USTC Dzero Collaborators achieved important measurements of fundamental physics parameter

时间:2011-07-05浏览:16

Together with electronic charge e, Fermi Constant GF, and W/Z boson mass MW/MZ, the weak mixing angle sin2qW is physical constant to determine fundamental Electro-Weak interaction. This elemental constant can be measured from forward-backward asymmetry in 2-body fermion scattering governed by Z0 neutral current interaction. Precise determinations of the effective weak mixing angle up to date are derived by LEP and SLD experiments at e+e- colliders. The two most precise measurements form final state b-quark forward-backward asymmetry at LEP and left-right asymmetry at SLD differ from each other by about 3 standard deviations, which cannot be explained by the Standard Model (SM) of particle physics. The LEP collaborations also measured the light-quark related effective sin2qW from the inclusive hadronic charge asymmetry Qfb, but were dominated by larger systematic uncertainties due to the ambiguity of charge separation for final state quark fragmentation.

 

 

USTC DZero group and collaborators proposed to extract the light-quark involved effective sin2qW from the forward-backward charge asymmetry AFB in Drell-Yan Z/g*àe+e- processes at the Tevatron Collider. The AFB distributions in the Drell-Yan processes at hadron collider is CP-conjugation of the inclusive hadronic charge asymmetry Qfb at LEP, and have advantage of less uncertainty from the quark composition of the proton, which has been well parametrized by the parton distribution functions. With good understanding on reconstructed electron energy resolution, electron charge mis-identification and modeling all backgrounds, we derived the effective weak mixing angle from a process involving predominantly the first generation of quarks as 0.2309 ±0.0008 (stat.)± 0.0006 (syst.), and the overall uncertainty of our measurement is smaller than the combined uncertainty in the LEP measurements of the inclusive hadronic charge asymmetry. We also present the most precise direct measurement of the vector and axial-vector couplings of u and d quarks to the Z boson.

 

The physics result has been open to public as

http://www-d0.fnal.gov/Run2Physics/WWW/results/final/EW/E11B/

 

Fermilab todayhttp://www.fnal.gov/pub/today/ has reported this achievement in March 24th 2011, Result of the Week ashttp://www.fnal.gov/pub/today/archive_2011/today11-03-24.html