Milestones for the Tevatron and LHC

By John Conway | June 18, 2011 12:42 pm

This past week saw two big milestones for the two big operating high energy particle colliders in the world. At these machines, we measure the number of collisions with the rather arcane unit of “inverse barns”, which is essentially a measure of inverse cross sectional area. It’s just like if you are throwing darts at a dart board across the room with your eyes closed: the bigger the dart board, the more likely you are to hit it, and the more darts you throw, the more hits you get.

The term “barn” came from the early days of nuclear physics when Fermi quipped that a nucleus is “as big as a barn.” And so a new physics unit was born: one barn is 10-28 m2, about the size of a big nucleus. At the Tevatron at Fermilab, we’ve just crossed over 10.0 inverse femtobarns of integrated luminosity, after over ten years of operation in what we call Run 2 of the Tevatron. At the LHC at CERN, we just saw the integrated luminosity counter roll over to 1.000 inverse femtobarns. It’s kind of like the difference between your 10-year old car rolling over to 100,000 miles, and your new year-old car rolling over to 10,000 miles.

Our old car, the Tevatron, has taken us on quite a ride this past decade. I’ll push the analogy further, though, and say that it’s been like driving across the Great Plains. We kept hoping to see mountains, but it’s been flatland the whole way. Though we’ve looked very hard, we just have not turned up any sign of new physics at this incredible machine, despite the recent excitement. The present schedule is that the Tevatron will collide its last proton and antiproton at 2:00 pm on September 30 of this year. We’re tradin’ her in.

With our new car, the LHC, expect to see the mountains very soon, and in fact we reached this amount of data far sooner than I would have predicted at the beginning of the year. Last year, starting in March and eventually stopping in early November, the LHC delivered 0.04 inverse femtobarns, 25 times less than the sample we have now. But that was the first good chunk of physics data, and an army of data-hungry students, postdocs, lab scientists and professors analyzed it frantically over the winter, publishing a huge torrent of papers in the spring as the LHC really started to hit the gas. (Okay, perhaps the analogy is stretching to the breaking point here.)

So are the white things on the horizon we are starting to see the snow-capped peaks we have hoped for, or just clouds? We’ll soon know, and this is bound to be a summer to remember in the history of particle physics, unlike any time since the “November Revolution” of 1974, when the charm quark and the tau lepton made their appearance at the Stanford Linear Accelerator and Brookhaven National Lab.

After the November Revolution, with the third generation of quarks and leptons established, the Standard Model took solid form: there soon followed the discovery of the bottom quark at Fermilab in 1977, the gluon at DESY in Hamburg in 1979, and the W and Z bosons at CERN in 1982. The hunt for the top quark and the Higgs boson, and whatever might lie beyond, was on.

But it took another thirteen years to find the top quark, and in 1995, the CDF and D0 experiments did just that at the Tevatron. It was clear as a bell, and surprisingly massive, weighing in at nearly the mass of a gold atom at 175 GeV. With the precise measurements of the W and Z from CERN it soon became clear that the Higgs might just lie within reach of the Tevatron, which could discover it before the LHC could be completed. (The SSC had been cancelled in 1993 in a budget climate eerily like our own.)

And so Run 2 of the Tevatron began in 2001 after major upgrades to both experiments. Slow at first, the accelerator luminosity steadily increased, and the physics flowed, with better and better measurements of the top quark and W boson, and searches for the Higgs and a host of other hypothetical particles. Two years ago the Tevatron experiments finally reached the level where, combined, the data from CDF and D0 ruled out the HIggs boson if its mass were twice that of the W boson, 160 GeV. But no sign of any new particles.

The data from the LHC in 2010 was not sufficient to improve upon this Higgs search result. In a wide swath of other physics studies, however, the LHC is surpassing the Tevatron. Basically, the LHC should be viewed as a gluon collider: a gluon in one incoming proton collides with a gluon from another, producing whatever gluons produce when they do this, which is anything that is strongly interacting (that is, feels the strong nuclear force). Even with over a factor of a hundred less integrated luminosity, the LHC can do far more than the Tevatron due to the LHC’s higher energy. But at the LHC as well, last year, there was no sign of new physics.

In the coming weeks, though, with the huge new data set, the LHC will blow past the Tevatron in nearly every category except in the search for the low mass Higgs boson, where there truly still is a race. There are two big conferences coming up at the end of July, in Boston and Grenoble, France, at which we can expect the announcements of any discoveries made by the LHC experiments CMS and ATLAS…or by the Tevatron. Fasten your seat belts!

  • Van

    Might we infer from this post that Atlas and CMS will be announcing the discovery of something new at the end of July?

  • DMPalmer

    To put it into human scale, 10 inverse femtobarns corresponds to a cross-section of 1e-44 square meters.

    Flipping it, 1e+44 square meters is about 1e+12 square light years.

    In other word, their search has been the equivalent of searching an entire galaxy for something the size of a human.

    (Q’lprogh of the Institute of Human Studies at 3C273 is doing a similar experiment by firing a beam of humans at a galaxy and looking for human-human interactions. Fortunately, she is aiming at M51, otherwise each of us would probably have met someone by now.)

  • Anadish Kumar Pal

    CERN is continues smashing research. Possibly, amidst all that particle gnashing a Higgs boson will drool out. 2012 is the deadline. Meanwhile, I slog on with my research which almost all the ‘wise’ men find stupendously stupid. I am impressed, because, I believed that man changes as society advances; but Prophet Mohammad was right, man’s nature is unchangeable. Modern man is as excellent in disbelief as any pagan of the dark ages or even earlier.

  • John

    Van: I certainly hope so, but, honestly I don’t know yet. I have only seen a fraction of what we have recorded, and with the very high intensities this year, we have many proton-ptoton collisions happening at the same time. We’re refining our simulations and our event selections, and learning as we go…

    I guess my point above is that, with such a dramatic increase in energy compared with the Tevatron, and such a huge increase in the number of collisions, this is the time when discoveries will be made, in the coming weeks.

  • jim

    john, go back to selling used cars.

  • Kim

    @DMPalmer: I still don’t understand (wouldn’t there be two human beams coliding?), but that sounds something like Qfwfq would have done back when only hadrons were a viable lifestyle.

  • Joseph Smidt

    This post does seem surprisingly optimistic given the dearth of new particles over the last few years and the recent CDF/D0 4-sigma fiasco. (I would think particle experimentalists would be fairly skeptical of new results right now.) John has to know something to throw around lines like “in the coming weeks”!

  • Phil

    Is it true that the “recent excitement” at the Tevatron was a trick to try to convince the US government to continue funding Fermilab?

  • OhDear

    Statements like

    “the recent CDF/D0 4-sigma fiasco.”


    “is it true that the “recent excitement” at the Tevatron was a trick to try to convince the US government to continue funding Fermilab?”

    really disappoint me. I know one should not expect reasonable opinions on the internet, but the degree of hostility and suspicion is shocking. There is no fiasco, there is simply an intriguing result which could not be reproduced. It could be due to many things. Regarding Phil’s suggestion of a conspiracy, consider what you are suggesting here. Hundreds of people would have to be in on it- do you really think all those people, who have spent their lives training as scientists, would conspire to fabricate results?

  • Evil

    There are rumors going around that CMS also sees the same excess as CDF….

  • chris

    Oh Dear,

    it has happened too often lately. HEP-ex people are a bit too nervous and hype-prone for the last couple of years.

    i don’t see these comments in such a negative light. they remind us all that scepticism is a basic necessity for science that should never be thrown overboard.

  • John

    OhDear: we played all the tricks we could to get the government to keep the Tevatron alive a bit longer. And when I say tricks, I don’t mean anything dishonest – you can’t really get away with that sort of thing in physics. There is always someone willing to shoot you down. But the machine will turn off for sure on Sept. 30, even if a big discovery is made at the Tevatron.

    I guess the point of my post is that with the increase in energy an the huge increase in integrated luminosity at the LHC, the time is now, if ever, to make new discoveries, if they are waiting for us. You can call it hype if you want but it’s the simple truth. There’s never been a more exciting moment in this field in my career, for sure.

    Now, if we *don’t* make a big discovery in the coming weeks, or within a few months, then the nature of the new physics which lies ahead must be quite subtle, or there may not be new physics for us to find. We’ll perhaps quadruple our sample by the end of 2012, but we won’t get another factor of 50-100 for sure, so in a sense, this is the year where we have the biggest chance for seeing something new.

    If there is nothing new – just a Standard Model Higgs boson, which we know will take another few years of data collection – then we will enter a strange and difficult time for high energy physics. Some of us call it The Nightmare Scenario. It will be awfully hard to convince anyone to build an even higher energy collider, for sure…

  • george briggs

    I find johns comment most interesting. I am predcting no higher energy point particles will be found, but we will keep trying until we create a black hole which will feed on fermibosonic matter left over from the previous universe, destroying earth in a process that appears to be two colliding galaxies to obververs alive in that era.

  • george briggs

    more on john $12: what to do with the LHC when it shows us no new physics? sell it to the power companies for superconductor field testing. It could be very useful there – maybe even pay for itself!

  • Anadish Kumar Pal

    It seems that on earth there is an inertial lock which prevents particles to behave exactly as they behaved moments after so called ‘big bang’. You can refer to my research and await a formal detailed disclosure. So LHC would not be able to exactly recreate conditions the conditions as expected. Doomsday fearing persons may take heart, it may not be possible for LHC to gobble up the earth, after all.

  • george briggs

    i’m relieved. I wonder what you think happeneg at tha big bang? I think we had a big burst of radiation but no transfer of mass from the previous universe (see penrose’s “cycles of time”)). that came later, with the growth of galaxies, transfering matter in the form of fermibosonic entities of E8 symmetry (see papers by Lisi)

  • Zoltan J Kiss

    As I see it, looking for the Higgs boson is a mistake.
    “Particle-based” physic gives no solution to our energy crisis today. At the same time the “Event-based” direction is not an acceptable way for today’s physical science.
    Do they really think that “the last particle ” as such exists? It would automtically mean Universe is with an end.
    We may measure a “particle” as result of the measurement of an event, function of the intensity of the event itself – but most importantly the intensity of our measurement. Both, function of the time system (or time flow).
    Time to wake up!

  • Sean Peters

    Extremely entertaining comments today. It’s regrettable, though, that it’s becoming a lot harder to distinguish the true crackpots from the mere trolls. Makes for a fun read all the same.

  • george briggs

    I don’t think my idea of a fermibosonic entity is so crazy, since Lisi thinks he has already found it as E8 symmetry matter (see sciam for jan this year). Fermibosonic matter is broken down into equal amounts of ordinary matter and dark matter by the strong electrogravitational fields of primordial black holes, It has zero net mass itself. Hi zoltan, we worked for the same co.

  • george briggs

    for the life of me, I can’t see how the studies of neutrinoes (and weak force particles) is going to give us any insight into the stable particles, and their masses, that need to be explained today. I think study of E8 symmetry could give us an answer, albeit very anthropic, I admit.

  • Zoltan J Kiss

    Accelerating Hydrogen is especially dangerous, as I see it, since the acceleration intensifies its neutron process, which is otherwise of infinite low intensity (the reason we cannot measure it). At speed level close to the speed of light the neutron collapse of the Hydrogen will be infinitely intensified. Closer and closer and more and more. The neutron collapse of the Hydrogen of infinite intensity will need proton expansion energy but that is limited with the Hydrogen proton. Strong interrelation will work and there will be an energy demand developed of infinite intensity.
    I do not know how we can call it. But this is an energy intake, like the neutron radiation of infinite intensity.
    Hi george, in my understanding, weak force is electron blue shift, the red shift load of the neutron collapse.

  • george briggs

    hi zoltan. i’m not sure i understand your physics yet. I’m trying to get folks to realize that there are only two entities yet to be found, dark matter and fermibosonic matter, and they are not point particles and probably can’t be detected by the LHC. only two other physicits,Lisi and Penrose seem to comprehend and i AM TOO UNKNOWN and too old, 87, to change things

  • george briggs

    I know I’m a terrible nuisance, but how about briggs fermibosnon to go along with higgs boson?

  • Zoltan J Kiss

    Hello George, you will agree with me that no event would mean no time and no time would mean no event. But what is the physical basis of time?
    There is only one answer to give:permanent mass-energy transformation and energy-mass re-transformation with a quantum entropy left-over of the balance all around, composing as I call it the quantum membrane.
    I vote for the Briggs-boson and you will find my email address in my web-site (just a click on my name)

  • george briggs

    The briggs fermiboson (not boson) should really be called briggs – lisi- weatherall fermiboson, to give credit to everybody involved

  • george briggs

    zoltan, my address is 37 broadripple dr,princeton,njo8540 phone 609 924 o755

  • Kabir Mustapha Yar’adua

    Suppose the Higgs is not found come 2012, what will that mean to the standard model?

  • Pingback: The LHC, the Tevatron, and the Higgs Boson | Cosmic Variance | Discover Magazine()


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