We perform a measurement of R(D()) for B → D()τντ using semileptonic tagging and τ decays to hadrons on the 429 fb-1 of data that BABAR collected at the Υ(4S) resonance. This is the first measurement of R(D()) using the specied reconstruction channels. Candidate selection was performed with supervised learning, where the training labels were obtained by solving an instance of subgraph isomorphism. The signal extraction was performed by solving an optimization problem whose objective function required the evaluation of kernel density estimates that were accelerated by a branch-and-bound algorithm as well as with a GPU. The training data for the density estimates were themselves the output of two classier scores. We present a 68% and 95% confidence regions of R(D()), which do not show enough evidence to reject the standard model prediction.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Porter, Frank C.}, } @phdthesis{10.7907/rep4-e059, author = {Tang, Hongxing}, title = {Semiconductor Magnetoelectronics for Spintronics and Suspended 2DEG for Mechanoelectronics}, school = {California Institute of Technology}, year = {2002}, doi = {10.7907/rep4-e059}, url = {https://resolver.caltech.edu/CaltechTHESIS:02032012-143137090}, abstract = {Part I of this thesis describes my experimental and theoretical efforts to understand spin injection into semiconductors. I present extensive discussions on the conditions required to achieve significant spin transfer from a ferromagnetic injector into a paramagnetic conductor. Theoretical calculations for ballistic spin-coupled transport are described. To circumvent conductivity mismatch that occurs for diffusive contacts between ferromagnetic metals and semiconductors, I designed and fabricated new spin injection devices that employ the recently discovered dilute semiconductor (Ga,Mn)As as a spin polarizer. Spin-coupled transport signals were observed in these novel devices.
In the course of this work, I discovered that bulk (Ga,Mn)As itself manifests what we have termed a “giant” planar Hall effect. This magnetoelectronic phenomenon arises from the strong, intrinsic spin-orbit interaction. This phenomenon offers new prospects for applications in magnetic sensors and storage media, extends the possibility of novel spintronic devices, and enables unprecedented, high resolution measurements of magnetic phenomena. By using the giant planar Hall effect, I have achieved a complete characterization of the magnetic properties of (Ga,Mn)As. This large effect also has enabled the first direct electrical measurements of the propagation of individual domain walls in microdevices. These experiments establish a new approach to the study of ferromagnetodynamics that does not require significant instrumentation. Individual domain walls can be monitored, trapped and manipulated in real time. By such techniques, I have been able to directly investigate the resistance ari sing from a single magnetic domain wall for the first time.
Part II describes my studies of the strain-dependent electrical properties of ballistic GaAs two-dimensional electron gases (2DEGs). I have developed techniques to realize freely suspended 2DEGs with moderately high mobility. These have been incorporated into novel GaAs nanoelectromechanical systems that yield high sensitivity for NEMS motion detection. They have also led to my discovery of a new, dipolar mechanism for electromechanical actuation. Suspended quantum dots have also been successfully fabricated using my newly developed freely-suspended 2DEG fabrication methods. These demonstrate pronounced charging effects, even at elevated temperature, and offer new prospects for observing electronic interactions with confined phonons.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Roukes, Michael Lee}, } @phdthesis{10.7907/KECQ-7R18, author = {Burgasser, Adam Jonathan}, title = {The Discovery and Characterization of Methane-bearing Brown Dwarfs and the Definition of the T Spectral Class}, school = {California Institute of Technology}, year = {2002}, doi = {10.7907/KECQ-7R18}, url = {https://resolver.caltech.edu/CaltechETD:etd-10162001-185319}, abstract = {
I present the discovery of 18 T dwarfs, brown dwarfs exhibiting CH4 absorption analogous to Gliese 229B, identified in the Two Micron All Sky Survey. Follow-up spectroscopic observations reveal the presence of strong H2O and CH4 bands in these objects, as well as broadened Na I and K I absorption in the red optical; fine lines of K I, Cs I, and Rb I; and FeH absorption at 9896 ® Three objects are analyzed in detail; the widely-separated companion brown dwarf Gliese 570D, the coolest known brown dwarf with Teff = 810+/-45 K; the active T dwarf 2MASS 1237+6526, whose unique and steady H alpha emission may be the result of Roche-lobe overflow accretion from a closely-separated companion; and 2MASS 0559-1404, the brightest T dwarf currently known, which appears to be overluminous but unresolved in HST images. The variation in spectral features amongst these objects and those identified by the Sloan Digital Sky Survey have been used to derive a near-infrared spectral classification scheme, tied to the observed strengths of H2O and CH4 bands, color ratios, and K-band spectral morphology. The grid of subclasses segregates the currently known population into seven distinct groups, ranging from T1 V to T8 V. I show that the possible presence of CH4 in the L7 V DENIS 0205-1159AB argues for few subtypes between the latest known L dwarfs and the earliest T dwarfs. One peculiar object, 2MASS 0937+2931, has a highly suppressed K-band peak, likely due to increased H2 opacity in a high-gravity or low-metallicity atmosphere. Examination of absolute brightness and effective temperature across the L/T transition indicates rapid evolution of spectral features, possibly linked to heterogenous cloud coverage as condensibles rain out of the photosphere. Finally, I have used the T dwarf search samples to constrain the substellar field mass function. Through rigorous analysis of selection biases and Monte Carlo simulations, I show that my results are consistent with a power-law mass function scaling as 0.5 [less than] alpha [less than] 1.0, consistent with young stellar cluster surveys but significantly less than current estimates in the field.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Janda, Kenneth C.}, } @phdthesis{10.7907/wmxe-ge51, author = {Jensen, John Steffen}, title = {Measurement of the Neutron (³He) Spin Structure Function at Low Q²: A Connection between the Bjorken and Drell-Hearn-Gerasimov Sum Rules}, school = {California Institute of Technology}, year = {2001}, doi = {10.7907/wmxe-ge51}, url = {https://resolver.caltech.edu/CaltechTHESIS:07142014-135205986}, abstract = {The spin dependent cross sections, σT1/2 and σT3/2 , and asymmetries, A∥ and A⊥ for 3He have been measured at the Jefferson Lab’s Hall A facility. The inclusive scattering process 3He(e,e)X was performed for initial beam energies ranging from 0.86 to 5.1 GeV, at a scattering angle of 15.5°. Data includes measurements from the quasielastic peak, resonance region, and the deep inelastic regime. An approximation for the extended Gerasimov-Drell-Hearn integral is presented at a 4-momentum transfer Q2 of 0.2-1.0 GeV2.
Also presented are results on the performance of the polarized 3He target. Polarization of 3He was achieved by the process of spin-exchange collisions with optically pumped rubidium vapor. The 3He polarization was monitored using the NMR technique of adiabatic fast passage (AFP). The average target polarization was approximately 35% and was determined to have a systematic uncertainty of roughly ±4% relative.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Hughes, Emlyn Willard}, } @phdthesis{10.7907/amrv-a028, author = {Mason, James Edward}, title = {Signal Extraction and Optical Design for an Advanced Gravitational Wave Interferometer}, school = {California Institute of Technology}, year = {2001}, doi = {10.7907/amrv-a028}, url = {https://resolver.caltech.edu/CaltechTHESIS:04302012-152752095}, abstract = {The LIGO project is two 4 km baseline interferometers which are currently being constructed in the quest to directly detect gravitational radiation. Concurrent with this effort is research aimed at increasing the strain sensitivity of the initial interferometers to 2.5 x 10^(-23)/√Hz. The optical configuration, which defines the detector gain and bandwidth, is one such area of research. Resonant sideband extraction (RSE) is the configuration which is proposed for advanced LIGO. RSE allows for much more freedom in the optimization of the detector response compared to the initial configuration.
The principle of RSE is examined in the context of a three mirror coupled cavity. The effect of optical losses on the design of an RSE interferometer is discussed. Two model optimizations of the interferometer design are done: one for binary inspiral sources and one for periodic sources at 1 kHz.
An optical heterodyne signal extraction scheme is proposed to sense the deviation of the mirrors away from their nominal positions, and to read out the gravitational wave signal. The scheme is applied to the two model interferometers previously designed, and its performance is analyzed for each case. Allowable residual deviations of the common mode degrees of freedom are also derived.
A tabletop prototype of an RSE interferometer has been constructed to demonstrate both the viability of the proposed signal extraction scheme and the tunability of the RSE interferometer. Good agreement on both counts is found between the measured experimental data and the modeled predictions.
The coupling of laser frequency and amplitude noise into the gravitational wave readout port is analyzed for the RSE configuration assuming the proposed gravitational wave signal readout scheme. Specifications for the allowable laser frequency and amplitude noise, as well as allowable residual deviations of the differential mode degrees of freedom, are derived for the two model interferometers.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Vogt, Rochus E. and Porter, Frank C.}, } @phdthesis{10.7907/6q1r-0m94, author = {Jones, Lawrence Aston}, title = {A measurement of the mass of the tau lepton}, school = {California Institute of Technology}, year = {1995}, doi = {10.7907/6q1r-0m94}, url = {https://resolver.caltech.edu/CaltechETD:etd-10102007-090831}, abstract = {
NOTE: Text or symbols not renderable in plain ASCII are indicated by […]. Abstract is included in .pdf document.
For a conventional charged lepton l under the Standard Model, the electronic branching ratio […], lifetime […], mass […], the dimensionless weak coupling constant […] and the W-boson mass […] are related by […] up to small radiative and electroweak corrections. This implies the following relationship among the above parameters for the […] and […] leptons: […]. In 1992, world averages for the above quantities yielded […], implying a 2.4 standard deviation disagreement with lepton universality.
A measurement of the […] production cross section in the region most sensitive to the […] mass–a few MeV around threshold–provides the opportunity to measure the r mass with greatly improved precision. This thesis presents such a measurement made using the Beijing Spectrometer at the Beijing Electron Positron Collider.
A search was conducted for threshold assuming a parameterized form for the […] cross section. After each search point a likelihood was generated using all the information from the search so far. This identified the energy where it would be most efficient to search next. The mass value is obtained from a fit to the energy dependence of the cross section. The measurement is independent of the […] mass.
A likelihood-driven search was carried out at BES based on […] events. The data has been re-analysed to take into account the additional decay modes […] , […], […], […], and […]. This new analysis yields […] MeV.
Using contemporary values for […] and […] and the result above, the ratio of the weak coupling constants becomes […], and lepton universality is supported.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Porter, Frank C.}, } @phdthesis{10.7907/XZPT-HV21, author = {Carico, David Paul}, title = {Properties of infrared-luminous galaxies, or, how I spent seven summer vacations}, school = {California Institute of Technology}, year = {1991}, doi = {10.7907/XZPT-HV21}, url = {https://resolver.caltech.edu/CaltechETD:etd-05162007-161518}, abstract = {NOTE: Text or symbols not renderable in plain ASCII are indicated by […]. Abstract is included in .pdf document. Galaxies selected from the IRAS database having unusually high 60 - 100µm luminosities are studied at wavelengths ranging from ~1 - 1000µm. It is found that these galaxies differ significantly from normal, optically-selected galaxies, not only in their far-infrared luminosities, but in their near-infrared properties as well. A substantial excess emission at near-infrared wavelengths is attributed to emission from hot dust, with temperatures ~500 - 1000 K. Furthermore, this hot dust emission is confined to the central nuclear regions, within characteristic scale sizes ~1 - 3 kpc. This suggests that the bulk of the infrared luminosity, and hence the processes responsible for the extreme activity in infrared-luminous galaxies, is highly localized about galaxy nuclei. High resolution images of a number of these nuclei reveals a high percentage of double-nucleus sources amongst the most luminous galaxies, giving evidence that galaxy-galaxy interactions play a significant role in the generation of high infrared luminosities. The distribution of the mass of, and luminosity from, dust in infrared-luminous galaxies is analyzed as a function of the temperature of the dust. It is found that, in galaxies for which the entire energy distribution is dominated by emission from dust heated to a steady-state, the mass of dust scales with steady-state temperature as […], where […] is typically in the range 6 - 6.5. Dust continues to contribute substantially to the total luminosity up to temperatures in excess of 300 K above the temperatures responsible for the peak in the infrared luminosity. At the lowest temperatures, however, it is very difficult to constrain the contribution to the observed emission: For the galaxies studied, the observations are consistent with models in which the amount of very cold dust ranges from essentially non-existent, to the dominant component of the total dust mass.}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Cowan, Eugene W. and Porter, Frank C. and Thorne, Kip S.}, }