Summary
By assuming that the total scattering function is the product of the usual Coulomb scattering function and a model nuclear-scattering function, which is an even function ofλ=l+1/2 having a simple pole atλ=λ 0 in the first quadrant of theλ-plane, it is shown that, for large values of |λ 0| and of the Sommerfeld parameter, the scattering amplitude can be expressed as the sum of a saddle-point contribution and a pole contribution. Owing to the presence of the Coulomb term in the scattering function, an angleθ c exists such that the pole contribution changes its form in going fromθ<θ c toθ>θ c. The two forms of the pole contribution are in agreement with the contribution to the scattering amplitude, calculated according to the Keller rules, of generalized Coulomb trajectories diffracted at the surface of a sphere whose radius is connected with Reλ 0. By using the fact that our amplitude in a certain limit becomes a representation of the Rutherford amplitude, it is shown that this quantity is completely «near-side».
Riassunto
Assumendo come funzione di diffusione il prodotto della funzione di diffusione coulombiana e di una funzione di diffusione nucleare, modellisticamente rappresentata tramite una funzione pari diλ=l+1/2 avente un polo aλ=λ 0 nel primo quadrante del piano del momento angolare complesso, si dimostra che, per grandi valori di |λ 0| e del parametro di Sommerfeld, l’ampiezza di diffusione è esprimibile tramite la somma del contributo di un punto a sella e del polo localizzato aλ 0. La presenza del termine coulombiano nella funzione di diffusione fa sì che esista un angoloθ c tale che il contributo del polo assuma forme diverse perθ<θ c eθ>θ c. Le due forme del contributo del polo sono in accordo con il contributo all’ampiezza di diffusione, calcolato secondo le regole di Keller, di traiettorie generalizzate coulombiane diffratte alla superficie di una sfera il cui raggio dipende da Reλ 0. Utilizzando il fatto che l’ampiezza di diffusione considerata, in un certo limite, si riduce ad una rappresentazione dell’ampiezza di Rutherford si dimostra che questa quantità può essere espressa tramite le funzioni di Legendre che asintoticamente, per grandi valori diλ, si comportano come un’onda angolare regressiva.
Реэюме
Предполагая, что функция полного рассеяния есть проиэведение обычной кулоновской функции рассеяния и модельной функции ядерного рассеяния, которая является четной функциейλ=l+1/2 и имеет простой полюс приλ=λ 0 в первом квадрантеλ плоскости, покаэывается, что при больщих эначениях |λ 0| и параметра Зоммерфельда амплитуда рассеяния может быть выражена как сумма вклада седловой точки и полюсного вклада. И3-3a наличия кулоновского члена в функции рассеяния сушествует такой уголθ c, что полюсной вклад иэменяет свою форму при переходе отθ<θ c кθ>θ c. Полученные две формы полюсного вклада согласуются с вкладом, вычисленным в соответствии с правилами Келлера, в амплитуду рассеяния обобшенных кулоновских траекторий, дифрагированных на поверхности сферы, радиус которой свяэан с Ееλ 0.
Similar content being viewed by others
References
R. Anni, L. Renna andL. Taffara:Lett. Nuovo Cimento,25, 121 (1979).
T. Takemasa andT. Tamura:Phys. Rev. C,18, 1282 (1978).
R. G. Newton:Scattering Theory of Waves and Particles (New York, N. Y., 1966), p. 401.
R. C. Fuller:Nucl. Phys. A,216, 199 (1973).
S. Landowne:Phys. Rev. Lett.,42, 633 (1979).
We notice that the imaginary part ofλ 0 obtained byLandowne atE lab=55 MeV is considerably smaller (at least about a factor of four) than the imaginary part of the poles responsible for the ALAS in the cross-sections of the potentials considered in ref. (1,2). Among these, no pole exists which, when considered alone, can justify the oscillatory behaviour of the excitation function.
R. C. Fuller andP. J. Moffa:Phys. Rev. C,15, 266 (1977).
H. M. Nussenzveig:Ann. Phys. (N. Y.),34, 23 (1965).
R. C. Fuller andY. Avishai:Nucl. Phys. A,222, 365 (1974).
The effect of the Coulomb interaction on the pole contribution to the scattering amplitude was previously studied in ref. (9) and in ref. (10) for the Ericson parametrization of the nuclear-scattering function in the framework of the strong-absorption model. There one obtains that the pole contribution changes its form in going from the forward to the backward directions owing to the dominance of different poles of the parametrized scattering function.
R. Anni andL. Taffara:Nuovo Cimento A,29, 595 (1974).
N. Rowley andC. Marty:Nucl. Phys. A,266, 494 (1976); see also ref. (15).
R. C. Fuller:Phys. Lett. B,57, 217 (1975).
H. M. Nussenzveig:J. Math. Phys. (N. Y.),10, 82 (1968).
R. Anni andL. Taffara:Nuovo Cimento A,31, 321 (1976).
The reflection property (1.6) is also characteristic of the scattering function of all the irregular potentials (14).
V. De Alfaro andT. Regge:Potential Scattering (Amsterdam, 1965), p. 177.
C. Marty: lectures given at SUNY, Stony-Brook, 1978, report No. IPNO/TH79-3 (1979).
R. B. Dingle:Asymptotic Expansions: Their Derivation and Interpretation (London and New York, N. Y., 1973), p. 131.
R. B. Dingle:Asymptotic Expansions: Their Derivation and Interpretation (London and New York, N. Y., 1973), p. 261.
B. R. Levy andJ. B. Keller:Commun. Pure Appl. Math.,12, 159 (1959).
R. B. Dingle:Asymptotic Expansions: Their Derivation and Interpretation (London and New York, N. Y., 1973), p. 8.
Author information
Authors and Affiliations
Additional information
Supported in part by INFN, Italy.
Rights and permissions
About this article
Cite this article
Anni, R., Renna, L. & Taffara, L. Forward- and backward-angle regge-pole contribution in the presence of coulomb interaction. Nuov Cim A 55, 456–474 (1980). https://doi.org/10.1007/BF02900498
Received:
Published:
Issue Date:
DOI: https://doi.org/10.1007/BF02900498