Doctoral Dissertations
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Browsing Doctoral Dissertations by Author "Abashian, Alexander"
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- Bhabha scattering in e⁺e⁻ collisions at TRISTANLai, Anzhi (Virginia Tech, 1992-05-05)Bhabha scattering, the process of e⁺e⁻ → e⁺e⁻, has been studied at center-of-mass energies from 50 to 58 GeV with the AMY detector at the KEK e⁺e⁻ storage ring TRISTAN. The study is based on a data sample of 79.7 pb⁻¹ integrated luminosity. The differential cross section of Bhabha scattering has been measured. The measured cross section is found to agree fairly well with the Standard Model of the electroweak theory. The measured cross section is also compared with various four-fermion contact interaction models, and confidence level lower limits on the composite scale, A, are determined. In addition, the limits on VV model are converted to SM-break-down scales, which indicate the validity of the SM down to the distance of order ~ 10⁻¹⁷ cm and the electron charge radius of ~ 10⁻¹⁶ cm. Attempts are made in searching for an additional boson Z'. No clear signal of the existence of a Z' boson is found up to energy of ~160 GeV/c². The effect of transverse beam polarization on Bhabha scattering is also studied. The ϕ dependence of Bhabha events are fitted to the QED prediction and found to agree with the theory. However, no quantitative conclusion on polarization effect can be drawn based on current data sample, which does not provide enough statistics. More data is being accumulated and further study should be carried out.
- Electron-positron annihilation into photons at √s = 50 to 64 GeVSterner, Kevin L. (Virginia Tech, 1993)We present a study of e⁺e⁻ collisions where only photons are visible in the final state in data taken with the AMY detector at TRISTAN. Data are presented at CM energies from 50 to 64 GeV, with a total integrated luminosity of 189.1 pb⁻¹. Differential cross sections for e⁺e⁻ → γγ, γγγ are measured and compared to 𝛰(α³) QED. A search for electron compositeness through an e⁺e⁻ γγ contact interaction is conducted, and limits are presented. A search for the pair production of unstable photinos is also presented with limits. Finally, the result of a search for anomalous γγ production is presented, based upon energy scan data taken in December, 1992.
- Inclusive hadron production in electron-positron collisions with center-of-mass energies from 50 to 61.4 GeVMattson, Mark Edward (Virginia Tech, 1994)The K⁰, K*(892), p⁰(770) and Φ(1020) mesons along with the Λ° baryon have been observed in the TRISTAN energy region of 50 to 61.4 GeV using a data sample of 245.4 pb⁻¹. Their multiplicities and total cross sections are found and compared with the results from experiments at other center-of-mass energies. The multiplicities are compared with various theoretical and phenomenological models. The differential cross sections for the K⁰ and Λ⁰ are calculated and compared with other experiments. Measurements of the ratio of production of vector mesons to vector plus pseudoscalar mesons and the ratio of the production of excited ss̄ quark pairs to the production of excited uū plus dd̄ quark pairs are compared with other experiments along with the phenomenological predictions. The HERWIG Monte Carlo is tuned with regard to the inclusive production of hadrons.
- Measurement of the Michel Parameter Rho Using the MEGA Positron SpectrometerLee, Fei-sheng (Virginia Tech, 2001-04-03)This experiment attempts to measure the Michel parameter Rho in normal muon decay Mu to e nu_{e} nu_{mu} with a precision of 0.001. The Standard Model with pure V-A interaction gives 0.75 for this parameter. The world average value is 0.7518 +/- 0.0026. A deviation of the value of Rho from 0.75 will indicate new physics. The experiment, RHO, was carried out at the Los Alamos Meson Physics Facility (LAMPF) of Los Alamos National Laboratory (LANL) in New Mexico, USA, in 1993. The existing experimental set-up that was built for the MEGA experiment was used for the RHO measurement. The experiment was a collaboration of about 50 physicists from Los Alamos National Laboratory, Stanford University, Fermi National Accelerator Laboratory, Virginia Tech, Texas A University, Indiana University, Valparaiso University, University of Houston, University of Chicago and University of Virginia. The result of the experiment is in agreement with Standard Model. The precision of this measurement was dominated by systematic uncertainties due to the fact that the positron spectrometer used in the measurement was designed for another experiment. Thus, the data analysis here focused mainly on the determination of systematic errors.
- Measurement of the Ratio of Charged and Neutral 𝐵 Mesons in Υ (4𝑆) Events via Partial Reconstruction of the Semileptonic Decays 𝛣̅⁰⟶𝐷∗⁺ℓ⁻𝜈̅ℓ and 𝛣̅⁻⟶𝐷∗⁰ℓ𝜈̅ℓGodang, Romulus (Virginia Tech, 2000-08-23)The decays,
and 
are studied using data collected at the CLEO II detector at the Cornell Electron Storage Ring. Both decays are identified using a partial reconstruction method where the D* is detected only through a pion daughter from the decay 
. Because of the similarities in the analyses of the two modes, the ratio of the rates is measured in a way that is independent of the decay model, limited mainly by the uncertainty in the relative efficiency for detecting neutral and charged pions. This ratio is equivalent to the ratio of the product of production fraction and lifetime for charged and neutral B mesons, 
.
It is combined with measurements of the lifetime ratio to obtain the ratio of charged and neutral B meson production at the Y(4S) resonance, 
. - Search for the rare decay of the muon into a positron and a photonZhang, Yiding (Virginia Tech, 1995)This dissertation examines some of the more subjective aspects of individuals' experiences of isolation within the context of racialized and gendered work organizations. This research develops two constructs--institutional and social isolation--and attempts to ascertain the extent to which racial and gender groups experience isolation similarly. Other attitudes, such as intent to turnover, affective commitment, and alienation, are analyzed with respect to feelings of isolation for these groups. Finally, because current thinking has advocated the use of organizational interventions, such as mentoring programs, to ameliorate individuals' feelings of separateness within the organization, the relationship of mentoring to the aforementioned constructs was examined for its usefulness in understanding similarities and differences between these groups. This research extends previous work by providing support for new conceptualizations of social isolation and isolation. It extends work done by Nkomio and Cox (1990) and others who found that individuals who had achieved some objective measures of success in organizations, still did not feel, subjectively, as if they were a part of the organization. Thus, the use of these isolation constructs will expand our knowledge of organizational processes in examining groups based on gender and race/ethnicity. The results indicate that isolation docs exist on two dimensions: institutional isolation and social isolation. Asian-Americans have higher levels of institutional isolation, and African-Americans have higher levels of social isolation than any other group. Females experience higher levels of social isolation--but not institutional isolation--than males. There are some differences when race and gender are examined simultaneously in levels of experienced institutional and social isolation. Younger faculty feel more institutionally and socially isolated than older faculty. There is no significant effect of the presence of mentoring on institutional or social isolation; nor is there differential access to mentoring relationships by race. However, females enter mentoring relationships in greater proportions than males. There are also effects from cross-racial mentoring relationships. Finally, there are no significant differences, by race or gender, in the levels of affective organizational commitment or intent to turnover.
- Study of photon production in e + e - collisions at TristanHu, Kangping Karen (Virginia Tech, 1991-08-04)A study of photon production in multi-hadronic final states has been made at center-of-mass energies from 55 to 58 GeV with the AMY detector at the KEK e+e- storage ring TRISTAN.