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Ted Kolberg | USLHC | USA

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Some Higgs are bigger than others

Thursday, March 12th, 2009
New Higgs mass limits from Tevatron

Update 13 March: The Tevatron experiments have just released new, stronger limits on the mass of the Higgs boson.  Read about it here.

There have been a couple new results from the Tevatron this week.

The first result, shown by both CDF and DØ experiments, is the observation of single top production. The top quark was first observed in 1995 by the same two experiments, but that observation was of top pair production (a top plus its antiparticle). This discovery was of single top quarks, with no antiparticle partner.  In the Standard Model of particle physics, top pair production occurs roughly twice as often as single top production, and the top pair signal is also somewhat easier to see in data. The observation of single top production is important, because even though everyone expected the process to exist, demonstrating sensitivity to such a rare and difficult signal is an important milestone on the way to searches for even rarer processes, like production of a Higgs boson.

The other result is the most precise measurement (by a single experiment) to date of the W boson mass, by DØ. Whereas the single top measurement demonstrates increasing sensitivity to the Higgs, the W mass tells us what mass of Higgs boson we might expect. Since the mass of the W is supposed to come from the Higgs mechanism, a more precise measurement narrows the window of likely Higgs masses. The mass of the Higgs has interesting implications for current searches at the Tevatron and the upcoming searches at the LHC, because the Higgs may be more difficult to see depending on its mass.

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HEP, publishing, and open access

Thursday, February 26th, 2009

Last Friday night, fellow blogger Seth, some of our friends, and I had a discussion (with what David Foster Wallace called “that special intensity that comes after about the fourth beer”) about some interesting results from the CDF collaboration. After a while, the conversation wandered towards discussing the role of open repositories versus refereed journals. This is an issue of interest for science in general. However, high energy physics is an especially visible example of the contrasts between the two, because of our field’s reliance on a culture of preprints. To quote an interesting study (itself available on the open arXiv repository, established in 1991) on HEP publishing practices:

The preprint culture in HEP pioneered the free distribution of scientific results. For decades, theoretical physicists and scientific collaborations, eager to disseminate their findings in a way faster than the distribution of scholarly publications, printed and mailed hundreds, even thousands, of copies of their manuscripts before submitting them to peer-reviewed journals. This preprint culture tended, however, to favour the large laboratories and universities that could afford mailing large numbers of preprints while receiving comprehensive regular mailings. The spread of the Internet and the inception of the arXiv repository ushered a new era for the preprint culture, offering all scientists a level playing field. In its current implementation, arXiv allows researchers to submit their preprints and browse or receive regular feeds on recent submissions in their area of interest.

Open repositories like the arXiv have some major advantages over traditional refereed journals. The first and most obvious advantage is that access to the materials is free (at least to the end user). Instead of a costly journal subscription (which may run to many thousands per year), anyone with a working internet connection can download and read the results for themselves. Another key advantage is speed. Papers on the arXiv are instantly available around the world, which is important in a fast-moving and competitive field. The same results can take months to appear in refereed journals. And as author lists for large HEP collaborations swell, free electronic distribution avoids the high printing costs and page count of reprinting author lists with each paper1.

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LHC luminosity and energy

Saturday, February 21st, 2009

As Steve mentioned last week, the new LHC schedule for this year and next was revealed last Monday. The most prominent features of the announcement were the anticipated start date (autumn) and duration (one year) of the run. However, there were two other important parameters that were also discussed at the Chamonix meeting last week. We learned the luminosity and beam energy that the LHC team would try to achieve during the run. Both of these choices have important implications for the physics we can do with the data from the run.

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