Monday, September 16, 2013

CMS Measures Fundamental Constants

The CMS experiment at the Large Hadron Collider has measured the strong force coupling constant at Z boson mass-energy to be 0.1151 +/- 0.0033.  This compares to and is consistent with a  four and a half times more precise previous measurement of 0.1184 +/- 0.0007.

It also measured top quark pole mass at 176.7 + 3.8 -3.4 GeV/c^2, which compares to and is consistent with a previous more accurate Tevatron measurement of 173.18 +/- 0.94 GeV/c^2.  The new result, again, is several times less precise than the current world standard estimate.

While the results are not terribly precise, because they are obtained using a different methodology than most previous measurements of these quantities, the results make the average measurements more robust and less subject to systemic errors that could be shared by all of the other experiments.

CMS has also made the most precise measurement ever of the relative momentum of up quarks and down quarks within the proton, something that could ultimately be used to more accurately estimate their masses, two of the least accurately known constants in the Standard Model.  These measurements now have more precision than the theoretically calculated prediction.

In January of this year, I summarized how precisely the various Standard Model constants have been measured.  In March of this year, I summarized how global electroweak precision fits fine tune some of these measurements by trying to reconcile individual measurements with their known relationships to each other.

No comments: