The results of the HARP-CDP group on the comparison of Geant4 Monte Carlo predictions versus experimental data are discussed. It is shown that the problems observed by the group are caused by an incorrect implementation of old features at the programming level, and by a lack of the nucleon Fermi motion in the simulation of quasi-elastic scattering. These drawbacks are not due to the physical models used. They do not manifest themselves in the most important applications of the Geant4 toolkit.

The CHIPS (CHiral Invariant Phase Space) model is used for approximation of the Drell-Yan process in hadron-nucleon interactions. It is proved that the Drell-Yan cross-section at low p T 2 is a function of only x1 and x2 and does not evolve as a function of the squared mass of the lepton pair M2. The CHIPS model predicts that the Drell-Yan structure functions evolve as a function of p T 2 . This p T 2 evolution can be measured in experiments at RHIC and LHC.

Two-proton correlations at small relative momentum q were studied in the eA(3He,4He,C,Fe)-->e(')ppX reaction at E(0)=4.46 GeV using the CLAS detector at Jefferson Lab. The enhancement of the correlation function at small q was found to be in accordance with theoretical expectations. Sizes of the emission region were extracted, and proved to be dependent on A and on the proton momentum. The size of the two-proton emission region for He was measured in eA reactions for the first time.

Photonuclear interaction cross-sections from the GEANT4 database are approximated for all nuclei and all energies (from the hadron production threshold to about 40 TeV). The approximation methods in the giant-dipole resonance region, nucleon resonance region, and high-energy region are improved with respect to existing approximations. As an application of the approximation for photonuclear cross-sections, an improved method of calculating electronuclear cross-sections is developed. The interaction cross-section of virtual photons with nuclei at high Q(2) are approximated and a simple algorithm for describing the electronuclear reactions, including high-Q(2) scattering, is proposed.

Nuclear fragment production in photonuclear reactions below pion production threshold is implemented in the developed version of the new event generator, based on the CHIPS model, within the GEANT4 simulation toolkit. The spectra of secondary nucleons in the photonuclear process are compared with experimental data.

The angular distributions of secondary pions, protons, and deuterons originating from π − Pb interactions at an incident-pion momentum of 5 GeV/ c was determined in a new run of measurements relying on track reconstruction. While showing a decrease over a large angular interval with increasing emission angle, the yield of cumulative particles of each species was found to be anomalously large near the backward direction.

Experimental Hall B at Jefferson Laboratory houses the CEBAF Large Acceptance Spectrometer, the magnetic field of which is produced by a superconducting toroid. The six coils of this toroid divide the detector azimuthally into six sectors, each of which contains three large multi-layer drift chambers for tracking charged particles produced from a fixed target on the toroidal axis. Within the 18 drift chambers are a total of 35,148 individually instrumented hexagonal drift cells. The novel geometry of these chambers provides for good tracking resolution and efficiency, along with large acceptance. The design and construction challenges posed by these large-scale detectors are described, and detailed results are presented from in-beam measurements.

The pp pi system whose quantum numbers may assume values that are forbidden for the NN system is investigated for the first time in the reaction pp --> pp pi(-)pi(+). The experiment was performed at ITEP (Moscow). The invariant-mass distribution of the pp pi(-) system reveals a resonance enhancement at M approximate to 2.06 GeV with a width about 10 MeV. The observed enhancement may signal the formation of a resonance state predicted by quark models and required for interpreting data on low-energy pion-nucleus scattering accompanied by double charge exchange.

We briefly describe the drift chamber system for the CLAS detector at CEBAF, concentrating on the method which will be used to calibrate the drift velocity function, We identify key features of the function which should apply to any small-cell drift chamber geometry in which the cathode and anode surfaces are wires. Using these ideas, we describe a simple method to compensate for variations in the drift velocity function due to environmental changes.

We report the results of analysis of correlations of the product protons from inelastic eA collisions at smallQ2. The experimental data were measured by the ARGUS detector. The correlation effect at small relative momentaq (interference and final state interaction) is closely associated with the angular correlations due to momentum conservation. The examined correlations in eA collisions also show features similar to correlations in hA collisions.

Multiple proton and pion electroproduction from nuclei are studied. Final states including at least two protons produced by the interaction of 14.5 GeV electrons and positrons with light nuclei (mainly $^{12}\mathrm{C}$ and $^{16}\mathrm{O}$) have been measured, and compared with analogous data from $^{40}\mathrm{Ar}$. Scattered electrons and positrons were detected in the energy transfer range from 0.2 to 12.5 GeV, and four-momentum transfer squared range from 0.1 to 5.0 ${\mathrm{GeV}}^{2}$/${\mathit{c}}^{2}$. Phenomenological characteristics of the secondary hadron production cross sections such as temperature and velocity of the effective source of hadrons were found to be dependent on energy transfer to the nucleus and independent on the four-momentum transfer squared at energy transfers greater than 2 GeV.

The “Lambdameter” detector was specially designed for the study of cumulative Λ0-hyperons in the region of fragmentation of a target nucleus at rest in hadron-nucleus interactions under various initial conditions (energy and species of primary particle, atomic number of the target nucleus, emission angle of a Λ0-particle). The detector is used to measure the spectra of Λ0-particles in the kinetic energy range T from 40 to 150 MeV with a ≈ 5 MeV resolution, a relative systematic error of dσdT within the experiment of ⩽ 5%, and an absolute systematic error of ⩽ 10%. It also makes it possible to determine production cross sections (yields) with the same accuracy and polarization with an accuracy of better than 4%. Cumulative lambdas were detected at an angle of 90° in the lab system in the first run of the ITEP accelerator.

This experiment is designed to measure the properties of vector mesons in nuclear matter. At high baryon density the masses of vector mesons are predicted to change due to chiral symmetry restoration. The predicted downward shift of the vector meson masses is 10 to 20%. The photoproduction of vector mesons near threshold can be used to measure the masses and widths of vector mesons embedded in nuclear matter. It may also be possible to measure the mass shift for narrow vector mesons. Because o f the long decay length cτ , only a small fraction of these vector mesons will decay inside the nucleus. However, since the mass shift is predicted to be substantial relative to the natural width, these decays will be easier t o separate from vector mesons decaying outside of the nucleus. Detecting the leptonic decays of vector mesons is the only reliable way t o measure the mass shift of vector mesons because the hadronic decay in nuclear matter is always distrubed by final state interactions. The small cross sections for incident photons and for secondary interactions of the outgoing electrons with nuclear matter makes this reaction the ideal probe for testing the properties of the dense central region of the nucleus without significant input and output distortions. We plan to measure the A(γ , e + e - ) ' A reactions by identifying the coincident electron pairs in the CLAS detector. Energy deposition in the electromagnetic calorimeter, the Cerenkov counter signal, and transverse momentum compensation define clear cuts f or the separation of the e + e - events from the large hadronic background.