Measurement of π−p → π0n at large momentum transfer

New results on a high statistics measurement of pion-nucleon charge exchange scattering at 40 GeV/c, extending in momentum transfer up to ?t = 1.8 (GeV/c)², are reported and compared with an optical impact parameter model, together with previous data for the reaction π^?p → ηn at the same energy. The imaginary part of the pole trajectory b₀(s) is determined from the slope of the tangent to the maxima of $\text{(?t)}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{d}\text{σ}\text{d}\text{t}$. The linear increase of Im b₀(s) with log s, which has been observed at low energies, continues up to 40 GeV/c.     

Inclusive processes at large transverse momenta

A general model for processes at large transverse momentum is constructed on the assumption that events with large transverse momentum particles posses short range correlations. It is shown that particle ratios and scaling properties are not sensitive to the detailed dynamics of large angle scattering, and also that the character of the inclusive spectrum can be understood in terms of (quasi-) elastic scattering.     

Particle composition at high transverse momenta in p-p-collisions in the central region at the CERN ISR

Preliminary measurements have been made at centre of mass energies √s = 31 and 44 GeV of the π, K and p production ratios at 90° for p_T between 2.0 and 3.5 GeV/c. The (K+p)/π ratio is given down to p_T = 1.4 GeV/c. No strong energy dependence is observed for these transverse momenta.     

Photoproduction of charged hadrons at large transverse momenta

A quantitative test of QCD from high energy photoproduction of large transverse momentum charged hadrons, using incident γ energies between 50 and 150 GeV, is presented. The inclusive hadron P₁ and P_t distributions show a clear excess over the VDM contribution. This excess is found to be in good agreement with second-order QCD calculations. This agreement does not depend critically on the choice of the gluon fragmentation function, and is observed over the large kinematical domain covered by this experiment.     

Production of charged kaons by e+e− collisions between √s = 3.6 and 5 GeV

The total cross section for K^± production in e⁺e^? collisions was measured for cms energies between 3.6 and 5 GeV and was found to increase by a factor of 2–3 from 3.6 to 4.1 GeV.     

Measurements of tau decay modes and a precise determination of the mass

The cross sections for e⁺e^? → e⁺(μ⁺ + non showering track + any photons have been measured for cm energies between 3.1 GeV and 5.2 GeV. We observe τ-pair production below the thresholdfor charm production and determine the τ mass to be 1.807 ± 0.020 GeV from a fit to the energy dependence of the cross section. The ration of the leptonic branching ratios B_μ/B_e = 0.92 ± 0.32 is consistent with eμ-universality. The following branching ratios are determined for a V-A coupling: $\text{B(τ → ν}{}_{\mathrm{\tau }}\text{e}\text{ν}\text{) = B(τ → ν}{}_{\mathrm{\tau }}\text{μ}\text{ν}\text{) = 0.182 + 0.028}$. B(τ → ν_τ + charged hadron + any photons) = 0.29 ± 0.11, B(τ → ν_τ + three or more charged hadrons + any photons) = 0.35 ± 0.11.     

Elliptic flow at large transverse momenta from quark coalescence

We show that hadronization via quark coalescence enhances hadron elliptic flow at large p(perpendicular) relative to that of partons at the same transverse momentum. Therefore, compared to earlier results based on covariant parton transport theory, more moderate initial parton densities dN/deta(b=0) approximately 1500-3000 can explain the differential elliptic flow v(2)(p(perpendicular)) data for Au+Au reactions at sqrt[s]=130 and 200A GeV from BNL RHIC. In addition, v(2)(p(perpendicular)) could saturate at about 50% higher values for baryons than for mesons. If strange quarks have weaker flow than light quarks, hadron v(2) at high p(perpendicular) decreases with relative strangeness content.     

Scaling distribution of large transverse momenta

We compute the structure function of large k_T scaling law in the framework of a multiperipheral or parton model. This function depends on two scaling variables. We show that recent NAL data are in perfect agreement with the same 1/k_T⁸ law observed at ISR. The observed apparent change of the scaling power is faked by the neglect of the dependence on one of the scaling variables.     

On the semileptonic decay of charmed hadrons

The semileptonic and leptonic decay modes of charmed hadrons produced in e⁺e^? collisions above 4 GeV in the cm have been investigated by selecting events with a single electron plus at least two charged tracks. The electron momentum spectrum peaks near 0.5 GeV/c with few events above 0.7 GeV/c. The spectrum excludes large rates for the decays $\text{D}\text{→}\text{e}\text{v}{}_{\mathrm{<mtext>e</mtext>}}$ and $\text{D}\text{→}\text{e}\text{v}{}_{\mathrm{<mtext>e</mtext>}}\text{π}$, but is compatible with $\text{D}\text{→}\text{e}\text{v}{}_{\mathrm{<mtext>e</mtext>}}\text{K}{}^1\text{(892)}$, $\text{D}\text{→}\text{e}\text{v}{}_{\mathrm{<mtext>e</mtext>}}\text{K}$ or a mixture of both. The semileptonic branching ratio is obtained both by comparing the inclusive electron cross section with the total cross section attributable to charm, and by studying the fraction of events containing a second electron. The semileptonic charm branching ratios obtained are 0.11 ± 0.03 and 0.16 ± 0.06 respectively. A single event with three electrons and hadrons is found, consistent with the estimated background. The 90% confidence upper limit for σ(e⁺e^? → 3e + hadrons) is 0.1 nb.     

Structure function relations at large transverse momenta in Lepton-pair production processes

Features of the lepton angular distributions due to hard parton sub-processes in lepton-pair production at relatively large q_⊥ are studied. Structure function relations which characterize these mechanisms are derived. Comparisons of these features with those derived from the Drell-Yan mechanism are made.     

Polarization in elastic eD-scattering at large transfer momenta and quark structure of the deuteron

It is shown that a small (5–8)% admixture of the six-quark component in the deuteron wave function which is to be introduced to describe elastic eD-scattering at large transfer momenta changes essentially the behaviour of the polarization tensorT ₂₀ and the ratioR of the vectorP _x to tensor polarizationP _xz compared to the models which do not take such admixtures into account. The corresponding experiments are emphasized to be important, which are aimed at testing the predictions of models including six-quark admixtures in the deuteron.     

Symmetric hadron pairs at large transverse momenta as a test of hard scattering models

The inclusive cross section of hadron pairs produced back-to-back with large transverse momenta is examined in the parton model. It is shown quantitatively that this cross section is determined directly by the hard scattering subprocesses, without being influenced by the internal momentum of the constituents, even for transverse momenta of the order of 2–3 GeV/c. The predictions of the phenomenological quark-quark scattering model and of the quantum chromodynamics model for the back-to-back cross section are compared with recent Fermi-lab data. Predictions are made for the corresponding cross section at ISR-energies.     

Quark-gluon collisions as the source of dimuon production at large transverse momenta in proton-nucleon scattering

The hard scattering of quarks and gluons calculated within QCD produces dimuons of large mass and large transverse momenta. The latter are compensated by the emission of a “quark jet” in the opposite direction. Antiproton beams are less effective than proton beam in producing dimuons with large transverse momenta. The transverse momenta of W and Z bosons produced in proton-nucleon scattering amount to a sizeable fraction of M_W(Z).     

Inclusive single-particle distributions and transverse momenta of forward produced charged hadrons in μp scattering at 470 GeV

Using data from the Fermilab fixed target experiment E665, general properties of forward produced charged hadrons in μp interactions at a primary muon energy of 470 GeV are investigated. The normalized inclusive singleparticle distributions for Feynman-x D(xF ) and for the transverse momentum D(p ² _t , xF ) are measured as a function of W and Q ². The dependence of the average transverse momentum squared 〈p ² _t〉 on xF , W and Q ² is studied. The increasing contribution from diffractive production as Q ² decreases leads to a reduction of the average charged hadron multiplicities at low (positive) xF and an enhancement at large xF , for Q ² ? 10 GeV². It also reduces 〈p ² _t〉 for Q2 ? 5 GeV2 and 0.4 ? xF < 1.0.     

A measurement of the transverse momenta of partons,and of jet fragmentation as a function of √s in p-p collisions

A large solid-angle apparatus consisting of a superconducting solenoid magnet, cylindrical drift chambers and two arrays of lead-glass counters was used to examine particles associated with a high transverse momentum trigger in p-p collisions with three √s values at the CERN ISR. The trigger was given by energy deposition in lead-glass arrays centred at 90°. The trigger transverse momentum range covered was 3 < $\text{p}{}_{\mathrm{<mtext>T\; trig</mtext>}}\text{< 11}\text{GeV}\text{c}$. Results are given for p_out for both individual charged particles, and also for the sum of charged particle momenta in the hemisphere opposite to the trigger. Mean values are then deduced for the parton transverse momentum k_T, and for the jet fragmentation momentum j_T.     

Rayleigh-like distribution of particle transverse momenta in collisions at high energies

The transverse momentum distributions of final-state particles produced in collisions at high en-ergies are studied by using a two-component Rayleigh-like distribution.This representation is based on Liu＇s multisource ideal gas model which describes protons and fragments in high energy nucleus-nucleus collisions.The calculated results are in good agreement with the experimental data of Au-Au,Cu-Cu,d-Au,and pp collisions at the relativistic heavy ion collider energies.The experimental particle momentum distributions of p-Be collisions at 6.4,12.3,and 17.5 GeV/c,as well as Au-Au collisions at 1.5 AGeV are well described by a model based on a single Rayleigh-like distribution of particle transverse momenta.