Experimental tests of the factorisation of Regge trajectories in the proton fragmentation region

We present double differential cross sections for the reactions K^? + p → π^± + anything at 8.25 GeV/c. Using published data for reactions K⁺ + p→ π^? + anything and p + p → π⁺ anything we predict the differential cross sections for γ + p → π^? + anything, π^? + p → π^? + anything and π^? + p → π⁺ + anything in the target fragmentation region based on factorisation of the pomeron and Regge trajectories. Our predictions agree with the experimental data and support the hypothesis of factorisation of the Regge trajectories in the target fragmentation region.     

Backward elastic scattering and ϱ− production in π−p collisions at 10 GeV/c

The reactions π^?p → p π^? and π^?p → p?^? (?^? → π^?π⁰) at 10 GeV/c with the proton in the forward direction in the c.m.s. are discussed on the basis of 953 elastic scattering events and 2240 events of the reaction π^?p → pπ^?π⁰. The total backward cross sections are 0.52±0.10 and 1.52±0.28 μb, respectively. In both cases the production mechanism is compatible with the dominance of the baryonic Δ_δ Regge trajectory exchange. The ?^? decay angular distributions are studied in the u-channel helicity frame and the spin density matrix elements are presented as functions of u.     

A spin-parity analysis of the K+K+K− system produced in the reaction K+p → K+K+K−p

We present the first spin-parity analysis of the K⁺K⁺K^?) system produced in the reaction K⁺p → K⁺K⁺K^?p, and show that the general features of this system resemble those of the (ππ⁺π^?) and Kπ⁺π^?) systems produced in the reactions π(K)p → π(K)π⁺π^?p. There is a low mass enhancement, (47 ± 11)% of which corresponds to 1⁺ states decaying to Kø. At higher (K⁺K⁺K^?) masses 2^? → Kf′ becomes increasingly significant and at all masses there is a 0^? contribution of roughly 30%.     

Measurement of the Baryon-exchange reactions K−p→Λη, K−p→Λπ0 at 6 GeV/c and the value of the ηNN coupling constant

In order to determine the ηNN coupling constant we have measured the two reactions K^?p→Λη and K^?p→Λπ⁰ with a magnetic wire chamber spectrometer which contained a gamma counter for the γγ decays of π⁰ and η. The Λ polarization and the differential cross sections are given. The latter have quite different u dependences. Their ratio is interpreted, in terms of a nucleon-Regge exchange model, as the effect of a small ηNN coupling constant for which we obtain G_ηNN² = G_πNN² · (0.26 ± 0.10) as allowed by SU(3). The large value given by Heisenberg's non-linear field theory, G_ηNN² = G_πNN² · 0.9, is excluded by this measurement if the characteristic u dependence of the Λπ⁰ channel is attributed to N_α Regge exchange.     

Exchange-component analysis of neutral pseudoscalar meson photoproduction

π⁰ and η photoproduction data in the region of 4 GeV are decomposed into t-channel exchange components of definite isospin and parity. The latter are discussed in terms of Regge exchange models and compared to vector-meson dominance related processes. The isospin-one natural parity-exchange component is smooth and structureless. The dominant unatural parity exchange in π⁰ photoproduction has isospin zero. As in π^± photoproduction the ratio of natural to unnatural parity exchange is found to be larger than the vector-dominance expectation. Complementary information from a recent spin decomposition of γp → π⁰p gives further insight into the SU (3) properties of the exchanges. We predict unmeasured quantities and stress, in particular, the importance of studying γn → π⁰n with polarised photons.     

The reactions K−p→π∓Σ±(1385) at 4.2 GeV/c

The reactions K^?p→π^?Σ⁺(1385) and K^?p→π⁺Σ^?(1385) are studied at 4.2 GeVc incident momentum using data from a high statistics bubble chamber experiment corresponding to ～80 events/μb. The total and differential cross sections are presented. Amplitude analyses are performed and the complete Σ^±(1385) helicity spin density matrices are extracted. The results are compared with the predictions of the additive quark model and exchange degeneracy. A substantial cross section is observed for the reaction K^?p→π⁺Σ^?(1385) in the forward direction, which implies exotic meson quantum numbers in the t-channel. One possible interpretation of this process provides an explanation for the small but significant violations of the additive quark model predictions observed in the reaction K^?p→π^?Σ⁺(1385) at low four-momentum transfer. In the backward direction unnatural parity exchange is shown to give a larger contribution to K^?p→Σ^?(1385)π⁺ than natural parity exchange.     

Applications of Mueller theory of two-particle inclusive processes

Assuming factorization, and extracting inclusive Reggeon vertices from one-particle inclusive data, we predict Regge corrections to scaling for several two-particle inclusive processes. The data on p + P → π^? + π^? + X, K⁺ + p → π^? + π^? + X, K^? + p → π⁺ + π^? + X, and π⁺ + p → π^? + π^? + X agree with our predictions.     

Two-nucleon production of hyperons and the search for strange dibaryons

The double charge exchange reaction³He(K^?,π ⁺)Xn was studied at 870 MeV/c. In the X missing mass range below the sigma-nucleon production threshold (2130 MeV/c²), events were detected which can be attributed to the two-nucleon process pp(K^?,π ⁺)λn. This reaction and mass range also offers good prospects for finding theI=1/2,l=1 (¹ P₁) spin-singlet dibaryon D_s suggested as the lowest massS=?1 dibaryon in the MIT Bag Model. Although the existence of the D_s is not ruled out by the present data, there is no need to invoke such an object to account for the observed events below σ production threshold. We show that the cross section level for these events is compatible with a dominant two-nucleon mechanism K^?p→π ⁰λ,π ⁰p →π ⁺n. We also offer an interpretation of the recent (K^?,K⁺) data on nuclear targets from Iijimaet al., which display a broad peak centered around a K⁺ momentum of 600 MeV/c. We find that the two-nucleon mechanism K^?N →πY,πN→K⁺Y produces cross sections which are at least an order of magnitude smaller than those observed, and we suggest that the one nucleon process K^?p →Φλ, followed by the decayΦ → K⁺K^?, accounts for the data.     

A study of ππ → KK using an experiment on π−p → KS0KS0n at 8.9 GeV/c

We present an analysis of the K_S⁰K_S⁰ system, based on 6380 events, produced in the reactions π^?p → K_S⁰K_S⁰n. Using a one-pion exchange model with absorption we determine the S- and D-wave amplitudes of ππ → $\text{K}\text{K}$. Several A₂ production amplitudes were also included in the fits and we conclude that an unnatural parity exchange amplitudes which does not interfere with pion exchange, seems to present. A branching ratio $\text{Γ(}\text{f}\text{→}\text{K}\text{K}\text{/ Γ(}\text{f}\text{→ ππ) = 0.029 ± 0.006}$ is determined. With this and other new values of branching ratios we have fitted the 2⁺ → 0^?0^? decay rates of the SU(3) relations resulting in (36.2 ± 1)° for the tensor nonet mixing angle.     

Inclusive π0 and η production in the all neutral mode from 100 GeV/cπ−p collisions

Results are givenfor π⁰ and η production in 100 GeV/cπ^?p collisions, summed over all final states with no charged particles present (the all neutral final states). The data are fitted for x?0.6 to a modification of triple Regge theory suggested by the multiperipheral model. We find good agreement between the values of the ? and A₂ trajectories determined in the all neutral process, the full inclusive mode, π^?p → (π⁰, η)X, and the exclusive reactions, π^?p → (π⁰, η)n. The ? exchange residue function shows evidence for a dip at t ≈ ?0.5 (GeV/c)² (the ? wrong signature nonsense zero), whereas the η data are quite smooth in this region. These successful predictions for both the trajectory and residue function are striking evidence for the validity of triple Regge theory.     

The reactions K−p → π∓Σ± at 4.2 GeV/c

We present differential cross sections and the Σ⁺ polarization for the reactions K^?p → π^?Σ^± using data from a high statistics bubble chamber experiment at 4.2 GeV/c incident momentum. The statistical level allows a detailed analysis of these reactions over the whole t range. Several significant structures are observed. Comparisons are made with SU(3)-related reactions; for backward production of π^?Σ⁺ such a comparison shows good evidence for Δ exchange. The exotic forward peak in K^?p → π⁺Σ^? is definitely confirmed.     

Pomeron dominance in a triple-Regge representation of inclusive Δ++ production in K−p and π−p reactions

Data are presented on the reactions K^?p → Δ⁺⁺ + anything at 10 and 16 GeV/c and π^?p → Δ⁺⁺ + anything at 16 GeV/c. In the K^?p reaction, scaling is observed between 10 and 16 GeV/c in the variable M²/s. The scaling occurs at relatively low values of M in marked contrast to the reaction π⁺p → Δ⁺⁺ + anything. This result can be explained by duality arguments on a triple Regge picture, since the exchanged reggeon-incident particle scattering is exotic. Comparison of the π^?p reaction, which is similarly exotic, with the K^?p reaction at the same energy gives further evidence for factorization in pomeron-dominated inclusive reactions.     

Analysis of the Kω spectrum

We present results of a spin-parity analysis of the Kω system from threshold to 1.52 MeV based on 12 500 events of the type K^?p→K^?π⁺π^?π^op at 7.3 GeV/c. We also present evidence for a possible resonant state decaying into Kω at a mass 1710 ± 15 MeV and width 110 ± 50 MeV.     

Cross section determination for the reaction K+p → K+pπ+π−π0 and K+π+π+π−n at 8.2 and 16 GeV/c

The cross sections for the reactions: (a) K⁺p → K⁺pπ⁺π^?π⁺ and (b) K⁺p → K⁺π⁺π⁺π^?n have been determined at 8.2 and 16 GeV/c with the following results:at 8.2 GeV/c: (a) 0.99 ± 0.07 mb, (b) 0.41 ± 0.04 mb;at 16 GeV/c: (a) 0.72 ± 0.05 mb, (b) 0.28 ± 0.05 mb.Using the available data at other energies, the cross-section dependence of these reactions on the incident momentum is discussed.     

A measurement of the branching ratios of the A2− meson produced in 3.9 GeV/cπ−ϱ interactions

We have measured the branching fractions of the A₂^? meson, produced in the reaction π^?p → pA₂^? at 3.9 GeV/c incident momentum. The rates for the ηπ and K$\text{K}$ modes relative to ?π are 0.211 ± 0.044 and 0.056 ± 0.014, respectively. The upper limit for the η′π mode is 0.056 at the 90% confidence level. We have also looked for an ωππ decay of the A₂^? and our data are consistent with a rate of 0.10 ± 0.05, relative to ?π.     

Analysis of K−K+ and π−π+ final states in 13 GeV K−p interactions

The differential cross sections and density matrix elements for the φ and ?⁰ mesons have been measured in the reactions K^?p → K^?K⁺ (Λ, Σ⁰) and K^?p → π^?π⁺ (Λ, Σ⁰) at 13 GeV using a wire chamber spectrometer. The analysis shows that while the vector meson production is dominated by the natural parity exchange amplitude, some unnatural parity exchange is also required. Furthermore the φ and ? natural exchange cross sections are identical in shape and have the 2:1 relative strength expected in the quark model with K¹ and K⁷ exchange degeneracy. The analysis of the clear peak-dip ?^0?ω interference pattern observed in the π^?π⁺ data indicates that the ω production is in phase with the ? and of similar magnitude. Both the S¹ and f′ meson are clearly observed in this experiment. The S¹ data are found to be consistent with S¹ parameters deduced from ππ scattering analyses. The f′ density matrix elements and a new limit of the f′ → π^?π⁺ branching ratio are presented.     

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/dt_pp 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 J^P = 1⁺ state with S-wave decay into Kø(1020) is dominant, (72 ± 11) % of all events with (KKK) masses below 2 GeV.     

Backward production of a spin parity 1+ϱπ enhancement at 1.04 GeV

A spin-parity 1⁺?π enhancement is observed for the 3π mass spectrum in the reaction K^?p → Σ^?π⁺π⁺π^? where events with a small (K^? → Σ^?) momentum transfer are selected. The mass (1040 MeV) and width (230 MeV) of this enhancement are reminiscent of the A₁ → ?π bump which has mainly been observed in the diffractive-like processes. The cross section for this enhancement at 4.15 GeV/c incident K^? momentum is (3.6 ± 0.5) μb.