Single Pion Photoproduction Research Articles

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.

Even-wave harmonic-oscillator theory of baryonic states. V. Polarized photoproduction of single pions

A variant of the harmonic-oscillator (h.o.) model, termed the even-wave h.o. model (with quarks having h.o. interaction in even waves only), which was developed by Mitra and co-workers in a series of recent papers, is applied to the phenomenon of polarized photoproduction. The model, which predicts a ground state of (70,${0}^{+}$) and assumes an ${8}_{d}$ mixing angle ($cot\ensuremath{\theta}=\sqrt{2}$) between 56 and 70 states, was recently found to give a good account of (i) the mass spectra of resonances, (ii) low-energy parameters such as $\frac{{G}_{A}}{{G}_{V}}$, $\ensuremath{\Delta}\ensuremath{\rightarrow}N\ensuremath{\pi}$ width, and $\mathrm{NN}\ensuremath{\pi}$ coupling constant, and (iii) resonance photocouplings, with no free parameters other than a universal spring constant ($\ensuremath{\Omega}\ensuremath{\approx}1$ ${\mathrm{GeV}}^{2}$). The present investigation reveals that this model agrees better with the data on polarized-target asymmetry as well as $d{\ensuremath{\sigma}}_{\ensuremath{\parallel}}$ and $d{\ensuremath{\sigma}}_{\ensuremath{\perp}}$ than does the conventional h.o. model.

On the reaction118Sn(?,p)117in at intermediate energies

A refined analytical calculation of the (γ, p) cross section on118Sn in the energy region 150–750 MeV has been performed, taking into account the contributions of single pion photoproduction. The result is in good agreement with experimental data.

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.

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.

A Phenomenological Analysis of Single Pion Photoproduction in the First Resonance Region

Single pion pholoprocluction in the first resonance region is inve,.;tigated on the basis of noe-particlc-exchange model. In addition to the Born terms, s-, t- and u-channel exchanges of _N11, Li,,, 1V1,, p ancl oJ are taken into consicleration. In order to guarantee the unitarily we use the K-matrix method. The coupling constants ancl off-mass-shell parameters are cletcrminecl by X 2 -fit. The coupling constants obtain eel arc consistent with the values estimatecl by the use of the radiative clecay widths and the results of low energy pion-nucleon or nucleon-nucleon analyses. Our predicted mullipoles are in fairly good agreement with the experiments. L!,, contribution is dominant to Jfi'! 2> and is very small to Ei';''. The main contribution to E;s,m is due to the Born terms and the double zero observed in this multipole is well reproduced by incorporating unitarily. p exchange is positively required to explain the absolute value and energy dependence o£ E6';. It is difficult to reproduce the characteristic feature of nP,fi':! 21 • It was argued that this structure will show the onset of N11 resonance. However, its contribution is too smaJl to support this argument.

Single Pion Photoproduction in the First Resonance Region and One-Particle-Exchange Model

The experimental data of single pion photoproduction in the first resonance region (E,. ~ 500 MeV) have been accumulated and there are a number of energy independent multipole analyses of the data.U Corresponding field theoretical investigations have been given by several authors on the basis of one-particle-exchange (OPE) model.21 ~ 41 In these works, however, the unitarity is not taken into consideration. In this short note considering the unitarity we present a result of the multipole analysis in the first resonance region on the basis of OPE model. In order to guarantee the unitarity we adopt the K-matrix method in which the lowest order Born amplitude is regarded as the K.matrix:

Differential Cross Sections for Single Pion Photoproduction from Protons in the Energy Range between 500 MeV and 930 MeV

Differential cross sections of the reactions, γ+ p → p +π°, and γ+ p → n +π + , are measured at about 85° and 65°, respectively, in the incident energy range from 500 MeV to 930 MeV. A tagged photon is used as an incident photon beam. Overall features are consistent with the theoretical analyses by Moorhouse Oberlack and Rosenfeld, and by Metcalf and Walker.

Proton Compton effect in the ?(1232) energy region

The proton Compton effectγ+p→γ+p in theΔ (1232) energy region has been thoroughly studied. At the Bonn 500 MeV synchrotron differential cross sections were measured covering a large range of the CM scattering angle (50°≦θγ≦130°) and an energy range from 240 to 440 MeV (LAB energy of the primary photon). A contribution to the counting rate from the competing process ofπ0 photoproduction was strongly suppressed by detecting both particles in the final state and by a proper choice of the endpoint energy of the gamma ray beam. The remaining contribution was monitored experimentally. The measured data were complemented by cross sections at 0° which were computed from the totalγ p cross sections with an input from a multipole analysis of single pion photoproduction.

Analysis of single pion photoproduction at high and low energies

Fixed- t dispersion relations are used in a combined analysis of single pion photoproduction in the resonance and high-energy regions. Data are fitted from threshold to a centre-of-mass energy W of 2 GeV and for W from 2.6 to 5.6 GeV. In the resonance region, a partial-wave analysis is performed and 44 resonance couplings are evaluated. In the high-energy region, the imaginary parts of the amplitudes are parametrized in terms of Regge-pole exchanges and their trajectories and couplings are evaluated.

Partial-wave analysis of single pion photoproduction in the resonance region using fixed- t dispersion relations

A partial-wave analysis is made of pion photoproduction from threshold to the fourth resonance region. The couplings of 16 resonances below 2 GeV are evaluated and the masses and widths of many of the resonances of the first to the third regions are determined from photoproduction data. Only the imaginary parts of the photoproduction amplitudes are parametrised and the real parts are calculated entirely from fixed- t dispersion relations.

Measurement of asymmetries in polarizedγN→πN, withEγfrom 600 to 900 MeV

We report on the measurement of asymmetries in the single-pion photoproduction reactions $\ensuremath{\gamma}p\ensuremath{\rightarrow}n{\ensuremath{\pi}}^{+}$, $\ensuremath{\gamma}p\ensuremath{\rightarrow}p{\ensuremath{\pi}}^{0}$, and $\ensuremath{\gamma}n\ensuremath{\rightarrow}p{\ensuremath{\pi}}^{\ensuremath{-}}$, induced by linearly polarized photons of energies from 610 to 940 MeV. The experiment was carried out using the back-scattered laser beam and the 82-in. dubble chamber at SLAC. We compare the new data with predictions from a partial-wave analysis.

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 phenomenological analysis of pion photoproduction

Data on single pion photoproduction in the resonance region have been fitted with a model used previously by one of the authors (RLW). In updating the older fit a considerable amount of new data has been incorporated, the energy range has been extended to a total c.m. energy W = 2.0 GeV, and the procedure followed in making the fit has been changed so as to make greater use of the computer. In the model used for the analysis the pion photoproduction amplitude is composed of three parts: (1) the electric Born approximation, (2) Breit-Wigner resonances, and (3) additional “background” contributions in the lower partial waves. The electromagnetic couplings of many of the πN resonances with masses below 2 GeV have been determined in the analysis, and the results are compared to quark model predictions.

Some Features of the Single Pion Photoproduction Amplitudes Constructed from Resonances

The behaviour of the amplitudes which are constructed from resonances in the single pion photoproduction processes is shown for each t-channel isospin state. The contributions of the unnatural-parity meson exchange are also shown. Among various scattering processes, two of the best analyzed are rc (K) N ->rc(K)N and rN->rcN. The latter gives information on properties of the double helicity fltp amplitude and contributions of the unnatural-parity meson exchange. It is one of the most important problems to study the properties of these contributions and to find the relation between s-channel resonances and t-channel Regge poles. Unfortunately we have scarcely data on the region between 2 Ge V and 3 Ge V which is considered to be a very important region of transition from resonance to Regge. In this paper we investigate the behaviour of the amplitudes constructed from s-channel resonances in the single pion photoproductions and look for the relation mentioned above. The resonance parameters in the single pion photoproduction processes have been extensively investigated by many authors, 1l and are well confirmed for dominant resonances. The couplings for the resonances including non-dominant ones with the mass below 2.2 Ge V have recently been obtained by Devenish, Lyth and Rankin (D.L.R.) .2l In the analyses, their fundamental assumption is that the imaginary parts of the amplitudes may be resonance-saturated, and this is requested from duality ideas. 3l The resonances with their parameters are shown in Fig. 1 and Table. I. These parameters offered us facilities for seeing the characteristic features of the resonance region, at least up to 2 Ge V in the lab. photon energy. We decompose the resonance amplitudes into t-channel isospin states and investigate the properties of the imaginary parts of the photo­ production amplitudes. In our calculation, the resonance amplitude for each process is evaluated by the use of a Breit-Wigner form with resonance parame­ ters obtained by Devenish et al_2l As for real parts of the amplitudes, an exact answer is much dependent on the estimation of the so-called electric Born term, 4l so at present we leave the problem unsolved as a future one.

πo and π+ production with polarized photons in the energy range 1–2 GeV

The asymmetry of π o and π + photoproduction from hydrogen has been measured. The π o-mesons were detected at 130° cms with E γ ranged from 0.9 to 1.65 GeV, and the π +-mesons at 40° cms with E γ ranged from 0.9 to 1.2 GeV. The results agree with model predictions of single pion photoproduction in the resonance region using fixed- t dispersion relations.

CMSR's for single charged pion photoproduction amplitudes and the role of the gauge invariant Born terms

Continuous moment sum rules (CMSR's) for the t-channel single pion photoproduction amplitudes F i (−) ( v, t), i = 1, …, 4, are considered in great detail. Information about the high energy behavior of the amplitudes is extracted from low energy data in terms of an effective Regge pole picture which in most cases turns out to strongly violate certain reasonable postulates about the behavior of pure Regge poles, (idealized Regge pole picture). We ask, whether the deviation of the effective Regge pole picture from the idealized one can be described in terms of fixed poles at J = 0 arising from certain parts of the gauge invariant Born term contributions to the amplitudes. Such a description does work for small | t| in case of the amplitudes F i (−) ( v, t), i = 2, 3, but, as | t| increases, further contributions also become important. Investigation of CMSR's for amplitudes from which appropriate parts of the Born terms have been separated out, leads to a definite finite energy sum rule (FESR) duality scheme where parts of the Born terms ‘build up’ the idealized Regge poles themselves, while other parts give rise to additional contributions on the high energy side of the CMSR's.

Application of K-matrix CMSR'S to single charged pion photoproduction

The background terms, required in addition to Regge poles with some definite properties, in order to describe the high energy behavior of the t-channel single pion photoproduction amplitudes F t (−)( v, t), i = 1, …, 4, are investigated in the framework of a reggeized K-matrix model. To this end continuous moment sum rules (CMSR's) are applied, not to the full amplitudes, but just to the two-particle K-matrix amplitudes assumed to show pure Regge pole asymptotic behavior. The K-matrix amplitudes are defined by taking into account in the Heitler equation the elastic ( πN) intermediate state alone. Such a definition corresponds to a weak-cut model with only final-state interactions included. It turns out that strong background contributions are still present on the high energy side of the K-matrix CMSR's. The Regge cut contributions generated within our formalism are found to be too weak to account for the background terms in the full amplitudes. This is presumably to a great extent due to the neglect of the ( ϱN) diffraction-dissociation intermediate state in the definition of the K-matrix amplitudes.

Vector-axial vector interference terms in inelastic neutrino reactions extrapolated from single-pion photoproduction

By use of the generalized scaling sum rules the vector-axial vector interference terms in the scaling limit of the inelastic neutrino reactions are calculated from the absorptive parts of the single-pion photoproduction amplitudes at zero momentum transfer. The photoproduction amplitudes are evaluated by use of the results of multipole analysis. With the optimum values for the two parameters of the generalized scaling as determined in previous works, we have obtained F 3 νN ( ω) which leads to good agreement with experiment in the ration of σ ν N /σ ν N . However, the zeroth moment in x( = 1/ω), ∫ 0 1 dx(F 3 ν p + F 3 ν p ) turns out to be smaller than half of the value predicted in the fractionally charged quark model.

Negative-pion photoproduction from neutrons by linearly polarized photons in the first resonance region

The angular dependence of the asymmetry for negative-pion photoproduction on neutrons by linearly polarized photons has been measured for photon energies 260, 300, 350, 400, 450, and 500 MeV at center-of-mass angles 60\ifmmode^\circ\else\textdegree\fi{}, 75\ifmmode^\circ\else\textdegree\fi{}, 90\ifmmode^\circ\else\textdegree\fi{}, 150\ifmmode^\circ\else\textdegree\fi{}, and 120\ifmmode^\circ\else\textdegree\fi{}. The results are compared with theoretical models of low-energy single-pion photoproduction. The observed asymmetry below 400 MeV shows good agreement with predictions of dispersion-theoretical models by Berends, Donnachie, and Weaver and by Schwela. The asymmetry values in the 400-500 MeV energy region suggest that smaller ${M}_{1\ensuremath{-}}$ amplitude is more favorable.