Born in Italy, revitalized at CERN and bound for the US, the ICARUS detector is emblematic of modern particle physics experiments: international, collaborative and really, really big.

The ICARUS T600 (if you’re inclined to use the full name) was a pioneer in particle physics technology and is still the largest detector of its kind. When operational, the detector is filled with 760 tons of liquid argon, the same element that, in gas form, makes up about 1 percent of our atmosphere. Since its creation, the ICARUS detector has become a model for modern experiments in the worldwide quest to better understand hard-to-catch particles called neutrinos.

Neutrinos are incredibly small, neutral and rarely interact with other particles, making them difficult to study. Even now, 60 years after their discovery, neutrinos continue to surprise and confound scientists. That’s why this detector with a special talent for neutrino-hunting is undertaking a long journey across the Atlantic to a new home in the United States.

Breaking boundaries at INFN: L’Aquila, Italy

ICARUS got its start in Italy. A groundbreaking large-scale detector, it was the prototype of a sci-fi-sounding instrument called a liquid argon time projection chamber. It functions like four giant cameras, each taking separate 3D images of the signals from neutrinos interacting inside. The active section of the detector is about twice the height of a refrigerator, a couple of meters wider than that and about the length of a bowling lane.

The concept of a liquid argon time projection chamber was proposed in 1977 by physicist Carlo Rubbia, who would later win the Nobel Prize for the discovery of the massive, short-lived subatomic W and Z particles, the carriers of the so-called electroweak force. ICARUS came to life in 2010 at the Gran Sasso National Laboratory, run by Italy’s National Institute for Nuclear Physics (INFN) after decades of development to advance technology and construct the experiment.

At the heart of Gran Sasso Mountain, shielded from cosmic rays raining down from space beneath 1400 meters of rock, it gathered thousands of neutrino interactions during its lifetime. The detector measured neutrinos that traveled 450 miles (730 kilometers) from CERN, but it also saw neutrinos born through natural processes in our sun and our atmosphere. Thus its name: Imaging Cosmic and Rare Underground Signals.

The ICARUS collaboration studied various properties of neutrinos, including a surprising phenomenon called neutrino oscillation. Neutrinos come in three varieties, or flavors, and have the uncommon ability to change from one type to another as they travel. But the proof of technology was just as important as the knowledge the experiment gained about neutrinos. ICARUS showed that liquid argon technology was an efficient, reliable and precise way to study the elusive particles.

“Following its initial conception, the experimental development from a table-top device to the huge ICARUS detector has required a number of successive steps in an experimental journey that has lasted almost 20 years,” says Carlo Rubbia, spokesperson of the ICARUS collaboration. “The liquid argon, although initially coming from air, must reduce impurities to a few parts per trillion, a tiny amount in volume and free electron lifetimes of 20 milliseconds. Many truly remarkable collaborators have participated in Italy in the creation of such a novel technology.”

CERN shut down its neutrino beam in 2012, but ICARUS had more to offer. Scientists decided to move the detector to the US Department of Energy’s Fermi National Accelerator Laboratory, to make use of one of its intense neutrino beams.

To make the transition, ICARUS needed an upgrade. Workers maneuvered ICARUS out of the crowded Gran Sasso lab, packed it in two modules (drained of liquid argon) onto special transporters, and wound their way through the Alps to just the place to get an upgrade, the European particle physics laboratory CERN.

A rebirth at CERN: Geneva, Switzerland

After traversing the Mont Blanc tunnel and winding through small French villages toward Geneva, the two large ICARUS modules arrived at CERN in December 2014. After several years of operation at Gran Sasso, the detector was ready for a reboot. One of the main tasks was updating all the electronics and the read-out system.

“The detector itself is very modern and sophisticated, but the supporting technology has evolved over the last 20 years,” says Andrea Zani, a CERN researcher working on the ICARUS experiment. “For example, the original cables are not produced anymore, and the new data read-out system will be higher-performing, exploiting newer components that are far more compact.”

Zani and his colleagues started disassembling parts of the detector at Gran Sasso and then continued their work at CERN. They are replacing the old electronics with 50,000 new read-out channels, which streamline the data collection process and will improve the experiment’s performance overall. Other upgrades involved realigning components to improve the detector’s precision.

“The high-voltage cathode plates were slightly deformed in a few places, which was fine when the experiment first started operation,” Zani says, “but we now we have the capability to make even more precise measurements. We had to heat and then press the plates until they were almost perfectly flat.”

The team also replaced a few dozen outdated light sensors with 360 new photomultiplier tubes, which are now nested behind the wires lining the inner walls of their detectors.

When neutrinos strike atoms of argon in one of the detectors, they release a flash of light and a cascade of charged particles. As these charged particles pass through the detector they ionize other argon atoms releasing electrons. An electric field across the detector causes these electrons to drift toward a plane of roughly 13,000 wires (52,000 in total, counting all four sections of the detector), which measure the incoming particles and enable scientists to reconstruct finely detailed images.

“In addition to the cascade of ionized particles, neutrinos produce a tiny flash of ultraviolet light when they interact with argon atoms,” Zani says. “We know the velocity of electrons as they travel through the liquid argon, and can calculate a particle’s distance from the wire detectors based on the time it takes for the electrical signal to arrive after this flash.

These precise location measurements help scientists distinguish between interesting neutrino interactions and ordinary cosmic rays. Before their installation, all 360 new photomultiplier tubes had to be dusted with a fine powder that shifts the original UV light into a deep blue glow. Over the course of several months, a dedicated team of physicists and technicians completed the process of dusting, testing and finally installing the new light sensors.

In addition to refurbishing the detector, CERN’s engineering team designed and built two huge coolers that will eventually hold the two large ICARUS modules. These containers work much like a thermos and use a vacuum between their inner and outer walls. A layer of solid foam between them will prevent heat from seeping into the experiment. An international collaboration of scientists and engineers are also developing the supporting infrastructure that will enable ICARUS to integrate into its new home at Fermilab.

The final step was stress-testing the containers and packaging the detector for its long journey across the Atlantic.

“It’s been a lot of work,” Zani says, “and putting this all together has been a close collaboration between many different institutions. But we all have the common goal of preparing this detector for its second life at Fermilab.”

New horizons at Fermilab: Batavia, Illinois

While the ICARUS detector was getting an upgrade at CERN, teams of people at Fermilab were preparing for its arrival.

In July 2015, work began on the building that will house the detector 30 feet underground, precisely in the path of Fermilab’s neutrino beam. To keep the cryogenic vessels cold, a team of workers from CERN and INFN visited Fermilab in May 2017 to help install a steel structure that will hold a hefty amount of insulation.

“We couldn’t do this without our partners around the world, and it’s been very rewarding to see it all come together,” says Peter Wilson, the head of Fermilab’s short-baseline neutrino program. “The steel vessel was designed by CERN and manufactured in Poland. The electronic systems were designed by INFN. We’re working with CERN, INFN and other institutions on cosmic-ray taggers that will go above, around and below the detector.”

When the ICARUS detector arrives, it will spend a couple of months undergoing tests and final preparations before being lowered by crane into the building. Once there, it will take its place as the largest in a suite of three detectors on site at Fermilab with a common purpose: to search for a theorized, but never seen, fourth type of neutrino.

Scientists have observed three types of neutrinos: the muon, the electron and the tau neutrino. But they have also seen hints that those three types might be changing into another type they can’t detect. Two experiments in particular—the Liquid Scintillator Neutrino Detector (LSND) at Los Alamos National Lab and MiniBooNE at Fermilab—saw an unexplained excess of charged particles of unexplained origin. One theory is that they were produced by so-called “sterile” neutrinos, which would not interact in the same way as the other three neutrinos.

ICARUS will join the Short-Baseline Near Detector, currently under construction, and MiniBooNE’s successor, MicroBooNE, which has been taking data for nearly two years, on the hunt for sterile neutrinos. All three detectors use the same liquid-argon technology pioneered for ICARUS.

The journey of the ICARUS detector could have a destination beyond its new home at Fermilab. If evidence of a new kind of neutrino were discovered, it could travel all the way to a new understanding of the universe.  

What do you get when you revive a beautiful 20-year-old physics machine, carefully transport it 3200 miles over land and sea to its new home, and then use it to probe strange happenings in a magnetic field? Hopefully you get new insights into the elementary particles that make up everything.

The Muon g-2 experiment, located at the US Department of Energy’s Fermi National Accelerator Laboratory, has begun its quest for those insights.

Take a 360-degree tour of the Muon g-2 experimental hall.

On May 31, the 50-foot-wide superconducting electromagnet at the center of the experiment saw its first beam of muon particles from Fermilab’s accelerators, kicking off a three-year effort to measure just what happens to those particles when placed in a stunningly precise magnetic field. The answer could rewrite scientists’ picture of the universe and how it works.

“The Muon g-2 experiment’s first beam truly signals the start of an important new research program at Fermilab, one that uses muon particles to look for rare and fascinating anomalies in nature,” says Fermilab Director Nigel Lockyer. “After years of preparation, I’m excited to see this experiment begin its search in earnest.”

Getting to this point was a long road for Muon g-2, both figuratively and literally. The first generation of this experiment took place at Brookhaven National Laboratory in New York State in the late 1990s and early 2000s. The goal of the experiment was to precisely measure one property of the muon—the particles’ precession, or wobble, in a magnetic field. The final results were surprising, hinting at the presence of previously unknown phantom particles or forces affecting the muon’s properties.

The new experiment at Fermilab will make use of the laboratory’s intense beam of muons to definitively answer the questions the Brookhaven experiment raised. And since it would have cost 10 times more to build a completely new machine at Brookhaven rather than move the magnet to Fermilab, the Muon g-2 team transported that large, fragile superconducting magnet in one piece from Long Island to the suburbs of Chicago in the summer of 2013.

The magnet took a barge south around Florida, up the Tennessee-Tombigbee waterway and the Illinois River, and was then driven on a specially designed truck over three nights to Fermilab. And thanks to a GPS-powered map online, it collected thousands of fans over its journey, making it one of the most well-known electromagnets in the world.

“Getting the magnet here was only half the battle,” says Chris Polly, project manager of the Muon g-2 experiment. “Since it arrived, the team here at Fermilab has been working around the clock installing detectors, building a control room and, for the past year, adjusting the uniformity of the magnetic field, which must be precisely known to an unprecedented level to obtain any new physics. It’s been a lot of work, but we’re ready now to really get started.”

That work has included the creation of a new beamline to deliver a pure beam of muons to the ring, the installation of a host of instrumentation to measure both the magnetic field and the muons as they circulate within it, and a year-long process of “shimming” the magnet, inserting tiny pieces of metal by hand to shape the magnetic field. The field created by the magnet is now three times more uniform than the one it created at Brookhaven. 

Over the next few weeks the Muon g-2 team will test the equipment installed around the magnet, which will be storing and measuring muons for the first time in 16 years. Later this year, they will start taking science-quality data, and if their results confirm the anomaly first seen at Brookhaven, it will mean that the elegant picture of the universe that scientists have been working on for decades is incomplete, and that new particles or forces may be out there, waiting to be discovered.

“It’s an exciting time for the whole team, and for physics,” says David Hertzog of the University of Washington, co-spokesperson of the Muon g-2 collaboration. “The magnet has been working, and working fantastically well. It won’t be long until we have our first results, and a better view through the window that the Brookhaven experiment opened for us.”

Editor's note: This article is based on a Fermilab press release.

For the third time, the LIGO and Virgo collaborations have announced directly detecting the merger of black holes many times the mass of our sun. In the process, they put general relativity to the test.

On January 4, the twin detectors of the Laser Interferometer Gravitational-Wave Observatory stretched and squeezed ever so slightly, breaking the symmetry between the motions of two sets of laser beams. This barely perceptible shiver, lasting a fraction of a second, was the consequence of a catastrophic event: About 3 billion light-years away, a pair of spinning black holes with a combined mass about 49 times that of our sun sank together into a single entity.

The merger produced more power than is radiated as light by the entire contents of the universe at any given time. “These are the most powerful astronomical events witnessed by human beings,” says Caltech scientist Mike Landry, head of the LIGO Hanford Observatory.

When the black holes merged, about two times the mass of the sun converted into energy and released in the form of ripples in the fabric of existence. These were gravitational waves, predicted by Albert Einstein’s theory of general relativity a century ago and first detected by LIGO in 2015.

“Gravitational waves are distortions in the medium that we live in,” Landry says. “Normally we don’t think of the nothing of space as having any properties of all. It’s counterintuitive to think it could expand or contract or vibrate.”

It was not a given that LIGO would be listening when the signal from the black holes arrived. “The machines don’t run 24-7,” says LIGO research engineer Brian Lantz of Stanford University. The list of distractions that can sabotage the stillness the detectors need includes earthquakes, wind, technical trouble, moving nitrogen tanks, mowing grass, harvesting trees and fires.

When the gravitational waves from the colliding black holes reached Earth in January, the LIGO detectors happened to be coming back online after a holiday break. The system that alerts scientists to possible detections wasn’t even fully back in service yet, but a scientist in Germany was poring over the data anyway.

“He woke us up in the middle of the night,” says MIT scientist David Shoemaker, newly elected spokesperson of the LIGO Scientific Collaboration, a body of more than 1000 scientists who perform LIGO research together with the European-based Virgo Collaboration.

The signal turned out to be worth getting out of bed for. “This clearly establishes a new population of black holes not known before LIGO discovered them,” says LIGO scientist Bangalore Sathyaprakash of Penn State and Cardiff University.

The merging black holes were more than twice as distant as the two pairs that LIGO previously detected, which were located 1.3 and 1.4 billion light-years away. This provided the best test yet of a second prediction of general relativity: gravitons without any mass.

Gravitons are hypothetical particles that would mediate the force of gravity, just as photons mediate the force of electromagnetism. Photons are quanta of light; gravitons would be quanta of gravitational waves.

General relativity predicts that, like photons, gravitons should have no mass, which means they should travel at the speed of light. However, if gravitons did have mass, they would travel at different speeds, depending on their energy.

As merging black holes spiral closer and closer together, they move at a faster and faster pace. If gravitons had no mass, this change would not faze them; they would uniformly obey the same speed limit as they traveled away from the event. But if gravitons did have mass, some of the gravitons produced would travel faster than others. The gravitational waves that arrived at the LIGO detectors would be distorted.

“That would mean general relativity is wrong,” says Stanford University Professor Emeritus Bob Wagoner. “Any one observation can kill a theory.”

LIGO scientists’ observations matched the first scenario, putting a new upper limit on the mass of the graviton—and letting general relativity live another day. “I wouldn’t bet against it, frankly,” Wagoner says.

Like a pair of circling black holes, research at LIGO seems to be picking up speed. Collaboration members continue to make improvements to their detectors. Soon the complementary Virgo detector is expected to come online in Italy, and in 2024 another LIGO detector is scheduled to start up in India. Scientists hope to eventually see new events as often as once per day, accumulating a pool of data with which to make new discoveries about the goings-on of our universe.

Over the years, physicists have given names to the smallest constituents of our universe.

This pantheon of particles has grown alongside progress in physics. Anointing a particle with a name is not just convenient; it marks a leap forward in our understanding of the world around us. 

The etymology of particle physics contains a story that connects these sometimes outlandish names to a lineage of scientific thought and experiment.

So, without further ado, Symmetry presents a detailed guide to the etymology of particles—some we’ve found and others we have yet to discover.

Editor’s note: PIE, referenced throughout, refers to proto-Indo-European, one of the earliest known languages.

In 2015, a group of researchers installed a particle detector just half of a millimeter away from an extremely powerful electron beam. The detector could either start them on a new search for a hidden world of particles and forces called the “dark sector”—or its sensitive parts could burn up in the beam.

Earlier this month, scientists presented the results from that very first test run at the Heavy Photon Search collaboration meeting at the US Department of Energy’s Thomas Jefferson National Accelerator Facility. To the scientists’ delight, the experiment is working flawlessly.

Dark sector particles could be the long-sought components of dark matter, the mysterious form of matter thought to be five times more abundant in the universe than regular matter. To be specific, HPS is looking for a dark-sector version of the photon, the elementary “particle of light” that carries the fundamental electromagnetic force in the Standard Model of particle physics.

Analogously, the dark photon would be the carrier of a force between dark-sector particles. But unlike the regular photon, the dark photon would have mass. That’s why it’s also called the heavy photon.

To search for dark photons, the HPS experiment uses a very intense, nearly continuous beam of highly energetic electrons from Jefferson Lab’s CEBAF accelerator. When slammed into a tungsten target, the electrons radiate energy that could potentially produce the mystery particles. Dark photons are believed to quickly decay into pairs of electrons and their antiparticles, positrons, which leave tracks in the HPS detector.

“Dark photons would show up as an anomaly in our data—a very narrow bump on a smooth background from other processes that produce electron-positron pairs,” says Omar Moreno from SLAC National Accelerator Laboratory, who led the analysis of the first data and presented the results at the collaboration meeting.

The challenge is that, due to the large beam energy, the decay products are compressed very narrowly in beam direction. To catch them, the detector must be very close to the electron beam. But not too close—the smallest beam movements could make the beam swerve into the detector. Even if the beam doesn’t directly hit the HPS apparatus, electrons interacting in the target can scatter into the detector and cause unwanted signals. 

The HPS team implemented a number of precautions to make sure their detector could handle the potentially destructive beam conditions. They installed and carefully aligned a system to intercept any large beam motions, made the detector’s support structure movable to bring the detector close to the beam and measure the exact beam position, and installed a feedback system that would shut the beam down if its motions were too large. They also placed their whole setup in vacuum because interactions of the beam with gas molecules would create too much background. Finally, they cooled the detector to negative 30 degrees Fahrenheit to reduce the effects of radiation damage. These measures allowed the team to operate their experiment so close to the beam.

“That’s maybe as close as anyone has ever come to such a particle beam,” says John Jaros, head of the HPS group at SLAC, which built the innermost part of the HPS detector, the Silicon Vertex Tracker. “So, it was fairly exciting when we gradually decreased the distance between the detector and the beam for the first time and saw that everything worked as planned. A large part of that success lies with the beautiful beams Jefferson Lab provided.” 

SLAC’s Mathew Graham, who oversees the HPS analysis group, says, “In addition to figuring out if we can actually do the experiment, the first run also helped us understand the background signals in the experiment and develop the data analysis tools we need for our search for dark photons.”

So far, the team has seen no signs of dark photons. But to be fair, the data they analyzed came from just 1.7 days of accumulated running time. HPS collects data in short spurts when the CLAS experiment, which studies protons and neutrons using the same beam line, is not in use.

A second part of the analysis is still ongoing: The researchers are also closely inspecting the exact location, or vertex, from which an electron-positron pair emerges.

“If a dark photon lives long enough, it might make it out of the tungsten target where it was produced and travel some distance through the detector before it decays into an electron-positron pair,” Moreno says. The detector was specifically designed to observe such a signal.

Jefferson Lab has approved the HPS project for a total of 180 days of experimental time. Slowly but surely, HPS scientists are finding chances to use it.

This morning at CERN, operators nudged two high-energy beams of protons into a collision course inside the world’s largest and most energetic particle accelerator, the Large Hadron Collider. These first stable beams inside the LHC since the extended winter shutdown usher in another season of particle hunting.

The LHC’s 2017 run is scheduled to last until December 10. The improvements made during the winter break will ensure that scientists can continue to search for new physics and study rare subatomic phenomena. The machine exploits Albert Einstein’s principle that energy and matter are equivalent and enables physicists to transform ordinary protons into the rare massive particles that existed when our universe was still in its infancy.

“Every time the protons collide, it’s like panning for gold,” says Richard Ruiz, a theorist at Durham University. “That’s why we need so much data. It’s very rare that the LHC produces something interesting like a Higgs boson, the subatomic equivalent of a huge gold nugget. We need to find lots of these rare particles so that we can measure their properties and be confident in our results.”

During the LHC’s four-month winter shutdown, engineers replaced one of its main dipole magnets and carried out essential upgrades and maintenance work. Meanwhile, the LHC experiments installed new hardware and revamped their detectors. Over the last several weeks, scientists and engineers have been performing the final checks and preparations for the first “stable beams” collisions.

“There’s no switch for the LHC that instantly turns it on,” says Guy Crockford, an LHC operator. “It’s a long process, and even if it’s all working perfectly, we still need to check and calibrate everything. There’s a lot of power stored in the beam and it can easily damage the machine if we’re not careful.”

In preparation for data-taking, the LHC operations team first did a cold checkout of the circuits and systems without beam and then performed a series of dress rehearsals with only a handful of protons racing around the machine.

“We set up the machine with low intensity beams that are safe enough that we could relax the safety interlocks and make all the necessary tweaks and adjustments,” Crockford says. “We then deliberately made the proton beams unstable to check that all the loose particles were caught cleanly. It’s a long and painstaking process, but we need complete confidence in our settings before ramping up the beam intensity to levels that could easily do damage to the machine.”

The LHC started collisions for physics with only three proton bunches per beam. Over the course of the next month, the operations team will gradually increase the number of proton bunches until they have 2760 per beam. The higher proton intensity greatly increases the rate of collisions, enabling the experiments to collect valuable data at a much faster rate.

“We’re always trying to improve the machine and increase the number of collisions we deliver to the experiments,” Crockford says. “It’s a personal challenge to do a little better every year.”

Scientific experiments are designed to determine facts about our world. But in complicated analyses, there’s a risk that researchers will unintentionally skew their results to match what they were expecting to find. To reduce or eliminate this potential bias, scientists apply a method known as “blind analysis.”

Blind studies are probably best known from their use in clinical drug trials, in which patients are kept in the dark about—or blind to—whether they’re receiving an actual drug or a placebo. This approach helps researchers judge whether their results stem from the treatment itself or from the patients’ belief that they are receiving it.

Particle physicists and astrophysicists do blind studies, too. The approach is particularly valuable when scientists search for extremely small effects hidden among background noise that point to the existence of something new, not accounted for in the current model. Examples include the much-publicized discoveries of the Higgs boson by experiments at CERN’s Large Hadron Collider and of gravitational waves by the Advanced LIGO detector.

“Scientific analyses are iterative processes, in which we make a series of small adjustments to theoretical models until the models accurately describe the experimental data,” says Elisabeth Krause, a postdoc at the Kavli Institute for Particle Astrophysics and Cosmology, which is jointly operated by Stanford University and the Department of Energy’s SLAC National Accelerator Laboratory. “At each step of an analysis, there is the danger that prior knowledge guides the way we make adjustments. Blind analyses help us make independent and better decisions.”

Krause was the main organizer of a recent workshop at KIPAC that looked into how blind analyses could be incorporated into next-generation astronomical surveys that aim to determine more precisely than ever what the universe is made of and how its components have driven cosmic evolution.

Black boxes and salt

One outcome of the workshop was a finding that there is no one-size-fits-all approach, says KIPAC postdoc Kyle Story, one of the event organizers. “Blind analyses need to be designed individually for each experiment.”

The way the blinding is done needs to leave researchers with enough information to allow a meaningful analysis, and it depends on the type of data coming out of a specific experiment.

A common approach is to base the analysis on only some of the data, excluding the part in which an anomaly is thought to be hiding. The excluded data is said to be in a “black box” or “hidden signal box.”

Take the search for the Higgs boson. Using data collected with the Large Hadron Collider until the end of 2011, researchers saw hints of a bump as a potential sign of a new particle with a mass of about 125 gigaelectronvolts. So when they looked at new data, they deliberately quarantined the mass range around this bump and focused on the remaining data instead.

They used that data to make sure they were working with a sufficiently accurate model. Then they “opened the box” and applied that same model to the untouched region. The bump turned out to be the long-sought Higgs particle.

That worked well for the Higgs researchers. However, as scientists involved with the Large Underground Xenon experiment reported at the workshop, the “black box” method of blind analysis can cause problems if the data you’re expressly not looking at contains rare events crucial to figuring out your model in the first place.

LUX has recently completed one of the world’s most sensitive searches for WIMPs—hypothetical particles of dark matter, an invisible form of matter that is five times more prevalent than regular matter. LUX scientists have done a lot of work to guard LUX against background particles—building the detector in a cleanroom, filling it with thoroughly purified liquid, surrounding it with shielding and installing it under a mile of rock. But a few stray particles make it through nonetheless, and the scientists need to look at all of their data to find and eliminate them.

For that reason, LUX researchers chose a different blinding approach for their analyses. Instead of using a “black box,” they use a process called “salting.”

LUX scientists not involved in the most recent LUX analysis added fake events to the data—simulated signals that just look like real ones. Just like the patients in a blind drug trial, the LUX scientists didn’t know whether they were analyzing real or placebo data. Once they completed their analysis, the scientists that did the “salting” revealed which events were false.

A similar technique was used by LIGO scientists, who eventually made the first detection of extremely tiny ripples in space-time called gravitational waves.

High-stakes astronomical surveys

The Blind Analysis workshop at KIPAC focused on future sky surveys that will make unprecedented measurements of dark energy and the Cosmic Microwave Background—observations that will help cosmologists better understand the evolution of our universe.

Dark energy is thought to be a force that is causing the universe to expand faster and faster as time goes by. The CMB is a faint microwave glow spread out over the entire sky. It is the oldest light in the universe, left over from the time the cosmos was only 380,000 years old.

To shed light on the mysterious properties of dark energy, the Dark Energy Science Collaboration is preparing to use data from the Large Synoptic Survey Telescope, which is under construction in Chile. With its unique 3.2-gigapixel camera, LSST will image billions of galaxies, the distribution of which is thought to be strongly influenced by dark energy.

“Blinding will help us look at the properties of galaxies picked for this analysis independent of the well-known cosmological implications of preceding studies,” DESC member Krause says. One way the collaboration plans on blinding its members to this prior knowledge is to distort the images of galaxies before they enter the analysis pipeline.

Not everyone in the scientific community is convinced that blinding is necessary. Blind analyses are more complicated to design than non-blind analyses and take more time to complete. Some scientists participating in blind analyses inevitably spend time looking at fake data, which can feel like a waste.

Yet others strongly advocate for going blind. KIPAC researcher Aaron Roodman, a particle-physicist-turned-astrophysicist, has been using blinding methods for the past 20 years.

“Blind analyses have already become pretty standard in the particle physics world,” he says. “They’ll be also crucial for taking bias out of next-generation cosmological surveys, particularly when the stakes are high. We’ll only build one LSST, for example, to provide us with unprecedented views of the sky.”

At a ceremony today, CERN European research center inaugurated its newest accelerator.

Linac 4 will eventually become the first step in CERN’s accelerator chain, delivering proton beams to a wide range of experiments, including those at the Large Hadron Collider.

After an extensive testing period, Linac 4 will be connected to CERN’s accelerator complex during a long technical shutdown in 2019-20. Linac 4 will replace Linac 2, which was put into service in 1978. Linac 4 will feed the CERN accelerator complex with particle beams of higher energy.

“We are delighted to celebrate this remarkable accomplishment,” says CERN Director General Fabiola Gianotti. “Linac 4 is a modern injector and the first key element of our ambitious upgrade program, leading to the High-Luminosity LHC. This high-luminosity phase will considerably increase the potential of the LHC experiments for discovering new physics and measuring the properties of the Higgs particle in more detail.”

“This is an achievement not only for CERN, but also for the partners from many countries who contributed in designing and building this new machine,” says CERN Director for Accelerators and Technology Frédérick Bordry. “We also today celebrate and thank the wide international collaboration that led this project, demonstrating once again what can be accomplished by bringing together the efforts of many nations.”

The linear accelerator is the first essential element of an accelerator chain. In the linear accelerator, the particles are produced and receive the initial acceleration. The density and intensity of the particle beams are also shaped in the linac. Linac 4 is an almost 90-meter-long machine sitting 12 meters below the ground. It took nearly 10 years to build it.

Linac 4 will send negative hydrogen ions, consisting of a hydrogen atom with two electrons, to CERN’s Proton Synchrotron Booster, which further accelerates the negative ions and removes the electrons. Linac 4 will bring the beam up to an energy of 160 million electronvolts, more than 3 times the energy of its predecessor. The increase in energy, together with the use of hydrogen ions, will enable doubling the beam intensity delivered to the LHC, contributing to an increase in the luminosity of the LHC by 2021.

Luminosity is a parameter indicating the number of particles colliding within a defined amount of time. The peak luminosity of the LHC is planned to be increased by a factor of 5 by the year 2025. This will make it possible for the experiments to accumulate about 10 times more data over the period 2025 to 2035 than before.

Editor's note: This article is based on a CERN press release.