Brookhaven: (
Satellite)
The following post has motivated me to record some thoughts concerning neutrino research.
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Michel Talbot posted
The Cowan–Reines Neutrino Experiment. Physicists Clyde L. Cowan and Frederick Reines confirmed the existence of neutrinos experimentally in 1956. In one of the largest physics experiments of its time, they detected the neutrino, a particle postulated by Wolfgang Pauli in 1930 to explain how beta decay could conserve energy, momentum, and spin. They conducted experiments to detect it using inverse beta decay, in which an electron antineutrino interacts with a proton inside an atomic nucleus producing a neutron and a positron. The idea was to detect a neutrino by looking for the particles it left behind after it interacted with something. They set up their experiment using a tank of water and layers of liquid scintillators that could pick up signals from the secondary particles; a nuclear reactor provided the neutrinos. When a neutrino interacted with a proton in the water tank, the resulting particles would leave signature tracks in the liquid scintillator, revealing the neutrino’s presence. They first performed the experiment at the Hanford Site in Washington, but the cosmic-ray background muddied their data too much. So they moved to the Savannah River Plant in South Carolina where they had better shielding against cosmic rays—and that’s where they got their definitive results. They were able to identify about three neutrinos per hour in the many months of data they had collected. The results, which were consistent with Fermi's predictions, were published in Science in July 1956. Frederick Reines was awarded the 1995 Nobel Prize in Physics for this experiment.
Bill Lah: 2nd far detector Nova https://novaexperiment.fnal.gov/ |
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Michel Talbot commented on his post
Those odometer-like things sticking out of the panels are event counters attached to 90 delayed peak detectors each connected to a photomultiplier tube (30 are visible in this photo). This is where the experimental neutrino counts came from. The oscilloscope is only for diagnosing the detection pulse waveforms when calibrating the timing circuits for the experiment, also for impressing the boss because oscilloscope traces are sexier than clicking mechanical counters that increment about once a day on average. |
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Michel Talbot commented on his post
Flash forwards 14 years to November 13, 1970 and Argonne National Laboratory detects the first 'Neutrino Event' in a hydrogen bubble chamber. Here a neutrino hits a proton in a hydrogen atom; the collision occurs at the point where three tracks emanate on the right of the photograph. |
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Michel Talbot commented on his post
A side view of the 300-litre Hanford Liquid Scintillation Neutrino Detector surrounded by 90 photomultiplier tubes, each with a 5 cm diameter face that had a thin, photosensitive surface. The liquid scintillator converts a fraction of the energy of the positron into a tiny flash of light that travels through the highly transparent liquid to the Photomultiplier tubes (PMT) where individual photons trigger a cascade of secondary electrons that generate an electronic pulse strong enough to be detected on an oscilloscope screen. |
g-2 Experiments
I've seen photos of a transport of a big magnet from the Chicago Sanitary and Ship Canal to Fermilab, but I can't find any notes on that move. It was the final leg of transferring the magnet from the Brookhaven National Lab to the Fermilab. Brookhaven used it for their Muon g-2 experiment. They found a discrepancy between what was predicted by the
Standard Model and their experimental result concerning the magnetic moment of the Muon neutrino. Because the results are statistical, the more neutrinos they measure, the more confidence they have in the result. Since Fermilab can produce a beam with more neutrinos [
7:36 video They can currently produce trillions of neutrinos every second.] in it than can Brookhaven, they moved the magnet to Fermilab. During that move, they also upgraded the instrumentation.
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fnal_Aug_10_2023
The ring is 50' in diameter.
The Brookhaven experiment shut down in 2001. The ring was moved in 2013. Fermilab ran the experiment for six years and shut off the muon beam on July 9, 2023. They now have a data set 21 times the size of the Brookhaven's data set. They plan to spend two more years to analyze the last three-years' worth of data. In the meantime, theorists are trying to figure out how to compute a value from the Standard Model with comparable precision. Since a 2020 computation, they invented a second way to compute the value. But it disagrees with the 2020 calculation! |
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anl
"Simon Corrodi installing a calibration probe at Argonne’s solenoid magnet test facility. (Image by Mark Lopez/Argonne National Laboratory.)"
Argonne National Laboratory is part of the collaboration that "consists of 181 scientists from seven countries and 33 institutions."
This magnet at Argonne is used to calibrate the probes that are used to measure the field in the main magnet at Fermilab. "The facility enabled the scientists to achieve field measurements down to just a few parts per billion — like measuring the volume of water in a swimming pool down to the drop." |
Generating neutrinos allows Fermilab to reuse all of their particle accelerator equipment except for the main ring. And the Muon g-2 is just one of several neutrino experiments that they have run, are running or plan to run.
A "fun fact" from the video is that the horn that is used to focus the particles coming from the photon target uses 200,000 amps. I wonder what the power supply looks like for that gizmo.
Building super-conducting magnets is an area of expertise at the BNL. [
bnl_magnets] That explains why the first g-2 experiment was run there. When it appeared that they may be discovering new science, it was moved to Fermilab to more efficiently get better results because Fermilab can generate more neutrinos.
A Little Theory
I can remember that for decades after they were discovered, they thought the mass of a neutrino was zero. And detectors were finding only a third of the expected number of neutrinos coming from the sun. There are three flavors of neutrinos: electron, muon and tau. When they determined that a neutrino changes it flavor, called oscillation, that indicated neutrinos have mass. And that explained why only a third of the expected number of neutrinos were arriving from the sun. But the mass is very small and is still unknown.
IceCube
After six years of boring 86 holes in the Antarctic ice, IceCube was completed in Dec 2010. It was built to help search for the source of cosmic rays. The DeepCore subdetector was added to help study neutrino oscillations. 100gb is sent each day by satellite to a data store in at UW-Madison.
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nsf
"The server room at the IceCube Neutrino Observatory. Photo Credit: Benjamin Eberhardt; ICECUBE/National Science Foundation"
It has been successful in its expected role in astronomy. In 2016, it helped determine that the source of a burst of neutrinos was from a blaser. A blasar is a quasar whose jet points at earth. This could be a source of cosmic rays. Cosmic rays themselves can't be used to determine a source because they are charged particles and their paths are distorted by interfering magnetic fields. Since neutrinos rarely interact with anything, they travel in straight lines.
IceCube has also made a couple of unexpected discoveries in fundamental physics. |
In June 2023, an image of the Milky Way made with neutrinos instead of photons was released.
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astronomy
"Each strip here shows the Milky Way using different techniques. At top is an optical image, showing clearly the dust and gas in the galactic plane. Below that are gamma-ray observations from the Fermi-LAT 12-year survey; the next two strips show the neutrinos astronomers expected to receive, based on the presence of gamma rays. At bottom is observed neutrino sources using the new technique. Credit: IceCube Collaboration"
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icecube-gen2
A second-generation detector is being planned that will expand the volume from 1 cubic km to 8 cubic km using new, more sophisticated light sensors. |
DUNE (Deep Underground Neutrino Experiment) and PIP-II
Fermilab has been shooting neutrinos 800 miles through the earth to a former underground mine, Sanford Underground Research Facility, in South Dakota for years. (I'm trying to remember if these include the experiments that discovered flavors and oscillation.) They are now working on a major upgrade of the detector, DUNE, and building a new accelerator, PIP-II.
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fnal_detectors
DUNE consists of two detectors, the near detector is on the Fermilab campus, and the far detector is in the mine. The far detector is huge and will be used for neutrino astronomy as well as particle physics experiments. The reason the far detector is deep underground is to shield it from cosmic rays and other surface noise. |
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| Chicago Tribune, Sep 14, 2023, p1 |
Feb 2026: I've been seeing videos that DUNE is way over budget and behind on their schedule. Also, experiments being built in other countries might get results earlier and make DUNE obsolete before it is finished.
