Charged Pion Photoproduction Research Articles

Pion photoproduction and T> versus < analog states in N> Z nuclei

The T > and T < components of giant resonance levels in N> Z nuclei cannot be unambiguously identified in photonuclear reactions. In charged pion photoproduction, their analogs may be so identified (at least for the spinflip levels), as illustrated here with a 13C target.

A study of photoproduction of charged pions from 16O

Photoproduction of π + from 16O leading to the four bound states in 16N has been studied using different dynamical amplitudes and considering particle-hole correlations in the nuclear wave functions. It is shown that the total cross section is strongly affected by the choice of dynamical amplitudes whereas the effect of 3p - 3h correlations in 16N is small.

Asymmetries in Charged-Pion Photoproduction on Nucleons by 16-GeV Polarized Photons

Asymmetries in charged-pion photoproduction from hydrogen and deuterium have been measured with 16-GeV linearly polarized photons. Considerable energy dependence is seen in the natural-parity contribution to the $\frac{{\ensuremath{\pi}}^{\ensuremath{-}}}{{\ensuremath{\pi}}^{+}}$ ratio from deuterium, and in the unnatural-parity part of the cross section for $\ensuremath{\gamma}n\ensuremath{\rightarrow}{\ensuremath{\pi}}^{\ensuremath{-}}p$. The energy dependence of this latter cross section is consistent with the expected from a conventional pion Regge trajectory.

Charged pion photoproduction from 12C with excitation of analog states

Differential cross sections of π +( π −) photoproduction near threshold on a 12C target with excitation of the 12B( 12N) analog levels are calculated. Charged pion photoproduction excites predominantly the spin flip states, so that such an experiment may determine the degree of spin flip strength of the ΔT=1 levels.

Effect of Woods-Saxon Wave Functions on Cross Sections for Charged-Pion Photoproduction fromO16

The cross sections for charged-pion photoproduction from $^{16}\mathrm{O}$(${0}^{+}$, g.s.) leading to the four low-lying bound states ${J}^{P}={2}^{\ensuremath{-}}, {0}^{\ensuremath{-}}, {3}^{\ensuremath{-}}, {1}^{\ensuremath{-}}$; $T=1$ in $^{16}\mathrm{N}$ are calculated in the Woods-Saxon basis. Two-particle-two-hole correlations in the ground-state wave function of $^{16}\mathrm{O}$ are taken into account. Calculations in the Woods-Saxon basis yield more realistic results for the cross sections near the first pion-nucleon resonance region, where high momentum transfers occur, than those obtained in the conventional harmonic-oscillator basis.

Construction of π± photoproduction amplitudes at high energy from dispersion relations and local duality

We investigate the charged-pion photoproduction amplitudes at all energies. We first show that low-energy s-channel helicity amplitudes exhibit, in most cases, a Bessel-function structure of zeroes. At high energy we therefore parametrize the imaginary parts of helicity amplitudes according to the Harari model, and compute the real parts using fixed- t dispersion relations as proposed recently. Such an evaluation of scattering amplitudes presents some very nice properties. In particular, it allows one to understand from duality arguments how the Born contribution may survive with full strength in the forward direction but not at large t-values. Furthermore FESR are identically satisfied by the model.

Polarization predictions for K + photoproduction

Using the existing data for charged pion photoproduction, some general features of the observables in K + photoproduction are obtained. Using the constraints imposed by duality allows further predictions to be made. Two versions of the Reggeized absorption model are presented and comparison is made with earlier models.

Charged and neutral double pion photoproduction cross-sections in the γ-ray energy range (600÷900) MeV

in hydrogen have been investigated at the Frascati electronsynehrotron for incident v-ray energies from 600 to 900 MeV, at fixed proton laboratory emission angle 0p~ = 32 ~ and for five proton laboratory momenta p = 410, 440, 475, 510, 550MeV/c. Reaction 2) has been investigated by detecting and analysing the protons by means of a weakfocusing magnetic spectrometer and a plastic scintillation counter system and a Cerenkov counter. Reaction 1) has been investigated by detecting in coincidence with the proton at least one charged particle by means of a plastic scintillation counter system placed around the target. The results have been corrected for the following effects: I) empty-target contributions (~ 20~o), II) accidental coincidences (~ 10%), I I I ) losses due to mnltiple scattering in the proton counters (~ 30%). The contribution from single-= ~ photoproduction (V_[_p__ > p__~:o) to the reaction 2) and the contribution to the proton-charged-particle coincidences due to the conversion of v-rays from the r~ ~ decays (~ 15%) have been evaluated with measurements below the double pion photoproduction threshold. Five yields Y ( E ) have been measured, corresponding to the five above-mentioned momenta, for reactions 1) and 2); as is known Y ( E ) is the number of events revealed by the apparatus per equivalent quantum as a function of the maximum energy of the bremsstrablung spectrum. All the corrections on each yield are practically constant in the measured energy range. The single-~ ~ photoproduction contributions have been subtracted from the yields of reaction 2). In conclusion the measured yields are

Predictions for ϱ production from pion photoproduction and vector meson dominance

A covariant formulation of the vector meson dominance hypothesis in terms of invariant amplitudes is presented. It is shown that explicit continuation in the external vector mass of the kinematical coefficients relating the invariant and helicity amplitudes allows the prediction of π −p→ ϱ 0n from charged pion photoproduction. Such predictions from a detailed fit to pion photoproduction, with the assumption that the extrapolation of the invariant amplitudes is free from dynamical dependence on the ϱ mass, are shown to be in excellent agreement with the ϱ 0 production data.

Parametrization of Charged-Pion Photoproduction in Terms of Complex Regge Poles

A fit of forward charged-pion photoproduction data is attempted by parametrizing Regge pole-cut combinations in the region $t&lt;0$ in terms of complex conjugate pairs of Regge poles. In particular, the pion-Pomeranchukon cut is taken into account by this parametrization; in addition to the pion, exchange of the ${A}_{2}$ meson is considered. Predictions are made for the differential cross section and the asymmetry parameters for pion production by linearly polarized photons and polarized target nucleons. The results are found to be in good agreement with pion photoproduction data for laboratory photon energies ranging from 3.4 to 18 GeV and $t$ values up to -0.2 ${(\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c})}^{2}$.

A Regge Pole Model for Charged Pion Photoproduction

A fit to high energy charged pion photoproduction in the relatively forward direction is performed on the basis of a Regge pole model, where the existence of the pion conspirator is assumed to explain the sharp forward peak. New experimental data on the asymmetry in the cross sections between two states of the polarization of the initial proton normal to the plane of scattering are taken account of, in addition to the other available data up to the present. Good fits are obtained with the inclusion of the strong fixed pole effect for the p residue function at the wrong signature nonsense point a P (t) = 0. It also becomes clear that the p and A 2 trajectories play very important role in the region 0.3< v' -t<0.7. Furthermore the difficulty of pion conspiracy in connection with the reaction n+p~pOJ++ is discussed.

Photoproduction of charged pions in the veneziano model

Photoproduction of charged pions in the veneziano model

Charged-pion photoproduction with NWSZ

where R(t) is e i ther a cons tan t or a l inear funct ion, is appl ied to the charged-pion photoproduct ion processes ,/p -> u+n and yn -~ ~-p . We consider the z~, A s and p Regge exchanges and the appropr ia te absorpt ion cuts, s t rongly enhanced by coherent inelast ic factors ~'s. Our ampl i tudes are wr i t t en in the s-channel hel ic i ty formalism of COnENTANNOUDJI et al. (~). The A factors appear expl ic i t ly in the following formula for the full ampl i tude :

Exotic currents in charged pion photoproduction

The existing data on charged pion photoproduction in the first resonance region is analysed using a dispersion theory model. The data can only be understood if isotensor and c-violating terms are introduced into the resonance coupling, when an excellent fit is achieved.

The generalized Veneziano model for charged pion photoproduction

Abstract Charged pion photoproduction is investigated in the framework of Veneziano B 5 amplitudes using Sugawara's “spurion” technique in order to introduce fixed J -plane poles. The Regge exchanges are taken to be evasive. The agreement with experiment for the differential cross section, the π − π + ratio and the polarisation asymmetries for photon energies between 3.4 and 18 GeV is quite reasonable.

Photoproduction of charged pions from nuclei

The yields of the reactions 41 K(γ,π +) 41 Ar, 65 Cu(γ, π +) 65 Ni , 88Sr( γ, π +) 88Rb and 138Ba( γ, π +) 138Cs have been measured by activation analysis. Data on the reactions 11 B(γ,π −) 11 C, 27 Al(γ, π +) 27 Mg and 51V( γ, π +) 51Ti obtained earlier have been reanalysed. The experimental cross sections have been compared to predictions from simple model calculations.

The high-energy data on charged-pion photoproduction

The data are examined on high-energy charged-pion photoproduction, for 0<|t|<0.5 (GeV)2 and for 7<s<35 (GeV)2. The observed large amount of isoscalar-isovector photon interference will violate a Pomeranchuk-type theorem unless it disappears with increasing energy. Resonance-saturated FESR’s predict, in agreement with experiment, that the isovector amplitudes become dominant as |t| decreases to zero.

Analysis of high-energy charged-pion photoproduction from deuterium (I)

The corrections to charged-pion photoproduction from deuterium due to two-step reactions are calculated from the Glauber model. The traditional assumption that the deuterium form factor varies rapidly in comparison with all reaction amplitudes is dropped in circumstances where, for this problem, it is manifestly untrue. The spin structure of the primary amplitudes is properly handled. Critical attention is paid to the role of inelastic intermediate states, the most important of which is the ϱ ONN channel, which is comparable in importance to the elastic πNN state. Assumptions made concerning the primary photoproduction amplitudes are extremely mild, and the results obtained are quite general, to be used in conjunction with any model for pion photoproduction for the purpose of extracting information about the amplitudes for a neutron target from the deuterium data.

A fit to high-energy pion photoproduction

A simultaneous fit to all the available data on high-energy pion photoproduction is performed. The model assumes dominance of the electric Born term in charged-pion photoproduction and dominance of ω-exchange in the neutral case. Good fits are obtained with the inclusion of phenomenological cuts as well as evasive ρ, ω and A 2 Regge poles.

Theoretische Untersuchungen zur Asymmetrie der Pionphotoproduktion mit einem polarisierten Target

AbstractThe theoretical importance of experiments with polarised targets for pion photoproduction at high energies is discussed.In an introductory chapter the basic formulas and simple Regge pole models are introduced in connection with elastic pion‐proton scattering. The relevance of Regge‐cut models is considered in connection with pion‐charge‐exchange scattering. In the main part we write down formulas for the polarisation parameters in terms of the helicity amplitudes for pion photoproduction. Then we concentrate on the target asymmetry A for photoproduction of neutral and charged pions. Several models with Regge poles and Regge cuts generated by absorption are presented and discussed concerning the results forA. In the last part we report a fit to π± photoproduction data and give predictions of A for γp → π+n and γn → π−p.