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Michele Parrinello Award honours innovation in computational physical science

In honour of Italian physicist professor Michele Parrinello, open-access publisher MDPI has launched the Michele Parrinello Award – a biennial award recognising senior academics in computational physical science. As the deadline for 2026 nominations approaches, we reflect on professor Parrinello’s remarkable career and enduring legacy.

Professor Michele Parrinello

Interview with Prof. Michele Parrinello: Pioneer in Computational Science

Known for his innovative approach to computational science, professor Parrinello’s role in the development of the Car–Parrinello method (with Roberto Car) remains one of his most influential contributions to molecular dynamics. He is similarly celebrated for his role in co-developing the Parrinello–Rahman method, alongside his recent work in metadynamics.

Testament to his global influence, professor Parrinello has received several accolades, such as the Rahman Prize, the Dirac Medal and the Erwin Schrödinger Institute for Mathematics and Physics Medal. He is also a member of several academies and learned societies, including the German Berlin-Brandenburgische Akademie der Wissenschaften, the British Royal Society and the Italian Accademia Nazionale dei Lincei.

Reflecting on his advice to young researchers, professor Parrinello says that they should not fear new ideas. He has observed that many early-career scientists hesitate to go against the mainstream, often worrying about potential consequences. Instead, he encourages them to remain confident in the value and meaning of their work, and to avoid being overly influenced by the opinions of others.

Through the Michele Parrinello Award, it is hoped that professor Parrinello’s remarkable legacy will inspire future generations to pursue excellence in their fields.

The full interview with professor Parrinello is available online.

The Michele Parrinello Award

Michele Parrinello’s work has been characterised by its interdisciplinary impact. Accordingly, the award welcomes nominees from a range of related fields, including physics, chemistry and materials science.

Nominations will close on 31 March 2026, with the winner announced on 31 July 2026. The awardee will receive a monetary prize of EUR 50,000, alongside a commemorative medal and a certificate.

For more information about the nomination process, visit the award homepage.

2025 Award Committee

Interview with Prof. Xin-Gao Gong: Chair of the Michele Parrinello Award Committee

The Michele Parrinello Award Committee is chaired by professor Xin-Gao Gong. Professor Gong studied with professor Parrinello in Italy during his early career. As an academician of the Chinese Academy of Sciences and a professor at Fudan University in China, he focuses his research on computational physical sciences and condensed-matter physics.

Much like how professor Parrinello inspired his early career, professor Gong hopes that “The Michele Parrinello Award will recognise scientists who have made significant contributions to the field of computational condensed-matter physics and at the same time set a benchmark for the younger generation, providing clear direction for their pursuit.”

Watch the full interview with professor Xin-Gao Gong online.

MDPI champions outstanding research

Recognising the exceptional work of academics lies at the heart of MDPI’s mission to foster open scientific exchange, and is reflected in its extensive awards programme.

The MDPI Sustainability Foundation furthers this mission through its commitment to advancing sustainable development, advocating for scientific progress and global collaboration.

Alongside the Michele Parrinello Award, the foundation oversees the World Sustainability Award, the Emerging Sustainability Leader Award and the Tu Youyou Award.

The most elusive higgsinos

ATLAS figure 1 — **Fig. 1.** Observed and expected limits at 95% CL for 1ℓ1T (purple) and displaced track (red) searches are shown in the chargino-neutralino mass difference versus chargino mass plane, along with previous limits from the LEP2 (grey) and ATLAS (blue, light green and orange) experiments. Credit: ATLAS Collab., adapted from arXiv:2511.20042

Supersymmetry has so far eluded discovery at the LHC, yet it retains strong theoretical appeal as an extension of the Standard Model (SM), and potential hiding places remain. In two recent analyses, the ATLAS collaboration sets new bounds on compressed higgsino models, where the proposed particles lie very close in mass. The collaboration used machine-learning techniques to target some of the most elusive signatures at the LHC: low-momentum decay products.

Without extreme fine tuning, quantum corrections would drive the Higgs-boson mass far above the electroweak scale. Supersymmetry prevents this by introducing fermion partners for the SM bosons (and vice versa) so that their quantum contributions naturally cancel. The result is a partner for every SM particle – including higgsinos, the fermionic counterparts of the Higgs field. Higgsinos mix with the partners of the electroweak gauge bosons to form electrically neutral and charged states known as neutralinos (χ̃⁰) and charginos (χ̃^±). The lightest neutralino (χ̃⁰₁) is stable in a wide class of models and may naturally account for the observed dark-matter abundance.

In compressed scenarios, the tiny mass-splitting between these new particles poses a distinct experimental challenge. When a heavier state decays to χ̃⁰₁, the small mass difference leaves little energy for the accompanying SM particles. The visible decay products therefore carry very low momentum and may fall below reconstruction and identification thresholds. The new analyses focus precisely on this regime using the full Run 2 dataset collected at √s = 13 TeV, with two complementary strategies optimised for different values of the mass splitting.

Firstly, a “displaced track” search targets scenarios with a mass difference between the lightest chargino χ̃^±₁ and χ̃⁰₁ of 0.3 to 1 GeV, in which the χ̃^±₁ has a non-negligible lifetime and can travel a few millimetres before decaying into an invisible χ̃⁰₁ and a low-momentum charged pion. The resulting event signature is a pion track with a large transverse impact parameter and high missing transverse momentum from the neutralinos. Significant improvement in signal sensitivity is achieved by the use of two dedicated neural networks (NNs), where one exploits the global event kinematics and the other focuses on the displaced track characteristics.

A “one-lepton-one-track (1ℓ1T)” search instead targets scenarios with a larger mass splitting of 1 to 3 GeV, in which the heavier neutralino χ̃⁰₂ promptly decays into the χ̃⁰₁ and two low-momentum leptons. Since these could elude the existing ATLAS identification techniques, dedicated low-momentum electron and muon identification algorithms have been developed using NNs that exploit track and calorimeter information. The new algorithms are applied to leptons with momentum as low as 0.5 GeV for electrons and 1 GeV for muons, below the standard reconstruction thresholds, resulting in a signature consisting of one lepton and one lepton-like track. An additional NN enhances sensitivity for event classification, exploiting kinematic features that depend strongly on the mass splitting.

The observed data are consistent with the SM predictions, with no signs of new physics emerging in the targeted phase-space. Based on this result, lower limits on the higgsino masses are set at 95% confidence level (CL) (see figure 1). The 1ℓ1T search excludes a mass-splitting region between 0.8 and 2.0 GeV, extending previous limits from the LEP experiments up to a maximum χ̃^±₁ mass of 132 GeV for a 1.8 GeV mass splitting. The displaced track search extends the exclusion limits previously set by the ATLAS experiment by about 30 GeV, reaching a χ̃^±₁ mass of 199 GeV for a 0.6 GeV mass splitting. Together, the two searches exclude χ̃^±₁ masses below 126 GeV at 95% CL over the targeted mass splitting range. Limits set by the ATLAS collaboration now supersede those from the LEP experiments in all mass-splitting ranges.

With this result, ATLAS is now able to set limits over the full range of higgsino mass splittings that are interesting for naturalness, marking a significant milestone in the search for supersymmetry. The new Run 3 dataset, along with advanced analysis techniques, will push these searches even further – perhaps towards the discovery of physics beyond the SM.

ICABU fishes for accelerator innovations in Pohang

The 27th International Conference on Accelerators and Beam Utilizations (ICABU2025) attracted 300 experts to Pohang, South Korea, from 12 to 14 November 2025. Once a small fishing village, Pohang has developed into a major research hub and now hosts more than 22 R&D institutions. These include Pohang University of Science and Technology (POSTECH), the Pohang Accelerator Laboratory – home to the 3 GeV PLS-II synchrotron radiation source and PAL-XFEL hard X-ray free-electron laser – and the Asia-Pacific Center for Theoretical Physics. ICABU itself began in 1997 as the International Proton Accelerator Workshop, hosted by the Korea Atomic Energy Research Institute. Since 2009, it has grown into an international conference.

Particle beams are becoming increasingly important to materials engineering. Yunseok Kim (Sungkyunkwan University) discussed how helium-ion irradiation can be used to manipulate hafnium oxide, a material widely employed as an insulating layer in modern microelectronics. In very thin films, hafnium oxide can sustain a switchable electric polarisation that allows information to be stored, known as ferroelectricity. Yet, this state is normally fragile. Kim showed that controlled irradiation with low-energy helium ions can introduce and rearrange atomic-scale defects in the crystal lattice, stabilising the polarised state.

The meeting also addressed applications in nuclear medicine. A team from the Institute for Rare Isotope Science (IRIS) reported progress towards a domestic production route for the therapeutic alpha-emitter actinium-225, based on irradiation of thorium-232 targets with 50–70 MeV protons. Actinium-225 is both expensive and scarce, with current clinical use relying heavily on imports. Even an initial domestic supply would improve clinical availability and support the wider adoption of targeted alpha therapies.

Alongside applications, there was also a focus on progress in accelerator hardware itself

Alongside applications, contributions also focused on progress in accelerator hardware itself. Garam Hahn (PAL) and collaborators reported on a compact 5 T magnet system based on high-temperature superconductors (see p30). Operating without liquid cryogens, it is designed to shift the wavelength of synchrotron radiation, since stronger magnetic fields force tighter beam curvature and raise the characteristic photon energy. The system drew substantial attention from the accelerator-technology community, as it has the potential to increase high-energy photon brilliance by many orders of magnitude.

Beyond technical developments, ICABU2025 also addressed the evolving policy landscape for large-scale research infrastructure. In South Korea, the Korea Large Accelerator Act was recently established to manage, support and govern large accelerator facilities. Dongsoo Jang, deputy director of the Ministry of Science and ICT (MSIT), outlined strategies aimed at improving coordination, access and long-term planning across the country’s accelerator infrastructure.

Next year, the event will be hosted by the Korea Multi-purpose Accelerator Complex (KOMAC) and held in Gyeongju. Often described as a “museum without walls,” Gyeongju is one of Korea’s most historic cities and a symbol of cultural diplomacy, aligning well with the spirit of ICABU.

Suppression grows with system size

CMS figure 1 — **Fig. 1.** Charged-particle nuclear modification factor R_AA in oxygen–oxygen, neon–neon, xenon–xenon and lead–lead collisions at the LHC. R_AA is shown as a function of the cube root of the nucleon number A, which is proportional to the nuclear radius. Credit: CMS Collab. 2026 arXiv:2602.21325

When atomic nuclei collide at the LHC, they produce tiny droplets of quark–gluon plasma (QGP) and energetic partons plough through it, slowing down in the process. In a new analysis, the CMS collaboration compared high transverse momentum (p_T) particle yields in oxygen–oxygen, neon–neon, xenon–xenon and lead–lead collisions, with the nucleon numbers of the colliding particles increasing in the sequence 16 < 20 < 129 < 208. The results suggest a steady growth of parton energy loss with the size of the colliding system.

High-p_T particles come from the fragmentation of quarks and gluons produced in the earliest hard scatterings of a collision. As these partons cross the QGP, they interact with the medium and radiate, losing energy in the process. This is one of the clearest signatures of QGP formation. How much energy partons lose depends on how far they travel inside the medium, which in turn grows with the size of the colliding nuclei. Although firmly established in xenon–xenon and lead–lead collisions, the precise way this quenching depends on the path length is not yet fully understood.

Light-ion collisions provide a controlled way to vary the system size and isolate this path-length dependence. In July 2025, the LHC delivered its first ever oxygen–oxygen and neon–neon collisions (CERN Courier November/December 2025 p8). The CMS collaboration analysed the data from this dedicated one-week run to perform a systematic study of high-p_Tcharged-particle suppression across multiple collision systems.

The analysis combines existing measurements in oxygen–oxygen, xenon–xenon and lead–lead collisions with the first measurement of the charged-particle nuclear modification factor, R_AA, in neon–neon collisions at a centre-of-mass energy of 5.36 TeV per nucleon pair. The observable R_AA quantifies how particle yields deviate from expectations based on proton–proton collisions. The four systems were analysed using identical p_T-intervals, enabling a consistent comparison across systems.

The results should help inform the choice of ion species

For smaller nuclei, such as oxygen and neon, many experimental uncertainties shared with the proton–proton reference largely cancel, for example, those related to tracking. This leads to particularly precise measurements of R_AA across a wide p_T range, which is difficult to achieve in larger systems. Combined with the wide span of nuclear sizes, this precision enables a more direct assessment of how parton energy loss depends on in-medium path length.

For a fixed transverse momentum interval, the suppression increases smoothly with system size, from light to heavy ion collisions (see figure 1). Conversely, for a given nuclear system, the suppression is stronger at lower transverse momenta and progressively weakens as it increases. Expressed in terms of the cube root of the nucleon number, which is proportional to the nuclear radius, the results follow a simple ordering with the size of the system, offering a natural framework to test the evolution of energy loss with system size.

The data indicate that nuclear suppression develops gradually as the nuclear system grows, consistent with a picture in which partons interact with QGP droplets whose extent and density evolve smoothly across collision systems. Calculations that omit energy loss show little variation with system size and do not describe the observed suppression, whereas models that include it qualitatively reproduce the observed trend within uncertainties. The data, presented this way, offer a guide for further improvements on their A-dependence.

This study places new quantitative constraints on parton-energy-loss mechanisms and on the emergence of QGP-like behaviour in small nuclear systems. The results should help guide future theoretical developments and inform the choice of ion species in upcoming heavy-ion studies at the LHC.

Quarkonium experts regroup at CERN

**Internal structure** The 17th Quarkonium Working Group attracted more than 200 researchers to CERN. Credit: N Brambilla

Quarkonium physics dates back to the November Revolution of 1974 and the discovery of the J/ψ, a bound state of a charm quark and its antiquark; this was soon followed by the excited ψ(2S) state and its bottom–antibottom analogue ϒ(1S) (CERN Courier September/October 2025 p35). These non-relativistic systems hold a unique place in QCD, encompassing a precise hierarchy of characteristic energy scales. Some, such as heavy-quark masses, are amenable to perturbative treatment, while others, such as the confinement scale, are inherently non-perturbative. To capture this interplay systematically, effective field theories such as non-relativistic quantum chromodynamics (NRQCD) were developed from the 1990s onwards.

The quest to interpret quarkonium phenomena within this unified framework, combined with an explosion of experimental results from B factories and hadron colliders, sparked the creation of the Quarkonium Working Group (QWG) Workshop in 2002. Now organised roughly every 18 months at research institutions around the world, the workshop has become a regular meeting point for the quarkonium community. The 17th QWG brought together more than 200 researchers at CERN from 17 to 21 November.

Renaissance

The first part of the workshop naturally reflected this historical and conceptual foundation, focusing on spectroscopy and decays. In recent years, quarkonium spectroscopy has become a driver of new discoveries in QCD. A prime example is the so-called charmonium renaissance, marked by the observation of several exotic states – including the χ_c1(3872), T_cc+(3875) and charged Z_c states. These “XYZ” states can’t be interpreted as conventional charmonia and their internal structure remains under active investigation both at the experimental and theoretical levels (CERN Courier November/December 2024 p33).

Experimental talks in the opening sessions reported on searches for exotic hadrons and their decay channels. Dmytro Meleshko (Giessen University) from the Belle II collaboration reported on excited bottomonium states, placing particular emphasis on the ongoing analysis of the ϒ(10753) resonance, and the experimental signatures that can distinguish between a tetraquark, a hybrid and a S–D mixed bottomonium state. Ilya Segal (Bochum University) presented recent results by the LHCb collaboration on the radiative decay χ_c1(3872) → ψ(2S)γ. Yue Xu (University of Washington) illustrated an analysis for fully-charmed tetraquarks in the J/ψ–ψ(2S) channel by the ATLAS collaboration, confirming the X(6900) resonance with high significance.

On the theory side, Abhishek Mohapatra (TUM) described ongoing efforts to extend effective-field-theory methods originally developed for quarkonium to more complex exotic systems using the Born–Oppenheimer (BOEFT) approach, which takes lattice QCD inputs to address the QCD non-perturbative dynamics without assuming a specific internal structure for the exotic states.

The third day turned to production. Some NRQCD calculations predict negative production rates for J/ψ and χ_c mesons at high transverse momentum, a clearly unphysical result. Hee Sok Chung (Gangneung-Wonju National University) highlighted how this problem can be addressed by improving the formal treatment of emissions near the production threshold. New production measurements for J/ψ and ψ(2S) from the CMS and ALICE collaborations were presented, alongside new calculations for the production of the χ_c1(3872) and of the pentaquarks P_cc(4312) and P_cc(4457).

The field’s rapid evolution makes the time ripe for a third, comprehensive QWG document

The programme then broadened to Standard Model applications, where quarkonium observables can constrain fundamental QCD parameters such as the strong coupling constant and gluelump masses – the gluonic mass contribution in quarkonium hybrid states, as obtained from lattice QCD. Laurids Jeppe (DESY) from the CMS collaboration discussed the enhancement observed around the top–antitop threshold in the invariant mass spectrum, first measured by CMS and later confirmed by ATLAS (CERN Courier September/October 2025 p9). In a round-table discussion, participants debated the signal’s interpretation in terms of a quasi-bound top–antitop meson or a possible new-physics origin, with both scenarios allowed by the current level of experimental precision, and with the main uncertainties coming from the background modelling. The workshop closed with sessions on quarkonium in media, featuring recent progress in calculating quarkonium transport coefficients from both lattice QCD and perturbation theory.

Progress and puzzles

The discussions across previous QWG workshops crystallised into two foundational documents named “Heavy quarkonium physics” and “Heavy quarkonium: progress, puzzles, and opportunities”, that have since trained generations of young physicists and stand as key references for the community. The field’s rapid evolution makes the time ripe for a third, comprehensive QWG document to capture the wide range of new and enduring topics that currently define it, including the BOEFT framework as a tool to achieve a unified description of all XYZ exotic states, studies of non-equilibrium quarkonium evolution in the QCD medium, informed by new data from the CBM experiment, and the recent development of new automated event generators for quarkonium production.

The next workshop will take place in spring 2027.

Photon detectors light up Bologna

The 7th international workshop on new Photon-Detectors (PD2025) took place from 3 to 5 December 2025 at Bologna’s Palazzo d’Accursio, attracting more than 150 researchers working on the development and application of photon-detection technologies. The medieval city-hall library, with its transparent floor above archaeological remains spanning more than two millennia, provided a striking setting for three days of discussion on state-of-the-art detector technologies.

Photon detectors lie at the heart of modern experimental physics. Their ability to measure extremely faint light signals, down to the single photons, makes them indispensable in areas ranging from high-energy and nuclear physics to astroparticle physics, astronomy, medical imaging and emerging quantum technologies. In recent years, rapid progress in devices such as silicon photomultipliers (SiPMs), avalanche photodiodes (APDs) and microchannel-plate (MCP-PMT) detectors has delivered improvements in timing resolution, radiation tolerance and large-scale integration. PD2025 provided a timely snapshot of this evolving field, combining technology-driven discussions with reports from experiments already exploiting these advances.

A significant fraction of the invited talks focused on the latest developments in SiPM technology, which has become the workhorse photodetector for many contemporary experiments. Alberto Gola (FBK) and Edoardo Charbon (EPFL) highlighted progress in custom SiPM and digital SPAD devices, respectively, stressing their improvements in photon-detection efficiency and sub-100 ps timing performance, as well as ongoing efforts to mitigate correlated noise and radiation-induced degradation. These technological developments were complemented by reports from large-scale experiments – such as ALICE3, CMS, DARKSIDE, DUNE, ePIC and JUNO-TAO – in high-energy and astroparticle physics, outlining the status of ongoing developments and the anticipated role of SiPM-based systems in large-area calorimetry, precision timing and Cherenkov imaging in future detectors.

Equally prominent were contributions on vacuum photodetectors and on enabling technologies. Albert Lehmann (University of Erlangen-Nürnberg) reviewed the status and future prospects of microchannel-plate photomultiplier tubes (MCP-PMT), while Angelo Rivetti (INFN Torino) addressed the challenges of fast, low-power front-end electronics capable of handling the ever-increasing channel counts of modern detectors. Modelling of photon-detection devices was discussed by Werner Riegler (CERN), who introduced an analytic description of timing and efficiency in SPADs and SiPMs, clarifying their performance limits for single-photon and charged-particle detection.

Several contributions underlined the increasingly close relationship between academia and industry in photon-detector development, touching on technology transfer, production scalability and long-term reliability, issues that are becoming central as detectors transition from small-scale prototypes to systems comprising hundreds of thousands, or even millions, of channels, such as in the case of the use of digital SiPMs for physics experiments.

The next edition of the conference will take place in May 2027 in Beijing.

The top turns thirty

The 18th International Workshop on Top Quark Physics (TOP2025) brought the top-quark community to Seoul, South Korea, from 21 to 26 September 2025. Hosted at Hanyang University, the event offered 135 experimentalists and theorists a chance to exchange results, discuss open questions and explore the future of top-quark physics.

2025 marked the 30th anniversary of the top quark’s discovery by the DØ and CDF experiments at Fermilab. Three decades on, and despite ever-increasing experimental precision, the top quark’s properties remain only partially understood. While its mass is now known at the sub-GeV level and its production cross sections agree well with Standard Model predictions, questions persist about its electroweak couplings, its interactions with the Higgs boson, and the detailed structure of top–antitop production at high energies. Because of its large mass and correspondingly strong coupling to the electroweak sector, many in the community continue to view the top quark as a sensitive probe of physics beyond the Standard Model.

The conference opened with an inspiring keynote address by Juan Antonio Aguilar Saavedra (IFT Madrid), who explored the connections between top-quark physics and quantum science and technology. A notable example is the recent observation of quantum entanglement in top-quark pair production by the ATLAS and CMS experiments, which has opened a promising new line of research linking collider physics with concepts more familiar to quantum information researchers. Entanglement can be measured in the top–antitop system because top quarks decay before hadronisation takes place, allowing direct access to their spin correlations.

Top physics is currently enjoying a golden era. Last year, the CMS collaboration reported an excess near the top–antitop threshold (CERN Courier May/June 2025 p7), later confirmed by ATLAS with a significance of 7.7σ above the background predicted by perturbative quantum chromodynamics (CERN Courier September/October 2025 p9). This excess is consistent with expectations from non-relativistic quantum chromodynamics, an effective theory that describes the dynamics of heavy quark pairs near threshold and with simplified models involving a pseudoscalar “quasi-bound-state”, called toponium.

During a mini-workshop dedicated to toponium, Benjamin Fuks (LPTHE) presented an intriguing scenario in which the excess could be explained by two contributions: one from a top–antitop bound state and another from a beyond-the-Standard-Model signature, although the data are also compatible with Standard-Model-only components.

The next edition of the TOP conference will take place in Antalya, Turkey, from 5 to 9 October 2026.

Charm and beauty alike in fragmentation

LHCb figure 1 — **Fig. 1.** Distribution of the longitudinal momentum fraction z of charged hadrons in light- (green/orange), charm- (blue) and beauty-quark-initiated (purple) jets. The lower panels show the ratios of beauty to light (purple) and charm to light (blue). Heavy-quark jets appear suppressed at high z. Credit: LHCb Collab. 2025 arXiv:2511.10216

Proton–proton collisions at the LHC fling quarks and gluons out at massive energies. As they radiate and split into ever more partons, the strong force confines them into sprays of hadrons called jets. The total momentum of a jet, split among its components, approximates that of the initial quark or gluon, which cannot be accessed directly. By tracking how much of a jet’s momentum each hadron carries, the LHCb collaboration has now compared how charm, beauty and light quarks hadronise.

While the production and radiation of individual quarks and gluons can be treated perturbatively, their conversion into hadrons occurs in the non-perturbative regime and cannot be calculated from first principles. Instead, the transition is described using phenomenological probability distributions, called fragmentation functions, which encode how a quark of a given flavour produces specific hadrons. Measuring the content and structure of jets, as well as their kinematic properties, can help constrain these functions.

Previously, the LHCb collaboration measured observables sensitive to fragmentation functions in samples dominated by light-quark-initiated jets. The same measurements were recently carried out for charm- and beauty-quark-initiated jets, allowing a direct comparison of hadronisation across three different jet flavour categories at a single experiment. The light-quark sample was obtained by selecting jets produced nearly back-to-back with a Z boson. In such events, the single parton initiating the jet is typically a gluon or a light quark. In the forward kinematic region accessible to the LHCb detector, where one incoming parton often carries a large fraction of the proton momentum, the proportion of light-quark jets gets further enhanced. Samples of predominantly charm- and beauty-quark-initiated jets were instead obtained using a dedicated flavour-tagging algorithm, which makes use of LHCb’s excellent performance at heavy flavour identification and reconstruction.

The new measurements allow a direct comparison of hadronisation across three different jet flavour categories

A key observable for constraining fragmentation functions is the longitudinal momentum fraction z, defined as the share of jet momentum carried by a hadron along its axis. With respect to their light-quark analogues, heavy-quark-initiated jets appear suppressed at high z, consistent with the leading heavy-flavour hadron carrying most of the jet momentum (see figure 1).

Previous measurements of the hadronisation of a heavy quark into a single heavy-flavour hadron showed that this hadron carries most of the parent quark’s momentum. The new LHCb analysis extends this picture to the full multi-hadron structure of heavy-quark-initiated jets and is consistent with single-hadron measurements: relatively few charged hadrons possess a large fraction of the jet momentum – a result compatible with the heavy-flavour hadron carrying most of it. This result demonstrates the complementarity of single- and multi-hadron measurements, which are both necessary to fully understand high-energy hadronisation.

The analysis also measured the transverse momentum of the hadron with respect to the jet axis, which is sensitive to transverse-momentum-dependent fragmentation functions. Experimental constraints on these functions remain limited, yet they are crucial in reconstructing a three-dimensional description of hadronisation.

Space radiobiology

Astronauts are exposed to elevated levels of cosmic radiation during spaceflight. As missions become longer and venture farther from Earth, understanding how this radiation affects the human body has become a pressing scientific challenge. This emerging field of space radiobiology has strong and perhaps unexpected links to the far better established discipline of radiobiology in medical physics, where physicists work closely with clinicians to design and optimise cancer treatments using ionising radiation. In both contexts, the central question is the same: how does radiation interact with living cells, and how can its harmful effects be predicted, mitigated and controlled?

Space Radiobiology is authored by Alessandro Bartoloni (INFN Roma) and Lidia Strigari (University Hospital of Bologna), whose combined expertise spans astroparticle physics, radiation transport and clinical radiobiology. The book explores a meeting point between two fields that have long followed separate paths but are now clearly converging around shared questions in radiation science.

At its core, the book argues for a closer integration of astroparticle physics and medical physics, demonstrating how both fields benefit from a common radiobiology perspective and a shared concern for radiation protection. At the heart of the volume is a thorough and well balanced discussion of space radiation and its implications for human spaceflight. The authors guide the reader through the complexity of the space-radiation environment – galactic cosmic rays, solar-particle events and their interactions – without losing clarity. These elements are consistently linked to real concerns for astronaut health, both for short missions and for the long-duration journeys that are becoming increasingly realistic. By connecting radiation sources, transport mechanisms and biological effects, the book builds a clear picture of where the risks lie and how they might be managed, making it especially relevant at a time when deep-space missions are moving from concept to planning.

What makes the book particularly engaging is that it never treats space research as an isolated niche. Instead, it repeatedly shows how ideas and tools developed for space can feed back into medical physics. From dosimetry and radiation monitoring to risk assessment, the authors highlight how methods refined for astroparticle experiments can be applied in clinical and research settings on Earth. Advances in detectors, modelling and data analysis developed for space missions are presented not as abstract achievements, but as practical contributions that can improve radiation therapy and diagnostic imaging.

From space to the hospital

This interdisciplinary spirit comes through especially well in the case study of the Alpha Magnetic Spectrometer group at INFN Roma Sapienza. Operating aboard the International Space Station, AMS was designed to study cosmic rays and search for signs of dark matter and antimatter. The book shows, however, that its high-precision measurements of charged-particle spectra, particle composition and energy deposition in low-Earth orbit have direct relevance for space radiobiology and radiation-protection research. In particular, AMS data helped characterise the flux, charge and energy distribution of galactic cosmic rays and solar energetic particles, key parameters for modelling dose, dose-rate and track-structure effects in biological tissue. These measurements inform risk assessments for astronaut exposure, improve shielding models, and support more realistic simulations of DNA damage and long-term health effects associated with chronic low-dose, high-energy radiation in space. Rather than serving as a standalone example, this case study acts as a concrete illustration of how cross-disciplinary collaboration actually works in practice: how shared technologies, experimental approaches and theoretical frameworks can produce insights that matter across fields.

Space Radiobiology — Credit: World Scientific

The sections on radiobiology strike a careful balance between accessibility and depth. Topics such as DNA damage, cellular responses and long-term health effects are explained clearly, without oversimplifying issues that are inherently complex (CERN Courier November/December 2025 p27). One of the book’s strongest messages is that space radiobiology, with its extreme and unconventional exposure conditions, offers a unique lens for understanding radiation effects that are also relevant to clinical and occupational environments on Earth.

By focusing on shared biological endpoints and common dosimetric challenges, the book shows how progress in one area can meaningfully inform the other. The discussion on developing common platforms for radiation measurement and monitoring reinforces this point, arguing that integrated approaches are not only efficient but scientifically necessary in increasingly complex radiation environments.

Space Radiobiology succeeds in bringing together different scientific communities around a common language and set of challenges. It will resonate with researchers in physics, space science, radiobiology and medical physics, as well as with graduate students looking for a broader, more connected view of radiation science. At a moment when deep-space exploration is becoming a tangible goal rather than a distant idea, the book offers a thoughtful and convincing picture of how lessons learned beyond Earth can shape safer and more effective uses of radiation here at home.

The flavour dependence of jet structures

ALICE figure 1 — **Fig. 1.** Away-side per-trigger nuclear modification factor I_AA as a function of the associated-particle transverse momentum. Blue circles show jets tagged by electrons from heavy-flavour hadron decays; black squares and red diamonds show light-flavour reference measurements. Credit: ALICE Collab. 2025 arXiv:2507.13197

Partons produced in heavy-ion collisions at the LHC must push their way through a hot, dense quark–gluon plasma (QGP). In doing so, they experience medium-induced energy loss that depends on the parton’s mass. In a recent analysis, the ALICE collaboration compared the yields of charged particles associated with electrons from heavy-flavour hadron decays with those of the light hadrons. Both show a suppression of high-momentum particles emitted opposite to the tagged particle, with no significant difference between the two.

After a hard scattering, high-energy partons fragment into collimated sprays of hadrons known as jets. These are well described in proton–proton (pp) collisions, where their substructures provide stringent tests of perturbative QCD. In heavy-ion collisions, instead, they propagate through the QGP and emerge modified – a phenomenon known as jet quenching. Previous measurements (CERN Courier March/April 2025 p13) suggest that jets initiated by charm and beauty quarks lose less energy than those from light quarks and gluons, owing to their larger mass. This difference is commonly attributed to the dead-cone effect, which suppresses gluon emission by heavy quarks at small angles. Jet-quenching effects can be further characterised by measuring the transverse-momentum distribution of particles within jets, providing insight into the redistribution of the quenched energy.

To study this, the ALICE collaboration employs azimuthal-correlation measurements. This technique measures the angular correlation between a heavy-flavour hadron or its decay daughter (“trigger” particle) and other associated charged particles in the same event. The resulting distribution features two correlation peaks: a near-side peak from particles produced alongside the trigger and an away-side one from the recoiling jet, particularly sensitive to jet-medium interactions. Jet quenching is then quantified by the per-trigger nuclear modification factor I_AA, which is the ratio of away-side charged-particle yield in heavy-ion collisions to pp collisions. Values of I_AA deviating from unity indicate QGP-induced modifications of the jet.

The ALICE collaboration now reports the measurements of jet-like structures in the heavy-flavour sector of lead-lead collisions at a centre-of-mass energy of 5.02 TeV per nucleon pair. The analysis, based on LHC Run 2 data, uses electrons from semi-leptonic decays of charm and beauty hadrons as trigger particles. Electron identification relies on a combination of energy-loss measurements in the time-projection chamber, energy-momentum matching in the calorimeter and selection of shower shapes. Invariant-mass tagging techniques allowed for the subtraction of the large backgrounds from photon conversions and light-meson decays to electron-positron pairs.

The measurement is challenging due to the high multiplicity of lead-lead collisions and the need to extract jet-like correlations from large combinatorial and collective-motion backgrounds. A corresponding analysis of pp collisions at the same energy provides the reference needed to compare jet evolution in the presence of the QGP.

The away-side shows a suppression for associated particles with transverse momenta between 4 and 7 GeV/c (see figure 1), indicating relevant jet quenching with a 2.5σ significance. Conversely, a hint of an enhancement is observed below 2 GeV/c, possibly signalling the redistribution of lost energy into the medium and the subsequent formation of additional low-momentum particles.

These results are consistent with corresponding measurements using light-flavour triggers across all measured intervals. While this suggests that the QGP modifies jets consistently regardless of the initiating parton’s mass, important caveats remain. Variations in parton-to-hadron momentum scaling, as well as the fact that the heavy flavour is tagged via decay electrons, could introduce kinematic differences that complicate a direct comparison. Whether QCD predicts a deviation remains an open question for future modelling of mass-dependent parton-medium interactions.

LHC Run 3 will provide an order of magnitude more heavy-ion events. This increased luminosity will enable higher-precision analyses, offering a deeper understanding of how QGP modifies heavy- and light-flavour jets.

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