Neutrino Oscillations Sterile Neutrinos Coherent CAPTAIN Mills

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Neutrino Oscillations Sterile Neutrinos Coherent CAPTAIN Mills

Transcript Of Neutrino Oscillations Sterile Neutrinos Coherent CAPTAIN Mills

Coherent Captain Mills: The Search for Sterile Neutrinos
Ashley Elliott1, Jeramy Gordon1, Jonah Greenwood1, and Ryder Moreno1 Dr. Darrel Smith1, Emily Strawn1, Kate Walker1
1Department of Physics and Astronomy, Embry-Riddle Aeronautical University, Prescott, AZ

Neutrino Oscillations
What is a Neutrino?: Simply put, a neutrino is a subatomic particle that is very similar to an electron, but has
no electrical charge and a mass less than 1/500,000 of an electron mass. They are some of the most abundant particles in the universe but have almost no interactions with matter, aside from the weak force and gravity.

There are currently three active

neutrinos, as seen in the standard

model to the left; not shown here are

the anti-neutrinos. With the

existence of a sterile neutrino, the

standard model would have to be


expanded to include its unique


Sterile Neutrinos
What is a sterile neutrino? In 1995, LSND reported the first observation of neutrino oscillations occurring in a short baseline experiment. These measurements were not compatible with the theoretical parameters ( (sin2(2θ), Δm2) observed in solar and atmospheric neutrino oscillations in long baseline experiments. This led to the supposition that there must be a fourth neutrino, a “sterile” neutrino, with a mass greater than the active neutrinos currently in the standard model. The “sterile” neutrino is similar to the active neutrinos (spin ½, neutrally charged). However, it does not participate in the three forces described in the standard model It only interacts via

Coherent “CAPTAIN” Mills
Coherent “CAPTAIN” Mills is a short baseline neutrino experiment located at Los Alamos National Lab in the Lujan Facility. Coherent describes the way the neutrinos interact with the liquid Argon in our detector. CAPTAIN stands for Cryogenic Apparatus for Precision Tests of Argon Interactions with Neutrinos. This experiment was dedicated to Dr. Mills, who came up with this novel idea to search for a sterile neutrino.

Fig.1: Standard model

Although each neutrino is unique and distinct, they have been detected to change or oscillate into other neutrinos; some of these oscillations are shown below:

Observed Oscillations:
1. Solar Neutrinos (νe➝νμ appearance) 2. Atmospheric (νμ➝νe disappearance) 3. Accelerator (Long Baseline)
4. Accelerator (Short Baseline)
- LSND/MiniBooNE - observe an enhanced production of νμ➝νe at low (L/Ev) in short baseline experiments

Fig. 2: Diagram of neutrino oscillations inside of the MiniBooNE detector

Fig. 3: (to the left): Part A shows an excess of positrons due to antineutrino oscillation. Part
B shows an excess of electron neutrinos compared to all known backgrounds. Part C shows the range of the parameter space for short baseline experiments observing neutrino
oscillations. Part D shows the excess of antineutrino events compared to all known

Fig. 4: (to the right) compares the observations of short baseline experiments
and long baseline experiments. This demonstrates the sensitivity of short baseline experiments to sterile neutrino
oscillations while long baseline experiments are more sensitive to neutrino
oscillations between active neutrinos.

The theoretical sterile neutrino would have a very small component in the first three mass eigenstates; however, it is the major component of the proposed fourth mass eigenstate. In order to measure this fourth mass eigenstate, an experiment must be
sensitive to the presence of sterile neutrinos (i.e., measure the decreasing flux of the
active neutrinos due to their oscillation into sterile neutrinos). The CCM experiment is
designed to measure this phenomenon.

Fig.6: Neutrino Mixing Angles [IceCube]

Fig. 7: shows the neutrino oscillations observed in the CCM experiment. The 800 MeV proton beam (located at Los Alamos National Laboratory) strikes a tungsten target producing stopped pions. The stopped pions subsequently decay into muons (μ⁺ and μ⁻) while producing muon neutrinos (𝜈μ ). Three possibilities of the muon neutrino oscillations are shown in the figure to the left. In the first case, there is no oscillation. However, it is observed in the CCM detector. In the second case, it oscillates into an electron neutrino, and again is observed in the CCM detector. In the third case, it oscillated into a sterile neutrino and is not observed in the CCM detector.
The CCM detector is sensitive to all neutrino oscillations when they oscillate into active neutrinos. In other words, the initial neutrino flux is observed in the CCM experiment for all active neutrinos. If a sterile neutrino exists, there will be a reduction in flux and we estimate this to about 10%, given the observations made by other neutrino experiments.

Fig. 9: This shows an Argon atom recoiling from a neutrino interaction and becoming excited or ionized. In either case, it makes an excited Argon molecule composed of two atoms. This molecule de-excites and releases ultraviolet scintillation light observed by photomultiplier tubes (PMTs)
in the CCM detector. [Rodgrigues]
Fig. 12: (to the right): We are currently analyzing data from a germanium
detector sensitive to gamma rays. The figure to the right shows the number of counts detected from gamma rays near the CCM detector (uncorrected for live time). The orange line represents data
with the beam off and the blue line represents data with the beam on. We investigated 18 of the peaks to measure their energies and widths to determine the elements participating in nuclear transitions that produced gamma rays at
these characteristic energies.

Fig. 10: The above images show the location and the inside of the CCM detector. The detector contains 120
PMTs along the interior wall of the detector with additional veto tubes placed on the top and bottom. A second detector will be added soon at 40 m from the neutrino production as shown in the above diagram.
The current detector is 20 m from the neutrino production.
Fig. 11: (to the left): This shows the timing distribution of events observed in the CCM detector. Events before -1 μs are pre-beam
events. The events between 0-2 μs are events traveling close to the speed of light (e.g., neutrinos and gamma rays). However, most of the gamma rays are absorbed by
the steel and concrete shielding surrounding the CCM experiment, thus leaving neutrinos as the only candidate events in time with the beam. After 2 μs, the events occuring in the CCM detector are contaminated by fast and slow neutrons.
NeutrinosNeutrino OscillationsNeutrinoCcm DetectorFig