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The LHCb experiment at CERN is nearing completion and is expected to begin operation in 2008. It will make precision measurements of Charge-Parity in the B meson system. Two Ring Imaging Cherenkov detectors provide excellent charged particle recognition, particularly in their separation of kaons and pions. This thesis outlines the production and testing of Hybrid Photon Detectors, used to measure Cherenkov light in the Ring Imaging Cherenkov detectors. We also report an analysis of the rare decay Bos -> ØØ.

Two experiments were carried out to search for and identify the mechanism for two proton emission from the 7.77 MeV (Jπ = 2⁺, Γ = 76 ± 10keV) excited state in ¹⁴O. The experiments were performed at the Radioactive Ion Beams Facility at Louvain­la­Neuve, in Belgium, using a 45 MeV beam of radioactive ¹³N³⁺ ions on a [CH₂]n target to populate the state. The protons and other particles were detected using the Louvain­Edinburgh Detector Array, LEDA, a large area annular silicon strip detector. Control experiments with a ¹²C target and with a degraded beam energy were also made. Proton­proton coincidence measurements made in the commissioning run identified a two proton decay component. However, the large background (~90%) caused by evaporation protons from the fusion of ¹³N with ¹²C prevented an analysis of the decay mechanism. The follow up experiment utilised two LEDA detectors whereby the protons of interest would be stopped in the front detector with the back detector acting as a veto for high energy protons. Comparison of data with simulations for the decay mechanisms revealed the decay to be dominantly a sequential emission of two protons via the 2.37 MeV (Jπ = 1/2⁺, Γ = 33.7 ± 0.9 keV) state in ¹³N to the ground state in ¹²C. This decay mode has a measured partial width of 125 ± 20 eV which represents a 0.16% branching ratio. Theoretical predictions for this value give a width of 3 ± 1 keV which gives a spectroscopic factor of θ² = 0:04. Simulations using a model for ²He or diproton emission have resulted in an upper limit of 5% being set which corresponds to ~6 eV (95% confidence limit). Calculation for this width with a spectroscopic factor of unity give a value of 15 ± 5 eV. Hence an upper limit for the spectroscopic factor of θ² = 0:4 can be set which is above the value of 0.22 predicted by B.A. Brown.

The radioactive nucleus ¹³N (t½ = 10 min, Jπ = ½) contains one loosely bound proton (Sp = 1.94 MeV) which can be considered to be bound to a core of ¹²C. Taking advantage of the recent availability of beams of radioactive nuclei at Louvain-la-Neuve, Belgium, a beam of ¹³N has been used to investigate the transfer reaction ¹¹B(¹³N,¹²C)¹²C. Particle-γ coincidence data was taken, using the LEDA silicon strip array and BaF₂ modules, gating on the 15.11 MeV γ-decay from the T = 1 state in ¹²C*. Two final states, corresponding to ¹²Cgs + ¹²C*(15.11 MeV) and ¹²C*(4.44 MeV)+ ¹²C*(15.11 MeV) have been observed and angular distributions have been measured for both transitions at each of two beam energies, 29.5 MeV and 45 MeV. The results are discussed with special reference to the loosely bound nature of the valence proton in ¹³N; the transfer reaction has been modelled using a DWBA code, with the ¹³N ground state constructed as a mixture of states: a p½ proton bound to ¹²Cgs , or a p3/2 proton bound to ¹²C*₂₊ (4.44 MeV). Fits to the experimental data have been obtained using a very shallow set of optical potentials, which are found to be energy dependent. The agreement with experiment is good, with the exception of the ¹²C*(4.44)+¹²C*(15.11) transition at the lower beam energy, which is significantly underestimated by the calculations, suggesting a contribution from a different reaction mechanism.

A series of experiments were carried out at Argonne National Laboratory to search for examples of proton emission from ground and low­lying states in odd­Z nuclei at the proton drip­line. Recoils from fusion evaporation reactions were separated from other reaction products and dispersed according to their mass to charge ratio by the Fragment Mass Analyser, before being implanted into a double­sided silicon strip detector system, where their subsequent particle decays (proton or alpha) were measured. Proton emission from 157 Ta was measured for the first time, with a proton energy of 927 +/- 7 keV and a half­life 10.1 +/- 0.4 ms, This was assigned to a 3.4 +/- 1.2 % proton branch from the s 1/2 ground state on the basis of comparisons of measured half­lives with those calculated using barrier penetration codes. Two new proton lines were observed from the s 1/2 ground state and h 11/2 state in 161 Re, with energies of 1192 +/- 6 keV and 1315 +/- 7 keV and half­lives of 0.37 +/- 0.04 ms and 16 +/- 1 ms, respectively. The proton branching ratios from these states were measured at 100 +/- 7 % and 4.8 +/- 0.6 %, respectively. New proton lines were also measured from states in 171 Au and 167 Ir. Proton radioactivity from the ground state of the deformed nucleus 141 Ho was measured with an energy of 1169 +/- 8 keV and a half­life of 4.2 +/- 0.4 ms and was assigned to the 7/2- [532] Nilsson orbital on the basis of proton decay rate calculated using a deformed model of the nucleus. Recent theoretical calculations which incorporate the above results, are presen­ ted and discussed, along with a new model for calculating spectroscopic factors for spherical nuclei in the region 65 < Z < 81. The effect of a large deformation on proton decay rates is discussed with reference to 141 Ho.

The total transmission probability of an asymmetric Aharonov-Bohm ring with an embedded scattering center in both branches and a magnetic flux passing through its center has been investigated. The transmission is calculated from the overall scattering matrix for the ring structure determined by cascading scattering matrices without the symmetric conditions. In this model, by imposing scattering centers with different strengths to the upper and lower arms of the ring, the effects of coupling between the ring and the leads and the magnetic flux in the total transmission probability as a function of transmission phase have been observed. We find the following results from our model study: 1) in the strong coupling limit, there is no zero transmission; 2) with a constant coupling and scatterer in each branch, the transmission peaks get closer together and the transmission becomes smoother as the magnetic flux increases; and 3) in the weak coupling limit with a constant magnetic flux and elastic scattering in each arm, transmission resonances become sharper due to the localized states in the ring and the magnitude of transmission is enhanced at smaller transmission phases.For the case of a single or double barrier in one arm of the ring, the discrete energy levels of the double barrier well in one branch are controlled by the width of the well and continuous levels in the other branch are controlled by a single scattering barrier. We find a peculiar quantum transport through this system such as a symmetric Breit-Wigner (BW) and an asymmetric Fano transmission resonance. The transition from BW to Fano resonance occurs by tuning either the transmission phase of the electrons through a single barrier or the magnetic AB flux threading through the AB ring. The characteristics of the Fano line-shape resonance will be examined by the asymmetric parameter that is a measure of the degree of coupling between the discrete state and the continuum. / Department of Physics and Astronomy

Graduate

We present searches for the leptonic decays B + &rarr; &ell;+nu and the lepton flavor violating decays B0 &rarr; &ell;+/-tau &mnplus;, where &ell; = e, mu, with data collected by the BABAR experiment at SLAC. These searches utilize a technique in which we fully reconstruct the accompanying B&macr; in Upsilon(4S) &rarr; BB&macr; events, and look for a monoenergetic lepton in the signal B frame. The signal yield in the data is extracted from a fit to the signal lepton candidate momentum distribution in the signal B rest frame. Using a data sample of approximately 378 million BB&macr; pairs (342 fb-1), we find no evidence of signal in any of the decay modes. Branching fraction upper limits of B (B+ &rarr; e +nu) &lt; 5.2 x 10-6, B (B+ &rarr; mu+nu) &lt; 5.6 x 10-6, B (B0 &rarr; e +tau-) &lt; 2.8 x 10-5 and B (B0 &rarr; mu+tau -) &lt; 2.2 x 10-5, are obtained at the 90% confidence level.

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