Nathaniel Tagg
University of Guelph
April 8, 1998
My research will consist of two parts, with emphasis to be determined by the results of the experiments. Each is related to the Sudbury Neutrino Observatory.
High-energy muons originating from cosmic-ray showers in the earth's atmosphere can penetrate to deep levels underground. Muon multiplicity in individual showers has been shown to be related to the chemical composition of the incident cosmic rays. This composition is not well understood at high energies, and various measurements have been made (MACRO, KGF detectors) to determine the ratios of light to heavy elements above the "knee" (1015 eV) in the cosmic ray spectrum[1].
SNO is the deepest underground detector in the world. In fact, the total flux of muons at this depth has not been directly observed. It is thus well situated to see to observe muons arising from primary cosmic rays above the knee; the lower energy interactions create less penetrating cosmic rays. It can be caluculated, using the monte-carlo parameterization of Forti, et. al. [2] that the ratio of mutliple-muon events to single-muon events detected at SNO depth will be indicative of the ratio of heavy to light nucleii in the primary particle spectrum above models found by other groups. This composition is currently in controversy, so this data should be welcomed.
However, SNO was designed [3] as a Cherenkov light detector, with the aim in mind of acting somewhat akin to a calorimeter, making the job of fitting high-energy events nontrivial. I am in the process of writing a fitter that can reconstruct high-energy tracks, and discern multiple events from single-muon events. This work will also aid in the hunt for atmospheric neutrino-induced events.
The second project I am currently involved with is the creation and deployment of the radioactive gas calibration system in SNO. The known 8B spectrum is not calculable in a model-independent manner, and experiments rely on measuring the two-alpha decay immediately following the beta decay. This introduces systematic error bars when SNO data (i.e. neutrinos resulting from this 8B decay in the sun) is used to determine what kind of neutrino oscillation, if any, is responsible for the solar neutrino problem. [4]
8Li is a mirror-image decay (a beta-minus decay, rather than a beta-plus) to the same set of intermediate 8Be states as the 8B decay. Thus, by analayzing the 8Li spectrum in SNO, the 8B systematic errors can be removed, or at least mitigated.[5] 8Li can be carried by a gas transport system into the active volume of SNO. [6]
This requires the design and construction of a decay chamber that can tag the beta-decay. The proposed design uses a proportional counter to catch the double-alpha decay, so the event in SNO can be correllated to it. Various pitfalls involve trigger efficiency and gas-transport effeciency.
I plan to develop this chamber and be involved it the deployment and analysis of this calibration.
[1] MACRO Collaboration (M. Ambrosio et. al.), Nucl Phys B, 52, pp 172-175, 1997
[2] C. Forti, et. al., Phys Rev D, v. 42, p. 3668, 1990
[3] See, for example, the 'Sudbury Neutrino Proposal', SNO-87-12, October 1987
[4] J. Bahcall and E. Lisi, (Draft) "Tests of Electron Flavor Conservation with the Sudbury Neutrino Observatory"
[5] G. Jonkmans, I.S. Towner, and B. Sur, "8B Neutrino Spectrum: Implications fot he Sudbury Neutrino Observatory", submitted for publication in ???
[6] B. Sur et al., Bull. Am. Phys. Soc. v. 39, p 1389 (1994)