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LEP II eliminated the Higgs up to 114.5GeV. If it had been run for longer could it have detected a Higgs at 125GeV?

I Googled for this without any luck, though I did find a comment that LEP II topped out at 209GeV collision energy, so it seems as though production of a 125GeV Higgs would have been possible. If so, how much longer would it have had to run?

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As I recall both LEP and the Tevatron would have had to run a long time to extend their reach very far. I'm not making this an answer as I don't want to take the time to find a reference. –  dmckee Feb 13 '12 at 18:05
    
I'll have to look up some info about LEP II but I'll try to take a crack at answering this soon... can't guarantee anything though since it is a busy week. –  David Z Feb 14 '12 at 9:16
    
Thanks David, though it's not a burning issue so don't waste too much time on it. Obviously I'm wondering if there is some irony here and whether if they'd delayed decommissioning LEP by a year we'd have found the Higgs a decade ago. –  John Rennie Feb 14 '12 at 10:41
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up vote 14 down vote accepted

The LEP experiment's limits on the Higgs mass were set by looking for a process where the experiment would have produced a Higgs boson together with a Z boson. The highest energy they achieved for the electron-positron pair which annihilated to make Z,Higgs was 209 GeV, and that was only achieved in the last months of the experiment. Since the Z boson mass is 91 GeV, the highest energy Higgs boson which could be produced this way would have a mass of 209-91=118 GeV. Some of the energy is always lost to getting the Z and Higgs to move apart from each other, so in practice the limit they could achieve was a little lower than this, 114 GeV. By running much longer and accumulating statistics they could have extended their reach a little bit, perhaps to 116 GeV; but not to 124 GeV. That could only have been achieved by significantly increasing the energy of the beams -- which I believe they had already pushed as far as they could.

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A look at the "ALEPH HIGGS" which was published in "physics letters" shows how the analysis was done, as far as numbers go cdsweb.cern.ch/record/476830/files/ep-2000-138.pdf –  anna v Feb 21 '12 at 18:58
    
Ah, thanks Guy and Anna, that's very clear. –  John Rennie Feb 22 '12 at 6:38
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