Abstract artists principle of neutrino particles.
CUORE Team Places New Limits on the Bizarre Behavior of Neutrinos
Physicists are surrounding the true nature of the neutrino– and may be closer to addressing an essential question about our own presence.
Researchers at the Cryogenic Underground Observatory for Rare Events (CUORE) announced this week that they had actually placed some of the most strict limits yet on the odd possibility that the neutrino is its own antiparticle. CUORE has actually spent the last three years patiently waiting to see evidence of a distinctive nuclear decay procedure, just possible if antineutrinos and neutrinos are the very same particle. CUOREs new data shows that this decay does not happen for trillions of trillions of years, if it happens at all.
CUORE scientists Dr. Paolo Gorla (LNGS, left) and Dr. Lucia Canonica (MIT, right) inspect the CUORE cryogenic systems. Credit: Yury Suvorov and the CUORE Collaboration
” Ultimately, we are trying to understand matter production,” stated Carlo Bucci, researcher at the Laboratori Nazionali del Gran Sasso (LNGS) in Italy and the representative for CUORE. “Were searching for a procedure that violates a fundamental symmetry of nature,” included Roger Huang, a postdoctoral scientist at the Department of Energys Lawrence Berkeley National Laboratory (Berkeley Lab) and one of the lead authors of the brand-new study.
CUORE– Italian for “heart”– is amongst the most sensitive neutrino experiments in the world. The brand-new outcomes from CUORE are based on an information set ten times larger than any other high-resolution search, gathered over the last three years. The CUORE detector itself is located under almost a mile of solid rock at LNGS, a center of the INFN.
Strange particles
Neutrinos are everywhere– there are trillions of neutrinos passing through your thumbnail alone as you read this sentence. They are undetectable to the two greatest forces in the universe, electromagnetism and the strong nuclear force, which enables them to pass right through you, the Earth, and almost anything else without interacting. In spite of their large numbers, their enigmatic nature makes them very difficult to study, and has left physicists scratching their heads ever because they were first postulated over 90 years earlier. It wasnt even understood whether neutrinos had any mass at all until the late 1990s– as it turns out, they do, albeit not really much.
One of the lots of staying open questions about neutrinos is whether they are their own antiparticles. Unlike all of those particles, its in theory possible for neutrinos to be their own antiparticles.
CUORE detector being set up into the cryostat. Credit: Yury Suvorov and the CUORE Collaboration
If neutrinos are Majorana fermions, that could describe a deep question at the root of our own presence: why theres a lot more matter than antimatter in the universe. Neutrinos and electrons are both leptons, a type of fundamental particle. Among the fundamental laws of nature appears to be that the variety of leptons is always conserved– if a procedure develops a lepton, it should also develop an anti-lepton to stabilize it out. Likewise, particles like protons and neutrons are called baryons, and baryon number likewise appears to be conserved. Yet if baryon and lepton numbers were constantly conserved, then there would be exactly as much matter in deep space as antimatter– and in the early universe, the matter and antimatter would have met and wiped out, and we would not exist. Something must breach the specific preservation of leptons and baryons. Go into the neutrino: if neutrinos are their own antiparticles, then lepton number wouldnt need to be saved, and our presence ends up being much less mystical.
” The matter-antimatter asymmetry in deep space is still unexplained,” said Huang. “If neutrinos are their own antiparticles, that might help discuss it.”
Nor is this the only question that might be addressed by a Majorana neutrino. The extreme lightness of neutrinos, about a million times lighter than the electron, has long been perplexing to particle physicists. But if neutrinos are their own antiparticles, then an existing solution referred to as the “seesaw mechanism” might explain the lightness of neutrinos in a stylish and natural method.
A rare gadget for uncommon decays
Determining whether neutrinos are their own antiparticles is difficult, precisely because they dont connect really typically at all. Physicists best tool for looking for Majorana neutrinos is a hypothetical kind of radioactive decay called neutrinoless double beta decay. If the neutrino is a Majorana fermion, then in theory, that would allow a single “virtual” neutrino, acting as its own antiparticle, to take the location of both anti-neutrinos in double beta decay.
The CUORE experiment has actually gone to great lengths to capture tellurium atoms in the act of this decay. There are trillions of trillions of atoms of tellurium in each one of the crystals CUORE uses, indicating that normal double beta decay takes place relatively regularly in the detector, around a couple of times a day in each crystal. Neutrinoless double beta decay, if it occurs at all, is even more rare, and therefore the CUORE team must work hard to remove as lots of sources of background radiation as possible.
Perhaps the most excellent piece of machinery used at CUORE is the cryostat, which keeps the detector cold. To spot neutrinoless double beta decay, the temperature of each crystal in the CUORE detector is thoroughly monitored with sensors capable of spotting a change in temperature as small as one ten-thousandth of a Celsius degree. Neutrinoless double beta decay has a particular energy signature and would raise the temperature level of a single crystal by a well-defined and identifiable amount. In order to keep that level of sensitivity, the detector needs to be kept very cold– specifically, its kept around 10 mK, a hundredth of a degree above absolute zero. “This is the coldest cubic meter in the known universe,” stated Laura Marini, a research fellow at Gran Sasso Science Institute and CUOREs Run Coordinator. The resulting sensitivity of the detector is genuinely extraordinary. “When there were big earthquakes in Chile and New Zealand, we really saw peeks of it in our detector,” stated Marini. “We can likewise see waves crashing on the seashore on the Adriatic Sea, 60 kilometers away. That signal grows in the winter season, when there are storms.”
A neutrino through the heart
Regardless of that sensational sensitivity, CUORE hasnt yet seen evidence of neutrinoless double beta decay. Rather, CUORE has actually developed that, typically, this decay takes place in a single tellurium atom no more often than when every 22 trillion years. “Neutrinoless double beta decay, if observed, will be the rarest process ever observed in nature, with a half-life more than a million billion times longer than the age of deep space,” said Danielle Speller, Assistant Professor at Johns Hopkins University and a member of the CUORE Physics Board. “CUORE may not be delicate adequate to detect this decay even if it does happen, however its crucial to inspect. In some cases physics yields unexpected results, and thats when we discover one of the most.” Even if CUORE does not find evidence of neutrinoless double-beta decay, it is leading the way for the next generation of experiments. CUOREs follower, the CUORE Upgrade with Particle Identification (CUPID) is currently in the works. CUPID will be over 10 times more sensitive than CUORE, potentially allowing it to peek proof of a Majorana neutrino.
Regardless of anything else, CUORE is a clinical and technological accomplishment– not only for its brand-new bounds on the rate of neutrinoless double beta decay, however likewise for its presentation of its cryostat innovation. “Its the biggest fridge of its kind in the world,” stated Paolo Gorla, a personnel researcher at LNGS and CUOREs Technical Coordinator.
Meanwhile, CUORE isnt done yet. “Well be running till 2024,” stated Bucci. “Im delighted to see what we find.”
Referral: “Search for Majorana neutrinos making use of millikelvin cryogenics with CUORE” by The CUORE Collaboration, 6 April 2022, Nature.DOI: 10.1038/ s41586-022-04497-4.
CUORE is supported by the U.S. Department of Energy, Italys National Institute of Nuclear Physics (Instituto Nazionale di Fisica Nucleare, or INFN), and the National Science Foundation (NSF). CUORE collaboration members include: INFN, University of Bologna, University of Genoa, University of Milano-Bicocca, and Sapienza University in Italy; California Polytechnic State University, San Luis Obispo; Berkeley Lab; Johns Hopkins University; Lawrence Livermore National Laboratory; Massachusetts Institute of Technology; University of California, Berkeley; University of California, Los Angeles; University of South Carolina; Virginia Polytechnic Institute and State University; and Yale University in the United States; Saclay Nuclear Research Center (CEA) and the Irène Joliot-Curie Laboratory (CNRS/IN2P3, Paris Saclay University) in France; and Fudan University and Shanghai Jiao Tong University in China.
Scientists at the Cryogenic Underground Observatory for Rare Events (CUORE) revealed this week that they had actually positioned some of the most stringent limits yet on the strange possibility that the neutrino is its own antiparticle. CUORE has spent the last three years patiently waiting to see evidence of a distinct nuclear decay procedure, only possible if antineutrinos and neutrinos are the very same particle. CUORE– Italian for “heart”– is among the most delicate neutrino experiments in the world. CUOREs successor, the CUORE Upgrade with Particle Identification (CUPID) is currently in the works. CUPID will be over 10 times more delicate than CUORE, possibly permitting it to look proof of a Majorana neutrino.
