Precise measurement of the top-quark mass from lepton+jets events at D0

D0 experiment has conducted new, more precise, measurements of the mass of top quark where the final system of top and anti-top quark decayal consists odf one lepton and jets. Measurements was performed in proton-antiproton collisions at the Tevatron Collider with center-of-mass energy 1,96 TeV. Resulting measured value m_t=176,01±1,64 GeV is one of the most precise measurements of the mass of top quark in a separate terminal channel. Compared to previous measurements the systematic errors were substantially reduced, mainly regarding the uncertainty associated with energetic calibration of b-jets. Our Prague group significantly contributed to in situ calibration method developed for correction of energetic calibration of b-jets used for inclusive spectrum of jet production measurements.

Top quark, the most massive of quarks, is in close connection to Higgs boson according to the Standard Model of particle physics. Masses of top quark and W boson are bound (albeit weakly) to the mass of intensively sought-after Higgs boson. Current measurements of masses of top quark and W boson shows that Higgs boson should have rather low mass. In case of discovery of the Higgs boson its determined mass could be compared with measured masses of top quark and W boson. Were there any significant discrepancies we could assume the detected Higgs boson is not in accordance with Standard Model predictions.

Fit of top quark mass (m_t)

¹Joint Institute for Nuclear Research, Dubna, Russia
²Institute of Physics ASCR, Na Slovance 2, 182 21 Prague 8, Czech Republic