The new superconducting crab cavities being assembled at CERN. These cavities will be used in the future High-Luminosity LHC to tilt the particle bunches before they collide. (Image: Jules Ordan/CERN)
Thanks to their amazing properties, superconductors have become a vital ally of particle physics. As well as using superconducting magnets to steer particles in the right direction, accelerators use superconducting cavities to accelerate them. During the EUCAS 2017 conference on superconductors and their applications, which is taking place this week in Geneva, many presentations are being made on this subject.
A radiofrequency accelerating cavity is basically a metal chamber in which electromagnetic waves generate an electrical field. As particles pass through the chamber, they receive an electrical impulse. Compared to traditional copper cavities, superconducting cavities generate very strong electrical fields. Those in the Large Hadron Collider (LHC), for example, generate an electrical field of 5 million volts per metre.
The first work on superconducting cavities for particle physics began in the 1960s. But it was not until the 1980s that they were actually used in an accelerator, an electron collider at Cornell University in the United States. Meanwhile, the designers working on the Large Electron-Positron Collider (LEP) at CERN were investigating the technology as a way of doubling the energy level of their machine. The 27-kilometre ring was fitted out with 280 such cavities, allowing the LEP to exceed 200 GeV in the 1990s. The LHC is equipped with similar cavities. The brand new XFEL synchrotron at the DESY laboratory in Germany is made up of no fewer than 800 accelerating cavities, which rely heavily on the work carried out in the 1990s by the TESLA collaboration.
Today, the development of new superconducting cavities continues, particularly at CERN, where so-called “crab cavities” are under development to tilt particle bunches before they collide in the High-Luminosity LHC. These cavities will help to maximise overlapping of the beams in order to increase the probability of collisions each time they meet, otherwise known as luminosity. At Fermilab, the Cornell Laboratory and SLAC in the United States, new coatings are also being studied to improve performance even further.
A superconducting magnet from the LHC on display outside the United Nations Office in Geneva during the EUCAS 2017 conference. (Image: Michael Struik/CERN)
A major conference on superconductors and their applications gets under way today in Geneva. Organised by CERN in collaboration with the University of Geneva and EPFL-SPC (Swiss Plasma Center) under the auspices of the European Society for Applied Superconductivity, EUCAS 2017 will welcome more than 1000 scientists and engineers to share the latest advances in superconductor technology and its applications.
It’s no coincidence that CERN is co-organising this conference. The Large Hadron Collider (LHC) is quite simply the biggest application of superconductivity in the world, with 23 kilometres of superconducting magnets around its 27-kilometre circumference.
The phenomenon of superconductivity was discovered in 1911. Below a very low critical temperature, some materials lose all of their electrical resistance. This amazing property opens up many exciting possibilities. Since there is no resistance to stop the flow of current and the superconductor does not heat up, it can carry far stronger electrical currents than “normal” or resistive conductors. A coil made from superconducting material can produce stronger magnetic fields than resistive electromagnets. This is the property that is of particular interest to particle physicists.
In circular accelerators like the LHC, particles are kept in their orbits by a magnetic field. But the higher the energy (speed) of the particles, the stronger the field needs to be. The energy of circular accelerators is therefore limited by the power of their magnets. At the end of the 1960s, this limit began to stand in the way of progress and superconductivity was exactly the innovation required to overcome it.
At the start of the 1970s, the idea really started being taken seriously. At the time, the most advanced work on the technology was being carried out by the “Energy Doubler” project at the Fermilab laboratory in the United States. This project later became the Tevatron, the first superconducting collider, which started operation in 1983. Its success really accelerated the use of superconductors for high-energy physics and since then, superconductivity and particle physics have driven each other on. Following the extraordinary technological achievement of the LHC, the future of superconductors is now taking shape in accelerator projects such as the High-Luminosity LHC and, in the longer term, bigger colliders able to push back even further the boundaries of the energy levels that humanity is able to explore.
Art McDonald presenting in CERN's main auditorium on 4 September (Image: Julien Ordan/CERN)
Watch Art McDonald, Nobel prize-winning physicist, speaking on the science involved in building the Sudbury Neutrino Observatory.
Speaking at CERN last week, he discusses how scientists and technicians building the machine took more than 70,000 showers as part of their efforts to maintain a completely clean and uncontaminated laboratory, and how at one point the team had to repair the 78-tonne tank of liquid scintillator after it sprung a leak, using the same principles that you would use to fix a flat tyre on your bike.
McDonald was jointly awarded the Nobel Prize in Physics 2015 with Takaaki Kajita "for the discovery of neutrino oscillations, which shows that neutrinos have mass". He is the director of this unique observatory, which hopes to detect solar neutrinos through their interactions with a large tank of heavy water.
Watch the recording here.
The LHCb cavern (Image: Maximilien Brice/CERN)
Today, the LHCb experiment at CERN presented a measurement of the masses of two particular particles with a precision that is unprecedented at a hadron collider for this type of particles. Until now, the precise study of these “charmonium” particles, invaluable source of insights into the subatomic world, required dedicated experiments to be built.
“Thanks to this result, the LHCb collaboration opens a new avenue to precision measurements of charmonium particles at hadron colliders, that was unexpected by the physics community”, says Giovanni Passaleva, Spokesperson for the LHCb collaboration. Indeed, this kind of measurement seemed impossible until recently.
The two particles, χc1 and χc2, are excited states of a better-known particle called J/ψ. An excited state is a particle that has a higher internal energy, namely a mass, than the absolute minimum configuration which is allowed. The J/ψ meson and its excited states, also referred to as charmonium, are formed by a charm quark and its antimatter correspondent, a charm antiquark, bound together by the strong nuclear force. The J/ψ revolutionary observation in November 1974 triggered rapid changes in high-energy physics at the time, and earned its discoverers the Nobel Prize in physics. Just like ordinary atoms, a meson can be observed in excited states where the two quarks move around each other in different configurations, and because of Einstein’s famous equivalence of energy and mass, after a tiny amount of time they can disappear and transform into some other particles of lower masses. The LHCb experiment studied, for the first time, the particular transformation of χc1 and χc2 mesons decaying into a J/ψ particle and a pair of muons in order to determine some of their properties very precisely.
Previous studies of χc1 and χc2 at particle colliders have exploited another type of decay of these particles, featuring a photon in the final state instead of a pair of muons. However, measuring the energy of a photon is experimentally very challenging in the harsh environment of a hadron collider. Owing to the specialised capabilities of the LHCb detector in measuring trajectories and properties of charged particles like muons, and exploiting the large dataset accumulated during the first and second runs of the LHC up to the end of 2016, it was possible to observe the two excited particles with an excellent mass resolution. Exploiting this novel decay with two muons in the final state, the new measurements of χc1 and χc2 masses and natural widths have a similar precision and are in good agreement with those obtained at previous dedicated experiments that were built with a specific experimental approach very different from that in use at colliders.
“Not only are we no longer obliged to resort to purpose-built experiments for such studies,” continues Passaleva, “but also, in the near future, we will be able to think about applying a similar approach for the study of a similar class of particles, known as bottomonium, where charm quarks are replaced with beauty quarks.” These new measurements, along with future updates with larger datasets of collisions accumulated at the LHC, will allow new, stringent tests of the predictions of quantum chromodynamics (QCD), which is the theory that describes the behaviour of the strong nuclear force, contributing to the challenge of fully understanding the elusive features of this fundamental interaction of nature.
Find out more on the LHCb website.
The image above shows the data points (black dots) of the reconstructed mass distribution resulting from the combination of the J/ψ and the two muons. The two particle states are the two narrow peaks standing out from the distribution of data. (Image: LHCb collaboration)
Could we create a perfect vacuum? In a universe filled with matter and energy, we often think of deepest outer space as a vacuum, empty of everything. But it is far from it, with a multitude of particles and electromagnetic radiation zooming through it. This new animation, made in collaboration with TED-Ed, explores why CERN’s accelerators need to be one of the emptiest spaces in the universe and asks if there is such a thing as totally empty space.
Read more about the content in this animation on the TED-Ed website.
Gravitational waves as emitted during a black hole merger. (Image credit: S. Ossokine, A. Buonanno, Max Planck Institute for Gravitational Physics, Simulating eXtreme Spacetimes project, D. Steinhauser, Airborne Hydro Mapping GmbH)
What do gravitational waves – ripples in the fabric of space-time caused by violent energetic processes in the universe – have to do with particle physics? At first sight, not much. But on 1 September scientists from the gravitational-wave community and CERN met to identify technology parallels.
As CERN works towards a major upgrade of the Large Hadron Collider (LHC), the High Luminosity LHC, gravitational wave scientists are also contemplating major upgrades to current facilities. These will enrich the vista of the universe opened up in February 2016 when the Laser Interferometer Gravitational-wave Observatory (LIGO) and Virgo collaborations announced the long-awaited first detection of gravitational waves, 100 years after their prediction by Einstein’s theory of gravity: general relativity.
Gravitational waves were detected using large “interferometers”. These L-shaped tubes with 4-km-long arms contain a series of mirrors and lasers that are sensitive to any slight distortion in the apparatus caused by a passing gravitational wave. Now the gravitational-wave community is exploring several technologies to improve the sensitivity of the current observatories.
“Technological R&D and design efforts for third-generation gravitational detectors may have interesting overlaps both with CERN capabilities and possible future directions,” says Barry Barish of the California Institute of Technology, one of the founders of the LIGO experiment.
Next-generation interferometers could have much longer arms, be located underground to reduce seismic noise, or be cooled to cryogenic temperatures to reduce thermal interference. Expertise in vacuum, cryogenics and control systems is therefore of particular relevance, as well as how to deal with large volumes of data. CERN can also offer insights into how to organise the large international collaborations necessary to design, build and operate tomorrow’s gravitational wave observatories.
More precise observations of the gravitational fingerprints of the most energetic phenomena in our universe may also help CERN in its quest to understand the fundamental constituents of matter. Collisions of black holes or neutron stars and supernovae explosions, for example, could shed light on open questions such as the nature of dark matter, the limits of the validity of general relativity and the behaviour of matter at extreme densities and pressures.
“Overall, we had a healthy exchange of ideas that opened the door to the exploration of possible further synergies and joint work,” said Barish.
The main linac driving the European XFEL, suspended from the ceiling to leave space at floor level, photographed in January 2017. (Image: D Nölle/DESY).
Today, an official ceremony marked the inauguration of the European X-ray Free-Electron Laser (European XFEL), in Schenefeld-Hamburg, Germany. Extending over a distance of 3.4 km in tunnels departing from DESY in Bahrenfeld-Hamburg, it will generate ultrashort X-ray flashes at a rate of 27 000 per second with an intensity one billion times higher than the best conventional X-ray sources. The facility will produce ultrafast snapshots of atomic and molecular movements in unprecedented detail, opening completely new research opportunities for science and industry users to image electronic, chemical and biological processes.
The story of the European XFEL is a wonderful example of the longstanding R&D synergies between the high-energy physics and light-source worlds. While traditional large X-ray facilities are based on storage rings in which energetic electrons circulate while emitting X-rays, X-ray free-electron lasers (XFELs) use special accelerating structures initially conceived for a linear collider for particle physics more than 20 years ago.
Driving the European XFEL is the longest and most advanced linear accelerator ever built, a 1.4-km-long machine that uses superconducting radio-frequency (SRF) cavities to accelerate electrons highly efficiently to an energy of 17.5 GeV. Despite the clear benefits of SRF cavities, before the mid-1990s the technology was not mature enough and too expensive to be practical for a large facility. Based on initial experience with individual cavities – including those of LEP – the TESLA collaboration, hosted at DESY, developed highly performing cavities and reduced the cost for a linear collider proposal and for the construction of the European XFEL. Today the European XFEL also serves as a prototype for a potential linear collider, the ILC.
Exiting the European XFEL linac, electrons are rapidly deflected in an undulating left–right pattern by traversing a long periodic array of magnets called an undulator, causing the electrons to emit intense and coherent beams of X-ray photons. X-rays emerging from the undulator, via one km-long photon-transport tunnels equipped with various X-ray optics elements, finally arrive at the European XFEL headquarters in Schenefeld where user experiments will take place.
The European XFEL is the culmination of a worldwide effort, with European XFEL GmbH being responsible for the construction and operation of the facility, especially the X-ray photon transport and experimental stations, and its largest shareholder DESY leading the construction and operation of the electron linac. The facility joins other major XFELs in the US (LCLS) and Japan (SACLA), and is expected to keep Europe at the forefront of X-ray science for at least the next 20 to 30 years.
Construction of the €1.2 billion European XFEL began in January 2009, funded by 11 countries, with Germany and Russia as the largest contributors, although no fewer than 17 European institutes contributed in-kind to the accelerator complex. “The European XFEL is the result of intense technological development in a worldwide collaboration that has exceeded expectations,” says Eckhard Elsen, CERN’s Director for Research and Computing. “It is an impressive example of how cutting-edge accelerator research can benefit society, and demonstrates the continuing links between the needs of fundamental research in particle physics and X-ray science.”
The European XFEL facility in Hamburg (on the right) and Schenefeld (Schleswig-Holstein) (Image: European XFEL)
Tonight, find out how two black holes colliding helped change our understanding of the universe forever.
David Reitze, Executive Director for LIGO, will speak at CERN tonight, 29 August 2017 at 7.30pm (CEST), on what unique insights into the nature of gravity, matter, space, and time have been revealed by the discovery of gravitational waves.
On September 14, 2015, scientists from the LIGO Scientific Collaboration and the Virgo Collaboration using the LIGO detectors observed the collision and fusion of two black holes by directly measuring the gravitational waves emitted during their collision. This detection came almost exactly 100 years after Einstein predicted their existence in his revolutionary general theory of relativity, and 50 years after scientists began searching for them in earnest.
This discovery has had truly profound implications on physics and astronomy, as gravitational waves provide unique information on the most energetic astrophysical events –opening a new window onto the cosmos.
Watch the webcast here, and follow the slides here.
The first Anode Plane Assembly module which will collect signals from particles passing through the protoDUNE single-phase detector has recently arrived at CERN. (Image: Julien Marius Ordan/CERN)
Two large neutrino detectors, called protoDUNE single and dual phase, are being built at CERN. They are prototypes of the future Deep Underground Neutrino Experiment (DUNE) detector, whose construction has recently started in the United States. Each of these detectors is a 10-metre cube Liquid Argon Time Project Chamber, in single (SP) or dual phase (DP), containing about 800 tons of liquid argon. While the two big cryostats hosting the detectors are about to be completed, the construction of the protoDUNE-SP detector has just started, following the arrival of two key components.
The first Anode Plane Assembly module, which will collect signals from particles passing through the detector, has recently arrived at CERN. It is going to be tested together with its electronics, before being installed in its final position inside the cryostat. The protoDUNE-SP detector will have six of these modules, which are 6-metres high and 2.5-metres wide. They are currently being built in the UK and in the US and will be shipped to CERN within the next few months.
The first field cage module of the protoDUNE-SP detector has been fully assembled at CERN. (Image: Julien Marius Ordan/CERN)
In parallel, other parts of the protoDUNE-SP detector are being assembled at CERN, including the field cage, which keeps the electrical field uniform inside the volume of the detector where particles are revealed. This is important because the electrical signal released by ionizing particles crossing the detector is extremely small so a perfectly uniform electrical field is needed to avoid introducing spurious signals. Four of the 28 field cage modules have been already assembled and stored in EHN1 hall, ready to be installed.
The assembly and installation of the detector parts is expected to be completed by spring next year, in order to have protoDUNE-SP ready to take data in autumn 2018, before the planned two-year shutdown of the LHC.
Around 85% of the matter in our Universe is a mystery. If this dark matter has never been observed, how do we know what it is, and how do scientists know where to start looking? This new animation, made in collaboration with TED-Ed, shows how the LHC is hoping to recreate these theoretical dark matter particles, and what this will tell us about our world.
A light-by-light scattering event measured in the ATLAS detector (Image: ATLAS/CERN)
Physicists from the ATLAS experiment at CERN have found the first direct evidence ofhigh energy light-by-light scattering, a very rare process in which two photons – particles of light – interact and change direction. The result, published today in Nature Physics, confirms one of the oldest predictions of quantum electrodynamics (QED).
"This is a milestone result: the first direct evidence of light interacting with itself at high energy,” says Dan Tovey(University of Sheffield), ATLAS Physics Coordinator. “This phenomenon is impossible in classical theories of electromagnetism; hence this result provides a sensitive test of our understanding of QED, the quantum theory of electromagnetism."
Direct evidence for light-by-light scattering at high energy had proven elusive for decades – until the Large Hadron Collider’s second run began in 2015. As the accelerator collided lead ions at unprecedented collision rates, obtaining evidence for light-by-light scattering became a real possibility. “This measurement has been of great interest to the heavy-ion and high-energy physics communities for several years, as calculations from several groups showed that we might achieve a significant signal by studying lead-ion collisions in Run 2,” says Peter Steinberg (Brookhaven National Laboratory), ATLAS Heavy Ion Physics Group Convener.
Heavy-ion collisions provide a uniquely clean environment tostudy light-by-light scattering. As bunches of lead ions are accelerated, an enormous flux of surrounding photons is generated. When ions meet at the centre of the ATLAS detector, very few collide, yet their surrounding photons can interact and scatter off one another. These interactions are known as ‘ultra-peripheral collisions’.
Studying more than 4 billion events taken in 2015, the ATLAS collaboration found 13 candidates for light-by-light scattering. This result has a significance of 4.4 standard deviations, allowing the ATLAS collaboration to report the first direct evidence of this phenomenon at high energy.
“Finding evidence of this rare signature required the development of a sensitive new ‘trigger’ for the ATLAS detector,” says Steinberg. “The resulting signature — two photons in an otherwise empty detector — is almost the diametric opposite of the tremendously complicated eventstypically expected from lead nuclei collisions. The new trigger’s success in selecting these events demonstrates the power and flexibility of the system, as well as the skill and expertise of the analysis and trigger groups who designed and developed it.”
ATLAS physicists will continue to study light-by-light scattering during the upcoming LHC heavy-ion run, scheduled for 2018. More data will further improve the precision of theresult and may open a new window to studies of new physics. In addition, the study of ultra-peripheral collisions should play a greater role in the LHC heavy-ion programme, as collision rates further increase in Run 3 and beyond.
Like hunters following the tracks of their prey, physicists compare real collision data with simulations of what they expect to see if a new particle is produced and decays in their detectors. (Supersymmetry simulation image: the CMS collaboration)
With the LHC now back smashing protons together at an energy of 13 TeV, what exotic beasts do physicists hope to find in this unfamiliar corner of the natural world?
Among the top priorities for the LHC experiments this year is the hunt for new particles suspected to lurk at the high-energy frontier: exotic beasts that do not fit within the Standard Model of particle physics and could lift the lid on an even deeper theory of nature’s basic workings.
New particles predicted by specific models of physics beyond the
Standard Model (Image: Daniel Dominguez, with permission from
Following the discovery of the Higgs boson five years ago, which was the final missing piece of the Standard Model of particle physics, physicists have good reason to expect that new particle species lie over the horizon. Among them is the mystery of what makes up dark matter, why the Standard Model particles of matter weigh what they do and come in three families of two, and, indeed, why the Higgs boson isn’t vastly heavier than it is – that is, why it isn't so heavy that it could have ended the evolution of the universe an instant after the Big Bang.Casting the net wide
These outlandish prey are just a few of the known unknowns for physicists. To ensure that no corner of the new-physics landscape is left unturned, the LHC experiments also employ a model-independent approach to search for general features such as pairs of high-energy quarks and leptons or for unexplained sources of missing energy.
Their most elusive quarry might not light up their detectors at all, forcing the LHC exploration teams to adopt stealth approaches, such as making ultra-precise measurements of known Standard Model processes and seeing if they diverge from predictions. While physicists are hoping for a clear shot at any new particle species – a distinctive “bump” in the data that can only be explained by the presence of a new, heavy particle – they could be faced with a mere rustling in the undergrowth or other indirect signs that something is awry. This quest is not just the preserve of all of the LHC experiments, but also of numerous other experiments at CERN that are not linked to the LHC.
Either way, physicists exploring this uncharted territory of the high-energy frontier have to take extreme care not to get tricked by numerous Standard Model doppelgängers or be teased by inconclusive statistics. Even after an exotic new beast has been snared statistically and it seems that the LHC experiments have a discovery on their hands, so begins the task of identifying what the beast really is: a mere mutant or close relative of a species we already know? Or the first glimpse of a new subatomic kingdom?
Ranging from the bizarre to the mind-boggling, and in no particular order, below is a summary of some of the quantum creatures that are in the LHC experimentalists’ sights this year.
The new deceleration ring ELENA will slow down antimatter particles further than ever to improve the efficiency of experiments studying antimatter. (Image: Maximilien Brice/CERN)
On 2 August, the first 5.3 MeV antiproton beam coming from CERN’s Antiproton Decelerator (AD) circulated in the Extra Low ENergy Antiproton (ELENA) decelerating ring.
ELENA is the new decelerator for antimatter experiments. It has a circumference of just 30 meters and will be connected to the AD experiments to increase the number of antiprotons available to several antimatter experiments. The slower the antiprotons (i.e. the less energy they have), the easier it is for the AD’s antimatter experiments to study or manipulate them. However, the AD decelerator can reliably only slow antiprotons down to 5.3 MeV, the lowest possible energy for a machine of this size. ELENA will reduce this energy by 50 times, to just 0.1 MeV. In addition, the density of the beams will be improved. The number of antiprotons that can be trapped will be increased by a factor of 10 to 100. The new decelerator will also enable several experiments to receive antiproton beams simultaneously, opening up the possibility for additional experiments, such as GBAR.
This is not the first time that a beam has circulated in ELENA. The first tests began last November, but this is the first time that antiprotons, the particle type this machine has been conceived for, have been injected. The beam of antiprotons has been successfully injected and it has been observed circulating for a few milliseconds (that is, a few thousand turns of the machine).
The commissioning of the machine will continue over the next coming months with setting-up of several systems such as the radio-frequency cavity, which will be used to decelerate the bunches of antiprotons. At that point, the commissioning team will start changing the energy of the beams. At the same time, a series of general adjustments of the beam optics is as well foreseen.
As antiprotons are difficult to produce and they need to be shared among many experiments, progress in the commissioning of ELENA will also be made using protons and ions coming from a local H– ion and proton source.
Alpha Experiment (Image: Maximilien Brice/CERN)
In a paper published today in Nature, the ALPHA experiment at CERN’s Antiproton Decelerator reports the first observation of the hyperfine structure of antihydrogen, the antimatter counterpart of hydrogen. These findings point the way to ever more detailed analyses of the structure of antihydrogen and could help understand any differences between matter and antimatter.
The researchers conducted spectroscopy measurements on homemade antihydrogen atoms, which drive transitions between different energy states of the anti-atoms. They could in this way improve previous measurements by identifying and measuring two spectral lines of antihydrogen. Spectroscopy is a way to probe the internal structure of atoms by studying their interaction with electromagnetic radiation.
In 2012, the ALPHA experiment demonstrated for the first time the technical ability to measure the internal structure of atoms of antimatter. In 2016, the team reported the first observation of an optical transition of antihydrogen. By exposing antihydrogen atoms to microwaves at a precise frequency, they have now induced hyperfine transitions and refined their measurements. The team were able to measure two spectral lines for antihydrogen, and observe no difference compared to the equivalent spectral lines for hydrogen, within experimental limits.
“Spectroscopy is a very important tool in all areas of physics. We are now entering a new era as we extend spectroscopy to antimatter,” said Jeffrey Hangst, Spokesperson for the ALPHA experiment. “With our unique techniques, we are now able to observe the detailed structure of antimatter atoms in hours rather than weeks, something we could not even imagine a few years ago.”
With their trapping techniques, ALPHA are now able to trap a significant number of antiatoms – up to 74 at a time – thereby facilitating precision measurements. With this new result, the ALPHA collaboration has clearly demonstrated the maturity of its techniques for probing the properties of antimatter atoms.
The rapid progress of CERN’s experiments at the unique Antiproton Decelerator facility is very promising for ever more precise measurements to be carried out in the near future.
The MPKI Penning-trap setup for precision mass measurements of single particles. A combination of strong electric and magnetic fields is able to store individual protons and highly charged carbon ions. (Image: Max Planck Institute for Nuclear Physics)
A team in Heidelberg, Germany has made the most precise measurement to date of the mass of a single proton, the particle that – together with the neutron and the electron – makes up all the matter in the universe, and therefore also us. They found that the proton is about 30 billionths of a percent lighter than previously thought. The result improves by a factor of three on the precision of the accepted value of the Committee on Data for Science and Technology (CODATA) – which regularly collects and publishes the recommended values of fundamental physical constants – and it also disagrees with its central value at a level of 3.3 standard deviations, which means that the new value is significantly different from the previous result.
Proton mass is a fundamental parameter in atomic and particle physics, influencing atomic spectra and allowing tests of ultra-precise calculations within Quantum Electrodynamics (QED), the theory that describes how light and matter interact. In particular, a detailed comparison between the masses of the proton and the antiproton offers a stringent test of the fundamental symmetry of the Standard Model, the so-called charge, parity and time (CPT) invariance. This proton lightness could also potentially shed light on other mysteries, such as the well-known discrepancies in the measured mass of the heaviest hydrogen isotope, tritium.
The team at the Max Planck Institute for Nuclear Physics (MPIK) in Heidelberg and their collaborators from RIKEN in Japan used a device known as Penning trap, in which a combination of strong electric and magnetic fields, cooled to 4 degrees Kelvin (- 269.15 °C) is able to store individual protons and highly charged carbon ions. In this trap, the magnetic field forces the particles to move in circle and by measuring the characteristic frequencies of the trapped particles when they spin around, the mass of the proton follows directly.
The sensitive single-particle detectors were partly developed by the RIKEN group, drawing on experience gained with similar traps for antimatter research at CERN’s Antiproton Decelerator (AD). “The group around Sven Sturm and Klaus Blaum from MPIK Heidelberg that did the measurement has great expertise with carbon, whereas the BASE group contributed proton expertise based on 12 years dealing with protons and antiprotons,” explains RIKEN group leader and spokesperson of the AD’s BASE experiment, Stefan Ulmer. “We shared knowledge such as know-how on ultra-sensitive proton detectors and the ‘fast shuttling’ method developed by BASE to perform the proton/antiproton charge-to-mass ratio measurement.”
Although carefully conducted cross-check measurements confirmed a series of published values of the proton mass and showed that no unexpected systematic effects were imposed by the new method, such a striking departure from the accepted value will likely challenge other teams to revisit the proton mass. The discrepancy has already inspired the MPIK-RIKEN team to further improve the precision of their measurement, for instance by storing a third ion in the trap and measuring it simultaneously to eliminate uncertainties originating from magnetic field fluctuations, which are the main source of systematic errors when using the new technique.
“It is also planned to tune the magnetic field to even higher homogeneity, which will reduce additional sources of systematic error,” explains BASE member Andreas Mooser. “The methods that will be pioneered in the next step of this experiment will have immediate positive feedback to future BASE measurements, for example in improving the precision in the antiproton-to-proton charge-to-mass ratio.”
The research was published on 18 July 2017 in Physical Review Letters.
Over the last six weeks, ICARUS has traveled across land and sea. Yesterday, the neutrino detector finally arrived at Fermilab near Chicago, Illinois. (Image © Fermilab)
After six weeks on the road, the two ICARUS modules have finally arrived at Fermilab near Chicago, Illinois. The Italian-made detector will be put to work, along with two others on the Fermilab site, to capture and inspect one of the most enigmatic particles in the cosmos: neutrinos. Neutrinos are among the most abundant particles in the universe, but little is known about them because they rarely interact with ordinary matter. The ICARUS detector will use Fermilab’s neutrino beam to measure the properties of the three types of neutrinos that have been seen, and search for a long-theorised but never-detected cousin.
“We’ve seen hints that there might be a fourth kind of neutrino, but we haven’t detected it yet,” said Fermilab scientist Angela Fava, a member of the ICARUS collaboration. “The ICARUS experiment will join our suite of neutrino detectors to help us resolve this long-standing, open question of whether there is indeed a fourth member of the neutrino family.”
The ICARUS experiment was designed and built at Gran Sasso Laboratory in Italy and started its career as a neutrino hunter in 2010. In 2014, scientists transported ICARUS to CERN for updating and refurbishment, and in June packaged and shipped it to Fermilab, where it will start the next phase of its life.
Over the last six weeks ICARUS has traveled across land and sea by truck, barge and ship. On the outside the two modules look like extra-large shipping containers, but inside the walls are lined with incredibly delicate panels of wires.
“The wire planes look like enormous harps and are very fragile,” says Andrea Zani, a researcher at CERN. “We worked for several months to prepare for the shipment and ensure that our detectors arrive in the US safety. However, you can never control everything, especially the passage across the sea.”
Zani and his colleagues attached impact sensors onto the shipping containers to measure if their irreplaceable detectors met any unexpected turbulence during their journey to the United States. From CERN, the modules traveled by truck to Basel, where they were lifted onto a barge and then cruised down the Rhine river to Antwerp, Belgium, and then into the Atlantic. Luckily, the ocean was calm during the two-week voyage to the Gulf of Saint Lawrence in Quebec, Canada. From there, ICARUS snaked its way up the Saint Lawrence River, drifted through Montreal, traversed the Great Lakes and finally docked in Burns Harbor, Indiana, on Lake Michigan. The last leg of the journey was a slow three-day drive to Fermilab.
“We met the convoy every time it stopped to check the shock sensors and verify that CERN’s handling instructions were respected during all operations of movement from one means of transport to the other,” Zani said. “An unexpected challenge was learning about and abiding by the different transport regulations in Europe and the United States.”
Now that ICARUS has finally arrived at Fermilab, the next step will be a series of final checks followed by its installation inside a building specifically constructed and outfitted for it, and preparing it for operation.
“It feels good to have ICARUS here in its new Midwestern U.S. home," Fava said. "And now that it is, we can go full-bore in hunting down that elusive fourth.”
The first African-led experiment has taken place at CERN, supported by UK researchers. Students and staff from the University of the Western Cape, South Africa, have investigated the isotope Selenium 70 using Isolde, CERN’s nuclear physics facility. (Video: Christoph Madsen/CERN)
The first African-led experiment has taken place at CERN. Students and staff from the University of the Western Cape (UWC) have investigated the isotope selenium 70 at CERN's Isolde facility. The nucleus of this isotope is known to have two possible shapes, depending on its excitation state, and the team wanted to examine the relationship between shape and energy more closely.
South Africa joined the Isolde collaboration in March 2017 to benefit from HIE-Isolde’s beams of unstable, exotic particles – the country’s own nuclear physics facility has a source of stable beams. The selenium 70 experiment, using Miniball, is the first to be approved.
“We’re going to be accelerating a selenium beam into a platinum target,” explains PhD student Kenzo Abrahams, as the team configures the experiment around him. "By colliding two nuclei, we will cause the excitation of the selenium 70 isotope, and by measuring the intensity of the gamma ray decay, we’ll know which shape has been excited.”
The UWC team, comprising masters and PhD students from the coulomb excitation group, led by Professor Nico Orce and supported by experiment co-lead, Professor David Jenkins from the University of York, certainly feel that they are blazing the way for other South African universities to submit proposals. “The University of the Western Cape is a historically disadvantaged institution,” explains Nico, “we have team members from rural areas of the Eastern Cape, and others who live in townships. I hope this experiment will have a domino effect, encouraging similar students and universities to aim for the top.”
Totalling 11 people, the experimental team is much larger than Isolde would normally welcome, but Nico was determined to give as many of his students as possible the opportunity to use one of the world’s best research facilities.
Senamile Masango is a masters student, “this is my first time outside South Africa and it’s very exciting to be at CERN,” she says, “it’s every scientist’s dream to come to facilities like this!”
Passionate about her subject, and highly motivated, Senamile is also well aware that she is an important role model, “you will hardly find any women doing physics in South Africa, and you will hardly find any black physicists. Nico treats us all equally and he’s making us hungry to break every barrier. We’re making history!”
“The skills that the students are learning at CERN are transformational.” says George O’Neill. Having finished his PhD at Liverpool, George wanted the challenge of working in a new lab; he was attracted by both the facilities at UWC and Nico’s ethos, “Everyone in this group will go on to be a professor,” he adds.
David Jenkins is co-leading the experiment. “I’ve worked with Nico for a long time and I’ve been teaching at his ‘Tastes of Nuclear Physics’ summer school for five years. UWC has a real battle to get funding and Nico has jumped through so many hoops to get here. I wanted to get them involved at Isolde and help build the research expertise in the team.”
If the extraordinary levels of energy and motivation demonstrated by the team are mirrored by the experimental results, then UWC is set to become a significant name in international nuclear physics.
*Ubuntu is a Xhosa word, translated by one of the team as “I am, because we are”. It sums up the essence of this passionate and motivated group of young scientists.
This 11-meter high prototype at CERN will refine neutrino detector technology. The final DUNE detectors will be 20 times larger than this prototype and located in the new LBNF cavern in the United States. (Image: M. Brice, J. Ordan/CERN)
Today construction started on international mega-science facility which will employ the expertise of CERN to study the properties of neutrinos; ghostly fundamental particles that play by an unknown set of rules. The mile-deep experimental cavern is part of the Long Baseline Neutrino Facility, an international research center located in the United States that will eventually host four giant neutrino detectors. Researchers at CERN are currently building prototypes for these detectors and experimenting with new technologies that will enhance our pictures of these ghostly cosmic nomads.
“Some of the open questions in fundamental physics today are related to extremely fascinating and elusive particles called neutrinos.”, said CERN’s Director-General Fabiola Gianotti. “The Long-Baseline Neutrino Facility in the United States, whose start of construction is officially inaugurated with today’s ground-breaking ceremony, brings together the international particle physics community to explore some of the most interesting properties of neutrinos.’
This animation explains how the Long-Baseline Neutrino Facility will operate and supply neutrino beams to the Deep Underground Neutrino Experiment (DUNE) 1300 km from the source. (Video: Fermilab)
Neutrinos are among the most abundant fundamental particle in the universe, but little is known about them because they rarely interact with ordinary matter. Previous research has shown that neutrinos play by a different set of rules than all other particles, giving scientist hope that neutrinos might be the key to many lingering questions about the origin and evolution of the cosmos.
“Studying neutrinos could provide answers to some major mysteries in physics, such as why is the universe made entirely of matter and not antimatter,” said Filippo Resnati, a CERN researcher working at the Neutrino Platform. “We need a powerful neutrino beam and huge detectors if we want to measure and understand their properties.”
Neutrinos can traverse thousands of kilometers through rock and dirt before bumping into a terrestrial atom. While this aloofness makes neutrinos incredibly difficult to detect, it is also the principle underlying the Deep Under Ground Neutrino Experiment, which will be the first tenant in the new LBNF cavern. As neutrinos travel, they change their properties—a phenomenon which is little understood. The LBNF/DUNE Experiment will catch and measure neutrinos generated by a proton beam at Fermilab near Chicago, Illinois, before and after their 1300-kilometer subterranean sprint to Sanford Lab located in Lead, South Dakota. CERN’s Neutrino Platform is hosting an international community of researchers as they design and build prototypes for DUNE’s far detectors.
“Building and testing large prototypes is a necessary intermediary step for a project as massive as LBNF/DUNE,” said Marzio Nessi, the head of CERN’s Neutrino Platform. “We’re figuring out how to adapt the existing technology to thrive inside a house-sized detector. Once we’ve proven that it can work, we will then scale it up by a factor of 25 for the final DUNE detectors.”
Workers stand on scaffolding inside the DUNE prototype (ProtoDUNE). The metallic paneling will act as an expandable tank for the liquid argon, which will generate electrons and light when a particle interacts with the atoms of the liquid. (Image: Maximilien Brice, Julien Ordan/CERN)
The CERN prototypes are refining a detection technology originally developed by Carlo Rubbia, a Nobel prize winning physicist and former CERN Director General. Hatched panels of delicate wires and photon sensors record the electrical and light signals generated by neutrinos as they crash into argon atoms. This information enables physicists to triangulate the positions of neutrinos and measure their properties. These panels will be submerged in liquid argon in one prototype, and the other prototype will test a newer technology which uses electron multipliers suspended in argon vapor.
In addition to building and testing the detector prototypes for LBNF/DUNE, CERN will serve as the European hub for neutrino physicists working on research based in the United States and elsewhere in the world. CERN has a rich history of neutrino research and contributed to past discoveries, such as the direct observation of neutrino shape-shifting made by the OPERA experiment at Gran Sasso laboratory in Italy. CERN also provides the infrastructure for DUNE researchers to build and test their detectors using CERN’s test beam facility. This is the first-time CERN is joining projects located in the United States, with an active role designing final DUNE detectors and building the cryogenics infrastructure.
“Things are changing,” Resnati said. “CERN’s mission is to seek answers to the big questions in physics, and we want to be part of this worldwide quest for knowledge. We’re pulling together as a global community of physicists and making it happen.”
The groundbreaking ceremony at Sanford Lab in South Dakota starting at 11:20 pm CEST will be webcast. Watch the webcast!
Take a look at the CERN Neutrino platform with the eye of a drone. The huge red cube is the ProtoDUNE, a prototype for the DUNE detectors which will be installed in South-Dakota, USA, in the new Long-Baseline Neutrino Facility cavern. (Video: CERN)
This is the Miniball germanium array, which is using the first HIE-ISOLDE beams for the experiments described below (Image: Julien Ordan /CERN)
For the first time in 2017, the HIE- ISOLDE linear accelerator began sending beams to an experiment, marking the start of ISOLDE’s high-energy physics programme for this year.
The HIE-ISOLDE (High-Intensity and Energy upgrade of ISOLDE) project incorporates a new linear accelerator (Linac) into CERN’s ISOLDE facility (which stands for the Isotope mass Separator On-Line). ISOLDE is a unique nuclear research facility, which produces radioactive nuclei (ones with too many, or too few, neutrons) that physicists use to research a range of topics, from studying the properties of atomic nuclei to biomedical research and to astrophysics.
Although ISOLDE has been running since April, when the accelerator chain at CERN woke up from its technical stop over winter, HIE-ISOLDE had to wait until now as new components, specifically a new cryomodule, needed to be installed, calibrated, aligned and tested.
Each cryomodule is built in the CERN clean room before being installed one-by-one into the HIE-ISOLDE accelerator. This video shows work being done on the first cryomodule of the new HIE-ISOLDE instalation. The work was carried out in building SM18 in a specially dedicated clean room. (Video: Christoph Madsen/CERN)
Each cryomodule contains five superconducting cavities used to accelerate the beam to higher energies. With a third module installed, HIE-ISOLDE is able to accelerate the nuclei up to an average energy of 7.5 MeV per nucleon, compared with the 5.5 MeV per nucleon reached in 2016.
This higher energy also allows physicists to study the properties of heavier isotopes – ones with a mass up to 200, with a study of 206 planned later this year, compared to last year when the heaviest beam was 142. From 2018, the HIE-ISOLDE Linac will contain four of these cryomodules and be able to reach up to 10 MeV per nucleon.
“Each isotope we study is unique, so each experiment either studies a different isotope or a different property of that isotope. The HIE-ISOLDE linac gives us the ability to tailor make a beam for each experiment’s energy and mass needs,” explains Liam Gaffney, who runs the Miniball station where many of HIE-ISOLDE’s experiments are connected.
The HIE-ISOLDE beams will be available until the end of November, with thirteen experiments hoping to use the facility during that time – more than double the number that took data last year. The first experiment, which begins today, will study the electromagnetic interactions between colliding nuclei of the radioactive isotope Selenium 72 and a platinum target. With this reaction they can measure whether or not the nuclei is more like a squashed disc or stretched out, like a rugby ball; or some quantum mechanical mixture of both shapes.