Dr. Emily Maher, Chair
BS Physics, Hendrix College, Conway AR
Ph.D Physics, University of Minnesota, Twin Cities
My research field is experimental particle physics. The universe is made of 12 fundamental particles: electron, electron neutrino, muon, muon neutrino, tau, tau neutrino, up quark, down quark, charm quark, strange quark, top (or truth) quark, and bottom (or beauty) quark. Of these 12 particles, I am most interested in the neutrinos, which come in three types: electron neutrino, muon neutrino, and tau neutrino. These guys are the most abundant particles in the universe, but we know the least about them. In fact, for a long time we thought they were massless, but now we know better.
Neutrinos are difficult to study because they are virtually massless, they are neutral, and they only interact through the weak interaction. This means neutrinos almost never interact. In fact, if we took a bunch of neutrinos produced inside the sun and we sent them through a light-year of lead, only about HALF of them would interact. The other half would travel right through a light-year of lead as if it were nothing! By the way, you have about 10,000 neutrinos traveling through your fingertip each second.
The only way we can "see" an elementary particle is through its electromagnetic interaction. We build detectors to "see" particles through the electromagnetic interactions. Of course, the neutrino is neutral, so it doesn't interact through the electromagnetic force. We can only "see" neutrinos when they interact with other particles. But, from above, we know they don't interact very often. To see a neutrino, we must send MANY, MANY neutrinos through a very MASSIVE target. Then, occasionally, the neutrino will interact, and we will see the particles that are produced in the interaction. We use those particles to study the interaction of the neutrino and the neutrino itself. A good analogy: if you are walking through a snowy forest, and you see tracks, you can tell which animal was there. You don't see the animal, but you see its interaction with the snow.
I began working with the elusive neutrino in graduate school. I worked on an experiment called DONuT (Direct Observation for Nu Tau). You can find some information about DONuT here. The goal of the DONuT experiment was the FIRST observation of the tau neutrino. The electron and muon neutrinos were observed decades earlier, but the tau-neutrino was difficult to observe. When a tau neutrino interactions (through the charged-current interaction), it produces a tau particle. If we see a tau particle (along with no other leptons), then we have seen a tau neutrino interact. The problem is the tau - it is a heavy, short-lived particle. The taus in DONuT only traveled ~ 5mm before decaying. We had to use a detector made of photographic film to capture the tau lepton. But we did, and we saw 9 tau neutrinos!!! You can read our last paper here:
By the way, all of these experiment are done at Fermilab, which is an amazing particle physics laboratory.
While in graduate school, I also worked on the MINOS experiment. We shot a beam of muon neutrinos from Fermilab, a lab outside of Chicago, through the earth and into an underground iron mine in Northern Minnesota. The goal of this experiment was to catch neutrinos changing flavor, meaning a muon neutrino changes to a tau neutrino. You can read more about MINOS here. MINOS did, indeed, find that these neutrinos were changing flavor. They did this by counting all of the muon neutrinos made at Fermilab and counting all of the muon neutrinos that arrived in Northern Minnesota. There were fewer muon neutrinos than expected in Northern Minnesota. The fact that neutrinos oscillate mean that neutrinos cannot be massless. This is direct evidence for physics beyond the Standard Model! Here are a couple of papers from the MINOS collaboration:
Current, I am working on the MINERvA experiment. Again, we are studying neutrinos. This time, we are trying to measure the probability that neutrinos interact, and, when they do interact, which types of particles do they create and how often do they create that set of particles. You can read more about MINERvA here. In addition to studying neutrinos, we are actually using neutrinos to study what happens inside the nucleus. It turns out there is all kind of crazy stuff happening inside of the nucleus that we don't understand. For example, the first MINERvA results suggest that neutrons and protons like to hang out in pairs inside the nucleus - who knew they were so social? Here is an article that ran in the CERN courier last year:
Below you will find my list of publications, where you can read much more about all of these experiments.
My Publications:"Single neutral pion production by charged-current anti-neutrino interactions on hydrocarbon at an average neutrino energy of 3.6 GeV", T. Le et. al. (MINERvA Collaboration). (2015)
"MINERvA neutrino detector response measured with test beam data", L. Aliaga et. al. (MINERvA Collaboration) (2015)
"Measurement of muon proton final states in muon-neutrino interaction on hydrocarbon at <E>=4.0GeV'', T. Walton et. al. (MINERvA Collaboration). Submitted to Physical Review. (2015)
"Measurement of Coherent Production of Pi+ and Pi- in Neutrino and Anti-Neutrino Beams on Carbon from neutrinos energy of 1.5 to 20 GeV", A. Higuera, A. Mislivec, et. al. (MINERvA Collaboration). Phys. Rev. Lett. 113, 261802 (2014)
"MINERvA Searches for Wisdom Among Neutrinos'', E. Maher, D. Harris, and K. McFarland, CERN Courier, April, 2014, 26-29. (2014)
"Measurement of Ratios of Muon Neutrino Charged-Current Cross Sections on C, Fe, and Pb to CH at Neutrino Energies 2-20 GeV'', B.G. Tice et al. (MINERvA Collaboration) Phys. Rev. Lett. 112, 231801. (2014)
"Design, Calibration, and Performance of the MINER$\nu$A Detector", L. Aliagia,et. al., Nuclear Instruments and Methods, A743 (2014) 130. (2014)
"Measurement of Muon Neutrino Quasi-Elastic Scattering on a Hydrocarbon Target at <E> ~ 3.5 GeV'', G. A. Fiorentini, D. W. Schmitz, P. A. Rodrigues et al. (MINERvA Collaboration), Phys. Rev. Lett. 111, 022502. (2013)
"Measurement of Muon Antineutrino Quasi-Elastic Scattering on a Hydrocarbon Target at <E> ~ 3.5 GeV'', L. Fields, J. Chvojka et al. (MINERvA Collaboration), Phys. Rev. Lett. 111, 022501. (2013)
"The MINERvA Data Acquisition System and Infrastructure", G. N. Perdue, et. al. (MINERvA Collaboration), Nuclear Instruments and Methods A: Volume 694, 179. (2012)
"Demonstration of Communication using Neutrinos", D. D. Stancil, et. al. (MINERvA Collaboration), Modern Physics Letters A 27, 1250077. (2012)
"Arachne - A web-based event viewer for MINERvA", N. Tagg, et. al. (MINERvA Collaboration), Nuclear Instruments and Methods, v. 676, 44. (2012)
"A First Measurement of the Interaction Cross Section of the Tau Neutrino", K. Kodama, et. al., Physical Review D78. (2008)
"Observation of Muon Neutrino Disappearance with the MINOS Detectors in the NuMI Neutrino Beam", D. G. Michael, et. al., Phys. Rev. Lett. 97, 191801. (2006)
"First Observation of Separated Atmospheric Muon Neutrino and Muon Anti-neutrino Events in the MINOS Detector'', P. Adamson et. al., Phys. Rev. Lett. 97, 191801. (2006)
"Charged Pion Production in muon neutrino interactions on hydrocarbons at <E> = 4.0 GeV'', B. Eberly et. al. (MINERvA Collaboration). Submitted to Physical Review Letters. (2015)