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There's a fairly broad mass spread in the new results out of Atlas and CMS. I'm curious how this fits with the expected SM width.

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Tiny, << 1 GeV. The only significant modes are b-bbar and tau-taubar and both are relatively light. Found the answer and references here: math.columbia.edu/~woit/wordpress/… The observed width and uncertainty is all from the detectors. –  Foster Boondoggle Dec 13 '11 at 17:15
nice find, perhaps you could post that as an answer. –  David Z Dec 13 '11 at 17:47

1 Answer 1

up vote 4 down vote accepted

It's about 0.003 GeV, see

enter image description here

Just to be sure, the measured width of the bumps is due to experimental errors and other things that depend on the situation, not because of the Higgs' intrinsic width.

The width dramatically increases with the mass. As one approaches a TeV, the width would be almost exactly equal to the mass itself. For the sake of completeness, this is the graph of the branching ratios (proportions of the decays ending with a given final state):

enter image description here

The 125 Higgs decays to (virtual or real) $b\bar b$ (messy final state, a bit hard to isolate from the background) in 65% of cases, $WW$ (neutrinos from the decayed $W$ are missing energy) in 20%, $gg$ (messy) in 7% of cases, $\tau\tau$ in 6% of cases, $ZZ$ in 3% of cases, $c\bar c$ in 2% of cases, $\gamma\gamma$ in 0.2%, $\gamma Z$ in 0.15% of cases. The numbers were estimated by looking at the graph above so they don't quite add to 100 percent, sorry.

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