Search for the Pentaquark via the<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msubsup><mml:mrow><mml:mi mathvariant="italic">P</mml:mi></mml:mrow><mml:mrow><mml:mrow><mml:mrow><mml:mover><mml:mrow><mml:mi mathvariant="italic">c</mml:mi><mml:mi mathvariant="italic">s</mml:mi></mml:mrow><mml:mrow><mml:mi>¯</mml:mi></mml:mrow></mml:mover></mml:mrow></mml:mrow></mml:mrow><mml:mrow><mml:mn>0</mml:mn></mml:mrow></mml:msubsup></mml:mrow><mml:mi/><mml:mo>→</mml:mo><mml:mi/><mml:mi mathvariant="italic">φ</mml:mi><mml:mi mathvariant="italic">π</mml:mi><mml:mi mathvariant="italic">p</mml:mi></mml:math>Decay

We report results of the first search for the pentaquark ${P}_{\overline{c}s}$ which is predicted to be a doublet of states: ${P}_{\overline{c}s}^{0}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}|\overline{c}\mathrm{suud}〉$ and ${P}_{\overline{c}s}^{\ensuremath{-}}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}|\overline{c}\mathrm{sddu}〉$. A search was made for the decay ${P}_{\overline{c}s}^{0}\ensuremath{\rightarrow}\ensuremath{\varphi}\ensuremath{\pi}p$ in data from Fermilab experiment E791, in which a $500\mathrm{GeV}/c$ ${\ensuremath{\pi}}^{\ensuremath{-}}$ beam interacted with nuclear targets. We present upper limits at 90% confidence level for the ratio of cross section times branching fraction of this decay to that for the decay ${D}_{s}^{\ifmmode\pm\else\textpm\fi{}}\ensuremath{\rightarrow}\ensuremath{\varphi}{\ensuremath{\pi}}^{\ifmmode\pm\else\textpm\fi{}}$. The upper limits vary between 0.022 and 0.046 for $M({P}_{\overline{c}s}^{0})$ between $2.750$ and $2.907\mathrm{GeV}{/c}^{2}$, assuming a ${P}_{\overline{c}s}^{0}$ lifetime of 0.4 ps.