Could the Higgs boson have been discovered with earlier accelerators?

[John Peterson]

Could the Higgs boson have been confirmed with earlier accelerators?

The LEP collider operated at a maximum of 209 GeV. Could it have been used to confirm the existence of the 125.3 GeV Higgs boson?

I also read on Wikipedia that the CERN teams were apparently examining the 145–466 GeV range first in the search for the Higgs boson with the LHC, as they reported a year ago that no Higgs boson existed in that range, before examining the 125 GeV range that it's now found at. What is the reason for this? Was it considered more probably to find the Higgs boson in the 145–466 GeV range than in the 125 GeV range?

Thanks!

 

[mfb]

With electron-positron collisions, you do not get a Higgs alone with a relevant rate. The dominant production channel is e^- e^+ \to Z \to ZH. For a reasonable rate, the energy has to be high enough to produce a Higgs (~126 GeV if LHC found it) and a Z-boson (~90 GeV) at the same time. As you can see, LEP probably just missed it.

I also read on Wikipedia that the CERN teams were apparently examining the 145–466 GeV range first in the search for the Higgs boson with the LHC, as they reported a year ago that no Higgs boson existed in that range, before examining the 125 GeV range that it's now found at.

They examined the whole range at the same time. In the range of 145-400 GeV, it is easier (requires less data) to exclude or find the Higgs boson, as it would decay into two W or two Z bosons quite frequently.

 

[John Peterson]

For a reasonable rate, the energy has to be high enough to produce a Higgs (~126 GeV if LHC found it) and a Z-boson (~90 GeV) at the same time. As you can see, LEP probably just missed it.

So the required collision energy to observe a H is the sum of the Z (91.2 GeV) and H (125.3 GeV) masses, 216.5 GeV?

Whats the minimum number of collisions (or samples) required to reach a five standard deviation significance for H existence? Tevatron place it at 125 GeV (halfway between their 115 and 135 range) with a 2.9 standard deviation significance from 500 trillion collisions[1].

How long does it take to observe 500 trillion collisions? The D0 experiment observe p⁺p^– collisions at a 1.7 M/s rate, meaning 9 years to observe 500 trillion collisions.

 

[mfb]

So the required collision energy to observe a H is the sum of the Z (91.2 GeV) and H (125.3 GeV) masses, 216.5 GeV?

It is not a sharp line between "possible" and "impossible", as the Z boson has a very short lifetime and therefore a broad energy spectrum, but the general concept is correct.

Whats the minimum number of collisions (or samples) required to reach a five standard deviation significance for H existence?

That depends on the amount of background. It is impossible to give any number, if you do not know the background level.

How long does it take to observe 500 trillion collisions? The D0 experiment observe p⁺p^– collisions at a 1.7 M/s rate, meaning 224 years to observe 500 trillion collisions.

A simple division would yield 9 years. However, the 1.7MHz refers to beam crossings - each crossing can have multiple proton-antiproton collisions. Therefore, the collision rate is higher in operation, and lower during downtimes (of course :p), and the total time required to take this data is something like 10 years again.