Experiments with photons at MAMI

Abstract

Abstract. A very successful experimental program with real photons has been achieved in 20 years of operation at the Mainz Microtron (MAMI) facility. The different detector setups, like DAPHNE, TAPS and the Crystal Ball are centered around the tagged photon facility the so-called Glasgow Tagger. From the rich spectrum of results only a few highlights will be discussed here, the proton polarizabilities, the pion polarizabilities, pion photoproduction close to the pion threshold and in the ∆(1232)-resonance region.

Neutral pion photoproduction on the nucleon in a chiral quark model

“…The model parameters are determined by fitting the 450 data points of differential cross section from MAMI [4,5] and CB-ELSA [9] in the beam energy region 240 MeV≤ E γ ≤ 862 MeV, and the 53 data points of total cross section from MAMI [72] and CB-ELSA [9] in the beam energy region 240 ≤ E γ ≤ 1138 MeV (see Tab. [4] (solid circles), [5] (solid squares), [75] (solid triangles), and [9] (open triangles). The first and second numbers in each figure correspond to the photon energy E γ (MeV) and the πN center-of-mass (c.m.)…”

“…However, our quark model explana- S11 (1535) P13 (1720) D13 (1520) c.m. [5] (left triangles), [77] (open squares), [78] (solid stars), [79] (open triangles), [80] (open circles), [81] (solid squares), [82] (solid circles), [9] (down triangles), [11] (up triangles), [12] (diamonds). The partial cross sections for ∆(1232)P 33 , N(1535)S 11 , N(1520)D 13 and N(1720)P 13 tion of the third bump structure differs from that of the isobar model [7][8][9].…”

“…Below the photon energy E γ ≃ 700 MeV, only a few old data with a very small angle coverage were obtained. Recently, some precise data with larger angle coverage in the higher The data are taken from [5] (solid left triangles), [83] (open squares), [84] (open up triangles), [85] (solid circles), [11] (solid squares), [13] (diamonds), [86] (solid down triangles), [14] (stars). The first and second number in each figure correspond to the photon energy E γ (MeV) and the πN center-of-mass energy W (MeV), respectively.…”

“…In the past few years, great progress has been achieved in experiments studying of the γp → π 0 p reaction at JLab, CB-ELSA, MAMI, and GRAAL. These experimental groups have carried out precise measurements of the differential cross sections and single-polarization observables with a large solid angle coverage and a wide photon energy range [4][5][6][7][8][9][10][11][12][13][14][15]. Recently they also have finished some measurements of the doublepolarization observables [10,[16][17][18].…”

Experimental Facility at A2 Collaboration (MAINZ) for Photoproduction reaction

“…Polarized photon beams, linear and circular, are available as well as polarized targets. Groups from several institutions and countries have provided different detector components like the photon spectrometer TAPS , PID, photon tagger and more recent the photon spectrometer Crystal Ball (e.g., Beck, 2006). A very successful experimental program with real photons has been achieved in 20 years of operation at the Mainz Microtron (MAMI) facility.…”