Eta and omega meson production in medium energy π+-p and K−p interactions

The production of η(550) and ω(780) mesons is studied in π^±p interactions at 16 GeV/c and K^?p interactions at 10 and 16 GeV/c. Cross sections for exclusive channels are presented, and for the π⁺p data differential cross sections are given for quasi-inclusive production where the η or ω is required to be accompanied by charged particles only. Close similarities are observed between η, ω and also ?⁰(770) production in terms of longitudinal and transverse variables. By a rough estimate, the η, ω and ?⁰ inclusive yields are found to be in the ratio 0.32 : 0.85 : 1, respectively, for 16 GeV/cπ⁺p collisions. For non-peripheral production we estimate this same ratio to be 0.34 : 0.9 : 1.     

S-wave structure in the Kπ system

We have analysed the Kπ spectrum (4 827 events) of the reaction K⁺n→K⁺π^?p at 9 GeV/c and find evidence of a broad S-wave enhancement which may be interpreted as a resonance. For production of Kπ masses above 890 GeV/c², we have assumed the dominance of pion exchange.     

Search for narrow four-baryon states

Highly excited (4.10?mass?5.35 GeV/c²) four-baryon resonances have been searched for in the missing-mass spectrum of the reaction π^?+⁴He→π^?+X at 5 GeV/c in the region of small four-momentum transfer (0.005?6t6?0.15 (GeV/c)²), where one of the decay products of the X is either proton or deuteron or triton. No resonance signal is seen in the mass spectrum of X. Within our limited acceptance, the cross section for the production of a narrow (Γ ～ 20 MeV/c²) four-baryon state with mass 4.9 GeV/c² is estimated to be smaller than ～ 100 nb.     

Analysis of the reaction K−p → K−π−π+p at 40 GeV/c

The reaction K^?p → K^?π^?π⁺p has been measured at 25 and 40 GeV/c at the Serpukhov Proton Accelerator. The production cross section at 25 and 40 GeV/c as a function of momentum transfer and Kππ mass is presented, and results of the partial-wave analysis of the Kππ system yielding information about Q(1300), K¹(1400) and L(1770) mesons are discussed.     

A new indication of diquarks in baryons

In data from 100 GeV/c \(\bar p\) d, 200 GeV/cpd and 200 GeV/cπ ^? d collisions there is evidence that the probability for a double-collisiondecreases slowly with increasing number of hadrons produced in the first projectile-nucleon collision. We argue that the presence of diquarks in baryons is the only plausible explanation of such an effect.     

Pair production of pions with symmetric momenta in the range 0.5⩽pT⩽2.0 GeV/c In 70 GeV p-p collisions

The invariant cross-section slope of the pp→π⁺π^?+X process as a function of p_T is found to have a break near 1 GeV/c. Fitting the cross section by a sum of two exponents gives the values of powers (12.3±0.9)(GeV/c)^?1 and (8.7±0.6)(GeV/c)^?1. The experimental points at p_T?1 GeV/c are significantly higher than predictions based on hard scattering models such as QCD and CIM.     

The inclusive reactions π+d → π− + anything and π+d → π−π− + anything at 6 and 24 GeV/c

Inclusive production of π^? mesons has been studied with 6 and 24 GeV/cπ⁺ beams interacting in deuterium bubble chambers. The energy dependence of the inclusive spectra is discussed. In comparisons with π⁺p inclusive interactions, we observe that projectile fragmentation is not independent of the nature of the target at 6 GeV/c. Cross sections and ratios of cross sections are presented. Two-particle correlations are found to be similar at both energies.     

Structure in momentum-transfer for (pπ−) systems produced in diffractive dissociation of neutrons on protons

The four-momentum transfer distribution of (pπ^?) systems produced in the neutron dissociation reaction n + p → (pπ^?) + p has substantial structure which depends strongly on the mass and on the angular decay properties of the produced (pπ^?) system. No significant energy dependence is observed in the data for incident neutrons in the momentum range between 50 GeV/c and 300 GeV/c. The results are compared with a Deck-type of model.     

Study of Ξ− and Ω− production from K−n and K−p interactions at 4.93 GeV/c

Cross sections, mass spectra, angular distributions and several other features of Ξ^? and Ω^? production from photons and neutrons in K^?d interactions at 4.93 GeV/c are presented. A five standard deviation peak is observed in ΞKπ mass spectra near 2.6 GeV/c². A sharp rise in the Ξ^? three- and four-body cross sections from K^?n interactions suggests direct-channel Σ¹ (3.0–3.5) formation.     

Single-spin asymmetry of inclusive π 0-meson production in 40-GeV pion interactions with a polarized target in the target-fragmentation region

Data on the single-spin asymmetry (A _N) of inclusive π ⁰ production in 40-GeV pion interactions with a polarized target, π^? + _↑→π⁰+X, are presented for the target-fragmentation region. The result is A _N=(?13.8±3.8)% for ?0.8<x _Fp _T<2 GeV/c and is compatible with zero for ?0.4<x _Fp _T<1.5 GeV/c. At a π ⁰ momentum of about 1.7 GeV/c in the c.m. frame, the asymmetry becomes nonzero both in the central and in the target-fragmentation region. The behavior of the asymmetry is similar to that observed in the beam-fragmentation region of the E-704 (FNAL, 200 GeV) and STAR (BNL, 20 TeV) experiments, which employed a polarized proton beam.     

Analysis of the reaction np → dπ+π− below 3.5 GeV/c

The reaction np → dπ⁺π^? was studied from threshold up to 3.5 GeV/c neutron beam momentum. Cross-section values for this reaction are evaluated as a function of the beam momentum. The deuteron production features and the enhancement observed in the dπ mass spectrum at 2.17 GeV are adequately described in terms of an OPE model and nucleon-nucleon final-state interactions.     

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.     

Gamma and π0 production by 4 GeV/cπ+p interactions

Inclusive data for the production of γ rays and π⁰ are presented from an experiment with a 4 GeV/cπ⁺ beam, using a track-sensitive target. The results are compared with data at other energies and with π⁺and π^? distributions.     

A partial-wave analysis of the neutral 3π system produced in the reaction π−p → (π+π−π0) n at 12 and 15 GeV/c

Data on the charge-exchange reaction π^?p → (π⁺π^?π⁰)n have been taken at beam momenta of 12 and 15 GeV/c, using the CERN Omega Multiparticle Spectrometer. A partial-wave analysis has been made of the (3π)⁰ system. We observe both natural and unnatural spin-parity production. The natural parity states can be identified with established resonances. In addition a natural spin-parity enhancement is observed at a mass of about 2 GeV/c² with J^P = 4⁺ preferred. We have called this effect the A₂¹ (2030). The unnatural spin-parity production found is consistent with reggeized Deck model predictions. No unambiguous A₁ or A₃ production is observed.     

Multiparticle emission in the interactions of hadrons with complex nuclei at incident momenta from 2 to 4 GeV/c

The charged secondary particles emitted in inelastic reactions of 4 GeV/cπ⁺ and π^? with the nuclei Be, Cu and Ta are thoroughly studied in their multiplicities, particle correlations and the distributions of kinematical variables, with the 1 m hydrogen bubble chamber into which the three nuclear target plates were installed. The numbers of charged secondaries emitted in the π^?(2.3 GeV/c), π⁺(2 GeV/c) and p(4 GeV/c) reactions are also investigated. From these data, characteristic features of the multiplication process of secondaries in nuclear matter are clarified. The experimental results are compared with the calculation of an intra-nuclear cascade model which takes into account the process of pion absorption by two-nucleon clusters in the nucleus. It is found that the experimental results on the properties of charged secondaries are consistently explained by the model. The model can also give an account of the experimental finding that fairly high momentum protons are emitted from the heavier nuclei into the backward hemisphere in the lab system.     

Measurement of the polarization in the forward peak of π−p→K0λ at 5 GeV/c

The π^?p→K⁰λ polarization has been measured at 5 GeV/c in the range 0<?t<1.4 (GeV/c)². The polarization is small for ?t?0.4 (GeV/c)², becoming negative at the higher values of ?t.     

Inclusive production of muon pairs and vector mesons in π−N collisions at momenta 27 and 40 GeV/c

Experimental results on the investigation of inclusive production of muon pairs and vector mesons (J/ψ, ?⁰(ω)) in π^?N collisions at 27 and 40 GeV/c momenta are presented.     

A critical discussion of a prism plot analysis of the four-body reaction π−p → π−pπ+π− at 3.93 GeV/c

A multidimensional analysis of the reaction π^?p → π^?pπ⁺π^? at 3.93 GeV/c is presented. Its results are compared to those obtained with conventional methods and its limitations are discussed.     

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.