Thesis Experiments
Is the Tau Neutrino a
Standard Model Particle?
The DONuT (Direct Observation of Nu Tau) Experiment, or Fermilab Experiment
872, was
designed to observe the first charged-current
interaction of the tau neutrino. The tau neutrino was the last of the fundamental
particles predicted by the Standard Model
of particle physics
whose interaction had not been observed. The existence of the tau neutrino is
inferred experimentally through missing energy and momentum in tau lepton decays. Since this
was the first time the tau neutrino interaction was observed, the DONuT experiment had the
opportunity to make the first measurement of the tau neutrino cross
section. The Standard Model of particle
physics predicts lepton
universality, which means the tau, muon, and electron neutrinos should
behave identically with the exception of kinematic factors. My thesis
topics consists of making a measurement of the tau neutrino charged-current
interaction cross section using the DONuT data and comparing it to the prediction of the
Standard Model.
In the final state of a tau neutrino charged-current interaction, a tau lepton is
produced. The tau lepton decays very quickly (usually within 5 mm) to either a
single charged particle or three charged particles. It is this decay that must be
observed in order to observe the interaction of the tau neutrino. The detector
used was an emulsion-spectrometer hybrid. The emulsion, which is
similar to photographic film, was used to record the tau lepton decay. The
spectrometer was used to tell us where to look in the emulsion. The spectrometer
also provided information about the charged particles which left the detector,
such as particle-ID and momentum. The decay of the tau lepton was observed in 6
candidate events.
Do Neutrinos Oscillate?
Neutrinos are constantly raining down on Earth. Many of these neutrinos come from
reactions inside our sun and interactions which occur in the atmosphere. Experiments which
look at neutrinos from these two sources have measured a deficit of certain types of
neutrinos.
The solar neutrino experiments detected about one-third of the predicted electron
neutrinos. The atmospheric neutrino experiments measured a deficit of muon
neutrinos. One way to explain these deficits is through neutrino oscillations. The
neutrinos could be switching flavour as they travel through space. For example, if a
neutrino starts as an electron neutrino originating in the sun, it could oscillate to a muon
neutrino before it reaches the earth, and, therefore, a deficit of electron neutrinos would
be measured.
MINOS (Main Injector Neutrino Oscillation Search), or Fermilab Experiment 875, is an experiment designed to
detect neutrino oscillations. This experiment will use an intense beam of muon neutrinos produced from
the Main Injector particle accelerator at Fermilab. These neutrinos will travel 735 km through the earth
to the Soudan mine in northern Minnesota. One-half a mile down in the Soudan mine, a 5.4 kiloton detector was
built to measure the flux. A similar, but smaller, detector was built at Fermilab to measure the flux. If there
are no neutrino oscillations, we expect to see the same flux at each site. If there are neutrinos oscillations, we
will see a lower flux in the mine because some of the muon neutrinos will have oscillated to electron or tau
neutrinos. My participation in the MINOS experiment was aiding in the construction of the far detector in the
Soudan mine. I mainly installed and checked electronics as the detector was built. Here
is a nice picture of the Soudan detector.
Research Links
Thesis Event Sets
University of Minnesota DONuT Homepage
University of Minnesota MINOS Homepage
