Multi-nucleon mechanism for subthreshold antiproton production in proton-nucleus reactions

Abstract

Abstract. We study a many-body (multipion) mechanism for p subthreshold production in proton-nucleus collisions. The incoming proton and the interacting nucleons in the target act as sources of pions that merge to produce a nucleon-antiproton pair. The calculation takes fully into account the initial state interaction and antiproton absorption in the final state. The cooperation of several nucleons in the initial state reduces the threshold for the reaction allowing for production rates that may account for 15-50% of the total p production. We point out that this contribution should be added to the primary ~ production mechanism due to A formation and rescattering, as found by other groups, and should be taken into account when trying to extract information about ~ properties in the nuclear medium.

Subthreshold antiproton production in pC, dC and C reactions

“…Most of the descriptions proposed so far are based on transport calculations [13][14][15][16][17][18][19][20][21][22], thermodynamical considerations [23][24][25][26] or multi-particle interactions [27] and are devoted to proton and/or heavy-ion induced reactions. By measuring lightion-induced subthreshold p production the KEK group [12] intended to provide an experimental test for models in this transition region between proton and heavy-ioninduced reactions.…”

Probing hadronic formation times with antiprotons in p+A reactions at AGS energies

“…Especially in nucleus-nucleus collisions at subthreshold energies traditional cascade calculations, that employ free NN production andpN annihilation cross sections, essentially fail in describing the high cross sections seen from 1.5 -2.1 A·GeV [7,8]. Thus multiparticle nucleon interactions [9,10] have been suggested as a possible solution to this problem. On the other hand it has been pointed out that the quasi-particle properties of the nucleons and antinucleons might be important for thep production process which become more significant with increasing nuclear density [11,12,13,14,15,16].…”

Delta excitation in antiproton-deuteron annihilation

“…The ∆-excitation in pd annihilation at rest was studied. We use the annihilation amplitude from the statistical model [13]. The πN amplitude was calculated with the resonance model accounting only for the ∆(1232) resonance.…”

“…which are different from ν = 5.05 and σ = 0.76 suggested in [15] for the annihilation at rest, but as we studied [17] do not change the results noticably. Accordingly to Hernandez et al [13] the annihilation amplitude has a smooth momentum dependence and the momentum distribution of the pions are described by the n-body phase space.…”

“…The deutron wave function φ(Q) for the Bonn potential [12] was adopted. We use the annihilation probability from [13] as…”