Search for neutrinoless double-βdecay inXe136with a time projection chamber

A xenon time projection chamber (TPC) with an active volume of 180 liters has been built to study neutrinoless double-$\beta$ 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 $0\nu 0^{+}\to 0^{+}$ transition. Half-life limits of $T_{\frac{1}{2}}^{0\nu }>3.4\mathrm{}\left(6.4\right)\mathrm{}\times {10}^{23}$ yr in the mass mechanism mode, and $T_{\frac{1}{2}}^{0\nu }>2.6\mathrm{}\left(4.9\right)\mathrm{}\times {10}^{23}$ 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 $〈m_{\nu }〉$ of about 2.8 eV. Limits on two-neutrino double-$\beta$ decay of $T_{\frac{1}{2}}^{2\nu }>2.1\mathrm{}\times {10}^{20}$ yr, and on neutrinoless double-$\beta$ decay with Majoron emission of $T_{\frac{1}{2}}^{0\nu \chi }>4.9\mathrm{}\times {10}^{21}$ yr, both at 90% C.L., were also derived. Accordingly, a limit on the effective Majoron-neutrino coupling parameter of $〈g_M〉<2.4\mathrm{}\times {10}^{-4\mathrm{}}$ was deduced.