Nucleon Structure from Neutrino Interactions in an Iron Target with a Study of the Singlet Quark Distribution

Nucleon structure functions have been extracted from a large sample of neutrino and anti-neutrino inclusive charged-current events. These data were obtained over the period from June, 1979 through January, 1980, using the Lab E detector in the N30 dichromatic beam at Fermilab (experiment E616). The use of the narrow-band beam made possible flux normalized cross section and structure function measurements. Neutrinos were obtained from sign and momentum selected pions and kaons produced from 400GeV primary protons. Details of the methods used to monitor and determine properties of the secondary beam are provided. The flux of neutrinos at the detector was calculated from this knowledge. The Lab E detector performed the function of neutrino target, as well as measuring final state properties of the events. Hadron energy was measured using calorimetry. Spark chambers interspersed throughout the target and following toroidal spectrometer were used to sample the position of the outgoing muon. From these measurements, the muon angle and momentum could be determined. The procedure used for reconstructing physics variables from detector measurements is presented with estimates of systematic errors. The methods used to extract structure functions from the data are detailed. An analysis of sources of systematic error on these results is made. A comparison of our results for F2 is made with other measurements from both neutrino and charged lepton scattering. Differences in overall normalization and in the x dependence of the structure function are found. The mean square quark charge rule from the quark-parton model is confirmed at the 10% level. Quantum Chromodynamics (QCD) predicts a pattern of scaling violations in F2 which is observed in our results. This has been quantified by making fits to the data using numerical integration of the Altarelli-Parisi equations. The value of ΛMS, the QCD scale parameter, is found to be 340±100±60MeV with an additional uncertainty of ±50MeV due to the unknown form of the gluon distribution.