P. Lundborg

Exchange mechanisms and energy dependence of isospin amplitudes for the reaction pN → NNπ in the energy range 5–1480 GeV☆

Data on the reactions pp → ppπ0, pp → pnπ+ and new data on pn → ppπ− at 19 GeV/c are used to study the reaction N1N2 → N3(N4π) in terms of the three isospin amplitudes MIIx, where Ix and I are the isospins of the exchanged particle and the N4π combination respectively. The result is that the amplitude with isospin zero exchange is dominating at 19 GeV/c. Analysis of available data from 5 to 1480 GeV yields that the isoscalar amplitude M120 is interpreted to be dominated by pomeron exchange and the isovector amplitude M321 by π exchange. The isovector amplitude M121 seems to be a mixture of A2(ϱ) and π exchanges. The only interference term which is definitely non-zero, is the one between M120 and M121 which is large in magnitude and negative.

Some features of one, two and three pion production in pd collisions at 19 GeV/c

Abstract We present cross sections for coherent and non-coherent production of one, two and three pions in pd reactions at 19 GeV/ c . The mass distributions of the two pion non-coherent channels are studied. Strong single Δ(1236) and also some double Δ production is observed. Clear evidence for ϱ production is seen.

Antiproton-neutron interactions at 100 GeV/c

Abstract From an exposure of the 30-inch deuterium filled bubble chamber to a 100 GeV/ c antiproton-enriched beam at FNAL, we have calculated the topological cross sections for antiproton-neutron interactions with three or more charged particles in the final state. A comparison of our data with pn data at the same momentum allows us to estimate the annihilation contribution to each multiplicity, and hence calculate the average value, and width, of the annihilation multiplicity distribution. Our results are consistent with those from p p data at 100 GeV/ c , but depart from the trend of lower-energy p p data.

Isospin analysis of single ϱ and f0 production in pN collisions in the energy range 7–24 GeV

New data on the reactions pp → ppϱ0, pn → pnϱ0, pn → ppϱ−, pp → ppf0, and pn → pnf0 at 7, 11.6 and 19 GeV/c are used to study the reactions pN → NNϱ and pN → NNf0 in terms of isospin amplitudes. In the ϱ case there are three such amplitudes MI1I2 where I1 and I2 are the isospins of the exchanges in a double peripheral diagram. The result is that the amplitude with I1 = 1 and I2 = 0 is dominating. The properties of this amplitude are such that it is likely to be dominated by the pair of exchanges ϱ + η. In the f0 case there are only two amplitudes. It is found that the I1 = I2 = 0 amplitude is larger than the I1 = I2 = 1 amplitude and that it has an energy dependence such that it could be dominated by the pair of exchanges η + η.

Crossed Channel Isospin Amplitude Analysis of the Reaction pN→Nπ Δ(1236) above 6 GeV/c Incident Momentum

Data on the reactions pn → NπΔ(1236) and pp → NπΔ(1236) at 19 GeV/c have been used to study the reactions pN → N(πΔ) and pN → (Nπ)Δ in terms of crossed channel isospin amplitudes. The cross section of the reaction pN → N(πΔ) is about twice that of pN → (Nπ)Δ. Each reaction can be described by three amplitudes MIIx, where Ix and I are the isospins of the exchange and of the Δπ or Nπ system, respectively. We find that for the reaction where the pion clusters to the Δ, i.e., pN → N(πΔ), the isoscalar exchange is the leading mechanism, but the M3/21 amplitude also gives a large contribution. For the other reaction, i.e., pN → (Nπ)Δ, the isovector exchange amplitude leading to a I = 3/2 Nπ state, is dominating. The Ix = 2 exchange amplitude is unimportant. These results have been compared with the results of similar analyses of other three-body reactions and some common features and differences have been pointed out. Available data at other energies have been used to investigate the energy dependence of the isospin amplitudes for the reaction pN → ΔπN in a double exchange representation. It is found that the amplitude involving isoscalar exchange is dominating above 20 GeV/c and has a weak energy dependence while the amplitude with double isovector exchange has an energy dependence pnlab with n ≈ - 1.5.