Search for neutrinoless double-<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>β</mml:mi></mml:math>decay in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mmultiscripts><mml:mrow><mml:mi mathvariant="normal">Xe</mml:mi></mml:mrow><mml:mprescripts/><mml:mrow/><mml:mrow><mml:mn>136</mml:mn></mml:mrow><mml:mrow/><mml:mrow/></mml:mmultiscripts></mml:mrow></mml:math>with a time projection chamber

A xenon time projection chamber (TPC) with an active volume of 180 liters has been built to study neutrinoless double-$\ensuremath{\beta}$ decay in $^{136}\mathrm{Xe}$. The experiment was performed in the Gotthard Underground Laboratory, with 5 atm of xenon enriched to 62.5% in $^{136}\mathrm{Xe}$. The experimental details, background considerations, detector performance, and data analysis are discussed. From 6830 h of data, no evidence has been found for the $0\ensuremath{\nu}{0}^{+}\ensuremath{\rightarrow}{0}^{+}$ transition. Half-life limits of ${T}_{\frac{1}{2}}^{0\ensuremath{\nu}}&gt;3.4(6.4)\ifmmode\times\else\texttimes\fi{}{10}^{23}$ yr in the mass mechanism mode, and ${T}_{\frac{1}{2}}^{0\ensuremath{\nu}}&gt;2.6(4.9)\ifmmode\times\else\texttimes\fi{}{10}^{23}$ yr in the right-handed currents mode, at the 90(68)% C.L., were derived, corresponding to an upper limit on the Majorana neutrino mass parameter $〈{m}_{\ensuremath{\nu}}〉$ of about 2.8 eV. Limits on two-neutrino double-$\ensuremath{\beta}$ decay of ${T}_{\frac{1}{2}}^{2\ensuremath{\nu}}&gt;2.1\ifmmode\times\else\texttimes\fi{}{10}^{20}$ yr, and on neutrinoless double-$\ensuremath{\beta}$ decay with Majoron emission of ${T}_{\frac{1}{2}}^{0\ensuremath{\nu}\ensuremath{\chi}}&gt;4.9\ifmmode\times\else\texttimes\fi{}{10}^{21}$ yr, both at 90% C.L., were also derived. Accordingly, a limit on the effective Majoron-neutrino coupling parameter of $〈{g}_{M}〉&lt;2.4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$ was deduced.