Searches for charginos and neutralinos in $e^{+}e^{-}$ collisions at $\sqrt{s}$ =161 and 172 GeV

The data recorded by the ALEPH detector at centre-of-mass energies of 161, 170, and 172~GeV have been analysed for signals of chargino and neutralino production. Events consistent with the expectation from Standard Model processes were observed in the data. No evidence for a signal was found. Limits are derived on the production cross sections and extended to interpretation in the Minimal Supersymmetric Standard Model. The limit on the mass of the lightest chargino is 85.5 GeV/c^2 for gaugino-like charginos (mu = -500 GeV/c^2), and 85.0 GeV/c^2 for Higgsino-like charginos (M_2 = 500 GeV/c^2), for heavy sneutrinos (m_0 >= 200 GeV/c^2) and tan(beta) = sqrt(2). The effect of light sleptons is investigated, and limits are derived for both the chargino and neutralino analyses under that scenario. Assumptions of universal scalar or gaugino masses have been relaxed, allowing less model-dependent limits to be obtained.