For World Environment Day, celebrated by the United Nations on 5 June, CERN reaffirms its commitment to environmentally responsible research. Among numerous actions, CERN has a dedicated strategy to reduce emissions, which targets gas recirculation, gas recovery and exploring the use of alternative gases. Currently, the majority of CERN’s direct greenhouse gas emissions come from its particle detectors, which use a range of gas mixtures for particle detection and detector cooling. These gases are mainly synthetic refrigerants, including fluorinated gases with a particularly high global warming potential.

Since 2017, CERN has been developing a novel approach to detector cooling using carbon dioxide (CO₂). CO₂ has a global warming potential of 1, which is several thousand times lower than the synthetic refrigerants currently used in low-temperature refrigeration systems, making it an excellent alternative. The Engineering department’s Cooling and Ventilation group and the Experimental Physics department’s Detector Technology group, with the support of other teams across CERN and partners in science and industry, are currently renovating the cooling systems of the ATLAS and CMS inner detectors. Surface work is already under way, while underground work will take place during the next long shutdown, LS3, scheduled to begin at the end of 2025. The objective is to achieve a drastic reduction of direct emissions of fluorinated gases, saving the equivalent of 40 000 tonnes of CO₂ each year.

How? Every technical parameter has been optimised to cool CO₂ to -53 °C, close to the temperature where CO₂ becomes solid (-56.6 °C), pushing the performance of the equipment and the standard cooling cycles. Not only will this technology contribute to CERN’s objective of reducing its emissions, but it could also have applications in other low‑temperature industries, notably the food and pharmaceutical industries, furthering CERN’s tradition of knowledge and technology transfer for the benefit of society. Find out more in the new video below.

This is just one of CERN’s initiatives to minimise its impact on the environment in key domains, including energy, water, waste, sustainable land use, noise and emissions. Find out more here.

On 5 July 2022, protons began colliding again in the LHCb detector after a three-and-a-half-year break known as Long Shutdown 2 (LS2), marking the start of the third run of the Large Hadron Collider (LHC). During this period, the original LHCb detector at the LHC was largely dismantled and an almost completely new detector constructed. The 2020 update of the European Strategy for Particle Physics approved by the CERN Council strongly supported exploiting the full potential of the LHC for studying flavour physics. A further upgrade of the LHCb detector, known as Upgrade II, is planned to allow LHCb to operate at a much higher instantaneous luminosity and cope with the demanding data-taking conditions of the High-Luminosity LHC (HL-LHC). The latest technological developments will be taken into account to design the new detectors.

Electromagnetic calorimeter

The new revolutionary electromagnetic calorimeter being developed for LHCb Upgrade II will be able to precisely measure the arrival time of electromagnetic particles. Its test measurements demonstrated detection of high-energy electrons within 20 picoseconds of precision. This is the first time that such excellent performance has been achieved with an electromagnetic calorimeter in particle physics. The new calorimeter will have finer granularity, enabling it to cope with a much higher particle density at higher instantaneous luminosity. Luminosity is an important indicator of the performance of an accelerator: it is proportional to the number of particle collisions that occur in a given amount of time.

The technology for the new LHCb calorimeter modules is based on the “Spaghetti Calorimeter” (SpaCal) concept, in which the scintillators resemble strands of spaghetti. These scintillating fibres are housed in the 5180 longitudinal holes in the SpaCal module. The calorimeter is constructed with modules with two types of absorbers: tungsten-based SpaCal-W modules, which will be built using tungsten 3D-printing technology, and lead-based SpaCal-Pb modules.

The number of particles crossing the detector is extremely high in the central region surrounding the beam pipe, inside which the proton beams of the LHC circulate. The current LHCb calorimeter is composed of Shashlik modules. The performance of these modules decreases over time due to radiation damage caused by the large flux of particles when the LHC is running. During the next Long Shutdown, these degraded Shashlik modules in the very central region around the LHC beampipe will be replaced with 32 SpaCal-W modules, and an additional 144 SpaCal-Pb modules will be placed around them.

Ring-imaging Cherenkov system

In the upgrade of the ring-imaging Cherenkov (RICH) system, the whole electronics chain will be replaced. The detector will be equipped with a high-rate data acquisition system and a novel readout application-specific integrated circuit, called FastRICH, which is capable of providing precise timestamps of Cherenkov photons. These photons are produced when electrically charged particles, such as protons or electrons, travel faster than light in a medium.

The new LHCb RICH will be the first system featuring fast timing capabilities for single photons at the hundred-picosecond level, demonstrating once again how the challenging conditions of a flavour physics experiment at the LHC can lead to technological breakthroughs.

Prototypes of both subdetectors, SpaCal and RICH, have been successfully tested at CERN’s accelerator complex with beams from the Super Proton Synchrotron in preparation for the HL-LHC era.