From Fermi National Accelerator Lab: “Discovery of a new type of particle beam instability”

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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.

November 14, 2019
Alexey Burov

Accelerated, charged particle beams do what light does for microscopes: illuminate matter. The more intense the beams, the more easily scientists can examine the object they are looking at. But intensity comes with a cost: the more intense the beams, the more they become prone to instabilities.

One type of instability occurs when the average energy of accelerated particles traveling through a circular machine reaches its transition value. The transition point occurs when the particles revolve around the ring at the same rate, even though they do not all carry the same energy — in fact, they exhibit a range of energies. The specific motion of the particles near the transition energy makes them extremely prone to collective instabilities.

These particular instabilities were observed for decades, but they were not sufficiently understood. In fact, they were misinterpreted. In a paper published this year, I suggest a new theory about these instabilities. The application of this theory to the Fermilab Booster accelerator predicted the main features of the instability there at the transition crossing, suggesting better ways to suppress the instability. Recent measurements confirmed the predictions, and more detailed experimental beam studies are planned in the near future.

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Recent measurements at the Fermilab Booster accelerator confirmed existence of a certain kind of particle beam instability. More measurements are planned for the near future to examine new methods proposed to mitigate it.

Accelerating high-intensity beams is a crucial part of the Fermilab scientific program. A solid theoretical understanding of particle beam behavior equips experimentalists to better manipulate the accelerator parameters to suppress instability. This leads to the high-intensity beams needed for Fermilab’s experiments in fundamental physics. It is also useful for any experiment or institution operating circular accelerators.

Beam protons talk to each other by electromagnetic fields, which are of two kinds. One is called the Coulomb field. These fields are local and, by themselves, cannot drive instabilities. The second kind is the wake field. Wake fields are radiated by the particles and trail behind them, sometimes far behind.

When a particle strays from the beam path, the wake field translates this departure backward — in the wake left by the particle. Even a small departure from the path may not escape being carried backward by these electromagnetic fields. If the beams are intense enough, their wakes can destabilize them.

In the new theory, I suggested a compact mathematical model that effectively takes both sorts of fields into account, realizing that both of them are important when they are strong enough, as they typically are near transition energy.

This kind of huge amplification happens at CERN’s Proton Synchrotron, for example, as I showed in my more recent paper, submitted to Physical Review Accelerators and Beams. If not suppressed one way or another, this amplification may grow until the beam touches the vacuum chamber wall and becomes lost. Recent measurements at the Fermilab Booster confirmed existence of a similar instability there; more measurements are planned for the near future to examine new methods proposed to mitigate it.

These phenomena are called transverse convective instabilities, and the discoveries of how they arise open new doors to theoretical, numerical and experimental ways to better understanding and better dealing with the intense proton beams.

This work is supported by the DOE Office of Science.

Science paper:
Convective instabilities of bunched beams with space charge
Physical Review Accelerators and Beams

See the full 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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From Symmetry: “How do you make the world’s most powerful neutrino beam?”

Symmetry Mag
From Symmetry<

11/13/19
Lauren Biron

DUNE will need lots of neutrinos—and to make them, scientists and engineers will use extreme versions of some common sounding ingredients: magnets and pencil lead.

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Photo by Reidar Hahn, Fermilab

What do you need to make the most intense beam of neutrinos in the world? Just a few magnets and some pencil lead. But not your usual household stuff. After all, this is the world’s most intense high-energy neutrino beam, so we’re talking about jumbo-sized parts: magnets the size of park benches and ultrapure rods of graphite as tall as Danny DeVito.

Physics experiments that push the extent of human knowledge tend to work at the extremes: the biggest and smallest scales, the highest intensities. All three are true for the international Deep Underground Neutrino Experiment, hosted by the Department of Energy’s Fermilab.

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

The design of the experiment is elegant—produce neutrinos and measure them at Fermilab, send them straight through 1,300 kilometers of earth, then measure them again in giant liquid-argon detectors at Sanford Lab.
Courtesy of Fermilab

The experiment brings together more than 1000 people from 30-plus countries to tackle questions that have kept many a person awake at night: Why is the universe full of matter and not antimatter, or no matter at all? Do protons, one of the building blocks of atoms (and of us), ever decay? How do black holes form? And did I leave the stove on?

Maybe not the last one.

To tackle the biggest questions, DUNE will look at mysterious subatomic particles called neutrinos: neutral, wispy wraiths that rarely interact with matter. Because neutrinos are so antisocial, scientists will build enormous particle detectors to catch and study them. More matter inside the DUNE detectors means more things for neutrinos to interact with, and these behemoth neutrino traps will contain a total of 70,000 tons of liquid argon. At their home 1.5 kilometers below the rock in the Sanford Underground Research Facility in South Dakota, they’ll be shielded from interfering cosmic rays—though neutrinos will have no trouble passing through that buffer and hitting their mark.

SURF-Sanford Underground Research Facility, Lead, South Dakota, USA

The detectors can pick up neutrinos from exploding stars that might evolve into black holes and capture interactions from a deliberately aimed beam of neutrinos.

Neutrinos (and their antimatter counterparts, antineutrinos) are born as other particles decay, carrying away small amounts of energy to balance the cosmic ledger. You’ll find them coming in droves from stars like our sun, inside Earth, even the potassium in bananas. But if you want to make trillions of high-energy neutrinos every second and send them to a particle detector deep underground, you’d be hard-pressed to do it by throwing fruit toward South Dakota.

That’s where Fermilab’s particle accelerator complex comes in.

Fermilab sends particles through a series of accelerators, each adding a burst of speed and energy. Work has started for an upgrade to the complex that will include a new linear accelerator at the start of the journey: PIP-II. This is the first accelerator project in the United States with major international contributions, and it will propel particles to 84% of the speed of light as they travel about the length of two football fields. Particles then enter the booster for another… well, boost, and finally head to the Main Injector, Fermilab’s most powerful accelerator.

FNAL booster

FNAL Main Injector Accelerator

The twist? Fermilab’s particle accelerators propel protons—useful particles, but not the ones that neutrino scientists want to study.

So how do researchers plan to turn Fermilab’s first megawatt beam of protons into the trillions of high-energy neutrinos they need for DUNE every second? This calls for some extra infrastructure: The Long-Baseline Neutrino Facility, or LBNF. A long baseline means that LBNF will send its neutrinos a long distance—1300 kilometers, from Fermilab to Sanford Lab—and the neutrino facility means … let’s make some neutrinos.

Step 1: Grab some protons

The first step is to siphon off particles from the Main Injector—otherwise, the circular accelerator will act more like a merry-go-round. Engineers will need to build and connect a new beamline. That’s no easy feat, considering all the utilities, other beamlines, and Main Injector magnets around.

“It’s in one of the most congested areas of the Fermilab accelerator complex,” says Elaine McCluskey, the LBNF project manager at Fermilab. Site prep work starting at Fermilab in 2019 will move some of the utilities out of the way. Later, when it’s time for the LBNF beamline construction, the accelerator complex will temporarily power down.

Crews will move some of the Main Injector magnets safely out of the way and punch into the accelerator’s enclosure. They’ll construct a new extraction area and beam enclosure, then reinstall the Main Injector magnets with a new Fermilab-built addition: kicker magnets to change the beam’s course. They’ll also build the new LBNF beamline itself, using 24 dipole and 17 quadrupole magnets, most of them built by the Bhabha Atomic Research Centre in India.

Step 2: Aim

Neutrinos are tricky particles. Because they are neutral, they can’t be steered by magnetic forces in the same way that charged particles (such as protons) are. Once a neutrino is born, it keeps heading in whatever direction it was going, like a kid riding the world’s longest Slip ‘N Slide. This property makes neutrinos great cosmic messengers but means an extra step for Earth-bound engineers: aiming.

As they build the LBNF beamline, crews will drape it along the curve of an 18-meter-tall hill. When the protons descend the hill, they’ll be pointed toward the DUNE detectors in South Dakota. Once the neutrinos are born, they’ll continue in that same direction, no tunnel required.

With all the magnets in place and everything sealed up tight, accelerator operators will be able to direct protons down the new beamline, like switching a train on a track. But instead of pulling into a station, the particles will run full speed into a target.

Step 3: Smash things

The target is a crucial piece of engineering. While still being designed, it’s likely to be a 1.5-meter-long rod of pure graphite—think of your pencil lead on steroids.

Together with some other equipment, it will sit inside the target hall, a sealed room filled with gaseous nitrogen. DUNE will start up with a proton beam that will run at more than 1 megawatt of power, and there are already plans to upgrade the beam to 2.4 megawatts. Almost everything being built for LBNF is designed to withstand that higher beam intensity.

Because of the record-breaking beam power, manipulating anything inside the sealed hall will likely require the help of some robot friends controlled from outside the thick walls. Engineers at KEK, the high-energy accelerator research organization in Japan, are working on prototypes for elements of the sealed LBNF target hall design.

KEK-Accelerator Laboratory, Tsukuba, Japan

The high-power beam of protons will enter the target hall and smash into the graphite like bowling balls hitting pins, depositing their energy and unleashing a spray of new particles—mostly pions and kaons.

“These targets have a very hard life,” says Chris Densham, group leader for high-power targets at STFC’s Rutherford Appleton Laboratory in the UK, which is responsible for the design and production of the target for the one-megawatt beam.

STFC Rutherford Appleton Laboratory at Harwell in Oxfordshire

“Each proton pulse causes the temperature to jump up by a few hundred degrees in a few microseconds.”

The LBNF target will operate around 500 degrees Celsius in a sort of Goldilocks scenario. Graphite performs well when it’s hot, but not too hot, so engineers will need to remove excess heat. But they can’t let it get too cool, either. Water, which is used in some current target designs, would provide too much cooling, so specialists at RAL are also developing a new method. The current proposed design circulates gaseous helium, which will be moving about 720 kilometers per hour—the speed of a cruising airliner—by the time it exits the system.

Step 4: Focus the debris

As protons strike the target and produce pions and kaons, devices called focusing horns take over. The pions and kaons are electrically charged, and these giant magnets direct the spray back into a focused beam. A series of three horns that will be designed and built at Fermilab will correct the particle paths and aim them at the detectors at Sanford Lab.

For the design to work, the target—a cylindrical tube—must sit inside the first horn, cantilevered into place from the upstream side. This causes some interesting engineering challenges. It boils down to a balance between what physicists want—a lengthier target that can stay in service for longer—with what engineers can build. The target is only a couple of centimeters in diameter, and every extra centimeter of length makes it more likely to droop under the barrage of protons and the pull of Earth’s gravity.

Much like a game of Operation, physicists don’t want the target to touch the sides of the horn.

To create the focusing field, the metallic horns receive a 300,000-amp electromagnetic pulse about once per second—delivering more charge than a powerful lightning bolt. If you were standing next to it, you’d want to stick your fingers in your ears to block out the noise—and you certainly wouldn’t want anything touching the horns, including graphite. Engineers could support the target from both ends, but that would make the inevitable removal and replacement much more complicated.

“The simpler you can make it, the better,” Densham says. “There’s always a temptation to make something clever and complicated, but we want to make it as dumb as possible, so there’s less to go wrong.”

Step 5: Physics happens

Focused into a beam, the pions and kaons exit the target hall and travel through a 200-meter-long tunnel full of helium. As they do, they decay, giving birth to neutrinos and some particle friends. Researchers can also switch the horns to focus particles with the opposite charge, which will then decay into antineutrinos. Shielding at the end of the tunnel absorbs the extra particles, while the neutrinos or antineutrinos sail on, unperturbed, straight through dirt and rock, toward their South Dakota destiny.

“LBNF is a complex project, with a lot of pieces that have to work together,” says Jonathan Lewis, the LBNF Beamline project manager. “It’s the future of the lab, the future of the field in the United States, and an exciting and challenging project. The prospect of uncovering the properties of neutrinos is exciting science.”

Time to science

DUNE scientists will examine the neutrino beam at Fermilab just after its production using a sophisticated particle detector on site, placed right in the path of the beam. Most neutrinos will pass straight through the detector, like they do with all matter. But a small fraction will collide with atoms inside the DUNE near-site detector, providing valuable information on the composition of the neutrino beam as well as high-energy neutrino interactions with matter.

Then it’s time to wave farewell to the other neutrinos. Be quick—their 1300-kilometer journey at close to the speed of light will take four milliseconds, not even close to how long it takes to blink your eye. But for DUNE scientists, the work will be only beginning.

FNAL Long-Baseline Neutrino Facility – South Dakota Site


DUNE’s far detector will use four modules to capture interactions between argon atoms and the neutrinos sent from the LBNF beamline at Fermilab.

Scientists will measure the neutrinos again with their gigantic particle detectors in South Dakota. Researchers will collect mountains of data, examine how neutrinos change, and try to figure out some of the many neutrino puzzles, including: which of the three types of neutrinos is actually the lightest? Do neutrinos behave the same as their antimatter counterparts? And the biggest question of all, are neutrinos the key to why matter won the battle with antimatter at the dawn of the universe?

They’re lofty topics, and scientists have been preparing for this monumental work. Fermilab has a rich history of neutrino research, including short-distance experiments like MicroBooNE and MINERvA and long-distance projects like NOvA and MINOS.

FNAL/MicrobooNE

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

NOvA Far Detector Block

FNAL/NOvA experiment map

FNAL/MINOS

DUNE will benefit from the experience gained building and running those experiments, much like LBNF will benefit from the experience of building the NuMI (Neutrinos from the Main Injector) beamline, built to make neutrinos for the MINOS detectors at Fermilab and in Minnesota.

Fermilab NuMI Tunnel

“The NuMI beamline was something we had never made at Fermilab, and it enabled us to learn a lot of things about how to make neutrinos, operate a beamline efficiently, and replace components,” McCluskey says. “We have a lot of people who worked on that beamline who are designing the new one, and incorporating those lessons to make an effective, efficient, and unprecedented beam power for DUNE.”

And that’s how you make the world’s most powerful neutrino beam.

See the full article here .


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Symmetry is a joint Fermilab/SLAC publication.


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From U Wisconsin IceCube Collaboration: “What can cascade events tell us about neutrino sources?”

U Wisconsin ICECUBE neutrino detector at the South Pole

From From U Wisconsin IceCube Collaboration

13 Nov 2019
Madeleine O’Keefe

On a dark, clear night, you can look up and see the Milky Way galaxy: billions of stars shining in visible light. But we also expect our galaxy to “shine” in neutrinos, elusive particles whose origins are still mysterious. There are cosmic-ray sources within our galaxy, so these sources must also produce neutrinos.

Cosmic rays produced by high-energy astrophysics sources (ASPERA collaboration – AStroParticle ERAnet)

We cannot see neutrinos with our eyes, but the IceCube Neutrino Observatory can detect them. IceCube “sees” with 5,160 optical sensors buried deep in glacial ice at the South Pole.

When neutrinos pass through IceCube, they will sometimes leave signals, known as “events,” primarily as either tracks or cascades. The former occur when a neutrino collides with matter in or near IceCube, resulting in a high-energy muon that travels a long distance, leaving an elongated “track” of signals in its wake. Cascades happen when all or most of the neutrino’s energy is deposited in a small region and results in a nearly spherical event, making it hard to measure the direction from which the parent neutrino came.

Cascades are more difficult to reconstruct than tracks, which are usually used in searches for astrophysical neutrino sources, but they have their own advantages, including providing a better measurement of neutrino energy. By studying cascade events, researchers enhance IceCube’s sensitivity to possible neutrino sources in the southern sky, including the Galactic Center.

In a paper published today in The Astrophysical Journal, the IceCube Collaboration outlined recent results from a source search that used seven years of data from cascade events. While they did not find any statistically significant sources of neutrino emissions, this work is an improvement on the previous source search with cascades.

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Results from the all-sky scan for neutrino point sources, with the center and plane of the Milky Way shown by the grey dot and curve, respectively. No statistically significant emission was identified. Credit: IceCube Collaboration

Cascades have the advantage that atmospheric backgrounds are small and relatively uniform throughout the sky. IceCube collaborators previously used two years of cascades in a similar analysis. The current work is an improvement on that analysis in three ways: the use of seven years of data, greatly improved directional reconstruction, and the added emphasis on testing for possible sources within the Milky Way.

To perform their analysis, IceCube scientists first improved the directional reconstruction by using a deep convolutional neural network inspired by recent work in image recognition, rather than the traditional statistical approach. “In principle, the traditional approach should perform better,” says Mike Richman, a postdoctoral researcher at Drexel University and the lead on the analysis, “but in practice, our model of the glacial ice is sufficiently complex that it’s difficult to guarantee that method converges on the optimal result.”

Richman credits fellow IceCube collaborator Mirco Huennefeld of Universität Dortmund for his extensive work on the angular reconstruction used in the analysis. “Mirco has trained a model with an implicit understanding of the detector and the ice, and it’s able to obtain good results without resorting to expensive numerical scans.”

Armed with this improved reconstruction applied to seven years of data, the researchers performed two types of analysis: searches for point sources and searches for broad emission regions in our galaxy. The point source searches included a scan of the whole sky, a scan over 74 preselected potential sources, and a test for sum-total emission from three short lists of interesting supernova remnants. The broad emission regions included gas and dust distributed throughout the Milky Way and the giant “Fermi bubbles” near the center of our galaxy. Many of these tests were the most sensitive performed to date by any experiment.

Ultimately, the researchers did not find evidence for neutrino emission. However, they did acknowledge an interesting trend: As the Milky Way measurements become more sensitive (from using just IceCube tracks, to IceCube tracks and ANTARES events [The Astrophysical Journal Letters], and now to just IceCube cascades), the result becomes increasingly significant. Furthermore, the galactic neutrino energy spectrum suggested by the cascade data agrees with previous IceCube work with tracks. While not conclusive, this is consistent with emission that is just below the sensitivity of analyses done so far.

This work solidifies the importance of using all neutrino flavors to search for sources—at least with current-generation detectors. Going forward, Richman says they plan to improve the cascade analysis by applying the latest reconstructions to data collected over more time and extending to even lower energies (below 1 TeV). They expect data from the IceCube Upgrade to reduce systematic uncertainties, leading to still better sensitivity.

In the future, the plan is to study additional source types, including ones with time-dependent—and potentially very short-lived—emission. They also plan to combine IceCube tracks and cascades and ultimately to perform a “global” analysis that includes all event types from all available data.

See the full article here .

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IceCube is a particle detector at the South Pole that records the interactions of a nearly massless sub-atomic particle called the neutrino. IceCube searches for neutrinos from the most violent astrophysical sources: events like exploding stars, gamma ray bursts, and cataclysmic phenomena involving black holes and neutron stars. The IceCube telescope is a powerful tool to search for dark matter, and could reveal the new physical processes associated with the enigmatic origin of the highest energy particles in nature. In addition, exploring the background of neutrinos produced in the atmosphere, IceCube studies the neutrinos themselves; their energies far exceed those produced by accelerator beams. IceCube is the world’s largest neutrino detector, encompassing a cubic kilometer of ice.

IceCube employs more than 5000 detectors lowered on 86 strings into almost 100 holes in the Antarctic ice NSF B. Gudbjartsson, IceCube Collaboration

Lunar Icecube

IceCube DeepCore annotated

IceCube PINGU annotated


DM-Ice II at IceCube annotated

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From CERN: “LHCf gears up to probe birth of cosmic-ray showers”

Cern New Bloc

Cern New Particle Event


From CERN

11 November, 2019
Ana Lopes


CERN LHCf

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One of the LHCf experiment’s two detectors, LHCf Arm2, seen here during installation into a particle absorber that surrounds the LHC’s beam pipe. (Image: Lorenzo Bonechi)

Cosmic rays are particles from outer space, typically protons, travelling at almost the speed of light. When the most energetic of these particles strike the atmosphere of our planet, they interact with atomic nuclei in the atmosphere and produce cascades of secondary particles that shower down to the Earth’s surface. These extensive air showers, as they are known, are similar to the cascades of particles that are created in collisions inside particle colliders such as CERN’s Large Hadron Collider (LHC). In the next LHC, run starting in 2021, the smallest of the LHC experiments – the LHCf experiment – is set to probe the first interaction that triggers these cosmic showers.

Observations of extensive air showers are generally interpreted using computer simulations that involve a model of how cosmic rays interact with atomic nuclei in the atmosphere. But different models exist and it’s unclear which one is the most appropriate. The LHCf experiment is in an ideal position to test these models and help shed light on cosmic-ray interactions.

In contrast to the main LHC experiments, which measure particles emitted at large angles from the collision line, the LHCf experiment measures particles that fly out in the “forward” direction, that is, at small angles from the collision line. These particles, which carry a large portion of the collision energy, can be used to probe the small angles and high energies at which the predictions from the different models don’t match.

Using data from proton–proton LHC collisions at an energy of 13 TeV, LHCf has recently measured how the number of forward photons and neutrons varies with particle energy at previously unexplored high energies. These measurements agree better with some models than others, and they are being factored in by modellers of extensive air showers.

In the next LHC run, LHCf should extend the range of particle energies probed, due to the planned higher collision energy. In addition, and thanks to ongoing upgrade work, the experiment should also increase the number and type of particles that are detected and studied.

What’s more, the experiment plans to measure forward particles emitted from collisions of protons with light ions, most likely oxygen ions. The first interactions that trigger extensive air showers in the atmosphere involve mainly light atomic nuclei such as oxygen and nitrogen. LHCf could therefore probe such an interaction in the next run, casting new light on cosmic-ray interaction models at high energies.

Find out more in the Experimental Physics newsletter article.

See the full article here.


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Meet CERN in a variety of places:

Quantum Diaries
QuantumDiaries

Cern Courier

THE FOUR MAJOR PROJECT COLLABORATIONS

ATLAS

CERN ATLAS Image Claudia Marcelloni CERN/ATLAS


ALICE

CERN/ALICE Detector


CMS
CERN CMS New

LHCb
CERN LHCb New II

LHC

CERN map

CERN LHC Tunnel

CERN LHC particles

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From Fermi National Accelerator Lab: “Gotta catch ’em all: new NOvA results with neutrinos and antineutrinos”

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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.

November 7, 2019
Steven Calvez
Erika Catano Mur

The latest results from the Fermilab NOvA experiment are taking us closer to describing the most basic properties of the mysterious neutrino — the most abundant particle of matter in the universe.

Neutrinos appear in a variety of natural processes, from formidable supernova explosions and nuclear reactions in the sun to radioactive decays in your banana. They are also produced in abundance in nuclear reactors and particle accelerators. Yet neutrinos barely interact with matter: a light-year of lead would hardly stop your average neutrino. Their elusive nature makes them extremely challenging to study, which explains both why we still know very little about their properties and why many scientists and experiments around the world have so much fun hunting them down.

The observation that neutrinos are able to change type — a behavior called oscillation — proved that neutrinos have masses, albeit very small. This phenomenon explains how neutrinos that are produced in one of the three “flavor” states (electron neutrino, muon neutrino or tau neutrino) transition in and out of these types as they travel a certain distance and may be detected as a different type. The probability of these transitions depends on a number of factors: the energy of the neutrino, the distance between the particle beam source and the detector, the differences in neutrino masses, the amount of blending between neutrino types, which scientists describe with three “mixing” angles, and additional complex phases.

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Fermilab’s NOvA neutrino experiment studies neutrino oscillations using a powerful neutrino beam produced by the lab’s accelerator complex. The beam, made of muon neutrinos, is sent to NOvA’s two detectors — one located at Fermilab and one located about 800 kilometers away in Minnesota, pictured here.

Fermilab’s NOvA neutrino experiment studies neutrino oscillations using the powerful NuMI neutrino beam produced by the lab’s accelerator complex. The beam, made of muon neutrinos, is sent to NOvA’s two detectors — one located at Fermilab and one located about 800 kilometers away in Minnesota. The NOvA far detector looks to identify the fraction of muon neutrinos in the NuMI beam that oscillated into electron neutrinos (called electron neutrino appearance) and the fraction of muon neutrinos that oscillated to a different flavor (called muon neutrino disappearance).

The NuMI beam is generally described as a muon neutrino beam, but it can also be made of muon antineutrinos. The antineutrino is the antiparticle of the neutrino. Just as muon neutrinos can oscillate into electron neutrinos, muon antineutrinos can oscillate into electron antineutrinos.

Experimentalists can use information from the combination of the measurements of electron and muon neutrinos, as well as their antiparticle equivalents, to draw their conclusions. For example, if the oscillation rates of antineutrinos compared to those of neutrinos are different, the implication could be a violation of a symmetry called charge parity, commonly called CP. The existence of this type of CP violation is one of the great unknowns in particle physics that NOvA is investigating.

NOvA’s latest measurements of neutrino oscillation parameters have been published in Physical Review Letters. The data were recorded between 2014 and 2019 and correspond to 8.85 x 1020 protons-on-target of neutrino beam and 12.33 x 1020 protons-on-target of antineutrino beam. This represents a 78% increase in the amount of antineutrino data compared to NOvA’s previous results, presented at the Neutrino 2018 conference.

NOvA identified 27 electron antineutrino candidate events in the NOvA far detector, compared to the 10.3 events expected if muon antineutrinos did not oscillate into electron antineutrinos. This remains the strongest evidence (4.4 sigma) of electron antineutrino appearance in a muon antineutrino beam for a long-baseline experiment. (In particle physics, 3 sigma is usually considered “strong evidence” that the conclusions of the data analysis are unlikely to be a fluke, while 5 sigma means that the experimental results qualify as a discovery.)

In addition to those 27 electron antineutrino events, 102 surviving muon antineutrino candidates were detected in the far detector, where 476 events would have been expected if muon antineutrinos did not oscillate at all. NOvA scientists combined these new events with previously recorded neutrino data and analyzed them jointly. Pictures of such neutrino and antineutrino events as recorded by the NOvA far detector are shown below.

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Four events observed in the NOvA far detector, classified as muon (left) or electron (right) neutrino interactions, with the beam in neutrino (top) or antineutrino (bottom) mode. Each panel shows two views of the same event, and the color represents the energy deposited by particles that emerged from the interaction. The latest NOvA results comprise four data samples with 113 muon neutrino to muon neutrino, 58 muon neutrino to electron neutrino, 102 muon antineutrino to muon antineutrino and 27 muon antineutrino to electron antineutrino candidates.

The results help scientists chip away another problem in neutrino physics: the ordering of the three neutrino masses — which of the three is the lightest? NOvA’s combined neutrino-antineutrino appearance and disappearance fit shows a preference (1.9 sigma) for what is called normal mass ordering: The three neutrino mass states are ordered m1 ≤ m2 ≤ m3.

NOvA is also working to measure one of the least known oscillation parameters, θ23, that governs the degree of flavor mixing in the third mass state. The fit shows a slight preference (1.6 sigma) for the value of this angle to be in the upper octant (θ23 > 45 degrees) and therefore points towards an absence of symmetry in the way muon and tau neutrino flavors contribute to the third neutrino mass state. The data recorded thus far does not allow us to draw conclusions about CP violation in neutrino interactions.

The experiment is scheduled to collect new data until 2025. NOvA collaborators are continually working to improve the experiment and analysis techniques to potentially provide a definitive statement about the neutrino mass ordering, the value of θ23, and strong constraints on the CP-violating phase. These measurements are paramount if we want to understand the neutrino properties and the role they played in the formation of the universe as we know it.

This work is supported in part by the DOE Office of Science and the National Science Foundation.

See the full 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
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From CERN: “CERN Council appoints Fabiola Gianotti for second term of office as CERN Director General”

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From CERN

6 November, 2019

At its 195th Session today, the CERN Council selected Fabiola Gianotti, as the Organization’s next Director-General, for her second term of office.

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President of the CERN Council, Ursula Bassler and Director-General of CERN, Fabiola Gianotti (Image: CERN)

At its 195th Session today, the CERN Council selected Fabiola Gianotti, as the Organization’s next Director-General, for her second term of office. The appointment will be formalised at the December Session of the Council, and Gianotti’s new five-year term of office will begin on 1 January 2021. This is the first time in CERN’s history that a Director-General has been appointed for a full second term.

“I congratulate Fabiola Gianotti very warmly for her reappointment as Director-General for another five-year term of office. With her at the helm, CERN will continue to benefit from her strong leadership and experience, especially for important upcoming projects such as the High-Luminosity LHC, implementation of the European Strategy for Particle Physics, and the construction of the Science Gateway,” said President of the CERN Council, Ursula Bassler. “During her first term, she excelled in leading our diverse and international scientific organisation, becoming a role model, especially for women in science”.

“I am deeply grateful to the CERN Council for their renewed trust. It is a great privilege and a huge responsibility,” said CERN Director-General, Fabiola Gianotti. “The following years will be crucial for laying the foundations of CERN’s future projects and I am honoured to have the opportunity to work with the CERN Member States, Associate Member States, other international partners and the worldwide particle physics community.”

Gianotti has been CERN’s Director-General since 1 January 2016. She received her Ph.D. in experimental particle physics from the University of Milano in 1989 and has been a research physicist at CERN since 1994. She was the leader of the ATLAS experiment’s collaboration from March 2009 to February 2013, including the period in which the LHC experiments ATLAS and CMS announced the discovery of the Higgs boson. The discovery was recognised in 2013 with the Nobel Prize in Physics being awarded to theorists François Englert and Peter Higgs. Gianotti is a member of many international committees, and has received numerous prestigious awards. She was the first woman to become the Director-General of CERN.

See the full article here.


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From Symmetry: “Put it to the test beam”

Symmetry Mag
From Symmetry<

11/05/19
Lauren Biron

Before a detector component can head to its forever home, it has to pass the test.

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Photo by Reidar Hahn, Fermilab

If building a modern particle physics experiment is a marathon, then visiting a test beam facility is the 100-meter dash. Over the course of just a few weeks, small teams work non-stop to gather as much data as they can about a piece of equipment they are thinking of installing in an experiment.

“It is stressful, but I think it’s super fun,” says Jessica Metcalfe, a researcher at Argonne working on upgrades for the innermost part of the ATLAS detector, one of the two major detectors at CERN that co-discovered the Higgs boson.

CERN ATLAS Credit CERN SCIENCE PHOTO LIBRARY

“You’re all there squeezed together in the tiny control room, problem solving, all very focused on a very specific goal, and you learn a lot—really fast.”

Test beams generally sit to the side of full-on accelerators, sipping beam and passing it to the reconfigurable spaces housing temporary experiments. Scientists bring pieces of their detectors—sensors, chips, electronics or other material—and blast them with the well understood beam to see if things work how they expect, and if their software performs as expected. If things check out, they’re one step closer to being installed in a detector, and if not, it’s a chance to do some R&D, tinker and make things work.

“We’re typically testing pieces that are going into a larger experiment, but you’re also doing research on the detector technology, which is a form of research in itself,” Metcalfe says. “We’re not just getting ready to build something, we’re also learning a lot about the devices. There’s often many iterations of design and redevelopment.”

Test beam visits are typically short, and getting time can be competitive because there are only a handful of places around the world that have high-energy particle beams available for testing. When it comes to hadrons—particles made of quarks—there are really just two: the Department of Energy’s Fermilab in the United States and CERN in Europe.

Other test beams specialize in different particles, for example, electrons (at Germany’s DESY or California’s SLAC National Accelerator Laboratory) and photons (like at the Research Center for Electron Photon Science in Japan).

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“It’s part of the lifecycle of any detector you build,” says Mandy Rominsky, who manages the Fermilab Test Beam Facility. “You start on a bench with an idea, and before you put something into a running experiment, you always put it in a test beam. You need to be able to characterize it, change it and go back and forth—and you can’t do that on a bench.”

Groups come with components of all shapes and sizes to the test beam. At the Fermilab test beam alone, researchers have tested teeny, tiny pieces of scintillator (the material that captures particles of light) and detector panels taller than people. Researchers come from many scientific fields, including nuclear physics, neutrino physics, collider physics, dark matter physics and astronomy. There are people working on general research and development without a specific experiment in mind, and ultra-specific tasks, like the crew working on turning smartphones into cosmic ray detectors. Still others are interested in learning how the materials they plan to put in a detector will change over time, especially in the harsh environment surrounding particle collisions.

Test-beam facilities try to keep useful experimental infrastructure on hand for visiting researchers: There are movable tables to pull equipment in and out, cooling systems and electronics, cables, different kinds of gas, cranes, and, of course, the beam itself, which often comes in many flavors of particles and energies. But some experiments need to bring in a little something extra, creating odd requests for facility managers—like when a visiting group from the IceCube experiment needed about 1000 gallons of deionized water to test their modules before similar detectors were shipped to the South Pole and entombed in the ice.

“It is surprisingly difficult to get that much deionized water,” Rominsky notes. “We couldn’t use a tanker and had to ship it in from Indiana in 55-gallon drums.”

And while most components will have only a short stay in the test beam, some facilities do have areas for longer-term experiments. For example, the LArIAT (Liquid Argon in a Test beam) detector lived its full existence in the test beam, collecting data for three years at Fermilab.

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Its goal was to better understand how particles interact with argon, the material now being used in massive neutrino detectors such as MicroBooNE and the international Deep Underground Neutrino Experiment hosted by Fermilab.

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

“I like that we help everybody,” Rominsky says. “It doesn’t matter which groups come to us. Our policy is to be very helpful to everyone.”

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IceCube PMT beam test at Fermilab Test Beam Facility. Photo by Reidar Hahn, Fermilab.

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Meson Test Beam Facility with LArIAT Detector. Photo by Reidar Hahn, Fermilab

Research crucible

Test beams are not only important for detectors themselves—the test beam experience is also formative for the researchers who come to do the hands-on work. Teams work together over long hours, sharing both shifts and meals, ups and downs.

“For me, it was really communal,” says Clara Nellist, an ATLAS researcher at Radboud University in the Netherlands and former co-organizer of the annual Beam Telescope and Test Beams Workshop. “I learned so much from other people, even though we were from different universities and, in essence, we were competing.”

Nellist did her PhD thesis on proposed technology for the ATLAS pixel detector and spent many night shifts at the CERN test beam facility. Sometimes, groups working on a different proposed sensor intended for the same slot in the detector would share the same experimental setup. When the competing team didn’t have enough people to run their shifts, she volunteered to take data for them. A few months later, she unexpectedly found herself on their research paper for contributing to their data.

“We needed each other’s expertise,” Nellist says. “There are friends I made in the first week of my PhD who, 10 years later, I’m still friends with and check up on.”

The diverse nature of projects also means researchers from all different stages of their careers make their way through the test beam facility doors.

“You get people who are legends in the detector R&D community, and they need beam time like everyone else, and then there are undergrads having their first lab experience,” explains Aria Soha, an engineering physicist at Fermilab who managed the test beam facility until 2013. For those new to hardware testing—and even the more seasoned pros—it’s a thrill to watch those first particle tracks splash across the detector.

“I remember knowing when the beam was coming and watching the particles show up, and thinking, ‘This is cool, this is why I went to school for physics,’” Soha says.

Those moments of triumph often come after a stressful period of testing and debugging.

“You test everything in the lab before you go. Everything works perfectly and then you go [to the test beam] and nothing works,” Metcalfe says. “Checking the cables and turning things on and off solves about 80% of the problems.”

The granular, hands-on experience can make a big difference in understanding the results coming out of the detector later on. Visiting a test beam teaches researchers how particles are going through their detector, how they interact, how the data looks when it comes out, and much more. If researchers see a problem in their data analysis, they can recognize the potential causes more quickly, Metcalfe says. These are skills for the future of physics.

“There’s going to be a next generation of experiments, and people need to know how to design them and how to make that design motivated by the physics you want to do,” Metcalfe says. “It’s part of the training.”

See the full article here .


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Symmetry is a joint Fermilab/SLAC publication.


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