Thesis: S.M., Massachusetts Institute of Technology, Department of Physics, 2010. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 67-69). / An ideal spin-% kagomé lattice has been a long sought material. This system is characterized by strong magnetic frustration and is a likely candidate for a spin-liquid ground state. The spin-liquid state was originally proposed to exist in the parent compounds of the high temperature superconducting cuprates as originally proposed by Anderson. However, the lack of ideal samples have hampered experimental tests of the theories. A few years ago, a kagomé lattice material called herbertsmithite (ZnCu3(OH)6Cl2) has been successfully synthesized and studied. Since then, many experiments have been performed which have produced a lot of new guidance for our theoretical understanding of this frustrated magnetic system. However, single crystals are crucial for further progress. We have successfully produced high quality single crystals ZnCu3(OH)6Cl2 . These crystals are large enough for measurements, such as x-ray diffraction, magnetism, heat capacity, neutron scattering, thermal conductivity, muon-scattering and optical measurement. In this thesis, I will summarize the current state of knowledge for herbertsmithite and its family, the single crystal growth technique, and characterization of the resulting samples. A discussion of further directions of growth and measurement is at the end. / by Tianheng Han. / S.M.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Physics, 2014. / 71 / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 119-123). / Results are presented on 5.1 fb- 1 of proton-proton collisions at a center of mass energy of 7 TeV and 19.7 fb- 1 at 8 TeV in a search for decays of the Standard Model (SM) Higgs boson to two Z bosons to four charged leptons. We observe a single excess above background expectation with a significance of 7.4 standard deviations at a mass of 125.6 ±0.4(stat) ±0.2(syst) GeV. This excess has a signal strength parameter ... We examine the transverse momentum spectrum of the new particle and find it to be consistent with the SM expectation, and also determine that the Standard Model JPC = 0++ is favored over the plausible alternative hypotheses. / by Duncan Ralph. / Ph. D.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Physics, 2016. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 185-190). / Elastic electron-proton scattering has long been the tool of choice for the study of the proton form factors, GE(Q 2 ) and GM(Q2 ), which describe the electric and magnetic distributions of the proton as a function of momentum transfer. Recent experiments, measuring the form factors from polarization observables in polarized elastic electron-proton scattering, have found values of the ratio GE(Q2 )/GM(Q2) at high Q2 that contradict the results from unpolarized measurements. A proposed explanation for this discrepancy is the unaccounted two-photon exchange radiative correction, which could affect the unpolarized measurements. As this effect is currently not possible to calculate in a model-independent way, the OLYMPUS experiment was designed to make a direct measurement of it by measuring the elastic positron-proton to electron-proton scattering cross section ratio. The experiment was run in 2012 at DESY using the BLAST spectrometer and the DORIS positron and electron beams at 2 GeV incident on a gaseous hydrogen target. To analyze the data, a careful reconstruction of the scattering events, detailed simulation of the experimental setup, and full radiative corrections to the measured cross sections were performed. Preliminary results for the experiment show a statistically significant two-photon exchange effect, increasing over the measurement range of 0.6 GeV2 < Q2 < 2.35 GeV2 . These preliminary results suggest that two-photon exchange could explain the GE(Q2)/Gm(Q2 ) puzzle. / by Rebecca Lynn Russell. / Ph. D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2005. / Includes bibliographical references (p. 155-164). / In this thesis, we propose and investigate the "Gapless Color-Flavor Locked" (gCFL) phase, a possible new phase of dense and cold quark matter. At high enough densities, quarks interact with each other and form pairs similarly to electrons in superconductors. This phenomenon in the case of quark matter is called Color Superconductivity. Color superconducting matter must be electrically and color neutral, because otherwise there are huge energy costs, due to the charges. At asymptotically high densities, equal numbers of up, down, and strange quarks make the system neutral, all the quarks pair, and the quark matter is in the Color-Flavor-Locked phase. At intermediate densities however, the strange quark mass changes the number densities of the quarks and this makes the CFL phase unstable. The gCFL phase emerges as a result of the strange quark mass effect and the neutrality conditions. The gCFL phase has gapless modes and non-zero electron density, unlike CFL. These new properties of gCFL have significant astrophysical implications. The interior of neutron stars might have densities at the regime where gCFL dominates. If this is the case, we argue that gCFL will change significantly the cooling of such a star, keeping it hot, even for late times. Also in this thesis we explore the rest of the phase diagram of neutral quark matter at high density as a function of temperature and strange quark mass. We investigate how zero temperature superconducting phases evolve if we heat the system. We derive the phase diagram of dense quark matter using a Nambu-Jona- Lasinio (NJL) model, that might be a good guide for understanding the QCD phase diagram. / by Christoforos N. Kouvaris. / Ph.D.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Physics, 2006. / Includes bibliographical references (leaf 49). / We use the composite fermion approach for theoretical studies of the Coulomb drag between two parallel layers of two-dimensional electron gases in the quantum Hall regime near Landau level filling fraction v = 1/2. Within the composite fermion approach, we use Boltzmann transport theory to determine the polarizability of the composite fermions. While this approach works at filling fraction v = 1/2, a straight-forward expansion of the solution of the Boltzmann equation around v = 1/2 results in spurious divergences that stem from inaccuracies in the expansion at long wavelength. We then attempt to find expressions for the polarizability that are more accurate in this long wavelength limit. The excitation spectrum of the system in the absence of scattering consists of a discrete spectrum of 6 function poles. We introduce tools to deal with such expressions, but we find that we cannot yield any exact results from this approach due to complications in determining the location of poles and the resulting residues. / by Nurit Baytch. / S.M.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Physics, 2013. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 71-74). / Dynamic nuclear polarization (DNP) is a valuable tool which can be used to enhance nuclear magnetic resonance (NMR) signal intensities in a variety of biological and materials science systems, by transferring polarization from unpaired electrons to nuclei. In this thesis, the mechanical design and radio frequency NMR circuit for a triple channel magic angle spinning (MAS) DNP NMR probe for operation at 5 Tesla are developed, and the construction of the probe is detailed. The probe carries out NMR in three frequency ranges, corresponding to the 1H, 1 3C, and 15N Larmor frequencies at 5 T, but can be tuned to other nuclei as well, in particular 2 H. A 1H cross effect DNP enhancement of 40 on 1 3C labeled urea, using 10 mM TOTAPOL, is reported after cross polarization to 13C. As of writing, the probe is undergoing further optimization to improve the enhancement. The dynamics and interactions of water molecules are studied in lanthanum magnesium nitrate hydrate (La 2Mg3 (NO 3 )12 24H 20) (LMN) using a variety of 2H and 170 NMR techniques. Variable temperature 2H spectra are studied to characterize water dynamics in LMN, and the 170 quadrupole interaction is studied in an attempt to resolve crystallographically distinct water sites. 170 MQMAS is performed. Gadolinium is explored as a polarizing agent for DNP enhanced NMR. LMN crystals doped with Gd are synthesized, with the goal of using the enhancement from DNP to allow further characterization of crystalline solids. Polarization transfer to 1H in LMN doped with 3% Gd through the solid effect at 5 T is observed, and an NMR enhancement of 2.5 is recorded at 85 K. Planned future work on 2H and 15N DNP in LMN, using the MAS DNP NMR probe described here, is outlined. / by Christopher Blake Wilson. / S.B.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Physics, 2000. / Includes bibliographical references (p. 89-90). / Many extensions of the standard model predict heavy metastable particles which may be modeled as solitons (skyrmions of the Higgs field), relating their particle number to a winding number. Previous work has shown that the electroweak interactions admit processes in which these solitons decay, violating standard model baryon number. We motivate the hypothesis that baryon-number-violating decay is a generic outcome of collisions between these heavy particles. We do so by exploring a 2+ 1 dimensional theory which also possesses metastable skyrmions. We use relaxation techniques to determine the size, shape and energy of static solitons in their ground state. These solitons could decay by quantum mechanical tunneling. Classically, they are metastable: only a finite excitation energy is required to induce their decay. We attempt to induce soliton decay in a classical simulation by colliding pairs of solitons. We analyze the collision of solitons with varying inherent stabilities and varying incident velocities and orientations. Our results suggest that winding-number violating decay is a generic outcome of collisions. All that is required is sufficient (not necessarily very large) incident velocity; no fine-tuning of initial conditions is required. / by Daniel D. Dwyer. / S.B.

Thesis (B.S.)--Massachusetts Institute of Technology, Dept. of Physics, 1996. / Includes bibliographical references (leaf 28). / by Michael B. Schulz. / B.S.

Massachusetts Institute of Technology. Dept. of Physics. Thesis. 1968. Ph.D. / Vita. / Bibliography: leaves 196-200. / Ph.D.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Physics, 1994. / Includes bibliographical references (leaves 65-66). / by Wen Hu. / M.S.