A. Edwards

The ratio of the nucleon structure functions

Abstract Using the data on deep inelastic muon scattering on iron and deuterium the ratio of the nucleon structure functions F 2 N ( Fe )/ F 2 N ( D ) is presented. The observed x -dependence of this ratio is in disagreement with existing theoretical predictions.

F^N_2

Abstract The x and Q 2 dependence of the single photon exchange cross section d 2 σ /d Q 2 d x and the proton structure functions F 2 ( x , Q 2 ) and R ( x , Q 2 ) have been measured in deep inelastic muon proton scattering in the region 0.02 x Q 2 2 . By comparing data at different incident muon energies R was found to have little kinematic dependence and an average value of −0.010 ± 0.037 (stat.) ± 0.102 (stat.). The observed deviations from scaling gave the value of Λ MS , the QCD mass scale parameter, to be 105 −45 +55 (stat.) −45 +85 (syst.) MeV. The fraction of the momentum of the nucleon carried by gluons was found to be ∼56% at Q 2 ∼22.5 GeV 2 . It is shown that to obtain a description of the data for F 2 ( x , Q 2 ) together with that measured in deep inelastic electron-proton scattering at lower Q 2 it is necessary to include additional higher twist contributions. The value of Λ MS remains unchanged with the inclusion of these contributions which were found to have an x -dependence of the form x 3 /(1 − x ).

for iron and deuterium

Abstract Dimuon and trimuon events produced by the interaction of 250 GeV muons in an iron target have been studied and are shown to originate predominantly from charm production. The data are used to measure the contribution of charm to the nucleon structure function F 2 . The cross sections for real photoproduction ( Q 2 =0) of charm in the current fragmentation region are derived as a function of photon energy and are found to be ∼0.6% of the total, hadronic photoproduction cross section in this energy range. The measured cross sections are found to be well represented by the photon-gluon fusion model. The charmed quark fragmentation function is obtained by using this model to fit the measured decay muon energy distribution and is found to be well represented by exp(1.6±1.6) Z . The data are used to study the momentum distribution of the gluons in the nucleon. An upper limit of 1.4% (90% confidence level) is set on the branching ratio D→ μν and a model-dependent upper limit on the branching ratio F→ μν is derived.

A Detailed Study of the Proton Structure Functions In Deep Inelastic Muon-proton Scattering

Abstract The European Muon Collaboration has built a large magnetic spectrometer system for deep inelastic muon scattering experiments at the CERN SPS muon beam. The general characteristics of the apparatus — composed of a target of either liquid hydrogen or deuterium, or iron plus scintillator, followed by a large magnet with wire chambers before and after it for precise angle and momentum measurement, a muon identifier, large trigger hodoscopes, and hadron identifiers — are explained and each part is described in some detail. The main features of the data-acquisition and apparatus-monitoring systems and of the off-line event reconstruction are given.

Production of charmed particles in 250 GeV μ+-iron interactions

The production of J/ϑ and ϑ′ has been measured in 250 GeV muon iron interactions. The measured total cross sections are σ(μN → μJ/ϑX)=0.74±0.14 nb and σ(μN → μϑ′X)=0.16 ± 0.07 nb. An upper limit on the cross section times branching ratio for ϒ production of BR · σ (μN → μϒX) < 5.2 × 10−38 cm2 (at 90% confidence level) is obtained. About half the J/ϑ cross section is found to have Z ⩾ 0.95 (where Z=E(J/ϑ/ν). The first-order photon-gluon fusion model agrees well with the measured Q2 and ν dependence of the J/ϑ data and is used to extract the gluon momentum distribution. However, higher order QCD effects are needed to explain the Z distribution of the J/ϑ and the observed broadening of the Pt2 distribution with decreasing Z. The decay angular distributions of the J/ϑ are found to be flat in the s-channel frame, but there is evidence for polarisation in the t-channel frame.

A large magnetic spectrometer system for high-energy muon physics

Abstract The deuteron structure function F 2 d has been measured in 280 GeV μ + d interactions. Existing measurements of F 2 p , made with the same apparatus, are used to calculate F 2 p − F 2 n and F 2 n F 2 p . The ratio F 2 n F 2 p has a similar x dependence to that of earlier measurements at lower Q 2 .

Production of charmonium in 250 GeV μ+-iron interactions

Abstract The proton structure function F2 has been measured in the range 2.5 ⪕ Q 2 ⪕ 170 GeV 2 and 0.03 ⪕ x ⪕ 0.65 . Scaling violation is clearly seen in the data. Results of fits to leading-order QCD are presented, together with values of the scale-breaking parameter λ.

Measurement of the deuteron structure function

Exclusive ϱ0 production has been measured in 120, 200 and 280 GeV muon-proton interactions at high Q2 (1 GeV2 < Q2 < 25 GeV2) and W (6 GeV < W < 19 GeV). The photoproduction cross section decreases as 1/Q4. A shallow t distribution, typical of a hard scattering process is observed and the ϱ0 is found to be dominantly in the helicity zero spin state. The ϱ0s are mainly produced by transverse photons and s-channel helicity conservation seems to be invalid. The data cannot be described by the vector meson dominance model. These data show that at high Q2 even exclusive ϱ0 muoproduction is a hard scattering process and that the soft hadron-like properties of the photon have disappeared.

F^{d}_{2}

Abstract Charm production has been studied through multimuon events produced in 250 GeV μ + -interactions. The measured dimuon cross section is in agreement with the photon gluon fusion model at low values of Bjorken x within statistical and systematic errors. At larger values of x Bi the data do not support the magnitude of intrinsic charm used to explain hadro-production of charm. Upper limits on the intrinsic charm content of the nucleon are derived from the data.

and a comparison of proton and neutron structure

Abstract The transverse momenta of charged hadrons produced in high energy muon-proton scattering have been studied. The average squared transverse momentum 〈 p 2 ⊥ 〉 shows a strong dependence on z = E h / v characteristic of intrinsic momentum effects and a significant rise as a function of s = W 2 . The W 2 , q 2 , x and z dependences of the data are compared with the predictions of a perturbative QCD model.