Top mass: now at 1.2% uncertainty August 3, 2006
Posted by dorigo in news, physics, science.trackback
The Tevatron electroweak working group has issued two weeks ago a combination of CDF and D0 results on the top quark mass which includes preliminary measurements (that is, blessed but as of yet unpublished). You can find the documentation and plots in http://tevewwg.fnal.gov/top/ .
The bottomline ? The top quark is getting leaner by the day. The global average is now M = 171.4 +- 2.1 GeV, mostly driven down by the dilepton decay mode result of CDF, but basically confirmed by the two most accurate measurements in the single lepton channel (see the plot at the bottom for a compilation of the results entering the average).
A leaner top quark means that the Standard Model predictions for the Higgs boson mass are getting uncomfortably squeezed against the experimental wall of the LEP II lower limit, set at 114 GeV. In other words, the direct top quark mass and W boson mass measurements, together with determinations of other electroweak observables made by LEP and SLD, start to be in conflict with the fact that the Higgs is heavier than 114 GeV.
Whether that conflict is the result of a fluctuation in the experimental determinations entering the global electroweak fits or the smoking gun of an inconsistency of the symmetry breaking mechanism of Electroweak theory, it remains to be seen, and probably will stay so for the next three years, regardless of the accuracy with which top and W boson masses are measured. That is, we still need direct searches of the Higgs to be able to say whether the Higgs exists or not, despite the unprecedented level of accuracy of the electroweak parameters.
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A Quantum Diaries Survivor 
I’m interested in comparing this to Tony Smith’s prediction at http://valdostamuseum.org/hamsmith/TCZ.html :
“The Truth Quark, through its strong interaction with Higgs Vacua, may have two excited energy levels at 225 GeV and 173 GeV, above a ground state at 130 GeV. The 173 GeV excited state may exist due to appearance of a Planck-energy vaccum with = 10^19 GeV in addition to the low-energy Standard Model vacuum with = 252 GeV.”
The new value of 171.4 +/- 2.1 is fully compatible with the 173 excited state Tony Smith gives.
Nigel, the problem with Tony Smith’s theory, apart from the fact of being based on unscientific grounds like Sufism etc., is that its 130 GeV ground state for the top quark has never been observed.
He tries to convince himself that the first spurious events observed by tevatron were real top quark candidates, but now that so many years have passed, they look like background even more than in those days.
For sure there is no resonance at 130 GeV… A 130 GeV Top was excluded once, when we still were looking for the top quark and had not found it yet, but with the data we have now, even a 0.1pb resonance would be evident in our data.
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