A precise determination of the W and Z masses at the CERN pp collider

Abstract The UA2 experiment has collected large samples of W and Z events during recent runs at the CERN p p Collider at s = 630 GeV . These samples have been used to perform precise measurements of the masses of the W and Z bosons. After a careful analysis of systematic errors, an improved result is obtained for the mass ratio m w m z . This provides a new value for the weak mixing parameter sin 2 θ w . Furthermore, it can be combined with recent measurements of the Z mass from e + e − colliders to give an absolute measurement of the W mass, leading to the result m w =80.49±0.43 (stat) ± 0.24 (syst) GeV .