R. Steinberg

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 ΔO(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 fO-exchanges are possible, they dominate over pion-exchange; pion exchange dominates over ϱ or A2-exchange in ΔQ = 1 or ΔI = 1 reactions, at least up to 10 GeV/c. (vi) Differential cross sections dσ/dt′ 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.

A dual diffractive model for the Q- and L-mesons

The contribution to the reaction K−p→pK−π+π− due to pomeron exchange is studied, assuming that the system (pomeron + mesons) is described by a dual five-point Veneziano-type amplitude. The calculations are compared with the experimental results at 10 GeV/c and good agreement is obtained for the Kππ mass distribution, the t-dependence of the differential cross section and the Dalitz plots for the Kππ systems in the mass regions of the Q- and L-mesons.

A study of the reaction K−p → pKoπ− with the Veneziano model

Abstract The five-point function Veneziano model has been applied to the reaction K − p → p K 0 π − in the energy range from ≈ 3 to 10 GeV/c. The predictions of the model are shown to be sensitive to the choices made for the assumptions and the parameters involved in the expression of the amplitude. Several choices can be made that give a satisfactory general description of this reaction. However, the mass spectra are not described in detail and the differential cross sections do not have the correct t-dependence, especially at the lower energies. These difficulties derive mostly from the fact that the simple model used does not consider the possibility that more than one trajectory is exchanged between a pair of particles.

Quark-model predictions for joint decay distributions in π+p double resonance production reactions at 8 GeV/c

Abstract The quark-model predictions of Bialas and Zalewski are compared with the experimental results for the joint decay distributions in the double resonance production reactions π + p → N ∗++ ϱ 0 , π + p → N ∗++ ω at 8 GeV /c . The relations fall into three categories, which differ in the assumptions made. Those of class A, which depend only on the additivity assumption, are found to be well satisfied for both reactions, within large errors. Similar agreement is found for relations of class B. A number of class C relations are badly violated in Jackson and helicity frames but are found to be valid in the Donohue-Hogaasen system.

Production of proton-antiproton and kaon-antikaon pairs in four-body reactions of 8 GeV/c π+ and 10 GeV/c K− on protons

The production of (pp), (K+K−) and (π+π−) pairs in four-body reactions of 8 GeV/c π+ and 10 GeV/c K− on protons has been studied. The cross sections for these processes are smaller in K−p interactions than in π+p interactions. For both π+ and K− induced reactions, the production of a K+K− pair is about 30 times less probable than that of a π+π− pair. In K−p interactions frequent production of φ but not of fo is observed, whereas in π+p interactions fo production is observed but not φ production. The production of the N∗(3755) isobar decaying into (ppp), reported by other authors, is not confirmed. The results are discussed in terms of a simple additive quark model.

Isospin analysis of the reactions

Abstract An analysis has been made of the reaction K − p → K (π N ) in terms of the isospins of the t- channel ( K − → K ) exchange and of the (πN)-system. It is found that the dominant process is isoscalar exchange, which is identified with the diffractive dissociation of the proton. The (πN) mass spectrum corresponding to this process presents an asymmetric enhancement of very large width peaked at about 1.3 GeV, well below the mass of any established N ∗ isobar. The d σ /d t distribution is well-fitted in the t -range 0.0–0.2 GeV 2 by an exponential with slope parameter ≈ 7 GeV −2 , the same as for elastic K − p scattering at the same energy. The diffractive K − p → K − ( π N) + cross section is found to be (10 ± 2)% of the elastic K − p cross section, which is equal to the corresponding ratio found for πp interactions at 16 GeV/ c . A similar isospin analysis of the reactions K − p → K ∗ (890) (π N ) reveals an isoscalar exchange cross section in this case smaller than that for isovector exchange.Abstract An analysis has been made of the reaction K − p → K (π N ) in terms of the isospins of the t- channel ( K − → K ) exchange and of the (πN)-system. It is found that the dominant process is isoscalar exchange, which is identified with the diffractive dissociation of the proton. The (πN) mass spectrum corresponding to this process presents an asymmetric enhancement of very large width peaked at about 1.3 GeV, well below the mass of any established N ∗ isobar. The d σ /d t distribution is well-fitted in the t -range 0.0–0.2 GeV 2 by an exponential with slope parameter ≈ 7 GeV −2 , the same as for elastic K − p scattering at the same energy. The diffractive K − p → K − ( π N) + cross section is found to be (10 ± 2)% of the elastic K − p cross section, which is equal to the corresponding ratio found for πp interactions at 16 GeV/ c . A similar isospin analysis of the reactions K − p → K ∗ (890) (π N ) reveals an isoscalar exchange cross section in this case smaller than that for isovector exchange.

ππ scattering effects in π+p interactions at 8 GeV/c

Abstract The reaction π + p → Δ ++ π + π − at 8 GeV/c has been used to study ππ scattering in the ϱ-meson mass region. Two different methods have been used. In the first, it is assumed that ππ scattering in this mass range is entirely elastic and confined to S-, P- and D-waves. The P- and D-waves are assumed to be given by the ϱ0 and f0 resonant amplitudes extrapolated off-shell using Durr-Pilkuhn form factors. The remaining cross section (which by our assumption is S-wave) fits a Breit-Wigner distribution with mS = 680 ± 30 MeV and ΓS0 = 310 ± 70 MeV. In the second method a ππ phase-shift analysis has been used to obtain the S-wave phase shifts. There are two possible solutions here, one of which resonates at mS = 710 ±a 80 MeV and ΓS0 = 140 ± 20 MeV.

Isospin analysis of the reactions K−p → KπN and K−p → K∗ (890)πN at 10 GeV/c

Abstract An analysis has been made of the reaction K − p → K (π N ) in terms of the isospins of the t- channel ( K − → K ) exchange and of the (πN)-system. It is found that the dominant process is isoscalar exchange, which is identified with the diffractive dissociation of the proton. The (πN) mass spectrum corresponding to this process presents an asymmetric enhancement of very large width peaked at about 1.3 GeV, well below the mass of any established N ∗ isobar. The d σ /d t distribution is well-fitted in the t -range 0.0–0.2 GeV 2 by an exponential with slope parameter ≈ 7 GeV −2 , the same as for elastic K − p scattering at the same energy. The diffractive K − p → K − ( π N) + cross section is found to be (10 ± 2)% of the elastic K − p cross section, which is equal to the corresponding ratio found for πp interactions at 16 GeV/ c . A similar isospin analysis of the reactions K − p → K ∗ (890) (π N ) reveals an isoscalar exchange cross section in this case smaller than that for isovector exchange.Abstract An analysis has been made of the reaction K − p → K (π N ) in terms of the isospins of the t- channel ( K − → K ) exchange and of the (πN)-system. It is found that the dominant process is isoscalar exchange, which is identified with the diffractive dissociation of the proton. The (πN) mass spectrum corresponding to this process presents an asymmetric enhancement of very large width peaked at about 1.3 GeV, well below the mass of any established N ∗ isobar. The d σ /d t distribution is well-fitted in the t -range 0.0–0.2 GeV 2 by an exponential with slope parameter ≈ 7 GeV −2 , the same as for elastic K − p scattering at the same energy. The diffractive K − p → K − ( π N) + cross section is found to be (10 ± 2)% of the elastic K − p cross section, which is equal to the corresponding ratio found for πp interactions at 16 GeV/ c . A similar isospin analysis of the reactions K − p → K ∗ (890) (π N ) reveals an isoscalar exchange cross section in this case smaller than that for isovector exchange.

Isospin analysis of the reactions K−p → KπN and K−p → K∗∗Visiting Scientist, now at the University of Bonn. (890)πN at 10 GeV/c

Abstract An analysis has been made of the reaction K − p → K (π N ) in terms of the isospins of the t- channel ( K − → K ) exchange and of the (πN)-system. It is found that the dominant process is isoscalar exchange, which is identified with the diffractive dissociation of the proton. The (πN) mass spectrum corresponding to this process presents an asymmetric enhancement of very large width peaked at about 1.3 GeV, well below the mass of any established N ∗ isobar. The d σ /d t distribution is well-fitted in the t -range 0.0–0.2 GeV 2 by an exponential with slope parameter ≈ 7 GeV −2 , the same as for elastic K − p scattering at the same energy. The diffractive K − p → K − ( π N) + cross section is found to be (10 ± 2)% of the elastic K − p cross section, which is equal to the corresponding ratio found for πp interactions at 16 GeV/ c . A similar isospin analysis of the reactions K − p → K ∗ (890) (π N ) reveals an isoscalar exchange cross section in this case smaller than that for isovector exchange.Abstract An analysis has been made of the reaction K − p → K (π N ) in terms of the isospins of the t- channel ( K − → K ) exchange and of the (πN)-system. It is found that the dominant process is isoscalar exchange, which is identified with the diffractive dissociation of the proton. The (πN) mass spectrum corresponding to this process presents an asymmetric enhancement of very large width peaked at about 1.3 GeV, well below the mass of any established N ∗ isobar. The d σ /d t distribution is well-fitted in the t -range 0.0–0.2 GeV 2 by an exponential with slope parameter ≈ 7 GeV −2 , the same as for elastic K − p scattering at the same energy. The diffractive K − p → K − ( π N) + cross section is found to be (10 ± 2)% of the elastic K − p cross section, which is equal to the corresponding ratio found for πp interactions at 16 GeV/ c . A similar isospin analysis of the reactions K − p → K ∗ (890) (π N ) reveals an isoscalar exchange cross section in this case smaller than that for isovector exchange.