Determination of the LEP centre-of-mass energy from Zgamma events

TL;DR

This paper uses Zgamma events from ALEPH 1997 data to measure the LEP2 centre-of-mass energy with high precision, providing a cross-check against other methods and implications for W mass measurements.

Contribution

It presents a novel method to determine the LEP2 energy using radiative return events, achieving competitive precision and validating previous measurements.

Findings

Measured LEP2 energy as 182.50 ± 0.19 (stat) ± 0.08 (syst) GeV

Results agree with LEP energy working group’s measurement within uncertainties

Systematic error impact on W mass measurement is minimal.

Abstract

Radiative returns to the Z resonance (Zgamma events) are used to determine the LEP2 centre-of-mass energy from the data collected with the ALEPH detector in 1997. The average centre-of-mass energy is measured to be: E_CM = 182.50 +- 0.19(stat) +- 0.08(syst) GeV in good agreement with the precise determination by the LEP energy working group of 182.652 +- 0.050 GeV. If applied to the measurement of the W mass, its precision translates into a systematic error on M_W which is smaller than the statistical error achieved from the corresponding dataset.