Physicists may set the standard for obdurate stubbornness. For the past 12 years, scientists in Japan have fired trillions of neutrinos through Earth to the Super-Kamiokande to study their shifting properties. The T2K experiment has captured less than 600 of the particles that interact with other matter.
Physicists are going to vastly scale up efforts to make and trap them because they are so attractive. One of the most profound questions in physics is how the newborn universe created more matter than antimatter so that it is filled with something.
There is a race to build two massive subterranean detectors at a cost of hundreds of millions of dollars. Hyper-Kamiokande, a gargantuan successor to Super-K, will be built in an old zinc mine near the former town of Kamioka. The Deep Underground Neutrino Experiment (DUNE) is being developed in a former gold mine in Lead, South Dakota, 1300 kilometers away from the Fermilab.
Hyper-K might have an advantage because it will likely start taking data a year or two before DUNE. Chang Kee Jung, a T2K member who also works on DUNE, said thatHyper-K and DUNE are vastly different.
Hyper-K, which will be bigger but cheaper than DUNE, is the next in a series of larger detectors of the same basic design developed by Japanese physicists. According to Masato Shiozawa, co-spokesperson for the Hyper-K collaboration, it is all but certain to work. He saysHyper-K is more established than DUNE. I proposed it for that reason.
Physicists will be able to test their understanding of the particles with unprecedented rigor thanks to a new technology that DUNE will use. One of the co-spokespersons for the 1300-member DUNE collaboration says that they are best in class. Bertolucci acknowledges that there is more risk with the technological edge.
Factors as mundane as the cost of underground excavation and as exciting as the possibility that neutrinos will change physicists' understanding of nature will determine how the rivalry will play out.
The everyday objects around us are unaffected by the common particles in the universe. They were capable of carrying clues to deeper mysteries. Neutrinos and their antimatter counterparts are available in three different flavors. The radioactive decay of some atomic nuclei creates electron neutrinos. A beam of protons can be smashed into a target to produce muon neutrinos. The identities are not fixed, as a neutrino of one type can change into another.
A neutrino has no mass. It is a combination of three states. A decaying pi-plus spits out a muon neutrino. Mass states change their combination at different rates. There's a chance that a particle that started out as an electron may end up being a tau neutrino.
The three-flavor model can be used by theorists to explain all of this. There are just a few parameters, such as the probabilities with which one flavor will change and the differences between the three mass states. There are gaps in the picture Two mass states are close but not if the two similar states are lighter or heavier than the third.
The charge-parity violation is caused by the different amounts of the two particles. Physicists want to know how the soup of fundamental particles in the early universe created more matter than antimatter.
Comprising two rectangular tanks filled with 17,000 tons of liquid argon, DUNE will track the charged particles produced when a high-energy neutrino is fired from a distant laboratory.
Hyper-Kamiokande is an underground tank filled with 260,000 tons of water and lined with photodetectors.
The matter-antimatter balance was not tilted by the wispy neutrinos. The familiar neutrinos are mirrored by vastly heavier "sterile" neutrinos that would interact with nothing. In the early universe, sterile neutrinos and antineutrinos could have generated more electrons than antielectrons if they behaved asymmetrically.
Patrick Huber is a theorist at Virginia Polytechnic Institute and State University. Not seeing a violation among ordinary neutrinos would make it less likely that the hypothetical powerhouses have the key asymmetry. He says it is not impossible.
Scientists need to determine if the asymmetry is real. The teams in Japan and the US will use the same method. They will create a beam of muon neutrinos and shoot it toward a distant underground detector by smashing protons into a target. The electron and muon neutrinos will be counted there. They will use pi-pluses from the target to make a beam of muon antineutrinos. They will look for any differences after repeating the measurement.
Several other factors could make the experiment harder than it seems. There will be slight differences in the intensity and energy of the beams. The researchers need to sample the particles as they start their journey by placing a small detector in front of the beam source.
The results could be skewed by the physics of the particles. The matter they travel on their flight to the detector will be absorbed more strongly. The effect depends on the solution to the problem. Physicists will have to solve the hierarchy problem in order to spot the violation.
The harvest of neutrinos from the biggest experiments has been the biggest barrier to sorting this out. Physicists in the U.S. have an experiment that shoots particles from Fermilab to a detector in Minnesota. Similar to T2K, it has netted just a few hundred particles.
Hyper-K will provide a bigger target for the neutrinos to hit. The scaled-up version of the Super-K detector will be 78 meters tall and 74 meters wide and hold 260,000 tons of ultra pure water.
The optical equivalent of a sonic boom will be used to spot the particles. A muon neutrino zipping through the water can knock out an oxygen atom and turn it into a protons. The muon will exceed the speed of light in water, which is 25% slower than in a vacuum, and create a shock wave of light, just as a supersonic jet creates a shock wave. The ring of light on the tank's side is lined with photo detector.
The high-speed electron is lighter than a muon and will be buffeted by the water molecule. A fuzzier light ring will be created. With about half the efficiency of the neutrino interactions, muon and electron antineutrinos can be used to create antimuons and antielectrons.
Hyper-K will be located in the same mining area. The Kamioka Nucleon Decay Experiment tried to spot the rare decays of protons that some theorists predict. In 1987, it glimpsed neutrinos from a supernova, an advance that won a share of the prize. Super-K was launched in 1996. The muon neutrinos were studied when the atmosphere was hit by rays. There are fewer people coming up from the ground than from the sky. In 2015, the discovery was shared with the prize. A Hyper-K member who was drawn by the dynasty of Super-K says that Japanese physicists have done amazing things.
The neutrino beam from J-PARC is being upgraded to increase its power by 2.5. Stephen Playfer is a particle physicist at the University of Edinburgh and the University of Tokyo. They considered joining DUNE before joining Hyper-K. He says that Hyper-K was in a good position because it had a well-known technology.
Hyper-K will have limits. It won't measure the neutrinos' energies in a precise way. The rate at which a neutrino is oscillated depends on the energy of the beam. The experiment wouldn't be able to make sense of the rates without a way to figure out the energy of the neutrinos.
Hyper-K will use a trick in order to avoid this problem. The lower energy neutrinos spread more than the higher energy one. If a detector sits to the side of the beam's path, it will see neutrinos with a narrower range of energies. Hyper-K will sit off the beam axis by 2.5 degrees.
Physicists can tune the beam's energy to make sure the neutrinos get to the detector at the right time. The number of arriving muon neutrinos, electron neutrinos, and their antimatter counterparts are counted by physicists. The ratio of electron antineutrinos with muon antineutrinos is what determines Hyper-K's measurement.
The excavation for Hyper-K will take two years. The project will cost Japan $600 million, with international partners chipping in up to $200 million. Shiozawa says that the detector will be finished in the year 2027. Hyper-K researchers say the hardest part of the project is the digging. Shiozawa says that they need to build the world's largest underground caverns. This is the biggest challenge when it comes to technology and costs.
DUNE wants to be something completely different if Hyper-K is more of the same. It will use a technology that has been used in only one other large experiment but that should allow physicists to see neutrino interactions as never before. Chris Marshall is a particle physicist at the University of Rochester. This is an experiment that will be world leading in a lot of things.
DUNE will consist of two tanks 66 meters long, 19 meters wide, and 18 meters tall. A muon or an electron can be created by a neutrino in an argon nucleus. The neutrinos will pack more energy than the Hyper-K ones. In addition to the muon or electron, a collision will usually produce a spurt of other particles.
DUNE wants to use a liquid argon time projection chamber to track all those particles. The charged particle will ionize some of the atoms. The electrons will be pushed sideways by a strong electric field until they hit three parallel wires. Physicists can reconstruct the original particle with millimeter precision by noting when the electrons hit the wires. They can determine its type and energy from the amount of ionized it produced.
The details are not easy to understand. The electrons will need to travel as far as 3.5 meters. DUNE will sit in the beam from the lab. It will capture a bigger but messier harvest of neutrinos with energies ranging from less than 1 giga-electronvolt to more than 5 GeV.
The ability of DUNE to track all the particles should allow it to measure the energy of each incoming neutrino to create an energy spectrum for eachflavor. A plot of each spectrum should have a different wiggle or oscillation. Bertolucci says physicists should be able to nail down the entire model by analyzing all of the spectrum. He says it's possible to measure all the parameters in the same experiment.
The technology hasn't been fully developed yet. Carlo Rubbia came up with the idea of a liquid argon detector. It wasn't until 2010 that the Gran Sasso National Laboratory caught a few neutrinos from the European particle physics laboratory. Kate Scholberg, a DUNE team member at Duke University, said that the prototypes built by the crash program have worked better than anticipated. She says that looking at the event displays is kind of fascinating. It is amazing detail.
It comes at a cost. The project is split in two by the DOE. There is a new neutrino beam at the Long Baseline Neutrino Facility. The guts of the detectors will be built by DUNE. LBNF/DUNE would cost over a billion dollars and come online in the year 2077. The bill was raised to $3.1 billion last year due to unforeseen construction costs. The beam will lag until early 2031, giving Hyper-K a head start of more than two years.
DUNE developers are confident that the new cost and timelines will hold. Mossey says that excavation should be finished in May. We are doing big things. The project is riskier than Hyper-K. The trade-off is a leap into the unknown. More scariness is going to be associated with something that is moretransformational.
There are other goals for both experiments. There, Hyper-K has an advantage as it is larger and has more hydrogen in it's water molecule. Another payoff is possible if a giant star collapses and explodes as a supernova. DUNE would see the release of electron antineutrinos as the core collapses and Hyper-K would see the release of electron antineutrinos as the explosion takes place.
The purpose of both experiments is still to find out what is going on with the neutrino oscillations. How could a gambler handicap this race?
Hyper-K physicists could make big discoveries before DUNE even starts. Shiozawa says that they may discover the violation in 3 years if it's as big as possible. We may discover the decay of the protons in three years. He says it depends on nature.
If the three-flavor model is the final word on neutrino oscillations, then Hyper-K is the best way to measure it. The assumptions may not hold. With its simpler counting technique and shorter baseline, the experiment may not be able to distinguish the matter effect from theCP violation. More external inputs are required for hyper-K.
DUNE should be able to untangle itself on its own. Shiozawa doesn't count out his opponent. He notes that the Japanese project was scaled back from an initial 1 million ton design. Project leaders are put in constant tension with contractors because the Japanese government won't approve of cost increases. There is no difference between the two projects.
Hyper-K and DUNE may not be a dash for glory, but rather a long wait through uncertainty. The two teams could end up collaborating more informally if that's the case. There will be a long time where the most accurate results will come from a combination of the twoexperiments.
The results could end the theory. There are deviations from the three-flavor model that could hint at new particles. Physicists used to think that the particles came in one type and were massless and not real. In the past, neutrino experiments have shown us that we rarely take data in a neutrino beam and get what we want.
There is a chance that the unexpected is a long shot.
All Rights Reserved © 2024
