C. Gössling

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

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 ).

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

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.

Production of charmonium 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.

Measurement of the proton structure function F2 in muon-hydrogen interactions at 120 and 280 GeV

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.

Transverse momentum of charged hadrons observed in deep inelastic muon scattering

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.

QCD analysis of the structure function F2 in muon nucleon scattering

Abstract A QCD analysis in leading and next to leading order of the structure function F 2 measured in deep inelastic muon nucleon scattering is presented. Taking into account several phenomenological uncertainties, including the gluon description and the charm contribution, fits to the data give values of the QCD scale parameter Λ LO in the range 7-–250 MeV. A consistent description of muon scattering and lower Q 2 electron scattering requires the presence of higher twist 1/ Q 2 contributions to the scale breaking which are then determined as a function of x from the data.

Forward produced protons and antiprotons in deep inelastic muon-proton scattering

Abstract A significant rate of forward proton and antiproton production has been observed in 120 and 280 GeV muon-proton scattering. The z and pT2 distributions are presented. The dependence of the normalized production cross section on the muon variables x and Q2 is studied.

Measurement of the Q2, x and W2 dependence of single hadron production in deep inelastic muon scattering

Abstract Measurements are presented of the distributions in scaled energy of the hadrons produced in high energy muon scattering. The observed dependence on x (non-factorisation) and Q 2 (scaling violation) is similar to that expected from next to leading order QCD calculations. These variations in the data can be equivalently represented by a dependence on the single variable W 2 .

Evidence for planar events and a forward double jet structure in deep inelastic Muon scattering

Abstract The final states of charged hadrons produced in 280 GeV μp scattering are analysed with respect to their planarity and jet structure. Distributions of p ⊥ 2 in and p ⊥ out 2 are presented. A two jet structure in the forward hemisphere is observed for events with high p ⊥ tracks are predicted by QCD models.

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 D0−D0 mixing. The data give upper limits of 12×10−36 cm2 for the cross section of beauty pair production by muons, and 20% for D0 ↔ D0 transitions due to mixing, both at 90% confidence level.