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論文

First measurement of differential cross sections and photon beam asymmetries for photoproduction of the $$f_0$$ (980) meson decaying into $$pi^0 pi^0$$ at $$E_gamma <$$ 2.4 GeV

村松 憲仁*; 土川 雄介; LEPS2 BGOegg Collaboration*; 他61名*

Physical Review C, 107(4), p.L042201_1 - L042201_5, 2023/04

https://doi.org/10.1103/PhysRevC.107.L042201
 被引用回数：0 パーセンタイル：0.02(Physics, Nuclear)

For the first time, differential cross sections and photon beam asymmetries were measured for the reaction $$gamma p to f_0 (980) p to pi^0 pi^0 p$$ by using a linearly polarized photon beam up to 2.4 GeV and a liquid hydrogen target. The $$f_0$$ (980) photoproduction signal was clearly observed owing to the absence of contributions from vector-meson photoproduction. The results indicate the $$t$$-channel exchange of vector mesons as a mechanism of the $$f_0$$ (980) photoproduction at $$E_gamma$$ approximate to 2.1 GeV, putting constraints on the nature of $$f_0$$ (980).

論文

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

橋本 敏和*; 土川 雄介; LEPS BGOegg Collaboration*; 他58名*

Physical Review C, 106(3), p.035201_1 - 035201_15, 2022/09

https://doi.org/10.1103/PhysRevC.106.035201
 被引用回数：3 パーセンタイル：66.85(Physics, Nuclear)

We report exclusive measurements for the $$eta$$ photoproduction on a proton target. 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 $$-1.0 < cos theta_{c.m.}^eta < 0.6$$ by using a large acceptance calorimeter (BGOegg) and forward-angle charged-particle detectors at the SPring-8 LEPS2 beamline. The reaction is identified with a kinematic fitting method to select a recoil proton and two photons produced in an $$eta$$ meson decay. 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 $$sbar{s}$$ quarks. The photon beam asymmetries in a wide $$eta$$ polar angle range for the photon beam energies above 2.1 GeV are reported for the first time, providing an additional constraint to nucleon resonance studies at high energies.

論文

Differential cross sections, photon beam asymmetries, and spin density matrix elements of $$omega$$ photoproduction off the proton at $$E_gamma$$ = 1.3-2.4 GeV

村松 憲仁*; 土川 雄介; LEPS2/BGOegg Collaboration*; 他59名*

Physical Review C, 102(2), p.025201_1 - 025201_10, 2020/08

https://doi.org/10.1103/PhysRevC.102.025201
 被引用回数：8 パーセンタイル：69.78(Physics, Nuclear)

For the reaction $$gamma p to omega p$$, differential cross sections, photon beam asymmetries, and spin density matrix elements have been measured in the BGOegg experiment at the SPring-8 LEPS2 beamline by using a large acceptance electromagnetic calorimeter. A 1.3-2.4 GeV photon beam with high linear polarization has enabled a precision measurement of photon beam asymmetries $$Sigma$$ and polarized spin density matrix elements $$rho^1_{1-1}$$ over a wide angular range, especially above the total energy of about 2 GeV for the first time. The measured $$rho^1_{1-1}$$ indicates the dominance of $$s$$-channel resonances even at higher energies. The $$Sigma$$ values at backward angles are not reproduced by the existing partial-wave analysis in the highest-energy region, providing new constraints to the contribution of nucleon resonances with high spins.

論文

Search for $$eta$$' bound nuclei in the $$^{12}$$C($$gamma,p$$) reaction with simultaneous detection of decay products

冨田 夏希*; 土川 雄介; LEPS2/BGOegg Collaboration*; 他61名*

Physical Review Letters, 124(20), p.202501_1 - 202501_7, 2020/05

https://doi.org/10.1103/PhysRevLett.124.202501
 被引用回数：9 パーセンタイル：62.22(Physics, Multidisciplinary)

We measured missing mass spectrum of the $$^{12}$$C($$gamma,p$$) reaction for the first time in coincidence with potential decay products from $$eta^prime$$ bound nuclei. We tagged an $$(eta + p)$$ pair associated with the $$eta^prime N to eta N$$ process in a nucleus. After applying kinematical selections to reduce backgrounds, no signal events were observed in the bound-state region. An upper limit of the signal cross section was obtained to be 2.2~nb/sr at the 90% confidence level. It is compared with theoretical cross sections, whose normalization ambiguity is suppressed by measuring a quasifree $$eta^prime$$ production rate. Our results indicate a small branching fraction of the $$eta^prime N to eta N$$ process and/or a shallow $$eta^prime$$-nucleus potential.

論文

Backward-angle photoproduction of $$omega$$ and $$eta'$$ mesons from protons in the photon energy range from 1.5 to 3.0 GeV

森野 雄平*; Hwang, S.; 今井 憲一; 谷田 聖; LEPS Collaboration*; 他46名*

Progress of Theoretical and Experimental Physics (Internet), 2015(1), p.013D01_1 - 013D01_11, 2015/01

AA2015-0719.pdf:1.08MB

https://doi.org/10.1093/ptep/ptu167
 被引用回数：9 パーセンタイル：55.91(Physics, Multidisciplinary)

We report the measurement of differential cross sections for $$omega$$ and $$eta '$$ photoproduction from protons at backward angles ($$-1.0 < cos Theta_{C.M}^{X} < -0.8$$) using linearly polarized photons at $$E_{gamma }=1.5$$-$$3.0$$ GeV. The differential cross sections for $$omega$$ mesons are larger than the predicted $$u$$-channel contribution based on amplitude analysis in the energy range $$2.0leq sqrt {s}leq 2.4$$ GeV. The differential cross sections for $$omega$$ and $$eta '$$ mesons become closer to the predicted $$u$$-channel contribution at $$sqrt {s} > 2.4$$ GeV. A bump structure in the $$sqrt {s}$$ dependence of the differential cross sections for $$eta'$$ mesons was observed at $$sqrt {s}sim 2.35$$ GeV.

論文

Search for the $$K^-pp$$ bound state via $$gamma d rightarrow K^+pi^- X$$ reaction at $$E_{gamma}$$ = 1.5 - 2.4 GeV

時安 敦史*; 今井 憲一; Hwang, S. H.*; LEPS Collaboration*

Physics Letters B, 728, p.616 - 621, 2014/01

https://doi.org/10.1016/j.physletb.2013.12.039
 被引用回数：61 パーセンタイル：95.9(Astronomy & Astrophysics)

A search for the $$K^- pp$$ bound state (the lightest kaonic nucleus) has been performed using the $$gamma d rightarrow K^+pi^-X$$ reaction at $$E_gamma$$ = 1.5 $$-$$ 2.4 GeV at LEPS/SPring-8. The differential cross section of the $$K^+pi^-$$ photo-production off deuterium ($$d^2 sigma / d rm{cos}theta^{lab}_{K^+}/drm{cos}theta^{lab}_{pi^-}$$) has been measured for the first time in this $$K^+ pi^-$$ energy region. A peak structure was searched for in the inclusive missing mass spectrum. A statistically significant peak structure was not observed in the region from 2.22 to 2.36 GeV/$$c^2$$. The upper limits of the differential cross section of the $$K^-pp$$ bound state production were determined to be (0.17$$-$$0.55), (0.55$$-$$1.7) and (1.1$$-$$2.9) $$mu b$$ at 95% confidence level with the assumed widths of 20 MeV, 60 MeV and 100 MeV.

論文

Spin-density matrix elements for $$gamma p rightarrow K^{*0} Sigma^+$$ at $$E_{gamma} = 1.85 - 3.0$$ GeV with evidence for $$kappa (800)$$ meson exchange

今井 憲一; Hwang, S. H.*; Hicks, K.*; LEPS Collaboration*

Physical Review Letters, 108(9), p.092001_1 - 092001_5, 2012/03

https://doi.org/10.1103/PhysRevLett.108.092001
 被引用回数：21 パーセンタイル：71.66(Physics, Multidisciplinary)

$$E_{gamma}$$=1.85-3.0GeVの直線偏光した$$gamma$$線を用いて$$gamma p rightarrow K^{*0} Sigma^+ $$反応を測定した。$$K^{*0}$$の崩壊粒子である$$K^+ pi^-$$の角度分布から$$K^{*0}$$のスピン密度行列を求めた。得られたパリティ非対称はこの反応においてはnatural parityの交換が主であることを示している。この結果はスカラーメソンの$$kappa$$(800)の$$t$$チャネル交換が必要なことをはっきりと示している。

論文

Measurement of spin-density matrix elements for $$phi$$-meson photoproduction from protons and deuterons near threshold

Chang, W. C.*; 今井 憲一; LEPS Collaboration*

Physical Review C, 82(1), p.015205_1 - 015205_11, 2010/07

https://doi.org/10.1103/PhysRevC.82.015205
 被引用回数：25 パーセンタイル：79.43(Physics, Nuclear)

SPring-8-LEPSでの直線偏光した1.6-2.4GeVの$$gamma$$線ビームを用いて、陽子及び重陽子を標的として$$phi$$中間子生成を測定した。(1)しきい値近くにおいてもポメロン交換過程が支配的である。(2)擬スカラー粒子交換過程も小さいが存在し、helicityを保存しないスピン密度行列要素が小さいが存在する、ことを明らかにした。

論文

Near-threshold $$Lambda (1520)$$ production by the $$vec{gamma}$$ $$p$$ $$rightarrow$$ $$K$$$$^{+}$$ $$Lambda$$ (1520) reaction at forward $$K^+$$ angles

郡 英輝*; 今井 憲一; LEPS Collaboration*

Physical Review Letters, 104(17), p.172001_1 - 172001_5, 2010/04

https://doi.org/10.1103/PhysRevLett.104.172001
 被引用回数：41 パーセンタイル：83.33(Physics, Multidisciplinary)

$$vec{gamma}$$ $$p$$ $$rightarrow$$ $$K$$$$^{+}$$ $$Lambda$$(1520)反応の微分断面積と直線偏光による非対称を、反応のしきい値から2.4GeVまでのエネルギー範囲で測定した。重心系エネルギーで2.11GeVのところに新しいバンプ構造を見つけた。このバンプ構造はスピン5/2以上の核子共鳴によるものか、又は新しい反応過程、たとえば同じようなバンプ構造が見つかっている$$phi$$生成との干渉効果によるものと思われる。

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