, delayed coincidence with neutron absorption signal on Gd, and requirement of event topology of the charged current ν e +Pb reaction, together with thick neutron and γ -ray shields. With two years of data taking, the cross section is expected to be measured with 20% of precision. We performed on-site background measurements at J-PARC MLF in 2021 to understand the real backgrounds. This background measurements are also described in the appendix.

Σ 0 reactions at forward angles with photon energies from 1 . 5 to 2 . 4

Abstract: M. Sumihama, J.K. Ahn, H. Akimune, Y. Asano, C. Bennhold, W.C. Chang, T. Corthals, S. Daté, H. Ejiri, H. Fujimura, M. Fujiwara, 10 M. Guidal, K. Hicks, T. Hotta, K. Imai, T. Ishikawa, T. Iwata, H. Kawai, Z.Y. Kim, K. Kino, H. Kohri, N. Kumagai, S. Makino, T. Mart, T. Matsumura, N. Matsuoka, T. Mibe, M. Miyabe, Y. Miyachi, M. Morita, N. Muramatsu, T. Nakano, M. Niiyama, M. Nomachi, Y. Ohashi, T. Ooba, H. Ohkuma, D.S. Oshuev, C. Rangacharyulu, A. Sakaguchi, T. Sasaki, P.M. Shagin, Y. Shiino, H. Shimizu, Y. Sugaya, H. Toyokawa, A. Wakai, C.W. Wang, S.C. Wang, K. Yonehara, T. Yorita, M. Yosoi, and R.G.T. Zegers

Differential cross sections and photon beam asymmetries of $\eta$ photoproduction on the proton at $E_\gamma$ = 1.3-2.4 GeV

Abstract: We have carried out exclusive measurements for the photoproduction of an η meson from a proton target with an egg-shaped calorimeter made of BGO crystals (BGOegg) and forward charged-particle detectors at the SPring-8 LEPS2 beamline. The differential cross sections and photon beam asymmetries of the γp → ηp reaction are measured in a center-of-mass energy ( W ) range of 1 . 82– 2 . 32 GeV and a polar angle range of − 1 . 0 < cos θ η c . m . < 0 . 6. The reaction is identified by selecting a proton and two γ ’s produced by an η -meson decay. The kinematic fit method was employed to select the reaction candidate with the confidence level larger than 1%. A bump structure at W = 2 . 0–2 . 3 GeV in the differential cross section is confirmed at extremely backward η polar angles, where the existing data are inconsistent with each other. This bump structure is likely associated with high-spin resonances that couple with s ¯ s quarks. The results of the photon beam asymmetries in a wide η polar angle range are new for the photon beam energies exceeding 2 . 1 GeV. These results are not reproduced by the existing partial wave analyses. They provide an additional constraint to nucleon resonance studies at high energies.