J. Gayler

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

Results are presented on the energy calibration of the H1 liquid argon calorimeter modules with electrons from a test beam in the energy range of 3.7 GeV to 80 GeV. The method to determine the calibration for the Hl experiment from these measurements by the use of detailed simulations is described . Various systematic checks of this calibration are given. The calorimeter response is uniform in space within ±1% and linear with energy within ±1%. An average energy resolution of about 11.5%/ E [GeV] is achieved .

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.

Beam tests and calibration of the H1 liquid argon calorimeter with electrons

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 All existing data on γvp total cross sections in the resonance region are fitted in the absolute value of the three-momentum transfers | q | independently for small bins of W in the range 1.11 ⩽ W ⩽ 1.99 GeV. The data are divided into three ranges of the polarization ϵ : ϵ ⩾ 0.9, 0.9 > ϵ > 0.6, ϵ ⩽ 0.6. Taking into account statistical and possible systematic errors, a comparison of the fits for different ranges of ϵ indicate that longitudinal contributions to the cross sections in the resonance region are in general small. In the range 1.3 2 GeV2 and above W = 1.6 GeV for q2 > 0.5 GeV2, up to 20% contribution of σl is possible.

Measurement of the deuteron structure function

The electroproduction of the Δ(1236) has been investigated through the π0 channel at a four-momentum transfer of 15 fm−2. Angles and momenta of the secondary electron and of the proton were measured in coincidence to obtain the differential cross section for the reaction ep→epπ0. The angular distribution for s- and p-waves of the outgoing pion and nucleon in their c.m. system was fitted to the cross sections. The resultant coefficients of the angular distributions are given as functions of the mass W of the pion nucleon system for 15 fm−2. In a small range of W around the resonance, the contributions of the resonant multipoles M1+, E1+ and S1+ to the cross section are also given. Further results with respect to non-resonant multipoles, as well as for momentum transfers of 25 and 40 fm−2, will be published later.

F^{d}_{2}

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.