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CERN | Geneva | Switzerland

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Small ripple shakes a roomful of physicists

This Friday afternoon, the 750 physicists attending the European Physics Society meeting in Grenoble, France, were pleasantly surprised. The audience was waiting with some anticipation to see the first important set of results from the two large LHC experiments, ATLAS and CMS on the search for the Higgs boson.  In fact, for the past two days, results had been shown from both experiments as well as from the Tevatron experiments in various individual channels. But today, the latest combined results from each experiment were shown in public for the first time. Of course, all physicists belonging either to the CMS or ATLAS experiment had had a chance to see their own results in advance, since they had been widely distributed and discussed. A small excess was seen in ATLAS, but nothing particularly convincing. In physicist’s jargon, we refer to these as mildly significant excesses.  This was found in one of the Higgs decay channels, namely when the Higgs boson decays into two W bosons. But unbeknown to the ATLAS people, the CMS collaboration was also observing a similar excess that would correspond to a Higgs with the same mass and is seen in the same channel.  So taken alone, none of these small ripples were compelling but once they show up in two completely different detectors, it starts being intriguing. Both experiments also reported small excesses for a Higgs to two Z bosons when the Z themselves decay into an electron or muon pair. What might turn out to be the first hint of a much sought after particle also occurred in a mass range not excluded by the Tevatron experiments.

It might not seem like much but this could be the first interesting bite we have in some decades. We are all researchers. This could turn us into “finders”, something very few of us had a chance to live in their career. Hence the lively discussions that followed this session during the coffee break.

But at the same time, we all know it is way too early to get excited. We need more data to be able to say something conclusive, something we do not risk regretting a few months down the line. Today, both experiments showed what they had after analyzing one inverse femtobarn of data (counted in the unit we use to see how much data we have). We already have another 0.4 inverse femtobarn ready to be analyzed. As soon as we can look at them in the coming weeks, we will see if the trend is maintained. The other important missing ingredient at this point is a full fledge combination of both results, taking into account all the common uncertainties. For example, we both use the same simulations to describe our backgrounds. Even though we crosscheck these simulations with real data, there is always a chance a small inaccuracy would trick us both in the same way. The combination team is getting to work on this combination tonight but it will take up weeks to complete this task.

Everybody agrees: We need more data and the combined results. But it is already interesting enough to keep staring in that direction. We might be seeing the caravan appearing in the far horizon. In just a few months, we will see it clearly or discover we all had sand in our eyes…

The CMS collaboration combined results for the Higgs boson search covering a possible Higgs in the region from  110 to 600 GeV.

 

ATLAS collaboration combined results for the Higgs boson in the low Higgs mass range

Within the red ellipses in the above two figures, one can see a small excess of events that could be the first signs of the presence of a Higgs boson within that mass range. The black lines should lie within the yellow band if there is no Higgs boson. This is what one could say but only with a 95% confidence. The fact that both experiments see a small excess in this region is the reason that makes it more interesting. But only with more data and a very rigorous combination of the two results will we able to say more in the near future. At this point, we can only hope something more definite will come out of this, nothing more!

Another major conference is planned in late August in Mumbai, India. For sure, this combination and hopefully, more new analyzed data will be shown there.

But why do we care? Very simple. As much as we like to say we know about the particles that make up all matter we see around us, to this day, we, physicists, have no clue how fundamental particles like electrons or quarks (that make up all matter) get their mass. As it is, our current theoretical model predicts they are all massless like photons, when we know this is not true. That Higgs boson, if it exists, would provide a mechanism to fix that.

 

Pauline Gagnon

To be alerted of new postings, follow me on Twitter: @GagnonPauline
 

 

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  • The Higgs is required because the Standard Model arrives massless. The Standard Model arrives massless because it postulates fundamental, elegant, facile mathematical vacuum mirror-symmetries that do not empirically obtain (e.g., SUSY, SUGRA; arxiv:1106.4804, hep-th/0511086; a contingent flurry of manually inserted symmetry breakings). Candidates for Higgs’ evidence are decayed vector bosons of the 100% homochiral Weak interaction. One entertains doubt that the Higgs has been detected.

    The Shroud of Turin – a projection of an ellipsoidal face upon a Euclidean plane absent distortion – is either a miracle of projected disjoint geometries or a forgery. That it can be trivially reproduced in all its aspects with a kitchen oven, a flat bas relief sculpture, and a bedsheet emphasizes the magnitude of the miracle, doesn’t it?

  • its good to hear that the probability of finding HIGGS PARTICLE HAS increased…………..

  • Slow down guys. Give us SF writers a break, or at least time for me to get my novel “Technical Difficulties” published before you find the answer to the ultimate question of life, the universe and everything.

  • Bob

    Plots or it didn’t happen.

  • nsetzer

    While the individual particles of the Standard Model acquire mass from the Higgs mechanism, everyday matter gets the bulk of its mass from the proton and neutron. These masses are almost entirely due to QCD, so it is misleading to say that we do not understand why any matter has mass. The existence of the Higgs boson will affirm that we understand why, for example, the electron has mass, but not why macroscopic objects have mass.

  • Of course, you’re right, binding energy is an important component but if all basic constituents of matter (electrons and quarks) were massless, as they appear in actual equations without including the Higgs, then we would still be in trouble. The point is to give an idea to lay people why we care about this, not get entangled in details.

  • Upward

    A cultural shift toward discouraging overstatement would be a healthy development in science. Eroding public trust causes diffuse but incalculable harm. Climate science, for example, suffers collateral damage.

    (Because the problem is in the culture, however, I don’t much blame the authors who reflect it. Overall, this is a good article.)

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  • hehe

    >Roughly speaking, that means we have no idea why any basic constituents of matter has a mass, (or weight),

    we know why matter has a weight, even Newton knew that 🙂