Latest on the Higgs

The news media are full of stories about the observation at the Tevatron of “single top” production, at a rate consistent with that expected from the Standard Model. There are talks at Fermilab going on about this today, and the papers are here and here. For an expository account, you can’t possibly do better than this one from Tommaso Dorigo.

While these results represent an experimental tour de force, they just confirm what is expected based on the standard model. Much more exciting would be if the Tevatron experiments can tell us something new about the Higgs and the Standard Model, and it looks like that may be coming this Friday afternoon, when a joint talk by the two experiments entitled “Higgs Results from CDF and D0” is scheduled at Fermilab. The two experiments have each collected about 5 fb-1 and started announcing limits on the Higgs based on analysis of up to 4 fb-1, but this is not quite enough for either experiment to be able to on its own exclude at 95% confidence level the Higgs at any particular mass. For this, one needs to combine the data from the two experiments. This was done last year, with results announced last August based on 3 fb-1 per experiment of data. This analysis allowed exclusion of the Higgs at 95% confidence level only in an extremely narrow range, basically just at exactly 170 GeV.

I’m guessing that what will be announced on Friday is exclusion of a Higgs over a much larger mass range. For a preview of this, see page 24 of the slides of a recent talk, where a graph shows what things would look like if you took twice CDF’s data set. This would come very close to excluding a range from 160-165 GeV, and perhaps within reach of excluding a region as large as 155-175 GeV, if not now, with only a moderate amount of more data and effort. It will be very interesting to see what they have…

For more evidence that this is what we’ll be hearing, Newsweek reports that:

This week scientists at Fermilab in Batavia, Illinois, will announce new data that not only narrows the gap between them and the coveted God Particle, but also suggests that the LHC may not be particularly well placed to make the discovery at all. The finding is a public-relations blow to the LHC and tarnishes Europe’s newly burnished image as a leader in Big Science….

The Higgs, the new Fermilab data show, does not exist for a portion of the upper range, putting it in the Tevatron’s cross hairs and suggesting that the LHC may be more peripheral to the search than previously thought. “We’ve made their jobs a little bit harder,” says Fermilab physicist Dmitry Denisov, “because we’ve excluded the region they’re good at.”

As the Tevatron shows that it can exclude the Higgs in the higher end of the expected mass region, where the LHC has a huge advantage, that means that either there is no Higgs (and presumably something else more interesting to find), or it exists in the lower part of the expected mass range (above the LEP limit of 114 GeV), where it is hard to find, but the Tevatron is not at such a disadvantage to the LHC. In any case, even if things work out as currently planned, the LHC will not start accumulating the kind of luminosity needed to compete with the Tevatron in this game until their 2011 run. It now appears highly likely that the Tevatron will be running at least through FY 2011 and possibly longer(for more about this, see here).

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11 Responses to Latest on the Higgs

  1. Xerxes says:

    The physics is quite interesting, but politically the spin is completely stupid. If the Fermilab public-relations machine cannot see the short-sightedness of a “the LHC is a big waste of money” message, then we will shortly be doomed to repeat the harsh lessons of the SSC.

  2. Well said Xerxes. That passage in Newsweek could have been put a lot more diplomatically.

    Speaking of science and the media, is there any chance you could all stop talking about “single top” quark production? This sounds awfully close to single quark production, guaranteed to confuse the rest of us…

  3. Stan says:

    Frankly, I just wish people would stop calling the Higgs the “God Particle.” It’s ridiculous and only serves to confuse people. Lederman is a smart guy and a great speaker, but his whimsical name for the Higgs is far to appealing to newspaper writers who want to allude to the “science vs. religion” fights in a strictly scientific story.

    (The last thing we need if the Higgs is discovered is a bunch of smug editorials laughing at physicists who “think they found God.”)

    I also wonder how much of the Fermilab vs. CERN friendly professional rivalry is getting misinterpreted and magnified by the popular media into something more like a race or conflict. Even if CDF and D0 actually find the Higgs, it will be at such low significance you’ll want the LHC experiments to confirm it and check its properties. Still, Fermilab wants to show what their machine can do, and so is pushing it to the limit in the few years left to run. Conflict is exciting, and so I’m not surprised the media is pushing that angle.

  4. Hi Peter,

    thank you very much for the appreciation of my account of the single top discovery.

    As for the Higgs, although I sometimes let go myself with optimism about CDF, I think that one should be a bit cautious about the over-optimistic interpretations of the Tevatron claims, for one reason.

    Take the single top discovery plots and for one moment imagine that we jump four years ahead in the future and what we’re looking at is a Higgs signal instead than single top: would you claim that such excess is an observation ? Yes, five sigmas are still five sigmas, but those global combined-multi-likelihood distributions contain just too many ingredients to be conclusive, if they claim to be the discovery of something that might not be there. Only because single top cannot possibly NOT be there, those plots can be really believed, in my humble opinion.

    Mind you, I am not saying there is anything wrong in either the CDF or the DZERO analyses (although in my blog I explain why the DZERO result is slightly less convincing than the CDF one). All I mean to say is that the Tevatron will never be able to show a conclusive signal for the Higgs, because the Signal to noise ratio is really too small: only by combining many channels, and cooking up powerful complicated discriminants, can the Tevatron experiments obtain results on the Higgs.

    The LHC advantage is there: eventually, they will have enough statistics to show a signal that has all the characteristics needed to convince everybody.

    To stress the point: somebody in CDF in 1993 had seen the first evidence for top pair production by using a likelihood discriminant. Now, those were quite different times, and likelihoods were still looked at with suspicion. But back then the top quark was still not compelling, it had already been claimed falsely once, and most people were really, really sceptical with a signal shown only on a not easily interpreted variable: until a counting experiment showed a signal, no publication was allowed.


  5. Shantanu says:

    I looked at the agenda pointed to my Peter. The
    antimatter gravity experiment looks cool.
    Hope it gets funded.

  6. Nobody says:

    To the first two posts: you are absolutely right; but certainly statements like “In one year, we will be competitive. After that, we will swamp them.” (Lyn Evans at the AAAS meeting, middle of February) do not help to mantain the relationship on a pure scientific level

  7. Peter Woit says:

    Thanks Tommaso!

    You make a very good point. My main reaction to seeing the details you explained of the single top result was something like “Wow, those plots are not exactly obviously convincing of anything…”, and presumably any Tevatron Higgs “observation” will be of a similar nature.

    But, if the Higgs really is down at 115 GeV, is it really true that the LHC will be able to see it in a really convincing way? How much luminosity will this take?

    About the public relations aspects of this: I don’t see any problem at all with a well-publicized Tevatron/LHC competition, trash-talking and all. Given that it’s often the same people on both sides of this, I can’t believe it will generate any serious bad blood among the physicists involved. It might generate some real public interest and appreciation for the subject, more so than the uncomplicated “wondrous new machine finds obscure particle” story that has been pre-sold already, and doesn’t draw the public in that much. It’s also true that the way the LHC story was going, Fermilab and US HEP in general were in danger of being left for dead as road-kill, something which is not exactly healthy for the subject.

  8. Coin says:

    The finding is a public-relations blow to the LHC and tarnishes Europe’s newly burnished image as a leader in Big Science

    Although I don’t really see anything wrong with the idea of a friendly LHC/Tevatron rivalry, this specifically seems like a weird interpretation for Newsweek to take. From anything I’ve ever been able to tell there seem to be an incredible number of Europeans working at Fermilab and an incredible number of Americans working at CERN.

  9. John Baez says:

    If the Higgs is found, what can we do to keep the public interested in particle physics? How can we possibly top the “God particle”?

    Here’s my suggestion: say that “sparticle” stands for SATAN PARTICLE!

  10. PV says:

    Europe lost many good scientific minds during World War II so CERN was developed to bring those minds back and establish Europe as a center of scientific power. Big Science is never really about science. NASA is another example of Big Science but its roots are in the Cold War. If you want real science, it begins with good conceptual physics. If we had any real conceptual idea of what the Higgs is we would know how likely it is of finding it before the experiment.

  11. J.J. van der Bij says:

    There has to be a Higgs field, but not necessarily a particle.
    The Higgs field may have been seen at LEP (Phy. Lett. B638, 234 (2006)).
    In this case neither the LHC or the Tevatron can see the Higgs.

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