Single-pion Photoproduction Data Research Articles

Analysis of pion photoproduction data

A partial-wave analysis of single-pion photoproduction data has been completed. This study extends from threshold to 2 GeV in the laboratory photon energy, focusing mainly on the influence of new measurements and model-dependence in the choice of parameterization employed above the two-pion threshold. Results are used to evaluate sum rules and estimate resonance photo-decay amplitudes. These are compared to values obtained in the MAID analysis.

Updated resonance photodecay amplitudes to 2 GeV.

We present the results of an energy-dependent and set of single-energy partial-wave analyses of single-pion photoproduction data. These analyses extend from threshold to 2 GeV in the laboratory photon energy, and update our previous analyses to 1.8 GeV. Photo-decay amplitudes are extracted for the baryon resonances within this energy range. We consider two photoproduction sum rules and the contributions of two additional resonance

Differential cross sections of proton compton scattering in the resonance region

Differential cross sections of proton Compton scattering have been measured in the energy range between 375 MeV and 1150 MeV in steps of 25 MeV at c.m. angles of 130°, 100° and 70°. The recoil proton was detected with a magnetic spectrometer. In coincidence with the proton, the scattered photon was detected with a lead-glass Čerenkov counter of the total absorption type. Theoretical calculations based on an isobar model with two components, that is, the resonance plus the background, were practiced. The photon couplings of the second resonance region were determined from the proton Compton data for the firs time. The results were that the helicity 1 2 photon couplings of P 11(1470) and S 11(1535), and the helicity 3 2 photon coupling of D 13(1520) were consistent with those determined from the single-pion photoproduction data; however, the helicity 1 2 photon coupling of D 13(1520) required a somewhat larger value than that from the single-pion photoproduction data.

Note on low-energy proton Compton scattering

The unpolarized differential cross section for spin-1/2 Compton scattering is shown to be completely specified up to terms of the sixth power of the photon frequency by the mass, charge, anomalous magnetic moment, and dynamic electromagnetic polarizabilities of the target and four other sturcture dependent constants. The two polarizabilities and the four new constants are expressed in terms of the threshold values and threshold derivatives of the invariant amplitudes of the process. Their parts which can be expected to satisfy fixed-$t=0$ unsubtracted dispersion relations are evaluated in terms of single-pion photoproduction data. The extraction of the proton polarizabilities from low-energy elastic $\ensuremath{\gamma}$-proton scattering is discussed in the light of the results obtained.

An analysis of single-pion photoproduction between threshold and 16 GeV lab energy

A multipole analysis at low energies is combined with an amplitude analysis at higher energies through the constraints imposed by fixed- t dispersion relations in an attempt to fit simultaneously to the single-pion photoproduction data between threshold and 16 GeV. The photonic couplings of all well-established resonances below 2.5 GeV have been studied and the high-energy structure of the amplitudes examined.

Test of the vector dominance model by forward and backward ϱ o and ω o production

We compare new data on π +n → ϱ o p and π +n → ω o p at 4 GeV/ c with single-pion photoproduction data. Good agreement is obtained with the predictions of the vector dominance model from unpolarized photoproduction data. However, in the forward direction, the proportion of natural parity exchange observed in vector meson production is much smaller than that predicted by the VDM from polarized photoproduction data.

A determination of the pion-nucleon coupling constant from pion photoproduction

Three different methods for the determination of the pion nucleon coupling constant ƒ 2 from single pion photoproduction data in the first resonance region are discussed. They all yield results for ƒ 2 compatible with each other and with the results from investigations of πN and NN scattering. The determination from π + data alone (independent of πN phase shifts) yield the value ƒ 2 = (79.2 ± 3.9) × 10 −3 , while the determination using the Bonn multipole analysis (dependent on πN phase shifts) yields ƒ 2 = (76.9 ± 4.5) × 10 −3 .

Phenomenology of backward photoproduction

We investigate backward photoproduction reactions both empirically and in the context of specific models. First, salient features of backward single-pion photoproduction data are examined and contrasted with corresponding properties of purely hadronic data. We show that although γ p and πN data are qualitatively similar below 5 GeV/ c, remarkable differences become apparent at higher energies. Second, four models are studied in detail to see whether they offer an explanation for the distinctive energy and momentum transfer dependence of photoproduction cross sections. In these models, we include contributions from Regge (moving) and fixed poles, as well as absorptive (moving) and fixed cuts. Satisfactory fits to data are obtained with the fixed-pole model, the strong absorption model and the fixed-cut model of Carlitz, Kislinger, Bardakçi and Halpern. However, none of these profoundly different models is adequately tested by available data. Suggestions for many useful new experiments emerge from our study; the most important are backward πN → N ϱ, backward γN → Δπ, γd → pn, and the inclusive processes γp → h + anything (h = π ±, K ±, p and p.

Comparison ofπ−p→ρ0nwith Single-Pion Photoproduction at 15GeVc

We present a comparison of new data on ${\ensuremath{\pi}}^{\ensuremath{-}}p\ensuremath{\rightarrow}{\ensuremath{\rho}}^{0}n$ at 15 $\frac{\mathrm{GeV}}{c}$ with polarized and unpolarized single-pion photoproduction data. Particular emphasis is placed upon the behavior of the differential cross sections and asymmetries in the forward direction ($\ensuremath{-}t<{{m}_{\ensuremath{\pi}}}^{2}$). Qualitative agreement with the vector-dominance model is found. Quantitative agreement is found for the unnatural-parity---exchange cross section and for the asymmetry at low momentum transfer. Elsewhere there are disagreements in detail which may not be explained by changes of normalization.