π±andπ0Production by Polarized Photons in the Resonance Region

Abstract

We have measured the cross sections at 90° cm. for n* and 7r° photoproduction with polarized photons. The photon energies ranged from 0.8 to 2.2 GeV. We compare the resonant "bumps" in the cross section with theoretical models. The measured asymmetry agrees with a quark-model calculation though the predicted cross sections are low.

Measurement of the cross section asymmetry of the reactionγp→π°pin the resonance energy regionE<

“…7a, one can see, as a whole, a good agreement between the values of prior measurements and our present results. Near 900 MeV, our data disagree with data from MIT [14] and some early SLAC [13] measurements, but are in good agreement with later measurements from another SLAC group [15]. Our points are also consistent with the results of this group for the angle θ * π = 110…”

“…Some of the measured energy and angular distributions are shown in Figs. 7 − 9 together with the experimental data of other groups [13][14][15][16][17] and predictions of different phenomenological analyses [18,19].…”

“…• (b), respectively. Experimental data are from Yerevan, present experiment (filled circles), SLAC [13] (open triangles), MIT [14] (open circles), SLAC [15] (open squares), Kharkov [16] (filled triangles), and Yerevan, previous measurements [17] (filled squares). Solid (dash-dotted) curves give WI00 (FA00) results by GW [19] versus MAID2000 results by the Mainz group [18] (dashed curves).…”

Measurement of the beam asymmetryΣin the forward direction forγ⃗p→pπ0

“…Polarization observables for single-π 0 photoproduction have been determined mostly by using a linearly polarized beam [11,12,14,15,[17][18][19][20][21][22][23][24]. In the following, a summary is given of the experiments performed after 1970, which allowed the extraction of the beam asymmetry .…”

Final technical report on research in high energy physics. 1. Photoproduction of pions. 2. Colliding e$sup +$e$sup -$ beam physics

“…, at -t = 2.4 (GeV) 2 showed again a strongly negative asymmetry, a fact which was verified in a later experiment by our collaboration. 10 Thus, the essential conclusions from this experiment were that natural-parity exchange dominates the cross section both at small -t The cm. angle of 90° was chosen to maximize the contribution of resonance excitation compared to t-and u-channel exchange contributions, and the 45° -50° points were chosen to supply us with some initial information regarding the angular distribution of the resonances excited.…”