• John
  • Felde
  • University of Maryland
  • USA

Latest Posts

  • 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

  • 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
  • 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 November, 2011

Dispatches from the Intensity Frontier

Wednesday, November 30th, 2011

Hi everyone! I’m currently at the “Fundamental Physics at the Intensity Frontier” workshop in Rockville, Maryland. There are about 500 high energy physicists here who have gathered to discuss the future of “intensity frontier” physics in the United States. You can find a nice summary on Symmetry Breaking and can follow along on Twitter (#intensityfrontier). For those interested in checking out some of the slides, you can find the agenda here.

In short, the “intensity frontier” is shorthand the exploration of fundamental physics from high luminosity, that is looking for very rare processes that probe the quantum effects of new physics. (I may have to revise this personal definition after attending the workshop!) This should be contrasted with the “energy frontier,” which is what we usually discuss on this blog with the direct production of new physics at the LHC.

I’ll whet your appetite , here’s a teaser image from Nima Arkani-Hamed‘s opening talk in which he plots the “coolness” and “importance” of intensity frontier physics with respect to time:

From Nima Arkani-Hamed's talk at the Intensity Frontier Workshop

Fermilab has now passed the “energy frontier” torch to the LHC and is restructuring towards a particle physics lab dedicated to pushing the forefront of the intensity frontier. The workshop is a very unique and very special opportunity for theoretical and experimental physicists to get together and discuss the future of particle physics in the United States. There are over 500 high energy physicists here for the next three days, which perhaps makes this the center of particle physics this side of CERN. 🙂

As stated by Henry Weerts in his welcome talk, the workshop has four goals:

  1. Produce a single coherent document that explains the science opportunities at the intensity frontier.
  2. Identify the experiments and facilities needed to explore the intensity frontier.
  3. Demonstrate the importance of the intensity frontier to the physics and broader community.
  4. Educate the community.

The last item was particularly directed to the broader community, not just physicists but also to congress and—by extension—to the general public which ultimately supports research into fundamental science. To that end, it’s a busy workshop, but I’ll do my best to provide some updates about what’s going on.


Vacuum storage tank for helium lowered into a tunnel at Fermilab to the waiting MINERvA detector 350 feet below. Photo: Tona Kunz

The MINERvA experiment is all about trying to understand what happens when neutrinos collide with ordinary matter, as we’ve mentioned a few other times here on Fermilab’s Quantum Diaries blog:  Meet MINERvA: a blend of particle and nuclear physics and A particle physics private eye takes on the great interaction caper.

One thing we really want to understand is how neutrino interactions change depending on what kind of atomic nucleus is involved in the interaction. To study this, MINERvA has several layers of special materials — iron, lead and carbon – interspersed between the plastic layers that make up most of our detector.

This past month, we got an exciting new target made of liquid helium. Designing and building the target was no small feat. The helium has to be kept ultra cold, and because MINERvA sits in an underground cavern, lots of care had to be taken so that people working in the cavern would be safe in the event of a gas leak.

Helium target attached to MINERvA detector. Photo: Laura Fields

Although helium is tricky from a logistical perspective, it’s very exciting from a scientific one. There aren’t many particles in a helium nucleus – only four protons and neutrons, compared to 56 for iron and over 200 for lead. This means that particles that result from neutrino interactions within helium nuclei are relatively unlikely to run into anything else on their way out of the nucleus. Comparing neutrino interactions in helium with the heavier target materials will help us untangle primary neutrino interactions from secondary interactions that can occur as the primary particles try to exit the nucleus.

The MINERvA collaboration is currently hard at work analyzing the data from our iron, lead and carbon detectors, and looking forward to analyzing the data from our helium target soon!
— Laura Fields

Editor’s note: Follow the hashtag #intensityfrontier for information from the workshop.

At the Intensity Frontier, scientists use high energy beams and sensitive particle detectors to explore rare subatomic processes in search of answers to profound questions. More than 500 scientists are gathering this week to discuss the future role of the U.S. in these experiments. They will discuss the most exciting opportunities, the potential for new discoveries and the equipment and technology required for these new experiments.

The workshop, named “Fundamental Physics at the Intensity Frontier” and held from Nov. 30 to Dec. 2 near Washington, D.C., is split into six working groups. Speakers from each group will provide an overview of their study area and its future goals to an audience spanning the breadth of the physics community. Then medium-sized groups will break away for debates and discussions designed to stimulate open conversations.

“This will be a good opportunity for people in more specialized areas to interact and learn from each other and hopefully reinforce each other’s case for this physics,” said Jack Ritchie, a co-convener for the Heavy Quarks group and professor in the physics department at the University of Texas, Austin.

In recent years, the Intensity Frontier has become a top priority for fields like nuclear physics, according to Michael Ramsey-Musolf, a physics professor at the University of Wisconsin at Madison and a co-convener for the Nucleons, Nuclei and Atoms group.

“There’s a lot of synergy between high-energy physics, nuclear physics and cosmology and they all meet at the Intensity Frontier field,” he said.

The workshop also brings together scientists from similar research areas, such as muon physicists from experiments like Muon g-2, Mu2e and the proposed Long-Baseline Neutrino Experiment, according to David Hertzog, a University of Washington physics professor and member of the Charged Leptons group.

“This community is scattered all over the planet,” he said. “In any one snapshot you don’t have everybody in the same room like this.”

While the DOE’s Office of Science will use the event to evaluate the science opportunities for the U.S. particle physics community in this field, the workshop will also be a learning experience for those new to the Intensity Frontier.

“It will be very good for me to learn more about what the physics goals are,” said Gerben Stavenga, a postdoctoral fellow researching theoretical physics and a speaker for the Proton Decay group. “We’re looking forward to what the Intensity Frontier will bring us.”

From graduate students to Fermilab physicists and DOE staff, the community in attendance will comprise a large spectrum of physics professionals. The working groups have spent months preparing for the workshop.

“It’s going to be a big crowd of people and a wide range of physics to cover,” said Rouven Essig, an assistant professor from Stony Brook University and co-convener for the Hidden Sector Photons, Axions, and WISPs group. “Many eyes are on the workshop and it will have an important impact on the future direction of this field.”

—Brad Hooker


Walking Across the LHC

Monday, November 28th, 2011

About a month ago, I walked back to Saint-Genis-Pouilly, France from the CMS experiment site after my last meeting of the day, which basically amounts to walking the width of the LHC ring: about 6 miles. Here are a few pictures from the walk:

More pictures, and commentary, on Google+…


In Defense of Nuclear Physics

Friday, November 25th, 2011

Mr. In-Between, Mr. In-Between, Pickin’s mighty lean, Mr. In-Between[1].

This song always reminds me of nuclear physics. The scales (i.e. sizes) involved in nuclear physics are too large to be of interest to the reductionists, also known as particle physicists. They say it is just chemistry. The chemists, on the other hand, are not interested because the scales are too small.  Nuclear physics, the archetypal in-between science, has scales too short to apply directly to everyday life and too long to be at the cutting edge of short-distance physics. In-between science includes atomic physics, low energy nuclear physics, QCD and, if the LHC is successful, electro-weak physics. At the other end of the scale, we have the solar system and galactic science which have too a short a scale to be of interest to the cosmologists who are doing science at scales the size of the visible universe.

So, why do in-between science? Let’s take low-energy nuclear physics, the physics done at rare isotope facilities like TRIUMF’s ISAC facility, as an example.  The nucleus is an intriguing object. It is built of neutrons and protons which are themselves emergent objects, that is, objects that are not present explicitly in the underlying QCD model. They emerge from solving that model. It is somewhat like building on sand, but as in the case of sand castles, that can be productive and interesting.  Actually, things are not so bad. We now have a very good understanding of the relation between low-energy nuclear physics and QCD.

The nucleus is self-bound: the forces between the components hold it together. This allows all kinds of behaviour: it rotates, vibrates, has single-particle excitations, and pairing. It slices, it dices… well let’s not get carried away, this isn’t a TV commercial.  Disentangling the various types of excitation can be fun—just get any of my experimental colleagues going on the topic. There are real intellectual challenges in sorting it all out.  Great progress has been made but we are not at the end of the trail yet.

We also know a lot about nuclear power (no not in reactors, but in the stars). Stars are powered by gravitationally confined nuclear fusion. No need to build tokomaks—the universe has been powered by nuclear fusion from the beginning. To understand how the universe evolves through time, it is necessary to understand this energy source. And it’s not just ordinary stars, but novae and super novae are powered by nuclear energy as well. We are composed of the remnants of stars, remnants blown into space by novae and super novae explosions. We are star dust. Billion year old carbon.[2] To understand all this, is to understand nuclear physics. Explosive, short lived, and dynamic processes in the heavens depend on the properties of short-lived nuclear isotopes. Coming back down to our planet, the need for studying these isotopes and their associated reactions is fulfilled by facilities like ISAC which make and study short lived isotopes.

Even more down to earth, is nuclear medicine. Medical imaging, using short lived nuclear isotopes, explores questions such as, ‘What causes Parkinsonism?’ and ‘Can we catch Alzheimer’s disease at an early stage and cure it?’ Radiation has been used to cure cancer for a long time now and more progress is being made. In diagnosis and treatment, nuclear medicine is now mainstream. Cyclotrons, once the hallmark of elite physics departments, are now almost a necessity at research hospitals. The pure research in nuclear physics had led to benefits beyond our wildest dreams

And finally nuclear bombs; destruction beyond our wildest dreams. I would guess that in the USA, the right to keep and bear nuclear arms is covered by the second amendment. In any event, as with any science, nuclear physics can cure or kill. Fire keeps us warm, yet wood smoke is carcinogenic. What we need, always and everywhere, is reality-based thinking and responsible people.

To conclude, in-between science is driven by the same impulse that drives all science: a longing to know and a hope to help. Science at any scale is cool (or is that fundamental?).

I work like a dog with no recreation and they call me Mr In-between

Mr In-between, Mr In-between, makes a fellow mean, Mr In-between[1]

[1] From a song written by Harlan Howard and made popular by Burl Ives.

[2] From Woodstock by Joni Mitchell


Change of state

Friday, November 25th, 2011

A few weeks ago I bumped into one my group’s former students, Rozmin. She’s still jetlagged from her journey here and she had the look on her face that told me she’d been through the change of state. She’d transitioned from a grad student to a postdoc. The metamorphosis is not an easy one, and in fact no matter how much time you spend preparing for it, and how long it takes, there are always some surprises.

A while back she was still editing her thesis. Today she is finding her feet in a new role, one with more responsibilities, more challenges and fewer safety nets. From now on, students will look to her for help, and expect to get answers. I should point out that grad students do a great deal of the work here at ATLAS, and they answer a lot of the questions we have, and perform a lot of the studies that we need. But they’re here primarily to learn, the postdocs are primarily here to work, and at the back of our minds we have prejudices about our roles. As a postdoc I feel that I should be mentoring students and helping them, rather than having them help me, even though I spent most of my first year here playing catch up with students who knew the experiment inside out. As a student on BaBar, what mattered most was getting the thesis written, and I felt that it was okay to make mistakes, ask for help and tell people I didn’t really know what I was doing.

Becoming a postdoc

Becoming a postdoc

The difference between being a student and a postdoc is mostly cosmetic, and a lot of the time it’s hard to tell whether someone has graduated yet. The real difference is one of attitude. When Rozmin was a student she was impressed that I seemed to know a little bit about every part of particle physics, especially the history. She would ask me how I knew about the history of CP violation and the tau-theta puzzle, and I’d reply knowingly “It’s a postdoc thing.” “Like a special power?” “Yeah, postdoc power!” Of course at that point she knew it was a bit of an act. I knew little more than she did, but I said it with confidence, and that inspires confidence in others. I’ve had quite a few roles where I had to put on an act of confidence like that. One of my favorite examples was when I worked for a telephone helpline where there was a locked desk drawer full of secret help for the coordinators. When I finally saw what was inside I was surprised to find nothing but a bottle of gin, some chocolate, and an electric drill. I asked what the drill was for and they replied “To stop volunteers messing around with it.” Huh. It looks like sometimes we need to be told that the only source of reassurance is feigned confidence.

Sometimes this is all the help you get...

Sometimes this is all the help you get...

There’s no magic solution, no ancient wisdom and in research, everything is new. Once you realize that, and once you realize that everyone is out of their depth and everyone is working without a safety net, life becomes much easier. Then you can tell your grad students what they need to hear. “That’s an interesting question, let’s look it up online” means “I don’t know any more than you do”, “Let’s talk to Frank about this over coffee” means “I have no idea how to even get started on this problem, but I could use a break”, and “A similar study was tried at UA1” means “I have a tiny amount of information about this from a long time ago, but at least that means it’s not completely new.” And so on. It’s takes a while to get used to. I even managed to get a taste of life as a Professor recently. When faced with a particularly challenging problem the head of our department told me simply “Welcome to the world of supervision!” In that world, the stakes are higher, the help is rarer and it takes even more courage to make decisions with so much uncertainty.

Naturally there are more changes than a slightly different day job. Rozmin has had to move house (to a different continent) again and settle down somewhere new. This is one of the most traumatizing experiences a person can go through, so doing it in French, when your husband is thousands of miles away and you’ve got a high pressure job (as well as your student’s high pressure job) taking up all your time, it can get even more tricky. The dynamic of our friendship has changed since she got back, as we spend more time together, going for a coffee or a drink, talking about our respective jobs and problems. The shift in our friendship has brought us closer and now we’re both free of our theses, and can focus on what we came here for, the physics.

It's all about the small achievements

It's all about the small achievements

It’s challenging, it’s scary, it’s all about the unknown and even the unknowable. But it’s like I always say: We don’t these things because they’re easy, we do them because they’re hard.

Happy Thanksgiving Weekend! Thanks to Jorg Cham for the comics. PHD Comics


What is the QGP?

Wednesday, November 23rd, 2011

Heavy ion collisions allow us to recreate the density and temperature that existed at the very beginning of the universe, before the universe was 10-6 s old, in a laboratory environment. Studying the resulting hot dense matter, which we call a quark gluon plasma (QGP), allows us to both better understand the evolution of the universe and one of the four fundamental forces of nature, the strong force. The strong force, which is more properly called Quantum Chromodynamics (QCD), is the force that binds protons and all other hadrons together.

The evolution of matter in the universe from the Big Bang to the present.

I will take a brief moment to remind everyone about some QCD basics before discussing the quark gluon plasma. QCD is one piece of the Standard Model, the theory that describes all subatomic particle interactions outside of gravity. QCD is carried by particles that physicists gave the tongue-in-cheek label of gluons. The only subatomic particles that can interact with gluons are quarks, of which there are 6: up, down, strange, charm, bottom and top. Each quark contains a QCD charge, which we call color. The anti-quarks have an anti-color charge, while gluons carry both color and anti-color charge. What does this mean? This means that gluons can interact with each other! This makes QCD calculations quite complicated.

There are two aspects to QCD that are important to understand with respect to the quark gluon plasma: quark confinement and asymptotic freedom. At the temperatures and densities that we observe outside of heavy ion collisions, QCD keeps quarks confined within their parent hadrons. This means we have never observed a bare quark! At extremely high energies, the QCD field strength lowers until the quarks no longer feel the force, which we call asymptotic freedom. In a very dense medium, such as what we create in heavy ion collisions it easier for quark-antiquark pairs to pop into existence than it is for these pairs to do so in a vacuum. These quark anti-quark pairs lower the QCD field strength, which lowers the energy needed for the quarks to be free.

So returning to the original question. What is a QGP? The QGP is a medium so dense and hot that the quarks and gluons within it are no longer confined to their original hadrons. But in order to discuss the properties of a medium, it needs to be in local thermalization. The concept of temperature only has meaning when thermalization has occurred because temperature is a bulk matter quantity. How hot is it? The QGP is hotter than 175 MeV, or 400,000,000 times the temperature of the surface of the sun!

What does it mean for the quarks to be deconfined? Originally, physicists tried to model the QGP as a weakly-coupled gas, but those models failed. The idea was that the deconfined quarks would behave similar to an ideal gas. Physicists have achieved reasonable success in modeling the QGP as an ideal fluid, in fact the most perfect liquid known to man . The fact that this model fits the data better means that even though the quarks are not confined within hadrons, they still interact with each other. This model of QGP is sometimes called sQGP, where the s stands for strongly coupled.

Next I will discuss some key QGP signatures and how we are looking for them at ALICE.


Une des particules les plus recherchées en physique des particules, le boson de Higgs, semble jouer à la cachette. C’est peut-être parce qu’il n’existe tout simplement pas! Tout ce que nous physiciennes et physiciens savons c’est que quelque chose manque à la théorie actuelle. Ce pourrait être le boson de Higgs, ce qui serait la solution la plus simple. Ou encore il n’existe pas, ce qu’on doit prouver définitivement et passer à la prochaine hypothèse.

Nous possédons un modèle théorique appelé le modèle standard qui a résisté à des décennies de vérifications expérimentales sans révéler la moindre faille. Ce modèle prédit combien d’évènements contenant un boson de Higgs on devrait observer s’il existe, mais sans rien révéler sur sa masse, nous obligeant à chercher à l’aveuglette.

Un événement est un instantané de ce qui se produit quand des protons voyageant à près de la vitesse de la lumière entrent en collision dans le Grand Accélérateur de Hadrons ou LHC. Le modèle standard nous donne aussi le nombre d’évènements d’autres types qui pourraient simuler la signature d’une désintégration d’un boson de Higgs. Ces évènements qu’on appelle bruit de fond compliquent les mesures. Nous établissons des critères de sélection spécifiques afin de sélectionner un signal en particulier tout en minimisant la quantité de bruit de fond qui réussira à se faufiler. On utilise les prédictions théoriques pour évaluer le nombre d’événements pouvant émaner du signal ou du bruit de fond qui seront  retenu pour chaque critère de sélection. Il suffit de comparer ces prédictions avec ce que l’on recueille réellement avec nos détecteurs pour déduire si certains contiennent un Higgs ou pas.

Imaginez tous les évènements recueillis comme le contenu d’un lac par une journée sans vent. Si un poisson vient à passer, on peut détecter sa présence par l’apparition de vagues à la surface de l’eau. La présence d’un boson de Higgs se révèlerait de la même manière: une vague à la surface de l’eau calme. Mais en cas de vent, les rides à la surface masqueront la présence du poisson. Le bruit de fond agit comme le vent: il varier aussi selon les lois de la statistique, créant une surface inégale qu’il est facile de méprendre pour un signal venant du boson de Higgs. Plus on a de données, moins ces variations sont importantes proportionnellement parlant et plus on a de poissons au même endroit, les rendant beaucoup plus facile à détecter.

Pour résumer, si on espère trouver le boson de Higgs ou tout autre nouvelle particule, plus on a de données, et plus ça devient facile. En attendant, on reste au niveau des suppositions puisque la moindre fluctuation statistique peut nous berner.

C’est ce qui s’est passé cet été quand nous avions cru apercevoir les signes avant-coureurs du boson de Higgs en juillet. Nous n’avions alors qu’un femtobarn inverse de données, ceci étant l’unité de mesure utilisée pour le volume de données. Le mois suivant, avec deux fois plus de données, les expériences CMS et ATLAS ont constaté que le petit excès avait disparu, et devait donc être imputé à une variation statistique, la hantise des physiciens et physiciennes des particules. Si on reprend l’analogie du lac d’apparence calme, les vaguelettes qu’on avait aperçues n’étaient pas dues à la présence de poissons, mais seulement l’effet d’une petite brise.

Après bien des efforts, la première combinaison des résultats d’août ont été rendu public vendredi dernier. Ceci est équivalent à un volume de données de quatre femtobarns inverses collecté par une expérience, soit quatre fois plus qu’en juillet. Ceci nous permet maintenant d’exclure la possibilité d’un boson de Higgs ayant une masse comprise entre 141 et 476 GeV avec un taux de confiance de 95%. Il reste donc de moins en moins d’espace où ce boson pourrait se cacher, soit entre 114 et 141 GeV, ou au-delà de 476 GeV.

C’est à basse masse qu’on s’attend le plus  à le trouver selon certaines considérations théoriques. Mais c’est justement là où il est le plus difficile à discerner, ce qui veut dire qu’on aura besoin de plus de données pour parvenir à voir une vraie vague au-dessus des rides du lac.

Cette année, les expériences ATLAS et CMS ont chacune accumulé environ cinq femtobarns inverses de données. Des centaines de personnes travaillent sans relâche en ce moment pour analyser  toutes ces données avant la mi-décembre, date à laquelle les résultats seront rendus public lors de la réunion du Conseil du CERN. Espérons que nous y parviendrons à temps et qu’un signal émergera enfin. La combinaison de toutes les données disponibles est prévue pour mars.

Une chose est sûre: si le LHC mais aussi les expériences CMS et ATLAS continuent à performer comme cette année, nous devrions avoir la réponse définitive sur l’existence ou l’exclusion du Higgs à jamais d’ici la fin 2012.

Avec un peu de chance, il y a peut-être un beau cadeau de Noël en perspective…

Pauline Gagnon

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

Les résultats combinés d’ATLAS et CMS basés sur deux femtobarns inverses de données. La ligne en pointillés représente ce que la théorie prévoit pour un tel volume de données. Les bandes verte et jaune donnent la marge d’erreur sur ces prévisions selon les lois de la statistique, et correspondent à des niveaux de confiance de 68% et 95% de chances d’être correct si toutes les sources d’erreurs expérimentales et théoriques ont bien été prises en compte. Les points en noir montrent les résultats expérimentaux. L’axe horizontal donne les valeurs potentielles pour la masse du boson de Higgs sur une échelle logarithmique. Chaque fois que la courbe expérimentale (les points noirs) tombent sous la ligne horizontale rouge, la valeur de masse correspondante est exclue. La région entre 141 et 476 GeV est donc exclue. Il ne reste que la partie sous cette zone ou au-dessus, quoique des considérations théoriques favorisent une petite masse. Sous 141 GeV en fait, la courbe expérimentale excède la bande jaune par endroits, c’est-à-dire qu’on y observe déjà un tout petit excès d’évènements par rapport à ce que l’on y attendait avec 95% de certitude. Plus les excursions en dehors de la bande jaune sont prononcées, plus les chances d’y trouver le boson de Higgs y sont augmentées.


Where do we stand on the Higgs boson search?

Wednesday, November 23rd, 2011

One of the most sought after particles in our field, the Higgs boson, is playing hard to catch. It might be that it does not even exist. All we physicists know is that something new is required by the theory. It might be the Higgs boson: that’d be the simplest solution, or we need to exclude its existence and move on to explore the next set of possibilities.

We have a theory called the Standard Model of particle physics that has withstood decades of experimental scrutiny without showing any cracks. The Standard Model tells us how many events containing a Higgs boson we should see if it exists but it does not predict its exact mass, making it much harder to find.

Each event is just a snapshot of what happens when protons moving at near the speed of light collide in the Large Hadron Collider (LHC). The Standard Model also tells us how many other types of events collected in our detectors could mimic the signature of a Higgs boson decay. These events are called the background. We design our searches specifically to select the desired signal events while minimizing the background. In the end, we work out how many signal events from Higgs boson decays and how many events from other processes we should retain given a specific set of selection criteria. Then we compare these estimates with what is collected with our detectors to see if Higgs bosons were present or not.

Imagine that all selected events were like the contents of a small lake. If a hidden fish creates a disturbance underneath, we will see a wave on a calm water surface. But of course, if there is some wind, ripples would appear, making it harder to spot the wave caused by a fish. The presence of a Higgs boson would do just that: appear like a wave on top of the calm water. As with the wind, the background creates small ripples one could easily mistake for a signal. The background can also fluctuate following statistical laws, like a random wind. In our case, having more data is equivalent to having more fish in the same spot, making their presence easier to detect.

To see if the Higgs boson or any new particle exists, we need to collect as many events as possible. Until then, it is pure guesswork since statistical fluctuations can easily fool us.

This is what happened this summer, when the first Higgs results were presented in July. We only had about one inverse femtobarn of data available (those are just the units we use to measure the data sample size). Some tantalizing ripples appeared as if we were seeing something. A month later, the CMS and ATLAS experiments each had two inverse femtobarns of data analyzed. The initial hint had completely disappeared, making statistical fluctuations once more the bane of a particle physicist’s existence. In the calm lake analogy, the first ripples we had seen were not caused by a real source like a hidden fish but simply by small variations at the water surface.

Now after much effort, the first combination of these August results was made public last Friday.  This is equivalent to one experiment having four inverse femtobarn of data, four times more than in July. This time, a wide mass range is excluded, namely between 141 and 476 GeV at the 95% confidence level. This means there is less and less space where the Higgs might still be hiding. In fact, it is now limited to be between 114 and 141 GeV.

This low mass range is where it was most expected, based on various theoretical hints and experimental factors. But this is also the range where it is most difficult to see, meaning more data is needed to see a real wave above all the small ripples.

This year, the ATLAS and CMS experiments each collected five inverse femtobarns of data. People are now bending over backwards to analyze these data and present new results at the scheduled meeting of the CERN Council planned at CERN in mid-December . Let’s hope both teams will manage and that some interesting signal will emerge. Combining this data will take a few more months and is expected in March.

What’s for sure, if the LHC, and the CMS and ATLAS experiments continue to perform as they did this year, we will have a final answer on finding the Higgs boson or excluding it definitively by the end of next year.

Let’s keep our fingers crossed…

Pauline Gagnon

To be alerted of new postings, follow me on Twitter: @GagnonPauline or sign-up on this mailing list to receive and e-mail notification.

The combined Higgs boson search result for the ATLAS and CMS experiments using 2 inverse femtobarns of data. The dotted line represents what one would expect with this much data based on theoretical predictions and statistical laws. The green and yellow bands indicate the error margin around this prediction, respectively with 68% and 95% chances of being correct, if all sources of experimental and theoretical errors have properly been accounted for. The black points are the experimental results. The horizontal axis gives the possible Higgs mass value on a logarithmic scale. Every time the data (black line) falls below the horizontal red line means we exclude a Higgs boson with this possible mass. The region above 476 GeV is still allowed but disfavored by theoretical considerations, meaning all eyes and efforts are now on the low mass region. In fact, below 141 GeV, what we observe experimentally is slightly more events than expected, that is, the black line goes above the yellow band. The bigger the deviation, the more likely we are to find the Higgs boson in that area.



Dr Matthews, I presume? 🙂

A lot has been building to this: a lifetime of obsession with physics and discovery; four years of hard study; about three and a half of the most exciting years of my life, working on the ALICE experiment; eight months of balancing an awesome career in nuclear physics with the mammoth task of writing a book…Now, at long last, my PhD journey is finally over: viva painfully anticipated, prepared for, worried about and finally completed (“Surviving a viva” blog to follow); minor corrections exacted; final edit of thesis printed and submitted to be hard bound for the library; I will graduate this Christmas and henceforth be known as Dr Matthews (…at least, for a few months. Then I will get married and become Dr/Mrs Chater.)

I am now buzzing with the notion that I have somehow passed the grand test of being a scientist. People say you don’t feel any different – it’s not true. I do. A younger me would say, “This is well mint”. (I used to insist that my A level in English Language was a license to use language “creatively” – to indulge in slang and occasionally use certain nouns as adjectives as I deemed appropriate. Actually I still do this!) This has been the biggest challenge I have faced to date, and now that it’s done it feels like I can finally start believing in myself.

I think lack of confidence can be an issue for many scientists. It comes in all shapes and sizes: from causing mild panic or reservation with a looming challenge, or feeling nervous talking about what they know for fear of scary questions; to shying away from responsibility or limelight and feeling faintly like a fraud sometimes. In fact I think in general a lack of confidence makes science very difficult. I’d love it if any readers who feel this is true for them could comment. It can be really damaging to a person’s learning – you start out wanting to understand something, to find the correct way of thinking about it; but you don’t want to be seen as foolish, you don’t want to make a mistake or look stupid, so you start to withdraw from asking questions. You internalise your confusion and the problem becomes more and more intimidating. One tiny bit of confusion, if left unchecked, can leave a person so lost they start to disengage from the subject area and it starts to seem a bit like another language.

However, scientists are all about asking questions. They are all about getting it wrong. They are all about being unafraid of looking foolish. Why is this? It is because all of these things are essential for advancing our knowledge of the world. We have to test what we think to be true and adjust our current thinking accordingly, even if that means throwing out a huge misunderstanding and looking mightily silly in the process. If we are shown to be mistaken, we change our view to a more correct one. Being wrong, then, isn’t something to fear but something to embrace and accept. I want any aspiring scientist out there reading this to promise themselves that whenever they are confused, stuck, puzzled, lost, or just curious, they will always find the bravery to ask; whether that means trying it out in an experiment, reading papers on it, getting their pen and paper/calculator/text book/whiteboard out, or literally finding someone who knows and insisting they explain and explain until the penny drops. Does anyone remember Big Bang Theory’s Sheldon fishing through a ball pit, desperately trying to mould his surroundings to make sense of the behaviour of electrons in graphene? (a great blog about this is here) This is the kind of commitment to getting answers I am talking about 🙂

And those of you out there who can call yourselves bachelors, masters or even doctors of science, have achieved something remarkable – you are now qualified to ask anything from the biggest questions in science today to the most seemingly daft questions you can think of, and when anyone threatens to call you silly you can simply say, “Ahem, excuse me. I am a scientist…and there is no such thing as a silly question when it comes to science.” Just like my A-Level English Language gave me license to be creative, I am hereby giving scientists everywhere license to be bludgeoningly inquisitive. We owe it to today’s budding scientific thinkers to set this example.

I wonder if “bludgeoningly” is a word… 😉

planning on having a babywhen did alicia keys have her baby a girl having a baby having a baby games onlinehow to have a twin baby