Measurement of the direct CP asymmetry in b-->s+gamma via sum of exclusive B Meson decays using the BABAR detector

We perform a measurement of direct CP violation in b to s+gamma Acp, and the measurement of a difference between Acp for neutral B and charged B mesons, Delta A_{X_s\gamma}, using 429 inverse femtobarn of data recorded at the Upsilon(4S) resonance with the BABAR detector. B mesons are reconstructed from 16 exclusive final states. Particle identification is done using an algorithm based on Error Correcting Output Code with an exhaustive matrix. Background rejection and best candidate selection are done using two decision tree-based classifiers. We found $\acp = 1.73%+-1.93%+-1.02% and Delta A_X_sgamma = 4.97%+-3.90%+-1.45% where the uncertainties are statistical and systematic respectively. Based on the measured value of Delta A_X_sgamma, we determine a 90% confidence interval for Im C_8g/C_7gamma, where C_7gamma and C_8g are Wilson coefficients for New Physics amplitudes, at -1.64 < Im C_8g/C_7gamma < 6.52.

Experimental chemical physics of droplets and clusters

Time-of-flight measurements of energetic He atoms, field ionization of cryogenic liquid helium clusters, and time-of-flight and REMPI spectroscopy of radical salt clusters were investigated experimentally. The excited He atoms were generated in a corona discharge. Two strong neutral peaks were observed, accompanied by a prompt photon peak and a charged peak. All peaks were correlated with the pulsing of the discharge. The neutral hyperthermal and metastable atoms were formed by different mechanisms at different stages of the corona discharge. Positively charged helium droplets were produced by ionization of liquid helium in an electrostatic spraying experiment. The fluid emerging from a thin glass capillary was ionized by a high voltage applied to a needle inside the capillary. Fine droplets (less than 10 µm in diameter) were produced in showers with currents as high as 0.4 µA at 2-4 kV. The high currents resulting from field ionization in helium and the low surface tension of He I, led to charge densities that greatly exceeded the Rayleigh limit, thus resulting in coulombic explosion of the liquid. In contrast, liquid nitrogen formed a well-defined Taylor cone with droplets having diameters comparable to the jet (≈100 µm) at lower currents (10 nA) and higher voltages (8 kV). The metal-halide clusters of calcium and chlorine were generated by laser ablation of calcium metal in a Ar/CClb>4b> expansion. A visible spectrum of the Cab>2b>Clb>3b> cluster was observed from 651 to 630 nm by 1 +1' REMPI. The spectra were composed of a strong origin band at 15 350.8 cm^-1 and several weak vibronic bands. Density functional calculations predicted three minimum energy isomers. The spectrum was assigned to the ²Bb>2b> ← X ²Ab>1b> transition of a planar Cb>2Vb> structure having a ring of two Cl and two Ca atoms and a terminal Cl atom. The ring isomer of Cab>2b>Clb>3b> has the unpaired electron localized on one Ca²⁺ ion to form a Ca⁺ chromophore. A second electronic band of Cab>2b>Clb>3b> was observed at 720 nm. The band is sharply different from the 650 nm band and likely due to a different isomer.

Baryon and lepton numbers in particle physics beyond the standard model

The works presented in this thesis explore a variety of extensions of the standard model of particle physics which are motivated by baryon number (B) and lepton number (L), or some combination thereof. In the standard model, both baryon number and lepton number are accidental global symmetries violated only by non-perturbative weak effects, though the combination B-L is exactly conserved. Although there is currently no evidence for considering these symmetries as fundamental, there are strong phenomenological bounds restricting the existence of new physics violating B or L. In particular, there are strict limits on the lifetime of the proton whose decay would violate baryon number by one unit and lepton number by an odd number of units.

The first paper included in this thesis explores some of the simplest possible extensions of the standard model in which baryon number is violated, but the proton does not decay as a result. The second paper extends this analysis to explore models in which baryon number is conserved, but lepton flavor violation is present. Special attention is given to the processes of μ to e conversion and μ → eγ which are bound by existing experimental limits and relevant to future experiments.

The final two papers explore extensions of the minimal supersymmetric standard model (MSSM) in which both baryon number and lepton number, or the combination B-L, are elevated to the status of being spontaneously broken local symmetries. These models have a rich phenomenology including new collider signatures, stable dark matter candidates, and alternatives to the discrete R-parity symmetry usually built into the MSSM in order to protect against baryon and lepton number violating processes.