Antiprotons to test the Standard Model

The PAX (antiProtonic Atom X-ray spectroscopy) experiment is the first to use TELMAX, the new antiproton test beamline at CERN’s antimatter factory. It aims to test the theory describing the interactions between light and charged particles, known as quantum electrodynamics (QED), under conditions of intense electric fields. But why these conditions? “Although QED is well understood for light systems such as hydrogen atoms, it hasn’t yet been explored in detail for highly charged atoms in the presence of strong electric fields," explains the experiment’s spokesperson, Nancy Paul. “This is due to experimental challenges and uncertainties linked to unknown nuclear properties. In fact, the effects of QED are magnified by intense electric fields, and this gives us a better chance of measuring them.”

Adiabatic Demagnetisation Refrigerator (ADR) cryostat for the PAX prototype TES detector, open on the bottom, where one can see the 80 mK cold plate connected to the readout electronics. Insert: The PAX prototype TES detector (2 x 2 x 4 cm), consisting of 64 pixels and integrated microwave multiplexed readout electronics. For the experiment, this detector is mounted on the end of the cold-finger in the ADR cryostat. (Image: PAX/NIST Quantum Sensors Division).

The PAX experiment is being conducted by a team from France’s Centre national de la recherche scientifique (CNRS) and is funded by the European Research Council (ERC). It is employing a novel approach, namely very high-precision spectroscopy of the X-rays emitted by antiprotonic atoms, i.e. atoms that contain an antiproton orbiting around the nucleus. By studying the transitions between the various states of these atoms, the team will obtain more accurate results than through other approaches. Two novel technologies are being harnessed in tandem to achieve this: the low-intensity antiproton beams delivered by TELMAX and a quantum-sensing X-ray detector.

To create antiprotonic atoms – atoms in which an electron is replaced by an antiproton – TELMAX's antiproton beam is directed at a solid target (made of zirconium, silicon or gold) or a gas target (neon, argon, krypton or xenon), depending on the case. “These antiprotonic atoms generate Coulomb fields that are much more powerful than those generated by 'conventional' atoms; this is what magnifies the effects of QED,” Nancy Paul explains. By studying QED under these special conditions, the collaboration hopes to detect minuscule deviations from the predictions, which could point to unknown phenomena. “The Standard Model of particle physics is incomplete, and precision measurements in quantum systems are crucial to deepening our knowledge of QED and possibly discovering new physics”, notes Nancy Paul.

The brand new quantum-sensing X-ray detector used by PAX also improves sensitivity beyond what was previously available with traditional approaches. “For our experiment, we are using a new microcalorimeter X-ray detector based on Transition Edge Sensors (TES). This kind of detector offers energy precision that is 50 to 100 times better than semi-conductor detectors – with attainable accuracies of 1 eV on 100 keV X-rays”, she adds. The detector was built by a team from the Quantum Sensors Division of the US National Institute of Standards and Technology (NIST). The same types of detectors are used in areas such as X-ray astronomy on satellites, in the ATHENA project, for example. PAX is the first application of this novel technology for antimatter.

anschaef Thu, 06/05/2025 - 13:44 Byline Anaïs Schaeffer Publication Date Fri, 06/06/2025 - 08:34

Alasdair Smith (1942–2025) (Image: Christiane Smith-Duplan)

Alasdair Smith passed away in March at the age of 82. After receiving a PhD in physics from the University of Glasgow in 1970, Alasdair began a long career at CERN, working on experiments at the ISR, then on OPAL at LEP and, finally, on LHCb at the LHC.

At the ISR, Alasdair worked on three experiments: R103, R105 and R108, contributing to the construction and set-up of the detectors and associated electronics. In particular, he took part in the design and construction of the cylindrical drift chambers located inside the superconducting solenoidal magnet of the R108 detector.

After the closure of the ISR, Alasdair moved on to LEP, where he was the OPAL liaison officer in the CERN Experimental Support group. Alasdair played an instrumental role in the OPAL experiment throughout its existence. As OPAL’s Technical Coordinator, he piloted the technical project from before any hardware existed right through to when the last piece left LEP Point 6 for disposal. In many ways, he pioneered the concept of what the technical coordinator of a large experiment should do.

Alasdair was competent, efficient, always available to give advice and seemingly never nervous, constantly reassuring and minimising stress for everyone. He remained on top of all the details while still creating an atmosphere of mutual trust: delegating responsibility to team members and supporting all the subsystem technical communities, as well as those involved in detector operations.

Finally, in October 2001, Alasdair joined the LHCb experiment, where he remained until his retirement in December 2007. He joined the collaboration’s management as Resource Coordinator, taking over from Hans-Jurgen Hilke, who had been both Resource Coordinator and Technical Coordinator simultaneously. Alasdair joined at a very timely moment for LHCb, as the experiment entered a phase where the work of Technical Coordinator was rapidly increasing. Alasdair was a fantastic Resource Coordinator, keeping everybody in the collaboration on their toes while not being bureaucratic. He also ensured good relations with the funding agencies, which trusted him. Given the size of the LHCb collaboration at that time – comparable to that of a LEP experiment – his approach was a perfect match.

Alasdair also took advantage of opportunities to relax, bringing his Scottish traditions to CERN. For example, he and two fellow bagpipers symbolically piped the OPAL detector into the LEP Point 6 cavern.

Alasdair will be sorely missed by those who worked with him, as well as by those who had only occasional contact with him. Much sympathy goes to his wife, Christiane, and to all of his relatives.

His colleagues and friends

 

ndinmore Wed, 04/30/2025 - 10:20 Publication Date Wed, 04/30/2025 - 10:19

AEgIS transforms smartphone sensors into an antimatter camera of unprecedented resolution

Did you know that the camera sensor in your smartphone could help unlock the secrets of antimatter? The AEgIS collaboration, led by Professor Christoph Hugenschmidt’s team from the research neutron source FRM II at the Technical University of Munich (TUM), has developed a detector using modified mobile camera sensors to image in real time the points where antimatter annihilates with matter. This new device, described in a paper just published in Science Advances, can pinpoint antiproton annihilations with a resolution of about 0.6 micrometres, a 35-fold improvement over previous real-time methods.

AEgIS and other experiments at CERN’s Antimatter Factory, such as ALPHA and GBAR, are on a mission to measure the free-fall of antihydrogen within Earth’s gravitational field with high precision, each using a different technique. AEgIS’s approach involves producing a horizontal beam of antihydrogen and measuring its vertical displacement using a device called a moiré deflectometer that reveals tiny deviations in motion and a detector that records the antihydrogen annihilation points.

“For AEgIS to work, we need a detector with incredibly high spatial resolution, and mobile camera sensors have pixels smaller than 1 micrometre,” says Francesco Guatieri, the principal investigator on the paper. “We’ve integrated 60 camera sensors into our detector, enabling it to achieve a resolution of 3840 mega pixels – the highest pixel count of any imaging detector to date.”

"Previously, photographic plates were the only option, but they lacked real-time capabilities,” added Guatieri. “Our solution, demonstrated for antiprotons and directly applicable to antihydrogen, combines photographic-plate-level resolution, real-time diagnostics, self-calibration and a good particle collection surface, all in one device.”

The researchers used commercial optical image sensors that had previously been shown to be capable of imaging low-energy positrons in real time with unprecedented resolution. “We had to strip away the first layers of the sensors, which are made to deal with the advanced integrated electronics of mobile phones,” says Guatieri. “This required high-level electronic design and micro-engineering.”

A key factor in achieving the record resolution was an unexpected element: crowdsourcing. “We found that human intuition currently outperforms automated methods,” says Guatieri. The AEgIS team asked their colleagues to manually determine the position of the antiproton annihilation points in each of the more than 2500 detector images, a procedure that turned out to be far more accurate and precise than any algorithm. The only downside: it took up to 10 hours for each colleague to plough through every annihilation event.

“The extraordinary resolution also enables us to distinguish between different annihilation fragments,” says AEgIS spokesperson Ruggero Caravita. By measuring the width of tracks of different annihilation products, the researchers can investigate whether the tracks are produced by protons or pions.

“The new detector paves the way for new research on low-energy antiparticle annihilation, and is a game-changing technology for the observation of the tiny shifts in antihydrogen caused by gravity,” says Caravita.

Read more:

Paper: Real-time antiproton annihilation vertexing with sub-micron resolution

anschaef Wed, 04/02/2025 - 13:23 Byline Alex Epshtein Publication Date Wed, 04/02/2025 - 16:22