Double crystal channelling was observed for the first time at the LHC, a milestone for future short-lived particle research Geneva, 29th August, 2025, by Insa Meinke, CERN Might two bent crystals pave the way to finding new physics? The Standard Model of particle physics describes our world at its smallest scales exceptionally well. However, it leaves some important questions unanswered, such as the imbalance between matter and antimatter, the existence of dark matter and other mysteries. One method to find “new physics” beyond the Standard Model is to measure the properties of different particles as precisely as possible and then compare measurement with theory. If the two don’t agree, it might hint at new physics and let us slowly piece together a fuller picture of our Universe – like pieces of a jigsaw puzzle. An example of particles that physicists wish to study more closely are “charm baryons” such as the “Lambda-c-plus” (Λc+) which is a heavier “cousin” of the proton, consisting of three quarks: one up, one down and one charm. These particles decay after less than a trillionth of a second (10-13 s), which makes any measurement of their properties a race against time. Some of their properties have not yet been measured to high precision, leaving room for new physics to hide. The particles’ magnetic and electric dipole moments are of particular interest. In the past, precise measurements of dipole moments in other particles have provided key tests of established theories and, sometimes, uncovered surprises that pointed to new physics. A novel experimental concept aims to measure the properties of charm baryons using a fixed target and two bent crystals. Electric and magnetic dipole moments can be measured by forcing particles on a curved trajectory. Since charm baryons decay extremely quickly, however, conventional techniques using magnetic fields are not strong enough to obtain measurable results. An alternative approach could be to exploit the fact that the atoms inside a crystal are neatly organised as a three-dimensional lattice, forming tiny channels when viewed from certain directions. If a bent crystal is placed inside a stream of charged particles, the particles may follow these channels, experiencing deflections otherwise out of reach within such a short distance. Thus, this makes measurements on extremely short-lived particles possible. In the full set-up, one bent silicon crystal is inserted close to the proton beam inside a stream of particles called the “secondary halo” – protons that strayed too far from the beam centre and would normally be absorbed by the LHC collimation system. This first crystal steers the particles away from the main LHC beam towards a tungsten target where the collisions produce charm baryons. A second silicon crystal then bends the path of the produced particles strongly enough that their dipole moments can be precisely measured with a specialised detector. TWOCRYST was conceived as a proof-of-principle experiment, designed to test whether the concept really works in practice – from the performance of the crystals to the precision of their alignment. After only two years of preparation, TWOCRYST was installed in the LHC at the beginning of the year. “The experimental set-up is a simplified version of a full-fledged experiment, consisting of two bent silicon crystals, a target and two 2D detectors (a pixel tracker and a fibre tracker),” explains TWOCRYST study leader Pascal Hermes. “One goal is to verify if the particles can be deflected through both crystals in sequence – the so-called ‘double channelling’.” The first TWOCRYST measurements in June at an energy of 450 GeV showed promising results. All the newly installed hardware is functional and operational and, after both silicon crystals had been carefully aligned, “double-channelled” particles were observed for the first time at the LHC and at the highest energy ever achieved. The team will now complete a set of further tests at higher energies of several TeV. All the measurements will be analysed in detail to determine whether enough deflected charm baryons could be collected to justify a full-scale experiment. Whatever the outcome, TWOCRYST has already opened a new chapter of crystal applications at the LHC. The results from TWOCRYST may well shape the design of future fixed-target experiments and novel beam-control concepts at the LHC and beyond.

CERN, 21st August 2025 Herwig Schopper, Director-General of CERN from 1981 to 1988, passed away on 19 August at the age of 101. An eminent physicist and a visionary diplomat, he played a key role in shaping fundamental physics in Europe and in making CERN the prestigious laboratory we know today. After obtaining a doctorate in optics at the University of Hamburg in 1951, Herwig Schopper turned first to nuclear physics and then to particle physics, working in several European laboratories, including on the weak interaction at the Royal Institute of Technology in Stockholm, Sweden, under Lise Meitner. After becoming a professor at the University of Erlangen, Germany, in 1954, he spent a year’s sabbatical in Cambridge, United Kingdom, and then went on to be appointed as a professor at the University of Mainz, Germany, in 1957. At that time, Germany was rebuilding its fundamental physics infrastructure: the DESY research centre was created in 1959, for example, and was developing its first accelerators. Herwig Schopper played a key role in these trailblazing activities. In 1960, he left for the University of Cornell in the United States, where he carried out physics research at its powerful electron synchrotron. The following year, he became Director of the Nuclear Physics Institute at the University of Karlsruhe. In 1973, he was appointed Director of DESY, a position he held until 1981. Under his leadership, several accelerators were developed and commissioned. Alongside his brilliant career in Germany, he was involved in research at CERN from the 1960s onwards and held several strategic posts as of the 1970s: Leader of the Nuclear Physics division from 1970 to 1971, Chair of the ISR Committee from 1973 to 1976 and member of the Scientific Policy Committee from 1978 to 1980. During his term as CERN Director-General, which began in 1981, his scientific vision and diplomatic skills played a key role in securing the approval of the Large Electron–Positron Collider (LEP) project, and then in completing the construction of this accelerator, the largest ever built. He contributed to CERN’s global expansion and was one of the architects of the international cooperation model for the LEP experiments, which paved the way for today’s large experimental collaborations. His mandate was also marked by the discovery of the W and Z bosons by the UA1 and UA2 experiments at the SPS proton-antiproton collider in 1983, which was recognised by the Nobel Prize in Physics awarded to Carlo Rubbia and Simon van der Meer the following year. In the years that followed his term as CERN Director-General, Herwig Schopper continued to work for science, serving on the scientific councils of several laboratories and presiding over the German Physical Society and later the European Physical Society. One of his greatest achievements was SESAME, the international centre for Synchrotron-Light for Experimental Science and Applications in the Middle East, of which he was a co-founder and the first President of the Council. A tireless ambassador for fundamental science, he maintained a keen interest in the future of his field and continued to lend support to his successors through his vision and vast experience. Until his very last moments, he never ceased to care deeply about CERN and its work. “We have lost a brilliant scientist and one of the greatest contributors to CERN and to our field, who really embodied the core values of our Laboratory. We have also lost a cherished friend, who was admired for his insight, his dedication and his warmth”, said Fabiola Gianotti, CERN Director-General. “He will forever remain in our memories.” Video filmed on the occasion of Herwig Schopper’s 100th birthday in February 2024. (Video: CERN) A full obituary will appear later in the CERN Courier.