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Play it safe, or… August 17, 2008

Posted by gordonwatts in ATLAS, CERN, D0, Fermilab.

There was an unspoken theme at the DZERO workshop this week. Stick with the Tevatron for a huge, but iffy, payoff. Or switch to the LHC now because it is a “sure” bet (as sure as anything gets in research).

This is all about the Standard Model Higgs search at the two accelerators. If such a Higgs does exist the LHC is bound to discover it. The LHC has some “difficulty” at low mass Higgs (below about 125 or so). Difficulty for the LHC means it could take up to 3 years for a single experiment to declare a 5 sigma discovery, the gold standard of “discovery”.

At the Tevatron the Higgs analysis is all about difficulty. Each new Higgs result you hear or read about is a tour-de-force of new techniques and new methods of extracting every last bit of signal out of the experiments. As a graduate student I never remember techniques this sophisticated. And the LHC pre-trial analyses are not as sophisticated either (on the other hand, they don’t need to be).

Global fits to the Standard Model currently predict the Higgs to be low mass – between 114 GeV and 120 or 125 GeV. The Tevatron is currently x2 away from being sensitive to this mass range. By doubling our dataset to 6 fb-1 of data and making a number of improvements to our analyses, we expect that we should be there. These improvements are not easy – it will require a lot of work and a lot of people. Nor are they assured. At best, if the Higgs is there, and we aren’t unlucky, we should be able to see it at the 3 sigma level. But never the 5 sigma discovery level. That will have to be left to the LHC in any case.

So is it worth sticking with the Tevatron? Well… the payoff would be huge to see something at the 3 sigma level. So it is like a lottery with high stakes. The chance of winning is not all that sure, but the jackpot is big!

Me? Well, I’m working on both the LHC and the Tevatron (as are many US physicists). I have a student working on the Higgs search at Fermilab, for example. I’m deeply involved in a number of topics at the LHC as well.

What will happen? Hard to tell. Things to watch? Well, that is easy. There are only two things that really matter here – the performance of the Tevatron and the performance of the LHC. Each physicist who is on both collaborations is performing some complex calculus to optimize their time on the two experiments depending on the chances of success.

I wish us all luck. 🙂



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