A revisitation of Higgs reach by D0 February 1, 2008Posted by dorigo in news, physics, politics, science.
A top-notch theoretical physicist who sometimes reads this blog recently asked me how much trust could be given to the Higgs discovery projections of the Tevatron experiments, in light of the fact that current averages appear quite a bit worse.
I explained that my understanding is that one must not just look at the availability of data, but also consider the time available to make the analyses, because of the complexity of the required tools and the need of understanding the subtlest details about the detector, the backgrounds, and the algorithms. I made the example of the top quark mass, whose uncertainty decreased by a half in the five years following the end of Run I, as CDF and D0 refined their analyses. However, I could not provide quantitative information about the Higgs in addition to current limits and 2003 projections on the Tevatron reach.
I can add a bit of information here, since from a talk by Darien Wood which was given today at a P5 meeting at Fermilab I obtained a plot of more recent predictions made by the D0 experiment. It is shown below.
In the graph you see, as a function of the unknown mass of the standard model Higgs boson, the luminosity needed by each of two “D0-like” experiments to exclude at 95% C.L. (red curve) or find at three-sigma significance (blue curve) a Higgs boson by combining their results. The red curve is computed by assuming the Higgs boson is not there, while the blue curve assumes the presence of the boson. Please also note that these curves are a median of wide distributions of the luminosity required to exclude or find the Higgs: the two experiments may “get lucky” and find a 3-sigma signal with much less data than the one shown by the black curve; similarly, no guarantee is given that given a certain amount of luminosity, an exclusion or a signal will be obtained. Finally, the blue lines at 5.5 and 6.8 inverse femtobarns of analyzed data per experiment refer to what is now expected that the Tevatron will obtain by running through 2009 or through 2010.
The graph implicitly assumes that D0 and CDF will more or less obtain the same sensitivity on the Higgs with their searches; it also pictures the “state of the art” of the searches, and thus does not include the possible improvements that more time and more experience will certainly bring. Nonetheless, it is a reasonable datum with which to argue whether the Tevatron will be justified in running through 2010, as will be done in the ongoing P5 meeting at Fermilab.
If one were to assume that no improvements will be made to present-day analyses, one would conclude that by the end of 2009 the Higgs could be probably excluded up to 120 GeV and in the range 145-180 GeV. These are very conservative estimates, but bear in mind they are averages. The real result may be different. I however continue to hold that the Tevatron will do better than that…