Summary
The np and\(\bar p\)p charge exchange processes are analysed in the very forward region (|t|≲2m 2π ), independently of any particular model, within the general hypothesis that only thet-channel π exchange term can vary appreciably in such a smallt-interval. This hypothesis is shown to be quite restrictive: it implies in particular that the fall-off of the differential cross-section betweent=0 and |t| ⋍m 2π cannot exceed a factor 2, whatever the energy (provided it is not too near to threshold). Now such a factor 2 seems to be actually found experimentally, in np charge exchange, for all incident momenta between 600 MeV/c and 24 GeV/c; it then turns out that the 3 linear combinations of the 5 invariant amplitudes which can contribute att=0 (besidest-channel π exchange) are practically determined in the corresponding range of values ofs. These approximate relations between the amplitudes are discussed and compared with the predictions of some specific models. Finally, they are analysed using fixed-t dispersion relations; the approximate values obtained for the amplitudes in the np → pn channel give nontrivial restrictions on the absorptive parts in the crossed\(\bar p\)p →\(\bar n\)n channel.
Riassunto
Si analizzano i processi di scambio della carica np e\(\bar p\)p nella regione estrema in avanti (|t|≲2m 2π ), indipendentemente da qualsiasi modello particolare, nell’ipotesi generale che solo il termine di scambio di un pione nel canalet possa variare apprezzabilmente in questo piccolo intervallo di valori dit. Si mostra che questa ipotesi è assai restrittiva: in particolare che essa implica che la caduta della sezione d’urto differenziale nei pressi dit=0 e |t| ≃m 2π non può superare un fattore 2, per qualsiasi energia (purché non sia troppo vicina alla soglia). Ora sembra che un tale fattore 2 si sia trovato sperimentalmente, nello scambio di carica np, per tutti i valori dell’impulso incidente compresi fra 600 MeV/c e 24 GeV/c; risulta allora che le 3 combinazioni lineari delle 5 ampiezze invarianti che possono contribuire at=0 (oltre allo scambio di un pione nel canalet) sono praticamente determinate nel corrispondente campo di valori dis. Si discutono queste relazioni approssimate tra le ampiezze e si confrontano con le previsioni di certi modelli specifici. Infine le si analizzano usando relazioni di dispersione at fissato; i valori approssimati delle ampiezze ottenuti nel canale np → pn danno restrizioni non banali per le parti relative all’assorbimento nel canale incrociato\(\bar p\)p →\(\bar n\)n.
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References
NN andNDinteractions. A compilation, URCL 20000 NN (1970), p. 146, and references therein.
E. L. Miller, M. Elfild, N. W. Reay, N. R. Stanton, M. A. Abolins, M. T. Lin andK. W. Edwards:Phys. Rev. Lett.,26, 984 (1971).
J. Engler, K. Horn, F. Mönning, P. Schludecker, W. Schmidt-Parzefall, H. Schopper, P. Sievers andH. Ullrich:Phys. Lett.,34 B, 528 (1971).
M. B. Davis, B. G. Gibbard, M. N. Kreisler, T. Dobrowolski, M. J. Longo, D. D. O’Brien andT. Toohig:Phys. Rev. Lett.,29, 139 (1972).
R. J. N. Phillips:Phys. Lett.,4, 19 (1963)
D. Amati, G. Cohen-Tannoudji, R. Jengo andPh. Salin:Phys. Lett.,26 B, 510 (1968).
D. V. Volkov andV. N. Gribov:Sov. Phys. JETP,17, 720 (1963).
R. J. N. Phillips:Nucl. Phys.,2 B, 394 (1967).
M. Le Bellac:Phys. Lett.,25 B, 524 (1967).
Ph. Salin:Topical Conference on High-Energy Collisions of Hadrons (Geneva, 1968), p. 478.
F. Henyey, G. L. Kane, J. Pumplin andM. H. Ross:Phys. Rev.,182, 1579 (1969).
G. L. Kane, F. Henyey, D. R. Richards, M. Ross andG. Williamson:Phys. Rev. Lett.,25, 1519 (1970).
J. M. Drouffe andH. Navelet:Nuovo Cimento,2 A, 39 (1971).
J. Froyland andG. A. Winbow:Nucl. Phys.,35 B, 351 (1971).
P. Finkler:Phys. Rev. D,2, 173 (1970).
A. Capella, B. Diu andJ. M. Kaplan:Nucl. Phys.,47 B, 365 (1972).
P. K. Williams:Phys. Rev.,181, 1963 (1969).
G. C. Fox:Phenomenology in Particle Physics, Proceedings of the Conference held at Cal. Tech. (1971), p. 703.
M. L. Goldberger, M. T. Grisaru, S. W. Mac Dowell andD. Y. Wong:Phys. Rev.,120, 2250 (1960).
A similar expression was already written down in ref. (16) for the high-energy limit of the differential cross-section.
Similar results were already obtained in ref. (16) for the asymptotic energy region.
Such a small rise can be wiped out by the «normal» decrease of dσ/dt beyond the forward region; it may however be seen as a «shoulder» at the end of the spike (see ref. (2)).
M. Gourdin, M. Le Bellac, F. M. Renard andJ. Tran Thanh Van:Nuovo Cimento,37, 524 (1965).
P. Astbury, G. Brautti, G. Finocchiaro, A. Michelini, D. Websdale, C. H. West, E. Polgar, W. Beusch, W. E. Fischer, B. Gobbi andM. Pepin:Phys. Lett.,22, 537 (1966).
P. Astbury, G. Brautti, G. Finocchiaro, A. Michelini, D. Websdale, C. H. West, E. Polgar, W. Beusch, W. E. Fischer, B. Gobbi andM. Pepin:Phys. Lett.,23, 160 (1966).
W. Atwood, B. Barish, H. W. Nicholson, J. Pine, A. V. Tollestrup, J. K. Yoh, A. S. Carroll, F. Lobkowicz andY. Nagashima:Phys. Rev. D,2, 2519 (1970).
R. Lacaze: Thèse, Saclay report DPh-T/72-34 (unpublished).
The possible importance of theu-channel pion pole has been recently «rediscovered» (M. Glück:Phys. Rev. Lett.,29, 1762 (1972)), but in a pure Born-approximation model, without any justification such as the existence of fixed poles.
Notice however that, contrary to what Fig. 25 of ref. (18) suggests, dσ/dt only falls by a factor 2 as shown in Sect.2 (φ4 has been omitted in drawing this Figure).
Interesting discussions on this point withL. Łukaszuk and withJ. M. Kaplan are gratefully acknowledged.
J. S. Bell:Theory of Weak Interactions, Les Houches Summer School (London, 1965).
The numerical values of the residues at the deuteron poles can be calculated from the coupling constants given in ref. (27).
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Diu, B. Analysis of the forward np and\(\bar p\)p charge exchange amplitudes at intermediate and high energiesp charge exchange amplitudes at intermediate and high energies. Nuov Cim A 20, 115–133 (1974). https://doi.org/10.1007/BF02727441
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DOI: https://doi.org/10.1007/BF02727441