First measurement of charged current cross sections at HERA with longitudinally polarised positrons

DESY-HERA. Measurement of the total cross sections for the charged current reaction E+ P --& gt; NUEBAR X with a longitudinally polarized E+ beam of energy 27.5 GeV colliding with an unpolarized proton beam of energy 920 GeV. The data come from the 2003-2004 HERA running period with 26.9 +- 0.6 pb-1 at a polarization of +33.6 +- 0.7 PCT and 20.7 +- 0.5 pb-1 at a polarization of -40.2 +- 1.1 PCT. Results are also given for an unpolarized E+ beam of luminosity 65.2 pb-1 taken during the period 1999-2000.