Seminar

Las mañanas IFCA con Alberto Ruiz: "W mass measurement at the CDF experiment of the Tevatron"

"The precise measurement of the mass of the W boson intermediate of charged electroweak interactions is a very important test of the standard model. The CDF experiment at the Tevatron has, over the last ten years, performed a very precise study of 4 million W bosons selected in proton-antiproton collisions at 2 TeV energy, calibrating and aligning the 30000 elements of the central trace chamber, to the order of microns, with 450 000 cosmic muons, and correcting for slight deformations or non-uniformity of the magnetic field, with measurements of the mass of J/psi and Upsilon particles. It has also validated the procedure using about 300000 selected Z bosons. The calorimeters were calibrated by comparing the energy and linear momentum measurements and validating with the Z bosons. The simulation of the process was performed with theoretical generators, at high orders of radiative corrections, using experimental data of the linear momentum distributions of quarks and antiquarks.

A final result of Mw = 8433 MeV/c2 was obtained with a precision of 9 MeV/c2, a value which deviates from the value expected by the standard model by 7 sigma and with some tension with previous experimental results. The standard model is therefore awaiting confirmation, or not, of whether or not the CDF measurements agree with those being made at the LHC and, consequently, the field is open to discussions about theoretical models of new physics, or corrections to the present theoretical predictions of the standard model."