From Fermi National Accelerator Lab: “MINERvA successfully completes its physics run”

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FNAL Art Image by Angela Gonzales

From Fermi National Accelerator Lab , an enduring source of strength for the US contribution to scientific research world wide.

April 5, 2019
Caitlyn Buongiorno

FNAL MINERvA front face Photo Reidar Hahn

On Feb. 26, a crowd of engineers, technicians and analysts crowded around a computer screen as Fermilab scientist Deborah Harris pressed “stop” on the data collection for the MINERvA neutrino experiment.

“We’re all just really excited by what we’ve accomplished,” said Harris, MINERvA co-spokesperson and future professor at York University. “The detector worked wonderfully, we collected the data we need, and we did it on schedule.”

MINERvA studies how neutrinos and their antimatter twins, antineutrinos, interact with the nuclei of different atoms. Scientists use that data to help discover the best models of these interactions. Now, after nine years of operation, the data taking has come to an end, but the analysis will continue for a while. MINERvA scientists have published more than 30 scientific papers so far, with more to come. As of today, 58 students have obtained their master’s or Ph.D. degrees doing research with this experiment.

Neutrinos could hold the answer to one of the most pressing mysteries in physics: why matter was not completely annihilated by antimatter after the Big Bang. That imbalance from 13.7 billion years ago led the universe to develop into what we see today. Studying neutrinos (and antineutrinos) could uncover the mystery and help us understand why we are here at all.

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The MINERvA collaboration gathers to celebrate the end of data taking. MINERvA co-spokesperson Laura Fields, kneeling at center, holds a 3-D-printed model of the MINERvA neutrino detector. Photo: Reidar Hahn

A number of neutrino experiments investigate this mystery, including Fermilab’s NOvA experiment and the upcoming international Deep Underground Neutrino Experiment, hosted by Fermilab.

FNAL/NOvA experiment map


FNAL NOvA Near Detector

FNAL LBNF/DUNE from FNAL to SURF, Lead, South Dakota, USA


FNAL DUNE Argon tank at SURF


SURF DUNE LBNF Caverns at Sanford Lab

To be as successful as possible, these experiments need precise models that describe what happens before and after a neutrino collides with an atom.

Every time a neutrino collides with part of an atom inside a detector, a spray of new particles flies off and travels through the rest of the detector. In order to understand the nuances of neutrinos, scientists need to know the energy of the neutrino when it first enters the detector and the energy of all the particles produced after the interaction. This task is complicated by the fact that some of the outgoing particles are invisible to the detector — and must still be accounted for.

Imagine you’re playing pool and you shoot the cue ball at another ball. You can easily predict where that second ball will go. That prediction, however, gets much more complex when your cue ball strikes a collection of balls. After the break shot, they scatter in all directions, and it’s hard to predict where each will go. The same thing is true when a neutrino interacts with a lone particle: You can easily predict where the lone ball will go. But when a neutrino interacts with an atom’s nucleus — a collection of protons and neutrons — the calculation is much more difficult because, like the pool balls, particles may go off in many different directions.

“It’s actually worse than that,” said Kevin McFarland, former MINERvA co-spokesperson and professor of physics at the University of Rochester. “All the balls in the break shot are also connected by springs.”

MINERvA provides a neutrino-nucleus interaction guidebook for neutrino researchers. The experiment measured neutrino interactions with polystyrene, carbon, iron, lead, water and helium. Without MINERvA’s findings, researchers at other experiments would have a much tougher time understanding the outcomes of these interactions and how to interpret their data.

“I really am proud of what we’ve been able to accomplish so far,” said Laura Fields, Fermilab scientist and co-spokesperson for MINERvA. “Already the world has a much greater understanding of these interactions.”

See the full article here.


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Fermi National Accelerator Laboratory (Fermilab), located just outside Batavia, Illinois, near Chicago, is a US Department of Energy national laboratory specializing in high-energy particle physics. Fermilab is America’s premier laboratory for particle physics and accelerator research, funded by the U.S. Department of Energy. Thousands of scientists from universities and laboratories around the world collaborate at Fermilab on experiments at the frontiers of discovery.

FNAL MINERvA front face Photo Reidar Hahn

FNAL DAMIC

FNAL Muon g-2 studio

FNAL Short-Baseline Near Detector under construction

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Dark Energy Camera [DECam], built at FNAL

FNAL DUNE Argon tank at SURF

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FNAL MINOS Far Detector in the Soudan Mine in northern Minnesota

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From Fermilab: “The secret to measuring the energy of an antineutrino”

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FNAL Art Image by Angela Gonzales

From Fermilab , an enduring source of strength for the US contribution to scientific research world wide.

June 18, 2018
No writer credit found

Scientists study tiny particles called neutrinos to learn about how our universe evolved. These particles, well-known for being tough to detect, could tell the story of how matter won out over antimatter a fraction of a second after the Big Bang and, consequently, why we’re here at all.

Getting to the bottom of that split-second history means uncovering the differences, if any, between the neutrino and its antimatter counterpart, the antineutrino.

The MINERvA neutrino experiment at Fermilab recently added some detail to the behavior profiles of neutrinos and antineutrinos: Scientists measured the likelihood that these famously fleeting particles would stop in the MINERvA detector. In particular, they looked at cases in which an antineutrino interacting in the detector produced another particle, a neutron — that familiar particle that, along with the proton, makes up an atom’s nucleus.

MINERvA’s studies of such cases benefit other neutrino experiments, which can use the results to refine their own measurements of similar interactions.

It’s typical to study the particles produced by the interaction of a neutrino (or antineutrino) to get a bead on the neutrino’s behavior. Neutrinos are effortless escape artists, and their Houdini-like nature makes it difficult to measure their energies directly. They sail unimpeded through everything — even lead. Scientists are tipped off to the rare neutrino interaction by the production of other, more easily detected particles. They measure and sum the energies of these exiting particles and thus indirectly measure the energy of the neutrino that kicked everything off.

This particular MINERvA study — antineutrino enters, neutron leaves — is a difficult case. Most postinteraction particles deposit their energies in the particle detector, leaving tracks that scientists can trace back to the original antineutrino (or neutrino, as the case may be).

But in this experiment, the neutron doesn’t. It holds on to its energy, leaving almost none in the detector. The result is a practically untraceable, unaccounted energy that can’t easily be entered in the energy books. And unfortunately, antineutrinos are good at producing energy-absconding neutrons.

Researchers make the best of missing-energy situations. They predict, based on other studies, how much energy is lost and correct for it.

To give the scientific community a data-based, predictive tool for missing-energy moments, MINERvA collected data from the worst-case situation: An antineutrino strikes a nucleus in the detector and knocks out the untraceable neutron so nearly all of the energy bestowed to the nucleus goes “poof.” (These interactions also produce positively charged particles called muons which signal the antineutrino interaction.) By studying this particular disappearing act, scientists could directly measure the effects of the missing energy.

FNAL/MINERvA

Scientists at Fermilab use the MINERvA to make measurements of neutrino interactions that can support the work of other neutrino experiments. Photo Reidar Hahn

Other researchers can now look for these effects, applying the lessons learned to similar cases. For example, researchers on Fermilab’s largest operating neutrino experiment, NOvA, and the Japanese T2K experiment will use this technique in their antineutrino measurements.

FNAL/NOvA experiment map

FNAL Near Detector

NOvA Far detector 15 metric-kiloton far detector in Minnesota just south of the U.S.-Canada border schematic


NOvA Far Detector Block

T2K Experiment, Tokai to Kamioka, Japan


T2K map, T2K Experiment, Tokai to Kamioka, Japan

And the Fermilab-hosted international Deep Underground Neutrino Experiment, centerpiece of a world-leading neutrino program, will also benefit from this once it begins collecting data in the 2020s.

SURF DUNE LBNF Caverns at Sanford Lab


FNAL DUNE Argon tank at SURF


FNAL LBNF/DUNE from FNAL to SURF, Lead, South Dakota, USA

The neutron production case is just one type of missing-energy interaction, one of many. So the model that comes out of this MINERvA study is an admittedly imperfect one. There can’t be a one-size-fits-all-missing-energy-scenarios model. But it still provides a useful tool for piecing together a neutrino’s energy — and that’s a tough task no matter what particles come out of the interaction.

“This analysis is a great testament to both the detector’s ability to measure neutrino interactions and to the collaboration’s ability to develop new strategies,” said Fermilab scientist and MINERvA co-spokesperson Deborah Harris. “When we started MINERvA, this analysis was not even a gleam in anyone’s eye.”

There’s a bonus to this recent study, too, one that bolsters an investigation conducted last year.

For the earlier investigation, MINERvA focused on neutrino (instead of antineutrino) interactions that knocked out proton-neutron pairs (instead of lone neutrons or protons). In a detector such as MINERvA, a proton’s energy is much easier to measure than a neutron’s, so the earlier study presumably yielded more precise measurements than the recent antineutrino study.

How good were these measurements? MINERvA scientists plugged the values of the earlier neutrino study into a model of this recent antineutrino study to see what would pop out. Lo and behold, the adjustment to the antineutrino model improved its ability to predict the data.

The combination of the two studies gives the neutrino physics community new information about how well models do and where they fall short. Searches for the phenomenon known as CP violation — the thing that makes matter special compared to antimatter and enabled it to conquer in the post-Big Bang battle — depend on comparing neutrino and antineutrino samples and looking for small differences. Large, unknown differences between neutrino and antineutrino reaction products would hide the presence or absence of CP signatures.

“We are no longer worried about large differences, and our neutrino program can work with small adjustments to known differences,” said University of Minnesota–Duluth physicist Rik Gran, lead author on this result.

MINERvA is homing in on models that, with each new test, better describe both neutrino and antineutrino data — and thus the story of how the universe came to be.

These results appeared on June 1, 2018, in Physical Review Letters.

See the full article here .


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Fermi National Accelerator Laboratory (Fermilab), located just outside Batavia, Illinois, near Chicago, is a US Department of Energy national laboratory specializing in high-energy particle physics. Fermilab is America’s premier laboratory for particle physics and accelerator research, funded by the U.S. Department of Energy. Thousands of scientists from universities and laboratories around the world
collaborate at Fermilab on experiments at the frontiers of discovery.


FNAL/MINERvA

FNAL DAMIC

FNAL Muon g-2 studio

FNAL Short-Baseline Near Detector under construction

FNAL Mu2e solenoid

Dark Energy Camera [DECam], built at FNAL

FNAL DUNE Argon tank at SURF

FNAL/MicrobooNE

FNAL Don Lincoln

FNAL/MINOS

FNAL Cryomodule Testing Facility

FNAL Minos Far Detector

FNAL LBNF/DUNE from FNAL to SURF, Lead, South Dakota, USA

FNAL/NOvA experiment map

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From Yale University: “PROSPECTing for antineutrinos”

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From Yale University

ORNL

May 18, 2018
Jim Shelton
james.shelton@yale.edu
203-361-8332

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Assembly of the PROSPECT neutrino detector. (Image credit: PROSPECT collaboration/Mara Lavitt)

The Precision Reactor Oscillation and Spectrum Experiment (PROSPECT) has completed the installation of a novel antineutrino detector that will probe the possible existence of a new form of matter.

PROSPECT, located at the High Flux Isotope Reactor (HFIR) at the Department of Energy’s Oak Ridge National Laboratory (ORNL), has begun taking data to study electron antineutrinos that are emitted from nuclear decays in the reactor to search for so-called sterile neutrinos and to learn about the underlying nuclear reactions that power fission reactors.

Antineutrinos are elusive, elementary particles produced in nuclear beta decay. The antineutrino is an antimatter particle, the counterpart to the neutrino.

“Neutrinos are among the most abundant particles in the universe,” said Yale University physicist Karsten Heeger, principal investigator and co-spokesperson for PROSPECT. “The discovery of neutrino oscillation has opened a window to physics beyond the Standard Model of Physics. The study of antineutrinos with PROSPECT allows us to search for a previously unobserved particle, the so-called sterile neutrino, while probing the nuclear processes inside a reactor.”

Over the past few years several neutrino experiments at nuclear reactors have detected fewer antineutrinos than scientists had predicted, and the energy of the neutrinos did not match expectations. This, in combination with earlier anomalous results, led to the hypothesis that a fraction of electron antineutrinos may transform into sterile neutrinos that would have remained undetected in previous experiments.

This hypothesized transformation would take place through a quantum mechanical process called neutrino oscillation. The first observation of neutrino oscillation amongst known types of neutrinos from the sun and the atmosphere led to the 2015 Nobel Prize in physics.

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(Image credit: PROSPECT collaboration/Mara Lavitt)

The installation of PROSPECT follows four years of intensive research and development by a collaboration of more than 60 participants from 10 universities and four national laboratories.

“The development of PROSPECT is based on years of research in the detection of reactor antineutrinos with surface-based detectors, an extremely challenging task because of high backgrounds,” said PROSPECT co-spokesperson Pieter Mumm, a scientist at the National Institute of Standards and Technology (NIST).

The experiment uses a novel antineutrino detector system based on a segmented liquid scintillator detector technology. The combination of segmentation and a unique, lithium-doped liquid scintillator formulation allows PROSPECT to identify particle types and interaction points. These design features, along with extensive, tailored shielding, will enable PROSPECT to make a precise measurement of neutrinos in the high-background environment of a nuclear reactor.

PROSPECT’s detector technology also may have applications in the monitoring of nuclear reactors for non-proliferation purposes and the measurement of neutrons from nuclear processes.

“The successful operation of PROSPECT will allow us to gain insight into one of the fundamental puzzles in neutrino physics and develop a better understanding of reactor fuel, while also providing a new tool for nuclear safeguards,” said co-spokesperson Nathaniel Bowden, a scientist at Lawrence Livermore National Laboratory and an expert in nuclear non-proliferation technology.

After two years of construction and final assembly at the Yale Wright Laboratory, the PROSPECT detector was transported to HFIR in early 2018.

“The development and construction of PROSPECT has been a significant team effort, making use of the complementary expertise at U.S. national laboratories and universities,” said Alfredo Galindo-Uribarri, leader of the Neutrino and Advanced Detectors group in ORNL’s Physics Division.

PROSPECT is the latest in a series of fundamental science experiments located at HFIR. “We are excited to work with PROSPECT scientists to support their research,” said Chris Bryan, who manages experiments at HFIR for ORNL’s Research Reactors Division.

The experiment is supported by the U.S. Department of Energy Office of Science, the Heising-Simons Foundation, and the National Science Foundation. Additional support comes from Yale University, the Illinois Institute of Technology, and the Lawrence Livermore National Laboratory LDRD program. The collaboration also benefits from the support and hospitality of the High Flux Isotope Reactor, a DOE Office of Science User Facility, and Oak Ridge National Laboratory, managed by UT-Battelle for the U.S. Department of Energy.

See the full article here .

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Yale University comprises three major academic components: Yale College (the undergraduate program), the Graduate School of Arts and Sciences, and the professional schools. In addition, Yale encompasses a wide array of centers and programs, libraries, museums, and administrative support offices. Approximately 11,250 students attend Yale.

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From astrobites: “Antineutrinos, Left-Handed Molecules, and You”

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From astrobites

May 10, 2018
Kerrin Hensley

Title: Sites That Can Produce Left-Handed Amino Acids in the Supernova Neutrino Amino Acid Processing Model
Authors: Richard N. Boyd, Michael A. Famiano, Takashi Onaka, and Toshitaka Kajino
First Author’s Institution: The Ohio State University

Status: Published in The Astrophysical Journal, open access on arXiv

Scientists are enamored with the search for life. They’ve scoured spectra for hints of life-supporting gases in the atmospheres of exoplanets. They’ve assessed the friendliness of galaxies near and far, and found the universe to be an unforgiving place. They’ve plumbed the depths of the oceans and studied pristine Antarctic lakes to understand the harsh conditions life might be able to withstand elsewhere in the cosmos.

The search for life on other worlds has been guided by what we know about life on Earth. Life as we know it depends on amino acids to survive. Today’s paper explores the effects of exotic astrophysical settings on amino acids, which could tell us something about how life came to be on Earth — and where else in the universe life like Earth’s might be found.

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Figure 1. A simple amino acid, alanine. The two forms of alanine, shown on the left, are a chiral pair. The rightmost drawing shows that right-handed alanine (center, right) can’t be converted to left-handed alanine (left) just by turning the molecule over. The solid triangle indicates that that part of the molecule sticks out of the plane of the page, while the dashed triangle indicates that that part of the molecule is directed backward, into the page.

See the full article here .

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Astrobites is a daily astrophysical literature journal written by graduate students in astronomy. Our goal is to present one interesting paper per day in a brief format that is accessible to undergraduate students in the physical sciences who are interested in active research.
Why read Astrobites?

Reading a technical paper from an unfamiliar subfield is intimidating. It may not be obvious how the techniques used by the researchers really work or what role the new research plays in answering the bigger questions motivating that field, not to mention the obscure jargon! For most people, it takes years for scientific papers to become meaningful.
Our goal is to solve this problem, one paper at a time. In 5 minutes a day reading Astrobites, you should not only learn about one interesting piece of current work, but also get a peek at the broader picture of research in a new area of astronomy.

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From FNAL: “The secret to measuring an antineutrino’s energy”

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FNAL Art Image by Angela Gonzales

Fermilab is an enduring source of strength for the US contribution to scientific research world wide.

March 28, 2018
Miranda Elkins
Rik Gran

1
These plots show the reconstructed available energy transferred for two different regions of momentum transfer for antineutrino data at MINERvA along with predictions both before (above) and after (below) a model that was tuned on neutrino data. The antineutrino data seem to agree with the prediction that was based on the neutrino data for most events.

It is no secret that neutrinos change flavor or oscillate as they travel from one place to another, and that the amount they change depends on how much time they have to change. This time is directly related to the distance the neutrino traveled and the energy of the neutrino itself. Measuring the distance is easy. The hard part is measuring the neutrino energy.

Experiments do this by measuring the energies of particles that get produced by the neutrino when it interacts in their detectors. But what happens if one of the produced particles, for example a neutron, leaves barely any of its energy in the detector?

Oscillation experiments have to predict how much energy is lost and then correct for that loss. These predictions depend on accurate models of how neutrinos interact, and those models have to be right not only for neutrinos but also for antineutrinos, which are particularly good at making neutrons.

The MINERvA collaboration analyzed data from interactions of antineutrinos that produced positively charged muons. Scientists looked at both the momentum and energy that was transferred to the nucleus in those interactions. By focusing on the kinematic region where only a neutron should be knocked out, they looked at the worst-case situation: Most of the hadronic energy will go missing. In this way, scientists directly measured the effects of an imperfect model for missing energy.

In order to appreciate why this new analysis of antineutrino interactions is exciting, you should know that over a year ago, MINERvA published a similar measurement with neutrino interactions producing negatively charged muons, where a proton is much more likely to be produced than a neutron. A proton’s energy is much easier to measure than a neutron’s in a detector such as MINERvA. This analysis found that, for neutrino interactions on a proton-neutron pair (rather than on only one of those two particles), scientists observed a much larger number of events than the state-of-the art models predicted. Neutrino cross section enthusiasts are never surprised when models don’t describe data. So here is the surprise: When they used the neutrino results to change the antineutrino model to predict the antineutrino data described above, it worked. You can see the improvement in the middle of the plots above.

This is interesting, because this is new information about how well models do and where they fall short. Searches for CP violation or “what makes matter special compared to antimatter” depend on comparing neutrino and antineutrino samples and looking for small differences. Large, unknown differences between neutrino and antineutrino reaction rates would hide the presence or absence of CP signatures. We are converging on better models that describe both neutrino and antineutrino data.

Those results were just released to the world this week [arXiv.org], and you can watch the seminar where they were presented.

See the full article here .

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Fermi National Accelerator Laboratory (Fermilab), located just outside Batavia, Illinois, near Chicago, is a US Department of Energy national laboratory specializing in high-energy particle physics. Fermilab is America’s premier laboratory for particle physics and accelerator research, funded by the U.S. Department of Energy. Thousands of scientists from universities and laboratories around the world collaborate at Fermilab on experiments at the frontiers of discovery.

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FNAL DAMIC

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FNAL Short-Baseline Near Detector under construction

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Dark Energy Camera [DECam], built at FNAL

FNAL DUNE Argon tank at SURF

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From LBNL: “Experiment Provides Deeper Look into the Nature of Neutrinos”

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Berkeley Lab

October 23, 2017
Glenn Roberts Jr.
geroberts@lbl.gov
(510) 486-5582

The first glimpse of data from the full array of a deeply chilled particle detector operating beneath a mountain in Italy sets the most precise limits yet on where scientists might find a theorized process to help explain why there is more matter than antimatter in the universe.

This new result, submitted today to the journal Physical Review Letters, is based on two months of data collected from the full detector of the CUORE (Cryogenic Underground Observatory for Rare Events) experiment at the Italian National Institute for Nuclear Physics’ (INFN’s) Gran Sasso National Laboratories (LNGS) in Italy. CUORE means “heart” in Italian.

The CUORE detector array, shown here in this rendering is formed by 19 copper-framed “towers” that each house a matrix of 52 cube-shaped crystals Credit CUORE collaboration

CUORE experiment UC Berkeley, experiment at the Italian National Institute for Nuclear Physics’ (INFN’s) Gran Sasso National Laboratories (LNGS), a search for neutrinoless double beta decay

Gran Sasso LABORATORI NAZIONALI del GRAN SASSO, located in the Abruzzo region of central Italy

The Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) leads the U.S. nuclear physics effort for the international CUORE collaboration, which has about 150 members from 25 institutions. The U.S. nuclear physics program has made substantial contributions to the fabrication and scientific leadership of the CUORE detector.

CUORE is considered one of the most promising efforts to determine whether tiny elementary particles called neutrinos, which interact only rarely with matter, are “Majorana particles” – identical to their own antiparticles. Most other particles are known to have antiparticles that have the same mass but a different charge, for example. CUORE could also help us home in on the exact masses of the three types, or “flavors,” of neutrinos – neutrinos have the unusual ability to morph into different forms.

“This is the first preview of what an instrument this size is able to do,” said Oliviero Cremonesi, a senior faculty scientist at INFN and spokesperson for the CUORE collaboration. Already, the full detector array’s sensitivity has exceeded the precision of the measurements reported in April 2015 after a successful two-year test run that enlisted one detector tower. Over the next five years CUORE will collect about 100 times more data.

Yury Kolomensky, a senior faculty scientist in the Nuclear Science Division at Lawrence Berkeley National Laboratory (Berkeley Lab) and U.S. spokesperson for the CUORE collaboration, said, “The detector is working exceptionally well and these two months of data are enough to exceed the previous limits.” Kolomensky is also a professor in the UC Berkeley Physics Department.

The new data provide a narrow range in which scientists might expect to see any indication of the particle process it is designed to find, known as neutrinoless double beta decay.

“CUORE is, in essence, one of the world’s most sensitive thermometers,” said Carlo Bucci, technical coordinator of the experiment and Italian spokesperson for the CUORE collaboration. Its detectors, formed by 19 copper-framed “towers” that each house a matrix of 52 cube-shaped, highly purified tellurium dioxide crystals, are suspended within the innermost chamber of six nested tanks.

Cooled by the most powerful refrigerator of its kind, the tanks subject the detector to the coldest known temperature recorded in a cubic meter volume in the entire universe: minus 459 degrees Fahrenheit (10 milliKelvin).

The detector array was designed and assembled over a 10-year period. It is shielded from many outside particles, such as cosmic rays that constantly bombard the Earth, by the 1,400 meters of rock above it, and by thick lead shielding that includes a radiation-depleted form of lead rescued from an ancient Roman shipwreck. Other detector materials were also prepared in ultrapure conditions, and the detectors were assembled in nitrogen-filled, sealed glove boxes to prevent contamination from regular air.

“Designing, building, and operating CUORE has been a long journey and a fantastic achievement,” said Ettore Fiorini, an Italian physicist who developed the concept of CUORE’s heat-sensitive detectors (tellurium dioxide bolometers), and the spokesperson-emeritus of the CUORE collaboration. “Employing thermal detectors to study neutrinos took several decades and brought to the development of technologies that can now be applied in many fields of research.”

Together weighing over 1,600 pounds, CUORE’s matrix of roughly fist-sized crystals is extremely sensitive to particle processes, especially at this extreme temperature. Associated instruments can precisely measure ever-slight temperature changes in the crystals resulting from these processes.

Berkeley Lab and Lawrence Livermore National Laboratory scientists supplied roughly half of the crystals for the CUORE project. In addition, the Berkeley Lab team designed and fabricated the highly sensitive temperature sensors – called neutron transmutation doped thermistors – invented by Eugene Haller, a senior faculty scientist in Berkeley Lab’s Materials Sciences Division and a UC Berkeley faculty member.

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CUORE was assembled in this specially designed clean room to help protect it from contaminants. (Credit: CUORE collaboration)

Berkeley Lab researchers also designed and built a specialized clean room supplied with air depleted of natural radioactivity, so that the CUORE detectors could be installed into the cryostat in ultraclean conditions. And Berkeley Lab scientists and engineers, under the leadership of UC Berkeley postdoc Vivek Singh, worked with Italian colleagues to commission the CUORE cryogenic systems, including a uniquely powerful cooling system called a dilution refrigerator.

Former UC Berkeley postdoctoral students Tom Banks and Tommy O’Donnell, who also had joint appointments in the Nuclear Science Division at Berkeley Lab, led the international team of physicists, engineers, and technicians to assemble over 10,000 parts into towers in nitrogen-filled glove boxes. They bonded almost 8,000 gold wires, measuring just 25 microns in diameter, to 100-micron sized pads on the temperature sensors, and on copper pads connected to detector wiring.

CUORE measurements carry the telltale signature of specific types of particle interactions or particle decays – a spontaneous process by which a particle or particles transform into other particles.

In double beta decay, which has been observed in previous experiments, two neutrons in the atomic nucleus of a radioactive element become two protons. Also, two electrons are emitted, along with two other particles called antineutrinos.

Neutrinoless double beta decay, meanwhile – the specific process that CUORE is designed to find or to rule out – would not produce any antineutrinos. This would mean that neutrinos are their own antiparticles. During this decay process the two antineutrino particles would effectively wipe each other out, leaving no trace in the CUORE detector. Evidence for this type of decay process would also help scientists explain neutrinos’ role in the imbalance of matter vs. antimatter in our universe.

Neutrinoless double beta decay is expected to be exceedingly rare, occurring at most (if at all) once every 100 septillion (1 followed by 26 zeros) years in a given atom’s nucleus. The large volume of detector crystals is intended to greatly increase the likelihood of recording such an event during the lifetime of the experiment.

There is growing competition from new and planned experiments to resolve whether this process exists using a variety of search techniques, and Kolomensky noted, “The competition always helps. It drives progress, and also we can verify each other’s results, and help each other with materials screening and data analysis techniques.”

Lindley Winslow of the Massachusetts Institute of Technology, who coordinated the analysis of the CUORE data, said, “We are tantalizingly close to completely unexplored territory and there is great possibility for discovery. It is an exciting time to be on the experiment.”

CUORE is supported jointly by the Italian National Institute for Nuclear Physics Istituto Nazionale di Fisica Nucleare (INFN) in Italy, and the U.S. Department of Energy’s Office of Nuclear Physics, the National Science Foundation, and the Alfred P. Sloan Foundation in the U.S. The CORE collaboration includes about 150 scientists from Italy, U.S., China, France, and Spain, and is based in the underground Italian facility called INFN Gran Sasso National Laboratories (LNGS) of the INFN.

CUORE collaboration members include: Italian National Institute for Nuclear Physics (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; 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 US; Saclay Nuclear Research Center (CEA) and the Center for Nuclear Science and Materials Science (CNRS/IN2P3) in France; and the Shanghai Institute of Applied Physics and Shanghai Jiao Tong University in China.

The U.S.-CUORE team was lead by late Prof. Stuart Freedman until his untimely passing in 2012. Other current and former Berkeley Lab members of the CUORE collaboration not previously mentioned include US Contractor Project Manager Sergio Zimmermann (Engineering Division), former U.S. Contractor Project Manager Richard Kadel, staff scientists Jeffrey Beeman, Brian Fujikawa, Sarah Morgan, Alan Smith, postdocs Giovanni Benato, Raul Hennings-Yeomans, Ke Han, Yuan Mei, Bradford Welliver, Benjamin Schmidt, graduate students Adam Bryant, Alexey Drobizhev, Roger Huang, Laura Kogler, Jonathan Ouellet, and Sachi Wagaarachchi, and engineers David Biare, Luigi Cappelli, Lucio di Paolo, and Joseph Wallig.

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From LBNL: “New Measurements Suggest ‘Antineutrino Anomaly’ Fueled by Modeling Error”

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Berkeley Lab

April 5, 2017

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Antineutrinos produced by reactors at the Daya Bay Nuclear Power Plant complex in Shenzhen, China, are measured in a particle physics experiment that is conducted by an international collaboration involving Berkeley Lab researchers. (Credit: Roy Kaltschmidt/Berkeley Lab)

Daya Bay, approximately 52 kilometers northeast of Hong Kong and 45 kilometers east of Shenzhen, China

Results from a new scientific study may shed light on a mismatch between predictions and recent measurements of ghostly particles streaming from nuclear reactors—the so-called “reactor antineutrino anomaly,” which has puzzled physicists since 2011.

The anomaly refers to the fact that scientists tracking the production of antineutrinos—emitted as a byproduct of the nuclear reactions that generate electric power—have routinely detected fewer antineutrinos than they expected. One theory is that some neutrinos are morphing into an undetectable form known as “sterile” neutrinos.

But the latest results [submitted to Phys. Rev. Letters] from the Daya Bay reactor neutrino experiment, located at a nuclear power complex in China, suggest a simpler explanation—a miscalculation in the predicted rate of antineutrino production for one particular component of nuclear reactor fuel.

Antineutrinos carry away about 5 percent of the energy released as the uranium and plutonium atoms that fuel the reactor split, or “fission.” The composition of the fuel changes as the reactor operates, with the decays of different forms of uranium and plutonium (called “isotopes”) producing different numbers of antineutrinos with different energy ranges over time, even as the reactor steadily produces electrical power.

The new results from Daya Bay—where scientists have measured more than 2 million antineutrinos produced by six reactors during almost four years of operation—have led scientists to reconsider how the composition of the fuel changes over time and how many neutrinos come from each of the decay chains.

The scientists found that antineutrinos produced by nuclear reactions that result from the fission of uranium-235, a fissile isotope of uranium common in nuclear fuel, were inconsistent with predictions.

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In this chart, the yields of reactor antineutrinos produced by plutonium-239 (vertical) and uranium-235 (horizontal) measured by the Daya Bay experiment (red triangle at center) are compared to the theoretical prediction (black dot at right), showing a discrepancy that could explain the so-called “antineutrino anomaly.” (Credit: Daya Bay Collaboration)

“The model predicts almost 8 percent more antineutrinos coming from decays of uranium-235 than what we have measured,” said Kam-Biu Luk, a Daya Bay Collaboration co-spokesperson who is a faculty senior scientist at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) and a physics professor at UC Berkeley.

Patrick Tsang, who conceptualized a new data-analysis technique that was key in this study while working as a postdoctoral fellow in Berkeley Lab’s Physics Division, added, “The finding is surprising because it is the first time we are able to identify the disagreement with predictions for a particular fission isotope.” Tsang is now a project scientist working at SLAC National Accelerator Laboratory.

Meanwhile, the number of antineutrinos from plutonium-239, the second most common fuel ingredient, was found to agree with predictions, although this measurement is less precise than that for uraninum-235.

If sterile neutrinos—theoretical particles that are a possible source of the universe’s vast unseen or “dark” matter—were the source of the anomaly, then the experimenters would observe an equal depletion in the number of antineutrinos for each of the fuel ingredients, but the experimental results disfavor this hypothesis.

The latest analysis suggests that a miscalculation of the rate of antineutrinos produced by the fission of uranium-235 over time, rather than the presence of sterile neutrinos, may be the explanation for the anomaly. These results can be confirmed by new experiments that will measure antineutrinos from reactors fueled almost entirely by uranium-235.

The work could help scientists at Daya Bay and similar experiments understand the fluctuating rates and energies of those antineutrinos produced by specific ingredients in the nuclear fission process throughout the nuclear fuel cycle. An improved understanding of the fuel evolution inside a nuclear reactor may also be helpful for other nuclear science applications.

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A view inside a particle detector tank at Daya Bay, where photomultiplier tubes measure signals from antineutrinos. (Credit: Roy Kaltschmidt/Berkeley Lab)

Situated about 32 miles northeast of Hong Kong, the Daya Bay experiment uses an array of detectors to capture antineutrino signals from particle interactions occurring in a series of liquid tanks. The Daya Bay collaboration involves 243 researchers at 41 institutions in the U.S., China, Chile, Russia and the Czech Republic.

Daya Bay physics research is supported by the U.S. Department of Energy’s Office of Science and the National Science Foundation.

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