T. Coghen

A study of second-order interference for pions produced in various hadronic interactions

Second-order interference of pion pairs of equal charge is observed in good statistics samples of 16 GeV/c π+p and K−p interactions (2 × 106 and 106 pion pair combinations, respectively) and in a smaller sample of pp annihilations at rest. The effective radius R of the pion source is found to be approximately 1.4 fm for all three types of interaction. The interference does not appear to be “total”, about 60–80% of the like pairs interfering. It is shown that the numerical results for the radius R, for the depth cτ of the source “photosphere” and for the fraction λ of the interfering pairs are sensitive to any dynamical correlation in the background, and hence depend on the background chosen. It is argued that further refinements in the theoretical formulation of the phenomenon and in the experimental approach are needed for truly quantitative results.

Inclusive single-particle distributions in π±p reactions at 8 and 16 GeV/c

Abstract Invariant single-particle cross sections for pion and proton production in π ± p interactions at 8 and 16 GeV/ c are presented in terms of integrated distributions as functions of x , reduced rapidity ζ and p ⊥ 2 , and also in terms of double differential cross sections E d 2 σ /(d x d p ⊥ 2 ) and d ζ d p ⊥ 2 ). A comparison of π ± and π − induced reactions is made and the energy dependence is discussed. It is shown that the single-particle structure function cannot be factorized in its dependece on transverse and longitudinal momentum. For the beam-unlike pion, there is an indication for factorizability in terms of rapidity and transverse momentum in a small central region.

Production of ρ0 and f in π−p interactions at 16 GeV/c and separation into fragmentation and central components

The production of ρ0(770) and f(1270) is studied in π−p interactions at 16 GeV/c. By comparison with inclusive K∗0 production in the reaction K−p → K∗0 + anything, and with inclusive ρ0 production in the reaction pp → ρ0 + anything, it is found that the data can be interpreted in terms of two production processes: the central production of resonances and the fragmentation of the beam particle. For the π−p reaction, the inclusive ρ0 beam fragmentation cross section is 3.1 ± 0.3 mb while that for central production is 1.6 ± 0.5 mb. The ρ0 central production cross section is consistent with increasing with energy as ln s behaviour. The ratio of ρ0 to π− inclusive cross sections (excluding the leading π−) is ∼0.2, independent of energy. The ρ0 to π− ratio increases as a function of pT to a constant value of ∼12 above 1 GeV/c. The ρ (charged and neutral) and f decays account for (25 ± 4)% and (1.4 ± 0.3)%, respectively, of all pions produced.

Inclusive K∗±(892) production in pp and π+p interactions

A study is presented of the inclusive production cross sections of K∗±(892) vector mesons in pp interactions at 12 and 24 GeV/c and in π+p interactions at 16 GeV/c. The K∗± inclusive cross section is ∼0.9 mb for both pp at 24 GeV/c and π+p interactions at 16 GeV/c. For pp interactions, σ(K∗+) and σ(K∗−) are seen to rise with energy, showing a threshold behaviour. In both pp and π+p interactions, σ(K∗+) largely exceeds σ(K∗−) at these energies and this excess is interpreted as K∗+ production by beam and target fragmentations. The decays of K∗±0 yield ∼30% of the K0 observed in the final states. The pT2 dependence of both K∗+ and K∗− cross sections is described by an exponential with slope of ∼3.3 (GeV/c)−2. The longitudinal momentum spectra for K∗+ in 16 GeV/c π+p and 24 GeV/c pp interactions are similar in shape in the target hemisphere. The K∗− spectra are similar over the whole kinematic region when viewed in the quark c.m.s. and point to a central production mechanism. Comparing K∗+ and ρ0 production, striking similarities are found.

Inclusive strange particle production in π+p interactions at 16 GeV/c

The production of KS0, Λ and Λ is measured in π+p reactions at 16 GeV/c. The total strange particle cross section is found to be 4.0 ± 0.3 mb, about 20% of the inelastic cross section. Cross sections for single strange particles and for strange particle pairs are determined, both inclusively and as functions of the charged multiplicity. Relative production rates for different strange particle combinations are compared with the prediction of the isospin statistical model. Inclusive spectra for single particles are studied and it is found the KS0 are produced mostly in the forward hemisphere, most probably by fragmentation of the incident pion into KKπ. The Λ are mostly backwards, probably deriving from fragmentation of the proton into ΛK pairs. The Λ tend to be produced forwards, but evidence is found for central ΛΛ production. Distributions in rapidity of the Λ particles from π+p interactions are compared in terms of the factorisation hypothesis. Results are given on the Λ transversal polarisation.

Multiplicity cross sections for 100 GeV/c π−p interactions

Abstract Charged particle multiplicity cross sections for 100 GeV/ c π − p inelastic interactions are presented and compared with results at other energies. The results for multiplicities n ⪖ 4 show a consistent trend in their energy dependence. The two-prong cross section curve differs as it tends to flatten off at the higher energies. The zero-prong cross section values decrease steeply as p lab −1.1 . The results for n ⩾ 2 for π − p and pp reactions appear to lie on a “universal” curve if nσ n / σ inel is plotted against 〈 n 〉/ n . This “scaling” rule is equivalent to KNO scaling, but the plot suggested here is more useful in studying low multiplicities. An interpretation in terms of a two-component model and a possible extrapolation to higher energies are proposed.

Inclusive Δ++ production and a test of the triple regge limit

Abstract Results on the inclusive reaction π+ p→Δ++ X0 at 8, 16 and 23GeV/c are used for quantitative tests of the triple Regge formula. As predicted, the slopes ofthe missing mass (M) spectra at fixed t are independent of s. Furthermore the trajectory α(t) obtained from the s-iependence at fixed M appears consistent with that obtained from the M-dependence at fixed s. However, the pomeron intercept α (0) is found to depend on t, suggesting that no single triple Regge diagram dominates at the M and s values studied in this reaction. Provided such a t-dependence is allowed, a single term triple Regge formula gives a very satisfactory parametrisation of our data.

Prism plot analysis of the reaction π+p → pπ+πo at 16 GeV/c

Abstract A study of the reaction π + p → p π + π o at 16 GeV/ c incident momentum has been made using the prism plot analysis to reject background events arising from elastic and multineutral contaminations and to separate different reaction channels ( ϱ + p, g + p, Δ + π + , Δ ++ π o , π + (p π o ) DD ). Cross sections, invariant mass distributions and production and decay angular distributions are presented. For the channel corresponding to proton diffraction dissociation strong violation of both s - and t -channel helicity conservation is found for low values of the (p π o ) mass. We demonstrate that the prism plot method provides a better separation of background events than conventional methods using kinematic cuts.

The effect of resonance production on angular correlations

Abstract Angular correlations between pairs of secondary particles emitted in 4- and 6-prong events of π + p interactions at 16 GeV/ c are studied as functions of the effective mass M of the two particles involved. It is argued that this is superior to the usual technique of studying correlations as functions of Δy (the difference in the rapidities of two particles), because effects of different origins such as resonance production and Bose-Einstein interference, which all occur predominantly at Δy ≈ 0, are well separated when plotted in terms of the mass. It is shown that the angular correlations are strongly affected by the production of two-particle resonances such as ϱ 0 , f, and g mesons for ( π + π − ) pairs, and Δ ++ (1232) and Δ ++ (1890) isobars for the (p π + ) pairs. A variable D ( M ) is proposed, related to the difference in angular correlations of pairs of like and unlike charges, which is shown to be effective in enhancing resonance signals and could be useful also at higher energies.

Three- and four-pion angular correlations in high-multiplicity πp interactions

Abstract A new set of parameters is introduced to describe charge dependence of three- and four-pion correlations. An effect similar to the GGLP effect observed for pion pairs, but stronger, is found for three- and four-pion systems. This effect, however, can be interpreted as a reflection of the GGLP effect.