Search for new physics using lepton flavor violating signatures in modern particle colliders.

Charged lepton flavor violation is a clear signal of new physics. Such decays are not allowed in the Standard Model but highly anticipated in a large class of new physics models. A direct search for lepton flavor violation in decays of the Higgs boson with the ATLAS detector at the LHC is presented here. The analysis is performed in the H → l tau channel, where the leading lepton (l) can be either an electron or a muon, and the tau lepton decays into an opposite flavored lighter lepton or via the hadronic decay channel. Published results of this search are presented in this thesis based on a data sample of proton-proton collisions collected by the ATLAS detector corresponding to an integrated luminosity of 36 inverse femtobarns (fb−1) at center-of-mass energy (√s) of 13 TeV during the 2015-2016 data-taking period. The analysis is found to be three times more sensitive than the previous analysis performed with 20 fb−1 of data collected at √s = 8 TeV during the 2012 data-taking period, and comparable to the one obtained by the CMS experiment with a similar-sized dataset at √s = 13 TeV during the 2015-2016 data-taking period. The direct search for lepton flavor violating decays of the Higgs boson obtained with the present analysis at the Large Hadron Collider is about twenty-five times more constraining than the indirect prediction. To complement my research goal of searching for new physics with lepton flavor violating signatures in final states containing the tau lepton, the generator level modeling of decays of the tau lepton decaying into Standard Model processes at the Belle II experiment at the world’s highest luminosity collider is also presented

Charged Particle Identification Using Calorimetry and Tracking at the Belle II Experiment

Particle identification (PID) is a critical procedure carried out in high energy physics experiments in search of new physics. When particles of matter (i.e., an electron) and antimatter (i.e., a positron) collide, new types of particles may form given certain conditions. Such particles may be classified as hadrons--which feel the strong nuclear force--and leptons--which do not. Identifying particles at the Belle II experiment is done by combining the measurement of energy deposited in the calorimeter with the measurement of track momentum in the tracker. In a tau lepton ($\tau$) decay sample, particles such as electrons, muons, and pions may be separated and identified using such measurements.https://ir.library.louisville.edu/uars/1031/thumbnail.jp

Validating the Belle2 PhysicsList in Geant4 v10.1.2

Since the start of software development at the Belle II experiment operating at the KEK national laboratory in Tsukuba, Japan, the simulation tool kit Geant4 has undergone several updates. As a member in the ongoing collaboration, the University of Louisville’s High Energy Physics (HEP) group is striving to validate newer versions of Geant4 to maximize improvements of physics performance.We have simulated the performance of a new physics list sub-module, the Belle2 PhysicsList , with improved modeling of hadronic shower shape and standard electromagnetic processes. Using a reconstruction-based selection procedure on tau-pair events decaying into a final state consisting ofe lectrons, photons, and pions, we have concluded that the Belle2 PhysicsList is consistent with the default present in Geant4 v10.1.2. Furthermore, using a sample of bb-bar events, we find that the Belle2 PhysicsList decreases CPU requirements by up to 25%https://ir.library.louisville.edu/uars/1028/thumbnail.jp

Crystal structure of the catalytic domain of HIV-1 restriction factor APOBEC3G in complex with ssDNA

The human APOBEC3G protein is a cytidine deaminase that generates cytidine to deoxy-uridine mutations in single-stranded DNA (ssDNA), and capable of restricting replication of HIV-1 by generating mutations in viral genome. The mechanism by which APOBEC3G specifically deaminates 5\u27-CC motifs has remained elusive since structural studies have been hampered due to apparently weak ssDNA binding of the catalytic domain of APOBEC3G. We overcame the problem by generating a highly active variant with higher ssDNA affinity. Here, we present the crystal structure of this variant complexed with a ssDNA substrate at 1.86 A resolution. This structure reveals atomic-level interactions by which APOBEC3G recognizes a functionally-relevant 5\u27-TCCCA sequence. This complex also reveals a key role of W211 in substrate recognition, implicating a similar recognition in activation-induced cytidine deaminase (AID) with a conserved tryptophan

Vinyl sulfone- and vinyl sulfoxide-modified tetrahydrofurans: a preliminary account of the enantiomeric synthesis of and diastereoselectivity of addition to new classes of Michael acceptors

Enantiomerically pure 2-hydroxymethylene substituted-2,5-dihydro-3-(arylsulfonyl)- and 2-hydroxymethylene substituted-2,5-dihydro-3-(arylsulfinyl)-furans have been prepared from easily accessible carbohydrate derivatives for the first time. The strategy for accessing both these sulfones and sulfoxides is more efficient than the methods reported so far for the synthesis of this type of compounds. Hydroxymethylene group is sufficient to impose diastereoselectivity on the addition of a wide range of nucleophiles to vinyl sulfone-modified tetrahydrofurans. The benzyl protected hydroxymethylene group also suppresses the influence of chirally pure sulfoxides as two diastereomeric vinyl sulfoxide-modified tetrahydrofurans afforded the Michael adducts with same configurations at C-3 and C-4; this has been established by oxidizing the adducts, which were found to be identical to the products obtained by adding the same nucleophiles to the corresponding vinyl sulfones. These highly reactive Michael acceptors may be considered as a new addition to the arsenals of synthetic chemists interested in the functionalization of tetrahydrofurans

Methyl-α‑d‑2-selenonyl Pent-2-enofuranoside: A Reactive Selenosugar for the Diversity Oriented Synthesis of Enantiomerically Pure Heterocycles, Carbocycles, and Isonucleosides

The construction of vinyl selenone on a furanoside led to a highly reactive synthetic intermediate methyl-α-d-2-selenonyl pent-2-enofuranoside composed of a masked aldehyde, an electron-deficient double bond along with an excellent leaving group. This new Michael acceptor on reactions with different nucleophiles afforded bicyclic azasugars, cyclopropanated carbohydrate, dihydrofuran- and dihydroisoxazole- substituted furanosides, and isonucleosides in moderate to good yields. Hydrolysis of the hemiacetal linkage of some of these modified carbohydrates afforded enantiopure aziridines, nitrocyclopropane, and dihydrofuran

Methyl-α‑d‑2-selenonyl Pent-2-enofuranoside: A Reactive Selenosugar for the Diversity Oriented Synthesis of Enantiomerically Pure Heterocycles, Carbocycles, and Isonucleosides

The construction of vinyl selenone on a furanoside led to a highly reactive synthetic intermediate methyl-α-d-2-selenonyl pent-2-enofuranoside composed of a masked aldehyde, an electron-deficient double bond along with an excellent leaving group. This new Michael acceptor on reactions with different nucleophiles afforded bicyclic azasugars, cyclopropanated carbohydrate, dihydrofuran- and dihydroisoxazole- substituted furanosides, and isonucleosides in moderate to good yields. Hydrolysis of the hemiacetal linkage of some of these modified carbohydrates afforded enantiopure aziridines, nitrocyclopropane, and dihydrofuran

Enantiopure 1,4,5-trisubstituted 1,2,3-triazoles from carbohydrates: applications of organoselenium chemistry

A wide range of stable vinyl selenone-modified furanosides has been synthesized for the first time. These 2π-partners undergo 1,3-dipolar cycloaddition reactions with a wide range of organic azides to afford enantiopure trisubstituted triazoles. Furanosyl rings opened up during triazole synthesis to generate polyfunctionalized molecules, ready to undergo further transformations. This strategy is one of the most convenient methods for the synthesis of enantiopure 1,4,5-trisubstituted 1,2,3-triazoles where the chiral components are attached to C-4 or C-5 position of triazole ring. These triazoles are formed in a regioselective manner, and several pairs of regioisomeric triazoles have also been synthesized. The approach affords densely functionalized triazoles, which are amenable to further modifications because of the presence of aldehyde and hydroxyl groups. This powerful and practical route adds to the arsenals of chemists and biologists interested in the synthesis and applications of triazoles

Enantiopure 1,4,5-Trisubstituted 1,2,3-Triazoles from Carbohydrates: Applications of Organoselenium Chemistry

A wide range of stable vinyl selenone-modified furanosides has been synthesized for the first time. These 2π-partners undergo 1,3-dipolar cycloaddition reactions with a wide range of organic azides to afford enantiopure trisubstituted triazoles. Furanosyl rings opened up during triazole synthesis to generate polyfunctionalized molecules, ready to undergo further transformations. This strategy is one of the most convenient methods for the synthesis of enantiopure 1,4,5-trisubstituted 1,2,3-triazoles where the chiral components are attached to C-4 or C-5 position of triazole ring. These triazoles are formed in a regioselective manner, and several pairs of regioisomeric triazoles have also been synthesized. The approach affords densely functionalized triazoles, which are amenable to further modifications because of the presence of aldehyde and hydroxyl groups. This powerful and practical route adds to the arsenals of chemists and biologists interested in the synthesis and applications of triazoles

Synthesis of vinyl sulfoxide-modified pent-2-enofuranosides and hex-2-enopyranosides and preliminary studies of their reactivity

Vinyl sulfoxide-modified pent-2-enofuranosides and hex-2-enopyranosides have been synthesized by using a controlled oxidation of C-3-deoxy-C-3-thioaryl furanosides and pyranosides, respectively, followed by mesylation of the C-2-hydroxyl group and elimination. In the furanose system, both diastereomers were formed in almost equal ratio, whereas the pyranose ring imposed diastereoselectivity of oxidation of the sulfur atom to produce only Ss isomers in good overall yields. Vinyl sulfoxide-modified 2-enofuranosides were treated with NaCH2NO2 to obtain C-2 branched chain sugars. Furanosyl sulfoxides yielded products that were similar to the adducts obtained by treatment of the corresponding sulfones with nitromethane. The sulfinyl group in thepyranosides influenced the diastereoselectivity of addition to produce adducts that differed from the products obtained from the corresponding vinyl sulfones under similar reaction conditions