Search

The inclusive production of Σ+(1385), Σ−(1385), Λ(1405) and Λ(1523) in K−p interactions at 14.3 GeV/c is studied. Cross sections are presented and the x dependence of the invariant cross sections is discussed. The density matrices for production of the spin-32 resonances at small momentum transfer to the target are consistent with spin-0 exchange.

We present evidence for the double dissociation process K−p → QN12∗ → (K∗0π−)(nπ+) at 14.3 GeV/c. The cross section for this process is of the order of 10 μb. The production differential cross section is steep (for near-threshold excitation masses), as typical of diffractive processes, and exhibits a strong correlation between the production slope and the masses of the dissociated systems. The spin-parity composition and states of the two dissociation systems closely resemble those found in single dissociation, indicating that a common diffraction-like mechanism is responsible for both processes. The mass variations of the differential cross-section slope, the decay angular correlations and the total cross section of the double dissociation component are consistent with the predictions of a factorisable pomeron exchange model.

The π+π− system produced in the reaction K−p → K−(π+π−)p at 14.3 GeV/c is strongly enhanced in the ππ near-threshold region and is consistent with having a large ππS-wave component. The double-pomeron-exchange mechanism contribution to its production is found to be at most 4% for the mass regionM(π+π−)⩽0.6 GeV. The lowmass π+π− system is consistent with being entirely produced in conjunction with the Kππ andNππ diffraction dissociation clusters corresponding to incident K and proton fragmentations respectively.

The reaction K−p→Δ++ + anything was studied at 14.3 GeV/c and is production mechanism was found to be consistent with one pion exchange at low momentum transfer. K−π− inelastic and total cross sections have been determined by a Chew-Low extrapolation method in the c.m. energy range from threshold to 2.8 GeV. Cross sections for various K−π− final states are presented.

Results are presented of a bubble chamber experiment on K − p elastic scattering at 14.3 GeV/ c , in four-momentum transfer range 0.04 t | 2 using an initial set of 40 000 events. The total elastic cross section is (2.96 ± 0.10) mb. The results are compared with K + p elastic scattering data at 13.8 GeV/ c , and the effective Regge trajectory is calculated using K − p data from 5 to 100 GeV/ c .

Results are presented on γ production in K− p interactions at 14.3 GeV/c. The analysis is based on 2 541 fitted e+e− pairs in a hydrogen bubble chamber. The inclusive cross section for γ production is found to be (54.5 ± 1.8) mb. The average number of γ's per inelastic event is 2.93 ± 0.12; it exhibits no strong dependence on charged multiplicity. From the PL and PT2 invariant distributions of the γ, a simple function describing the π° invariant distribution is determined.

We have measured the reaction K − p → pX at 14.3 GeV/ c , in the fragmentation region of the target proton. The differential cross section is studied as a function of momentum transfer and missing mass squared. In the triple-Regge limit, it is consistent with the dominance of a MMP coupling at large t but it is possible that couplings of the type PPP and ππ P also contribute at small | t | values.

Results on the inclusive reactions K−p → K∗−(890) + X+ and K−p → K∗0 (890) + X0 at 14.3 GeV/c are presented. A comparison is made with previous data and with the reaction K−p → K0 + X at 14.3 GeV/c. Predictions of a triple-Regge model for the variation of the unnatural and natural parity exchanges with the mass of the X system are examined. The experimental values of the structure functions are compared with those calculated from a quark model.

Inclusive production of Σ + , Σ − and Σ 0 hyperons in K − p interactions at 14.3 GeV/ c has been studied and compared to Λ production. Cross sections are presented as a function of longitudinal and transverse momenta and compared to the pp → Σ + + anything data.

We have studied the reactions K−p → K−π+π−p and K−p → K0π−π0p at 14.3 GeV/c using respectively 15 992 and 3723 events. Partial-wave analysis of the region 1.0 < m(Kππ) < 1.7 GeV have been made using a modified version of the method developed at the University of Illinois. We have measured the cross section as a function of mass for each spin-parity state of the Kππ system. Results from the two reactions are in excellent agreement and indicate an overall isospin of 12. We find that the Q enhancement is predominantly JP = 1+ but that the partial-wave substates have very different branching ratios into Kϱ and K∗π, the K∗π component of the 1+ state being similar to the 1+ state of the 3π system produced in the reaction πp → (3π)p.

Preliminary results are presented on K ∗ (890) and K ∗ (1420) production in three-body final states of 14.3 GeV/ c K − p interactions. For K ∗ō (890) production, the total and differential cross-sections and the density matrix elements are determined. The K ∗− reaction is found to be dominated by natural parity exchange and the charge exchange reaction by unnatural parity exchange. The total cross sections are given for K ∗ō (1420) production.

New data from the reactions K − p → Λ + X and K − p → K 0 + K at 14 GeV /c are presented. From an analysis of the distributions of M X 2 within the framework of a triple Regge formalism we obtain the effective Regge trajectories corresponding to ϱ, K or K ∗ and nucleon exchange.

Event selection and weighting. In Fig. 1 a), the distribution of the square of the missing mass to the K0 in all zero-prong plus one K ~ events is displayed; a clear neutron signal is visible with a half-width of approximately 0.4 (GeV)L In the study of reaction (1) we use all events with missing mass less than the A(1236) mass. The cross-section is corrected for the few neutron events above this cut by double-counting the symmetrical region below the neutron mass. We also correct for the background reaction

Results are presented on a measurement of the I = 3/2 Kπ elastic scattering cross section by applying the Chew-Low extrapolation method in the reaction K−p → K−π−Δ++at14.3GeV/c. The magnitude of σ(K−π− → K−π−) is found to be about 3 mb at threshold and slowly falling with energy to about 1.5 mb at 2.8 GeV. The off-mass-shell moments of the differential elastic cross section are given. The absolute value of δ30 is found to be increasing slowly from 0° to 20° between threshold and 1.2 GeV.

Results are presented on differential (total) cross sections and decay parameters for four two-body reactions (π+p → pπ+, π+p → pϱ+, π+p → Δ++π0 and π+p → Δ++η0) obtained from a sample of approximately 30 000 two-pronged interactions 5 GeV/c incident momentum. In the forward direction the dσ/dt′ distribution of reaction pϱ+, Δ++π0 and Δ++η0 show a dip or flat region. The general dσ/dt′ structure of the elastic channel and the reaction pϱ+ requires a ”double-slope” fit. The dσ/dt′ distribution of reaction π+p → Δ++π0 shows a clear-cut dip at t′ ≈ 0.6 GeV/2. In the backward region we observe peaks for reactions π+p → pϱ+, pϱ and N∗+ (1660)π0. The dσ/d|u| distribution of the elastic channel shows a dip at |u| ≈ −0.2 GeV2. The spin-density matrix elements of the ϱ+ particle in reaction pϱ+ indicate the presence of both π- and ω-trajectory exchange. The spin density matrix elements of the Δ++ in the reactions with final state Δ++π0 and Δ++η0 are compatible with pure ϱ and A2 Regge trajectory exchange respectively. Where applicable, our dσ/dt′ and density matrix element results are compared with the Dar-Weisskopf absorption model and with the predictions resulting from Regge-pole model fits.

We have studied the Kππ system in the 14.3 GeV/c reactions K−p → K−π+π−p, K−p → K0π−π0 and K−p → K0π+π−n. The data have been obtained from a 500 000 picture exposure of the CERN 2m HBC. The first two final states are dominated by Q-production in the Kππ system; there is also an L-signal at M (Kππ) ∼ 1.75 GeV. The reaction cross sections are compared to K−p data at other energies. We discuss the Kππ mass dependence of the diffractive production slope. Evidence is presented for a Q−p versus Q+p differential cross section cross-over around |t| = 0.17 GeV2. A t-channel isospin analysis for the KN → K∗(890)πN channels in the Q-region shows that the I = 1 exchange amplitude is ⋍ 10% of the dominant I = 0 exchange amplitude. The Kππ decay distributions indicate a predominant JP = 1+ state in the Q-region, and an important JP = 2− contribution in the L-region. We find neither s-channel nor t-channel helicity conservation at the meson vertex in the Q- or L-regions. The Kπ angular correlation moments within the Kππ diffractive system are characteristic of Kπ elastic scattering, suggesting a π-exchange Deck-type production mechanism. There is evidence for a Kf0 and κπ contribution (where κ is the JP(Kπ) = 0+ state) to the diffractive Kππ system. A fit to the K−π+π− and K0π−π0 Dalitz-plot distributions for the Q-re gion indicates that the ratio of Kϱ to K∗π decay amplitudes decreases with increasing Kππ mass.

A test is made of the factorisation scheme proposed by Miettinen for the inclusive reaction π±p → Λ + X at 18.5 GeV/c and K−p→ Λ + X at 14.3 GeV/c. The test is applied to the lambda differential cross section and polarisation via a sum rule derived within the concepts of duality and exchange degeneracy, and SU3. The original scheme is found not to agree with the experimental data. A possible explanation of the disagreement is discussed.

New high energy results for the reactions K − p → K ∗− (890) p and K − p → K ∗− (1420) p confirm a definite flattering in the energy dependence of the cross sections; such a flattering is not observed in the corresponding K+ channels. The contributions of natural parity exchange at small t accounts for this effect and suggests a possible explanation in terms of pomeron (P) trajectory exchange, giving rise to ωP interference.