Enhancements observed in the two-proton invariant mass distribution in the pionless deuteron breakup at 3.3 GeV/c

A sample of “non-spectator” events in the pionless deuteron breakup at a 3.3 GeV/c momentum has been investigated by means of a 1 m HBC at the JINR, Dubna. The two-proton invariant mass spectrum in the charge exchange channel exhibits two enhancements for masses of 2,010 MeV/c² and 2,160 MeV/c². Theoretical calculations taking into account one-pion exchange diagrams and virtual pion absorption by the deuteron have been carried out. It has been shown that the enhancement atM _pp=2,010 MeV/c² can be explained if some kind of singularity near theN-N threshold is required. The observed maximum atM _pp=2,160 MeV/c² is caused mainly by intermediate Δ production and pion absorption on the deuteron.     

Antiproton-neutron interactions at 100 GeV/c

From an exposure of the 30-inch deuterium filled bubble chamber to a 100 GeV/c antiproton-enriched beam at FNAL, we have calculated the topological cross sections for antiproton-neutron interactions with three or more charged particles in the final state. A comparison of our data with pn data at the same momentum allows us to estimate the annihilation contribution to each multiplicity, and hence calculate the average value, and width, of the annihilation multiplicity distribution. Our results are consistent with those from $\text{p}\text{p}$ data at 100 GeV/c, but depart from the trend of lower-energy $\text{p}\text{p}$ data.     

Inelastic hadron-nucleus interactions at 20 and 37 GeV/c

The experiment studies charged particle production for π^?, K^?, and $\text{p}$ interactions on nuclei at 20 and 37 GeV/c at the CERN SPS. A non-magnetic detector, consisting of CsI(Tl) scintillation and lucite ?erenkov counters, distinguishes between fast particles, mainly pions, and slow particles, mainly nucleons, with a cut at velocity β ≈ 0.7. Angular distributions, multiplicity distributions and correlations of slow and fast particles were analysed. It is shown that the measurement of the correlations can provide a critical test for different theoretical models of the hadron-nucleus interaction. At the energies studied so far a systematic deviation from KNO scaling is observed. This gives further support to the “standard picture” of the hadron-nucleus interaction and it contrasts with predictions of the coherent-tube model. The regularity observed for the angular distribution of fast secondaries as a function of the number of slow particles can only be explained by combining features predicted by different models.     

Hyperon and multi-kaon production in K+p interactions at 4.3 GeV/c incident momentum

We present results of a study of hyperon and multikaon production in K⁺p. The data were obtained from a 7.37±0.18 event/μb exposure of the 30″ MURA-ANL hydrogen bubble chamber to a 4.27 GeV/c separated K⁺ beam. Cross-section results for 3, 4, 5, and 6-body hyperon and multi-kaon final states are presented. We observe production of φ(1019), K¹(892), and Y¹(1385), but find no evidence for a Y = 2, B = 0 exotic resonance in the KK invariant mass distributions. A study of the inclusive reaction K⁺p→Λ+ anything is also reported.     

Resonance production and clustering effects in reactions K−p → Λ0 + pions at an incident beam momentum 8.25 GeV/c

We have estimated cross sections for the production of resonances in the reactions K^?p → Λ⁰ + pions. The data have also been analysed by a method which examines event-to-event fluctuations. Within the framework of the simple parametrization of resonance production assumed, the contribution from the resonances is insufficient to explain the observed fluctuations in the longitudinal emission of the final-state particles. These features are well reproduced by an independent cluster emission model.     

K+ nucleon elastic scattering at 180° between 1.0 and 1.5 GeV/c incident momentum

We have measured the cross section at 180° for K⁺p and K⁺n elastic scattering in the momentum range 1.0 to 1.5 GeV/c. The K⁺n cross section was measured on deuterium and the K⁺p on hydrogen and deuterium. We were thus able to measure directly the difference between free nucleon (proton) scattering and bound nucleon (proton) scattering at large angles. This difference was found to be small and within our experimental accuracy the K⁺p(n) cross section should be equal to the K⁺p (free) cross section at 180°. We found no evidence for an s-channel resonance Z¹ in either the K⁺p or K⁺n system. A comparison of our data and those of other groups with theoretical predictions is given.     

A study of the proton momentum spectrum from deuteron fragmentation at 8.9 GeV/c and an estimate of admixture parameters for the six-quark state in the deuteron

The momentum spectrum of protons emitted at small angles in the stripping reaction d + ¹²C → p + X has been measured at a deuteron momentum of 8.9 GeV/c. The data are described in the framework of the Glauber-Sitenko theory using the hybrid model of the deuteron wave function which includes a six-quark state. The parameters of this state are determined. A shoulder in the spectrum has been observed in the proton momenta region which kinematically corresponds to the production of a dibaryon resonance with a mass from 2.0 to 2.2 GeV.     

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

The production of $\text{K}{}_{\mathrm{S}}{}^0\text{, Λ}\text{and}\text{Λ}$ 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 K_S⁰ are produced mostly in the forward hemisphere, most probably by fragmentation of the incident pion into $\text{K}\text{K}\text{π}$. The Λ are mostly backwards, probably deriving from fragmentation of the proton into ΛK pairs. The $\text{Λ}$ tend to be produced forwards, but evidence is found for central $\text{Λ}\text{Λ}$ 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.     

Search for charmed hadrons in neutral strange particle events in pp interactions at 19 GeV/c

A search for charmed hadrons has been made in proton-proton interactions at 19 GeV/c using events with one or two observed neutral strange particles. No evidence for charmed particles has been found. Upper limits for their production cross sections are presented.     

Coulomb dissociation of incident 16O at 4.5 GeV/c

Projectile multifragment breakup of ¹⁶O, ²C and ⁷Li at energies 3.0–4.5 A-GeV is studied by means of the Weizsäcker-Williams method. The fragmentation channels of the ¹⁶O projectile at 4.5 A-GeV are investigated and compared with that of ¹⁶O at 200 A-GeV. The events characterized by N _h=0 and the events due to both Coulomb and diffraction dissociation have been selected and analyzed as a function of impact parameter. Also, the dependence of the electromagnetic dissociation cross-section on incident energy and the charge of projectile and target is found.     

Momentum transfer distributions of some diffractive enhancements in K−p interactions at 14.3 GeV/c

We discuss the structure of the momentum transfer distributions for the diffractive dissociation processes p → nπ⁺, p → Δ⁺⁺π^? and $\text{K}{}^{\mathrm{?}}\text{→}\text{K}{}_{890}{}^{10}\text{π}{}^{\mathrm{?}}$. In the near-threshold mass region a clear break of slope is found around t′KK ～ 0.25 GeV² for the two baryonic channels, whereas no comparable structure is seen for the mesonic system. The $\text{K}\text{→}\text{K}{}^1\text{π}$ differential cross section exhibits a nearly exponential behaviour up to t′_pp ～ 0.6 GeV², falling over three orders of magnitude. The slope variations and breaks are strongly correlated both to the mass region considered and to the decay angle of the fragmentation system.     

Study of the low-mass diffractive system produced in pp collisions at 12 and 24 GeV/c

We present an analysis of the decay of the low-mass diffractive system X produced in the reaction pp → p + X at 12 and 24 GeV/c. The various decay channels of the system have been separated; the decay multiplicity distribution is investigated and compared with the expectations of a two-step picture of diffraction dissociation. A comparison of virtual $\text{P}$_p with on-shell γp and pp processes is discussed.     

Measurement of high momentum transfer π−p → π0n at 5.9 GeV/c

The differential cross section for π^?p → π⁰n has been measured in the t range 1.8 ? |t| ? 8.2 (GeV/c)² by a counter-spark chamber experiment detecting the neutron and both π⁰ decay photons. A broad minimum was found, centered at |t| = 5.2 (GeV/c)².     

Inclusive production of vector and tensor mesons in antiproton-proton annihilation and non-annihilation interactions at 9.1 GeV/c

Cross sections have been determined for the inclusive production of vector $\text{(?}{}^0\text{, ω,}\text{K}{}^1\text{)}$ and tensor (f, A₂^±) mesons in $\text{p}\text{p}$ reactions at 9.1 GeV/c for both annihilation and non-annihilation processes. Distributions in the Feynman variable x and transverse momentum squared, p_T², have been examined for the ?⁰, ω and f mesons. The slopes for p_T² appear to be exponential and decrease with increasing particle mass for both annihilation and non-annihilation reactions, furthermore the slopes have consistently higher values for non-annihilation reactions. Comparisons with other data indicate that the ratio ?⁰/π^? is independent of antiproton momentum in annihilation processes.     

Charge asymmetry at large pT in inelastic pp reactions at 22.4 GeV/c

Charge asymmetry in $\text{p}\text{p}$ reactions at 22.4 GeV/c is investigated as a function of transverse momentum in the c.m. rapidity interval |y¹| < 1. The charge asymmetries in the forward and backward directions are increasing with increasing transverse momentum. The increase seems to be present both in annihilation and non-annihilation processes.     

Cross sections of annihilation and inelastic final states for pp interactions at 9.1 GeV/c

Topological and channel cross sections are given for annihilation and inelastic final states produced in $\text{p}\text{p}$ interactions at 9.1 GeV/c. Cross sections for prominent resonances in specific channels and charged pion, ?⁰ and Δ⁺⁺ inclusive cross sections are also presented.     

First results on low momentum transfer elastic scattering at the CERN proton-antiproton collider

Proton-antiproton elastic scattering at a centre-of-mass energy of 540 GeV was measured in the four-momentum transfer range 0.05 < ?t < s.19 GeV². The t-distribution can be fitted by the exponential exp(b) with b=17.2±1.0 GeV^?2. This result indicates a rapid decrease of the width of the diffraction peak between ISR and Collider energies.     

A study of inclusive Ξ− production from K−p interactions at 4.2 GeV/c

A study of inclusive Ξ^? production from a high statistics K^?p experiment at 4.2 GeV/c has been made. The total Ξ^? production cross section is 157 ± 8 μb. Approximately 15% of the Ξ^? arise from decay of the Ξ¹⁰(1530) resonance. The polarization of the Ξ^? is found to be negative and is nearly equal in value to that of the Λ⁰ from the inclusive reaction K^? + p → Λ⁰ + anything. An analysis of the inclusive production of Ξ^? has been made in the framework of the triple-Reege formalism.     

s-and t-channel helicity conservation of pion induced nucleon diffraction dissociation at 3.9 GeV/c and the implications of a two-component model

A study of schannel and t-channel helicity conservation has been carried out on a prism plot separated sample of 3.9 GeV/cπ^±p → π (Nπ)_dd diffraction dissociation events. s-channel helicity conservation is found to be strongly violated while t-channel helicity conservation is found to be mildly violated. These results are similar to that found at 11.7 GeV/c. We explain these violations on the basis of a “two-component model” of which the first component is a single exchange amplitude. We postulate that this amplitude is the generalization of the pomeron exchange amplitude which may conserve s-channel helicity. The second component of the model is a double exchange mechanism which strongly violates s-channel helicity. The predictions of this model agree with the experimental data.