M.S. - Physics
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ItemLeptonic and hadronic branching fractions for J/psi via psi(2S) --> pi⁺pi⁻ J/psi( 2007)The BES II detector was used to collect 14 x 106 ψ(2S) events, in order to study the dynamics of channonium bound states ψ(2S) and J/ψ. The ratio of the branching ratios ψ(2S)→ π+π- J/ψ, J/ψ →pṗ and ψ(2S) → π+π- J/ψ, J/ψ → e+e- is determined. In addition, the ratio of the branching ratios ψ(2S) → π+π- J/ψ, J/ψ → pṗ and ψ(2S)→ π+π- J/ψ, J/ψ →µ+µ- is determined in two independent ways. The angular distributions for each of these processes are also analyzed.
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ItemObservation of the Askaryan effect in ice with the ANITA experiment( 2007)First hypothesized by Gurgen Askaryan in the 1960's and later confirmed in 2001 at SLAC (Stanford Linear Accelerator Center), radio Cherenkov detection techniques are possible in the ultra-high energy regime (1018 -> 1022 eV) while observing electromagnetic cascades in dielectric media. This method of detection has now moved into the field of neutrino astrophysics. Recently, the interest in using ice as a dielectric medium to observe coherent microwave Cherenkov pulses from ultra-high energy neutrino induced particle showers has grown considerably with advances from experiments such as RICE, FORTE, and ANITA-lite. ANITA (ANtarctic Impulsive Transient Antenna), is a radio telescope designed to exploit this effect while looking for UHE neutrino interactions in Antarctic ice. In June 2006, ANITA observed these highly coherent radio impulses in SLAC's ESA (End Station A) with 28.5 GeV electrons interacting with a 7.5 tonne ice target to produce the EM shower. These first measurements of the Askaryan effect in ice were consistent with shower and electrodynamics simulations for ice and provided a clear indication that the radiation is coherent over the 200-1200 MHz frequency window. In addition to the ANITA payload in SLAC's ESA, four log-period dipole array antennas, two monocone antennas, and one high frequency gain horn (nominally 2.6-3.95 GHz) recorded impulsive events emanating from the ice target. I report on further analysis of coherent radio Cherenkov impulses using the standard gain horn and demonstrate that the results are fully consistent with theoretical expectations.
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ItemPhysical properties of liquid scintillators( 2006)Neutrino oscillation studies at KamLAND in Japan using a liquid scintillator detector concluded the "Solar Neutrino Problem" by observing that the electron anti-neutrinos from the reactors around Japan were oscillating. The parameters of the oscillation matched those deduced from solar neutrinos, so additionally demonstrated that the electron anti-neutrinos are not behaving differently from electron neutrinos in any significant manner. The data fits also eliminate some models competing with the oscillatory hypothesis [I, 2]. The secondary signal observed and presented by the collaboration involves the signal coming from the Earth itself, the "Geo Nu's" or geo-neutrinos [3,4]. The next step in studying the geological neutrinos is to characterize radioactivity within the layers of the earth using anti-electron neutrinos emanating from the Earth's mantle and core. This characterization requires the ability to discriminate radiation coming from the mantle and core separately from the crust. This characterization requires that the detector is far removed from significant background signal contribution due to the crust and man-made nuclear reactors [5, 6]. Modeling the parameters of this type of neutrino experiment demonstrated the need for a 10 kilotonne liquid scintillator detector, ten or more times the size of the KamLAND detector. In order to avoid the neutrino background from regional manmade reactors and escape the contribution from the continental crust, we plan to place a detector over the thin mid-ocean crust. Submerging the detector in the deep ocean (> 3000 m) provides excellent shielding from the cosmic ray muons which otherwise induce background events. A key to the success of this detector is the liquid scintillator and its physical properties. Any design for an underwater neutrino detector at a depth of a few thousand meters adds two new key parameters beyond land-based detectors such as KamLAND [2] and BOREXINO [14]. The first constraint on the scintillator to be employed is temperature; the temperature of seawater is approximately 4°C at depth. The second constraint is pressure; the pressure is approximately -6000 psi (400 atmos.) at 4 km depth. The goal is to find a liquid scintillator candidate that does not exhibit significant deterioration of the scintillators optical properties due to change in pressure and temperature. The concerns are mechanical and optical properties, about which there is little or no available relevant literature. Viable candidates must demonstrate little if any pressure dependence over a temperature between 0°C and 25°C. They must also maintain a stable attenuation length at 0°C comparable to their attenuation length at ambient near surface conditions, between 20°C and 25°C.
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ItemRelaxation and doppler effects of molecular iodine( 2008)This thesis looks into the aspects of molecular rot-vibrational energy level relaxation of iodine when it is excited by a resonant laser. In addition, the effects of Doppler detuning of molecular levels are explored. The proposed Active Hyperspectral Imaging Project [1] will detect in the atmosphere, low concentrations of a specific element's molecules by using remote sensing optical techniques. In order to improve the signal to noise ratio, a 'high field' coherent excitation technique is proposed. However such coherent excitation should take less time than the typical relaxation time of the system to avoid de-coherence effects. The purpose of the present study is to assess the values of the de-population and de-phasing relaxation times in iodine. The result of this experiment will be used for the design of an intra-cavity coherent excitation experiment in which the power needed for excitation would be obtained by a resonant enhancement inside a low-loss optical storage cavity. We can estimate the minimum power required for coherent excitation based on our findings of the relaxation times. This high field experiment would gain information regarding the coupling between the molecule and the laser field. In the present 'low field' experiment, output from a low-powered tunable diode laser was sent through a Pockels cell to create a top hat pulse which was used to excite gaseous iodine, located in an evacuated cell. The time dependence of a spectrally resolved fluorescence signal was used to observe the relaxation behavior of some targeted excited state and the behavior was fitted to a model resulting in estimates of de-phasing and depopulation relaxation parameters. The experiment was also set-up to observe the effects of Doppler broadening due to molecular velocities. Fluorescence was collected from a narrow strip inside the iodine cell (see figure 3.3) whose short axis was parallel to the laser beam and its length was altered to assess the Doppler contribution. The information of de-phasing and de-population collected from the low field experiment would be useful for the high field experiment in which enough intensity will be created to induce Rabi oscillations [2] by the placement of a custom iodine cell inside a short near-confocal cavity. These oscillations would aid in the estimation of the dipole matrix element (which quantifies the coupling between the molecule and the laser field). The time duration of de-phasing and de-population will determine the minimum field intensity required to produce a Rabi oscillation whose period is less than the de-phasing and de-population times. The situation for the low field experiment was modeled by a two-level energy system interacting with a single mode field. In chapter 2, equation of motion is developed which includes the detuning effect. An output intensity model designed to fit the data is presented that would be used to calculate the rise and decay times helping us to ascertain the relaxation effects. The practical setup is presented in chapter 3. Details regarding the beam line, stabilization of the diode laser, selection of the iodine absorption line by tuning the laser and selection of a fluorescence line of iodine are all described in that chapter. The procedure of placement of the Pockels cell, production of a 1 µs laser pulse and data collection are also given. The chapter concludes with a representative data-set. For the Analysis, the model from the second chapter is used to fit to the experimental data. Values of rise and fall times are presented and the relationship between these values is explored. The average value of de-phasing due to molecular collision is calculated and the power requirements for the Rabi oscillations are discussed in this chapter. The thesis concludes with a summary and suggestions for further work.
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