CERN Accelerating science

Article
Report number	hep-ex/9809008 ; CERN-OPEN-98-026 ; CERN-OPEN-98-026
Title	The Estimation of the Effective Centre of Mass Energy in $q\overline{q} \gamma$ Events from DELPHI
Author(s)	Abreu, P. (Lisbon, IST) ; De Angelis, A. (CERN) ; Della Ricca, G. (INFN, Trieste ; Trieste U.) ; Fassouliotis, D. (Athens U.) ; Grefrath, A. (Wuppertal U.) ; Kjaer, N. (NIKHEF, Amsterdam) ; Henriques, R.P. (Lisbon, IST) ; Mulders, M. (NIKHEF, Amsterdam) ; Pimenta, M. (Lisbon, IST) ; Vitale, L. (INFN, Trieste ; Trieste U.)
Affiliation	(CERN) ; (LIP Lisboa) ; (Univ. Trieste and INFN Trieste) ; (Univ. Athens) ; (Univ. Wuppertal) ; (NIKHEF Amsterdam)
Publication	1999
Imprint	6 Sep 1998
Number of pages	12
Note	12 pages, 6 figures Report-no: CERN-OPEN-98-026
In:	Nucl. Instrum. Methods Phys. Res., A 427 (1999) 487
DOI	10.1016/S0168-9002(98)01394-1
Subject category	Detectors and Experimental Techniques
Accelerator/Facility, Experiment	CERN LEP ; DELPHI
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.

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