H. Wieczorek

Evidence for structure in the 1+ state of the Q region

We have performed a partial-wave analysis of the mainly diffractively produced low-mass (Kππ) system in the reactions K−p→K−π+π−p and K−p → K0π −π0p at 10, 14 and 16 GeV/c. We find that the dominant 1+S(K∗π) state has possibly a two-peak structure (around 1.27 and 1.37 GeV). In contrast the 1+S(Kϱ) state shows one narrow peak near thershold (around 1.27 GeV). These states are found to be of different origin. The results favour the interpretation of the 1+S(Kϱ) as a 1+ resonance below the (Kϱ) threshold. The t′pp dependence is found to be different for the 1+ and 0− states.

A comparative investigation of low mass π+ω and K−ω systems at various energies

A comparison is made of the properties and production mechanisms of the π+ω and K−ω systems produced in the reactions π+p → π+ ωp at 4, 5, 8 and 16 GeV/c and K− p → K−ωp at 10 and 16 GeV/c. In the π+ω case apeak is observed at 1.23 GeV (the B meson), while the K−ω mass distribution has a threshold enhancement. The cross section of the low mass (<2.0 GeV) π+ω system falls as plab−2, while that of the low mass (<2.0 GeV) K−ω system is almost constant with energy, indicating diffractive production of the K−ω system, but not of the πω system. Using a modified version of the Illinois partial-wave analysis program, it is found that the K−ω system is dominantly produced in the JP = 1+ state with small contributions of 0− and 2+, mainly by natural parity exchange - as is found for reactions such as K−p → (K−π+π−)p which are predominantly diffractive. For the π+ω system in the B mass region, JP = 1+ states, produced mainly by natural parity exchange are found; the contributions of 0−P, 1−P, 2−P and 2+D are consistent with zero. The 1+D state occurs in the π+ω case but not in the K−ω system, nor in the Kππ− system produced in the K−p → Kππp reaction.

Spin-parity structure of the (Kπ) system produced in the reaction K−p → (K−π+)n

Abstract A spin-parity analysis is presented of the (K−π+) system produced in the reaction K−p → (K−π+)n at 10 and 16 GeV/c for M(Kπ)

Partial-wave analysis of the (KKK) system in the reaction K−p→K−K−K+p at 10 and 16 GeV/c

The reaction K−p→K−K−K+p is shown to have properties similar to those of the diffractive reaction K−p→K−π−π+p. This is true, at least in first approximation, for (a) the energy dependence of the cross sections, (b) the shape of the three meson spectra and (c) the differential cross sections dσ/dtpp which have the same slope for the same mass of the three-meson system. Furthermore, the partial-wave composition of the (KKK) system is similar to that of the (Kππ) system, both systems being produced mostly in unnatural spin-parity states by natural parity exchange. In the KKK system, the JP = 1+ state with S-wave decay into Ko(1020) is dominant, (72 ± 11) % of all events with (KKK) masses below 2 GeV.

Diffraction dissociation, resonances and deck mechanism in the Kω systems of the reactions K±p→(K±ω)p

A study is presented of the reactions K+p→(K+ω)p at 8.25 and 16 GeV/c and K−p→(K−ω)p at 10 and 16 GeV/c and comparison is made with K+ results at 10 GeV/c and K− at 7.3 GeV/c. The (K+ω) and (K−ω) mass spectra both present a strong enhancement very near threshold, while a second peak at ∼1.7 GeV is evident only with incident K− at the lower energies. The threshold peak has very weak energy dependence and is mostly due to the 1+S state which is produced conserving s-channel helicity. It is suggested that this is another decay mode of the resonance Q1(1290) known to decay mainly into Kϱ. The ratio of the Q1 coupling constants to the Kω and Kϱ decay channels, Rω = gKω2/gKϱ2 is determined to be 0.21±0.04. The enhancement at 1.7 GeV is predominantly, but not exclusively, due to the 2− state. While the K+ and K− induced reactions give basically similar results, small differences are observed that can be qualitatively explained in the framework of the Deck model.

Inclusive production of Σ±(1385) in K−p interactions at 10 and 16 GeV/c

Abstract The inclusive production of Σ + (1385) and Σ − (1385) has been studied in K − p interactions at 10 and 10 and 16 GeV/ c . It is found that the cross sections for the reactions K − p → Σ ± (1385) + anything are approximately constant in the energy range form 10 to 32 GeV/ c , being ≈ 350 μ b for Σ + (1385) and ≈ 250 μ b for Σ − (1385). The d σ d p ⊥ 2 distributions for Σ ± (1385) fall off exponentially with increasing p ⊥ 2 , with sloped of about 3 (GeV/ c ) −2 . The d σ /d x distributions for Σ + (1385) and Σ − (1385) are markedly different: the production of Σ − (1385) is symmetrical forwards and backwards in the c.m.s.; for Σ + (1385), the distribution is the same as for Σ − (1385) in the forward direction, but presents a large excess of events in the backward direction. This indicates that for the production of both Σ + (1385) and Σ − (1385) the fragmentation of the incoming kaon is negligible. The fragmentation of the target proton is negligible for Σ − (1385), but it is important for Σ + (1385) and is responsible for the excess (∼100 μ b) of its cross section over that for Σ − (1385).

Spin-parity analysis of the diffractively produced low-mass Nπ system in the reaction π±p → π± (Nπ)+ at GeV/c

The dominant partial waves of the diffractively produced Nπ system at low Nπ masses (⩽ 1.4 GeV) are determined in the reactions π±p → π(Nπ) at 16 GeV/c. A satisfactory description of our data can only be obtained by strong contributions of both a 12− S-wave and a 32+ P-wave, violating the Gribov-Morrison rule. Spin and parity of the diffractively produced states are found from the interference between diffraction and Δ (1236) production. The interference term is obtained by an isospin analysis.