Summary
The cross-sections σ(Eγ,ϑ ) for the reaction pγ→ n+ have been measured near threshold as a function of photon energy and at four angles. See Table I. These results combined with previously known data, have given a fairly complete and accurate description of σ(Eγ,θ) between the limits 30°≤θ≤180° and 170≤ Eγ 270 MeV. See Table II and Pig. 2. Writing σ(Eγ,θ) = W·a0 + a1 cos θ + a2 cos2 θ× withW= ηωl +(μ/Ei)ξ −1·l + (μ/E f )ω×−1 (see formula (5)) the experimental data indicate that (Table III) a0 is constant up to about Eγ ≃ 260 MeV; and that (Table V) the three ai coefficients analyzed in terms ofS andP waves give a very small spin flippingP-amplitudeK. The presumption that theS amplitudeE 1 ismainly due to the gauge invariance requirement is definitely not consistent with the data (see Table IV). A discussion based on the Kroll and Rudermann theorem leads to the conclusion that this inconsistency may be eliminated if allowance is made for the contribution of fairly large nucleon recoils. However, it turns out that only the changing sign part of these recoils is really large and apparently so up to terms of order higher than μM. The amount of the recoil at threshold is estimated and consequently a value for the pspv interaction constant is derived.
Riassunto
La sezione d’urto σ(Eγ,θ) per la reazione p → n+ è stata misurata in prossimità della soglia in funzione dell’energia fotonica e sotto quattro angoli. Vedi Tab. I. I risultati ottenuti combinati con dati precedentemente noti lianno fornito una descrizione abbastanza completa ed esatta di σ(Eγ,θ ) tra i limiti 30° ≤θ ≤180° e 170≤ ≤Eγ≤270MeV. Vedi Tab. II e Fig. 2. Scrivendo σ(E γ,θ) = W·a0+a1 cos θ+a2 cos2 θ× conW= nω·1+(μ/Ei)×-1 ·1+(μ/Efω×-1 (vedi formula (5)), i dati sperimentali indicano che (Tab. III) a0 è costante fino a circa Eγ ≃ 260 MeV, e che (Tab. V) i tre coefficienti ai analizzati in termini di ondeS e P danno una piccolissima ampiezza P di spin-flipping,K. La presunzione che l’ampiezzaSE, siaprincipalmente dovuta all’imposizione dell’invarianza di gauge non si accorda in alcun modo coi dati (vedi Tab. IV). Una discussione basata sul teorema di Kroll e Rudermann porta alla conclusione che questa incongruenza puó essere eliminata se si tien conto del contributo di rinculi nucleonici abbastanza energici. Tuttavia, risulta che solo la parte di tali rinculi che cambia di segno è realmente energetica ed apparentemente tale fino a termini di ordine superiore a μ/M. Si valuta la quantità di rinculo alla soglia e se ne deriva un valore per la costante di interazione pspv.
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References
B. T. Feld:Fhys. Rev.,89, 330 (1953);K. Aizu:Proceeding of the International Conference of Theor. Phys., Kyoto and Tokyo, 1953, p. 200;E. Fermi: 1954 Varenna Lecture,Suppl. Nuovo Cimento,2, 17 (1955);K. Watson:Phys. Rev.,95, 228 (1954); see alsoK. A. Brueckner andK. M. Watson:Phys. Rev.,86, 923 (1952);S. Hayakawa, M. Kawaguchi andS. Minami:Prog. Theor. Phys.,12, 355 (1954);12, 789 (1954).
M. Gell-Mann andK. M. Watson:Annual Review of Nuclear Science,4, 219 (1954).
G. F. Chew:Phys. Rev.,95, 669 (1954);G. F. Chew andF. E. Low:Phys. Rev.,101 1570, 1579 (1956). nication.
G. Wick:Rev. Mod. Phys.,27, 339 (1955).
N. Kroll andM. Ruderman:Phys. Rev.,93, 233 (1954).
G. P. Chew, ref. (4); Fermi’s Varenna lectures 1954,Suppl. Nuovo Cimento,2, 17 (1955);K. M. Watson, ref. (1) andProceeding of the V Annual Rochester Conference, p.32, 1955.
R. G. Sachs:Phys. Rev.,95, 065 (1954);W. G. Holladay andR. G. Sachs:Phys. Rev.,96, 810 (1954) and preprints.
J. Steinberger andA. S. Bishop:Phys. Rev.,86, 171 (1952).
R. S. White, M. J. Jacobson andA. G. Schulz:Phys. Rev.,88, 836 (1952).
N. Jarmie, G. V. Repp andR. S. White:Phys. Rev.,91, 1023 (1953).
R. L. Walker, J. G. Teasdale, V. Z. Peterson andJ. I. Vette:Phys. Rev.,99, 210 (1955).
A. V. Tollestrup, J. C. Keck andR. M. Worlock:Phys. Rev.,99, 220 (1955).
T. L. Jenkins, D. Lockey, T. R. Palfrey andR. R. Wilson:Phys. Rev.,95, 179 (1954).
B. T. Feld, D. H. Frisch, I. L. Lebow, L. S. Osborne andJ. S. Clark:Phys. Rev.,85, 680 (1952).
G. S. Janes andW. L. Kraushaar:Phys. Rev.,93, 900 (1954).
G. Bernardini, E. L. Goldwasser:Phys. Rev.,94, 729 (1954).
J. E. Leiss, C. S. Robinson andS. Penner:Phys. Rev.,98, 201 (1955).
J. E. Leiss andC. S. Robinson:Phys. Rev.,95, 638 (A) (1954).
G. Bernardini andE. L. Goldwasser:Phys. Rev.,95, 857 (1954).
E. A. Whalin Jr. andR. A. Reitz:Rev. Sci. Instr.,26, 59 (1955).
P. D. Edwards, D. W. Kerst:Rev. Sci. Instr.,24, 490 (1953).
J. Leiss, T. Yamagata andA. O. Hanson:Illinois Reports, 1954.
L. I. Schiff:Phys. Rev.,83, 252 (1951).
D. H. Stork:Phys. Rev.,93, 868 (1954).
Proceedings of the V Annual Conference, Rochester, 1955.
R. Hofstadter:Proceedings of the V Annual Rochester Conference, 1955.
E. Fermi, unpublished: Dr.A. H. Rosenfeld kindly sent the authors a photostatic copy of the C-18 notes made by Fermi in preparation for the Summer Schools of Les Houches and Varenna, 1954.
L. Ferretti, E. Manaresi, G. Puppi, A. Ranzi andG. Quareni:Nuovo Cimento,1, 1239 (1955);M. O. Stern et al.: Bull. Am. Phys. Soc.,Z6, SeriesII, vol.1, Jan., 1956.
K. M. Watson, J. C. Keck, A. V. Tollestrup andR. L. Walker:Phys. Rev.,101, 1159 (1956).
M. Sands, J. G. Teasdale andR. L. Walker:Phys. Rev.,95, 592 (1954);M. Beneventano, G. Bernardini, D. Carlson-Lee, E. L. Goldwasser, G. Stoppini:Nuovo Cimento,12, 156 (1954);D. Carlson-Lee, G. Stoppini andL. Tau:Nuovo Cimente,2, 162 (1955);M. Beneventano, G. Bernardini, D. Carlson-Lee, G. Stoppini andL. Tau:Proceeding of International Conference, Pisa, 1955, and forthcoming paper inNuovo Cimento.
K. Watson:Phys. Rev.,85, 852 (1952).
A. Klein:Phys. Rev.,99, 998 (1955).
H. P. Noyes:Phys. Rev.,101, 320 (1956).
H. L. Anderson andE. Fermi:Phys. Rev.,86, 794 (1952).
L. Lederman:Phys. Rev., andProceedings VI Annual Rochester Conference, April 1956.
Cassel andPanofsky:Proceedings of VI Annual Rochester Conference, 1956. It is likely that the total error is less than 20%.
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Beneventano, M., Bernardini, G., Carlson-Lee, D. et al. Differential cross-sections for photoproduction of positive pions in hydrogen. Nuovo Cim 4, 323–356 (1956). https://doi.org/10.1007/BF02745453
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DOI: https://doi.org/10.1007/BF02745453