• John
  • Felde
  • University of Maryland
  • USA

Latest Posts

  • USLHC
  • USLHC
  • USA

  • James
  • Doherty
  • Open University
  • United Kingdom

Latest Posts

  • Andrea
  • Signori
  • Nikhef
  • Netherlands

Latest Posts

  • CERN
  • Geneva
  • Switzerland

Latest Posts

  • Aidan
  • Randle-Conde
  • Université Libre de Bruxelles
  • Belgium

Latest Posts

  • TRIUMF
  • Vancouver, BC
  • Canada

Latest Posts

  • Laura
  • Gladstone
  • MIT
  • USA

Latest Posts

  • Steven
  • Goldfarb
  • University of Michigan

Latest Posts

  • Fermilab
  • Batavia, IL
  • USA

Latest Posts

  • Seth
  • Zenz
  • Imperial College London
  • UK

Latest Posts

  • Nhan
  • Tran
  • Fermilab
  • USA

Latest Posts

  • Alex
  • Millar
  • University of Melbourne
  • Australia

Latest Posts

  • Ken
  • Bloom
  • USLHC
  • USA

Latest Posts


Warning: file_put_contents(/srv/bindings/215f6720ac674a2d94a96e55caf4a892/code/wp-content/uploads/cache.dat): failed to open stream: No such file or directory in /home/customer/www/quantumdiaries.org/releases/3/web/wp-content/plugins/quantum_diaries_user_pics_header/quantum_diaries_user_pics_header.php on line 170

Archive for October, 2013

Last week, I was in Arlington, Virginia to give a talk at a cybersecurity research workshop called LASER 2013.  Why did they want to hear a particle physicist speak?  Well, this particular workshop is focused on “properly conducted experimental (cyber) security research,” so they want to hear from people in other fields about how we run experiments, publish the results, and think about science in general.  So I gave a talk, slightly over an hour long, that used the Higgs boson to illustrate the giant experiments we do at the LHC, the social organization required to do them, and their results.  I said a lot of things here that you don’t normally say explicitly as part of a particle physics conference, and I also heard what sort of experiments one can do in cybersecurity research.  We had some very interesting discussions about how experimentation and data analysis really work, and I really appreciate the opportunity I had to participate in the workshop.

You can watch my whole talk here, and I would definitely appreciate your feedback:

Share

The Humble Scientist

Tuesday, October 22nd, 2013
Peter Higgs at a press conference at Edinburgh University on 11 October 2013.

Peter Higgs at a press conference at Edinburgh University on 11 October 2013.

As the dust settles following the announcement of the winners of the 2013 Nobel prize for physics, it is worth pausing for a moment to contemplate the man who – reluctantly – gave his name to a boson.

On 8 October 2013, at around 10am GMT, the Nobel committee concluded its deliberations, identified this year’s laureates, and made a few phone calls. In an apartment in Edinburgh a telephone rang, and rang…

Peter Higgs was in a little pub in Leith, a beautiful area to the north of Edinburgh, enjoying a nice bowl of soup, some fish and a pint. It was only when he returned to Edinburgh that an old neighbour congratulated him on the ‘good news’. He replied, “oh, what news?”. On being informed that he had been awarded science’s highest honour, the 84 year-old Emeritus professor resignedly trudged back to his apartment – and its ringing telephone.

Higgs was born in Newcastle in 1925, the son of an Englishman and Scotswoman. He was home-schooled in his early years then, when his family relocated to Bristol, he attended Cotham Grammar School where he was a prize-winning pupil – but not in physics. It was only when he read the works of Paul Dirac, an old boy of his school, that physics really captured his imagination. Higgs went on to be awarded first class honours in undergraduate physics at Kings College London before completing a Masters and PhD in molecular physics. In 1960 he took up a permanent lecture post in Edinburgh.

The Highland air clearly agreed with Higgs, for it was during his walks in Scotland’s rugged mountain ranges that he is said to have conceived a theory of how certain fundamental particles acquire mass. In October 1964 he submitted two papers to the journal Physics Letters, the second of which related to this theory and what is now known as the Higgs field. The first paper was published but the second was rejected and stated to have “no obvious relevance to physics”. On reviewing the paper, Yoichiro Nambu, a respected physicist of the time, suggested Higgs may like to explain the physical implications of his theory. So Higgs inserted a paragraph explaining that the excitation of the Higgs field would yield a particle, which would come to be known as the Higgs boson. Higgs resubmitted the amended paper to rival journal Physical Review Letters, which published it later in 1964.

Around the same time other theorists were working on similar ideas. Belgium’s Robert Brout and Francois Englert published a paper prior to Higgs in 1964 and, although their paper didn’t explicitly refer to the boson, it was the first to propose the mechanism now known as the Brout-Englert-Higgs mechanism.  Another trio of scientists, Kibble, Guralnik and Hagen, also helped to refine the theory behind this mechanism, which is now a keystone of the Standard Model.

Higgs went on to enjoy a successful career in physics, be appointed to various distinguished posts, and win many awards. It was however his work on the Brout-Englert-Higgs mechanism which remains his most notable contribution to the field.

On attending a conference in Sicily in early July 2012, Higgs was tipped off by CERN veteran John Ellis that the observation of the Higgs boson may be announced at a seminar planned for the 4th July at CERN, Geneva. Once he and his travel companion, Alan Walker, were satisfied they had sufficient clean underpants between them to extend their trip, they changed their flights. The observation of the Higgs boson was indeed announced and both Higgs and Englert, who had never previously met, were present. Higgs shed a tear of joy following the announcement and on being asked why he was so moved, he stated that it was people’s reaction to the news and how much it meant to them that so profoundly affected him. On the plane back to Edinburgh he celebrated with a bottle of London pride – a working-man’s ale.

Back to 2013, and Higgs must endure the media storm which inevitably follows a Nobel laureate to be. He will patiently give interviews and press conferences but one strongly suspects that he would prefer to be back in Leith having a pint. What I so admire about Higgs, other than his obvious scientific brilliance, is what an understated and humble man he is. Where some seem to ravenously crave a Nobel, one suspects Higgs would prefer not to have to bother with the accompanying kerfuffle. Indeed Higgs rejected a knighthood as he did not want “that sort of title”. He has been at pains to emphasise the contributions of the five other original authors of the Brout-Englert-Higgs mechanism, and the thousands of other scientists at CERN and beyond involved with the observation of the Higgs boson. He belittles his contribution to science as compared to the likes of Einstein as it only took “two or three weeks in 1964” to concoct. And to top it all he is just about the only person who refers to the Higgs boson as the ‘scalar boson’. In today’s highly competitive, often cut-throat, social media driven society, his dignified, gentle and modest character is wonderfully refreshing.

Higgs plans to retire from his busy lecture schedule when he hits the ripe age of 85. He leaves behind a world of science full of uncertainty. The Higgs boson looks awfully like the Standard Model Higgs boson but is it a supersymmetrical Higgs boson? Are there other types of Higgs boson waiting to be discovered when the Large Hadron Collider is switched back on in 2015? And what about dark matter and dark energy – what on Earth are they all about?

One thing is certain however – they don’t make ’em like Peter Higgs anymore.

Share

Unanswered questions

Tuesday, October 22nd, 2013

This article appeared in symmetry on Oct. 22, 2013.

Do you think scientists have the answers to all the questions? As these researchers admit, there’s still so much to discover. Particle physics is brimming with mysteries and unknowns. Photo: Sandbox Studio, Chicago

Do you think scientists have the answers to all the questions? As these researchers admit, there’s still so much to discover. Particle physics is brimming with mysteries and unknowns. Photo: Sandbox Studio, Chicago

Bring hundreds of smart physicists together and what do you get? Lots of questions!

This summer, more than 700 particle physicists from nearly 100 universities and laboratories across the United States came together on the University of Minnesota’s Twin Cities campus for the Snowmass Community Summer Study meeting. There, they discussed the decades ahead in US particle physics, carefully considering the next steps in their studies of energy, matter, space and time.

During coffee breaks, symmetry asked attendees to share open questions in particle physics. Here’s a sample of what particle physicists think about and what they hope to discover in the coming decades.

View an image gallery of particle physicists asking their most pressing questions.

Share

Grad School in the sciences is a life-changing endeavour, so do not be afraid to ask questions.

Hi Folks,

Quantum Diaries is not just a place to learn the latest news in particle physics; it is also a resource. It is a forum for sharing ideas and experiences.

In science, it is almost always necessary to have a PhD, but what is a PhD? It is a certification that the holder has demonstrated unambiguously her or his ability to thoroughly carry out an independent investigation addressing a well-defined question. Unsurprisingly, the journey to earning a PhD is never light work, but nor should it be. Scientists undertake painstaking work to learn about nature, its underpinnings, and all the wonderful phenomena that occur in everyday life. This journey, however, is also filled with unexpected consequences, disappointment, and sometimes even heartbreak.

It is also that time of year again when people start compiling their CVs, resumes, research statements, and personal statements, that time of year when people begin applying for graduate programs. For this post, I have asked a number of good friends and colleagues, from current graduate students to current post docs, what questions they wished they had asked when apply for graduate school, selecting a school, and selecting a research group.

However, if you are interested in applying to for PhD programs, you should always first yourself,  “Why do I want a research degree like a PhD?”

If you have an experience, question, or thought that you would like to share, comment below! A longer list only provides more information for applicants.

As Always, Happy Colliding

– Richard (@bravelittlemuon)

PS I would like to thank Adam, Amy, John, Josh, Lauren, Mike, Riti, and Sam for their contributions.

Applying to Graduate School:

“When scouting for grad schools, I investigated the top 40 schools in my program of interest.  For chemistry, research primarily occurs in one or two research labs, so for each school, I investigated the faculty list and group research pages.  I eliminated any school where there werre fewer than two faculty members whose fields I could see myself pursuing.  This narrowed down my list to about a dozen schools.  I then filtered based on location: I enjoy being near a big city, so I removed any school in a non-ideal location.  This let me with half a dozen schools, to which I applied.” – Adam Weingarten, Chemistry, Northwestern

“If there is faculty member you are interested in working for, ask both the professor and especially the students separately about the average length of time it takes students to graduate, and how long financial support might be available.” – Lauren Jarocha, Chemistry, UNC

“My university has a pretty small physics program that, presently, only specializes in a few areas. A great deal of the research from my lab happens in conjunction with other local institutes (such as NIST and NIH) or with members of the chemistry or biology departments. If you are interested in a smaller department, ask professors about Institutes and interdisciplinary studies that they might have some connection to, be it within academia or industry.” – Marguerite Brown, Physics, Georgetown

“If you can afford the application fees and the time, apply as broadly as you can.  It’s good to have options when it comes time to make final decisions about where to go. That said, don’t aim too high (you want to make sure you have realistic schools on your list, whatever “realistic” means given your grades and experience), and don’t aim too low (don’t waste time and money applying to a school that you wouldn’t go to even if it was the only school that accepted you, whether because of academics, location, or anything else).  Be as honest as possible with yourself on that front and get input from trusted older students and professors.  On the flip side, if you don’t get rejected from at least one or two schools, you didn’t aim high enough.  You want a blend of reach schools and realistic schools.” – Amy Lowitz, Physics, Wisconsin

Choosing a School

“One of the most common mistakes I see prospective graduate students make is choosing their institution based on wanting to work with a specific professor without getting a clear enough idea of the funding situation in that lab.  Don’t just ask the professor about funding.  Also ask their graduate students when the professor isn’t present.  Even then, you may have to read between the lines; funding can be a delicate subject, especially when it is lacking.” – Amy Lowitz, Physics, Wisconsin

“If you have a particular subfield/group you *know* you are interested in, check how many profs/postdocs/grads are in these groups, check if there are likely to be open slots, and if there are only 1 or 2 open slots make sure you know how to secure one. If they tell you there are currently no open slots, take this to mean that this group is probably closed for everything but the most exceptional circumstances, and do not take into account that group when making your decision.” – Samuel Ducatman, Physics, Wisconsin

“When choosing a school, I based my decision on how happy the grad students seemed, how energetic/curious the faculty appeared, and if the location would allow me to have extracurricular pursuits (such as writing, improv, playing games with people, going to the movies…basically a location where I could live in for 4-6 years).” – Adam Weingarten, Chemistry, Northwestern

“At the visitor weekend, pay attention to how happy the [current] grads seem. Remember they are likely to be primarily 1st years, who generally are the most happy, but still check. Pay attention to the other students visiting, some of them will be in your incoming class. Make sure there is a good social vibe.” – Samuel Ducatman, Physics, Wisconsin

“When I was visiting a prospective grad student, there was a professor at a university I was visiting whose research I was really interested in, but the university would only allow tuition support for 5 years. When I asked his students about graduation rates and times, however, the answer I got was, ‘Anyone who graduates in 5 years hasn’t actually learned anything, it takes at least 7 or 8 years before people should really graduate anyway. Seven years is average for our group.’ In some fields, there is a stigma associated with longer graduation times and a financial burden that you may have to plan for in advance.” – Lauren Jarocha, Chemistry, UNC

Choosing a Group

“When considering a sub-field, look for what interests you of course, but bear in mind that many people change their focus, many don’t know exactly what they want to do immediately upon entering grad school, and your picture of the different areas of research may change over time. Ask around among your contemporaries and older students, especially when it comes to particular advisers.” – Joshua Sayre, PhD, Physics, Pittsburgh
“If you know that you’re interested in an academic career that is more teaching oriented or research oriented, ask about teaching or grant writing opportunities, respectively. I know plenty of fellow students who didn’t start asking about teaching opportunities their 4th or 5th year of their program, and often by then it was too late. If you know that finding funding will be a big part of your future, joining a group where the students take an active part in writing grants and grant renewals is invaluable experience.” –  Lauren Jarocha, Chemistry, UNC
“For choosing groups, I attended group and subgroup meetings, met with faculty to discuss research and ideas, and read several recent publications from each group of interest.  What I did not do (and wish I had) was talk with the graduate students, see how they and the group operated.  For example, I am very motivated and curious to try new ideas, so in my current research group my PI plays a minimal role in my life.  The most important aspect is how well one’s working style fits with the group mentality, followed by research interest.  There’s a ton of cool, exciting research going on, but finding a group with fun, happy, motivated people will make or break the PhD experience.” – Adam Weingarten, Chemistry, Northwestern
“I went into [Condensed Matter Theory] and not [X] because (1) In the summer of my first year I had no research, and I came close to having no income because of this. I realized I needed someone who could promise me research/funding and real advising. The [X] group was pretty filled up (and there were some politics), so it was impossible to get more than this. (2) I thought the professors in CMT treated me with more respect then the [X] profs I talked to.” – John Doe, Physics
“I believe that choosing which grad schools to apply to should primarily be about the research, so this question is more for after you’ve (hopefully) been accepted to a couple schools.  If you are going into theoretical physics, and if you don’t have some sort of fellowship from them or an outside agency, ask them how much their theory students [teach].  Do they have to TA every semester for their funding?  Do they at least get summers off?  Or do they only have to TA for the first one or two years?  This shouldn’t be the primary factor in deciding where to go – research always is – but it’s not something that should be ignored completely.  Teaching is usually somewhat rewarding in my experience, but it adds absolutely no benefit to your career if you are focused on a professorship at a research university.  Every hour you spend steaching is an hour someone else is researching and you aren’t.  And 10-20 hours a week of teaching adds up.” – Michael Saelim, Physics, Cornell
Share

Can you think of anything that all the men who won the Nobel Prizes in science this year have in common? I’ll give you a hint: the answer is already in the question. In fact, out of 195 people awarded the Nobel Prize in Physics since 1901, only two have been women: Marie Curie in 1901 and Maria Goeppert Mayer in 1963.

I have been thinking quite a bit about the status of women in science and what we say about it lately, ever since reading the most recent posts on the subject here on Quantum Diaries. Both were written by James Doherty: “Girls, at CERN – loads of ’em!” and “Five Lessons from a Summer at CERN” (formerly titled, in part, “Italians are Hot,” and still with a subsection by that name). I think it should become clear that I don’t approve of James’s tone in some places, although I understand that he was aiming to convey his experience as a summer student in “an open, honest and light-hearted way.” At the same time, Quantum Diaries is a place for voices from the physics community: writers here usually don’t speak for anyone, but we are supposed to be representative. So, if we are going to talk about the issues faced by women in physics, we also need voices from professional particle physicists, who have thought and learned a bit about where gender inequalities arise and their implications for our field. In that spirit, let me put forward my viewpoint, along with links to many other views I’ve found educational; I’m sorry to say that from my perspective there’s a bit less to be light-hearted about.

Particle physics is my job. I come to CERN every day and work with my colleagues to learn more about the universe. Some of my colleagues are women. Some are men. Some are Italian. Who they are, how they look, or what they’re wearing cannot be my foremost concerns. If I don’t look all of my colleagues in the eye and listen to what they’re saying, then I am doing poorly at my job. I’m likely to suffer for it later, because whoever I didn’t listen to probably said something I need to know. The starting point is to treat everyone professionally and with respect.

Easy enough to agree with so far; I think almost everyone would. The problem is that, well, we still have a problem. As Pauline Gagnon wrote here last year, more and more women are joining our field, but they are still greatly underrepresented. Unless you believe that women are inherently bad at physics – and there are pretty straightforward reasons to believe that that can’t possibly be causing the imbalance – then something is going wrong somewhere. A lot of excellent potential physicists are deciding against physics as a career at one stage or another, or perhaps never learning about it in the first place, or are even being pushed or nudged out by sexism. Anywhere we lose potential colleagues makes our work poorer.

Where is it going wrong, and what can we do about it? Well, my experience actually isn’t very informative. I have never seen an example of deliberate ill-will toward female participation in physics, and indeed I’ve only recognized a few situations that were even accidentally awkward. But bias can be unconscious and difficult to recognize. As a scientist, I know two things:

1. Just because I’ve never seen something, that doesn’t mean it doesn’t exist.
2. I can read what other people have written to learn about stuff.

So here are some articles and blogs I have found enlightening, in particular on the question of what actions we can take as scientists to help bring about more even participation by women:

The literature on women in science, technology, engineering, and math is enormous, and I’m very far from knowing all of it well. Do you have a favorite article or study, especially on what we as scientists can do better? Post the link and I’ll add it below.

Update, Oct 16: Some suggested links (thanks, Ben, Sarah, and Ken!):

Update, Oct 21 (thanks, Marga!): http://www.newyorker.com/online/blogs/elements/2013/10/a-ripple-of-voices-against-sexism.html

Share

Jacques Martino, Directeur de l’Institut national de physique nucléaire et des particules du CNRS, adresse ses félicitations à François Englert et Peter Higgs pour le Prix Nobel de physique 2013, et rappelle la contribution en France du CNRS à la découverte du fameux boson.

Enthousiasme général des physiciens et ingénieurs des expériences Atlas et CMS lors de l'annonce du Prix Nobel de Physique 2013. © CERN

Enthousiasme général des physiciens et ingénieurs des expériences Atlas et CMS lors de l’annonce du Prix Nobel de Physique 2013. © CERN


« Au nom du CNRS, je veux féliciter François Englert et Peter Higgs pour l’intuition extraordinaire dont ils ont fait preuve il y a presque 50 ans, en “inventant” le “boson de Higgs”. Le boson de Higgs a été théorisé dans les années 1960, notamment pour expliquer pourquoi certaines particules ont une masse alors que d’autres n’en ont pas. Il est alors devenu un véritable Graal pour nos physiciens. Il est en effet la clé de voûte du Modèle standard de la physique des particules, un ensemble théorique cohérent permettant de décrire le monde des particules subatomiques. Sans nul doute, la découverte d’un boson de Higgs vient donc de manière éclatante conforter ce modèle standard !

Il est indéniable que cette prédiction a animé des milliers de chercheurs durant toutes ces années, et je veux saluer aussi le travail titanesque accompli par les chercheurs,  ingénieurs et techniciens qui ont construit le LHC au CERN ainsi que les détecteurs Atlas et CMS. Ce prix Nobel célébré aujourd’hui, il nous appartient un peu aussi, car nos chercheurs français ont participé de manière très importante à cette grande quête collective qu’a été la traque du boson de Higgs.

Il aura fallu relever des défis technologiques colossaux qu’il s’agisse de l’accélérateur, des détecteurs ou bien encore des infrastructures de calcul permettant de traiter l’énorme quantité de données produites. Car rechercher le boson de Higgs revient véritablement à chercher une aiguille dans une botte de foin !

Plusieurs centaines de personnes du CNRS ont apporté leur pierre à la construction des  expériences du LHC et joué un rôle décisif dans l’exploitation scientifique des données. L’action déterminante du CNRS dans ce domaine serait sans aucun doute impossible sans l’expertise reconnue de l’IN2P3 qui fédère l’ensemble de ces activités et qui participe ainsi avec force au rayonnement national et international du CNRS. Ces recherches rappellent aussi de manière remarquable combien la collaboration internationale peut être porteuse de réussite.

Cette découverte majeure est le premier succès du LHC et vient ainsi couronner le succès de toute une communauté. Pour toute cette communauté, aujourd’hui est un jour de fête. Et pour le CNRS, cette découverte récompense 20 années d’investissements technologiques et humains dans lesquels une douzaine de laboratoires de CNRS, ont joué un rôle majeur aux côtés du CERN, ainsi que 200 chercheurs français.

La vie du LHC ne fait que commencer et cette réussite est certainement porteuse d’un avenir riche de nouvelles découvertes qui mobiliseront nos équipes dans les années qui viennent. Le Higgs a encore bien des secrets à nous livrer, nous l’avons pour l’instant seulement “aperçu”, et il convient de préciser sa nature et ses caractéristiques. Il s’agit là d’un énorme chantier à venir. Mais le programme de recherche du LHC dépasse largement ce cadre !  Le Modèle standard de la physique des particules s’il se voit conforté, laisse de nombreuses questions en suspens. Matière noire, supersymétrie… La recherche d’une nouvelle physique au-delà du Modèle standard va ainsi se poursuivre dans les années pour repousser toujours les frontières de notre compréhension de la matière et de l’Univers. »

À voir également :

Jacques Martino réagit à l’annonce du Prix Nobel de Physique 2013


François Englert et Peter W. Higgs, Prix Nobel… par CNRS

Comment chasse-t-on le boson ?


La chasse au boson de Higgs par CNRS

et pour tout savoir sur le LHC et le boson de Higgs (actus, BDs, vidéos): http://lhc-france.fr/higgs

Share

You’re looking at the title and thinking, “Now that’s not true! Francois Englert is Belgian, and Peter Higgs is from the UK. And CERN, where the Higgs discovery was made, is a European lab, not in the US.”

That is all true, but on behalf of the US LHC blog, let’s take a few minutes to review the role of the United States in the Higgs observation that made this prize possible. To be sure, the US was part of an international effort on this, with essential contributions from thousands of people at hundreds of institutes from all over the world, and the Nobel Prize is a validation of the great work of all of them. (Not to mention the work of Higgs, Englert and many other contributing theorists!) But at the same time, I do want to combat the notion that this was somehow a non-US discovery (as some have implied). For many more details, see this link.

US collaborators, about 2000 strong, are a major contingent within both of the biggest LHC experiments, ATLAS and CMS. I’m a member of CMS, where people from US institutions are about one third of the membership of the collaboration. This makes the US physicists the largest single national contingent on the experiment — by no means a majority, but because of our size we have a critical role to play in the construction and operation of the experiment, and the data analysis that follows. American physicists are represented throughout the management structure (including Joe Incandela, the current CMS spokesperson) and deep in the trenches.

While the detectors were painstakingly assembled at CERN, many of the parts were designed, prototyped and fabricated in the US. On CMS, for instance, there has been US involvement in every major piece of the instrument: charged particle tracking, energy measurements, muon detection, and the big solenoid magnet that gives the experiment its name. Along with the construction responsibilities come maintenance and operational responsibilities too; we expect to carry these for the lifetime of the experiment.

The data that these amazing instruments record must then be processed, stored, and analyzed. This requires powerful computers, and the expertise to operate them efficiently. The US is a strong contributor here too. On CMS, about 40% of the data processing is handled at facilities in the US. And then there is the last step in the chain, the data analysis itself that leads to the measurements that allow us to claim a discovery. This is harder to quantify, but I can’t think of a single piece of the Higgs search analysis that didn’t have some US involvement.

Again, this is not to say that the US is the only player here — just to point out that thanks to the long history that the United States has in supporting this science, the US too can share some of the glory of today’s announcement.

Share

Today the 2013 Nobel Prize in Physics was awarded to François Englert (Université Libre de Bruxelles, Belgium) and Peter W. Higgs (University of Edinburgh, UK). The official citation is “for the theoretical discovery of a mechanism that contributes to our understanding of the origin of mass of subatomic particles, and which recently was confirmed through the discovery of the predicted fundamental particle, by the ATLAS and CMS experiments at CERN’s Large Hadron Collider.” What did they do almost 50 years ago that warranted their Nobel Prize today? Let’s see (for the simple analogy see my previous post from yesterday).

The overriding principle of building a theory of elementary particle interactions is symmetry. A theory must be invariant under a set of space-time symmetries (such as rotations, boosts), as well as under a set of “internal” symmetries, the ones that are specified by the model builder. This set of symmetries restrict how particles interact and also puts constraints on the properties of those particles. In particular, the symmetries of the Standard Model of particle physics require that W and Z bosons (particles that mediate weak interactions) must be massless. Since we know they must be massive, a new mechanism that generates those masses (i.e. breaks the symmetry) must be put in place. Note that a theory with massive W’s and Z that are “put in theory by hand” is not consistent (renormalizable).

The appropriate mechanism was known in the beginning of the 1960’s. It goes under the name of spontaneous symmetry breaking. In one variant it involves a spin-zero field whose self-interactions are governed by a “Mexican hat”-shaped potential

MexicanHat

It is postulated that the theory ends up in vacuum state that “breaks” the original symmetries of the model (like the valley in the picture above). One problem with this idea was that a theorem by G. Goldstone required a presence of a massless spin-zero particle, which was not experimentally observed. It was Robert Brout, François Englert, Peter Higgs, and somewhat later (but independently), by Gerry Guralnik, C. R. Hagen, Tom Kibble who showed a loophole in a version of Goldstone theorem when it is applied to relativistic gauge theories. In the proposed mechanism massless spin-zero particle does not show up, but gets “eaten” by the massless vector bosons giving them a mass. Precisely as needed for the electroweak bosons W and Z to get their masses!  A massive particle, the Higgs boson, is a consequence of this (BEH or Englert-Brout-Higgs-Guralnik-Hagen-Kibble) mechanism and represents excitation of the Higgs field about its new vacuum state.

It took about 50 years to experimentally confirm the idea by finding the Higgs boson! Tracking the historic timeline, the first paper by Englert and Brout, was sent to Physical Review Letter on 26 June 1964 and published in the issue dated 31 August 1964. Higgs’ paper, received by Physical Review Letters on 31 August 1964 (on the same day Englert and Brout’s paper was published)  and published in the issue dated 19 October 1964. What is interesting is that the original version of the paper by Higgs, submitted to the journal Physics Letters, was rejected (on the grounds that it did not warrant rapid publication). Higgs revised the paper and resubmitted it to Physical Review Letters, where it was published after another revision in which he actually pointed out the possibility of the spin-zero particle — the one that now carries his name. CERN’s announcement of Higgs boson discovery came 4 July 2012.

Is this the last Nobel Prize for particle physics? I think not. There are still many unanswered questions — and the answers would warrant Nobel Prizes. Theory of strong interactions (which ARE responsible for masses of all luminous matter in the Universe) is not yet solved analytically, the nature of dark matter is not known, the picture of how the Universe came to have baryon asymmetry is not cleared. Is there new physics beyond what we already know? And if yes, what is it? These are very interesting questions that need answers.

Share

Another day at the office

Tuesday, October 8th, 2013

I suppose that my grandchildren might ask me, “Where were you when the Nobel Prize for the Higgs boson was announced?” I was at CERN, where the boson was discovered, thus giving the observational support required for the prize. And was I in the atrium of Building 40, where CERN Director General Rolf Heuer and hundreds of physicists had gathered to watch the broadcast of the announcement? Well no; I was in a small, stuffy conference room with about twenty other people.

We were in the midst of a meeting where we were hammering out the possible architecture of the submission system that physicists will be using to submit computing jobs for analyzing the data in the next LHC run and beyond. Not at all glamorous, I know. But that’s my point: the work that is needed to make big scientific discoveries, be it the Higgs or whatever might come next (we hope!) usually not the least bit glamorous. It’s a slog, where you have to work with a lot of other people to figure out all the difficult little details. And you really have to do this day after day, to make the science work. And there are many aspects of making science work — building advanced scientific instruments, harnessing the power of computers, coming up with clever ways to look at the data (and not making mistakes while at it), and working with colleagues to build confidence in a measurement. Each one of them takes time, effort and patience.

So in the end, today was just another day at the office — where we did the same things we’ve been doing for years to make this Nobel Prize possible, and are laying the groundwork for the next one.

Share

L’ensemble du CERN a été ravi ce matin d’apprendre que le prix Nobel de physique a été décerné cette année aux professeurs François Englert et Peter Higgs pour leurs travaux théoriques sur ce qui est maintenant connu comme le mécanisme de Brout-Englert-Higgs. Ce mécanisme explique comment les particules élémentaires obtiennent leurs masses.
Le CERN a aussi de bonnes raisons de célébrer, puisque le 4 juillet 2012, les scientifiques travaillant sur les expériences du LHC avaient fièrement annoncé la découverte d’une nouvelle particule. Ils et elles ont pu confirmé depuis qu’il s’agissait bien d’un boson de Higgs. Cette particule prouve que la théorie élaborée par Robert Brout, François Englert, Peter Higgs et autres en 1964 était bien correcte.

higgs-and-englert

Au CERN, nous sommes donc tous et toutes très heureuses de voir leur travail (et dans une certaine mesure, notre travail) récompensé par ce prix fort prestigieux.

Ce n’est pourtant qu’une décennie après leurs publications que Steve Weinberg, co-lauréat du prix Nobel en 1979, réalisa la pleine portée de leur travail en unifiant deux forces fondamentales, les forces électromagnétique et faible. C’est ce que Peter Higgs a expliqué en juillet dernier lors de la réunion de la division de physique des particules de la Société européenne de physique, où il a fait une présentation fort appréciée. Il y avait détaillé les contributions de tous ceux qui l’avaient précédé, y compris Englert et Brout, chacun fournissant un des éléments clés qui lui ont permis de concevoir son propre travail.

Il a rappelé comment tout a commencé avec Yoichiro Nambu et son travail de pionnier sur la « brisure de symétrie spontanée » dès 1960 (travail pour lequel il a partagé le prix Nobel en 2008). Nambu s’était lui-même inspiré des travaux de Robert Schrieffer, un physicien de la matière condensée qui avait développé des concepts similaires pour la théorie de la supraconductivité avec John Bardeen et Leon Cooper (prix Nobel de 1972).

La brisure spontanée de symétrie est au centre du mécanisme de Brout-Englert-Higgs récompensé aujourd’hui par l’Académie des sciences de Suède.
Le physicien Jeffrey Goldstone a ensuite proposé un modèle de champ scalaire souvent désigné comme le potentiel du “chapeau mexicain”, tandis qu’un autre théoricien de la matière condensée, Philip Anderson, (prix Nobel de 1977), a montré comment contourner certains problèmes soulevés par Goldstone.

Par la suite, Englert et Brout ont publié leur article, où leur mécanisme a finalement été révélé. Peter Higgs, qui travaillait indépendamment de Brout et Englert, a publié son article un mois plus tard en mentionnant spécifiquement l’existence d’un boson associé à ce mécanisme. Tom Kibble, Gerald Guralnik et Carl Hagen ont peu après contribué des éléments clés supplémentaires venant compléter cette théorie.

«J’ai du mentionner ce boson explicitement parce que mon article avait d’abord été rejeté pour manque de prévisions concrètes”, a expliqué Peter Higgs en riant lors de son discours l’été dernier. Cette référence à un nouveau boson explique en partie pourquoi son nom fut associé avec le désormais célèbre boson.

L’histoire du mécanisme de Brout-Englert-Higgs montre bien comment, en théorie tout comme en physique expérimentale, il faut beaucoup de monde contribuant de bonnes idées, un peu de chance mais surtout une grande collaboration pour aboutir à des découvertes révolutionnaires.

Les milliers de physicien-nes, ingénieur-e-s et technicien-ne-s ayant participé à la découverte du boson de Higgs avec le LHC ont également d’excellentes raisons de célébrer aujourd’hui.

Pauline Gagnon

Pour en savoir plus sur le boson de Higgs, voici une conférence grand public de 25 minutes que j’ai donnée au CERN lors des Journées portes ouvertes

Pour être averti-e lors de la parution de nouveaux blogs, suivez-moi sur Twitter: @GagnonPauline ou par e-mail en ajoutant votre nom à cette liste de distribution

 

Share