Scalar quark searches in $e^+ e^-$ collisions at $\sqrt{s}$ = 181-184 GeV

Searches for scalar top, scalar bottom and degenerate scalar quarks have been performed with data collected with the ALEPH detector at LEP. The data sample consists of 57~$\mathrm{pb}^{-1}$ taken at $\rts$ = 181--184~GeV. No evidence for scalar top, scalar bottom or degenerate scalar quarks was found in the channels $\stop \rightarrow \mathrm{c}\neu$, $\stop \rightarrow \mathrm{b}\ell\sn u$, $\sbot \rightarrow \mathrm{b}\neu$, and $\mathrm{\tilde{q}} \rightarrow \mathrm{q}\neu$. From the channel $\stop \rightarrow \mathrm{c}\neu$ a limit of 74~$\gev$ has been set on the scalar top quark mass, independent of the mixing angle. This limit assumes a mass difference between the $\stop$ and the $\neu$ in the range 10--40~$\gev$. From the channel $\stop \rightarrow \mathrm{b}\ell\ snu$ the mixing-angle-independent scalar top limit is 82~$\gev$, assuming $m_{\mathrm{\tilde{t}}}-m_{\tilde{\nu}}$ $>$ 10~$\gev$. From the channel $\sbot \rightarrow \mathrm{b}\neu$, a limit of 79 ~$\gev$ has been set on the mass of the supersymmetric partner of the left-handed state of the bottom quark. This limit is valid for $m_{\mathrm{\tilde{b}}}-m_{\neu}$ $>$ 10~$\gev$. From the chan nel $\mathrm{\tilde{q}} \rightarrow \mathrm{q}\neu$, a limit of 87~$\gev$ has been set on the mass of supersymmetric partners of light quarks assuming five degenerate flavours and the production o f both ``left-handed'' and ``right-handed'' squarks. This limit is valid for $m_{\mathrm{\tilde{q}}}-m_{\neu}$ $>$ 5~$\gev$.