Praxis Archives – Page 24 of 179

High-energy interactions in Bologna

**Welcome back** Discussions at ICHEP showed the field to be in a fascinating period. Credit: ICHEP

Involving around 1500 participants, 17 parallel sessions, 900 talks and 250 posters, ICHEP2022 (which took place in Bologna from 6 to 13 July) was a remarkable week of physics, technology and praxis. The energy and enthusiasm among the more than 1200 delegates who were able to attend in person was palpable. As the largest gathering of the community since the beginning of the pandemic – buoyed by the start of LHC Run 3 and the 10th anniversary of the Higgs-boson discovery – ICHEP2022 served as a powerful reminder of the importance of non-digital interactions.

Roberto Tenchini’s (INFN Pisa) heroic conference summary began with a reminder: it is 10 years since ICHEP included a session titled “Standard Model”, the theory being so successful that it now permeates most sessions. As an example, he highlighted cross-section predictions tested over 14 orders of magnitude at the LHC. Building on the Higgs@10 symposium at CERN on 4 July, the immense progress in understanding the properties and interactions of the Higgs boson (including legacy results with full Run 2 statistics in two papers by ATLAS and CMS published in Nature on 4 July) was centre stage. CERN Director-General Fabiola Gianotti gave a sweeping tour of the path to discovery and emphasised the connections between the Higgs boson and profound structural problems in the SM. Many speakers highlighted the concomitant role of the Higgs boson in exploring new physics, dashing notions that future precision measurements are “business as usual”. Chiara Mariotti (INFN Torino) pointed out that only 3% of the total Higgs data expected at the LHC has been analysed so far.

Hot topics

Another hot electroweak topic was CDF’s recent measurement of the mass of the W boson, as physicists try to understand what could cause it to lie so far from its prediction and from previous measurements. Andrea Rizzi (Pisa) confirmed that CMS is working hard on a W-mass analysis that will bring crucial information, on a time-scale to be decided. Patience is king with such a complex analysis, he said: “we are really trying to do the measurement the way we want to do it.”

CMS presented a total of 85 parallel talks and 28 posters, including new searches related to b-anomalies with taus, and the most precise measurement of B_s → μ⁺μ^–. Among new results presented by ATLAS in 71 parallel talks and 59 posters were the observation of a four charm–quark state consistent with one seen by LHCb, joint-polarisation measurements of the W and Z bosons, and measurements of the total proton–proton cross section and the ratio of the real vs imaginary parts of the elastic-scattering amplitude. ATLAS and CMS also updated participants on many searches for new particles, in particular leptoquarks. Among highlights were searches by ATLAS for events with displaced vertices, which could be caused by long-lived particles, and by CMS for resonances decaying to Higgs bosons and pairs of either photons or b quarks, which show interesting excesses. “Se son rose fioriranno!” said Tenchini.

The sigmas are rather higher for exotic hadrons. LHCb presented the discovery of a new strange pentaquark (with a minimum quark content ccuds) and two tetraquarks (one corresponding to the first doubly charged open-charm tetraquark with csud), taking the number of hadrons discovered at the LHC so far to well over 60, and introducing a new exotic-hadron naming scheme for “particle zoo 2.0” (Exotic hadrons brought into order by LHCb). LHCb also reported the first evidence for direct CP violation in the charm system (LHCb digs deeper in CP-violating charm decays) and a new precise measurement of the CKM angle γ. Vladimir Gligorov (LPNHE) described how, in addition to the flavour factories LHCb and Belle II, experiments including ATLAS, CMS, BESIII, NA62 and KOTO will be crucial to enable the next level of understanding in quark mixing. Despite no significant new results having been presented, the status of tests of lepton flavour universality (LFU) in B decays by LHCb generated lively discussions, while Toshinori Mori (Tokyo) described exciting prospects for LFU tests in charged-lepton flavour experiments, in particular MEG-II, which has just started operations at PSI, and the upcoming Mu2e and MUonE experiments.

ICHEP2022 served as a powerful reminder of the importance of non-digital interactions

Moving to leptons that are known to mix, neutrinos continue to play very important roles in understanding the smallest and largest scales, said Takaaki Kajita (Tokyo) via a link from the IUPAP Centennial Symposium taking place in parallel at ICTP Trieste. Status reports on DUNE, Hyper-K, JUNO, KM3NeT and SNB showed how these detectors will help constrain the still poorly-known PNMS matrix that describes leptonic mixing, while new results from NOvA and STEREO further reveal anomalous behaviour. Among the major open questions in neutrino physics summed-up by theorist Joachim Kopp (Mainz and CERN) were: how do neutrinos interact? What explains the oscillation anomalies? And how do supernova neutrinos oscillate?

Several plenary presentations showcased the increasing complementarity with astroparticle physics and cosmology, with the release of the first-science images from the James Webb Space Telescope on 12 July adding spice (Webb opens new era in observational astrophysics). Multiband gravitational-wave astronomy across 12 or more orders of magnitude in frequency will bloom in the next decade, predicted Giovanni Andrea Prodi (Trento), while larger datasets and synchronisation of experiments offer a bright future in all messengers, said Gwenhael De Wasseige (Louvain): “We are just at the beginning of the story.” The first results from the Lux–Zeplin experiment were presented, setting the tightest limits on spin-independent WIMP–nucleon cross-sections for WIMP masses above 9 GeV (CERN Courier September/October 2022 p13), while the increasingly crowded plot showing limits from direct searches for axions illustrate the vibrancy and shifting focus of dark-matter research. Indeed, among several sessions devoted to the exploration of high-energy QCD in heavy-ion, proton–lead and proton–proton collisions, Andrea Dainese (INFN Padova) described how the LHC is not only a collider of nuclei but an (anti-)nuclei factory relevant for dark-matter searches.

The unique ability of theorists to put numerous results and experiments in perspective was on full display. We should all renew the enthusiasm that built the LHC, and be a lot more outspoken about the profound ideas we explore, urged Veronica Sanz (Sussex); after all, she said, “we are searching for something that we know should be somewhere.” A timely talk by Gavin Salam (Oxford) summarised the latest understanding of QCD effects relevant to the muon g-2 and W-mass anomalies and also to future Higgs-boson measurements, concluding that, as we approach high precision, we should expect to be confronted by conceptual problems that we could, so far, ignore.

The unique ability of theorists to put numerous results and experiments in perspective was on full display

Accelerators (including a fast-paced summary of the HL-LHC niobium-tin magnet programme from Lucio Rossi), detectors (68 talks and posters revealing an increasingly holistic approach to detector design), computing (highlighting a period of rapid evolution thanks to optimisation, modernisation, machine-learning algorithms and increasing hardware diversity), industry, diversity and outreach were addressed in detail. A highly acclaimed outreach event in Bologna’s Piazza Maggiore on the evening of 12 July saw thousands of people listen to Fabiola Gianotti, Guido Tonelli, Gian Giudice and Antonio Zoccoli discuss the implications of the Higgs-boson discovery.

Only the narrowest snapshot of proceedings is possible in such a short report. What was abundantly clear from ICHEP2022 is that, following the discovery of the Higgs boson and as-yet no new particles beyond the SM, the field is in a fascinating and challenging period where confusion is more than matched by confidence that new physics must exist. The strategic direction of the field was addressed in two wide-ranging round-table discussions where laboratory directors and senior physicists answered questions submitted by participants. Much discussion concerned future colliders, and addressed a perceived worry in some quarters that the field is entering a period of decline. For anyone following the presentations at ICHEP2022, nothing could be further from the truth.

Your guide to becoming a CERN guide

**Going underground** Bryan Pérez Tapia in the ATLAS cavern in December 2021. Credit: B Pérez Tapia

Do you remember the first time you heard about CERN? The first time someone told you about that magical place where bright minds from all over the world work together towards a common goal? Perhaps you saw a picture in a book, or had the chance to visit in person as a student? It is experiences like these that motivate many people to pursue a career in science, whether in particle physics or beyond.

In 2016 I had the pleasure of visiting CERN on a school trip. We toured the Synchrocyclotron and the SM18 magnet test facility. I was hooked. The tour guides talked with passion about the laboratory, the film presenting CERN’s first particle accelerator and the laboratory’s mission, and all those big magnets being tested in SM18. It was this experience that motivated me to study physics at university and to try to come back as soon as I could.

Accreditation

That chance arrived in September 2021 when I started a one-year technical studentship as editorial assistant on the Courier. From the first day I was eager to see as much as I could. During the final months of Long Shutdown 2, my supervisor and I visited the ATLAS cavern. The experience motivated me to ask one of my newly made friends, also a technical student who had recently become a tour guide, how to apply. The process was positive and efficient. After completing all the required courses from the learning hub and shadowing experienced guides, I became a certified ATLAS underground guide in November 2021 and gave my first tour soon after. I was nervous and struggled with the iris scanner when accessing the cavern, but all ended well, and further tours were scheduled. Then, in mid-December, all in-person tours were cancelled due to COVID-19 restrictions. I needn’t have worried, as CERN was fully geared up to provide virtual visits. Among my first virtual audience members were students from the high school that brought me to CERN five years earlier and from my university, Nottingham Trent in the UK.

The most satisfying thing is people’s enthusiasm and their desire to learn more about CERN and its mission

The virtual visits were quite challenging at first. It was harder to connect with the audience than during an in-person visit. But managing these difficulties helped me to improve my communication skills and to develop self-confidence. During this period, I conducted more than 10 virtual visits for different institutes, universities, family and friends, in both English and Spanish.

At the beginning of March 2022, CERN moved into “level yellow” and in-person visits were resumed. Although only possible for a short period, I had the chance to guide visitors underground and had the honour of guiding the last in-person visit into the ATLAS cavern on 23 March before preparations for LHC Run 3 got under way. With the ATLAS cavern then off-limits, I signed up to present at as many CERN visit points as possible. At the time of writing, I am a guide for the Synchrocyclotron, the ATLAS Visitor Centre, Antimatter Factory, Data Centre, Low Energy Ion Ring and CERN Control Centre.

Get involved

The CERN visits service always welcomes new guides and is working towards opening new visit points. Anyone working at CERN or registered as a user can take part by signing up for visit-point training on the tour-guide website: guides.web.cern.ch. General training for new guides is also available. All you need to show CERN to the public is passion and enthusiasm, and you can sign up for as many or as few as your day job allows. Diversity is encouraged and those who are multilingual are also highly valued.

Today, visits are handled by a dedicated section in the Education, Communications and Outreach group. The number of visitors has gradually increased over recent years, with 152,000 annual visitors before the pandemic started, excluding special events such as the CERN Open Days. The profile of visitors ranges from school pupils and university students to common-interest groups such as engineers and scientists, politicians and VIPs, and people with a wide range of interests and educational levels.

The benefits of becoming a CERN guide are immense. It gives you access to areas that would otherwise not be possible, the chance to experience important events in-person and to see your work at CERN, whatever it involves, from a fresh perspective. My personal highlight was watching test collisions at 13.6 TeV before the official start of Run 3 while showing Portuguese high-school students the ATLAS control room. The most satisfying thing is people’s enthusiasm and their desire to learn more about CERN and its mission. I particularly remember how a small child asked me a question about the matter–antimatter asymmetry of the universe, and how another young visitor ran from Entrance B at the end of a tour just to tell me how much she loved the visit.

The visits service makes it as easy as possible to get involved, and exciting times for guides lie ahead with the opening of the CERN Science Gateway next year, which will enable CERN to welcome even more visitors. If a technical student based at CERN for just one year can get involved, so can you!

Science for peace? More than ever!

What happened? A tragedy fell upon Ukraine and found many in despair or in a dilemma. After 70 mainly peaceful years for much of Europe, we were surprised by war, because we had forgotten that it takes an effort to maintain peace.

Having witnessed the horrors of war first hand, several years as a soldier and then as a displaced person, I could not imagine that humanity would unleash another war on the continent. As one of its last witnesses, I wonder what advice should be passed on, especially to younger colleagues, about what to do in the short term, and perhaps more importantly, what to do afterwards.

Scientists have a special responsibility. Fortunately, there is no doubt today that science is independent of political doctrines. There is no “German physics” any more. We have established human relationships with our colleagues based on our enthusiasm for our profession, which has led to mutual trust and tolerance.

This has been practised at CERN for 70 years and continued at SESAME, where delegates from Israel, Palestine, Iran, Cyprus, Turkey and other governments sit peacefully around a table. Another offshoot of CERN, the South East European International Institute for Sustainable Technologies (SEEIIST), is in the making in the Balkans. Apart from fostering science, the aim is to transfer ethical achievements from science to politics: science diplomacy, as it has come to be known. In practice, this is done, for example, in the CERN Council where each government sends a representative and an additional scientist who work effectively together on a daily basis.

**Herwig Schopper** was CERN Director-General from 1981 to 1988, and is a founder of SESAME and the future SEEIIST facility. Credit: CERN-PHOTO-201906-169-6

In the case of imminent political conflicts, “Science for Peace” cannot of course help immediately, but occasionally opportunities arise even for this. In 1985, when disarmament negotiations between Gorbachev and Reagan in Geneva reached an impasse, one of the negotiators asked me to invite the key experts to CERN on neutral territory, and at a confidential dinner the knot was untied. This showed how trust built up in scientific cooperation can impact politics.

Hot crises put us in particularly difficult dilemmas. It is therefore understandable that the CERN Council has to follow, to a large extent, the guidelines of the individual governments and sometimes introduce harsh sanctions. This leads to considerable damage for many excellent projects, which should be mitigated as much as possible. But it seems equally important to prevent or at least alleviate human suffering among scientific colleagues and their families, and in doing so we should allow them tolerance and full freedom of expression. I am sure the CERN management will try to achieve this, as in the past.

Day after

But what I consider most important is to prepare for the situation after the war. Somehow and sometime there will be a solution to the Russian invasion. On that “day after”, it will be necessary to talk to each other again and build a new world out of the ruins. This was facilitated after World War II because, despite the Nazi reign of terror, some far-sighted scientists maintained human relations as well as scientific ones. I remember with pleasure how I was invited to spend a sabbatical year in 1948 in Sweden with Lise Meitner. I was also one of the first German citizens to be invited to a scientific conference in Israel in 1957, where I was received without resentment.

CERN was the first scientific organisation whose mission was not only to conduct excellent science, but also to help improve relations between nations. CERN did this initially in Europe with great success. Later, during the most intense period of the Cold War, it was CERN that signed an agreement with the Russian laboratory in Serpukhov in the 1960s. Together with contacts with JINR in Dubna, this offered one of the few opportunities for scientific West–East cooperation. CERN followed these principles during the occupation of the Czechoslovak Socialist Republic in 1968 and during the Afghanistan crisis in 1979.

The aim is to transfer ethical achievements from science to politics

CERN has become a symbol of what can be achieved when working on a common project without discrimination, for the benefit of science and humanity. In recent decades, when peace has reigned in Europe, this second goal of CERN has somewhat receded into the background. The present crisis reminds us to make greater efforts in this direction again, even more so when many powers disregard ethical principles or formal treaties by pretending that their fundamental interests are violated. Science for Peace tries to help create a minimum of human trust between governments. Without this, we run the risk that future political treaties will be based only on deterrence. That would be a gloomy world.

A vision for the day after requires courage and more Science for Peace than ever before.

Counting down to LISA

**Looking forward** Stefano Vitale of the University of Trento is co-lead of the LISA consortium and principal investigator for LISA Pathfinder. Credit: S Vitale

What is LISA?

LISA (Laser Interferometer Space Antenna) is a giant Michelson interferometer comprising three spacecraft that form an equilateral triangle with sides of about 2.5 million km. You can think of one satellite as the central building of a terrestrial observatory like Virgo or LIGO, and the other two as the end stations of the two interferometer arms. Mirrors at the two ends of each arm are replaced by a pair of free-falling test masses, the relative distance between which is measured by a laser interferometer. When a gravitational wave (GW) passes, it alternately stretches one arm and squeezes the other, causing these distances to oscillate by an almost imperceptible amount (just a few nm). The nature and position of the GW sources is encoded in the time evolution of this distortion. Unlike terrestrial observatories, which keep their arms locked in a fixed position, LISA must keep track of the satellite positions by counting the millions of wavelengths by which their separation changes each second. All interferometer signals are combined on the ground and a sophisticated analysis is used to determine the differential distance changes between the test masses.

What will LISA tell us that ground-based observatories can’t?

Most GW sources, such as the merger of two black holes detected for the first time by LIGO and Virgo in 2015, consist of binary systems; as the two compact companions spiral into each other, they generate GWs. In these extreme binary mergers, the frequency of the GWs decrease both with the increasing mass of the objects and with increasing distance from their final merger. GWs with frequencies down to about a few Hz, corresponding to objects with masses up to a few thousand solar masses, are detectable from the ground. Below that, however, Earth’s gravity is too noisy. To access milli-Hertz and sub-milli-Hertz frequencies we need to go to space. This low-frequency regime is the realm of supermassive objects with millions of solar masses located in galactic centres, and also where tens of thousands of compact objects in our galaxy, including some of the Virgo/LIGO black holes, emit their signals for years and centuries as they peacefully rotate around each other before entering the final few seconds of their collapse. The LISA mission will therefore be highly complementary to existing and future ground-based observatories such as the Einstein Telescope. Theorists are excited about the physics that can be probed by multiband GW astronomy.

When and how did you get involved in LISA?

LISA was an idea by Pete Bender and colleagues in the 1980s. It was first proposed to the European Space Agency (ESA) in 1993 as a medium-sized mission, an envelope that it could not possibly fit. Nevertheless, ESA got excited by the idea and studies immediately began toward a larger mission. I became aware of the project around that time, immediately fell in love with it and, in 1995, joined the team of enthusiastic scientists, led by Karsten Danzmann. At the time it was not clear that a detection of GWs from ground was possible, whereas unless general relativity was deadly wrong, LISA would certainly detect binary systems in our galaxy. It soon became clear that such a daring project needed a technology precursor, to prove the feasibility of test-mass freefall. This built on my field of expertise, and I became principal investigator, with Karsten as a co-principal investigator, of LISA Pathfinder.

What were the key findings of LISA Pathfinder?

Pathfinder essentially squeezed one of LISA’s arms from millions of kilometres to half a metre and placed it into a single spacecraft: two test masses in a near-perfect gravitational freefall with their relative distance tracked by a laser interferometer. It launched in December 2015 and exceeded all expectations. We were able to control and measure the relative motion of the test masses with unprecedented accuracy using innovative technologies comprising capacitive sensors, optical metrology and a micro-Newton thruster system, among others. By reducing and eliminating all sources of disturbance, Pathfinder observed the most perfect freefall ever created: the test masses were almost motionless with respect to each other, with a relative acceleration less than a millionth of a billionth of Earth’s gravitational acceleration.

What is LISA’s status today?

LISA is in its final study phase (“B1”) and marching toward adoption, possibly late next year, after which ESA will release the large industrial contracts to build the mission. Following Pathfinder, many necessary technologies are in a high state of maturity: the test masses will be the same, with only minor adjustments, and we also demonstrated a pm-resolution interferometer to detect the motion of the test masses inside the spacecraft – something we need in LISA, too. What we could not test in Pathfinder is the million-kilometre-long pm-resolution interferometer, which is very challenging. Whereas LIGO’s 4 km-long arms allow you to send laser light back and forth between the mirrors and reach kW powers, LISA will have a 1 W laser: if you try to reflect it off a small test-mass 2.5 million km away, you get back just 20 photons per second! The instrument therefore needs a transponder scheme: one spacecraft sends light to another, which collects and measures the frequency to see if there is a shift due to a passing GW. You do this with all six test masses (two per spacecraft), combining the signals in one heck of an analysis to make a “synthetic” LIGO. Since this is mostly a case of optics, you don’t need zero-g space tests, and based on laboratory evidence we are confident it will work. Although LISA is no longer a technology-research project, it will take a few more years to iron out some of the small problems and build the actual flight hardware, so there is no shortage of papers or PhD theses to be written.

How is the LISA consortium organised?

ESA’s science missions are often a collaboration in which ESA builds, launches and operates the satellite and its member states – via their universities and industries – contribute all or part of the scientific instruments, such as a telescope or a camera. NASA is a major partner with responsibilities that include the lasers, the device to discharge the test masses as they get charged up by cosmic rays, and the telescope to exchange laser beams among the satellites. Germany, which holds the consortium’s leadership role, also shares responsibility for a large part of the interferometry with the UK. Italy leads the development of the test-mass system; France the science data centre and the sophisticated ground testing of LISA optics; and Spain the science-diagnostics development. Critical hardware components are also contributed by Switzerland, the Netherlands, Belgium, the Czech Republic, Denmark and Poland, while scientists worldwide contribute to various aspects of the preparation of mission operation, data analysis and science utilisation. The LISA consortium has around 1500 members.

What is the estimated cost of the mission, and what is industry’s role?

A very crude estimate of the sum of ESA, NASA and member-state contributions may add up to something below two billion dollars. One of the main drivers of ESA’s scientific programme is to maintain the technological level of European aerospace, so the involvement of industry, in close cooperation with scientific institutes, is crucial. After having passed the adoption phase, ESA will grant contracts to prime industrial contractors who take responsibility for the mission. To foster industrial competition during the study phase, ESA has awarded contracts to two independent contractors, in our case Airbus and Thales Alenia. In addition, international partners and member-state contributions often, if not always, involve industry.

What scientific and technological synergies exist with other fields?

LISA will look for deviations from general relativity, in particular the case where compact objects fall into a supermassive black hole. In terms of their importance, deviations in general relativity are a very close cousin of deviations from the Standard Model of particle physics. Which will come first we don’t know, but LISA is certainly an outstanding laboratory for fundamental gravitational physics. Then there are expectations for cosmology, such as tracing the history of black-hole formation or maybe detecting stochastic backgrounds of GWs, such as “cusps” predicted in string theory. Wherever you push the frontiers to investigate the universe at large, you push the frontiers of fundamental interactions – so it’s not surprising that one of our best cosmologists now works at CERN! Technologically speaking, we just started a collaboration with CERN’s vacuum group. In LISA we have a tiny vacuum volume in the region where the test masses are located, and it is full of components and cables. It was a big challenge for Pathfinder, but for LISA we definitely need to understand more. The CERN vacuum group is really interested in understanding this, so we are very happy with this new collaboration. As with LIGO, Advanced Virgo and the Einstein Telescope, LISA is a CERN-recognised experiment.

There is no other space mission with as many papers published about its science expectations before it even leaves the ground

What’s the secret to maintaining the momentum in a complex, long-term global project in fundamental physics?

The LISA mission is so fascinating that it is “self-selling”. Scientists liked it, engineers liked it, industry liked it, space agencies like it. Obviously Pathfinder helped a lot – it meant that even in the darkest moments we knew we were “real”. But in the meantime, our theory colleagues did so much work. As far as I know, there is no other space mission with as many papers published about its science expectations before it even leaves the ground. It’s not just that the science is inspiring, but the fact that you can calculate things. The instrumentation is also so fascinating that students want to do it. With Pathfinder, we faced many difficulties. We were naïve in thinking that we could take this thing that we built in the lab and turn it into an industrial project. Of course we needed to grow and learn, but because we loved the project so much, we never ever gave up. One needs this mind-set and resilience to make big scientific projects work.

When do you envision launch?

Currently it’s planned for the mid-2030s. This is a bit in the future at my age, but I am grateful to have seen the launch of LISA Pathfinder and I am happy to think that many of my young colleagues will see it, and share the same emotions we did with Pathfinder, as a new era in GW astronomy opens up.

Capturing the intangible

Every Nobel Prize comes with a story, and Leonard A Cole’s Chasing the Ghost offers a new perspective on that of Fred Reines, best known for discovering the electron neutrino with Clyde Cowan in 1956. While Cowan passed away in 1974, Reines went on to win the Nobel Prize in Physics for their discovery in 1995. Cole, Reines’s cousin, describes the life of Fred Reines – focusing on both his scientific career and extracurricular interests – in a personal way, showing obvious admiration for his elder cousin.

After participating in the Manhattan Project and assisting in developing nuclear weapons in the 1940s, Reines pivoted to study neutrinos, the fundamental particles emitted in nearly every nuclear reaction, which he describes as “the tiniest quantity of reality ever imagined by a human being”. While being tiny quantities, neutrinos are abundant, yet mysterious, and Reines’s work opened the door to better understand these particles. His research spanned the next five decades, and positions at universities and laboratories across the US, and the techniques that he developed to study neutrinos are used to this day.

Rainbows and Things

Throughout Chasing the Ghost, Cole splits his time between describing Reines’s career and his extracurricular pursuits. Even among his colleagues, Reines was known to be a prolific singer, performing with groups including the Los Alamos Light Opera Association and the Cleveland Orchestra Chorus. Time spent pondering these activities allowed Reines to connect better with non-science-major students when lecturing at universities. Reines famously taught his course “Rainbows and Things” to much acclaim at the University of California, Irvine, where he encouraged students to think deeply about the connection between classroom physics and the natural world. Cole explains that the course name, and much of its philosophy, stems from the play Finian’s Rainbow, which Reines performed in 1955.

Throughout his later life, it became apparent that Reines thought his accomplishments deserved more praise than they had received. In fact, it was only after he gave up hope of winning the Nobel Prize that he won it in 1995. Reines had been passed up on many occasions, including in 1988 when the team that discovered the second type of neutrinos was awarded the prize before him. Cole shares a humorous anecdote (in hindsight): at a CERN conference with both Reines and 1988 laureate Leon Lederman in attendance, a speaker suggested an experiment to search for the third type of neutrino, the tau neutrino. However, as the speaker lamented, it seemed as if no one would perform this type of experiment, “because evidently they only give a Nobel Prize for the detection of every other neutrino.” While the room may have burst into laughter, Fred Reines didn’t budge.

Regardless, Reines’s dedication to understand neutrinos persisted until the end of his life. Shortly before passing, when he heard of the ground-breaking news from Super-Kamiokande that neutrinos oscillate, he astutely asked “What’s the mass?”, understanding the implications of this result.

The work spearheaded by Reines and his contemporaries has made a lasting impact on the field of particle physics, that continues today. As Cole explains, the subfield of neutrino physics has blossomed to include large, international experimental collaborations, which have found even more unexpected results. Those results have spurred investigators to plan ambitious projects, such as the IceCube experiment in Antarctica, the DUNE experiment in the US, and Hyper-Kamiokande in Japan.

Inspiration

Today’s neutrino detectors are getting bigger and bigger. However, their forerunners can still serve a purpose: inspiration. Several detectors from Reines’s era are now exhibited, such as the Gargamelle detector at CERN. After discovering the electron neutrino, the race was on to build experiments to better understand neutrino properties, and Gargamelle was one such detector. Today, it is on display at the CERN Microcosm, perhaps inspiring a new generation of neutrino physicists.

Overall, Leonard A Cole’s Chasing the Ghost will inspire readers, especially those new to thinking about neutrino physics. Fred Reines’s work, with its focus on a deep understanding of these mysterious, abundant particles, continues to bear fruit to this day. There is no telling what the next neutrino experiments will uncover, but it’s a guarantee that sharp thinkers like Reines will be necessary in this field in the generations to come.

Accelerating knowledge transfer with physics

Countries in Africa participating in ACP2021 — **Science for society** Map showing the countries in Africa with home institutes participating in ACP2021 (green). Credit: K Assamagan

Science and technology are key instruments for a society’s economic growth and development. Yet Africa’s science, innovation and education have been chronically under-funded. Transferring knowledge, building research capacity and developing competencies through training and education are major priorities for Africa in the 21st century. Physics combines these priorities by extending the frontiers of knowledge and inspiring young people. It is therefore essential to make basic knowledge of emerging technologies available and accessible to all African citizens to build a steady supply of trained and competent researchers.

In this spirit, the African School of Fundamental Physics and Applications was initiated in 2010 as a three-week biennial event. To increase networking opportunities among participants, the African Conference on Fundamental and Applied Physics (ACP) was included as a one-week extension of the school. The first edition was held in Namibia in 2018 and the second, co-organised jointly by Mohammed V University and Cadi Ayyad University in Morocco, was rebranded ACP2021, originally scheduled to take place in December but postponed due to COVID-19. The virtual event held from 7 to 11 March attracted more than 600 registrants, an order of magnitude higher than its first edition.

The ACP2021 scientific programme covered the three major physics areas of interest in Africa defined by the African Physical Society: particles and related applications; light sources and their applications; and cross-cutting fields covering accelerator physics, computing, instrumentation and detectors. The programme also included topics in quantum computing and quantum information, as well as machine learning and artificial intelligence. Furthermore, ACP2021 focused on topics related to physics education, community engagement, women in physics and early-career physicists. The agenda was stretched to accommodate different time zones and 15 parallel sessions took place.

Welcome speeches by Hassan Hbid (Cadi Ayyad University) and by Mohammed Rhachi (Mohammed V University) were followed by a plenary talk by former CERN Director-General Rolf Heuer, “Science bridging Cultures and Nations” and an overview of the African Strategy for Fundamental and Applied Physics (ASFAP). Launched in 2021, the ASFAP aims to increase African education and research capabilities, build the foundations and frameworks to attract the participation of African physicists, and establish a culture of awareness of grassroots physics activities contrary to the top-down strategies initiated by governments. Shamila Nair-Bedouelle (UNESCO) conveyed a deep appreciation of and support for the ASFAP initiative, which is aligned with the agenda of the United Nations Sustainable Development Goals. A rich panel discussion followed, raising different views on physics education and research roadmaps in Africa.

A central element of the ACP2021 physics programme is the ASFAP community planning meeting, where physics and community-engagement groups discussed progress in soliciting the community input that is critical for the ASFAP report. The report will outline the direction for the next decade to encourage and strengthen higher education, capacity building and scientific research in Africa.

The motivation and enthusiasm of the ACP2021 participants was notable, and the efforts in support of research and education across Africa were encouraged. The next ACP in 2023 will be hosted by South Africa.

Seminar remembers eminent David Cox

**Giant of the field** Statistician David Cox was a long-time supporter of the PHYSTAT series. Credit: General Motors Cancer Research Foundation

David Cox, a giant in the world of statistics, passed away earlier this year at the age of 97. As he had been a contributor to PHYSTAT workshops and was a supporter of its activities, a seminar held on 23 March was dedicated to his memory. Brad Efron (Stanford) referred to Cox as the world’s most famous statistician – an assessment confirmed by Cox being the first recipient of the International Prize in Statistics, roughly the equivalent of a Nobel Prize. The citation mentioned a lifelong series of contributions to statistics spanning many subjects. In particular, it emphasised his work on what is now called Cox’s proportional hazards model, which provides a very useful way to implement regression analysis of survival times (the times to an event of interest such as the death of a person or failure of a machine). His contribution is ranked 16th in Nature’s list of most-cited papers in any subject.

Heather Battey (Imperial College), who collaborated closely with Cox for the past five years, described how he was still very active until his very last days, and highlighted his helpful and charming personality.

Long-time collaborator Nancy Reid (Toronto) concurred, admiring his ability to see through extraneous detail and concentrate on the essence of the problem. She remembers going with him to watch Verdi’s Ernani, sung in Italian, in Budapest when they were both attending a statistics meeting there. So that Reid wouldn’t be completely lost, Cox kindly summarised the lengthy and convoluted plot by telling her “The tenor is in love with the soprano, and the baritone is trying to keep them apart.”

It was a special pleasure to have Cox available at our meetings, and he was always prepared to explain statistical issues in informal discussions with particle physicists. Bob Cousins (UCLA) recalled the talks Cox had given at PHYSTAT meetings in 2005, 2007 and 2011. He compared and contrasted frequentist statistics and the “five faces” of Bayesian statistics, repeatedly warning of the dangers of “treacherous” uniform prior probability densities used in attempts to represent ignorance. He alluded to a general key problem in frequentist statistics, that of ensuring that the long run used to calibrate coverage is relevant to the specific data sample being analysed. He also discussed in more technical detail issues of testing multiple hypotheses, including graphical methods. Cox and Reid further offered published thoughts on problems presented to them by LHC physicists. Cousins concluded that we would do well to read Cox’s contributions again.

PHYSTAT is pleased and honoured to have had the opportunity of paying its respect to a very eminent statistician and a wonderful person. His memory will long be with us.

SLAC Summer Institute 2022 : Golden Opportunities Puzzles & Surprises – Past & Present (SSI 2022)

The SLAC Summer Institute (SSI) is an annual two-week-long Summer School tradition since 1973. The theme of the 50th SLAC Summer Institute for this Golden Anniversary year’s installment is “Golden Opportunities: Puzzles & Surprises – Past & Future”. These SSI lectures will discuss how our attempts to solve and understand the various puzzles and surprises presented to us by nature, whether we have been successful or not, have pushed – and continue to push – our field forward. This SSI intends to inspire reinvigorated effort for new revelations on these fundamental puzzles. SSI is especially targeted for graduate students and postdocs while senior researchers are also welcome.

This year’s SSI is proceeding with the on SLAC site full program in person, with lectures in the morning, Q&A discussions and projects in the afternoon. There will be also special 50th anniversary sessions at the end of SSI to look back at the history of SSI. We are evaluating the COVID-19 situation continuously and preparing precautionary measures, but unless the situation is taking a worse turn than the present orange level in California the program remains on site.

For SSI logistics questions, please use the contact us link on the web page

CERN Courier’s Higgstory

higgstory_collage — **Through the years** *CERN Courier* issues covering famous milestones of the Higgs discovery throughout the decades. Credit: K Bernhard-Novotny

It was March 1977 when the hypothetical Higgs boson first made its way onto the pages of this magazine. Reporting on a talk by Steven Weinberg at the Chicago Meeting of the American Physical Society, the editors noted the dramatic success of gauge theories in explaining recent discoveries at the time — beginning with the observation of the neutral current at CERN in 1973 and the “new physics” following the J/ψ discovery at Brookhaven and Stanford the following year, observing: “The theories also postulate a set of scalar particles in a similar mass range… If Higgs bosons exist, they will affect particle behaviour at all energies. However, their postulated interactions are even weaker than the normal weak interactions. The effects would only be observable on a very small scale and would usually be drowned out by the stronger interactions.”

vol19-issue9-p395figa — Harvard professors Sheldon Glashow (left) and Steven Weinberg at a news conference at Harvard after it was announced that they would share the 1979 Physics Nobel Prize with Abdus Salam. Credit: Photopress. Source: *CERN Courier* December 1979.

The topic clearly drew the attention of readers, as just a few issues later, in September 1977, the editors delved deeper into the origins of the Higgs boson and its role in spontaneous symmetry breaking, offering Abdus Salam’s “personal picture” to communicate this abstruse concept: “Imagine a banquet where guests sit at round tables. A bird’s eye view of the scene presents total symmetry, with serviettes alternating with people around each table. A person could equally well take a serviette from his right or from his left. The symmetry is spontaneously broken when one guest decides to pick up from his left and everyone else follows suit.”

Within a year, CERN Courier was on the trail of how the Higgs boson might show itself experimentally. Reporting on a “Workshop on Producing High Luminosity Proton–Antiproton Storage Rings” held at Berkeley, the April 1978 issue stated: “As well as the intermediate boson, the proton–antiproton colliders could give the first signs of the Higgs particles or of other unexpected states. While the discovery of weak neutral currents and charm provided impressive evidence for the gauge-theory picture that unifies electromagnetic and weak interactions, one prediction of this picture is the existence of spinless Higgs bosons. If these are not found at higher energies, some re-thinking might be required.” In the December 1978 issue, with apologies to Neil Armstrong, the Courier ran a piece titled “A giant LEP for mankind”. The hope was that with LEP, physicists had the tool to explore in depth the details of the symmetry breaking mechanism at the heart of weak interaction dynamics.

vol18-issue12-p434fig — A drawing of the LEP tunnel cross-section at the location of a bending magnet. The tunnel itself could be built using similar techniques to those used in the construction of the CERN SPS. Source: *CERN Courier* December 1978.

The award of the 1979 Nobel Prize in Physics to Weinberg, Glashow and Salam for the electroweak theory received full coverage in December that year, with the Courier expressing confidence in the Higgs: “Another vital ingredient of the theory which remains to be tested are the Higgs particles of the spontaneous symmetry breaking mechanism. Here the theory is still in a volatile state and no firm predictions are possible. But this mechanism is crucial to the theory, and something has to turn up.”

A Higgs for the masses

To many people, wrote US theorist Sam Treiman in November 1981, the Higgs particle looks somewhat artificial — “a kind of provisional stand-in for deeper effects at a more fundamental level”. Four years later, “with several experiments embarking on fresh Higgs searches”, Richard Dalitz and Louis Lyons organised a neatly titled workshop “Higgs for the masses” to review the theoretical and experimental status. Another oddity of the Higgs, wrote Lyons, is that unless it is very light (less than 10^–17 eV), the Higgs should make the universe curved, “contributing more to the cosmological constant than the known limit permits”. Lower limits (from spontaneous symmetry breaking) and higher limits (from the unitarity requirement) open up a wide range of masses for the Higgs to manoeuvre — between 7 and 1000 GeV, he noted. “From time to time, new ‘bumps’ and effects are tentatively put forward as candidate Higgs, but so far none are convincing.”

LEP’s electroweak adventure reached a dramatic climax in the summer of 2000, with hints that a light Higgs boson was showing itself. In October, the machine was granted a stay of Higgs execution. Alas, the signal faded, and the final curtain fell on LEP in November — a “LEPilogue” heralding the beginning of a new era: the LHC.

Discussions about a high-energy hadron collider were ongoing long before: ICFA’s Future Perspectives meeting at Brookhaven in October 1987 noted two major hadron collider projects on the market: “the US Superconducting Supercollider, with collision energies of 40 TeV in an 84 kilometre ring, and the CERN Large Hadron Collider, with up to 17 TeV collision energies”. In December 1994, shortly after CERN turned 40, Council provided the lab with “The ultimate birthday present“: the unanimous approval of the LHC. A quarter of a century later, the LHC started up and brought particle physics to the world.

vol35-issue1-p001fig — Pride, happiness and relief at LHC approval – left to right: CERN’s research director Lorenzo Foa, LHC project Leader Lyn Evans and Director-General Chris Llewellyn Smith (1995).

Together with LEP data, Fermilab’s CDF and DØ experiments and the LHC 2011 measurement campaign narrowed down the possible mass range for the Higgs boson to be between 115 and 127 GeV. First tantalising hints of the Higgs boson were presented on 13 December 2011. The quest remained open for another half a year, until Director-General Rolf Heuer, following the famous talks by ATLAS and CMS spokespersons Fabiola Gianotti and Joe Incandela, concluded: “As a layman I would say: I think we have it” on 4 July 2012. It was a day to remember: a breakthrough discovery rooted in decades of work by thousands of individuals that rocked the CERN auditorium and reverberated around the world. A new chapter in particle physics had begun…

To mark the 10^th anniversary of this momentous event, from Monday 4 July the Courier will be exploring the theoretical and experimental effort behind the Higgs-boson discovery, the immense progress made by ATLAS and CMS in our understanding of this enigmatic particle, and the deep connections between the Higgs boson and some of the most profound open questions in fundamental physics.

Wherever the Higgs boson leads, CERN Courier will be there to report!

Engines of knowledge and innovation

**One of a kind** As a large research infrastructure, CERN has a key role in shaping a globally competitive European research and innovation system. Credit: CERN-201808-226-1

The search for the Higgs boson is the kind of adventure that draws many young people to science, even if they go on to work in more applied areas. I first set out to become a nuclear physicist, and even applied for a position at CERN, before deciding to specialise in electrical engineering and then moving into science policy. Today, my job at the European Commission (EC) is to co-create policies with member states and stakeholders to shape a globally competitive European research and innovation system.

Large research infrastructures (RIs) such as CERN have a key role to play here. Having visited CERN for the first time last year, I was impressed not just by the basic research but also by the services that CERN provides the collaborations, its relationships with industry, and its work in training and educating young people. It is truly an example of what it means to collaborate on an international level, and it helped me understand better the role of RIs in research and innovation.

Innovation is one of three pillars of the EC’s €95.5 billion Horizon Europe programme for the period 2021–2027. The first pillar is basic science, and the second concerns applied research and knowledge diffusion. Much of the programme’s focus is “missions” geared to societal challenges such as soil, climate and cancer, driven by the UN’s 2030 Sustainable Development Goals. So where does a laboratory like CERN fit in? Pillar one is the natural home of particle physics, where there is well established support via European Research Council grants, Marie Skłodowska-Curie fellowships and RI funding. On the other hand, the success of the Horizon Europe missions relies on the knowledge and new technologies generated by the RIs.

**Anna Panagopoulou** is director of European Research Area and Innovation at the European Commission. Credit: CERN-202110-161-4

We view the role of RIs as driving knowledge and technology, and ensuring it is transferred in Europe – acting as engines in a local ecosystem involving other laboratories and institutes, hospitals and schools, attracting the best people and generating new labour forces. COVID-19 is a huge social challenge that we also managed to address using basic research, RIs and opening access to data. This is a clear socioeconomic impact of current research and also data collected in the past.

Open science is a backbone of Horizon Europe, and an area where particle physics and CERN in particular are well advanced. I chair the governance board of the European Open Science Cloud, a multi-disciplinary environment where researchers can publish, find and re-use data, tools and services, in which CERN has a long-standing involvement.

Indeed, the EC has established a very strong collaboration with CERN across several areas. Recently we have been meeting to discuss the proposed Future Circular Collider (FCC). The FCC is worthwhile not just to be discussed but supported, and we are already doing so via significant projects. We are now discussing possibilities in Horizon Europe to support more technological aspects, but clearly EU money is not enough. We need commitment from member states, so there needs to be a political decision. And to achieve that we need a very good business plan that turns the long-term FCC vision into clearly defined short-term goals and demonstrates its stability and sustainability.

Societal impact

Long-term projects are not new to the EC: we have ITER, for example, while even the neutrality targets for the green-deal and climate missions are for 2050. The key is to demonstrate their relevance. There is sometimes a perception that people doing basic research are closed in their bubble and don’t realise what’s going on in the “real” world. The space programme has managed to demonstrate over the years that there are sufficient applications providing value beyond its core purpose. Nowadays, with issues of defence, security and connectivity rising up political agendas, researchers can always bring to the table that their work can help society address its needs. For big RIs such as the FCC we need to demonstrate first: what is the added value, even if it’s not available today? Why is it important for Europe? And what is the business plan? The FCC is not a typical project. To attract and convince politicians and finance ministers of its merits, it has to be presented in terms of its uniqueness.

The FCC brings to mind the Moon landings

The FCC brings to mind the Moon landings. Contrary to popular depictions, this was a long-term project that built on decades of competitive research from different countries. Yes, it was a period during the Cold War, but it was also the basis of fruitful collaboration. If we don’t dare to spend money on projects that bring us to the future then we lose, as Europe, a competitive advantage.

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