DUKE

Abstract

We calculated the thresholds for charged–current electron neutrino and antineutrino interactions for most of the stable isotopes. Looking at the isotopes with the lowest thresholds, we found that 181 Ta and 160 Gd are reasonable candidates for low–threshold neutrino detectors, with thresholds at 0 . 188 MeV and 0 . 105 MeV respectively. These materials are both metals, have relatively high natural abundance, and are not frequently found in conjunction with radioactive substances, making them potentially viable for this task. Using the SNOwGLoBES software library, we computed estimated cross sections and event rates for supernova fluxes in these two materials. When neutron stars in a low mass x-ray binary system collect matter from their H or He rich companion star, nuclear burning can occur on the high temperature and pressure surface. If a critical accretion rate is reached, it can cause the nuclear reactions to run away, resulting in an X-Ray Burst (XRB). By studying the sensitivity of XRB models to different nuclear reactions, we can help identify which are most important in the burst process. The stellar model used for this study was of an XRB in Modules for Experiments with Stellar Astrophysics (MESA) with a co-processed nuclear network. A single stellar model was rerun once for each nuclear reaction and its inverse in the network, varying its reaction rate by 100. The models with the greatest change indicate reactions that are key to XRB nucleosynthesis. Preliminary results identified 5 significant nuclear reactions. While the study is in its preliminary stage, it has proved capable of highlighting reactions that significantly affect XRB properties. Λ 0 hyperons can be produced from hadronization of a struck quark in Semi-Inclusive Deep In- elastic Scattering (SIDIS). This process is of interest because the Λ 0 hyperon polarization may be inferred from its self-analyzing weak decay. Such probes allow one to extract information about the polarization of the constituent quarks within the proton and provide a test of fundamental aspects of Quantum Chromodynamics (QCD). In this study, we generated SIDIS events using a Lund Monte Carlo and simulated the response of the CLAS12 detector at Jefferson Lab’s Continuous Electron Beam Accelerator Facility (CEBAF)using GEANT4 with different toroidal magnet field strengths and configurations (either inbending or outbending). We then processed events using the CLAS12 reconstruction framework to find the optimal configuration and maximize our reconstruction efficiency from the Λ 0 → π − + p + decay channel. For Λ 0 hyperons coming from a struck quark ( x F > 0 ), we obtained our best reconstruction efficiency in the low field outbending toroidal configuration. Nuclear data for photo-nuclear reactions is scarce. By using the activation technique, ( γ,n ) cross sections can be measured to a high precision. 169 Tm( n, 2 n ) is a common neutron monitor reaction, but there is no available data on its photo-nuclear counterpart, the 169 Tm( γ,n ) reaction. Measurement of this reaction would allow use of thulium as a standard γ -ray monitor. Thulium, tin, and gold samples were irradiated by monoenergetic γ rays provided by the High Intensity γ -ray Source (HI γ S), located at Duke University. The resulting activity was quantified using γ -ray spectroscopy with high purity germanium (HPGe) detectors. The data confirmed the literature half-lives of 196 Au, 123 m Sn, and 168 Tm as 6.16 d, 40.1 m, and 93.1 d, respectively. Cross sections were extracted for the 124 Sn( γ,n ) 123 m Sn and 169 Tm( γ,n ) 168 Tm reactions, representing the first measurements of these reactions. Tritium, a radioactive isotope of hydrogen, will be the basis of experiment P-02-13 at HI γ S. This study will utilize a tritium gas target to obtain cross-section measurements of two-and three-body photodisintegration of the triton in order to further understand nuclear structure and reactions, specifically three-nucleon interactions. In order to reduce loss of the radioactive gas, safety systems will be implemented including a tritium scrubber system. This system will work in conjunction with a copper-zinc catalyst in order to utilize the reduction of copper to continuously transform elemental tritium into T 2 O or HTO, allowing the tritiated water to be collected within a molecular sieve and safely disposed of. Reactions catalyzed by the CuZn bed were examined using a Residual Gas Analyzer at temperatures of 23 ◦ C to 200 ◦ C to measure isotope concentrations and compositions of the various gas streams that will flow through the scrubbing system during normal operation. Low-mass nuclear Compton scattering projects at HI γ S are focused on determining experimentally the static electric ( α E ) and magnetic ( β M ) dipole polarizabilities of neutrons. Building on past experiments, the next iteration will use a liquid 3 He target volume to offer a new nuclear structure for analysis. This project is centered around preparing for the upcoming experiments. A new epoxy-lined gas storage tank was commissioned and sealed for the 3 He gas containment system. Leakage rates were measured, and a residual gas analysis was performed. The sealed tank was shown to have a leak rate of < 2 . 0 × 10 7 mbar*L/sec and main contamination from water, nitrogen, and oxygen at levels that can be removed by internal systems. A computational model was constructed based on particle beam flux attenuation in scattering processes. Values of the contaminate 4 He level C 4 (along with the percentage uncertainty in this value p ( C 4 ) ), the percentage uncertainty in the cross section of the experimental scattering with 4 He p ( σ 4 ) , and the experimental runtime T were varied to determine impact on the percentage uncertainty in the scattering cross section with 3 He. Optimal values (against cost) of T and p ( σ 4 ) were found to be 200h and 10% respectively for C 4 less than 10% and p ( C 4 ) less than 25%. When a proton is placed into an external magnetic field, it will attempt to align its magnetic moment to that field. Then if that external magnetic field is suddenly turned off, the proton will start to precess around the only other magnetic field available, the Earth’s. The goal of this project was to get an instrument operational that would take advantage of this concept. It would be used to find the spin relaxation time ( T 2 ), a measure of the magnetic field gradients, of the sample. This would then be used to test the magnetization of other materials for a larger project. An Earth’s field nuclear magnetic resonance control box and sample coil were used along with a sample of water (our proton source) to produce a waveform from the precession of the water molecules. From that waveform we were able to calculate our T 2 value. After many setbacks and multiple trials, we were successful in operating the instrument to produce waveforms in the correct shape and scale, thus getting a T 2 value that was close to the established value. While more testing and calibration is still needed, the instrument is now working and can be used in future testing of the magnetization of materials. We are developing a pulsed and tunable Pelletron accelerator to provide measurements of bremsstrahlung energy loss for next generation neutron beta decay experiments. The development of our Pelletron system is the first step before any measurements are made. The goals of our project are to improve the performance of an N 2 purge and implement a suppressor electrode to reduce arcing, understand possible sources of coronal discharge loss, make a first detection of the electron beam, and develop a test beam line. These first steps were successful, greatly reducing charge loss and arcing, and confirming the production of over 250 keV electron beams. If the Higgs Boson is made of new constituent particles, it is likely that the top quark is also made of similar particles based on how strongly they couple. In this case, events with four top quarks would be produced in excess of predictions from current theories. The purpose of this project is to study top quark kinematics to determine how to distinguish between background and signal top decays based on top quark transverse momentum. We used MADGRAPH to generate Monte Carlo events where t and ¯ t decay to a bottom quark and a W boson, and the W bosons decay to q ¯ q . Our analysis shows that as the top quark’s transverse momentum increases, the distance between the top quark and its decays in the η − φ space decreases, where η is the pseudo-rapidity and φ is the azimuthal angle. This decrease in distance in the η − φ space as top transverse momentum increases demonstrates that the two high momentum tops in a four top process can be tagged primarily by using position. Searches for c ¯ c from Higgs/ Z decays have been done exclusively for the ground J/ψ state using leptonic decay modes. This project aims to tag excited c ¯ c states via hadronic decay modes. The study of c ¯ c is relevant to Higgs coupling with the charm quark. Excited energy states such as ψ (2 S ) and χ c 0 ,c 1 ,c 2 are of interest as we can follow their decays into J/ψ γ . Excited states of c ¯ c are produced via the standard Higgs/ Z production chain gg → H which creates c ¯ c by H → c ¯ cγ . The purpose of creating this tagging algorithm is to apply it to ATLAS data. The tagging is done using machine learning. Training data for the machine learning algorithm comes from Monte Carlo simulations of particle decays and simulations of interactions in ATLAS. Other Monte Carlo simulations are being tested to verify the stability of the algorithm. The accuracy for the fully-connected neural network trained on J/ψ , ψ (2 S ) , and quark/gluon background is 93%. This novel approach to c ¯ c tagging resulted in a production-ready tagger. Further study is being done using a convolution neural network for c ¯ c tagging. This project explored the possibility of using pileup events, the proton-proto