Inclusive production of Δ++(1232) in pn interactions at 19 GeV/c

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We present a study of Δ++ production in pn interactions at 19 GeV/c, where the Δ++ is emitted in the protonlike (ΔF++) and neutronlike (ΔB++) c.m. hemispheres. The cross-section σ(pn→ΔF+++X)=(3.09±0.43) mb is about three times larger than σ(pn→ΔB+++X)=(0.94±0.34) mb. About 2/3 of ΔF++ is peripherally produced with |tp,Δ| <1 (GeV/c)2, while the cross-section for ΔB++ production is nearly zero for |tn,Δ|<1 (GeV/c)2. We have made a detailed study of the energy dppendence of the reaction ap→Δ+++X(a=p,p,n,π±,K±) for |tp,Δ|<1 (GeV/c)2, by applying the same fitting procedure to extract the Δ++ cross-section to all available mass spectra. All the normalized cross-sectionsR=σ(Δ++)/σinel can be well described byR=R0+R1aplab−α, whereR0 and α are the same for all reactions, whileR1avaries with the beam type a. The value of α is slightly below unity. The differential cross-section of pn→ΔF+++X has been determined as a function of the variablest, t′, x, y, pT2 andMx2 both in the whole kinematical region and for |tp,Δ|<1 (GeV/c)2. We show that the peripherally produced ΔF++ is consistent with the dominance of the one-pion exchange mechanism. This follows from a study of the density matrix elements, the comparison of some properties of the system X with real π+p data and from the results of a triple-Regge analysis. A substantial part of the peripheral ΔF++ is produced together with a π− in a low-mass Δ++π− system. However, we estimate that less than about 20% of the ΔF++ production with |tp,Δ|<1 (GeV/c)2 results from a diffractively produced Δ++π− state. Contrary to pn→ΔF+++X, the reaction pn→ΔB+++X has a small cross-section at |tn,Δ|<1 (GeV/c)2, but at largert-values the two reactions are similar.