F. Combley

AN INVESTIGATION OF THE SPIN STRUCTURE OF THE PROTON IN DEEP INELASTIC SCATTERING OF POLARISED MUONS ON POLARISED PROTONS

An investigation of the spin structure of the proton in deep inelastic scattering of polarised muons on polarised protons

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

A comprehensive description of the muon storage ring and its operation is given, and the final results of the experiment are presented and discussed. The anomalous magnetic moments of positive and negative muons are found to be aμ+ = 1165911(11) × 10−9 and aμ− = 1165937(12) × 10−9 giving an average value for muons of aμ = 1165924(8.5) × 10−9. The electric dipole moments were also measured with the results Dμ+= (8.6 ± 4.5) × 10−9e · cm and Dμ− = (0.8 ± 4.3) × 10−19e · cm. Under the assumption of the CPT theorem these yield a weighted average of Dμ = (3.7 ± 3.4) × 10−19e · cm. Finally the time transformation of special relativity is shown to be valid to (0.8 ± 0.7) × 10−3 at γ ≅ 29.3. All the errors quoted here are one standard deviation and contain both statistical and systematic effects.

for iron and deuterium

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 ).

Final report on the CERN muon storage ring including the anomalous magnetic moment and the electric dipole moment of the muon, and a direct test of relativistic time dilation

Measurement of the ratios of deep inelastic muon-nucleus cross sections on various nuclei compared to deuterium

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

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.

Measurement of the ratios of deep inelastic muon-nucleus cross sections on various nuclei compared to deuterium

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

Differential multiplicities of forward produced hadrons in deep inelastic muon scattering on nuclear targets have been compared with those from deuterium. The ratios are observed to increase towards unity as the virtual photon energy increases with no significant dependence on the other muon kinematic variables. The hadron transverse momentum distribution is observed to be broadened in nuclear targets. The dependence on the remaining hadron variables is investigated and the results are discussed in the framework of intranuclear interaction models and in the context of the EMC effect.

A large magnetic spectrometer system for high-energy muon physics

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.

Comparison of forward hadrons produced in muon interactions on nuclear targets and deuterium

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 .