We carry out photoproduction experiments by using linearly polarized photon beams with energies of 1.5-3 GeV at SPring-8/LEPS. One of our physics motivations is to understand reaction mechanisms of ...hadron photoproduction. We study (1)
y
→
p
→ π
-
Δ
++
, (2)
y
→
p
→ π
+
n, (3)
y
→
p
→
K
+
Λ(
K
+
Σ
0
), and (4)
y
→
p
→ π
+
Δ
0
reactions which produce (1)
u
u
, (2)
d
d
, (3)
s
s
, and (4)
d
d
quark-antiquark pairs in the final state. Differential cross sections and photon beam asymmetries have been measured at forward meson angles of 0.6 < cos
θ
cm
<1. Precise comparison between the π
-
Δ
++
and π
+
Δ
0
reactions plays an important role in the study of nucleon resonances. It enables to distinguish between
N*
and Δ* by taking the cross section ratios of the two reactions. We have measured preliminary cross section ratios
dσ
(π
+
Δ
0
)/
dσ
(π
-
Δ
++
). The ratios are found to be close to 1/3, which is expected from the exchange of isospin=1 in the
t
channel, for 0.966< cos
θ
cm
<1 and all the photon energies. The ratios become larger than 1/3 and close to 1 for larger angles and higher energy regions. The larger ratios might be due to A resonances, giving the ratio 4/3, excited in the intermediate state
The nuclear spin–lattice relaxation time (T1) of lanthanum and aluminum nuclei in a single crystal of lanthanum aluminate doped with neodymium ions is studied to estimate the feasibility of the ...dynamically polarized lanthanum target applicable to beam experiments. The application of our interest is the study of fundamental discrete symmetries in the spin optics of epithermal neutrons. This study requires a highly flexible choice of the applied magnetic field for neutron spin control and favors longer T1 under lower magnetic field and at higher temperature. The T1 of 139La and 27Al was measured under magnetic fields of 0.5–2.5 T and at temperatures of 0.1–1.5 K and found widely distributed up to 100 h. The result suggests that the T1 can be as long as T1∼ 1 h at 0.1 K with a magnetic field of 0.1 T, which partially fulfills the requirement of the neutron beam experiment. Possible improvements to achieve a longer T1 are discussed.
Differential cross sections and photon-beam asymmetries for the →γp → π−Δ++(1232) reaction have been measured for 0.7 < cos θc.m.π < 1 and Eγ = 1.5 – 2.95 GeV at SPring-8/LEPS. The first-ever high ...statistics cross-section data are obtained in this kinematical region, and the asymmetry data for 1.5 < Eγ (GeV) < 2.8 are obtained for the first time. This reaction has a unique feature for studying the production mechanisms of a pure uu quark pair in the final state from the proton. Although there is no distinct peak structure in the cross sections, a non-negligible excess over the theoretical predictions is observed at Eγ = 1.5–1.8 GeV . The asymmetries are found to be negative in most of the present kinematical regions, suggesting the dominance of π exchange in the t channel. The negative asymmetries at forward meson production angles are different from the asymmetries previously measured for the photoproduction reactions producing a dd or an ss quark pair in the final state. Advanced theoretical models introducing nucleon resonances and additional unnatural-parity exchanges are needed to reproduce the present data.
A laser-Compton backscattering beam, which we call a 'Laser-Electron Photon' beam, was upgraded at the LEPS beamline of SPring-8. We accomplished the gains in backscattered photon beam intensities by ...factors of 1.5-1.8 with the injection of two adjacent laser beams or a higher power laser beam into the storage ring. The maximum energy of the photon beam was also extended from 2.4 GeV to 2.9 GeV with deep-ultraviolet lasers. The upgraded beams have been utilized for hadron photoproduction experiments at the LEPS beamline. Based on the developed methods, we plan the simultaneous injection of four high power laser beams at the LEPS2 beamline, which has been newly constructed at SPring-8. As a simulation result, we expect an order of magnitude higher intensities close to 107 s-1 and 106 s-1 for tagged photons up to 2.4 GeV and 2.9 GeV, respectively.
We carry out photoproduction experiments by using linearly polarized photon beams with energies of 1.5–3.0 GeV at SPring-8/LEPS. There is no distinct peak structure due to nucleon or Δ resonances in ...the preliminary cross sections for the γp→π-Δ++, π+Δ0, and π+n reactions for 0.7<cosθπ<1. The cross section ratios σ(π+Δ0)/σ(π-Δ++) are close to 1/3, which is expected from the isospin = 1 exchange in the t-channel, at small π angles and become larger than 1/3 at large π angles. The photon beam asymmetries are small negative values, small positive values, and large positive values for the π-Δ++, π+Δ0, and π+n reactions, respectively. The asymmetries are sensitive to reaction mechanisms and are found to be largely different among these reactions. The asymmetries are strong constraint in theoretical studies and expected to play an important role in searching for new nucleon resonances.
The photo-production of ϕ mesons from Li, C, Al, and Cu at forward angles has been measured at Eγ=1.5–2.4GeV. The number of events for incoherent ϕ photo-production is found to have a target mass ...number dependence of A0.72±0.07 in the kinematical region of |t|⩽0.6GeV2/c2. The total cross section of the ϕ–nucleon interaction, σϕN, has been estimated as 35−11+17mb using the A-dependence of the ϕ photo-production yield and a Glauber-type multiple scattering theory. This value is much larger than σϕN in free space, suggesting that the ϕ properties might change in the nuclear medium.
We carry out photoproduction experiments by using linearly polarized photon beams with energies of 1.5–3.0 GeV at SPring-8/LEPS. There is no distinct peak structure due to nucleon or
Δ
resonances in ...the preliminary cross sections for the
γ
p
→
π
-
Δ
+
+
,
π
+
Δ
0
, and
π
+
n
reactions for 0.7
<
cos
θ
π
<
1. The cross section ratios
σ
(
π
+
Δ
0
)/
σ
(
π
-
Δ
+
+
) are close to 1/3, which is expected from the isospin = 1 exchange in the
t
-channel, at small
π
angles and become larger than 1/3 at large
π
angles. The photon beam asymmetries are small negative values, small positive values, and large positive values for the
π
-
Δ
+
+
,
π
+
Δ
0
, and
π
+
n
reactions, respectively. The asymmetries are sensitive to reaction mechanisms and are found to be largely different among these reactions. The asymmetries are strong constraint in theoretical studies and expected to play an important role in searching for new nucleon resonances.
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