Search for chargino and neutralino production at √s = 170 and 172 GeV at LEP

A search for charginosand neutralinos, predicted by supersymmetric theories, has been performed using a data sample of 57 pb −1−1 at centre-of-mass energies of 181–184 GeV taken with the OPAL detector at LEP. No evidence for charginoor neutralinoproduction has been found. Upper limits on charginoand neutralino pair production( χ~+1χ~−1χ~1+χ~1− , χ~01χ~02χ~10χ~20 ) cross-sections are obtained as a function of the charginomass ( mχ~±1mχ~1± ), the lightest neutralinomass ( mχ~01mχ~10 ) and the second lightest neutralinomass ( mχ~02mχ~20 ). For large charginomasses the limits have been improved with respect to the previous analyses at lower centre-of-mass energies. Exclusion regions at 95% confidence level (C.L.) of parameters of the Constrained Minimal Supersymmetric Standard Modelare determined for the case of a large universal scalar mass, m0m0 , implying heavy scalar fermions, and for the case of a small m0m0 resulting in light scalar fermions and giving the worst-case limits. Within this framework and for mχ~±1−mχ~01≥5mχ~1±−mχ~10≥5 GeV the 95% C.L. lower limits on mχ~±1mχ~1± for m0=500m0=500 GeV are 90.0 and 90.2 GeV for tanβ=1.5tan⁡β=1.5 and 35 respectively. These limits for all m0m0 (the worst-case) are 69.1 and 65.2 GeV for tanβ=1.5tan⁡β=1.5 and 35 respectively. Exclusion regions are also presented for neutralinomasses, including an absolute lower limit at 95% C.L. for the mass of the lightest neutralinoof 30.1 GeV for m0=500m0=500 GeV (24.2 GeV for all m0m0 ), with implications for experimental searches for the lightest neutralinoas a dark matter candidate.