After long months of preparation, the Beam Radiation, Instrumentation and Luminosity (BRIL) group has completed the installation of three instruments dedicated to the measurement of luminosity and beam conditions: the Beam Condition Monitor “Fast” (BCM1F), the Beam Condition Monitor for Losses (BCM1L) and the Pixel Luminosity Telescope (PLT). These three of the BRIL sub-detectors make up the BRIL sub-system which is segmented into 4 modules. They represent a new “generation” in their respective design history. Both PLT and BCM1F rely on silicon sensors, while BCM1L uses poly-crystalline diamond sensors.
Measuring the real-time rate of collisions at CMS is key to optimising both the trigger rates and the quality of the beams delivered by the Large Hadron Collider (LHC). Continuously assessing the beam conditions is also essential to the protection of the LHC machine and the sensitive CMS sub-detectors. Finally, the aggregated luminosity measurements need to be meticulously understood to determine the expected frequency of interactions in the analysis of data collected at CMS.
The design and production of new components, sensor characterisation, assembly, stress-testing under thermal cycles, troubleshooting, repairs and other tasks spanned a few years of challenging work, which ramped up as Long Shutdown 2 came to a close. The transport activities began before sunrise on 5 July 2021.
Each module of the sub-system was carefully loaded onto a special transport vehicle and dry air was circulated inside their transport boxes. Only days before, each module had been delicately readied for its journey, which included labelling them with their affectionately selected aliases: Calabrese, Capricciosa, Diavola and Margherita. After being lowered down the pit to the CMS experimental cavern, each module was craned up to the tracker sub-detector platform. The BRIL sub-detectors now lie at the heart of the CMS detector, about 1.8 m from the interaction point, just beside the forward pixel tracking sub-detector.
One of the most significant changes in the design of the instruments has been the implementation of a new active cooling circuit for BCM1F, which is essential for a silicon-based detector. The PLT cooling loop has been modified to include a new section for BCM1F. The design of the BCM1F cooling circuit follows the approach implemented for the PLT during Run 2: the cooling structure has been 3D printed in a titanium alloy using the selective laser melting technique.
The silicon sensors used for BCM1F and three of those used in one of the PLT channels were sourced from a batch currently being developed for the CMS Phase II upgrade for the High-Luminosity LHC. “This is the first time that these prototype Phase II silicon pixel sensors will be installed in CMS, so the whole community is eager to see how this material behaves,” says Anne Dabrowski, CMS BRIL project manager.
The installation of the BRIL sub-detectors was closely followed by the sealing of the bulkhead, which encloses them with the CMS silicon pixel and strip tracker sub-detectors. The work is now focused on the full commissioning of all BRIL systems in anticipation of the first beams of Run 3 of the LHC.
This story was originally published on the CMS website.
Neutrinos are tricky beasts. Alone among known fundamental particles, they suffer from an identity crisis — if it were possible to put them on a weighing scale, you would unpredictably measure one of three possible masses. As a result, the three neutrino “flavours” merge into each other as they race through space and matter, opening up the potential for matter-antimatter asymmetries relevant to open questions in cosmology. Neutrinos are today the subject of a vibrant worldwide research programme in particle physics, astrophysics and multi-messenger astronomy.
In an eye-catching example of international collaboration in particle physics, CERN has now agreed to produce a second “cryostat” for the detectors of the international Deep Underground Neutrino Experiment (DUNE) in the US. Cryostats are huge stainless-steel vessels that will eventually hold and cool 70,000 tonnes of liquid argon inside the DUNE experiment’s detectors. The large size and low temperatures of the cryostats needed for the DUNE detectors necessitated innovation in collaboration with the liquefied-natural-gas shipping industry. CERN had already committed to build the first of four DUNE cryostats. Following approval from the CERN Council, the Organization has now also agreed to provide a second.
The collaboration exploits CERN’s expertise with a technology which neutrino physicists have dreamt of deploying on such a scale for decades. Neutrinos are notoriously difficult to detect. They stream through matter with a miniscule chance of interacting. And when they do interact, it’s often with one of the least well understood objects in physics, the atomic nucleus, and a spray of particles and excitations emerges from the swirling mess of hadronic matter. To get enough of these ghostly particles to interact with nuclei in the first place, you need a dense target material, however that is a terrible starting point for building a detector sensitive enough to reconstruct these sprays of particles in detail.
Former CERN Director General and Nobel laureate Carlo Rubbia proposed a solution in 1977: neutrinos could interact in tanks of liquid argon, and electric fields could amplify tiny signals caused by the gentle ionization of neighbouring argon atoms by charged particles created in the collision, allowing the “event” to be reconstructed like a three-dimensional photograph, with exquisite resolution which would be unprecedented for a neutrino experiment. Such a “liquid-argon time-projection chamber” was first realized on a large scale by the ICARUS experiment at Gran Sasso, which was built by INFN in Italy, refurbished at CERN, and shipped to Fermilab’s short-baseline neutrino facility in 2017. Each DUNE detector module will be 20 times bigger. Work on these ground-breaking designs has been underway at CERN for several years already in the preparation and testing of two “ProtoDUNE” detectors, which have successfully demonstrated the operational principles of the technology.
For more details, read the full story in CERN Courier magazine.
After more than two years of maintenance and upgrades, the Pixel Tracker has been installed at the centre of the CMS detector and is now ready for commissioning.
Of all the CMS subdetectors, the Pixel Tracker is the closest to the interaction point (IP) – the point of collision between the proton beams. In the core of the detector, it reconstructs the paths of high-energy electrons, muons and electrically charged hadrons, but also the decay of very short-lived particles such as those containing beauty or “b” quarks. Those decays are used, among other things, to study the differences between matter and antimatter.
The Pixel Tracker is composed of concentric layers and rings of 1800 small silicon modules. Each of these modules contains about 66 000 individual pixels, for a total of 120 million pixels. The pixels’ tiny size (100x150 μm2) allows the trajectory of a particle passing through the detector to be precisely measured and its origin determined with a precision of about 10 μm.
Due to its location very close to the IP, the Pixel Tracker suffers a great deal of radiation damage from particle collisions. In the innermost layer, a mere 2.9 cm away from the beam pipe, around 600 million particles pass through one square centimetre of the detector every second. Low temperatures help to protect the Pixel Tracker from this high radiation (it is kept at -20 °C), but some damage still occurs.
To tackle this issue, the subdetector underwent extensive repairs and upgrades in the clean room where it was stored after its extraction from the cavern at the beginning of Long Shutdown 2. Its design was improved and its innermost layer replaced. The pixel detector was then reinstalled at the centre of the CMS detector and is now ready for commissioning.
The final installation was the latest of the many achievements of the CMS Tracker group, one of the largest sub-groups of the CMS collaboration with about 600 people from over 70 institutions in 19 countries.
Relive the event, including footage of the operations and interviews from Lea Caminada, John Conway and Erik Butz, on CERN’s social media channels:
The Super Proton Synchrotron (SPS) lives up to its superlative designation. It’s CERN’s second-largest accelerator and is the last link in the accelerator chain that feeds particle beams to the Large Hadron Collider (LHC). What’s more, it supplies beams to a range of non-LHC experiments that address an impressive array of topics, from precision tests of the Standard Model of particle physics to studies of the quark–gluon plasma, a state of matter believed to have existed shortly after the Big Bang.
Following hot on the heels of the restart of the Proton Synchrotron Booster and the Proton Synchrotron after the second long shutdown of CERN’s accelerator complex, the SPS and its experiments are now also back in action.
The SPS delivers particle beams to all of CERN’s North Area (NA) experiments, to the associated test beam areas, as well as to the AWAKE experiment, which investigates the use of a wakefield created by protons zipping through a plasma to accelerate charged particles, and to the HiRadMat facility, which tests materials and accelerator components in extreme conditions.
The NA experiments are an essential strand of the Laboratory’s experimental programme. NA58/COMPASS studies how quarks and gluons form composite particles such as protons and pions. NA61/SHINE investigates the quark–gluon plasma and takes particle measurements for neutrino and cosmic-ray experiments. NA62 studies rare kaon decays and searches for new heavy neutral leptons. NA63 investigates radiation processes in strong electromagnetic fields. NA64 searches for new particles that could carry a new force between visible matter and dark matter, or that could make up dark matter themselves. Last but not least, NA65, a new experiment that was approved in 2019, will take measurements of tau neutrinos for neutrino experiments and for tests of the Standard Model.
NA62 has just restarted taking data for physics studies, and the remaining experiments will start doing so in the coming weeks and months. Highlights include the start of NA65 in September and the first pilot runs in October for experiments proposed in the Physics Beyond Colliders initiative, such as AMBER (the successor of COMPASS) and NA64m (NA64 running with beams of muons).
“It’s always a thrill to witness the restart of the experiments, as is to see the fresh data that they deliver, not least after the extensive upgrades they have undergone over the past two years,” says Johannes Bernhard, the leader of the Liaison to Experiments section at CERN. “And if the past seasons of data-taking are any indication, there will be plenty of new physics results to digest and to direct future studies.”
The ALICE detector is being steadily reassembled after three years of dismantling, building, testing and reinstallation of the subdetectors. This major LHC experiment received its last new subdetector on Monday, 21 June 2021, when the Fast Interaction Trigger (FIT) was lowered into the Point 2 cavern. The 300-kg disk, together with the three other FIT arrays, will serve as an interaction trigger, online luminometer, initial indicator of the vertex position and forward multiplicity counter. It is now secured next to the central tracking detectors inside the L3 magnet.
This polyvalent subdetector was conceptualised, reviewed and approved by the ALICE Technical Board in early 2013. It is the fruit of an intense R&D effort involving prototype tests at the Proton Synchrotron. Among the 60-plus scientists from 17 institutions who contributed to the FIT design, construction, testing and installation, the Muscovite team at the Russian Institute for Nuclear Research faced major challenges with the design of the new, fully digital, front-end electronics and readout system.
FIT relies on three state-of-the-art detector technologies underpinning components grouped into five arrays surrounding the LHC beamline, at -1, +3, +17, and -19 metres from the interaction point. The diversity of the detection techniques and the scattered positions are needed in order to fulfil the subdetector’s many required functionalities. Among the three components that make up the FIT detector, the FT0 is the fastest: comprising 208 optically separated quartz radiators, its expected time resolution for high-multiplicity heavy-ion collisions is about 7 picoseconds, ranking FIT among the fastest detectors in high-energy physics experiments. This impressively precise timing is crucial for online vertex determination and for identifying charged lepton and hadron species using time-of-flight.
The second component, a segmented scintillator called FV0, innovates with a novel light-collection scheme designed and manufactured at UNAM, Mexico. The largest of the three components, the FV0 makes use of its size to provide optimal acceptance, which is vital for extracting centrality and determining the event plane – key parameters characterising a heavy-ion collision.
Finally, the Forward Diffractive Detector (FDD), consisting of two nearly identical scintillator arrays, can tag photon-induced or diffractive processes by recognising the absence of activity in the forward direction. It also serves as a background monitoring tool.
Now that it is soundly wedged inside the ALICE detector, the FIT is expected to stay there until the end of Run 4. Its installation, which comes after that of the Time Projection Chamber, the Muon Forward Tracker and the Inner Tracking System, brings ALICE one step closer to the end of LS2 activities. The closing of the L3 magnet door and the installation of the final station of the muon spectrometer are scheduled to take place by the end of July and the end of August, respectively. Then a few months of commissioning will take ALICE to the start of Run 3, scheduled for the end of February 2022.
The winners of the 2021 LHCb thesis prize are Tom Boettcher (MIT) and Dmitrii Pereima (Kurchatov Institute, Moscow). Tom’s thesis is on the LHCb GPU high-level trigger and measurements of neutral pion and photon production with the LHCb detector, and he was particularly commended for his contributions to the novel GPU-based first-level trigger of LHCb Upgrade I. Dmitrii’s thesis is on the search for new decays of beauty particles at the LHCb experiment, and he made significant contributions to our understanding of the X(3872) particle and the calibration of the hadronic calorimeter.
Six sets of prizes were awarded to early-career scientists: Scott Ely (Syracuse) was recognised for his leadership in the UT project; Preema Rennee Pais (CERN) was recognised for her contributions to the ST, SciFi and upgrade commissioning; Nicole Skidmore (Manchester) was recognised for her developments of offline software and data preparation; Adam Davis (Manchester) and Benedetto Siddi (INFN, Ferrara) were recognised for their innovative contributions to simulation; and Christoph Hasse (CERN), Arthur Hennequin (CERN), Louis Henry (CERN) and Niklas Nolte (MIT) were recognised for their developments of the software trigger.
Many congratulations to all the winners!
As the two-year-long shutdown of CERN’s accelerators comes to an end, some of the Laboratory’s many experiments are not waiting for the Large Hadron Collider (LHC) to wake up before starting to take data. The Proton Synchrotron (PS), CERN’s 60-year-old particle accelerator, and its injector, the Proton Synchrotron Booster, are back in full roar after a major overhaul. The Booster has begun delivering protons accelerated to 1,4 GeV to the ISOLDE facility (Isotope mass Separator On-Line Detector) and 2 GeV protons to the Proton Synchrotron, which, in turn, feeds its 26 GeV proton beam to the Antiproton Decelerator (AD, the first of the two particle decelerators of the Antimatter Factory). For the many experiments housed in these two world-class facilities, this can only mean one thing – the physics season is about to start, bringing with it the promise of exciting new results in nuclear and antimatter research.
“After optimising the experiment when the first proton beam reached the ISOLDE facility’s target on 21 June, physics data-taking started swiftly and the first experiment finished successfully after five days,” explains Gerda Neyens, Physics Group Leader at the ISOLDE facility. At ISOLDE, collisions between the Booster proton beam and heavy targets produce rare radioactive isotopes of elements from across the periodic table, of which specific ones are selected using a combination of lasers and electric and magnetic fields. This season’s first ISOLDE results came from the CRIS experiment in the form of hyperfine spectra of a series of silver isotopes synthesised within the walls of the facility. The atomic spectra of more than 20 exotic short-lived silver isotopes will reveal how the internal quantum structure, size and shape of the stable 107Ag and 109Ag isotopes change when neutrons are added to or removed from them.
For the upcoming physics season, ISOLDE will relies on new target stations to produce the radioisotopes, as well as an upgraded charge breeder (a device that removes electrons from the heavy isotopes) and a refurbished superconducting linear accelerator to accelerate the produced radioisotopes. The nuclear reactions occurring in the facility, which mimic and help understand those taking place inside stars, can thus be studied with greater precision.
Situated a few dozen metres away from ISOLDE, the Antimatter Factory uses the Proton Synchrotron beams to create its own peculiar substance. This process resumed on 28 June with the return of the beam on the new target: antimatter is being made at CERN again as you read. In this unique factory, antiprotons are synthesised by colliding the proton beams onto a target. The stray particles are then focused back into a beam thanks to a device called a “magnetic horn”, which was completely renovated in recent years, as was the target itself. The new target is an air-cooled piece of iridium placed in a graphite matrix and enclosed in a titanium alloy double shell. It will improve antiproton production, for a reliable and stable antimatter inflow over time.
The data-taking period that now awaits antimatter physicists has been given a boost by new machines such as ELENA (Extra Low Energy Antiproton deceleration ring), a ring that efficiently decelerates the antiprotons to unprecedented levels before feeding them into the experimental area. There, long-standing collaborations like AEGIS, ASACUSA and ALPHA stand next to fresh faces like ALPHA-G and GBAR, an experiment aiming to measure the freefall acceleration of antimatter under gravity. They will soon be joined by the PUMA and BASE-STEP collaborations, which were recently approved by the CERN Research Board. Both of these experiments will rely on the delicate process of transporting antimatter to neighbouring areas of the CERN site to study its properties.
Diversity is a defining characteristic of CERN, and this applies to the Organization’s research programme too. So, although the LHC and its detectors will not start buzzing and whirring for a few more months, there is no shortage of interesting developments: with antimatter and nuclear isotope data-taking and the forthcoming start of the physics season in the East and North experimental areas as well as at n_TOF, the next few months will be hectic ones for physics research.
A 360° virtual tour through the AD target area at CERN - use the arrows to change your perspective
When charged high-energy particles crash past noble-gas molecules, they leave a trail of ionisation in their wake. These tiny signals can be amplified using electric fields, and read out by electronics, revealing particle tracks with beautiful precision. This is the time-honoured concept behind the LHC’s gaseous detectors – an indispensable concept, thanks to its ability to instrument large volumes of a detector in an affordable way.
Unfortunately, environmentally harmful chlorofluorocarbons known as freons also play an essential role, dampening runaway effects to make sure that the amplified signals aren’t swallowed up by electronics noise. Physicists at the LHC are working on consolidating strategies for eliminating the current risks, and are studying novel “eco-gases” for the next generation of detectors. These were the topics of the workshop recently hosted online by CERN. To read more, check out the full report in the CERN Courier magazine.
These now-iconic detectors are critical to a new era of exploration for the ATLAS experiment. In the coming years, a major upgrade to the LHC – known as the High-Luminosity LHC – aims to crank up the collider's luminosity by a factor of ten beyond its design value. This will generate even more collisions, allowing ATLAS physicists to probe phenomena that are even rarer in nature.
A massive upgrade of the ATLAS experiment is underway to prepare for this increased luminosity. The first major system to be upgraded is the muon spectrometer, with the New Small Wheels set to be installed on either end of the experiment in summer and autumn 2021. The wheels use novel small-strip Thin Gap Chambers (sTGC) and Micromegas detectors. These new technologies will give ATLAS much more stringent selection criteria for muons, and better handle high background and pile-up rates – the two main requirements for the High-Luminosity LHC.
The New Small Wheels were built in ATLAS institutes around the world and mounted on the wheels at CERN over the course of several years. Following the installation of the last "wedge" of detectors, the first New Small Wheel is now complete, with just final testing and commissioning pending.
The photos below showcase the logistical complexity behind this milestone. Look forward to watching the installation of this “small” behemoth, set to be broadcast live on CERN and ATLAS channels this summer.
To find out more and view more photos, visit the ATLAS website.