A high energy muon beam polarimeter for the SMC experiment at CERN is described, as is the analysis of the beam polarization. The polarization is determined using the shape of the energy spectrum of the positrons from the decay $\mu\sp{+}\rightarrow e\sp{+}\nu\sb{e}\bar\nu\sb\mu$ which is described by the Michel spectrum. The parent muon is tagged upstream of a field-free decay region and its momentum is measured. A 30 m long muon decay path is defined between a shower veto hodoscope which identifies the $\mu\sp{+}$ and a dipole analyzing magnet. The spectrometer includes the dipole magnet and several multi-wire proportional chambers which measure the momentum of the $e\sp{+}.$ Identification of decay positrons is based on the energy deposited in a lead glass calorimeter. Muon polarization can be determined with 60 hours of data-taking to a statistical accuracy of 0.03 and a systematic uncertainty of the same order. Hence the muon beam polarization of $\simeq-0.8$ is measured to 5% relative accuracy.

Experiment 683 at Fermilab Wide Band Photon Laboratory observed events via $\gamma\rm p\to$ jets during the 1991-1992 fixed target run. The present analysis attempted to observe the higher-twist subprocess in QCD using that data to measure the p$\sb{\perp}$ spectrum via a clustering algorithm tuned to optimize the distinctive topology of higher-twist events. Results indicate a substantial k$\sb{\perp}$ promotion effect at lower p$\sb{\perp}$ and a significant NLO contribution to the photoproduction.

The Spin Muon Collaboration (SMC) measures the spin dependent structure function $g\sb1$ of the proton and nentron by measuring the scattering asymmetry of polarized 200 GeV muons off polarized protons and deuterons. The structure functions enable tests of theoretical sum rules, and a measurement of the spin contribution of the quarks to the nucleon. The uncertainty of the muon beam polarization was a major source of error in preliminary measurements of proton structure functions. A muon polarimeter measuring the shape of the Michel spectrum of positrons from muon decay was built. In this polarimeter muons enter and are allowed to decay $(\mu\sp+ \to e\sp+\nu\sb{e}\bar\nu\sb{\mu})$ in a 35 meter length. The shape of the momentum spectrum of electrons is sensitive to the muon polarization. The decay positrons are momentum-analyzed and the measured spectrum is fit to the Michel formula to determine the polarization. A data sample with a $\mu\sp-$ beam was used to estimate the effects of background events in the spectrum. Careful analysis of the polarimeter data determined the polarization to within 3%. The muon polarization was found to be stable in time and to vary with muon momentum. This variation will be included in the structure function analysis. A second polarimeter measuring the scattering asymmetry of polarized muons off polarized electrons obtained consistent results. The two independent polarization measurements were combined to give a polarization of $-$0.778 $\pm$ 0.019 at 186.9 GeV. With the improved structure function measurements, the Bjorken sum rule was tested and confirmed. Assuming that the gluons are unpolarized, the contribution of the quarks to the nucleon spin was estimated to be 20%, and the strange quark sea negatively polarized.

A Time-of-Flight (TOF) detector is used to provide particle identification in BNL-AGS Experiment 896. It is also used to assist in tracking and as a fast trigger. Results are presented from simulations which optimized the dimensions and position of the TOF system. Rates for measuring daughters of certain strange neutral particles are given for several cuts. Based on these simulation results, TOF detectors were added to the experiment. The analysis of data from a 1997 heavy ion beam run and a 1997 secondary beam run are discussed. The best method to estimate the location of the minimum ionizing peak of the ADC distribution was found among several different methods. Two different methods to slew correct the TDC data are investigated. Effects of momentum variance and path length variance on the time resolution of one of the TOF detector slats are studied. Plans to improve the detector for the upcoming 1998 heavy ion beam run are also discussed.

According to Quantum Chromodynamics Theory, highly compressed and heated nuclear matter should undergo a phase transition to a new state, called the Quark Gluon Plasma. These extreme conditions can probably be created in the collisions of relativistic heavy ions. We are looking for signatures of the phase transition to QGP such as enhancement of the strangeness production rates and reduction of the collective nuclear flow. The results of the invariant differential cross sections measurements for $\Lambda$ hyperon and $\pi\sp-$ meson production via track reconstruction in the Time Projection Chambers experiment BNL-AGS-E891 are presented. Comparison of our experimental data on the differential particle multiplicities for $\Lambda$ and $\pi\sp-$ with the cascade models ARC and RQMD is given. The shapes of the particles spectra indicate the strong collective expansion of nuclear matter. We employ the three dimensional expansion picture in order to parametrize the observed particle spectra and extract the flow parameters together with the mean temperature of the particle gas after the nuclear fluid freeze-out.

We investigate and compare two field theoretical formalisms, namely, the former state-of-the-art but noncovariant Ruckl formula-based formalism developed by K. Haglin and C. Gale, and a more recent covariant formalism developed by P. Lichard, for lepton pair production via soft virtual bremsstrahlung in hadronic reactions. A quantitative study of the discrepancy between both formalisms with regard to rates and total yields of $e sp{+}e sp{-}$ and $ mu sp{+} mu sp{-}$ pair production from radiative pion and quark (antiquark) scattering in ultrarelativistic heavy-ion collisions is made. Dilepton production rates are calculated using the independent particle approximation from kinetic theory, and total dilepton yields are obtained by integrating these rates over the space-time evolution of the heavy-ion collision as dictated by Bjorken's longitudinal hydrodynamic model. All rates and total yields of $e sp{+}e sp{-}$ and $ mu sp{+} mu sp{-}$ pair production with invariant masses less than 300 MeV turn out to be overestimated in the Ruckl formula-based formalism.

In the present thesis, the properties of hadrons in a dense medium are studied. The collective excitations related to the propagation of scalar and vector mesons in dense nuclear matter are discussed in a relativistic mean field model. Finite temperature effects on the meson properties in nuclear matter are also considered. One of the main concerns of the present thesis is the evaluation of symmetry-breaking effects induced by the dense matter. Special emphasis is put on the study of scalar-vector meson mixing effect, a pure density-dependent effect forbidden in vacuum on account of the Lorentz symmetry. In this direction, a new symmetry-breaking effect---the rho-a 0 meson mixing---is revealed and studied in detail along with a similar effect induced by the o-sigma mixing. The possibility of a new dilepton channel, arising from pi-eta collisions and mediated by rho-a 0 mixing, is further discussed in a relativistic kinetic model. The effects of o-sigma mixing on the amplitude of the dilepton production process from pion annihilation is also evaluated in a similar manner. The possibility of observing such symmetry-breaking effects in nucleus-nucleus collision experiments is investigated. For the space-time evolution of the matter formed during the collision, a thermal model is employed and the equation of state is determined from the interacting nuclear matter within the scope of a mean field model. We argue that such processes can be observed in the dilepton spectra at GSI/SIS energies, while they are not so evident at higher energy experiments performed at CERN/SPS.

Transverse energy and charged particle multiplicity produced in 14.6 GeV/c p + Al and p + Pb collisions have been studied using the E814 set-up at the BNL-AGS. Measurements of d$ sigma$/d$E sb{T}$, d$E sb{T}$/d$ eta$,d$ sigma$/d$N sb{c}$, and d$N sb{c}$/d$ eta$ are presented. From the present data the mean transverse energy per particle is obtained and it is compared to values observed in Si induced collisions at the same energy. In contrast to what is observed in nucleus-nucleus collisions, a very weak correlation is found between the transverse energy and the charged particle multiplicity. These results are compared to the predictions of various theoretical models used to describe heavy-ion collisions. The event generators RQMD and HIJET reproduce well the pseudorapidity distribution of both the transverse energy and charged particle multiplicity, whereas FRITIOF fails to reproduce the measured distributions. Contrary to what had been suggested previously in a Si + A study, the present study shows that the pseudorapidity dependence of charged particle multiplicity distributions do not follow KNO scaling.

A relativistic equation, known as the Kemmer-Duffin-Petiau (KDP) equation, for spin-0 particles is used to study low energy pion-nucleus scattering. This equation is linear and the optical potential is completely local in contrast to the quadratic Klein-Gordon equation which contains gradient terms in the p-wave part of the potential when applied to pion-nucleus scattering. Specifically, if we use an almost minimal coupling scheme (scalar and vector potentials), then this equation is equivalent to the Klein-Gordon equation with a Kisslinger potential and an effective Ericson-Ericson-Lorentz-Lorenz parameter $ lambda$ = 3. Experimentally, the $ lambda$ parameter is subject to uncertainty and no agreement has been reached about its value, though it must be greater than 1.6. The full KDP optical potential is obtained by taking the impulse terms from $ pi$-N scattering data and folding this with the nuclear density and then adding a true absorption contribution which is quadratic in the densities. It is shown that good agreement can be obtained for elastic scattering on light nuclei at low energies.

Electron arc therapy is the treatment modality for superficial tumors involving large curved surfaces. At the McGill University Health Centre, the characteristic angle beta concept was developed for the dosimetry and treatment planning of electron arc therapy. In this work, this concept was verified in dynamic mode with the new generation linac of Varian(TM), the Clinac-21 EX. / Radial PDDs were measured for beta angles varying from 60º--120º of electron arc beams with energies of 6 MeV, 9 MeV, and 12 MeV and 2-D isodose distributions of electron arc beams were studied as well. Dose penumbral regions exist at the beam start area and stop area, and the size of these regions is a function of the beam energy and the field width. When shielded with a tertiary collimator, the size of the penumbral regions and the dose levels in the penumbral regions were reduced significantly, and it is sufficient for the shielding to cover exactly the start field and the stop field of the arc beam in a clinical setting. / The dose rate of the electron arc beam was investigated. It was found that the dose rate at the depth of dose maximum linearly increased with the arc beam field width and was independent of the arc angle.