Polarization in charge exchange reaction π−+p→π0+n at 40 GeV/c for the 4-momentum transfer range 0<|t|<2 (GeV/c)2

The results on measuring polarization in charge exchange reaction π^?+p→π⁰+n at 40 GeV/c are presented for the 4-momentum transfer range from 0 up to 2 (GeV/c)². At |t|≦0.4 (GeV/c)² the polarization has a positive sign. In the “crossover” region of π^± elastic scattering a possible minimum in the polarization behaviour has been seen for the first time. the polarization is zero within the statistical accuracy near this point. In the “deep” region of the charge-exchange differential cross-section the polarization has a negative sign. The presented data are not in agreement with the modern theoretical models.     

Slow proton andΔ ++ production inK + p interactions at 70 GeV/c

The inclusive inelastic processesK ⁺ p→pX ⁺ andK ⁺ p→Δ ⁺⁺ X ⁰ are studied at an incident momentum of 70 GeV/c. The data comes from the Big European Bubble Chamber BEBC filled with hydrogen, exposed to an rf reparatedK ⁺ beam at the CERN SPS accelerator. The inclusive cross section for protons with laboratory momentump _LAB≦1.2 GeV/c is equal to (6.1±0.1) mb. InclusiveΔ ⁺⁺-production is studied for |t _{p, Δ}|<1.0(GeV/c)². Comparisons are made with otherK ⁺ p data and withpp data at 69 GeV/c. Evidence is found for Pomeron exchange at the beam vertex both for slow proton andΔ ⁺⁺-production as well as for absorptive pion exchange at the (p,Δ ⁺⁺) vertex.     

Elastic scattering and coherent single pion production in proton-helium interactions at 18.6 GeV/c

Proton-helium elastic scattering and coherent single-pion production have been studied at 18.6 GeV/c in the four-momentum transfer region (?0.06, ?0.17) GeV/c². The elastic t-distribution has a somewhat steeper slope than is predicted by the Glauber approximation. The invariant-mass distribution of the Nπ system agrees with the double Regge-pole model except at about 1.65 GeV/c² where an enhancement presumably due to N¹ resonances is seen. The model also predicts the correct magnitude of the slope for nπ⁺α events. By using our cross sections at t′ = ?0.06 (GeV/c)² where the impulse approximation should be valid, the isospin-zero exchange elementary cross section for the nπ⁺ production is evaluated. The inelastic angular distributions are consistent with several spinparity states contributing at all Nπ masses.     

Predictions of QCD fragmentation models ine + e − annihilation up to\sqrt s = 200 GeV

Results on event and single particle characteristics are presented for the three most successful perturbative QCD+fragmentation models in the c.m. energy range 12.0≦W≦200 GeV. The models were optimised to describe the properties of the large sample of hadronic events obtained by TASSO atW=35 GeV. The energy evolution of the observables across the range spanned by the PETRA and PEP data, 12.0≦〈W〉≦41.5 GeV, is reasonably well described by all the models. However, for some quantities the predictions of the different models diverge at higher energies; distributions of observables are shown at c.m. energies of 93 and 200 GeV, where data are expected from thee ⁺ e ^? colliders currently under construction. The ability to describe simultaneously, with the same parameter values, hadronic event features both at PETRA/PEP and LEP/SLC energies will provide a severe test of the models. The effects of top quark production on the event properties are illustrated for a top mass of 60 GeV/c². Predictions are given for the rates of multijet events up toW=200 GeV, where ≧4-jet events dominate the cross section and will form a background to events containing heavy states which decay into hadron jets.     

Direct photon production from pions and protons at 200 GeV/c

Direct photon production has been studied by an experiment performed with the NA3 spectrometer at CERN, using incident negative and positive beams at 200 GeV/c interacting with an isoscalar Carbon target. Two different triggers have been used; one of them requires the photon conversion. The experiment is sensitive to direct photons produced with 3.0≦P _T ≦6 GeV/c and center-of-mass rapidity ?0.4≦y ^*≦1.2. Inclusive cross sections are given for incident π^± and protons, and compared with second order QCD predictions; finally an estimation of the gluon structure function of the nucleon is given.     

C-odd exchange in high energypp andp \bar p elastic diffraction

Following the arguments of QCD, a proposed model takes into account the significant difference ofpp andp \(\bar p\) elasticd σ/dt discovered at the ISR. An expression forC-odd exchange is discussed and comparison with data is made. Starting from the ISR energies, the model is shown to describe well the data in a wide range of transverse momenta 0≦?t≦10 (GeV/c)² (including the Coulomb-nuclear interference region). Several peculiar predictions of the model will be testable in the TeV energy range and beyond.     

Neutron-proton elastic scattering from 10 to 70 GeV/c

The neutron-proton elastic differential cross section has been measured for incident momenta between 10 and 70 GeV/c and for values of the momentum transfer squared between 0.1 and 2.8 (GeV/c)². The forward peak and the break at about ∣t∣ = 1 (GeV/c)² are very similar to corresponding pp data.     

Measurement of theΞ - p elastic cross section at 102 and 135 GeV/c

TheΞ ^- p differential elastic cross section has been measured in the SPS hyperon beam at 102 and 135 GeV/c. In the range 0.012, thet distributions are found to be compatible with the formA exp(Bt) whereB is 7.7±0.4(GeV/c)^?2 at 102 GeV/c and 8.2 ±0.5(GeV/c)^?2 at 135 GeV/c. The corresponding total elastic cross sections areσ _el=4.9±0.7 mb andσ _el=5.6±0.9 mb, respectively. These results are compared with the predictions of phenomenological models.     

Antiproton-proton elastic scattering at 6.2 GeV/c

Antiproton-proton elastic scattering data at 6.2 GeV/c in the range 0.3 (GeV/c)² ? ?t ? 10.0 (GeV/c)² is presented. The experiment, using spark chambers and proportional chambers, was performed at the CERN Proton Synchroton.The dip at about ?t = 0.5 and the structure at about ?t = 2.2 (GeV/c)² are equally strong at 6.2 GeV/c as they are at 5.0 GeV/c. The differential cross sections around 90° c.m. are not very different at 5.0 GeV/c and at 6.2 GeV/c, whereas in the backward region there is a decrease of the order of one magnitude.     

Elastic pp scattering in the cern sps energy region

The pronounced dip-bump structure with a sharp minimum at |t| = 1.5 (GeV/c)², recently observed in elastic $\text{p}$p scattering at P_L = 50 GeV/c at the CERN SPS, is explained by the quark multiple scattering model with a realistic wavefunction for the proton and the antiproton. It is predicted that a second dip will appear around |t| = 7 (GeV/c)² at P_L = 50 GeV/ c and at higher energies.     

Single Regge pole model for large angle elasticp-p scattering at high energies

The elastic proton-proton angular distribution at large momentum transfers (?t?8 (GeV/c)²) and energies above 10 GeV laboratory momentum can be understood in the framework of a single Regge pole model.     

Investigation of inclusive production ofK 0 andK * (892)0 mesons inK + A interactions at 11.2 GeV

Inclusive production ofK ⁰ andK ^* (892)⁰ mesons inK ⁺ A-interactions (A=Be, Cu, Pb) at the energy 11.2 GeV has been investigated to study hadronisation of the leading \(\bar s\) -quark; the results are presented. Double differential cross sections d²σ/dx _f dp _t ² were measured in the region of incident particle fragmentation (0.4≦x _f ≦1,p _t ≦0.5 GeV/c). The experimental data obtained were analysed on the basis of the Lund model FRITIOF and a quark-gluon model that takes into account colour screening and hadron formation length effects. The experimental data confirm the picture of hadronisation of the leading \(\bar s\) -quark developed in the latter model.     

Four-momentum dependence of inelastic scattering of cosmic ray muons on nucleons

Data taken by a combination of a horizontal solid iron muon spectrograph and an interaction calorimeter have been analysed with respect to the process of inelasticμN-scattering. The muon momentum range covered by the spectrograph extended from 7 GeV/c≦p _μ ≦1000 GeV/c. Energy transfers to hadrons between 0.3 GeV≦v≦10 GeV were recorded. The results at low four-momentum transfers are consistent with precocious scaling.     

Fast proton production inπ ± Ne at 30 GeV/c

An isospin subtraction technique is used to derive distributions for π^± Ne→pX with an incident π momentum of 30 GeV/c, using precision bubble chamber measurements. Although final-state protons can only be identified by conventional techniques, i.e. ionization, forp _p ≦1 GeV/c, this technique allows us to statistically derive inclusive distributions for protons above 1 GeV/c. Combining these distributions with the identified proton distributions, the total inclusive proton distributions are compared with previously reported results at 10 GeV/c. The 10 and 30 GeV/c distributions are essentially identical, despite a factor of 1.7 increase inE ^CM between the two systems.     

Physics (and technique) of gas jet experiments

Recently gas jet targets have been used for the study of small momentum transfer p-p and p-d elastic and inelastic scattering. In these experiments, which were performed at Serpukhov in the USSR and at the Fermilab in the USA, the gas jet is introduced in the main ring of the accelerator. We review the techniques associated with these measurements and summarize the published results which cover 4-momentum transfers 0.001< |t|< 0.12 (GeV/c)^?2 and incident energies 8<E< 400 GeV. Elastic scattering data have yielded precise values for the slope of the nuclear scattering amplitude and for the ratio of the real to imaginary part as a function of energy. The implications of these data on the understanding of high energy hadronic interactions are discussed in some detail. We also present and discuss information on the diffractive dissociation of the proton to low mass states, obtained from inelastic scattering using the gas jet target.     

The real part of the πN diffraction amplitude

The real part of the invariant isospin evenπ N amplitudeC ⁺≡A′ ⁺ at ¦t¦?0.4 (GeV/c)² is determined from the condition thatC ⁺ fulfills the fixed-t dispersion relation, is compatible with this amplitude as reconstructed from phase shifts up to 1.5 GeV/c and leads to differential cross sections above 3 GeV/c in agreement with the experimental data.-The result for ReC ⁺/ImC ⁺ is remarkably large (?0.5 att=?0.3 (GeV/c)² and 6 GeV/c) and up to 20 GeV/c its uncertainty is comparable with that in the upper part of the phase shift region.-Even at 40 GeV/c ReC ⁺ is far from being asymptotic because of large energy independent low energy contributions. The deviations from our simple high energy ansatz (k>4GeV/c): ImC ⁺(k, t)～(k + m)exp(9t/2) are almost comparable with the experimental errors.     

Elastic and inelastic effects in proton-proton scattering from states of pure spin

Modified phase-shift analyses of pp scattering are presented at p_L = 1.25 and 1.66 GeV/c and shown to give large negative elastic effects in Δσ_L^tot. Using a combination of phase-shift analyses from low energies up to 1.66 GeV/c and simple models of both elastic (pp → pp) and inelastic (pp → NΔ) scattering we conclude that the measured behaviour of Δσ_T^tot is mostly inelastic, but the large negative value of Δσ_L^tot is predominantly elastic with fluctuations produced by inelastic effects. We find no evidence for a dibaryon resonance.     

Analysis of decay of πN resonances into Nππ channels

Couplings of πN resonances with masses between 1.65 and 1.97 GeV/c² to Δπ and ?N channels are determined using the scattering matrix elements resulting from inelastic partial-wave analyses of πN → Nππ. The inelastic amplitudes were derived using an isobar model with a π-exchange based high partial-wave input. These couplings are compared to those derived from an analysis of πN → Nππ without a high partial-wave input. Some (weak) evidence for coupling of the ?N channel to the P31(1910) resonance seen in elastic phase-shift analyses is found.     

Measurement of Large-angle πp elastic scattering at 5 GeV/c

The differential cross-section for 5 GeV/cπ⁺p and π⁻p elastic scattering have been measured in the c.m. angular region 27° < θ_cm < 130° corresponding to 0.5 < |t| < 7.8 (GeV/c)². Dips are observed in both reactions at −t = 2.8 and 4.8 (GeV/c)² where the cross-sections are approximately 0.1 μb/(GeV/c)².     

The polarised beam asymmetry in photoproduction of eta mesons from protons at 2.5 GeV and 3.0 GeV

Measurements of the polarised beam asymmetry parameter Σ for eta photoproduction from protons, have been carried out at incident energies of 2.5 GeV and 3.0 GeV, and for various t-values between ?0.2 (GeV/c)² and ?1.2 (GeV/c)². The values of Σ are close to +1 for values of |t| less than 0.7 (GeV/c)², showing that there can be little contribution from unnatural parity exchange in any Regge exchange model of the process, in disagreement with present theories. Differential cross sections for the process werre also measured, and are consistent with those from other experiments.