Theses and Dissertations from UMD
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Item Study of the decay B+ → K+ π0 at LHCb and mechanical development for the design of the Upstream Tracker(2018) Andrews, Jason Emory; Jawahery, Abolhassan; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The LHCb experiment at the Large Hadron Collider (LHC) is designed to measure the properties of particles containing charm (c) and bottom (b) quarks. This dissertation documents two major studies I have completed, one analyzing data collected by the LHCb detector, and another contributing to the design and development of an extensive upgrade to the detector. The pattern of CP asymmetry measurements of the B → K π family of decays deviates from expectations derived from the SM, a contradiction known as the “K π puzzle.” The present size of the experimental errors are such that more precise measurements in the B+ → K+ π0 decay channel are especially important. An analysis of the B+ → K+ π0 decay using data collected during Run 1 is performed. Despite low reconstruction and trigger efficiencies and enormous combinatorial backgrounds, a signal is found with a statistical significance of 3.7σ. This achievement has led to the creation of a dedicated B+ → K+ π0 trigger, and has inspired the creation of a number of dedicated triggers for decay modes with similar topologies. A preliminary analysis of data collected during Run 2 demonstrates that the new trigger is a major success, with excellent prospects for making the world’s best measurements in the B+ → K+ π0 decay channel using the entire Run 2 data set. Run 2 of the LHC will conclude at the end of 2018, and will be followed by Run 3, scheduled to begin in early 2021. In the interim, the LHCb detector will be upgraded to be read-out in real-time at 40 MHz, and to withstand the radiation damage associated with collecting 50 fb^(−1) of integrated luminosity by the conclusion of Run 4. A key part of this upgrade is the design and construction of a new silicon-strip tracking detector—the upstream tracker (UT). Regions at the periphery of the UT suffer from severe electrical and mechanical constraints, making a high-fidelity CAD model a critical element of the design process. The result is a mechanical integration solution that is entirely non-trivial, and which has had significant influences on the UT design. This solution and the constraints that influence it are shown in detail.Item Left-right symmetric model and its TeV-scale phenomenology(2017) Lee, Chang Hun; Mohapatra, Rabindra Nath; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The Standard Model of particle physics is a chiral theory with a broken parity symmetry, and the left-right symmetric model is an extension of the SM with the parity symmetry restored at high energies. Its extended particle content allows us not only to find the solution to the parity problem of the SM but also to solve the problem of understanding the neutrino masses via the seesaw mechanism. If the scale of parity restoration is in the few TeV range, we can expect new physics signals that are not present in the Standard Model in planned future experiments. We investigate the TeV-scale phenomenology of the various classes of left-right symmetric models, focusing on the charged lepton flavour violation, neutrinoless double beta decay, electric dipole moments of charged leptons, and leptogenesis.Item Minimal Left-Right Symmetric Model, Neutron Electric Dipole Moment and Dark Matter(2011) An, Haipeng; Ji, Xiangdong; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)In a class of other beyond-standard-model theories, CP-odd observables, such as the neutron electric dipole moment, receive significant contributions from flavorneutral P-odd and CP-odd four-quark operators. However, considerable uncertainties exist in the hadronic matrix elements of these operators strongly affecting the experimental constraints on CP-violating parameters in the theories. Here we study their hadronic matrix elements in combined chiral perturbation theory and nucleon models. We first classify the operators in chiral representations and present the leading-order QCD evolutions. We then match the four-quark operators to the corresponding ones in chiral hadronic theory, finding symmetry relations among the matrix elements. Although this makes lattice QCD calculations feasible, we choose to estimate the non-perturbative matching coefficients in simple quark models. We finally compare the results for the neutron electric dipole moment and P-odd and CP-odd pion-nucleon couplings with the previous studies using naive factorization and QCD sum rules. Our study shall provide valuable insights on the present hadronic physics uncertainties in these observables. Using an effective theory approach, the neutron electric dipole moment in the minimal left-right symmetric model with both explicit and spontaneous CP violations is recalculated systematically. Using the state-of-the-art hadronic matrix elements, nEDM as a function of right-handed W-boson mass and CP-violating parameters is obtained. The most stringent constraint yet on the left-right symmetric scale in the minimal version of left-right symmetric model is obtained to be MWR > (10 ± 3) TeV. Light WIMP (weakly interacting massive particle)-like signals were reported by dark matter direct detection experiments. WIMP candidates in this energy range can be constrained by various collider experiments. We show that colliders can impose strong constraints on models of low mass dark matter, in particular in the case that the direct detection interaction depends on the momentum of dark matter. We also find in the case of low mass dark matter, there are tensions between the observed relic abundance and collider constraints. Putting the constraints from collider physics, relic abundance and direct detection experiments, a large part of parameter space in different models can be ruled out.Item Search for physics beyond the Standard Model using measurements of CP violating asymmetries in rare B decays: B0->Ks pi0 and B0->Ks pi0 gamma(2005-12-05) Kovalskyi, Dmytro; Jawahery, Abolhassan; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This dissertation presents measurements of time-dependent CP violating asymmetries in the decays B0->KsPi0 and B0->KsPi0Gamma based on RUN 1-4 data collected with the BABAR detector at the Upsilon(4S) resonance operating at the PEP-II asymmetric e+e- collider at SLAC. It was found that the CP violating asymmetry parameters are S(KsPi0)=0.35+/-0.32+/-0.04, C(KsPi0)=0.06+/-0.18+/-0.03, S(KstarGamma)=-0.21+/-0.40+/-0.05, C(KstarGamma)=-0.40+/-0.23+/-0.03, S(KsPi0Gamma)=-0.9+/-1.0+/-0.2, C(KsPi0Gamma)=-1.0+/-0.5+/-0.2, where B0->KstarGamma decays correspond to the KsPi0 invariant mass interval of [0.8,1.0] GeV and B0->KsPi0Gamma of [1.1,1.8] GeV. All results are consistent with the Standard Model predictions.