March 28, 2024

Mysterious Physics Still Unexplained: MicroBooNE Experiment Shows No Hint of Sterile Neutrino

The international MicroBooNE experiment uses a 170-ton detector put in Fermilabs neutrino beam. The experiment research studies neutrino interactions and has found no tip of a theorized 4th neutrino called the sterilized neutrino. Credit: Reidar Hahn, Fermilab.
” MicroBooNE has made an extremely comprehensive exploration through numerous types of interactions, and numerous analysis and restoration methods,” said Bonnie Fleming, physics teacher at Yale University and co-spokesperson for MicroBooNE. “They all tell us the exact same thing, which gives us extremely high self-confidence in our outcomes that we are not seeing a hint of a sterile neutrino.”
MicroBooNE is a 170-ton neutrino detector approximately the size of a school bus that has actually run since 2015. The global experiment has near to 200 partners from 36 organizations in five nations. They utilized advanced innovation to tape-record marvelously exact 3D images of neutrino events and examine particle interactions in detail– a much-needed probe into the subatomic world.
Neutrinos are one of the fundamental particles in nature. Theyre neutral, incredibly tiny, and the most abundant particle with mass in our universe– though they rarely interact with other matter. Theyre likewise especially interesting to physicists, with a variety of unanswered concerns surrounding them. These puzzles include why their masses are so vanishingly small and whether they are accountable for matters dominance over antimatter in our universe. This makes neutrinos a special window into checking out how the universe works at the tiniest scales.
MicroBooNEs brand-new outcomes are an amazing pivotal moment in neutrino research study. With sterile neutrinos even more disfavored as the explanation for anomalies identified in neutrino information, scientists are examining other possibilities. These include things as intriguing as light developed by other procedures during neutrino accidents or as exotic as dark matter, inexplicable physics associated with the Higgs boson, or other physics beyond the Standard Model.
Hints of sterilized neutrinos
Neutrinos come in 3 known types– the tau, muon and electron neutrino– and can switch between these flavors in a particular way as they take a trip. This phenomenon is called “neutrino oscillation.” When measuring them at various ranges from their source, researchers can utilize their knowledge of oscillations to forecast how lots of neutrinos of any kind they expect to see.
MicroBooNEs innovative liquid argon technology enables scientists to capture comprehensive images of particle tracks. This electron neutrino event reveals an electron shower and a proton track. Credit: MicroBooNE cooperation
Neutrinos are produced by numerous sources, including the sun, the atmosphere, nuclear reactors and particle accelerators. Beginning around 2 decades earlier, information from 2 particle beam experiments tossed scientists for a loop.
In the 1990s, the Liquid Scintillator Neutrino Detector experiment at DOEs Los Alamos National Laboratory saw more particle interactions than anticipated. In 2002, the follow-up MiniBooNE experiment at Fermilab started collecting data to examine the LSND lead to more detail.
MiniBooNE scientists likewise saw more particle occasions than estimations predicted. These weird neutrino beam outcomes were followed by reports of missing out on electron neutrinos from radioactive sources and reactor neutrino experiments.
Sterile neutrinos became a popular prospect to discuss these odd outcomes. While neutrinos are already tricky to identify, the proposed sterilized neutrino would be a lot more elusive, reacting only to the force of gravity. Due to the fact that neutrinos flit in between the various types, a sterilized neutrino might impact the method neutrinos oscillate, leaving its signature in the information.
But studying the smallest things in nature isnt straightforward. Researchers never see neutrinos straight; instead, they see the particles that emerge when a neutrino hits an atom inside a detector
The MiniBooNE detector had a particular constraint: It was unable to tell the difference in between electrons and photons (particles of light) near to where the neutrino engaged. This ambiguity painted a muddled photo of what particles were emerging from crashes. You can consider it like having a box of chocolates– MiniBooNE might inform you it includes a dozen pieces, however MicroBooNE might inform you which ones have almonds, and which have caramel.
If MiniBooNE were genuinely seeing more electrons than anticipated, it would indicate extra electron neutrinos triggering the interactions. That would mean something unforeseen was taking place in the oscillations that researchers hadnt accounted for: sterilized neutrinos. However if photons were triggering the excess, it would likely be a background process rather than oscillations gone wild and a new particle.
It was clear that researchers needed a more nuanced detector. In 2007, the concept for MicroBooNE was born.
MicroBooNE: precision detector.
The MicroBooNE detector is constructed on modern strategies and technology. Neutrinos bump into the thick, transparent liquid, launching additional particles that the electronic devices can tape.
Employees install an element of MicroBooNEs accuracy detector (called a time projection chamber) into the cylindrical container, or cryostat. Credit: Reidar Hahn, Fermilab.
MicroBooNEs very first 3 years of information show no excess of electrons– but they also show no excess of photons from a background procedure that may suggest a mistake in MiniBooNEs information.
” Were not seeing what we would have anticipated from a MiniBooNE-like signal, neither electrons nor the most likely of the photon presumes,” said Fermilab scientist Sam Zeller, who served as MicroBooNE co-spokesperson for eight years. “But that earlier information from MiniBooNE doesnt lie. Theres something really fascinating happening that we still require to describe.”
MicroBooNE dismissed the most likely source of photons as the reason for MiniBooNEs excess occasions with 95% confidence and ruled out electrons as the sole source with higher than 99% self-confidence, and there is more to come.
MicroBooNE still has half of its information to examine and more ways yet to evaluate it. The granularity of the detector enables researchers to look at specific kinds of particle interactions. While the group began with the most likely causes for the MiniBooNE excess, there are extra channels to examine– such as the appearance of an electron and positron, or various results that include photons.
” Being able to search in detail at these various event outcomes is a real strength of our detector,” Zeller stated. “The information is guiding us away from the most likely descriptions and pointing toward something more intriguing and complicated, which is really exciting.”
While the very first analyses weighed in on the sterilized neutrino, extra analyses could supply more info about unique descriptions, including dark matter, axion-like particles, the hypothetical Z-prime boson and beyond. Theres even an opportunity it could still be a sterile neutrino, concealing in a lot more unanticipated methods.
Future neutrino expedition
Neutrinos are surrounded by mysteries. The anomalous data seen by the earlier MiniBooNE and LSND experiments still require a description. Too does the very phenomenon of neutrino oscillation and the reality that neutrinos have mass, neither of which is predicted by the Standard Model. There are likewise enticing tips that neutrinos could assist describe why there is so much matter in deep space, instead of a universe loaded with antimatter or absolutely nothing at all.
The group inserts the time-projection chamber into the MicroBooNE cryostat. Credit: Reidar Hahn, Fermilab
MicroBooNE is among a suite of neutrino experiments looking for answers. Most importantly, its also a long-running testbed for the liquid argon innovation that will be utilized in upcoming detectors.
” Weve built and checked the hardware, and weve likewise developed the infrastructure to process our enormous dataset,” said Justin Evans, a scientist at the University of Manchester and MicroBooNE co-spokesperson. “That consists of the simulations, calibrations, reconstruction algorithms, analysis methods and automation through strategies like artificial intelligence. This foundation is vital for future experiments.”
Together with MicroBooNE, the 3 experiments form the Short-Baseline Neutrino Program at Fermilab and will produce a wealth of neutrino data. In one month, SBND will tape more information than MicroBooNE collected in two years.
” Every time we look at neutrinos, we appear to find something brand-new or unforeseen,” said Evans. “MicroBooNEs outcomes are taking us in a new instructions, and our neutrino program is going to get to the bottom of some of these secrets.”
Liquid argon will likewise be utilized in the Deep Underground Neutrino Experiment, a flagship global experiment hosted by Fermilab that currently has more than 1,000 researchers from over 30 countries. DUNE will study oscillations by sending out neutrinos 800 miles (1,300 km) through the earth to detectors at the mile-deep Sanford Underground Research Facility. The combination of brief- and long-distance neutrino experiments will offer researchers insights into the functions of these fundamental particles.
” We have some huge, unanswered concerns in physics that many experiments are attempting to resolve,” Fleming said. “And neutrinos may be telling us where to discover some of those answers. I think if you desire to understand how the universe works, you need to understand neutrinos.”
References:
” Search for Neutrino-Induced Neutral Current Δ Radiative Decay in MicroBooNE and a First Test of the MiniBooNE Low Energy Excess Under a Single-Photon Hypothesis” by MicroBooNE partnership: P. Abratenko, R. An, J. Anthony, L. Arellano, J. Asaadi, A. Ashkenazi, S. Balasubramanian, B. Baller, C. Barnes, G. Barr, V. Basque, L. Bathe-Peters, O. Benevides Rodrigues, S. Berkman, A. Bhanderi, A. Bhat, M. Bishai, A. Blake, T. Bolton, J.Y. Book, L. Camilleri, D. Caratelli, I. Caro Terrazas, R. Castillo Fernandez, F. Cavanna, G. Cerati, Y. Chen, D. Cianci, J.M. Conrad, M. Convery, L. Cooper-Troendle, J.I. Crespo-Anadon, M. Del Tutto, S.R. Dennis, P. Detje, A. Devitt, R. Diurba, R. Dorrill, K. Duffy, S. Dytman, B. Eberly, A. Ereditato, J.J. Evans, R. Fine, G.A. Fiorentini Aguirre, R.S. Fitzpatrick, B.T. Fleming, N. Foppiani, D. Franco, A.P. Furmanski, D. Garcia-Gamez, S. Gardiner, G. Ge, S. Gollapinni, O. Goodwin, E. Gramellini, P. Green, H. Greenlee, W. Gu, R. Guenette, P. Guzowski, L. Hagaman, O. Hen, C. Hilgenberg, G.A. Horton-Smith, A. Hourlier, R. Itay, C. James, X. Ji, L. Jiang, J.H. Jo, R.A. Johnson, Y.J. Jwa, D. Kalra, N. Kamp, N. Kaneshige, G. Karagiorgi, W. Ketchum, M. Kirby, T. Kobilarcik, I. Kreslo, R. LaZur, I. Lepetic, K. Li, Y. Li, K. Lin, B.R. Littlejohn, W.C. Louis, X. Luo, K. Manivannan, C. Mariani, D. Marsden, J. Marshall, D.A. Martinez Caicedo, K. Mason, A. Mastbaum, N. McConkey, V. Meddage, T. Mettler, K. Miller, J. Mills, K. Mistry, T. Mohayai, A. Mogan, J. Moon, M. Mooney, A.F. Moor, C.D. Moore, L. Mora Lepin, J. Mousseau, M. Murphy, D. Naples, A. Navrer-Agasson, M. Nebot-Guinot, R.K. Neely, D.A. Newmark, J. Nowak, M. Nunes, O. Palamara, V. Paolone, A. Papadopoulou, V. Papavassiliou, S.F. Pate, N. Patel, A. Paudel, Z. Pavlovic, E. Piasetzky, I. Ponce-Pinto, S. Prince, X. Qian, J.L. Raaf, V. Radeka, A. Rafique, M. Reggiani-Guzzo, L. Ren, L.C.J. Rice, L. Rochester, J. Rodriguez Rondon, M. Rosenberg, M. Ross-Lonergan, G. Scanavini, D.W. Schmitz, A. Schukraft, W. Seligman, M.H. Shaevitz, R. Sharankova, J. Shi, J. Sinclair, A. Smith, E.L. Snider, M. Soderberg, S. Soldner-Rembold, P. Spentzouris, J. Spitz, M. Stancari, J. St. John, T. Strauss, K. Sutton, S. Sword-Fehlberg, A.M. Szelc, W. Tang, K. Terao, C.Thorpe, D. Totani, M. Toups, Y.-T. Tsai, M.A. Uchida, T. Usher, W. Van De Pontseele, B. Viren, M. Weber, H. Wei, Z. Williams, S. Wolbers, T. Wongjirad, M. Wospakrik, K. Wresilo, N. Wright, W. Wu, E. Yandel, T. Yang, G. Yarbrough, L.E. Yates, H.W. Yu, G.P. Zeller, J. Zennamo and C. Zhang, Submitted, Physical Review Letters.arXiv:2110.00409.
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Brand-new results from the MicroBooNE experiment at the U.S. Department of Energys Fermi National Accelerator Laboratory deal a blow to a theoretical particle understood as the sterilized neutrino. For more than two decades, this proposed fourth neutrino has actually stayed an appealing description for abnormalities seen in earlier physics experiments. Discovering a brand-new particle would be a major discovery and an extreme shift in our understanding of the universe.
4 complementary analyses released by the worldwide MicroBooNE collaboration and provided during a seminar today all reveal the very same thing: no indication of the sterile neutrino. Rather, the outcomes align with the Standard Model of Particle Physics, scientists best theory of how the universe works. The information follows what the Standard Model predicts: three sort of neutrinos– no more, no less.

The experiment studies neutrino interactions and has found no tip of a theorized fourth neutrino called the sterile neutrino. With sterile neutrinos even more disfavored as the explanation for abnormalities identified in neutrino information, researchers are examining other possibilities. While neutrinos are already difficult to spot, the proposed sterile neutrino would be even more elusive, responding just to the force of gravity. Because neutrinos sweep in between the different types, a sterile neutrino could affect the way neutrinos oscillate, leaving its signature in the data.
Together with MicroBooNE, the three experiments form the Short-Baseline Neutrino Program at Fermilab and will produce a wealth of neutrino information.