First limits on nuclear recoil events from the ZEPLIN I galactic dark matter detector UK Dark Matter Collaboration G.J. Alner a , H. Araujo b , G.J. Arnison a , J.C. Barton d,z , A. Bewick b , C. Bungau b , B. Camanzi a , M.J. Carson c , D. Davidge b , J.V.Dawson b , G.J. Davies b , J.C. Davies c , T. Durkin a , T. Gamble c , S.P. Hart a , R.J. Hollingworth c , G.J. Homer a , A.S. Howard b , I. Ivaniouchenkov a,b , W.G.Jones b ,M.K.Joshi b ,V.A.Kudryavtsev c ,T.B.Lawson c ,V.Lebedenko b , J.D. Lewin a , P.K. Lightfoot c , I. Liubarsky b , M.J. Lehner c,1 ,R.Lu ¨scher a,b , J.E. McMillan c , B. Morgan c , A. Nicholls a , G. Nicklin c , S.M. Paling c , R.M. Preece a , J.W. Roberts a,c , M. Robinson c , J.J. Quenby b , N.J.T. Smith a, * , P.F. Smith a , N.J.C. Spooner c , T.J. Sumner b , D.R. Tovey c a Particle Physics Department, Rutherford Appleton Laboratory, Chilton, Oxfordshire OX11 0QX, UK b Blackett Laboratory, Imperial College London, London SW7 2BZ, UK c Department of Physics and Astronomy, University of Sheffield, Hounsfield Road, Sheffield S3 7RH, UK d Department of Physics, University of London Queen Mary, London E1 4NS, UK Received 14 June 2004; received in revised form 1 February 2005; accepted 5 February 2005 Available online 16 March 2005 Abstract WereportfirstresultsfromtheZEPLINIdarkmatterdetector,basedonmeasurementofscintillationpulseshapes in a liquid xenon target of 3.2 kg fiducial mass. Neutron calibration shows nuclear recoil pulses to have a time con- stant ffi 0.5 that of gamma and beta background events. The detector is located in the 2800 mwe depth UK Boulby Mine, and is surrounded by a liquid scintillator Compton veto and passive lead shielding. Three runs totaling 293kgd fiducial exposure yielded data consistent with a single population of background pulses, with no significant 0927-6505/$ - see front matter Ó 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.astropartphys.2005.02.004 * Corresponding author. Tel.: +44 1235 445151; fax: +44 1234 446733. E-mail address: n.j.t.smith@rl.ac.uk (N.J.T. Smith). z Deceased. 1 Present address: U. Pennsylvania, Philadelphia, PA 19104, USA. Astroparticle Physics 23 (2005) 444–462 www.elsevier.com/locate/astropart