Particle Physicists See Something Little That Could be Really Big


Physicists from Fermilab have seen a “bump” in their data that could indicate a brand new particle unlike any ever seen before. If verified, this could re-write particle physics as we know it. “Essentially, the Tevatron has seen evidence for a new particle, 150 times mass of proton, that doesn’t behave like a standard Higgs particle,” said physicist Brian Cox on Twitter. “If this stands up to scrutiny and more data (there is not yet enough data for a “discovery”), then it is RIP Standard Model.”

“It was hard for us to not go crazy when we saw the results,” said Viviana Cavaliere from the University of Illinois (UIUC), one of the 500-member team working with the CDF particle detector at Fermi National Accelerator Laboratory in Batavia, Illinois, speaking on a webcast on April 6. “But for now, we need to stay focused on what we do know.”

The result comes from CDF’s (the Collider Detector at Fermilab) analysis of billions of collisions of protons and antiprotons produced by Fermilab’s Tevatron collider. In high energy collisions, subatomic particles can be detected that otherwise can’t be seen. Physicists try to identify the particles they see by studying the combinations of more-familiar particles into which they decay, while trying to find new particles, such as the theoretical Higgs Boson which is predicted by the Standard Model of particle physics.

The Standard Model contains a description of the elementary particles and forces inside atoms which make up everything around us. The model has been successful at making predictions that have been subsequently verified. There are sixteen named particles in the Standard Model, and the last particles discovered were the W and Z bosons in 1983, the top quark in 1995, and the tauon neutrino in 2000. But most physicists agree the Standard Model is probably not the final word in particle physics.

The researchers at Fermilab were searching for collisions that produced a W boson, which weighs about 87 times as much as a proton, as well as some other particles that disintegrate into two sprays of particles called “jets,” which are produced when a collision scatters out a particle called a quark.

Instead, they saw about 250 events which indicate a new particle weighing about 150 times as much as a proton, the team said at the webcast from Fermilab and in their paper on arXiv.

The researchers estimate the statistical chances of random jets or jet pairs from other sources producing a fake signal that strong at 1 in 1300.

The Standard Model does not predict anything like what was seen in the CDF experiment, and since this particle has not been seen before and appears to have some strange properties, the physicists want to verify and retest before claiming a discovery.

“If it is not a fluctuation, it is a new particle,” Cox said.

The Tevatron accelerator at Fermilab is scheduled to be shut down later this year, due to lack of funding and because of sentiments that it would be redundant to the Large Hadron Collider.

You can see more complete discussions and interpretations of the results at:

Cosmic Variance

Science News


24 Replies to “Particle Physicists See Something Little That Could be Really Big”

  1. See what collaborative science can do!

    “We thank the Fermilab theory group for helpful sug- gestions, particularly J. Campbell, E. Eichten, R. K. Ellis, C. Hill, and A. Martin. We are grateful to K. Lane
    and M. Mangano. We thank the Fermilab staff and the technical staffs of the participating institutions for their vital contributions. This work was supported by the U.S. Department of Energy and National Science Foundation; the Italian Istituto Nazionale di Fisica Nucleare; the Ministry of Education, Culture, Sports, Science and Technology of Japan; the Natural Sciences and Engineering Research Council of Canada; the National Science Council of the Republic of China; the Swiss National Science Foundation; the A.P. Sloan Foundation; the Bundesministerium fur Bildung und Forschung, Germany; the Korean World Class University Program, the National Re- search Foundation of Korea; the Science and Technology Facilities Council and the Royal Society, UK; the Institut National de Physique Nucleaire et Physique des Partic ules/CNRS; the Russian Foundation for Basic Research; the Ministerio de Ciencia e Innovacion, and Programa Consolider-Ingenio 2010, Spain; the Slovak R&D Agency; and the Academy of Finland.”

    Make me so proud to be part of the human race! The way of the future, methinks!!

    1. ‘And uncle Tom Cobley and aaaallllll, and uncle Tom Cobley and all’

  2. Slightly tangential to topic – can anyone explain in simple terms how a W Boson has 86 times the mass of a proton, but decays into proton, electron, and electron antineutrino?

    I looked it up on Wikipedia and don’t get it.

    1. There are four known forces in the universe. Two most familiar are gravity and electromagnetic force, and act on the large scale. The other is the so-called strong force which glues the positive charged protons in atomic nuclei together. The W boson is responsible for the weak force that controls the nature of radioactivity in atomic nuclei.
      W bosons, gauge bosons, come in the form of particles W+, W- and Z^0, and with photons make up the so-callled electroweak interaction. They were predicted before they were discovered. It is believed that in the earliest stages of the universe electromagnetism and the weak force (interaction) were joined as a more fundamental force known as the electroweak force.
      It is one of the great discovery of particle physics.

    2. The trick is to understand that energies and masses comes from many properties here. Energy goes into the particles momentum, which should explain the missing mass.

      [And relatedly, the sources of masses of protons are mostly unknown. I believe you get ~ 10 % of the mass from the constituent quarks and their momentum confined to the proton “bag”. The rest should be gluons and their interactions then, but is it?

      … *many* properties.]

      1. Thanks Torbjorn – I wasn’t thinking about energy

        Makes much more sense now – though I had no idea that ~90% of the mass of a proton was unknown… Great, more to ponder now 🙂

      2. For example: The proton contains 3 valence quarks: 2 up and 1 down quark. If you add up the rest masses of the quarks you end with a value that is of the order of 1% (!!) of the mass of a proton. The rest is in gluons and even virtual quark-antiquark pairs.

      3. I second this. The QCD potential held in the virtual gauge particles (gluons) and vacuum define the rest of the mass in addition to the u and d quarks with masses ~ 50 GeV


      4. Thanks guys for filling in the rest. (I got distracted by the X-ray source article. Sorry)

      5. @ Lawrence B. Crowell

        What exactly do you mean with 50GeV?
        A proton has 936MeV, the valence quarks together 12MeV (according to Wikipedia). So, what exactly has a mass of 50GeV in a proton?

      6. Oops. Not that what I wrote is entirely inconsistent. Luckily, what is an order of magnitude between friends!? :-/

      7. Um, maybe I fumbled the ball on this one. As other commenters note, it _is_ predicted (at the basics) by other theory. But I believe the details need to be worked out, and gluons to be tested if possible, so hence my question mark.

      8. I am quite sure, gluons ARE tested. Everything from the Standard Model (that includes gluons) is well tested and done so repeatedly.
        The question mark that remains is: What comes next? The Standard Model is not the answer, this is also known. Neutrinos with mass (and they certainly have!) are not part of the SM (in it, they are massless) and I think even the Higgs mechanism is not a real part of the SM (but on this one I am not sure).

  3. xkzd’s commentary on 3 sigma results of repeated experiments, that as they say “come and go”. And of course Fermilab is out of money soon.

    What could be exciting is that this result has AFAIU been stacking up, and for quite some time. And in some models it is connected to another recent Fermi (IIRC) 3 sigma result of asymmetries in p/p_ jets.

    But generally the Standard Model is named for what it has been for a long time… Not that there isn’t physics within (Higgs) and without (neutrino masses, # of generations) as well as theoretical (supersymmetry) to look at!

  4. “RIP Standard Model” sounds a bit harsh to me, like it would be ground shattering news, and everything we know would be meaningless. Everyone knows that the Standard Model is not the ultimate answer, so there will be a time when we will have a better theory, but still the Standard Model will be a part of it. Just like Newton mechanics is now a part of Relativity.

    The signal is about 3.2 sigma (according to the paper), so a little of work needs to be done, and I don’t know if they’ll be able to collect enough data at Fermilab before it is shut down. I guess, we will have to wait for LHC results to get a final answer on this one. (And it also doesn’t surprise me that the Fermilab collaboration tries to squeeze as many results as possible out of their data, even if they can’t show a “significant” result. The end is nigh!)

  5. My skepticism comes from the fact the LHC ran at much higher energy without this signal. I would be surprising in the Tevatron got something the LHC did not at lower energy. This is even though the luminosity for the LHC was low.


    1. I’ve read somewhere that someone of the LHC collaboration said something like “if you don’t look for that particular data in the LHC data you don’t see it. There is just too much to see”… I think, this is reasonable. They will start to look NOW.

  6. That is what I love in science.
    Science does not care what you think or find logical. It discovers things you might never have thought ever possible but the evidence is very clear.

    Now I don’t know if this discovery is just a fluke or not, but I find it very cool that once in a while we get a surprise.

    1. Indeed. But the problem here is that it is once again a “3-sigma-surprise”. There have been some of these in the history of science. And most of them have disappeared by now. That’s why I remain highly suspicious until there is a solid confirmation (more than 5 sigma).
      It may be unfair, but I am also thinking that collaborations at Fermilab, now, tend to publish as much as they can, because of the near end of the machine, and before the collaborations of the LHC can really begin to publish their results. So, it is even more possible in such times that false detections are published without the proper scrutiny. As I said, this may be unfair, but it makes me even more suspicious against “3-sigma-results” these days.

  7. Hyderabad April 8


    Recently Dr. B.G. Sidharth, of B.M. Birla Science Centre had predicted that there would be a hitherto unknown force between particles and anti particles with which would be associated a new type of an intermediary particle. This would be evidenced at very high energies, and the force itself would be short lived. There is now evidence for this which comes from Fermi Lab in the US. A large team of scientists called the CDF team has studied collisions between Protons and anti Protons and have just found evidence for the new force, as also the associated particle. They rule out that the new particle can be the elusive God particle, the Higgs Boson. This discovery, potentially the most sensational in fifty years ,would indicate a break with known ideas and the Physics community is eagerly waiting for further tests and results.

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