Authors: Gianluigi Arduini, CERN, Kristiane Bernhard-Novotny, CERN, Joerg Jaeckel, University of Heidelberg, Gunar Schnell, UPV/EHU & Ikerbasque Bilbao, and Claude Vallée, CPPM-Marseille

The Physics Beyond Colliders (PBC) Study was launched in 2016 to explore the opportunities offered by CERN’s unique accelerator and experimental area complex and expertise to address some of the outstanding questions in particle physics through experiments complementary to the high-energy frontier. Together with the Large Hadron Collider (LHC) experiments, the PBC proposals form a synergistic partnership, which fosters an ecosystem beyond collider-based research and diversifies CERN’s science programme at the precision and intensity frontiers.

The fifth PBC annual workshop was held from 25 to 27 March at CERN to explore new ideas and avenues aiming to answer open questions of the Standard Model and beyond, and to provide updates of ongoing projects.

The Super Proton Synchrotron (SPS) North Area (NA) is one of the major fixed-target experimental facilities available at CERN and it is at the very heart of many present and proposed explorations for Beyond the Standard Model (BSM) physics. The NA includes an underground cavern (ECN3) for experiments requiring high-energy/high-intensity proton beams. Several proposals have been made for experiments to operate in ECN3 in the next decade and beyond. All of them require higher intensity proton beams than currently available. One of these proposals studied within PBC, SHiP (Search for Hidden Particles), aiming for a comprehensive investigation of the Hidden Sector in the GeV mass range at a dedicated Beam Dump Facility (BDF) [1], has been recently approved. Together with the activities of NA64, an experiment leading the searches for light dark particles with a versatile setup suited for electron [2], positron [3], muon [4] and hadron beams [5], this will significantly strengthen CERN’s focus towards dark-sector searches.

The FASER [6] and SND [7] experiments, now taking data at the LHC and originated in the first phase of the PBC initiative, contribute to both New Physics searches and to the study of very high-energy neutrinos. The proposed Forward Physics Facility (FPF), located in the line of sight of the interaction point 1 of the High Luminosity LHC (HL-LHC) 620 m away from it, could increase sensitivity to BSM physics by a factor of about 10,000 over FASER and it could allow for the detection of  thousands of neutrinos at TeV-energies per day with the potential of contributing to the measurement of parton-distribution functions with improved precision, benefitting the HL-LHC physics reach. The experiment consists of a series of sub-detectors of relatively small size. The FPF detectors’ layout definition and the corresponding integration studies have made significant progress as one of the main PBC-supported studies in view of the publication of a document describing the facility’s technical infrastructure by mid-2024.

proANUBIS [8], CODEX-beta [9] and MATHUSLA [10] are also actively being studied and would be located at large angles to the collision line of sight at the ATLAS, LHCb and CMS experiments.

Remaining in the realm of the Standard Model, a new NA60+[11] experiment with lead ions and NA61/SHINE[12] with light ions aim to uncover the onset of the Quantum Chromo Dynamics (QCD) phase transition at energy scales only accessible at the SPS, holding promise to decode the phases of nuclear matter in the non-perturbative regime of QCD. Understanding QCD means further to unravel the emergent properties of baryons and mesons. The AMBER [13] experiment plans to determine the charge radii of kaons and pions and to perform meson spectroscopy, in particular with kaons, within a wide range of experimental activities proposed beyond the next accelerator long Lshutdown (LS3). A substantial study has been carried out to enhance the number of identifiable kaons in the hadron beam delivered to AMBER. This could be achieved by improving the vacuum conditions and by the implementation of a dedicated optics in the beamline to the experiment.

To complement results obtained at AMBER’s predecessors COMPASS, HERA, and other experiments using a polarized beam and/or target, the LHCSpin collaboration  presented their proposal [14] to open a new frontier and to introduce spin physics at the LHC with a gaseous polarised target following the successful commissioning of the SMOG2 unpolarised-gas cell [15]. This would result in a new probe for studying collective phenomena at the LHC. Moreover, this would provide access to the multi-dimensional nucleon structure in a kinematic domain of hitherto limited exploration and make use of new probes, for instance by using charm mesons.

The TWOCRYST collaboration aims to demonstrate the feasibility and the performance of a possible fixed-target experiment in the LHC to measure electric and magnetic dipole moments (EDMs and MDMs) of charmed baryons [16], offering a complementary platform for the study of Charge-Parity (CP) violation in the Standard Model. These baryons would be generated by the collision of the protons of the secondary beam halo channelled by a crystal onto a target. MDM and EDM would be determined by measuring the baryon spin precession in the strong electric field of a crystal installed immediately downstream of the target.

The conceptual design of a beamline to produce a tagged neutrino beam to improve the precision of neutrino cross-section measurements has been developed combining the ENUBET [17] and NuTag [18] proposals. This design would significantly increase the amount of tagged neutrinos generated within a given geometric acceptance and energy band.

The Gamma Factory (GF) collaboration, which aims to demonstrate the principle of the Gamma Factory in the SPS, reported the progress achieved at IJCLab (France) in the development of the laser system required for this facility. The GF scheme is based on resonant excitation of ultra-relativistic partially stripped ions (that could be made available at the SPS and LHC) with a laser beam tuned to the atomic transition frequencies, followed by the process of spontaneous emission of photons. The resonant excitation of atomic levels of highly ionised atoms (ions) is possible due to the large energies of the ions generating a Doppler frequency boost of the counter-propagating laser beam photons by a factor of up to 2g, where g is the relativistic factor. Spontaneously-emitted photons produced in the direction of the ion beam, when seen in the laboratory frame, have their energy boosted by a further factor of 2g. As a consequence, the process of absorption and emission results in a frequency boost of the incoming photon of up to 4g ². In the GF scheme, the SPS (LHC) atomic beams play the role of photon “frequency converters” of eV-photons into keV (MeV) X-rays (γ-rays). These intense and quasi-monochromatic beams could be used in a variety of atomic, nuclear and particle physics experiments [19] and they could potentially find application to energy production or nuclear-waste transmutation as well as the generation of intense positron and muon beams for future accelerator facilities.

High quality factor superconducting radio-frequency cavities, similar to those used for the acceleration of charged particles in accelerators, can also be used to detect axions (hypothetical particles that might be able to explain both the strong CP violation problem and account for dark matter) and even gravitational waves, and they can also be of interest for developing multi-qubit systems. The design and fabrication of a superconducting cavity for the heterodyne detection of axion-like particles over a wide range of masses [20] is the subject of a joint project between PBC and the CERN Quantum Technology Initiative. Atom Interferometry is another subject of common interest between the two CERN initiatives and PBC has demonstrated the technical feasibility of installing an atom interferometer with a baseline of 100 m in one of the LHC access shafts [21].

The charged-particle EDM collaboration presented the status of their approach to build a prototype ring that would validate the main concepts of a ring required to perform the first direct measurement of a proton EDM [22] and evaluate the sensitivity reach of such measurement.

The proposed injectors of the Future Circular electron-positron Collider (FCC-ee) [23] will significantly expand the variety of the offer of the CERN accelerator complex in terms of beam types and parameters, potentially opening up the possibility of new experiments. New ideas have been also presented, ranging from the measurement of molecular EDMs at the ISOLDE (Isotope Separator On Line DEvice) Radioactive Ion Beam Facility, over the prospects for antiproton physics at the Antiproton Decelerator (AD) and the Extra Low ENergy Antiproton (ELENA) ring, to the measurement of the gravitational effect of the LHC beam.

With these highlights in stock, many fruitful discussions, the annual workshop concluded as a resounding success. The PBC community thanked Claude Vallée (CPPM, Marseille), who retired as PBC co-coordinator and co-founder of the PBC initiative, after almost a decade of integral work, and welcomed Gunar Schnell (UPV/EHU & Ikerbasque, Bilbao) who will take on this role.

A small part of the community who contributes with lively discussions and innovative proposals and projects to the success of PBC.
Credit: K. Bernhard-Novotny (CERN)

[1] SHiP Collaboration, BDF/SHiP at the ECN3 high-intensity beam facility, CERN-SPSC-2022-032 ; SPSC-I-258

[2] Yu. M. Adreev et al. , Search for Light Dark Matter with NA64 at CERN,     Phys.Rev.Lett. 131 (2023) 16, 161801

[3] Yu. M. Adreev et al. , Probing light dark matter with positron beams at NA64,     Phys.Rev.D 109 (2024) 3, L031103

[4] Yu. M. Adreev et al. , Exploration of the Muon g−2 and Light Dark Matter explanations in NA64 with the CERN SPS high energy muon beam, arxiv:2401.01708 ; accepted by PRL

[5] S. Gninenko et al., Test of vector portal with dark fermions in the charge-exchange reactions in the NA64 experiment at CERN SPS, arxiv:2312.01703

[6] H. Abreu et al., First Direct Observation of Collider Neutrinos with FASER at the LHC, Phys.Rev.Lett. 131 (2023) 3, 031801

[7] R Albanese et al., Observation of Collider Muon Neutrinos with the SND@LHC Experiment, Phys.Rev.Lett. 131 (2023) 3, 031802

[8] A Shah et al., Searches for long-lived particles with the ANUBIS experiment, PoS EPS-HEP2023 (2024) 051 / A Shah et al., Installation of proANUBIS – a proof-of-concept demonstrator for the ANUBIS experiment, PoS LHCP2023 (2024) 168

[9] C Aielli et al., The Road Ahead for CODEX-b, arXiv:203.07316

[10] C Alpigani et al., An Update to the Letter of Intent for MATHUSLA: Search for Long-Lived Particles at the HL-LHC, arXiv:2009.01693

[11] NA60+ Collaboration, Letter of Intent: the NA60+ experiment, CERN-SPSC-2022-036; SPSC-I-259, Geneva, 2022, https://cds.cern.ch/record/2845241

[12] NA61/SHINE Collaboration, Addendum to the NA61/SHINE Proposal: A Low-Energy Beamline at the SPS H2, CERN-SPSC-2021-028 / SPSC-P-330-ADD-12, Geneva 2021, https://cds.cern.ch/record/2783037/files/SPSC-P-330-ADD-12.pdf

[13] C Quintas et al., The New AMBER Experiment at the CERN SPS, Few Body Syst. 63 (2022) 4, 72

[14] P. Di Nezza et al., The LHCspin Project, Acta Phys.Polon.Supp. 16 (2023) 7, 7-A4

[15] C. Boscolo Meneguolo, et al., Study of beam-gas interactions at the LHC for the Physics Beyond Colliders fixed-target study, JACoW proceedings (2019)

[16] S. Aiola et al., Progress towards the first measurement of charm baryon dipole

moments, Phys. Rev. D 103, 072003 (2021).

[17] F Acerbi et al., Design and performance of the ENUBET monitored neutrino beam, Eur.Phys.J.C 83 (2023) 10, 964

[18] A Baratto-Roldan et al., NuTag: proof-of-concept study for a long-baseline neutrino beam, arXiv:2401.17068

[19] D. Budker, M. Gorchtein, M. W. Krasny, A. Pálffy, A. Surzhykov (editors), Physics Opportunities with the Gamma Factory, Annalen der Physik, Volume 534, Issue 3 (2022)

[20] A Berlin et al., Heterodyne Broadband Detection of Axion Dark Matter, Phys. Rev. D 104, L111701

[21] G. Arduini et al., A Long-Baseline Atom Interferometer at CERN: Conceptual Feasibility Study, arXiv:2304.00614", CERN-PBC-REPORT-2023-002, Geneva, 2023, https://cds.cern.ch/record/2851946

[22] F. Abusaif, et al., Storage ring to search for electric dipole moments of charged particles: Feasibility study, CERN Yellow Reports: Monographs, CERN-2021-003, Geneva, 2021, https://cds.cern.ch/record/2654645, doi=10.23731/CYRM-2021-003

[23] M. Benedikt et al. (editors), Future Circular Collider Study. Volume 2: The Lepton Collider (FCC-ee) Conceptual Design Report, CERN-ACC-2018-0057, Geneva, December 2018. Published in Eur. Phys. J. ST.

Author: Thomas Lohse, chair of EPS HEPPD from 2013-2015

In 1964, Peter Higgs published his famous paper on a self-consistent theory of vector bosons with non-vanishing mass, paving the road towards today’s theory of electroweak interactions of elementary particles. The mass-creation mechanism implied the existence of a new particle, today known as the Higgs boson. This  spin-zero particle is fundamentally different from all other known elementary particles.

For several decades, all experimental efforts to find this new particle were unsuccessful, until in the 1990s precision experiments at highest energy electron positron colliders measured effects consistent with those created by virtual Higgs bosons in quantum fluctuations. Although not yet  an unambiguous discovery, the High Energy Particle Physics Division of the European Physical Society reacted by awarding at the 1997 International Europhysics Conference on High Energy Physics in Jerusalem the prestigious EPS HEPP Prize to Peter Higgs, together with Robert Brout and Fraçois Englert, who had independently and almost simultaneously discovered and published the mass-generation mechanism back in 1964.

The indisputable discovery of the Higgs boson, by then the holy grail of elementary particle physics, had to wait for new record energies to be reached at CERN’s Large Hadron Collider. In  2012 the ATLAS and CMS experiments independently announced the discovery of a new particle which was subsequently shown to have all the predicted properties of the precious Higgs boson. The European Physical Society reacted promptly and awarded the 2013 EPS HEPP Prize to the two experimental collaborations and three of their leading scientists at the EPS conference which took place in July 2013. Both, François Englert and Peter Higgs joined the conference. Peter Higgs gave a highlight talk – challenging the organizers by using a classical overhead projector – and explained the theoretical developments which allowed him and his colleagues to come up with nothing less than a brilliant break-through for elementary particle physics. Sadly, Robert Brout, who died in 2011, didn’t live to see this historical event. Not unexpectedly, only a few months after the conference, François Englert and Peter Higgs had to return to Stockholm, this time to receiving the 2013 Nobel Prize in Physics.

On the 8^th of April 2024, Peter Higgs died in Edinburgh at the age of 94. The elementary particle community has lost a visionary theorist and a very modest and polite friend.

Impressions of the EPS HEP conference with Peter Higgs and François Englert, Stockholm 2013 - image credit: Gina Gunaratnam/EPS

Author: Anne Pawsey

EPL is delighted to announce the arrival of a new Editor in Chief Richard Blythe of the University of Edinburgh who will take up the role on 1st May 2024. Prof. Blythe takes over from Dr. Alessandra S. Lanotte, of Consiglio Nazionale delle Ricerche, Istituto di Nanotecnologia, CNR-NANOTEC, who acted as interim Editor in Chief for the first quarter of 2024. 

Richard Blythe holds a personal chair in complex systems at the University of Edinburgh, UK. He studied Physics at the University of Bristol, UK, participating in an exchange year at the Technische Hochschule Darmstadt, Germany, before pursuing a PhD in nonequilibrium statistical mechanics at Edinburgh. In his research, Richard builds models of complex interacting systems at the microscopic scale and applies both mathematical and computational tools to understand the collective phenomena that emerge. He has particular interests in transport and structure formation by model active particles, whose dynamics are inspired by the motion of bacteria and birds. He has also collaborated extensively with linguists on modelling human social dynamics and the process of language change, gaining insights into how social and cognitive interactions at the individual scale shape the collective properties of language at the population scale. Throughout his career, Richard has played key roles in bringing research communities together through a variety of activities including collaboration networks, workshops and summer schools.

Richard Blythe - image R. Blythe

Author: Rüdiger Voss

Herwig Schopper, EPS President from 1995 to 1997, celebrated his 100^th birthday on 28 February

Herwig Schopper was born in Lanškroun (Landskron), in a German-speaking region of what is now the Czech Republic. Shortly after the end of World War II, he started studying physics at the University of Hamburg where he received his PhD in 1951. He soon embarked on a prestigious academic career which took him to professorships in Mainz, Karlsruhe, and later in Hamburg, making landmark contributions to experimental nuclear physics, particle physics, and accelerator technology. During these years, he already demonstrated his talents as a science administrator: in 1973, he was appointed chairman of the DESY board of directors; in 1981 he began an eight-years term as Director-General of CERN, notably overseeing the construction of the large electron-positron collider LEP in the same 27 km tunnel which today houses the Large Hadron Collider.

Following his term of office at CERN, Herwig started a new career as science diplomat that keeps him active to this day. From 1992-94, he served as president of the German Physical Society, and from 1995-97 he was president of the EPS. In subsequent years, he held several important positions at UNESCO, including chairing the advisory committee for the International Basic Science Programme (2003-2009). Guided by his strong personal vision of “science for peace”, he embarked on his most ambitious science diplomacy project: the SESAME light source in the middle east which was inaugurated in Jordan in 2017.

On 1 March, Herwig's unique personality and countless achievements were celebrated at CERN with a festive symposium, “A century in physics”, by a prestigious line-up of speakers who had witnessed different stages of his life and career, including Nobel Prize Winner Samuel Ting and Herwig's children Doris and Andreas. In a short message, EPS President-elect Mairi Sakellariadou recalled Herwig Schopper’s merits as the president who steered our society with his characteristic quiet and unassuming, but highly effective approach to management through the tumultuous period when the seat and the secretariat were moved from Geneva to Mulhouse, saving the EPS from a severe political and financial crisis. The EPS is immensely grateful to its former president for his leadership and for his lifelong devotion to science and peace: congratulations Herwig on your uncountable achievements, and good luck and good health for many more years to come!

A more comprehensive appraisal of Herwig Schopper’s life and work will appear in a forthcoming issue of Europhysics News (55/2).

Three generations of CERN Directors-General: Herwig Schopper and Fabiola Gianotti cutting the birthday cake, critically watched by Rolf Heuer - image credit: Rüdiger Voss

The 17^th Persian Young Physicists’ Tournament, PYPT, was held in February 2024 by Ariaian Young Innovative Minds Institute, AYIMI, and ADIB Cultural and Artistic Institute. Team members from different schools challenged with each other online in two days and six teams attended in final face to face who received gold medal as follows:

First Gold Medalist team members who also received the PYPT Trophy  :  Elyar Ferdosizadeh, Mohammadhossein Ezzati, Baran Bahman, Ava Alebouyeh from Valed School

Other five gold winners are from Valeh , Farzanegan 2 and 7 and Kish schools as follows: Aran Soufizadeh, Niki Abtahi, Niki Teimoori, Sarina Nosrati, Artin Radmatin, Niyayesh Vasegh, Negar Sharifi, Zahra Arab Beik , Nikoo Mohseni Zadeh Tehrani, Diana sadat Hashemi, Pariya Ahmadi, Mahtab Zare Dehnavi, Parinaz Farhadkhani, Saina Safarian, Saina Osanlou,Parmiss Khoshamal ,Maedeh Saeidi, Elena Zarei, Farin Daei, Shanli Omrany, Narges Alinezhad, Narvin Taheri,  Zahra Mahnavian, Baran nasrpour, Dina Karimizadeh, Sogand Radka, Nita Jafarzadeh 

The Silver medalists are from Farzanegan Rasht, Mihan, Kish,  Rahe Roshd , International, Shahid Soltani and Mofid 1schools as follows :  Seyedeh RoniaSahafi, Seyedeh Saba Sojasi, Taranom Jamshidi, Yasna Kamran,Sava Akbari Khalil Abad, Zahra Fazaie; Amir Hossein Karimi, SinaSaleh Abadi, Taha Sedaghat, Parsa Namjoo, parsa Shahrokhi ; soroosh salimzadeh,  Arad Khosravani, Roham Ghasemi, Amirali Rezaei, Reza Zaherbin, Amirreza Nadalizade, Arad Bayani, Kian Taghizadeh, Amirmohamad Poomohamad, Seyed Yazdan Seyed Mohseni,  Parmida Hosseinzade, Nazanin Zahra Mostafavi,  Aram Alimohammadi,  Yasaman Zarein,  Parmida Mehrian; Radin Qashqai, Kourosh Souri, Amirreza Babaei, Bahram JadidBonyad,  Mohammad Arshadfard; Mohammad Hussein Abdi, Shayan Shahri, Amirhossein Neshat, Mohammad Parsa Nazifi, Mohammad Hossein Pourbakht, Amirali Faryadras

AYIMI is an EPS Associate Member.