Praxis Archives – Page 50 of 181

CERN and the Higgs Boson

James Gillies’ slim volume CERN and the Higgs Boson conveys the sheer excitement of the hunt for the eponymous particle. It is a hunt that had its origins at the beginning of the last century, with the discovery of the electron, quantum mechanics and relativity, and which was only completed in the first decades of the next. It is also a hunt throughout which CERN’s science, technology and culture grew in importance. Gillies has produced a lively and enthusiastic text that explores the historical, theoretical, experimental, technical and political aspects of the search for the Higgs boson without going into oppressive scientific detail. It is rare that one comes across a monograph as good as this.

Gillies draws attention to the many interplays and dialectics that led to our present understanding of the Higgs boson. First of all, he brings to light the scientific issues associated with the basic constituents of matter, and the forces and interactions that give rise to the Standard Model. Secondly, he highlights the symbiotic relationship between theoretical and experimental research, each leading the other in turn, and taking the subject forward. Finally, he shows the inter-development of the accelerators, detectors and experimental methods to which massive computing power had eventually to be added. This is all coloured by a liberal sprinkling of anecdotes about the people that made it all possible.

Complementing this is the story of CERN, both as a laboratory and as an institution, traced over the past 60 years or so, through to its current pre-eminent standing. Throughout the book the reader learns just how important the people involved really are to the enterprise: their sheer pleasure, their commitment through the inevitable ups and downs, and their ability to collaborate and compete in the best of ways.

A ripping yarn, then, which it might seem churlish to criticise. But then again, that is the job of a reviewer. There is, perhaps, an excessively glossy presentation of progress, and the exposition continues forward apace without conveying the many downs of cutting-edge research: the technical difficulties and the many immensely hard and difficult decisions that have to be made during such enormous endeavours. Doing science is great fun but also very difficult – but then what are challenges for?

There is, perhaps, an excessively glossy presentation of progress

A pertinent example in the Higgs-boson story not emphasised in the book occurred in 2000. The Large Electron Positron collider (LEP) was due to be closed down to make way for the LHC, but late in the year LEP’s ALEPH detector recorded evidence suggesting a Higgs boson might be being observed at a mass of 114–115 GeV – although, unfortunately, not seen by the other experiments (see p32). Exactly this situation had been envisaged when not one but four LEP experiments were approved in the 1980s. After considerable discussion LEP’s closure went ahead, much to the unhappiness and anger of a large group of scientists who believed they were on the verge of a great discovery. This made for a very difficult environment at CERN for a considerable time thereafter. We now know the Higgs was found at the LHC with a mass of 125 GeV, vindicating the original decision of 2000.

A few more pictures might help the text and fix the various contributors in readers’ minds, though clearly the book, part of a series of short volumes by Icon Books called Hot Science, is formatted for brevity. I also found the positioning of the important material on applications such as positron emission tomography and the world wide web to be unfortunate, situated as it is in the final chapter, entitled “What’s the use?” Perhaps instead the book could have ended on a more upbeat note by returning to the excitement of the science and technology, and the enthusiasm of the people who were inspired to make the discovery happen.

CERN and the Higgs Boson is a jolly good read and recommended to everyone. Whilst far from the first book on the Higgs boson, Gillies’ offering distinguishes itself with its concise history and the insider perspective available to him as CERN’s head of communications from 2003 to 2015: the denouement of the hunt for the Higgs.

From SUSY to the boardroom

Former particle physicist Andy Yen has set himself a modest goal: to transform the business model of the internet. In the summer of 2013, following the Snowden security leaks, he and some colleagues at CERN started to become concerned about the lack of data privacy and the growing inability of individuals to control their own data on the internet. It prompted him, at the time a PhD student from Harvard University working on supersymmetry searches in the ATLAS experiment, and two others, to invent “ProtonMail” – an ultra-secure e-mail system based on end-to-end encryption.

The Courier met with Yen and Bart Butler, ProtonMail’s chief technology officer and fellow CERN alumnus, at the company’s Geneva headquarters to find out how a discussion in CERN’s Restaurant 1 was transformed into a company with more than 100 employees serving more than 10 million users.

If you are a Gmail user, then you are not Google’s customer, you are the product that Google sells to its real customer, which is advertisers

“The business model of the internet today really isn’t compatible with privacy,” explains Yen. “It’s all about the relationship between the provider and customer. If you are a Gmail user, then you are not Google’s customer, you are the product that Google sells to its real customer, which is advertisers. With ProtonMail, the people who are paying us are also our users. If we were ever to betray the trust of the user base, which is paying us precisely for reasons of privacy, then the whole business model collapses.”

Anyone can sign up for a ProtonMail account. Doing so generates a pair of public and private keys based on secure RSA-type encryption implementations and open-source cryptographic libraries. User data is encrypted using a key that ProtonMail does not have access to, which means the company cannot decrypt or access a user’s messages (nor offer data recovery if a password is forgotten). The challenge, says Yen, was not so much in developing the underlying algorithms, but in applying this level of security to an e-mail service in a user-friendly way.

In 2014 Yen and ProtonMail’s other co-founders, Jason Stockman and Wei Sun, entered a competition at MIT to pitch the idea. They lost, but reasoned that they had already built the thing and got a couple of hundred CERN people using it, so why not open it up to the world and see what happens? Within three days of launching the website 10,000 people had signed up. It was surprising and exciting, says Yen, but also scary. “E-mail has to work. A bank or something might close down their websites for an hour of maintenance once in a while, but you can’t do that with e-mail,” he says.

ProtonMail’s CERN origins (the name came from the fact that its founders were working on the Large Hadron Collider) meant that the technology could first come under the scrutiny of technically minded people – “early adopters”, who play a vital role in the life cycle of new products. But what might be acceptable to tech-minded people is not necessarily what the broader users want, says Yen. He quickly realised that the company had to grow, and that he had been forced into a “tough and high-risk” decision between ProtonMail and his academic career. Eventually deciding to take the leap, Harvard granted him a period of absence, and Yen set about dealing with the tens of thousands of users who were waiting to get onto the service.

In need of cash, the fledgling software outfit decided to try something unusual: crowd funding. This approach broke new ground in Switzerland, and ProtonMail soon became a test case in tax law as to whether such payments should be considered revenue or donation (the authorities eventually ruled on the former). But the effort was a huge success, raising 0.5 million Swiss Francs in a little over two months. “Venture capital (VC) was a mystery to us,” says Yen. “We didn’t know anybody, we didn’t have a business plan, we were just a few people writing code. But, funnily enough, the crowd sourcing, in addition to the money itself, got a lot of attention and this attracted interest from VCs.” A few months later, ProtonMail had received 2 million Swiss Francs in seed funding.

“It is one thing to have an idea – then we had to actually do what we’d promised: build a team, hire people, scale up the product and have some sort of company to run things, with corporate identity, accounting, tax compliance, etc. There wasn’t really a marketing plan… it was more of a technical challenge to build the service,” says Yen. “If I was to give advice to someone in my position five years ago, then there isn’t a lot I could say. Starting a company is something new for almost everybody who does it, and I don’t think physicists are at a disadvantage compared to someone who went to business school. All you have to do is work hard, keep learning and you have to have the right people around you.”

It’s not a traditional company – 10–15% of the staff today is CERN scientists

It was around that time, in 2015, when Butler, also a former ATLAS experimentalist working on supersymmetry and one-time supervisor of Yen, joined ProtonMail. “A lot of that year was based around evolving the product, he says. “There was a big difference between what the product originally was versus what it needed to be to scale up. It’s not a traditional company – 10–15% of the staff today is CERN scientists. A lot of former physicists have developed into really good software engineers, but we’ve had to bring in properly trained software engineers to add the rigour that we need. At the end of the day, it’s easier to teach a string theorist how to code than it is to teach advanced mathematics and complex cryptographic concepts to someone who codes.”

With the company, Proton Technologies, by then well established – and Yen having found time to hotfoot it back to Harvard for one “very painful and ridiculous” month to write up his PhD thesis – the next milestone came in 2016 when ProtonMail was actually launched. It was time to begin charging for accounts, and to provide those who already had signed up with premium paid-for services. It was the ultimate test of the business model: would enough people be prepared to pay for secure e-mail to make ProtonMail a viable and even profitable business? The answer turned out to be “yes”, says Yen. “2016 was make or break because eventually the funding was going to run out. We discussed whether we should raise money to buy us more time. But we decided just to work our asses off instead. We came very close but we started generating revenue just as the VC cash ran out.”

Since then, ProtonMail has continued to scale up its services, for instance introducing mobile apps, and its user base has grown to more than 10 million. “Our main competitors are the big players, Google and Microsoft,” says Yen. “If you look at what Google offers today, it’s actually really nice to use. So the longer vision is: can we offer what Google provides — services that are secure, private and beneficial to society? There is a lot to build there, ProtonDrive, ProtonCalendar, for example, and we are working to put together that whole ecosystem.”

A big part of the battle ahead is getting people to understand what is happening with the internet and their data, says Butler. “Nobody is saying that when Google or Facebook began they went out to grab people’s data. It’s just the way the internet evolved: people like free things. But the pitfalls of this model are becoming more and more apparent. If you talk to consumers, there is no choice in the market. It was just e-mail that sold your data. So we want to provide that private option online. I think this choice is really important for the world and it’s why we do what we do.”

Music of the muons

Subatomic Desire — **Subatomic desire** Les Atomes Dansants were inspired by muon tracks at the CMS experiment. Credit: R Carlin

Swiss composer Alexandre Traube and the Genevan video-performer Silvia Fabiani have collaborated to form music and dance troupe Les Atomes Dansants, with the aims of using CMS data to explore the links between science and art, and of establishing a dialogue between Eastern and Western culture. Premiering their show Subatomic Desire at CERN’s Globe of Science and Innovation on 21 June during Geneva’s annual Fête de la Musique, they took the act to the detector that served as their muse by performing in the hangar above the CMS experiment.

Muon tracks from W, Z and Higgs events served as inspiration for Traube, who was advised by CMS physicist Chiara Mariotti of INFN. He began by associating segments of the CMS’s muon system to notes. Inspired by the detectors’ arrangement as four nested dodecagons, he assigned a note from the chromatic scale to each of the 12 sides of the innermost layer, and to each note a sonorous perfect fourth above to the corresponding segment in the outer layer. Developing an initial plan to also link the intermediate two layers of the muon system to specific frequencies, he associated two intermediate microtonal notes to the transverse momentum and rapidity of the tracks. At several moments during the performance the musicians improvise using the resulting four-note sequences: an expression of quantum indeterminacy, according to Traube. Fabiani’s video projections add to the surreal atmosphere by transposing the sequences into colours, with an animation of bullets referencing the Russian Second World War navy shells that were used to build the CMS’s hadronic calorimeter.

Clad in lab coat, Einstein wig and reversed baseball cap, Doc MC Carré raps formulas and boogies around the stage

In concert with the audiovisual display, three performers sing about their love for the microcosm. Clad in lab coat, Einstein wig and reversed baseball cap, Doc MC Carré (David Charles) raps formulas and boogies around the stage. He is accompanied by Doc Lady Emmy, played by the soprano Marie-Najma Thomas, and Poète Atomique – the Persian singer Taghi Akhabari – who peppers the performance with mystical extracts from Sufi poets Rûmi and Attâr, and medieval German abbess Hildegard of Bingen, each of whom explores themes of the natural world in their writings. The performers contend that the lyrics speak about desire as the fuel for everything at the micro- and macroscale. Elaborate, contemporary and rich in metaphors, this is an experience that some will find abstruse but others will love.

Subatomic Desire will next be performed in Neuchâtel, Switzerland on 14 September.

Supergravity pioneers share $3m Breakthrough Prize

Peter van Nieuwenhuizen, Sergio Ferrara and Dan Freedman (left to right) at CERN in 2016 on the occasion of supergravity’s 40th anniversary. Credit: S Bennett/CERN

Theorists Sergio Ferrara (CERN), Dan Freedman (MIT/Stanford) and Peter van Nieuwenhuizen (Stony Brook) have been awarded a Special Breakthrough Prize in Fundamental Physics for their 1976 invention of supergravity. Supergravity marries general relativity with supersymmetry and, after more than 40 years, continues to carve out new directions in the search for a unified theory of the basic interactions.

“This award comes as a complete surprise,” says Ferrara. “Supergravity is an amazing thing because it extends general relativity to a higher symmetry – the dream of Einstein – but none of us expected this.”

Supergravity followed shortly after the invention of supersymmetry. This new symmetry of space–time, which enables fermions to be “rotated” into bosons and vice versa, implies that each elementary particle has a heavier supersymmetric partner and its arrival came at a pivotal moment for the field. The Standard Model (SM) of electroweak and strong interactions had just come into being, yet it was clear from the start that it was not a complete: it is not truly unified because the gluons of the strong force and the photons of electromagnetism do not emerge from a common symmetry, and it leaves out gravity, which is described by general relativity. Supersymmetry promised a way to tackle these and other problems with the SM.

It was clear that the next step was to extend supersymmetry to include gravity, says Ferrara, but it was not obvious how this could be done. During a short period lasting from autumn 1975 to spring the following year, Ferrara, Freedman and van Nieuwenhuizen succeeded – with the help of state-of-the-art computers – in producing a supersymmetric theory that included the gravitino as the supersymmetric partner of the graviton. The trio published their paper in June 1976. Chair of the prize selection committee, Edward Witten, says of the achievement:

“The discovery of supergravity was the beginning of including quantum variables in describing the dynamics of space–time. It is quite striking that Einstein’s equations admit the generalisation that we know as supergravity.”

It is quite striking that Einstein’s equations admit the generalisation that we know as supergravity

Despite numerous searches at ever higher energies during the past decades, no supersymmetric particles have ever been observed. But the importance of supergravity and its influence on physics is already considerable – especially on string theory, of which supergravity is a low-energy manifestation. Supergravity was a crucial ingredient in the 1984 proof by Michael Green and John Schwarz that string theory is mathematically consistent, and it was also instrumental in the M-theory string unification by Edward Witten in 1995. It played a role in Andrew Strominger and Cumrun Vafa’s 1996 derivation of the Bekenstein–Hawking entropy for quantum black holes, and is also important in the holographic AdS/CFT duality discovered by Juan Maldacena in 1997.

“Supergravity led to great improvements in mathematical physics, especially supergroups and supermoduli, and in the growing field of string phenomenology, which attempts to include particle physics in superstring theory,” adds Ferrara.

Ferrara, Freedman and van Nieuwenhuizen have received several awards for the invention of supergravity, including the 1993 ICTP Dirac Medal and the 2006 Dannie Heinemann Prize for Mathematical Physics. The Breakthrough Prize, founded in 2012 by former theoretical particle physicist and founder of DST Global, Yuri Milner, rewards achievements in fundamental physics, life sciences and mathematics. The $3m Special Breakthrough Prize can be awarded at any time “in recognition of an extraordinary scientific achievement”, and is not limited to recent discoveries. Previous winners of the Special Breakthrough Prize in Fundamental Physics are: Stephen Hawking; seven physicists whose leadership led to the discovery of the Higgs boson at CERN; the LIGO and Virgo collaborations for the detection of gravitational waves; and Jocelyn Bell Burnell for the discovery of pulsars.

The new laureates, along with the winners of the Breakthrough Prize in Life Sciences and Mathematics, will receive their awards at a ceremony at NASA’s “Hangar 1” on 3 November.

My contemporary and my friend

**A life in science** Murray Gell-Mann in the underground cavern of the ATLAS experiment during a visit to CERN in 2012. Credit: M Brice CERN-GE-1201006-1.

Murray Gell-Mann and I were born a few days apart, in September 1929. Being born on almost the same date as a genius does not help much, except for the fact that by having the same age there was a non-zero probability that we would meet. And, indeed, this is what happened; furthermore, we and our families became friends.

Murray’s family was heavily affected by the economic crash of October 1929. His father had to change job completely. However, if this had not happened, it is possible that Murray might have become a successful businessman instead of a brilliant physicist. Everybody knows that Murray was immensely cultured and had multiple interests. I can quote a few at random: penguins, other birds (tichodromes for instance), Swahili, Creole, Franco- Provençal (and more generally the history of languages), pre-Columbian art and American–Indian art, gastronomy (including French wines and medieval food), the history of religions, climatic change and its consequences, energy resources, protection of the environment, complexity, cosmology and the quantum theory of measurement. However, it is in the field of theoretical particle physics that he made his most creative and important contributions. For these, up until 24 May 2019, I personally considered him to be the best particle-physics theoretician alive.

Bright beginnings

I met Murray for the first time at Les Houches in 1952, one year after the foundation of the school by Cecile Morette-DeWitt. It was immediately obvious that he was extremely bright. Although I never had the occasion to collaborate with Murray, there was a time when his advice was very precious to me. Most of my own research in theoretical physics was extremely rigorous work but, for a time in 1980, I became a phenomenologist: I proposed a naïve potential model to calculate the energies of quarkonium, b–b̅ and c–c̅ systems. My colleagues were divided about this. In particular, my Russian friends were very critical. When I gave a talk about this in Aspen, Murray said: “We don’t understand why it works, but it works and you should continue.” I followed his advice, including treating strange quarks as “heavy”. Again it worked, and my colleague Jean Marc Richard adapted this model to baryons. It enabled the mass of the Ω^– baryon to be calculated with great accuracy, and also correctly predicted the mass of the b–s̅ meson, which was discovered years later by ALEPH. This is typical of Murray’s philosophy: if something works, go ahead: “non approfondire” as Italian writer Alberto Moravia says.

In 1955 I attended my first physics conference, in Pisa. After a breakfast with Erwin Schrödinger, I took the tram and met Murray. In the afternoon, at the University of Pisa, he made the first public presentation of the strangeness scheme. The auditorium was packed. I was completely bewildered by this extraordinary achievement, with its incredible predictive power (which was very soon checked), including the KK̅ system. I had already left Ecole Normale-Orsay for CERN when he and Maurice Levy wrote their famous paper featuring, for the first time, what was later called the “Cabibbo angle”.

I then had the good fortune to be sent to the La Jolla conference in 1961. There I met Nick Khuri for the first time, who also became a close friend, and I heard Murray presenting “the eightfold way” – i.e. the SU(3) octet model. Also attending were Marcel Froissart, who derived the “Froissart bound”, and Geoff Chew, who presented his version of the S-matrix programme. Both were most inspiring for my future work (sadly, both also passed away recently). What I did not realise at the time was that the Chew programme had been largely anticipated by Murray, who first was involved in the use of dispersion relations and then noticed, in 1956, that the combination of analyticity, unitarity and crossing symmetry could lead to field theory on the mass shell, with some interesting consequences.

In 1962, during the Geneva “Rochester” conference, I was again present when Murray, after a review of hadron spectroscopy by George Snow, stood up and pointed out that the sequence of particles Δ, ∑*, Ξ* could be completed by a particle that he called Ω^– to form a decuplet in the SU(3) scheme. He predicted its mode of production, its decay (which was to be weak) and its mass. This was followed by a period of deep scepticism among theoreticians, including some of the best. However, at the end of 1963, while I was in Princeton, Nick Samios and his group at Brookhaven announced that the Ω^– had been discovered, with exactly the correct mass within a few MeV. Frank Yang, one of the sceptics, called it “the most important experiment in particle physics in recent years”. I missed the invention of the quarks, being in Princeton, far from Caltech where Murray was, and from CERN where George Zweig was visiting. I met Bob Serber but was completely unaware of his catalytic role in that discovery.

Close friends

**The Gell-Manns** Murray and his wife Margaret pictured in Bois Conti, near Geneva, around 1980. Credit: A Martin.

My next important meeting with Murray was in Yerevan in Armenia in 1965, where Soviet physicists had invited a group of some eight western physicists. This time Murray came with his whole family: his wife, Margaret – a British archaeology student whom he met in Princeton – and his children, Lisa and Nick. During the following summer, which the Gell-Manns spent in Geneva, our families met several times. The Gell-Manns spent another year at CERN before Harold Fritzsch, Gell-Mann and Heinrich Leutwyler wrote the “Credo” of QCD.

Margaret and Murray came to Geneva again for the academic year 1979/1980. They were living in an apartment in the same group of buildings as us. Schu, my wife, who died at the same age as Murray from a similar disease, became a close friend of Margaret, who was a typically British girl: very reserved, very intelligent and possessing a good sense of humour. An extraordinary friendship grew between Margaret and Schu. When the Gell-Manns left Geneva for Pasadena, Margaret knew that there was something wrong with her health. Back in the US she discovered that she had cancer. I do not know the number of transatlantic trips that we made – sometimes both of us, sometimes Schu alone – to help. In between, Schu and Margaret had an extensive correspondence. It is nice that the ashes of Murray will be close to Margaret.

After Margaret’s death, we all kept in touch. We met in many places: Paris, Pasadena, Beyrouth, Geneva and Bern. Of these, two stand out. In 2004 Murray attended a meeting of linguists at the University of Geneva. He proposed to give a talk at CERN on the origin and evolution of languages. Luis Alvarez-Gaumé and I accepted. It was absolutely fantastic. I regret that we don’t have a written version, but we certainly have tapes. The second occasion was in Bern. Every year the Swiss confederation gives the Einstein Medal to someone suggested by the University of Bern. The 2005 medal was a special one because this was 100 years after Einstein’s trilogy of fundamental discoveries. The candidate had to be of an extremely high level, so Murray was chosen. At the ceremony in Bern, Schu decided to wear a brooch that had been given to her by Murray to thank her for what she did for Margaret. The brooch represented Hopi “skinwalkers”. During lunch, however, the brooch disappeared. Either it had been lost or stolen. We were extremely unhappy and could not refrain from telling this to Murray. Some time later, Schu received a parcel containing a new brooch; an illustration of Murray’s faithfulness in friendship.

This article is an updated version of a tribute published on the occasion of Gell-Mann’s 80th birthday (CERN Courier April 2010 p27).

European Strategy Update – Strategy Drafting Session

High-energy networking

**Variety** CERN alumni by employment sector (left) and the age range of members (right).

CERN has 65 years of history and more than 13,000 international users. The CERN Alumni Network, launched in June 2017 as a strategic objective of the CERN management, now has around 4600 members spanning all parts of the world. Alumni pursue careers across many fields, including industry, economics, information technology, medicine and finance. Several have gone on to launch successful start-ups, some of them directly applying CERN-inspired technologies.

So far, around 350 job opportunities, posted by alumni or companies aware of the skills and profiles developed at CERN, have been published on the alumni.cern platform. Approximately 25% of the jobs posted are for software developer/engineer positions, 16% for data science and 15% for IT engineering positions. Several members have already been successful in finding employment through the network.

Another objective of the alumni programme is to help early-career physicists make the transition from academia to industry if they choose to do so. Three highly successful “Moving out of academia” events have been held at CERN with the themes finance, big data and industrial engineering. Each involved inviting a panel of alumni working in a specific field to give candid and pragmatic advice, and was very well attended by soon-to-be CERN alumni, with more than 100 people at each event. In January the alumni network took part in an academia/industry event titled “Beyond the Lab – Astronomy and Particle Physics in Business” at the newly inaugurated Higgs Innovation Centre at the University of Edinburgh.

The data challenge

The network is still in its early days but has the potential to expand much further. Improving the number of alumni who have provided data (currently 37%) is an important aim for the coming years. Knowing where our alumni are located and their current professional activity allows us to reach out to them with relevant information, proposals or requests. Recently, to help demonstrate the impact of experience gained at CERN, we launched a campaign to invite those who have already signed up to update their profiles concerning their professional and educational experience. Increasing alumni interactions, engagement and empowerment is one of the most challenging objectives at this stage, as we are competing with many other communities and with mobile apps such as Facebook, WhatsApp and LinkedIn.

One very effective means for empowering local alumni communities are regional groups. At their own initiative, members have created seven of them (in Texas, New York, London, Eindhoven, Swiss Romandie, Boston and Athens) and two more are in the pipeline (Vienna and Zurich). Their main activities are to hold events ranging from a simple drink to getting to know each other at more formal events, for example as speakers in STEM-related fields.

One of the most rewarding aspects of running the network has been getting to know alumni and hearing their varied stories. “It’s great that CERN values the network of physicists past and present who’ve passed through or been based at the lab. The network has already led to some very useful contacts for me,” writes former summer student Matin Durrani, now editor of Physics World magazine. “Best wishes from Guyancourt (first office) as well as from Valenciennes (second office) and of course Stręgoborzyce (my family home). Let’s grow and grow and show where we are after our experience with CERN,” writes former technical student Wojciech Jasonek, now a mechanical engineering consultant.

After two years of existence we can say that the network is firmly taking root and that the CERN Office of Alumni Relations has seen engagement and interactions between alumni growing. Anyone who has been (or still is) a user, associate, fellow, staff or student at CERN, is eligible to join the network via alumni.cern.

Guido Altarelli’s legacy

“From my vast repertoire …” is a rather peculiar opening to a seminar or a lecture. The late CERN theorist Guido Altarelli probably intended it ironically, but his repertoire was indeed vast, and it spanned the whole of the “famous triumph of quantum field theory,” as Sidney Coleman puts it in his classic monograph Aspects of Symmetry. There can be little doubt that a conspicuous part of this triumph must be ascribed to the depth and breadth of Altarelli’s contributions: the HERA programme at DESY, the LEP and LHC programmes at CERN, and indeed the current paradigms of the strong and electroweak interactions themselves, bear the unmistakable marks of Guido’s criticism and inspiration.

From My Vast Repertoire … is a memorial volume that encompasses the scientific and human legacies of Guido. The book consists of 18 well-assorted contributions that cover his entire scientific trajectory. His wide interests, and even his fear of an untimely death, are described with care and respect. For these reasons the efforts of the authors and editors will be appreciated not only by his friends, collaborators and fellow practitioners in the field, but also by younger scientists, who will find a timely introduction to the current trends in particle physics, from the high-energy scales of collider physics to the low-energy frontier of the neutrino masses. The various private pictures, which include a selection from his family and friends, make the presence of Guido ubiquitous even though his personality emerges more vividly in some contributions than others. Guido’s readiness to debate the relevant physics issues of his time is one of the recurring themes of this volume; the interpretation of monojets at the SPS, precision tests of the Standard Model at LEP, the determination of the strong coupling constant, and even the notion of naturalness, are just a few examples.

While lecturing at CERN in 2005, Nobel prize-winning theorist David Gross outlined some future perspectives on physics, and warned about the risk of a progressive balkanisation. The legacy of Guido stands out among the powerful antidotes against a never-ending fission into smaller subfields. He understood which problems are ripe to study and which are not, and that is why he was able to contribute to so many conceptually different areas, as this monograph clearly shows. The lesson we must draw from Guido’s achievements and his passion for science is that fundamental physics must be inclusive and diverse. Lasting progress does not come by looking along a single line of sight, but by looking all around where there are mature phenomena to be scrutinised at the appropriate moment.

Radio-euphoria rebooted?

**Handle with care** Radiation measurement tools and samples. Credit: M Brice/CERN-PHOTO-201501-003-9.

Ilya Obodovskiy’s new book is the most detailed and fundamental survey of the subject of radiation safety that I have ever read.

The author assumes that while none of his readers will ever be exposed to large doses of radiation, all of them, irrespective of gender, age, financial situation, profession and habits, will be exposed to low doses throughout their lives. Therefore, he reasons, if it is not possible to get rid of radiation in small doses, it is necessary to study its effect on humans.

Obodovskiy adopts a broad approach. Addressing the problem of the narrowing of specialisations, which, he says, leads to poor mutual understanding between the different fields of science and industry, the author uses inclusive vocabulary, simultaneously quoting different units of measurement, and collecting information from atomic, molecular and nuclear physics, and biochemistry and biology. I would first, however, like to draw attention to the rather novel section ‘Quantum laws and a living cell’.

Quite a long time after the discovery of X-rays and radioactivity, the public was overwhelmed by “X-ray-mania and radio-euphoria”. But after World War II – and particularly after the Japanese vessel Fukuryū-Maru experienced the radioactive fallout from a thermonuclear explosion at Bikini Atoll – humanity got scared. The resulting radio-phobia determined today’s commonly negative attitudes towards radiation, radiation technologies and nuclear energy. In this book Obodovskiy shows that radio-phobia causes far greater harm to public health and economic development than the radiation itself.

The risks of ionising radiation can only be clarified experimentally. The author is quite right when he declares that medical experiments on human beings are ethically evil. Nevertheless, a large group of people have received small doses. An analysis of the effect of radiation on these groups can offer basic information, and the author asserts that in most cases results show that low-dose irradiation does not affect human health.

It is understandable that the greater part of the book, as for any textbook, is a kind of compilation, however, it does discuss several quite original issues. Here I will point out just one. To my knowledge, Obodovskiy is the first to draw attention to the fact that deep in the seas, oceans and lakes, the radiation background is two to four orders of magnitude lower than elsewhere on Earth. The author posits that one of the reasons for the substantially higher complexity and diversity of living organisms on land could be the higher levels of ionising radiation.

In the last chapter the author gives a detailed comparison of the various sources of danger that threaten people, such as accidents on transport, smoking, alcohol, drugs, fires, chemicals, terror and medical errors. Obodovskiy shows that the direct danger to human health from all nuclear applications in industry, power production, medicine and research is significantly lower than health hazards from every non-nuclear source of danger.

Lessons from LEP

**Looking forward** Herwig Schopper believes that the next machine has to be a world facility. Credit: S Hertzog/CERN-PHOTO-201906-169-6.

When was the first LEP proposal made, and by whom?

Discussions on how to organise a “world accelerator” took place at a pre-ICFA committee in New Orleans in the early 1970s. The talks went on for a long time, but nothing much came out of them. In 1978 John Adams and Leon Van Hove – the two CERN Director-Generals (DGs) at the time – agreed to build an electron–positron collider at CERN. There was worldwide support, but then there came competition from the US, worried that they might lose the edge in high-energy physics. Formal discussions about a Superconducting Supercollider (SSC) had already begun. While it was open to international contribution, Ronald Reagan’s “join it or not” approach to the SSC, and other reasons, put other countries off the project.

Was there scientific consensus for a collider four times bigger than anything before it?

Yes. The W and Z bosons hadn’t yet been discovered, but there were already strong indications that they were there. Measuring the electroweak bosons in detail was the guiding force for LEP. There was also the hunt for the Higgs and the top quark, yet there was no guidance on the masses of these particles. LEP was proposed in two phases, first to sit at the Z pole and then the WW threshold. We made the straight sections as long as possible so we could increase the energy during the LEP2 phase.

What about political consensus?

The first proposal for LEP was initially refused by the CERN Council because it had a 30 km circumference and cost 1.4 billion Swiss Francs. When I was appointed DG in February 1979, they asked me to sit down with both current DGs and make a common proposal, which we did. This was the proposal with the idea to make it 22 km in circumference. At that time CERN had a “basic” programme (which all Member States had to pay for) and a “special” programme whereby additional funds were sought. The latter was how the Intersecting Storage Rings (ISR) and the Super Proton Synchrotron (SPS) were built. But the cost of LEP made some Member States hesitate because they were worried that it would eat too much into the resources of CERN and national projects.

How was the situation resolved?

After long discussions, Council said: yes, you build it, but do so within a constant budget. It seemed like an impossible task because the CERN budget had peaked before I took over and it was already in decline. I was advised by some senior colleagues to resign because it was not possible to build LEP on a constant budget. So we found another idea: make advance payments and create debts. Council said we can’t make debts with a bank, so we raided the CERN pension fund instead. They agreed happily since I had to guarantee them 6% interest, and as soon as LEP was built we started to pay it back. With the LHC, CERN had to do the same (the only difference was that Council said we could go to a bank). CERN is still operating within essentially the same constant budget today (apart from compensation for inflation), with the number of users having more than doubled – a remarkable achievement! To get LEP approved, I also had to say to Council that CERN would fund the machine and others would fund the experiments. Before LEP, it was usual for CERN to pay for experiments. We also had to stop several activities like the ISR and the BEBC bubble chamber. So LEP changed CERN completely.

How do LEP’s findings compare with what was expected?

It was wonderful to see the W and Z discovered at the SPS while LEP was being built. Of course, we were disappointed that the Higgs and the top were not discovered. But, look, these things just weren’t known then. When I was at DESY, we spent 5 million Deutsche Marks to increase the radio-frequency power of the PETRA collider because theorists had guaranteed that the top quark would be lighter than 25 GeV! At LEP2 it was completely unknown what it would find.

What is LEP’s physics legacy?

These days, there is a climate where everything that is not a peak is not a discovery. People often say “not much came out from LEP”. That is completely wrong. What people forget is that LEP changed high-energy physics from a 10% to a 1% science. Apart from establishing the existence of three neutrino flavours, the LEP experiments enabled predictions of the top-quark mass that were confirmed at Fermilab’s Tevatron. This is because LEP was measuring the radiative corrections – the essential element that shows the Standard Model is a renormalisable theory, as shown theoretically by ’t Hooft and Veltman. It also showed that the strong coupling constant, α_s, runs with energy and allowed the coupling constants of all the gauge forces to be extrapolated to the Planck mass – where they do not meet. To my mind, this is the most concrete experimental evidence that the Standard Model doesn’t work, that there is something beyond it.

How did the idea come about to put a proton collider in the LEP tunnel?

When LEP was conceived, the Higgs was far in the future and nobody was really talking about it. When the LEP tunnel was discussed, it was only the competition with SSC. The question was: who would win the race to go to higher energy? It was clear in the long run that the proton machine would win, so we had the famous workshop in Lausanne in 1983 where we discussed the possibility of putting a proton collider in the LEP tunnel. It was foreseen then to put it on top of LEP and to have them running at the same time. With the LHC, we couldn’t compete in energy with the SSC so we went for higher luminosities. But when we looked into this, we realised we had to make the tunnel bigger. The original proposal, as approved by Council in October 1981, had a tunnel size of 22 km and making it bigger was a big problem because of the geology – basically we couldn’t go too far under the Jura mountains. Nevertheless, I decided to go to 27 km against the advice of most colleagues and some advisory committees, a decision that delayed LEP by about a year because of the water in the tunnel. But it is almost forgotten that the LEP tunnel size was only chosen in view of the LHC.

Are there parallels with CERN today concerning what comes next after the LHC?

Yes and no. One of the big differences compared to the LEP days is that, back then, the population around CERN did not know what we were doing – the policy of management was not to explain what we are doing because it is “too complicated”! I was very surprised to learn this when I arrived as DG, so we had many hundreds of meetings with the local community. There was a misunderstanding about the word “nuclear” in CERN’s name – they thought we were involved in generating nuclear power. That fortunately has completely changed and CERN is accepted in the area.

What is different concerns the physics. We are in a situation more similar to the 1970s before the famous J/ψ discovery when we had no indications from theory where to go. People were talking about all sorts of completely new ideas back then. Whatever one builds now is penetrating into unknown territory. One cannot be sure we will find something because there are no predictions of any thresholds.

What wisdom can today’s decision-makers take from the LEP experience?

In the end I think that the next machine has to be a world facility. The strange thing is that CERN formally is still a European lab. There are associates and countries who contribute in kind, which allows them to participate, but the boring things like staff salaries and electricity have to be paid for by the Member States. One therefore has to find out whether the next collider can be built under a constant budget or whether one has to change the constitutional model of CERN. In the end I think the next collider has to be a proton machine. Maybe the LEP approach of beginning with an electron–positron collider in a new tunnel would work. I wouldn’t exclude it. I don’t believe that an electron–positron linear collider would satisfy requests for a world machine as its energy will be lower than for a proton collider, and because it has just one interaction point. Whatever the next project is, it should be based on new technology such as higher field superconducting magnets, and not be just a bigger version of the LHC. Costs have gone up and I think the next collider will not fly without new technologies.

You were born before the Schrödinger equation and retired when LEP switched on in 1989. What have been the highs and lows of your remarkable career?

I was lucky in my career to be able to go through the whole of physics. My PhD was in optics and solid-state physics, then I later moved to nuclear and particle physics. So I’ve had this fantastic privilege. I still believe in the unity of physics in spite of all the specialisation that exists today. I am glad to have seen all of the highlights. Witnessing the discovery of parity violation while I was working in nuclear physics was one.

How do you see the future of curiosity-driven research, and of CERN?

The future of high-energy physics is to combine with astrophysics, because the real big questions now are things like dark matter and dark energy. This has already been done in a sense. Originally the idea in particle physics was to investigate the micro-cosmos; now we find out that measuring the micro-cosmos means investigating matter under conditions that existed nanoseconds after the Big Bang. Of course, many questions remain in particle physics itself, like neutrinos, matter–antimatter inequality and the real unification of the forces.

I was advised by some senior colleagues to resign because it was not possible to build LEP on a constant budget

With LEP and the LHC, the number of outside users who build and operate the experiments increased drastically, so the physics competence now rests to a large extent with them. CERN’s competence is mainly new technology, both for experiments and accelerators. At LEP, cheap “concrete” instead of iron magnets were used to save on investment, and coupled RF cavities to use power more efficiently were invented, and later complemented by superconducting cavities. New detector technologies following the CERN tradition of Charpak turned the LEP experiments into precision ones. This line was followed by the LHC, with the first large-scale use of high-field superconducting magnets and superfluid-helium cooling technology. Whatever happens in elementary particle physics, technology will remain one of CERN’s key competences. Above and beyond elementary particle physics, CERN has become such a symbol and big success for Europe, and a model for worldwide international cooperation, that it is worth a large political effort to guarantee its long-term future.

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