# Was the mass of the Higgs given at 125.8?

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1. Jun 14, 2013

### QuantumSkippy

Hi Everyone.

In the Resonaances blog, I recall that it was mentioned there that the particle physics group at CERN had made an updated statement of the mass of the Higgs as being 125.8.

When I look at the Resonaances blog I cannot find reference to this statement and they are only now talking about 125 GeV. Wikipedia does not help much as it simply gives the results of the Atlas and CMS experiments.

There must have been a good reason for the update of the mass being stated at some stage or other to be 125.8.

Best wishes, Quantum Skippy

2. Jun 14, 2013

### DimReg

As we collect more data, or (since we aren't collecting data at the moment) understand systematic errors better, we can get a more accurate measurement of the mass. So 125 GeV is just a less precise number than 125.8 GeV.

There were approximately 6 months of data taken after the official Higgs discovery.

As far as I know, there are no specific reasons for the change, other than a refined analysis. To count all the ways the analysis has changed would be very difficult, but presumably they are still publishing and you can read about the updates.

3. Jun 14, 2013

### Staff: Mentor

Mass measurements at proton-proton colliders are tricky. It is easy to get a rough estimate (like "about 125 GeV"), but it takes more time to get a more precise value. Therefore, there were multiple updates after the initial discovery, where the uncertainty went down slowly.
As far as I know, the current best estimates are $125.2\pm 0.3 \pm 0.6$ GeV from ATLAS and $125.7 \pm 0.3 \pm 0.3$ GeV from CMS. The first uncertainty value is statistical (it will go down with more data), the second is systematic (it will require more work, and a better understanding of the detector to go down).