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Tevatron Higgs limits, winter 2008 March 18, 2008

Posted by dorigo in news, physics, science.

 A comment by some anonymous reader just made me realize I never posted the updated Tevatron combination on Higgs boson cross section limits, recently updated and shown at winter conferences. It is shown below.


As you can see, the observed limit at 160 GeV is at a mere 1.09 times the Standard Model Higgs cross section: the Tevatron got this far with 2.4 inverse femtobarns of data because of a lucky negative fluctuation in the number of observed events with two W boson candidates -which may arise from H \to WW decays but whose main source is diboson production, q \bar q \to WW. If observed and expected events had been the same, the limit would have been 1.62 times the SM, as in the hatched black line.

One can also observe in the plot that CDF is doing slightly better with its analyses than D0 at low mass, while high-mass searches have the two experiments speak with a single voice. At low mass, CDF appears to have worked a bit harder – I think the difference is due to a larger lepton acceptance in CDF and better dijet mass resolution, since b-tagging sees D0 slightly ahead instead. Both experiments, in any case, see unlucky positive excesses at low mass, so that the observed limit at 115 GeV is 5.09 times the SM cross section, while the expected limit was x3.27. A unlucky excess in CDF and D0 which sits right where LEP II also saw an excess at 1.7 standard deviations. Not yet anything to get excited about – the Higgs contribution in the search datasets at 115 GeV would be still negligible- but maybe still suggestive: after all, a 3-sigma downward fluke of backgrounds would have already allowed the Tevatron to exclude the 115 GeV point!


1. anonymous - March 19, 2008

Is CDF actually doing better at low mass, or is it just expected to do better there?

I can’t see this from the plot, since the blue and red dotted lines are tagged “CDF Exp” and “D0 Exp” respectively.

2. dorigo - March 19, 2008


CDF is both doing better and expected to do so at low mass than D0:

At 110 GeV, CDF expected to find x4.09, they find x5.15; while D0 expected to find x5 and found x5.
At 115 GeV, CDF expected to find x4.50, they find x4.95; while D0 expected to find x5.3, found x6.
At 120 GeV, CDF expected to find x4.88, they find x5.70; while D0 expects to find x6, they find x10.

The hatched lines do show expected sensitivity by the two experiments alone. And CDF’s line is below.


3. Thou shalt have three generations « A Quantum Diaries Survivor - March 25, 2008

[…] mass region is the one where CDF and D0 are most sensitive to Higgs production: they are by now close to exclude a 160 GeV Higgs even in the regular, three-generation […]

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