K ∗(890) and K ∗(1420) production in quasi two-body K −p reactions at 10 GeV/c

Abstract

Results are presented for six reactions induced by K −p collisions at 10 GeV/ c, where K ∗(890) and K ∗(1420) resonances are produced in association with a proton, a neutron, a Δ +(1236) or Δ O(1236) isobar. Partial and differential cross sections as well as density matrix elements are compared to one another and to previous results at lower energies. The following observations are made: (i) There is a first indication of a difference in the energy dependence of the pK ∗− and nK ∗O cross sections. (ii) In the pK ∗−(890) channel the ratio of π to ω exchange decreases with increasing energy. (iii) The ratio of π to ω exchange increases with the mass produced, the pion exchange contribution to the pK ∗−(1420) channel being larger than that to the pK ∗−(890) channel. (iv) Natural spin-parity exchange dominates in the pK ∗−(890) channel, but there are significant contributions of both natural and unnatural parity exchanges in the nK ∗O(890) channel. (v) There exists a clear hierarchy of exchanges such that when ω or f O-exchanges are possible, they dominate over pion-exchange; pion exchange dominates over ϱ or A 2-exchange in ΔQ = 1 or ΔI = 1 reactions, at least up to 10 GeV/ c. (vi) Differential cross sections d σ/d t′ of reactions dominated by pion exchange are better fitted by a two-exponential formula of the type P[exp (− Qt′)+ R exp (− St′)], than by the pion propagator. (vii) At least ≈ 25% of the unnatural exchange in the nK ∗O(890) channel at 4–10 GeV/ c must be due to mechanisms other than simple pion exchange.