The Estimation of the Effective Centre of Mass Energy in q-qbar-gamma Events from DELPHI

TL;DR

This paper presents a method used by the DELPHI experiment at LEP to estimate the effective center-of-mass energy in electron-positron collisions affected by initial state radiation, achieving a resolution of 2-3 GeV.

Contribution

The paper introduces a procedure for estimating the effective center-of-mass energy in q-qbar-gamma events, accounting for undetected initial state radiation at LEP2 energies.

Findings

Achieved 2-3 GeV resolution on effective energy estimation.

Effective estimation method accounts for undetected initial state radiation.

Improved accuracy in analyzing hadronic events at LEP2.

Abstract

The photon radiation in the initial state lowers the energy available for the e$^+$e$^-$ collisions; this effect is particularly important at LEP2 energies (above the mass of the Z boson). Being aligned to the beam direction, such initial state radiation is mostly undetected. This article describes the procedure used by the DELPHI experiment at LEP to estimate the effective centre-of-mass energy in hadronic events collected at energies above the Z peak. Typical resolutions ranging from 2 to 3 GeV on the effective center-of-mass energy are achieved, depending on the event topology.