Search

The most commonly used, simple interaction models have not accurately described the nuclear effects on either neutrino-nucleus or anti-neutrino-nucleus interactions. Comparison of data collected by the MINERvA experiment and these models shows a discrepancy in the reconstructed hadronic energy distribution at momentum transfers below 0.8 GeV. Two nuclear model effects that were previously not modeled are possible culprits of this discrepancy. The first is known as random-phase-approximation and the second is the addition of a meson exchange current process, also known as two-particle two-hole due to its result in two particles leaving the nucleus with two holes left in their place. For the first time a neutron counting software algorithm has been created and used to compare the multiplicity and spatial distributions of neutrons between the simulation and data. There is localized sensitivity to the RPA and 2p2h effects and both help the simulation better describe the data. Additional systematic or model effects are present which cause the simulation to overproduce neutrons, and potential causes are discussed.

This analysis studies the reaction ep → e′p′ϕ in the kinematical range 1.6 ≤ Q² ≤ 3.8 GeV² and 2.0 ≤ W ≤ 3:0 GeV at CLAS. After successful signal identification, total and differential cross sections are measured and compared to the world data set. Comparisons are made to the predictions of the Jean-Marc Laget(JML) model based on Pomeron plus 2-gluon exchange. The overall scaling of the total cross section was determined to be 1/Q4.6±1.7 which is compatible within errors to the Vector Meson Dominance prediction of 1/Q⁴ as well as to the expected behavior of a quark and gluon exchange-dominated model described by Generalized Parton Distributions of 1/Q⁶. The differential cross section dσ/dφ was used to determine that the s-channel helicity conservation (SCHC) assumption is valid within the precision of the current data. SCHC leads to a simple expression for the decay angular distribution from which R, the ratio of the longitudinal to the transverse cross section, can be extracted. Under the assumption of SCHC, we determine R = 1.33 ± 0.18 at an average Q² of 2.21 GeV² which leads to a determination of the longitudinal cross section σL = 5.3 ± 1.3 nb for exclusive ϕ production.

We studied the reaction → ′′ with a 4.2 GeV incident electron beam in the region of the electroproduction variables Q² from 0.7 to 2.2 GeV² and W from 2.0 to 2.6 GeV. The data were taken and analyzed at the Thomas Jefferson National Accelerator Facility. For the first time, we observe the expected t-slope dependence on Q² and Δ in vector meson production. We find that the width of the forward -meson diffraction peak increases rapidly as the interaction time decreases below cΔ ≈ 1 fm. Within a simple optical model framework, the data show that meson has a smaller size than the . The measured cross-section dependence on Q² is in a good agreement with previous measurements and well-described by the phenomenological Pomeron-exchange model. Our cross-section data do not favor the standard Vector Meson Dominance and ̅-knockout model predictions. From the angular distribution of the decay → ⁺⁻, assuming the -channel helicity conservation, we extracted the longitudinal-to-transverse cross-section ratio, , and Vector Meson Dominance scaling parameter, ², which are consistent with the previous measurements and the model expectations.

Results are presented for a unified analysis of the reactions pp → pp, πd → πd and πd → pp over the center-of-mass energy interval from pion threshold to approximately 2.4 GeV. These results for πd → pp and πd elastic scattering are superior to previous VPI analyses of these reactions. In particular, the overall phase in πd → pp has now been determined. Comparisons and predictions are made with previous (separate and unified) analyses of this two-baryon system. Several partial wave amplitudes show resonance-like behavior in these reactions.

A search is made for nucleon decay via 23 channels having fully reconstructable two- and three-prong final states. Data are recorded with the Irvine-Michigan-Brookhaven 8 kton underground water Cherenkov calorimeter for 512 live days. The analysis technique selects events having invariant masses, residual momenta, and topological configurations consistent with those of the nucleon and its product mesons. The directions and energies of the individual tracks in the contained event sample are resolved. Particles are identified as showering or non-showering based upon their Cherenkov radiation patterns. The event sample is found to be consistent in all respects with that anticipated from atmospheric neutrino interactions. Although seven events pass all requirements for nucleon decay candidates, they are also individually consistent with being atmospheric neutrino background events. We report no evidence of a signal for nucleon decay. A background subtraction is performed, yielding 90% confidence level lower bounds on the nucleon partial lifetimes in the range 0.06-5. x 10('32) years. The latter 69 days of data are recorded with the detector in the first of two phases of light collection enhancement. This thesis documents the design, simulation, and development of the devices (waveshifter plates) which double the light collection in the first phase upgrade.