Determination of the e + e ! ( ) cross-section using data collected with the DELPHI detector up to the year 2000

The dieren tial and total cross-sections for the process e + e ! ( ) were measured using the data collected with the DELPHI detector during the year 2000. A good agreement with the QED prediction was found and 95% Condence Level (C.L.) upper limits on deviations from the Born dieren tial cross-section were derived combining these results with those obtained with previous data. Lower bounds on the QED cut-o parameters, , on the mass of an excited electron, Me (for =1), and on the string mass scale, Ms, were obtained.