A search for free quarks in deep inelastic muon scattering

A search was made at the CERN SPS for long-lived fractionally charged particles produced in deep inelastic muon interactions on a Be target using the existing muon beam line as a spectrometer. No such particles were found, leading to upper limits for the production cross section of the order of 10^?36 cm² for 200 GeV incident muon momentum and quark masses below 9 GeV for the $\text{2}\text{3}$ charge and 15 GeV for $\text{1}\text{3}$ charge.     

Hadron production in 200 GeV μ-copper and μ-carbon deep inelastic interactions

The measurements of the z and p_T² distribution of hadrons produced in the interactions of 200 GeV muons with copper and carbon nuclei are shown in different x_Bj and virtual photon energy intervals. Effects of the jet scattering are seen at the lowest virtual photon energies while for energies above 70 GeV there is no evidence of these effects. Comparison with a theoretical model indicates that at high jet energies the parton fragmentation distance is greater than the nuclear radius and that the parton absorption cross section is less than 10 mb.     

ϱ0 production in deep inelastic μ-p interactions

Inclusive ?⁰ meson production has been measured in 120 GeV and 280 GeV muon-proton interactions. Distributions of z and p_T² are presented. Primary ?⁰ production is found to be equal to that of π⁰ production within errors.     

A study of trimuon events in 280 GeV muon interactions

In 280 GeV μ⁺ iron interactions the inelastic production of muon pairs has been observed in excess of QED processes. For energies greater than 20 GeV deposited in the target calorimeter the interactions are found to be mainly hadronic. Cross sections are presented for this process in the mass range 1?2.5 GeV/c² and in the kinematic regions covered by the apparatus acceptance. The data are in good agreement with a photon-gluon fusion model for charmed particle production.     

A determination of the fragmentation functions of u-quarks into charged pions

The fragmentation functions of u-quarks into positive and negative pions are determined from an analysis of identified pions produced in deep inelastic muon-deuterium scattering. The method adopted is not sensitive to the knowledge of the primary quark distribution functions. The fragmentation of u quarks to positive pions is found to fall less steeply in z than that to negative pions as expected in the quark parton model.     

Transverse momentum in semi-inclusive deep inelastic scattering

Within the framework of perturbative quantum chromodynamics we derive the evolution equations for transverse momentum dependent distributions and apply them to the case of semi-inclusive deep inelastic scattering. The evolution equations encode the perturbative component of transverse momentum generated by collinear parton branchings. The current fragmentation is described via transverse momentum dependent parton densities and fragmentation functions. Target fragmentation instead is described via fracture functions. We present, to leading logarithmic accuracy, the corresponding semi-inclusive deep inelastic scattering cross-section, which applies to the entire phase space of the detected hadron. Some phenomenological implications and further developments are briefly outlined.     

Observation of wrong-sign tri-muon events in 250 GeV muon-nucleon interactions

Two trimuon events of the type μ⁺N→μ⁺μ⁺μ⁺X and one μ⁺N→μ⁺μ^?μ^?X have been observed in 250 GeV μ⁺ -iron interactions. The expected rate from the decay of hadrons (charm, π, K) is about one event. Other processes that may contribute are both beauty production and charm production with $\text{D}{}^0\text{?}\text{D}{}^0$ mixing. The data give upper limits of 12×10^?36 cm² for the cross section of beauty pair production by muons, and 20% for $\text{D}{}^0\text{?}\text{D}{}^0$ transitions due to mixing, both at 90% confidence level.     

The strangeness-conserving effective weak interaction in the quark basis

Strong interaction corrections to the Glashow-Salam-Weinberg model of electroweak interaction are studied, for the up and down quarks only, to all orders of leading logarithms using renormalization-group techniques. The resulting quark effective weak hamiltonian is explicitly written out in a form convenient for obtaining matrix elements. The accuracy of this result is estimated by a comparison with finite, one-loop calculations of parity-violating parts of the interaction.     

Gluonic regge singularities and anomalous dimensions in QCD

The Regge calculus results on the perturbative pomeron are applied to deep inelastic scattering. Explicit expressions are given for the anomalous dimensions γ_GGⁿ and γ_GFⁿ at n ? 1 to the lowest order in α and all orders in α/(n ? 1).     

Measurement of J/ψ production in 280 GeV/cμ+ iron interactions

Virtual photoproduction of J/ψ mesons has been measured for 280 GeV muon iron interactions in an iron/scintillator calorimeter target. The J/ψ's were identified by their decay into muon pairs. 315 events were observed, about half of which were elastic. The t, Q² and v distributions of these elastic events are presented. The v dependence is measured between 40 and 180 Mev and compared with lower energy photoproduction results. The Q² dependence is compared with the predictions of the vector dominance model.     

Decay of PSI and upsilon into a lepton pair and gluons

We calculate the decay of a heavy vector quarkonium state into a lepton pair and two gluon jets, in lowest order QCD. We present branching ratios, and the lepton pair spectrum as a function of its invariant mass, and of the missing mass recoiling against it.     

Interaction of the K0-K0 system with external fields

The energy-dependence of the $\text{K}{}^0\text{-}\text{K}{}^0$ parameters Δm, τ_S and η_+? suggested by Fermilab regeneration data is analyzed phenomenologically. Such variations with energy can arise from the interaction of the kaons with an external field or medium, and several specific examples are studied in detail.     

Comment on the η→3π, η→2γ decay rates

The main decay modes of the eta meson are discussed with emphasis on large symmetry breaking effects induced by the mass of the strange quark. It is argued that these SU3-breaking effects amount to corrections involving factors of 2 to 3 in rate in the above decay modes. This is in line with the well-known large correction factors in the nonleptonic decays K_S →2π and D⁰→K⁺K^?, π⁺π^?.     

Transverse momentum of charmed quarks produced in deep inelastic neutrino scattering

QCD predictions on the transverse momentum of charmed quarks produced in neutrino production are presented and contrasted to similar predictions of the transverse momentum of jets in electroproduction. The effects of including charmed quark mass are also considered and turn out to be significant.     

Gluon jet in deep inelastic muon scattering

We study the quark and gluon final state in deep inelastic μ-scattering. For a hadron observed at sufficiently large angleθ _h with respect to the virtual photon direction, and sufficiently large energy fractionz _h , this final state dominates the cross-section. Moreover, at the same time, most events in this regime are due to the fragmentation of the quark. In such cases the position of the gluon in phase space is determined, the quark acting as a trigger for gluon jet detection. We demonstrate that in the rest frame of the final quark and gluon, the gluon is energetic and well separated from quark and target fragments. We study the boost from the lab to this frame, and give expressions for the most probable boost in terms ofθ _h andz _h . This study should lead to a convenient visualization of the gluon jet.     

Energy spectra of hadrons in deep inelastic scattering

We summarize the results of perturbative QCD analysis of particle distributions in deep inelastic lepton-hadron scattering (DIS). The role of coherent phenomena in the structure of the final state in DIS is emphasized.     

Photon-hadron interactions revisited in deep inelastic muon scattering

New results for deep inelastic muon scattering are reviewed. These include shadowing results tox _bj ∼10⁻⁵, nucleon structure functions measurements, the Gottfried sum rule and the use of deep inelastic scattering to obtain information on gluon distributions. The future of muon scattering in the HERA era is discussed.     

Shadowing in deep inelastic muon scattering from nuclear targets

Results are presented on the ratio of the inelastic muon-nucleus cross section per nucleon for carbon and calcium relative to that for deuterium. The measurements were made in the kinematic range of low x (0.003–0.1) and low Q² (0.3–3.2 GeV²) at an incident muon energy of 280 GeV. The calcium to deuterium ratio shows a significant x dependence which is interpreted as a shadowing effect. No strong Q² dependence is observed. This suggests that the effect is due at least partially to parton interactions within the nucleus.