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Posts Tagged ‘ICHEP’

Les grandes percées sont rares en physique. La recherche est plutôt jalonnée d’innombrables petites avancées et c’est ce qui ressortira de la Conférence Internationale de la Physique des Hautes Énergies (ICHEP) qui s’est ouverte hier à Chicago. On y espérait un pas de géant mais aujourd’hui les expériences CMS et ATLAS ont toutes deux rapporté que l’effet prometteur observé à 750 GeV dans les données de 2015 avait disparu. Il est vrai que ce genre de choses n’est pas rare en physique des particules étant donné la nature statistique de tous les phénomènes que nous observons.

CMS-2016-750GeV

Sur chaque figure, l’axe vertical indique le nombre d’évènements trouvés contenant une paire de photons dont la masse combinée apparaît sur l’axe horizontal en unités de GeV. (À gauche) Les points en noir représentent les données expérimentales recueillies et analysées jusqu’à présent par la Collaboration CMS, soit 12.9 fb-1, à comparer aux 2.7 fb-1 disponibles en 2015. Le trait vertical associé à chaque point représente la marge d’erreur expérimentale. En tenant compte de ces erreurs, les données sont compatibles avec ce à quoi on s’attend pour le bruit de fond, tel qu’indiqué par la courbe en vert. (À droite) Une nouvelle particule se serait manifestée sous forme d’un pic tel que celui en rouge si elle avait eu les mêmes propriétés que celles pressenties dans les données de 2015 à 750 GeV. Visiblement, les données expérimentales (points noirs) reproduisent simplement le bruit de fond. Il faut donc conclure que ce qui avait été aperçu dans les données de 2015 n’était que le fruit d’une variation statistique.

Mais dans ce cas, c’était particulièrement convainquant car le même effet avait été observé indépendamment par deux équipes qui travaillent sans se consulter et utilisent des méthodes d’analyse et des détecteurs différents. Cela avait déclenché beaucoup d’activités et d’optimisme : à ce jour, 540 articles scientifiques ont été écrits sur cette particule hypothétique qui n’a jamais existé, tant l’implication de son existence serait profonde.

Mais les théoriciens et théoriciennes ne furent pas les seuls à nourrir autant d’espoir. Beaucoup d’expérimentalistes y ont cru et ont parié sur son existence, un de mes collègues allant jusqu’à mettre en jeu une caisse d’excellent vin.

Si beaucoup de physiciens et physiciennes avaient bon espoir ou étaient même convaincus de la présence d’une nouvelle particule, les deux expériences ont néanmoins affiché la plus grande prudence. En l’absence de preuves irréfutables de sa présence, aucune des deux collaborations, ATLAS et CMS, n’a revendiqué quoi que ce soit. Ceci est caractéristique des scientifiques : on parle de découvertes seulement lorsqu’il ne subsiste plus aucun doute.

Mais beaucoup de physiciens et physiciennes, moi y compris, ont délaissé un peu leurs réserves, non seulement parce que les chances que cet effet disparaisse étaient très minces, mais aussi parce que cela aurait été une découverte beaucoup plus grande que celle du boson de Higgs, générant du coup beaucoup d’enthousiasme. Tout le monde soupçonne qu’il doit exister d’autres particules au-delà de celles déjà connues et décrites par le Modèle standard de la physique des particules. Mais malgré des années passées à leur recherche, nous n’avons toujours rien à nous mettre sous la dent.

Depuis que le Grand collisionneur de hadrons (LHC) du CERN opère à plus haute énergie, ayant passé de 8 TeV à 13 TeV en 2015, les chances d’une découverte majeure sont plus fortes que jamais. Disposer de plus d’énergie donne accès à des territoires jamais explorés auparavant.

Jusqu’ici, les données de 2015 n’ont pas révélé la présence de particules ou phénomènes nouveaux mais la quantité de données recueillies était vraiment limitée. Au contraire, cette année le LHC se surpasse, ayant déjà produit cinq fois plus de données que l’année dernière. On espère y découvrir éventuellement les premiers signes d’un effet révolutionnaire. Des dizaines de nouvelles analyses basées sur ces données récentes seront présentées à la conférence ICHEP jusqu’au 10 août et j’en reparlerai sous peu.

Il a fallu 48 ans pour découvrir le boson de Higgs après qu’il fut postulé théoriquement alors qu’on savait ce que l’on voulait trouver. Mais aujourd’hui, nous ne savons même pas ce que nous cherchons. Cela pourrait donc prendre encore un peu de temps. Il y a autre chose, tout le monde le sait. Mais quand le trouverons nous, ça, c’est une autre histoire.

Pauline Gagnon

Pour en savoir plus sur la physique des particules et les enjeux du LHC, consultez mon livre : « Qu’est-ce que le boson de Higgs mange en hiver et autres détails essentiels».

Pour recevoir un avis 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.

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Giant leaps are rare in physics. Scientific research is rather a long process made of countless small steps and this is what will be presented throughout the week at the International Conference on High Energy Physics (ICHEP) in Chicago. While many hoped for a major breakthrough, today, both the CMS and ATLAS experiments reported that the promising effect observed at 750 GeV in last year’s data has vanished. True, this is not uncommon in particle physics given the statistical nature of all phenomena we observe.

CMS-2016-750GeV

On both plots, the vertical axis gives the number of events found containing a pair of photons with a combined mass given in units of GeV (horizontal axis) (Left plot) The black dots represent all data collected in 2016 and analysed so far by the CMS Collaboration, namely 12.9 fb-1, compared to the 2.7 fb-1 available in 2015. The vertical line associated with each data point represents the experimental error margin. Taking these errors into account, the data are compatible with what is expected from various backgrounds, as indicated by the green curve. (Right) A new particle would have manifested itself as a peak as big as the red one shown here if it had the same features as what had been seen in the 2015 data around 750 GeV. Clearly, the black data points pretty much reproduce the background. Hence, we must conclude that what was seen in the 2015 data was simply due to a statistical fluctuation.

What was particularly compelling in this case was that the very same effect had been observed by two independent teams, who worked without consulting each other and used different detectors and analysis methods. This triggered frantic activity and much expectation: to date, 540 scientific theory papers have been written on a hypothetical particle that never was, so profound the implications of the existence of such a new particle would be.

But theorists were not the only ones to be so hopeful. Many experimentalists had taken strong bets, one of my colleagues going as far as putting a case of very expensive wine on it.

If many physicists were hopeful or even convinced of the presence of a new particle, both experiments nevertheless had been very cautious. Without unambiguous signs of its presence, neither the ATLAS nor the CMS Collaborations had made claims. This is very typical of scientists: one should not claim anything until it has been established beyond any conceivable doubt.

But many theorists and experimentalists, including myself, threw some of our caution to the air, not only because the chances it would vanish were so small but also because it would have been a much bigger discovery than that of the Higgs boson, generating much enthusiasm. As it stands, we all suspect that there are other particles out there, beyond the known ones, those described by the Standard Model of particle physics. But despite years spent looking for them, we still have nothing to chew on. In 2015, the Large Hadron Collider at CERN raised its operating energy, going from 8 TeV to the current 13 TeV, making the odds for a discovery stronger than ever since higher energy means access to territories never explored before.

So far, the 2015 data has not revealed any new particle or phenomena but the amount of data collected was really small. On the contrary, this year, the LHC is outperforming itself, having already delivered five times more data than last year. The hope is that these data will eventually reveal the first signs of something revolutionary. Dozens of new analyses based on the recent data will be presented until August 10 at the ICHEP conference and I’ll present some of them later on.

It took 48 years to discover the Higgs boson after it was first theoretically predicted when we knew what to expect. This time, we don’t even know what we are looking for. So it could still take a little longer. There is more to be found, we all know it. But when will we find it, is another story.

Pauline Gagnon

To find out more about particle physics, check out my book « Who Cares about Particle Physics: making sense of the Higgs boson, the Large Hadron Collider and CERN ».

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Earlier last month, Romania became the 22nd Member State of the European Organisation for Nuclear Research, or CERN, home to the world’s most powerful atom-smasher. But the hundred Romanian scientists working on experiments there have already operated under a co-operation agreement with CERN for the last 25 years. So why have Romania decided to commit the money and resources needed to become a full member? Is this just bureaucratic reshuffling or the road to a more fruitful collaboration between scientists?

Image: CERN

On 18th July, Romania became a full member state of CERN. In doing so, it joined twenty one other countries, which over the years have created one of the largest scientific collaborations in the world. Last year, the two largest experimental groups at CERN, ATLAS and CMS, broke the world record for the total number of authors on a research article (detailing the mass of the Higgs Boson).

To meet its requirements for becoming a member, Romania has committed $11mil USD towards the CERN budget this year, three times as much as neighbouring member Bulgaria and more than seven times as much as Serbia, which holds Associate Membership, aiming to follow in Romania’s footsteps. In return, Romania now holds a place on CERN’s council, having a say in all the major research decisions of the ground-breaking organization where the forces of nature are probed, antimatter is created and Higgs Bosons discovered.

Romania’s accession to the CERN convention marks another milestone in the organisation’s history of international participation over the last sixty years. In that time it has built bridges between the members of nations where diplomacy and international relations were less than favourable, uniting researchers from across the globe towards the goal of understanding the universe on its most fundamental level.

CERN was founded in 1954 with the acceptance of its convention by twelve European nations in a joint effort for nuclear research, the year where “nuclear research” included the largest ever thermonuclear detonation by the US in its history and the USSR deliberately testing the effects of nuclear radiation from a bomb on 45,000 of its own soldiers. Despite the Cold War climate and the widespread use of nuclear physics as a means of creating apocalyptic weapons, CERN’s founding convention alongside UNESCO, which member states adhere to today, states:

“The Organization shall provide for collaboration among European States in nuclear research of a pure scientific and fundamental character…The Organization shall have no concern with work for military requirements,”

The provisional Conseil Européen pour la Recherche Nucléaire (European Council for Nuclear Research) was dissolved and its legacy was carried by the labs built and operated under the convention it had laid and the name it bore: CERN. Several years later in 1959, the British director of the Proton Synchrotron division at CERN, John Adams, received a gift of vodka from Soviet scientist Vladimir Nikitin of the Dubna accelerator, just north of Moscow, and at the time the most powerful accelerator in the world. 

The vodka was to be opened in the event the Proton Synchrotron accelerator at CERN was successfully operated at an energy greater than Dubna’s maximum capacity: 10 GeV. It more than doubled the feat, reaching 24 GeV, and with the vodka dutifully polished off, the bottle was stuffed with a photo of the proton beam readout and sent back to Moscow.

John Adams, holding the empty vodka bottle in celebration of the Proton Synchroton’s successful start (Image: CERN-HI-5901881-1 CERN Document Server)

Soviet scientists contributed more than vodka to the international effort in particle physics. Nikitin would later go on to work alongside other soviet and US scientists in a joint effort at Fermilab in 1972. Over the next few decades, ten more member states would join CERN permanently, including Israel, its first non-European member. On top of this, researchers at CERN now join from four associate member nations, four observer states (India, Japan, USA and Russia) and holds a score of cooperation agreements with other non-member states.

While certainly the largest collaboration of this kind, CERN is certainly no longer unique in being a collaborative effort in particle physics. Quantum Diaries is host to the blogs of many experiments all of whom comprise of a highly diverse and internationally sourced research cohort. The synchrotron lab for the Middle East, SESAME, expected to begin operation next year, will involve both the Palestinian and Israeli authorities with hopes it “will foster dialogue and better understanding between scientists of all ages with diverse cultural, political and religious backgrounds,”. It was co-ordinated in part, by CERN.

I have avoided speaking personally so far, but one needs to address the elephant in the room. As a British scientist, I speak from a nation where the dust is only just settling on the decision to cut ties with the European Union, against the wishes of the vast majority of researchers. Although our membership to CERN will remain secure, other projects and our relationship with european collaborators face uncertainty.

While I certainly won’t deign to give my view on the matter of a democratic vote, it is encouraging to take a look back at a fruitful history of unity between nations and celebrate Romania’s new Member State status as a sign that that particle physics community is still, largely an integrated and international one. In the short year that I have been at University College London, I have not yet attended any international conferences, yet have had the pleasure to meet and learn from visiting researchers from all over the globe. As this year’s International Conference on High Energy Physics kicks off this week, (chock-full of 5-σ BSM discovery announcements, no doubt*), there is something comforting in knowing I will be sharing my excitement, frustration and surprise with like-minded graduate students from the world over.

Kind regards to Ashwin Chopra and Daniel Quill of University College London for their corrections and contributions, all mistakes are unreservedly my own.
*this is, obviously, playful satire, except for the case of an announcement in which case it is prophetic foresight.

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Two anomalies worth noticing

Monday, July 14th, 2014

The 37th International Conference on High Energy Physics just finished in Valencia, Spain. This year, no big surprises were announced: no new boson, no signs from new particles or clear phenomena revealing the nature of dark matter or new theories such as Supersymmetry. But as always, a few small anomalies were reported.

Looking for deviations from the theoretical predictions is precisely how experimentalists are trying to find a way to reveal “new physics”. It would help discover a more encompassing theory since everybody realises the current theoretical model, the Standard Model, has its limits and must be superseded by something else. However, all physicists know that small deviations often come and go. All measurements made in physics follow statistical laws. Therefore deviations from the expected value by one standard deviation occur in three measurements out of ten. Larger deviations are less common but still possible. A two standard deviation happens 5% of the time. Then there are systematic uncertainties that relate to the experimental equipment. These are not purely statistical, but can be improved with a better understanding of our detectors. The total experimental uncertainty quoted with each result corresponds to one standard variation. Here are two small anomalies reported at this conference that attracted attention this year.

The ATLAS Collaboration showed its preliminary result on the production of a pair of W bosons. Measuring this rate provides excellent checks of the Standard Model since theorists can predict how often pairs of W bosons are produced when protons collide in the Large Hadron Collider (LHC). The production rate depends on the energy released during these collisions. So far, two measurements can be made since the LHC operated at two different energies, namely 7 TeV and 8 TeV.

CMS and ATLAS had already released their results on their 7 TeV data. The measured rates exceeded slightly the theoretical prediction but were both well within their experimental error with a deviation of 1.0 and 1.4 standard deviation, respectively. CMS had also published results based on about 20% of all data collected at 8 TeV. It exceeded slightly the theoretical prediction by 1.7 standard deviation. The latest ATLAS result adds one more element to the picture. It is based on the full 8 TeV data sample. Now ATLAS reports a slightly stronger deviation for this rate at 8 TeV with 2.1 standard deviations from the theoretical prediction.

WWResults

The four experimental measurements for the WW production rate (black dots) with the experimental uncertainty (horizontal bar) as well as the current theoretical prediction (blue triangle) with its own uncertainty (blue strip). One can see that all measurements are higher than the current prediction, indicating that the theoretical calculation fails to include everything.

The four individual measurements are each reasonably consistent with expectation, but the fact that all four measurements lie above the predictions becomes intriguing. Most likely, this means that theorists have not yet taken into account all the small corrections required by the Standard Model to precisely determine this rate. This would be like having forgotten a few small expenses in one’s budget, leading to an unexplained deficit at the end of the month. Moreover, there could be common factors in the experimental uncertainties, which would lower the overall significance of this anomaly. But if the theoretical predictions remain what they are even when adding all possible little corrections, it could indicate the existence of new phenomena, which would be exciting. It would then be something to watch for when the LHC resumes operation in 2015 at 13 TeV.

The CMS Collaboration presented another intriguing result. They found some events consistent with coming from a decay of a Higgs boson into a tau and a muon. Such decays are prohibited in the Standard Model since they violate lepton flavour conservation. There are three “flavours” or types of charged leptons (a category of fundamental particles): the electron, the muon and the tau. Each one comes with its own type of neutrinos. According to all observations made so far, leptons are always produced either with their own neutrino or with their antiparticle. Hence, the decay of a Higgs boson in leptons should always produce a charged lepton and its antiparticle, but never two charged leptons of different flavour. Violating a conservation laws in particle physics is simply not allowed.

This needs to be scrutinised with more data, which will be possible when the LHC resumes next year. Lepton flavour violation is allowed outside the Standard Model in various models such as models with more than one Higgs doublet or composite Higgs models or Randall-Sundrum models of extra dimensions for example. So if both ATLAS and CMS confirm this trend as a real effect, it would be a small revolution.

HtomutauThe results obtained by the CMS Collaboration showing that six different channels all give a non-zero value for the decay rate of Higgs boson into pairs of tau and muon.

Pauline Gagnon

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How Can We Hangout Better?

Wednesday, July 9th, 2014

Yesterday we had one of our regular Hangouts with CERN, live from ICHEP, at which we took questions from around the Internet and updated everyone on the latest results, live here at the ICEHP 2014 conference. You can see a replay here:

I sent it to my wife, like I usually do. (“Look, I’m on ‘TV’ again!”) And she told me something interesting: she didn’t really get too much out of it. As we discussed it, it became clear that that was because we really did try to give the latest news on different analyses from ICHEP. Although we (hopefully) kept the level of the discussion general, the importance of the different things we look for would be tough to follow unless you keep up with particle physics regularly. We do tend to get more viewers and more enthusiasm when the message is more general, and a lot of the questions we get are quite general as well. Sometimes it seems like we get “Do extra dimensions really exist?” almost every time we have a hangout. We don’t want to answer that every time!

So the question is: how do we provide you with an engaging discussion while also covering new ground? We want people who watch every hangout to learn something new, but people who haven’t probably would prefer to hear the most exciting and general stuff. The best answer I can come up with is that every hangout should have a balance of the basics with a few new details. But then, part of the fun of the hangouts is that they’re unscripted and have specialist guests who can report directly on what they’ve been doing, so we actually can’t balance anything too carefully.

So are we doing the best we can with a tough but interesting format? Should we organize our discussions and the questions we choose differently? Your suggestions are appreciated!

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My First Day at ICHEP (Again)

Thursday, July 3rd, 2014

ICHEPstartICHEP 2014 started today in Valencia, Spain. This is one of particle physics’s biggest conferences, held every two years. The last one, in 2012, coincided with the discovery of the Higgs boson. This year, we’re probably going to have more in the way of careful measurements than big new surprises. ATLAS and CMS have already released Higgs updates, and the pesky boson looks more and more like the Standard Model Higgs all the time.

This is the second ICHEP I’ve attended in person. I showed a poster at the first one, and wrote a blog post about it – which is a scary reminder of just how long I’ve been blogging. (I also still have my lanyard from that conference, which I’m wearing with my badge because it’s cooler than the boring black one we got this time.) This year, I’m here to give a parallel talk about the potential for even better measurements of the Higgs at the High-Luminosity LHC, which is a possible upgrade for the LHC that could take us well into the 2030s. By then, I suppose I should aspire to give an ICHEP plenary talk. 😉

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Dark matter: No model, just guesses

Wednesday, July 11th, 2012

On the last day of the International Conference on High Energy Physics dark matter took a central seat.

As many of you know, ourselves, the earth, all stars and galaxies are made of atoms. These atoms emit light when they are excited and that is how astronomers can explore the vast universe. But this matter only accounts for 4% of the content of the universe while dark matter makes up 24% of it. An unknown type of energy dubbed “dark energy” makes up the remaining 76%.

Dark matter was discovered in 1933 by Swiss physicist Fritz Zwicky. But to this day, scientists still don’t know what it is made of. This matter emits no light, which is why it was called “dark matter”.

Dark matter seems to react only to gravitational force and this is how it was discovered. Zwicky realized there was more matter in the universe than what was visible from the light emitted by stars and galaxies. This matter creates a much stronger gravitational field than what can be accounted for if you only rely on visible matter.

Neal Weiner, a theorist from New York University, started his lecture saying that contrary to the Higgs boson, for dark matter “we have no model, only guesses”. There is nothing within the Standard Model of particle physics to account for dark matter. This is one key reason we physicists are all convinced there is a bigger theory hiding behind the current known one.

So theorists and experimentalists are in the dark… As Neal stressed, there are many manifestations of dark matter. Different experiments observe strange signals where dark matter could be the explanation. But formulating an explanation is far from being trivial.

For example, several experiments have reported seeing more positrons than electrons coming from outer space. Positrons are the antimatter for electrons. Recently, the Pamela and the Fermi experiments both saw an excess of positrons, particularly at high energy. Given that the universe is made of matter, one needs to explain where these anti-electrons come from.

Some astronomers think it could be produced by pulsars but the jury is still out on this. Others argue that dark matter could annihilate into a pair of electron and positron, creating more positrons than expected. But it is not easy to cook up a theory that would do that. Hopefully, new data will come in 2013 from the Planck satellite to resolve this issue.

The DAMA/Libra experiment has been reporting a loud and clear signal (8.7 sigma) from dark matter for years. Unfortunately, nobody else can detect this signal as Lauren Hsu from Fermilab explained in her review of dark matter experiments. One possibility is that their detector, which is made of iodine, is sensitive to dark matter particles but other chemical elements used by the other experiments were not. Two new experiments were built using iodine, COUPP and KIMS, and should soon have enough data to get the final word on this long-standing anomaly.

Dark matter might interact with the Higgs boson. If that’s the case, now that we have a mass for it, we can test specific hypotheses. The XENON100 experiment is just at the limit of sensitivity for this and new results will come soon.

This is a huge, open question in particle physics. Let’s hope the new (Higgs?) boson discovery will soon be followed by some clues on the nature of dark matter. Exciting times ahead.

Pauline Gagnon

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Lors de la dernière journée de la Conférence Internationale sur la Physique des Hautes Energies, on a fait le point sur la matière noire. Comme plusieurs d’entre vous le savent, nous sommes tous: nous-mêmes, la terre, les étoiles et les galaxies faits d’atomes. Ces atomes émettent de la lumière lorsqu’ils sont excités, ce qui permet aux astronomes d’étudier l’univers. Mais toute cette matière ne compte que pour 4% du contenu total de l’univers alors que la matière noire en fait 24%. Les 76% restant viennent d’énergie d’un type inconnu surnommée « énergie noire. »

La matière noire fut découverte en 1933 par le physicien suisse Fritz Zwicky. Mais on ignore toujours de quoi il s’agit. Cette matière n’émet aucune lumière, d’où son nom.

La matière noire semble jusqu’à maintenant ne réagir qu’à la force gravitationnelle et c’est ce qui a permis de la déceler. Zwicky constata qu’il y avait plus de matière dans l’univers que ce qu’il voyait basé sur la lumière émise par les étoiles et les galaxies. Cette matière crée un champ gravitationnel bien plus fort que ce que la matière visible peut engendrer.

Neal Weiner, un théoricien de l’université de New York, a ouvert sa présentation en disant que, contrairement au boson de Higgs, pour la matière noire « on n’a aucun modèle, que des hypothèses ». Il n’y a rien dans le Modèle Standard de la physique des particules qui la décrive. C’est d’ailleurs un point clé indiquant clairement que le modèle standard a ses limites, et qu’une autre théorie plus globale devra le remplacer.

Les théoriciens et les expérimentatrices sont donc tous dans le noir… Come Neal l’a souligné, il y a déjà plusieurs manifestations de cette matière noire. Plusieurs expériences observent d’étranges signaux qui pourraient s’expliquer en termes de particules de matière noire. Mais formuler la bonne explication s’avère compliqué.

Par exemple, plusieurs expériences mesurent un excès de positons par rapport au nombre d’électrons observés venant du cosmos. Les positons sont l’antimatière des électrons. Récemment, les satellites Pamela et Fermi ont mesuré que cet excès est plus prononcé à haute énergie. Mais comme l’univers est fait de matière, d’où viennent ces positons?

Certains astronomes pensent qu’ils pourraient provenir de pulsars mais cela reste à prouver, ce qui est difficile. D’autres proposent plutôt qu’ils émanent de l’annihilation de particules de matière noire en une paire d’électron et positon.

Mais encore là, ce n’est pas facile à justifier théoriquement. Espérons que les nouvelles données attendues en 2013 par le satellite Planck aidera à résoudre ce problème.

Et puis il y a l’expérience DAMA/Libra qui clame depuis des années avoir obtenu un signal très fort (8.7 sigma). Le seul hic est que personne d’autre ne le capte comme l’a expliqué Lauren Hsu de Fermilab dans sa revue des résultats expérimentaux. Il est possible que les autres détecteurs n’y soient pas sensibles puisque seul DAMA/Libra utilisait un détecteur à l’iode. Deux nouvelles expériences COUPP et KIMS sont maintenant en cours ayant elles aussi de l’iode comme détecteur. Elles devraient avoir bientôt suffisamment de données pour trancher la question.

Autre possibilité: la matière noire interagit peut-être avec le boson de Higgs. Maintenant qu’on en connaît la masse, il se pourrait que l’expérience XENON100 puisse bientôt atteindre la sensibilité nécessaire pour tester cette hypothèse.

C’est donc une énorme question encore ouverte en physique des particules.

Peut-être que le nouveau boson (de Higgs?) apportera quelques indices qui nous permettront d’en apprendre plus.  Ça promet.

Pauline Gagnon

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There’s an interesting New York Times article out today, titled “New Data on Elusive Particle Shrouded in Secrecy”. The headline is misleading. There’s nothing to keep secret about our Higgs boson search, because we’re simply not done.

It’s true that we looked at some of our preliminary results last Friday. Every part of the search has more to do, and some don’t have their 2012 updates in their final form at all. And we’ve allowed ourselves only two or three weeks to go from first-pass results to the final product!

The article itself actually gets this more or less right:

Right now, most of the physicists doing the work do not even know what they have. In order to avoid bias, the physicists involved avoided looking at most of the crucial data until last week, when they “unblinded” it. About 500 physicists on each team are analyzing eight different ways a Higgs boson, once produced in the collider, might decay and leave its signature.

And, as it quotes Joe Incandela, the spokesperson for my experiment:

Our final [ICHEP] results will not be even seen by the collaboration before the last day of June and then will require the usual final cosmetics for presentation.

So you’ll have to forgive us if we keep quiet for a few more weeks about our results. They’ll be shown at ICHEP in Melbourne, Australia starting on July 4. Here at CERN, we’ll be dealing with the suspense by working on the final answer almost up to the very last minute.

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A Physicist’s Dinner in Paris

Thursday, August 19th, 2010

One of the nights at ICHEP, I ended up by myself and wandered around the middle of Paris a bit. At last I was hungry, and decided I wanted something easy and affordable if at all possible. The best solution for this, in Paris, is one of the touristy restaurants. So what I ate is below. Some aspects of it are typically French, but there is nothing unfamiliar to an American about it except the concept of an omelet at dinner.

Dinner in Paris

You can also see what I was reading: a book of papers on the “multiverse hypothesis” adapted from some conference lectures. Among some theoretical physicists trying to build a fundamental theory of life, the universe, and everything, there is serious research and debate on this subject — but to me as an experimentalist, it’s crazy far-out philosophy. But it’s also amusing dinner reading, and the university publishers who had booths set up at ICHEP were the only source of English-language books I knew of in Paris.

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