Jobs – Page 58 of 511

Tom Cormier 1947–2022

Long-time ALICE collaborator and authority in relativistic heavy-ion physics, Tom Cormier, passed away on 23 March after a brief illness. Tom was born in 1947 in Lexington, a suburb of Boston. After high school he went to MIT where he did both his undergraduate and graduate studies. He was an amazing physicist with a strong drive to explore the frontiers of relativistic nuclear physics, and a profound understanding of the field that enabled him to build the best tools to take us to those frontiers.

After obtaining his PhD from MIT in 1974, Tom took up postdoc positions at Stony Brook and the Max Planck Institute. He then joined the University of Rochester, where he later became director of the Nuclear Structure Research Laboratory. In 1988 he moved to the Cyclotron Institute at Texas A&M University where he stayed for three years. Wayne State University was his next move, where he was chair of the physics and astronomy department. Tom joined the ORNL Physics Division in 2013, and reinvigorated the relativistic nuclear physics group and expanded ORNL’s very successful involvement in the ALICE experiment at the LHC, sPHENIX at RHIC and most recently in the Electron-Ion Collider (EIC) under construction at Brookhaven.

Tom’s work spanned an amazing breadth of physics and technology. Early on he worked on carbon–carbon inelastic scattering and scattering resonances; he then moved to experiments with recoil mass spectrometers at Brookhaven. Tom shifted his focus to relativistic heavy-ion physics with the AGS-E864 experiment at Brookhaven, followed by the STAR experiment at RHIC. He was the project manager for the construction of the STAR electromagnetic calorimeter and worked on the experiment from 1996 to 2005.

Tom was one of the key scientists enabling the US heavy-ion community to join the LHC by proposing the large electromagnetic calorimeter EMCAL for ALICE and by forming the ALICE US collaboration. He was project manager for ALICE US, with a key responsibility for EMCAL and its later extension, the di-jet calorimeter, DCAL. Having successfully completed this project, he took on the leadership of the barrel tracker upgrade for ALICE. He was an architect of the TPC upgrade and was TPC deputy project leader from 2013. His true leadership and professionalism have been central to the success of ALICE in the past two decades. Tom most recently helped form the ECCE detector concept for the EIC.

Both a great leader and project manager, Tom was a real inspiration, not only to his close colleagues but also to the broader community that held him in such high regard. He has been a wonderful mentor to many of us, and his contributions to the global physics programme, and to the ORNL physics division in particular, have been immense. He was an expert navigator of the various funding agencies and always showed immense calm during numerous DOE reviews, his dry sense of humour reflected in one of his memorable quips: “If I would wear a suit today, the DOE would be sure we screwed up badly.” He will be sorely missed but his legacy will remain.

Alberto Sirlin 1930–2022

Theorist Alberto Sirlin, a pioneer in electroweak radiative corrections, passed away on 23 February aged 91. His work played a key role in confirming predictions of the Standard Model (SM) at the ±0.1% level. He was a professor at New York University for 62 years, mentored 14 PhD students and remained an active researcher until shortly before his death.

Born in Buenos Aires in 1930, Alberto received a physics and mathematics degree from the University of Buenos Aires in 1953. That year he went to Brazil where he took a quantum mechanics course taught by Richard Feynman. In a 2015 essay “Remembering a Great Teacher”, Alberto fondly recalled that experience and the enduring friendship that followed. In 1954 he travelled to UCLA and collaborated with Ralph Behrends and Robert Finkelstein on an early study of QED radiative corrections to muon decay in Fermi’s general theory of weak interactions. Alberto then moved to graduate school at Cornell University, where he collaborated with Toichiro Kinoshita on the QED corrections to muon and nuclear beta decays in the V-A Fermi theory. Their investigation showed that QED corrections increased the muon lifetime by about 0.4% – an effect still used to define the Fermi constant. For nuclear beta decay, where QED effects were logarithmically dependent on an arbitrary cutoff scale, Alberto would later show how electroweak unification determines this scale. After Cornell he spent two years (1957–1959) as a postdoc at Columbia University, supervised by T D Lee, before joining the faculty of New York University. He also held visiting appointments at BNL, CERN, Hamburg University, Rockefeller University and The Institute for Advanced Study.

When the SM came together in the early 1970s, Alberto’s early work on QED corrections to weak-interaction processes uniquely prepared him for a leading role in computing electroweak quantum loop corrections. For example, he showed how additional loop corrections involving W and Z bosons led to a replacement of the logarithmic cutoff found in semi-leptonic beta decays by the Z-boson mass, resulting in a ~2% increase for all semi-leptonic charged-current decay rates. This is essential for unitarity tests of the quark mixing matrix, and confirms the validity of the SM at more than 20σ!

In a 1980 paper that has been cited more than 1400 times, Alberto introduced the on-shell renormalisation scheme based on physical parameters and the quantity Δr, which encodes the radiative effects. This scheme has been used to study deep-inelastic neutrino–nucleus scattering, neutrino-electron scattering, atomic parity violation, polarised electron–electron scattering asymmetries, W&Z precise mass predictions, and more, not only by Alberto and his former students and collaborators, but by the entire particle-physics community in searches for new-physics effects. Together with his former student William Marciano, he won the 2002 J J Sakurai prize of the American Physical Society for their pioneering work on radiative corrections.

In witnessing the rise and then completion of the SM with the discovery of the Higgs boson in 2012, Alberto was able to enjoy the fruits of his labour. We, his students, have been inspired by Alberto’s dedication and enthusiasm. We are grateful that we could join his journey through life and physics. He was our great teacher.

Probing new physics with the Higgs boson

ATLAS figure 1 — **Fig. 1.** Observed (solid) and expected (dashed) upper limits at 95% CL on the production-cross section for pp → Wʹ → WH. The green (yellow) band indicates ±1 (±2) standard deviations from the expected limits. Source: ATLAS-CONF-2021-026

Due to its connection to the process of electroweak symmetry breaking, the Higgs boson plays a special role in the Standard Model (SM). Its properties, such as its mass and its couplings to fermions and bosons, have been measured with increasing precision. For these reasons, the Higgs boson has become an ideal tool to conduct new-physics searches. Prominent examples are direct searches for new heavy particles decaying into Higgs bosons or searches for exotic decays of the Higgs boson. Such phenomena have been predicted in many extensions of the SM motivated by long-standing open questions, including the hierarchy problem, dark matter and electroweak baryogenesis. Examples of new particles that couple to the Higgs boson are heavy vector bosons (as in models with Higgs compositeness or warped extra dimensions) and additional scalar particles (as in supersymmetric models or axion models).

Searches for resonances

The ATLAS collaboration recently released results of a search for a new heavy particle decaying into a Higgs and a W boson. The search was performed by probing for a localised excess in the invariant mass distribution of the ℓνbb final state. As no such excess was found, upper limits at 95% confidence level were set on the production-cross section times branching ratio of the new heavy resonance (figure 1). The results were also interpreted in the context of the heavy vector triplet (HVT) model, which extends the SM gauge group by an additional SU(2) group, to constrain the coupling strengths of heavy vector bosons to SM particles. In two HVT benchmark models, W′ masses below 2.95 and 3.15 TeV are excluded.

ATLAS figure 2 — **Fig. 2.** Invariant mass distribution of the two jets considered in the search for Higgs-boson decays into invisible particles for the vector-boson fusion production process. The signal (dashed red line) scaled to a branching ratio of 15% for Higgs-boson decays tends to higher masses, corresponding to large angular separation of the jets. Source: arXiv:2202.07953

Rare or exotic decays are excellent candidates to search for weakly coupled new physics. The Higgs boson is particularly sensitive to such new physics owing to its narrow total width, which is three orders of magnitude smaller than that of the W and Z bosons and the top quark. Several searches for exotic decays of the Higgs boson have been carried out by ATLAS, and they may be broadly classified as those scenarios where the possible new daughter particle decays promptly to SM particles, and those where it would be long-lived or stable.

A recent search from ATLAS targeted exotic decays of the Higgs boson into a final state into four electrons or muons, which benefit from a very clean experimental signature. Although a signal was not observed, the search put stringent constraints on decays to new light scalar bosons – particularly in the low mass range of a few GeV – and to new vector bosons, dubbed dark Z bosons or dark photons, in the mass range up to a few tens of GeV. Depending on the new-physics model, this search can exclude branching ratios of the Higgs boson to new particles as low as O(10^–5).

Invisibles

Another interesting possibility is the case where the Higgs boson decays to particles that are invisible in the detector, such as dark-matter candidates. To select such events, different strategies are pursued depending on the particles produced in association with the Higgs boson. The most powerful channel for such a search is the vector-boson fusion production process, where two energetic jets from quarks are produced with large angular separation alongside the invisibly decaying Higgs boson (figure 2). Another sensitive channel is the associated production of a Higgs boson with a Z boson that decays to a pair of leptons. Improvements in background predictions have made it possible to reach a sensitivity down to 10% on the branching ratio of invisible Higgs-boson decays, while the corresponding observed limit amounts to 15%.

These searches will greatly benefit from the large datasets expected in Run 3 and later High-Luminosity LHC runs, and will enable searches for even more feeble couplings of new particles to the Higgs boson.

Upsilon suppression in heavy-ion collisions

CMS figure 1 — **Fig. 1.** The nuclear modification factor R_AA of the three ϒ states, as a function of <N_part> (besides the centrality-integrated values). The error bars (boxes) represent the statistical (systematic) uncertainties. The boxes at unity represent global systematic uncertainties, for both the ϒ(2S) and ϒ(3S) points (open), and for only the ϒ(2S) (purple) or ϒ(3S) (green) mesons. Source: CMS-PAS-HIN-21-007

The bound states of a heavy quark and its antiquark, called quarkonia, have long been regarded as ideal probes to study the quark–gluon plasma (QGP) formed in high-energy heavy-ion collisions. The golden signature is the suppression of their production yield in lead–lead (PbPb) collisions with respect to extrapolations from proton–proton (pp) collisions, caused by modifications of the binding potential in the QGP. The suppression of the different quarkonium states is expected to depend on their binding energies. Quarkonia can also be produced by recombination processes. The ϒ states (bound states of b quarks and antiquarks) are much less affected by recombination effects than charmonium states, given the very small probability that b quarks are produced. A comparison of their suppression patterns is particularly informative because of the different binding energies of the ϒ(1S), ϒ(2S) and ϒ(3S) states.

The suppression of quarkonium production is quantified via the nuclear modification factor R_AA, defined as the ratio between the yield in nucleus–nucleus (AA) collisions and the yield extrapolated from pp data. Previous measurements of R_AA for the ϒ mesons by experiments at RHIC and the LHC revealed a significant suppression of the ϒ(1S) state and a larger suppression for the ϒ(2S) state. However, these experiments could only set upper limits for the ϒ(3S) state due to its very low production yield. The CMS experiment recently changed this situation by presenting the first observation of the ϒ(3S) meson in heavy-ion collisions. The ϒ mesons are detected using their decay to two muons. The analysis used the large PbPb data sample collected in 2018 and extracted the ϒ(3S) signals from the large background of muon pairs by using a boosted decision tree algorithm.

The new R_AA results are shown together with the previously published ϒ(1S) values as a function of the average number of nucleons participating in the PbPb collisions, <N_part> (figure 1). Collisions with larger <N_part> show a bigger overlap between the two nuclei, producing a larger and hotter QGP. As previously observed, the degree of suppression increases from peripheral to central collisions, i.e. as N_part increases, indicating a more substantial dissociation effect at higher QGP temperatures. The new ϒ(3S) suppression measurement completes the picture of suppression patterns for five different quarkonium states, which was started 35 years ago at the CERN SPS with the J/ψ and ψ(2S) results of NA38. The stage is set for a deeper understanding of deconfinement in the QGP.

Limbering up for the Einstein Telescope

On 14 April the government of the Netherlands announced that it intends to conditionally allocate €42 million to the development of the Einstein Telescope – a proposed next-generation gravitational-wave observatory in Europe. It also pledged a further €870 million for a potential future Dutch contribution to the construction. The decision was taken by the Dutch government based on the advice of the Advisory Committee of the National Growth Fund, stated a press release from Nikhef and the regional development agency for Limburg.

The Einstein Telescope (ET) is a triangular laser interferometer with sides 10 km-long that would be at least 10 times more sensitive than the Advanced LIGO and Virgo observatories, extending its scope for detections and enabling physicists to look back much further in cosmological time. To reach the required sensitivities, the interferometer has to be built at least 200 m underground in a geologically stable area. Its mirrors will have to operate in cryogenic conditions to reduce thermal disturbance, and be larger and heavier than those currently employed to allow for a larger and more powerful laser beam.

Activities have been taking place at two potential sites in Europe: the border region of South Limburg (the Euregio Meuse-Rhine) in the Netherlands; and the Sar-Grav laboratory in the Sos Enattos mine in Sardinia, Italy. For the Sardinia site, a similar proposal has been submitted to the Italian government and feedback is expected in July.

The Netherlands’ intended €42 million investment will go towards preparatory work such as innovation of the necessary technology, location research, building up a high-tech ecosystem and organisation, stated the press release, while the reservation of €870 million is intended to put the Netherlands in a strong position to apply in the future – together with Belgium and Germany – to host and build the ET.

It is fantastic that the cabinet embraces the ambition to make the Netherlands a world leader in research into gravity waves

“It is fantastic that the cabinet embraces the ambition to make the Netherlands a world leader in research into gravity waves,” said Nikhef director Stan Bentvelsen, who has been involved with the ET for several years. “These growth-fund resources form the basis for further cooperation with our partners in Germany and Belgium, and for research into the geological subsurface in the border region of South Limburg. A major project requires a careful process, and I am confident that we will meet the additional conditions.”

Housing the ET in the region could have a major positive impact on science, the economy and society in the Netherlands, said provincial executive member for Limburg Stephan Satijn. “With today’s decision, the cabinet places our country at the global forefront of high-tech and science. Limburg is the logical place to help shape this leading position. Not only because of the suitability of our soil, but also because we are accustomed to working together internationally and to connecting science and business.”

At the 12th ET symposium in Budapest on 7–8 June, the ET scientific collaboration was officially born – a crucial step in the project’s journey, said ad interim spokesperson Michele Punturo of the INFN: “We were a scientific community, today we are a scientific collaboration, that is, a structured and organised system that works following shared rules to achieve the common goal: the realisation of a large European research infrastructure that will allow us to maintain scientific and technological leadership in this promising field of fundamental physics research.”

In January, the ET was granted status as a CERN recognised experiment (RE43), with a collaboration agreement on vacuum technology already in place and a further agreement concerning cryogenics at an advanced stage.

X-ray polarisation probes extreme physics

Accretion disk around magnetar 4U 0142+61 — **Magnetar** Artistic depiction of the accretion disk around the magnetar 4U 0142+61, located in the Cassiopeia constellation 13,000 lights years away. Credit: NASA/JPL-Caltech/R Hurt (SSC)

X-ray astronomy has been around for more than 50 years and remains responsible for a wealth of discoveries. Astronomical breakthroughs have been the result of detailed measurements of the X-ray arrival time, direction and energy. But the fourth measurable parameter of X-rays, their polarisation, remains largely unexplored. Following the first rough measurements of a handful of objects in the 1970s by Martin Weisskopf and co-workers, there was a hiatus in X-ray polarimetry due to the complexity of the detection mechanism. In recent years, in parallel with the emergence of gamma-ray polarimetry, interest in the field has returned. Indeed, after some initial measurements using the Chinese–Italian PolarLight Cubesat launched in October 2018, X-ray polarimetry has reached full maturity with the launch of the first large-scale dedicated observatory in December 2021: the Imaging X-ray Polarimetry Explorer (IXPE), a joint project by NASA and the Italian Space Agency, led by Weisskopf.

The IXPE mission uses gas pixel detectors to measure the polarisation for a range of astronomical sources in the 2-8 keV energy range. Incoming X-rays are absorbed in a gas which results in the emission of a photoelectron, the azimuthal emission direction of which is correlated with the polarisation vector of the incoming photon. Tracking the path of the electron therefore allows the polarisation to be inferred. Accurately measuring the emission direction of the low-energy photoelectron, especially in a space-based detector, has been one of the main IXPE challenges and required decades of detector development.

X-ray polarimetry has reached full maturity with the launch of the first large-scale dedicated observatory

IXPE has already observed a range of sources. Its first public results, posted on arXiv on 18 May, concern a magnetar, a highly magnetic neutron star, called 4U 0142+61, which rotates around its axis in about 8 s and has a magnetic field of 10¹⁰ T. IXPE’s first ever measurement of polarised emission from a magnetar in the X-ray region shows this extreme object to have an energy-integrated polarisation degree of 12%, while in the thermal (2–4 keV) range this is about 12%, and as high as 41% for emission at higher energies (5.5–8 keV). The polarisation angles of the two emission components are orthogonal.

The results appear to agree best with a model where the thermal emission stems from a condensed iron atmosphere: the higher energy emission would be a result of some thermal photons being up-scattered to higher energies when interacting with charged particles following the magnetic field lines. However, since other models link the emission to a gaseous atmosphere heated by a constant bombardment of particles, measurements of additional magnetars are needed.

Fundamental physics

Apart from providing novel insights into neutron-star properties, time-resolved studies of the emission during the rotation period hints at more fundamental physics at play. The spectral profile of 4U 0142+61 was found to be rather constant during the rotation, indicating that the emission does not come from hot-spots, such as the poles, but rather from a large area on the surface. As the magnetic field over such a large area would, however, be expected to vary significantly, so would the polarisation angle of the emitted X-rays. As a result, the net polarisation seen on Earth would largely be blurred out, resulting in a much lower polarisation degree than is observed.

An intriguing explanation for this, note the authors, is vacuum birefringence – an effect predicted to be important in the presence of extreme magnetic fields, but which has never been observed. While for the magnetar the polarisation angle of the emission varies with the emission location, it gets altered as the photons travel through the strong magnetic field in which continuous electron–positron pairs affect their propagation. Only when the magnetic field is weak enough, at around 100 times the radius of the star, does the polarisation angle get frozen. Since this angle is aligned with the magnetic field, which at this point is smoother, the emission will realign the emission travelling towards Earth and allow for a net polarisation.

Although the polarisation degrees measured by IXPE are not high enough to definitively prove vacuum birefringence, the results give a clear hint. Furthermore, the measurements of 4U 0142+61 are only the first of many performed by the IXPE team. Throughout the coming months, detailed measurements of galactic objects such as the Crab Nebula, as well as extra-galactic sources, are predicted to be released. Among these objects there will be other magnetars, the X-ray emission from which will soon bring further understanding of these extreme objects and potentially confirm the existence of vacuum birefringence.

Superconducting magnets: an enabling technology for the discovery of the Higgs boson

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This webinar is focused on the technology of the superconducting magnets used in the LHC. After reviewing the equations for an electromagnet, we show how superconductivity enables much larger magnetic fields in very compact devices, thanks to the possibility of increasing the current density in the windings by more than two order of magnitudes with respect to resistive conductors. We then outline the development of superconducting accelerator magnets from the ISR quadrupoles, up to the LHC and beyond.

We conclude by describing the successive increases of LHC energy since 2008 up to the 6.8 TeV per beam recently achieved, and show how the control of field imperfections has been an essential element for reaching the ultimate luminosity.

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Ezio Todesco was born in Bologna Italy, where he got a PhD in physics. In the 90’s, after a master thesis at CERN, he worked at the Italian national institute of nuclear physics (INFN) on topics related to nonlinear dynamics of particle accelerators, and long-term stability in the planned Large Hadron Collider. He joined the magnet group at CERN in 1998, and has been in charge of the field quality follow-up of the LHC main dipoles and quadrupole during the five-year-long magnet production. After the completion of the production phase, he has been in charge of the magnetic field model of the LHC, following the initial commissioning and the successive energy increases up to 13 TeV centre of mass. Then, he has been involved in the studies of the LHC luminosity upgrade, and he leads the interaction region magnets for HL-LHC since the beginning of the project in 2015.

Why not watch our other related Higgs boson anniversary webinars?

• RF technology for LHC and HL-LHC

• The LHC cryogenics and its adaptation to the operational parameters for beams, related physics and energy preservation

RF technology for LHC and HL-LHC

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This webinar, presented by Frank Gerigk, will provide an overview of the LHC RF system, its superconducting cavities and RF power system. It also introduce the changes, which will be implemented to accelerate the high-intensity beams of the HL-LHC era.

Join this webinar to:
• Learn about the technology that accelerates LHC protons from 450 GeV to 7 TeV.
• Appreciate the development of the superconducting cavities used in the LHC.
• Understand how the LHC system will be modified for HL-LHC and how crab cavities will increase the number of collisions.

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Frank Gerigk is the leader of the Radio Frequency (RF) Group at CERN. After graduating at the Technical University Berlin in 1999, he came to CERN as a fellow to work on RF and beam dynamics for linear accelerators. In 2002, he became staff member at the Rutherford Appleton Laboratory in the UK, continuing with beam dynamics and focussing on halo development in hadron beams. After his return to CERN in 2005, Frank joined the RF group and soon became responsible for the Linac4 RF cavities. He became section leader for Linac RF in 2012, and then for Superconducting RF in 2018. Since 2020 he has been leading the RF group in the new Systems Department.

Why not sign up for our other related Higgs boson anniversary webinars?

• Superconducting magnets: an enabling technology for the discovery of the Higgs boson

• The LHC cryogenics and its adaptation to the operational parameters for beams, related physics and energy preservation

Council decides new measures for Russia and Belarus

Open meeting of the June Council — **Open council** Delegates from CERN’s Member States during the open meeting of the June Council. Credit: CERN-PHOTO-202206-111-1

At its 208th meeting on 16 June, the CERN Council announced further measures in response to the continuing illegal military invasion of Ukraine by the Russian Federation with the involvement of the Republic of Belarus. The Council declared that it intends to terminate CERN’s International Cooperation Agreements (ICAs) with both countries at their expiration dates in 2024. However, the situation will continue to be monitored carefully and the Council stands ready to take any further decision in the light of developments in Ukraine.

CERN’s ICAs normally run for five years and are tacitly renewed for the same period unless a written notice of termination is provided by one party to the other at least six months prior to the renewal date. The ICA with the Russian Federation expires in December 2024, and that with the Republic of Belarus in June 2024.

The latest measures follow those already adopted at an extraordinary meeting of the Council on 8 March, and at the Council’s regular session on 25 March. In addition to the promotion of initiatives to support Ukrainian collaborators and Ukrainian scientific activity in high-energy physics, these measures included the suspension of Russia’s Observer status and the decision not to engage in new collaborations with Russia and its institutions until further notice (CERN Courier May/June 2022 p7).

The Council also decided in June to review CERN’s future cooperation with the Joint Institute for Nuclear Research (JINR) well in advance of the expiration of the current ICA in January 2025. This follows measures adopted at the previous Council sessions to suspend the Observer status of JINR and the participation of CERN scientists in all JINR scientific committees, and vice versa, until further notice. The Council reaffirmed that all decisions taken to date, along with the actions undertaken by the CERN management, which have had a marked impact on the involvement of the Russian Federation and the Republic of Belarus in the scientific programme of the organisation, remain in force.

Ukraine joined CERN as an Associate Member State in 2016 and Ukrainian scientists have long been active in many of the laboratory’s activities. Russian scientists also have a long and distinguished involvement with CERN, and Russia was granted Observer status in recognition of its contributions to the construction of the LHC. At the June Council meeting, the Member States reiterated their denunciation of the continuing illegal military invasion, recalling that the core values of CERN (CERN Courier September/October 2022 p49) have always been based upon scientific collaboration across borders as a driver for peace, and stressing that the aggression of one country against another runs counter to these values.

Tour de QCD and beyond

The 56th Rencontres de Moriond on QCD and High Energy Interactions took place at the Italian resort of La Thuile from 19 to 26 March. More than 100 participants, almost equally split between experimentalists and theorists, were treated to an exciting scientific programme and many in-person interactions, which were especially appreciated after two years of pandemic isolation.

Keeping with the tradition of Moriond, several new experimental results were presented by major experimental collaborations, with participants enjoying ample opportunities to debate cases where measurements and theoretical predictions do not agree. Held 10 years after the Higgs discovery, the conference started with a review of how the Higgs boson came of age – from early exploration to a precision era. An exciting mix of new precision results and interesting observations in Higgs physics were presented, including the first measurement of the Higgs-charm coupling as well as studies of off-shell Higgs production and di-Higgs production by the ATLAS and CMS collaborations.

The first observation of tqγ production by ATLAS as well as many measurements in top-quark physics, including a mass measurement based on single top quarks by CMS, were discussed. Many recent studies of Z and W bosons and their interactions were reported, including a new CMS result that resolved an earlier mild LEP tension in the decay rates of W bosons to leptons, and the observation of triple-W production at the LHC by ATLAS. The LHCb collaboration presented its first measurement of the W mass, while CMS discussed the first observation of WW and triple-J/ψ production in double-parton scattering.

Several sessions were devoted to flavour measurements and anomalies, including possible lepton-flavour universality violations in B-meson decays. LHCb presented the most precise value of the CKM matrix angle γ measured in a single experiment, as well as the most precise measurement of the charm-mixing parameter y_CP. New results on lepton-flavour universality attracted a lot of attention. Among them are LHCb’s measurement of the ratio of Br(B⁺ → K⁺μ⁺μ^–) to Br(B⁺ → K⁺e⁺e^–), which is 3.1σ away from the SM, new LHCb limits on rare B⁰ decays, and the CMS measurement of the Drell–Yan forward–backward asymmetry difference between di-muons and di-electrons. The status of selected Standard Model (SM) calculations was described with the conclusion that the predictions are robust and therefore possible deficiencies of the SM a very unlikely source of the flavour anomalies. A number of talks demonstrated that there are many ways to accommodate the flavour anomalies into a consistent physics picture, which predicts subtle signals at the LHC that could have easily evaded detection so far.

Several speakers emphasised the importance of new creative analysis concepts

Continuing the topic of searches for new physics, several speakers emphasised the importance of new creative analysis concepts, including searching for anomalous energy losses, non-pointing tracks, delayed photons, displaced jets, displaced collimated leptons and tagging missing mass with forward detectors. Among the results of many interesting searches presented at Moriond, a 3σ excess in the number of highly ionising particles reported by the ATLAS collaboration caused some excitement and discussion, indicating that further studies (and statistics!) are very much needed.

Several talks presented theoretical predictions at high orders of perturbative QCD for basic SM processes at the LHC and future lepton colliders, such as the Drell–Yan and jet-production processes. These tour de force computations, representing cutting-edge applications of quantum field theory to collider physics, force us to think about how such advances in the theory of hard hadron collisions can be used to search for physics beyond the SM. Several talks addressed this issue by considering specific physics examples pointing towards new, exciting opportunities during LHC Run 3.

Emphasising the need for a refined knowledge of the fundamental input parameters used to describe hadron collisions, four new extractions of the strong coupling constant were reported, based on HERA, CDF, LEP and CMS data. The role of precision deep-inelastic scattering (HERA) and W/Z (ATLAS/CMS) data in constraining parton distribution functions was clearly elucidated.

An element of nonperturbative QCD that keeps theorists on their toes is hadronic spectroscopy

Turning towards the non-perturbative sector of QCD, a measurement of Λ_c production down to zero transverse momentum allowed the ALICE collaboration to extract the total charm cross-section in pp collisions. Interestingly, the fraction of Λ_c is significantly above the e⁺e^– baseline. Jet substructure measurements presented by ALICE and CMS allow a detailed comparison to Monte Carlo event generators. Furthermore, the first direct observation of the dead-cone effect, a suppression of forward gluon radiation in case of a massive emitter, was presented by the ALICE collaboration using charm-tagged jets.

An element of non-perturbative QCD that keeps theorists on their toes is hadronic spectroscopy. This trend continued at Moriond where the discoveries of several new states were presented, including the same-sign doubly charmed T⁺_cc(c–c–u–d) (LHCb) and the Z^–_cs (c–c–s–u) (BES III). The exploration of the χ_c1, earlier known as X(3872), with the hope of revealing its molecular or tetraquark nature, continues in pp as well as in PbPb collisions.

The best constraint of the charm diffusion coefficient in the quark–gluon plasma (ALICE), jet quenching studies with Z-hadron correlations (CMS) and surprising results on ridge structures in γp and γPb collisions (ATLAS) were presented during a dedicated heavy-ion session. Interestingly, by studying the abundant nuclei produced in heavy-ion collisions, the ALICE collaboration ruled out simple coalescence models for antideuteron production in PbPb collisions.

Finally, the current status of the muon anomalous magnetic moment was reviewed. The experimental value presented last year by the Fermilab g-2 collaboration shows a 1.5–4.2σ discrepancy with the SM prediction, depending on the theoretical baseline. An interesting comparison between continuum and lattice computations of the hadronic vacuum polarisation contributions was presented, and a new lattice result on hadronic light-by-light scattering was described, indicating that this “troublemaking” contribution is being brought under theoretical control.

Exciting experimental results and developments in the theory of QCD and high-energy interactions that, perhaps, remained somewhat hidden during the pandemic years, were on full display at Moriond, making the 56th edition of this conference a resounding success.

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