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.     

Two-prong events in π− p interactions at 4.45 GeV/c

(π^?p → π^?p)_el, π^?p → π^?π⁺n and π^?p → π^?π^op reactions at p_π? = 4.45 GeV/c were studied in a 50 cm hydrogen bubble chamber. Cross sections σ_tot and dσ/dt were measured for these reactions and also for the ?^o, f^o and ?^? resonances. The elastic π^?π⁺ and π^?π^o scattering cross sections were calculated by the Chew-Low extrapolation method and with the pseudoperipheric approximation.     

On the chiral-scalar contribution to the cross section for the reactions pp → ppπ + π − and pn → pnπ + π − near the threshold

A simple estimate of the cross sections for the reactions pp → ppπ ⁺ π ^? and pn → pnπ ⁺ π ^? is given with allowance for the contribution of a nonlinear chiral scalar field. The reaction amplitudes are calculated in the threshold approximation. The final-state interaction of nucleons is taken into account in calculating the cross sections in question. A comparison of the results of these calculations with experimental data leads to the conclusion that the contribution of the chiral scalar to the cross sections for the reactions under consideration is quite sizable.     

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.     

Dual properties of inclusive spectra

The dual properties of the inclusive reaction π^?p → pX are studied over a wide energy range by exploiting the scaling behaviour. Semi-local duality is found to be well satisfied. An energy-dependent triple-Regge analysis reveals a strong triple-pomeron coupling. There is some evidence of an abnormal component in which diffractively produced resonances are dual to pomeron exchange. Combining duality with factorization leads to relations between production cross sections of meson and baryon resonances in πp and pp collisions, which are compatible with existing experimental data.     

Measurement of the reaction γd → π−pp,and determination of cross sections for the reaction γn → π−p,at photon energies between 0.2 and 2.0 GeV

The reaction γd→π^?pp has been measured in a bubble chamber experiment at DESY with a bremsstrahlung beam of E_γ^max = 5.5 GeV. Total and differential cross sections are presented for the energy region from 0.2 to 2.0 GeV. The extraction of cross sections on the neutron is discussed in detail. The impulse approximation and the closure relation, with corrections for the exclusion principle and the Fermi motion effects, as well as the Chew-Low extrapolation technique are applied. Total cross sections and angular distributions for the reaction γn→π^?p, deduced by these methods, are presented in graohs and tables. The results are compared with other experiments and with various predictions. No positive evidence for an isotensor electromagnetic current is found. The results disagree with some of the measurements of radiative pion capture, if detailed balance is assumed to connect the two reactions.     

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.     

An experimental test of exchange degeneracy in the hyperchange exchange reactions π+p→K+Σ+and K−→π−Σ+

For the first time, the line reversed reactions π⁺p→K⁺Σ⁺and K^?p→π^?Σ⁺ have been studied in the same apparatus. We present the differential cross sections and polarizations over a large t range and at two momenta, 7.0 and 10.1 GeV/c. The differential cross sections as a function of t are shown for the first time to cross over. Going from the lower to the higher momentum, the differences in cross section between the two reactions diminish at low |t| by about a factor 2. We find large polarizations of opposite sign for the two reactions. The momentum dependence, presented in the form of α_eff(t) for the t range 0 to ?2 (GeV/c)², is compared with the expectations from the K¹?K⁷ trajectory.     

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.     

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.     

A study of K−p interactions in deuterium in the c.m. energy range from 1.60 to 1.74 GeV

We present results of a K^?d bubble-chamber experiment at four K^? momenta between 680 and 840 MeV/c. The validity of the spectator model for the analysisof KN interactions in deuterium is discussed. Cross sections are determined for the reactions K^?p → Σ^?π⁺, K^?p → Σ⁺π^? and K^?p → Λπ⁺π^? and are compared to those obtain ed on free protons.     

T = 1 excitation mechanism in pion induced reactions on 12C

The cross sections for the reactions π^± → π^±, π⁰ on ¹²C with excitation of the T = 1 states are calculated for the N₃₃¹ energy region. The Chew-Low amplitude for pion-nucleon scattering is used in the framework of impulse approximation which has been supported by recent calculation of pion scattering with excitation of definite nuclear states.     

Chiral anomaly in Kγ → Kπ reactions

Implications of the chiral anomaly for the cross sections of the reactions K ⁺γ → K ⁺π⁰, K ⁰γ → K ⁰π⁰, K ⁺γ → K ⁰π⁺, and K ⁰γ → K ⁺π^? are investigated. Near the threshold, the contribution of the chiral anomaly dominates the cross sections for the first and the second reaction. These cross sections are compared with the cross sections for the third and the fourth reaction, which receive no contribution from the chiral anomaly. Prospects for an experimental study of the KKπγ vertex in the Coulomb production of π mesons by a K-meson beam are discussed.     

Energy dependence of the cross sections for the e<Superscript>+</Superscript>e<Superscript>–</Superscript> → hadrons process near the production threshold for the <Emphasis Type="Italic">N</Emphasis><Emphasis Type="Italic">N̄</Emphasis> pair

The energy dependence of the cross sections for the processes e⁺e^? → π⁺π^?π⁰, K⁺K^?, ηπ⁺π^?, ωπ₀, and K⁺K^?π⁺π^? is studied near the production threshold for a nucleon–antinucleon pair. It is shown that, within the measurement errors, the cross sections in question behave smoothly in this energy region.     

Phenomenological model for describing pion-pair production on a proton by virtual photons in the energy region of nucleon-resonance excitation

A phenomenological model is developed for describing the production of π ⁺ π ^? pairs on a proton by virtual photons in the energy region of nucleon-resonance excitation.The cross sections are calculated for the channels γp → π ^?Δ⁺⁺, γp → π ⁺Δ⁰, and γp → ρp, which make a dominant contribution to pion-pair production, and the results are compared with available experimental data.The contributions of nucleon resonances to the cross section for the reaction γp → π ^?Δ⁺⁺ are predicted within the developed approach.     

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.     

Measurement of the cross sections for reaction π−p → Xo n in the momentum range up to 50 GeVc

The cross sections for the reaction π^?p → X^on, X^o → 2_λ are measured at 32.5 and $\text{48}\text{GeV}\text{c}$ momenta. The cross spectrometer of γ-quanta is used to select events of reaction, whose cross section is only about 0.05 μbarn. The cross section energy dependence has the power form ($\text{≈ p}{}^{\mathrm{?1.11\pm 0.12}}$. conclusion on U(6) symmetry of quark model is made when comparing the differential cross sections at zero angle for the reactions π^?p → X^o and π^?p → η^o. The angle of octet-singlet mixing for pseudo-scalar mesons β = ?(20.6 ± 2.2)° is defined.     

Experimental study of Λp and Ξ0p interactions in the range 1 – 10 GeV/c

The reactions Λp → Λp, → Σ^±pπ^?, → Λpπ⁺π^? and → Σ⁰p have been studied in the SLAC 82 inch bubble chamber for incident Λ particles in the momentum range 1–10 GeV/c. The incident Λ flux was produced by the exposure of a platinum target mounted inside the chamber to a 12 GeV K^? beam. A total of 992 events have been analyzed. The reactions are found to be qualitatively similar to corresponding nucleon-nucleon reactions. In particular, the slope parameter B in the elastic cross section dσ/dt = Ae^Bt has been determined as a function of incident momentum and found to be consistent with that for proton-proton elastic scattering. Angular distributions for the inelastic channels are compared with those of similar nucleon-nucleon reactions, and predictions of relevant exchange models.     

Double pomeron exchange in the reaction pp → ppπ+π−

We compute the cross section for pp → ppπ⁺π^? in the kinematical region for which two-pomeron exchange is important, assuming dominance of the pion-exchange pole. We include effects due to absorption, final-state interaction, and interference between the two contributing Feynman diagrams. These effects have been ignored in previous calculations. Consequently, our predicted cross section is smaller than previous predictions by a factor of ～ 3, and is consistent with experimental indications. We calculate the background cross section in the double pomeron exchange region, and find that it is sizable even at s ～ 3000 GeV². We discuss the two-particle inclusive process pp → ppX.     

Regge pole model for invariant functions. IV

TheNN→NN andγN→πN differential cross sections for polarized targets are discussed in terms of invariant functions. In former fits of high energy experimental data certain of these invariant functions came out to be small. Based on these fits thepn→np,p¯p→ n¯n, γp→ nπ ⁺ andγn→ pπ ^? differential cross sections are predicted to be independent of the target polarization.