Nightmare on Meyrin Street

’tis gone.
What seemed to hold the promise of a revolution in physics has fizzled out. Disappeared into oblivion. Is there really nothing more than the Higgs for the LHC to discover? Will the experiment just wander in an energy desert for the rest of its life? It is the most feared scenario physicists could have thought of before switching on the machine at CERN: a true nightmare. What now? Someone is probably hoping this nightmare will let us save money on curiosities that only experts care about and are of no public good for the majority. So wrong!

I have friends who work in theoretical particle physics: they are passionate, capable scientists and I’ve always wished the results found at LHC would help them land the permanent position they deserve to keep doing what they’re best at. Now that everyone in the field is back to square one, my friends are among the best positioned to start a new conversation with Nature through the screen of a blackboard: they are still professionally young enough to be as audaciously bold as the situation requires. So far, in fact, the community of theoreticians has mostly played by decade-old rules: no wonder we’re stuck. It is then a great opportunity to make tabula rasa and be daring. I’m confident the revolutionary men and women that’ll get us out of this morass are already born: hopefully they’re already at work and they are collaborating with each other to enjoy the benefits of complementarity.

However, things could turn out bad: the work toward a new description of Nature might take more time than my friends have to secure a job. As numerous as they can be, and even if they may come from your own country, I don’t think the destiny looming on them will move you. However, in such a case, a catastrophe will be pending above us all.

While it may look like CERN hunts for Pokemon-like entities in reality it does much more: it creates the basis for our future wellbeing. The past week, together with the sad announcement of the aborted physics revolution, CERN celebrated the 25th anniversary of the World Wide Web. It was invented there and you use it to read this piece or the news, to book the flight to go on holidays, to buy shoes and do many more things that are now given for granted in our everyday life.

CERN also has a medical research unit, where particle physics know-how from theory and experiments is put to service for health applications such as treating cancers. Moreover, for its computing needs CERN has been instrumental in the development of Grid computing, which

“… offers a way to solve Grand Challenge problems such as protein folding, financial modeling, earthquake simulation, and climate/weather modeling. Grids offer a way of using the information technology resources optimally inside an organization. They also provide a means for offering information technology as a utility for commercial and noncommercial clients, with those clients paying only for what they use, as with electricity or water.”

There is much more that CERN does for us all but I’m confident the overview I’ve given you can already let you share my concern that if we stop doing research in particle physics we stop creating needs that only this type of research can create, while their satisfaction provides the most fertile conditions for our future wellbeing and prosperity.

Before concluding, it is worth mentioning that the non-discovery of a new particle does not mean CERN should close shop just yet. In fact, knowing that the particle is not there is already a precious piece of information: we could not know beforehand, so disposing of a new piece of (non-)evidence is very useful, though painful.

At the same conference where the sad non-discovery announcement has been made a flood of other new results has been shared with the public by CERN. They still have some twenty years of activity in front of them to let the LHC machine continue its tremendously accurate and reliable work. This persistence is needed to allow new rare phenomena to show up in a significant way. Therefore, we can be “disappointed but not discouraged” as a physicist says at the end of a BBC Horizon documentary that just aired.

Last but not least, a note is in order about the title: Meyrin Street is CERN’s address for the public.

New physics, is that you?

Mysterious hints of long-awaited physics beyond the Standard Model seem to have emerged at CERN’s Large Hadron Collider

The collaborations behind ATLAS and CMS, the two general-purpose experiments at CERN’s Large Hadron Collider, have just published their latest reports. Their new data show a suspicious bump, similar to the one that gave away the existence of the Higgs boson: a detour in an otherwise smooth trajectory across the energy region explored by means of particle collisions. The reason why the new results could either hold great potential or have physicists endure a longer nerve-wracking wait has to do with how searching for the unknown works.

The Large Hadron Collider at CERN offers one the most favorable views of the Universe. Its behemoth experiments collide particles like bumper cars: in the particle dodgem debris are carefully scrutinized to reveal secrets about the interiors of the clashing entities and new types of particles can materialize into existence by converting the energy made available by the collision. Millions of particles are smashed into each other millions of times per second in order for the little sparse hints of every strike to accumulate into relevant information about the microscopic world.

Artist's rendition of a high-energy collision inside a particle detector (Image: CERN)

Artist’s rendition of a high-energy collision inside a particle detector (Image: CERN)

An everyday life equivalent of this would be tossing millions of coins millions of times and counting how many heads or tails you get. Both heads and tails being equally probable you should find that each occurs roughly 50% of the times. That’s in theory. In practice, if you throw a coin 10 times you can get heads 7 times in a row: how’s that possible?

It could be that your coin is rigged: knowing for sure this is not the case is what scientists call characterizing the experimental setup. Maybe your coin is responding to its surroundings in some unexpected way; before you can claim to have a magic coin you have to make sure you understand your environment and how this might interfere with your experiment. It could also be that, while you think you’re just throwing a standard coin, the one you got is no ordinary coin: it’s a completely new one that behaves in an unconventional way with respect to the others you have thrown in the past. More prosaically, it is possible that you did not conduct your experiment enough times to make any statistically significant claim, as scientists would say. When you toss a standard coin your outcomes will approach the 50-50% separation as you increase the number of tosses.

Counting occurrences and comparing results with expectations also characterized the hunt for the Higgs boson, when ATLAS and CMS were like Columbus’ caravels on their course to the Indies: they had to navigate an energy stretch delimited, though loosely, by previously available maps of the microscopic world; their promised land was the particle associated with the Brout-Englert-Higgs mechanism. We all know how the story went: Columbus found America instead, while the Higgs boson was indeed discovered and the duo Higgs-Englert was awarded the Nobel Prize for physics, absent the late Brout.


Professor Englert and Professor Higgs speaking at the Higgs seminar announcement at CERN in July 2012 (Image: CERN)

Since then CERN has been making history, though in a peculiar sense. Its LHC works in fact as a time machine, by concentrating energy to values that characterized the Universe only immediately after the Big Bang. Now we can rewind a movie no one has ever watched before and directly witness the story unfold as if it were the first time. We have some expectations about the movie but this time around the situation is trickier than in the Higgs-Columbus days: we have left America. The map we could use until then, the so-called Standard Model, is not adequate anymore.

Every model is a description of Nature that is optimized for a specific set of its features and the Standard Model makes no exception: it is very accurate in its domain but cannot explain 95% of the Universe. These dark sectors are like very dim, unexplored rooms in a castle: to build a detailed map of these rooms we need to probe them, to understand their architecture and the variety of their furniture we need landmarks that inform our bearings.

ATLAS and CMS scientists have just finished analyzing information that seem to suggest a new landmark could exist, what exactly is still up for debate: it could be as familiar as a cousin of the Higgs boson or as novel as a manifestation of extra dimensions. This uncertainty represents science in the making and is very fruitful for researchers because it compels them to go through a checklist that resembles the one about the coin toss: are we dealing with a completely new coin? Or will new tosses wash away the seven-heads-in-a-row occurrence?

Only time and more data will tell if we have finally found new physics beyond the Standard Model: after all we have just started watching the movie about the history of the Universe.

CERN at Rio’s Carnival

Hello everyone,
it’s been a while and I wanted to break my silence with a short post. I would like to share with you a curious video that a friend of mine just sent me: it is nothing less than CERN physics showcased at Rio’s Carnival! Go to 27′ and 40” and see for yourself; of course you can also watch the video in its entirety.

As we can read from the Facebook post that CERN dedicated to the occasion:

“Last year’s winning samba school, Unidos da Tijuca, presented a Swiss-themed procession at Rio de Janiero’s Sambadrome, including 200 people with costumes representing CERN’s “Acelerador de Partícula”. 

The school’s parade, in collaboration with swissnex Brazil and Swissando, featured everything from William Tell to Swiss chocolate to Einstein and included CERN’s flagship particle accelerator, which crosses the border between France and Switzerland.”

For more geeky moments at Rio’s carnival you can take a look here.
I hope this will keep you cheerful until my next post: I have a couple of drafts that have been lingering for a while now and I wish I had already shared them with you.

Talk to you soon!

Arrivederci, Professore

Ieri, 30 settembre 2015, è scomparso Guido Altarelli, professore di fisica e a lungo ricercatore del CERN. Qui di seguito il mio personalissimo ricordo dello scienziato e dell’uomo.

Il professor Altarelli riceve due dei numerosi riconoscimenti che la sua pioneristica attività di ricerca gli ha meritato (

Ecco la prima parola che ho pronunciato leggendo la notizia della sua scomparsa. Era già buio e stavo x lasciare il mio ufficio qui al Politecnico di Losanna. Ora lavoro qui, Professore, dove l’ho incontrata per la prima volta: lei ci ha tenuto il corso di Fisica oltre il Modello Standard durante il mio dottorato all’Università di Ginevra. Quello non era il mio campo e temevo che non avrei capito molto ma mi dissi che Guido Altarelli andava sentito almeno una volta nella vita di un fisico teorico come aspiravo ad essere. Con l’impazienza di incontrare per la prima volta un gigante mio connazionale e “collega”, venni alla sua prima lezione. Rimasi sorpreso di scoprire che lei era un gigante anche nel senso letterale del termine; ciononostante la trovai subito simpatico e alla mano, forse anche grazie a quell’accento romano che condividiamo nel parlare Inglese e Francese. Quello che mi stupì di più però furono i suoi occhi, anzi lo sguardo.
Se non ricordo male lei era appena andato in pensione dal CERN oppure stava per andarci. Eppure i suoi occhi erano ancora pieni di passione e curiosità per quella materia per la quale anche io come lei ho fatto una scelta di vita personale oltreché professionale. In questo credo fossimo veramente colleghi. Al corso lei ci spiegava i misteri del curioso mondo microscopico con la stessa vitalità e partecipazione con la quale un bambino racconta i giochi fatti all’asilo: c’è lui in quei giochi, non li ha “fatti”, li ha vissuti. Così lei, che ha inaugurato linee di ricerca che hanno fatto scuola e porteranno per sempre il suo nome. In questi giorni me le riguarderò cercando di capirle meglio e, come me, spero anche altri nostri connazionali.
Lascerò ad altri fisici spiegare i motivi tecnici per i quali lei era un motivo di orgoglio nazionale. Io mi limiterò a citare il fatto che mi sarebbe piaciuto che me li raccontasse lei di persona: era infatti un mio grande desiderio intervistarla, proprio per cercare insieme a lei di raccontare una storia che spiegasse a chi mi legge quali sono le scoperte con il suo nome, a che sono servite e come è stata l’avventura umana che ha portato a scalare quelle vette.
Ora sarà la stanchezza di fine giornata o la confusione dei tristi pensieri ma non ricordo se gliela feci questa proposta. Guarderò più tardi tra le mie email, dove cercherò elementi in più per vivere appieno la nostalgia della sua scomparsa. So però per certo che ci troverò un nostro scambio riguardo ai diagrammi di Feynman: io stavo scrivendo un articolo che ne parlasse in termini visivi, quasi artistici, come di uno strumento che ha potuto facilitare le ricerche sfociate nella scoperta del bosone di Higgs in quanto nuovo dizionario della comunicazione tra fisici. Lei non fu esattamente entusiasta di questo mio taglio: forse le scrissi a uno stadio troppo prematuro perché l’idea, sicuramente non convenzionale, potesse essere valutata nella sua pienezza. Ad ogni modo feci tesoro dei chiarimenti che lei volle fornirmi: ne ho tratto spunto per un progetto successivo che andava più nella direzione del rigore da lei preferita. La collaborazione che avevo messo in piedi per questo progetto si è interrotta per cui non è ancora concluso. Mai dire mai però: quando lo riprenderò sono sicuro che lei saprà ispirarmi ulteriormente, anche se purtroppo stavolta non sarà di persona.
Arrivederci, Professore!

Today we make history

Today the Large Hadron Collider at CERN restarts doing its business: colliding particles. How this works is best explained in this video from PhD Comics. As the video says, having energy is like having money: you can buy stuff. It’s like going to a restaurant and being able to buy dishes you never had the money for; the nice thing is that you do not know what those dishes are: it is as if the ingredients had not existed before you had enough money to order those dishes.

And that is also why today is so important. Until today we have never had so much energy to magnify the behavior of Nature at very small distance. Such a behavior has only been present once in the history of the Universe, some 14 billion years ago, when the cosmos was so young it only measured a teeny tiny speck, smaller than anything you have a feeling for.

So today CERN brings us back to those times, to see what was there before our atoms even existed. Today we go witness an untold chapter of the tale of our Universe. Today we travel back in time, today we make history!


How drawing a penguin can help cure cancer: physics diagrams as modern hieroglyphs and their applications

If you are a fan of The Big Bang Theory tv series you are used to laugh at Penny and Sheldon’s interactions, especially those when Doctor Cooper tries to explain physics to his blond friend.

 Sheldon and Penny during a discussion about particle physics; drawn on the blackboard, besides formulae, are pictograms known as Feynman diagrams, after their inventor Richard Feynman, physicist and Nobel Prize winner in 1965.

Sheldon and Penny during a discussion about particle physics; drawn on the blackboard, besides formulae, are pictograms known as Feynman diagrams, after their inventor Richard Feynman, physicist and Nobel Prize winner in 1965.

One such instance is captured in the picture above. If you look at it you can easily figure Sheldon say something like: “see, Penny: this equation accounts for the branching ratio of a top quark decaying into a W boson and a bottom quark, as depicted by the upper-left diagram”. Do you think Sheldon got into drawing to put himself in Penny’s shoes? Not at all: the pictograms on the blackboard are some serious piece of physics! They are known under the name of Feynman diagrams, after their inventor Richard Feynman, who first proposed their adoption in 1948 and later won the Nobel Prize thanks to, among other things, this visual handle on particle physics.

You don't get a postal stamp after you unless you've done something notable.

You don’t get a postal stamp after you unless you’ve done something notable.

Feynman was as much of an eccentric as his fictional colleague of The Big Bang Theory tv series: do you remember the episode “The Werewolf Transformation”, when Sheldon goes nuts and wakes up Leonard by playing bongos in the middle of the night? Well, Feynman used to play bongos, too (in fact, that’s probably where the authors of the series have taken inspiration from). However, quite differently from Doctor Cooper, Professor Feynman could drive a vehicle: this allowed him to have his van decorated with his own diagrams … how bloody cool!

Professor Feynman poses with his family in front of his van, which he decorated with instances of his very own visual handle on particle physics.

Professor Feynman poses with his family in front of his van, which he decorated with instances of his very own visual handle on particle physics.

But why would a scientist propose drawings to his colleagues? did they all get bored with their minds wandering? On the contrary: in the late 1940’s physicists were kind of stuck in their path to gain a better understanding of how the natural world works at an ever deeper level. Roughly speaking, they needed to know where to go next and how to reach their destination. That’s where the novelty of Feynman’s genius proved to be crucial: his diagrams provided the tools of a new language to formulate a new discourse.

Owing to their graphical character, Feynman diagrams bear resemblance to Egyptian hieroglyphs: just like that ancient pictogram system encoded a wealth of information in a single sign, a Feynman diagram encapsulates the description of an interaction among particles in a very clear and economic fashion; by means of this virtue, it is possible to streamline the computation of the measurable effect that a certain physical process has. Knowing what to compute and how were very much needed features at the time Feynman introduced his idea: the non-trivial advantage of adopting a common vocabulary lies in the univocal and universal standard of the naming this vocabulary provides; those who speak the same language are able to understand each other and, then, to communicate among themselves, sharing meaningful information.

Egypt Hieroglyphe4.jpg
Example of an Egyptian Hieroglyphe ” (licensed under CC BY-SA 3.0 via Wikimedia Commons).

As time passed, something very down-to-earth happened with Feynman diagrams and their adopters: when pondering about physical interactions, physicists began dubbing the configurations that particles assumed once arranged in a diagram, just like what we all do when we search for images of animals in the clouds. There are indeed particle interaction processes whose Feynman diagram resembles a bell, a sunrise, a tadpole, a seagull or even a penguin!

The Feynman diagram resembling a penguin.

The Feynman diagram resembling a penguin.

All this theoretical fun has brought physicists down the path recently crowned by the discovery of the Higgs boson, a.k.a. the God particle. Besides invaluable ideas, this endeavor was also made possible by the Large Hadron Collider, a machine whose name is inextricably linked to hadron-therapy, a branch of medicine that can accurately cure tumors lying deep in the human body.

A picture worth a thousand words. Radio-therapy employs X-ray photons, that is to say the same particles that make up visible light but with endowed higher energy. In their path to the tumor, X-rays deposit a non-negligible fraction of their radiation dose to healthy tissues. On the contrary, we can see from the picture that protons, the positively-charged constituents of atomic nuclei, are much more effective in reaching the deep-lying tumor, without damaging other body parts.

A picture worth a thousand words. Radio-therapy employs X-ray photons, that is to say the same particles that make up visible light but with endowed higher energy. In their path to the tumor, X-rays deposit a non-negligible fraction of their radiation dose to healthy tissues. On the contrary, we can see from the picture that protons, the positively-charged constituents of atomic nuclei, are much more effective in reaching the deep-lying tumor, without damaging other body parts.

More than sixty years after their proposal, Feynman diagrams are still largely employed in particle physics but not only: for example they are allowing new insight and better precision in calculating both the astrophysical signal to be expected when black holes collide and the modeling of molecular dynamics. Next time you see Penny trying to interpret some murky hieroglyph on Sheldon’s blackboard, think about these deep connections … after you have laughed, of course.


If you would like to know more about how the machinery of Feynman diagrams works you can take a look at the following references:
let’s draw Feynman diagams;
Physics and Feynman Diagrams.

For more fun, less mainstream uses of Feynman diagrams see:
– the ParticleZoo Feynman Diagram magnet set;
– the PhDComics’ Feynman Diagrams on Academic Interactions;
– the result of a Google search
art inspired by Feynman diagrams;
and much more …

A very passionate follower of Feynman diagrams chose to have one tattoed on his arm.

A very passionate follower of Feynman diagrams chose to have one tattoed on his arm.


In occasione del 60′ compleanno del CERN ecco una mia personalissima dedica a questo nostro grande orgoglio italiano e non solo (bella coincidenza che oggi sia la festa della Repubblica!).


CMS, uno dei quattro esperimenti disposti lungo l’anello dell’acceleratore LHC.
I diritti dell’immagine sono del CERN.

Ti toglie il fiato, ti lascia senza parole. È proprio un mostro nel senso originario del termine: il monstrum in latino è ciò che stupisce e inebetisce. Non è tanto affascinante solo perché è complicato: è bello perché è un capolavoro. Vorresti toccarlo, per provare a entrare in contatto più profondo con lui. Vorresti abbracciarlo per misurare quanto sei piccolo in confronto a lui ma questa è una lotta impari. Rappresenta infatti alcune delle caratteristiche più alte dell’essere umano:

– puntare alto, osare in maniera così spinta che neanche una coppia di novelli sposi;

– pianificare, con sudore e notti in bianco, stress e frustrazioni, da soli e insieme, per poi riuscire;

– mettere a frutto, rispettare e integrare le diversità delle etnie, culture, religioni, tradizioni, idee, modi di essere, di vestire, votare e intendere se stessi;

– il lavoro di squadra, quello dell’unione che fa la forza, accompagnato da un sano spirito di competizione verace e onesta, non influenzato da altro che l’evidenza, una delle più alte forme di democrazia, quella che garantisce il merito delle tue idee.

Questo è il CERN, il Centro Europeo per la Ricerca Nucleare, una moderna cattedrale eretta da alcuni esseri umani per il bene di tutti. E qual è questo bene? Non sarà mica aver messo un’etichetta su un altro esotico animale del mondo microscopico che ci dicono esistere ma noi non vediamo, non abbiamo mai visto e forse non vedremo mai? La domanda può accettare più risposte. Quella da scienziato è che il bene in questione è una sublimazione dell’intelletto, la quale deriva dal solo potersi porre il problema di quanti mattoni invisibili a occhio nudo compongono l’impalcatura dell’universo, quanti ne restano da etichettare e con che criterio.

La risposta digeribile a tutti, e forse anche la più interessante, è che, sebbene partecipino a quest’avventura solo delle menti sceltissime, i benefici dell’impresa sono veramente per tutti, è solo che non lo sappiamo: sebbene il CERN ci appartenga in quanto Italiani, ci interessiamo poco a lui e, quando lo facciamo, magari riceviamo anche poco in cambio. Per essere concreti riguardo ai benefici la maniera più immediata è partire dal nome del “mostro”: LHC, acronimo che in italiano diventa “grande collisore di adroni”, un’espressione che il correttore automatico del dispositivo elettronico con il quale sto scrivendo vorrebbe farmi correggere. Strano perché lui, il dispositivo, non sarebbe neanche qui se non fosse per il “mostro”, quello che è, ciò che rappresenta e come si è arrivati fino a lui. Un collisore di adroni è praticamente una gigantesca pista per l’autoscontro di particelle che si trovano anche dentro di noi, negli atomi che ci compongono. Studiandoli, negli ultimi 60 anni o giù di lì, qualche scienziato pazzo ha concepito un’idea che gli vale lo stereotipo: curarci i tumori! Pazzo lui e pazzesca l’idea: che legame ci potrà mai essere tra uno dei pochi lavori utili e rispettabili, quello del dottore, e il lavoro di un inutile fisico, che o ha la testa fra le nuvole oppure è chino a scrivere su qualunque cosa gli capiti a tiro, compresi i fazzoletti per il naso? Non sono materie diverse, fisica e medicina? Del resto per fare l’uno o l’altro dei due lavori devi iscriverti a facoltà diverse e, dopo che ti sei specializzato, solo in un caso ti fai chiamare dottore quando rispondi al telefono. Queste sono categorie di comodo, la Natura, quella con la maiuscola, è una sola ed è costruita secondo schemi logici che tendono a ripetersi: molta parte della differenza è dovuta a una grandissima varietà di comportamento di “attori” che, in realtà, sono molto meno numerosi di quanto non ci si aspetti a uno sguardo superficiale. Atomi nel corpo, atomi nell’universo: studio gli uni, capisco anche gli altri. Se poi ci aggiungo i tipi di interazioni e le particelle che fungono da messaggere dell’informazione “comportamentale”, posso pensare di passare da uno studio sugli acceleratori all’uso degli acceleratori per irradiare al meglio la zona colpita dalla malattia del secolo. Questo legame è di una profondità abissale, dà le vertigini ed è giusto che sia così. È un po’ meno giusto che lo sappiano in pochi, non tanto perché va venduto il progetto LHC o il suo successore, quanto piuttosto perché va pubblicizzata questa faccia della ricerca di base: ci apre la mente, ci migliora la vita, ci dà futuro. A tutti.

Ecco perché resto inebriato ogni volta che ho la fortuna di scendere 100 metri sotto terra a contemplare il “mostro”; auguro di cuore a tutti voi di poter sperimentare questa sensazione prima o poi: ci si sente così piccoli eppure così grandi.
Tanti auguri allora al CERN per i suoi primi 60 anni!