Cross section limits for the<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mmultiscripts><mml:mi mathvariant="normal">Cm</mml:mi><mml:mprescripts/><mml:none/><mml:mrow><mml:mn>248</mml:mn></mml:mrow></mml:mmultiscripts><mml:mrow><mml:mo stretchy="false">(</mml:mo></mml:mrow><mml:mmultiscripts><mml:mi mathvariant="normal">Mg</mml:mi><mml:mprescripts/><mml:none/><mml:mrow><mml:mn>25</mml:mn></mml:mrow></mml:mmultiscripts><mml:mrow><mml:mo>,</mml:mo><mml:mn>4</mml:mn><mml:mi>n</mml:mi><mml:mtext>−</mml:mtext><mml:mn>5</mml:mn><mml:mi>n</mml:mi><mml:mo stretchy="false">)</mml:mo></mml:mrow><mml:mmultiscripts><mml:mi mathvariant="normal">Hs</mml:mi><mml:mprescripts/><mml:none/><mml:mrow><mml:mn>268</mml:mn><mml:mo>,</mml:mo><mml:mn>269</mml:mn></mml:mrow></mml:mmultiscripts></mml:math>reactions

We report on an attempt to produce and detect $^{268}\mathrm{Hs}$ and $^{269}\mathrm{Hs}$ in the nuclear fusion reaction $^{25}\mathrm{Mg}+^{248}\mathrm{Cm}$ using the gas phase chemistry apparatus COMPACT. No decay chains attributable to the decay of hassium isotopes were observed during the course of this experiment. From the nonobservation of $^{269}\mathrm{Hs}$ we derive a cross section limit of 0.4 pb (63% confidence limit) for the reaction $^{248}\mathrm{Cm}(^{25}\mathrm{Mg},4n)^{269}\mathrm{Hs}$ at a center-of-target beam energy of 140 MeV. The evaluated cross section limit for the $^{248}\mathrm{Cm}(^{25}\mathrm{Mg},5n)^{268}\mathrm{Hs}$ reaction depends on the assumed half-life of unknown $^{268}\mathrm{Hs}$. Current systematics of the half-lives for even-even Hs isotopes suggests a value of 0.5 s, resulting in a cross section limit of 1.3 pb.

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