Physics
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Item Cryogenic Design and Thermal Analysis of the CURIE CryoTrap(2022) Osborn, Rebecca Caroline; Koeth, Timothy W; Chemical Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The decay rates of electron capture (EC) radioisotopes, such as 7Be, are demonstrativelysusceptible to alteration with change to the electron orbital structure [1] [2] [3] [4]. The Cryogenic Ultra-high vacuum Radioactive Isotope Experiment (CURIE) Project aims to isolate the various charge states of the low-Z radioisotope 7Be stably to perform novel half-life measurements. To achieve this, the system must be cooled to 4K to reach extreme high vacuum (XHV) conditions in excess of 10E−15 mbar and to ensure single ion resolution detection. The cryogenic design which achieves this is presented here. The design consists of the actively cooled 45K radiation shield, and the 4K stage which houses the Penning trap. The 4K stage is brought to XHV and maintained at these pressures through the design of a rotary “cryovalve”. This thesis details the entire apparatus, the heat loads incident on both stages through simulation, and outlines an experimental method for testing the “cryovalve”.Item Partonic Contributions to the Proton Spin in Lattice QCD(2015) Zhao, Yong; Ji, Xiangdong; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)In Feynman's parton picture, the proton spin can be understood as sum of the contributions from the spin and orbital angular momentum of the quark and gluon partons. However, in gauge theories, there is no local gauge-invariant notion of the spin or orbital angular momentum of the gauge particles. It is shown that in the infinite momentum frame of the proton, the gluons can be equivalent to free radiation, which is analogous to the Weizsaecker-Williams approximation in electrodynamics, and therefore one can talk about gluon helicity and longitudinal orbital angular momentum. We will justify the physical meaning of the Jaffe-Manohar sum rule for the longitudinal proton spin which uses the free-field expression of the QCD angular momentum operator in the light-cone gauge. Furthermore, it is discovered that each term in the Jaffe-Manohar sum rule can be related to the matrix element of a gauge-invariant, but frame-dependent operator through a factorization formula in large-momentum effective field theory. This provides a new approach for the nonperturbative calculation of the proton spin content in lattice QCD, and can be applied to the other parton observables as well. We present all the matching coefficients for the proton spin sum rule and non-singlet quark distributions at one-loop order in perturbation theory. These results will be useful for a first direct lattice calculation of the corresponding parton properties, especially the gluon helicity and parton orbital angular momentum.