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xii, 118 p. : ill. (some col.) A print copy of this thesis is available through the UO Libraries. Search the library catalog for the location and call number. / This dissertation describes a search for the decays B 0 [arrow right] invisible and B 0 [arrow right] invisible+γ, where invisible refers to a final state consisting of long lived particles with a low cross-section for interaction with matter, leading to a low probability of detection in typical particle detectors. While the branching fractions for these decays predicted by the Standard Model are far below what could be feasably measured by current experiments, new physics such as right-handed neutrinos propagating in large extra space-time dimensions or light R-parity violating neutralinos in supersymmetry could greatly enhance the branching fractions. The decays are searched for in data corresponding to 423.5 fb -1 integrated luminosity produced at the Υ(4 S ) resonance collected with the BABAR detector at the PEP-II B factory, corresponding to 2.30 × 10 8 B 0 B¯ 0 pairs. Using those events that contain a hadronically reconstructed neutral B meson, evidence for the signal decays is sought in the remainder of the event. In (5.00 ± 0.02) × 10 5 events with a fully reconstructed neutral B meson, a total of 39 events consistent with the B 0 [arrow right] invisible decay mode are seen in data with an expected background of 28.5 ± 7.8(stat.)±9.2(syst.) events, and 8 events consistent with the B 0 [arrow right] invisible+γ decay mode are seen in data mode with an expected background of 14.1 ± 5.5(stat.)±8.1(syst.) events, from which upper limits of [Special characters omitted.] ( B 0 [arrow right] invisible) < 11.7 × 10 -5 and of [Special characters omitted.] ( B 0 [arrow right] invisible+γ) < 4.3 × 10 -5 at the 90% confidence level are obtained. / Adviser: David Strom

This thesis is devoted to studies of the proper decay-time resolution function and particle decay vertex reconstruction tools, their applicability and role in the studies of time-dependent CP violation at the Belle II experiment. A positive effect of beam spot constraints and new beam spot calibration on the vertex reconstruction precision is seen via MC/data comparison. The core part of the work focuses on studying universality of the time resolution function across nine different neutral and charged B-meson decay channels. The possibility to use a single form of this function for all studied channels is demon- strated and supported by the consistency between the lifetime values used for simulation and obtained as results of the decay time difference fit. 1

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Thèse numérisée par la Division de la gestion de documents et des archives de l'Université de Montréal.

In this thesis, we applied Light Cone QCD sum rules (LCSR) to several problems in meson physics. Semileptonic B-&gt / eta l v decays are important to get information on Cabibbo-Kobayashi-Maskawa (CKM) matrix elements. We calculated form factors of this decay in LCSR frame. Our results are confirmed by later studies and these similar studies had been used for enhancing result on b to u quark transition matrix element of CKM matrix by BaBar collaboration. We used LCSR method also for calculating coupling constant of radiative rho -&gt / eta photon decay since the analysis of the vector particle to pseudoscalar particle radiative decay with eta and eta&#039 / mesons in final state can provide insights to the long standing issue of the eta and eta&#039 / mixing. Our result g_{rho eta photon}=(1.4 &plusmn / 0.2) is very close to experimental value g_{ rho eta photon} = (1.42 &plusmn / 0.12). We also calculated magnetic moment of the rho meson in LCSR frame which is an important parameter since it is strongly related to internal structure of hadron. Our result 2.3 &plusmn / 0.5 in units of (e/2m_rho), is in better agreement with lattice QCD results than traditional QCD sum rules. Quark contents of light scalar mesons are still under debate and we analyzed phi -&gt / K K decays which is important for understanding the quark content of the f0 meson. Our final result is g_{phi KK} = 4.9 &plusmn / 0.8 which is in well agreement with existing experimental result g_{phi KK} = 4.8.

Thèse numérisée par la Division de la gestion de documents et des archives de l'Université de Montréal

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This work presents a precision determination of the mass difference of neutral and charged B mesons, m(B0) - m(B+). The measurement is based on a data sample of about 232 million B-meson pairs recorded with the BABAR detector at the e+e- storage-ring system PEP-II. In events of e+e- --&amp;gt; Upsilon(4S) --&amp;gt; B Bbar, B0 and B+ mesons are fully reconstructed in decays B+ --&amp;gt; J/psi K+ and B0 --&amp;gt; J/psi K*0 using the subsequent decays J/psi --&amp;gt; l+ l- and K*0 --&amp;gt; K+ pi- for the reconstruction of J/psi mesons and K*0 resonances, respectively. The determination of the mass difference from the measurement of the invariant B-meson masses suffers from detector-resolution effects. To reach the desired sensitivity, the B-meson momenta are measured in the center-of-mass system, the Upsilon(4S) rest frame. Since their energy is also known in the center-of-mass system, this method leads to the mass difference using the relativistic energy-momentum relation. For this purpose, three different fit methods are performed to the spectra of the B momenta. The obtained result is m(B0) - m(B+) = (+0.33 +- 0.05 +- 0.03) MeV/c^2, where the first error is statistical and the second estimates the systematic uncertainty of this measurement, which agrees well with the current world average. However, the combined error of this measurement is substantially smaller than that in the current world average, and the significance of m(B0) - m(B+) being non-zero has exceeded the 5 sigma level.