Search for Majoron-emitting modes of Xe-136 double beta decay with the complete EXO-200 dataset

A search for Majoron-emitting modes of the neutrinoless double beta decay of Xe-136 is performed with the full EXO-200 dataset. This dataset consists of a total Xe-136 exposure of 234.1 kg . yr, and includes data with detector upgrades that have improved the energy threshold relative to previous searches. A lower limit of (T1/2Xe)-Xe-136 4.3 x 10(24) yr at 90% C.L. on the half-life of the spectral index n = 1 Majoron decay was obtained, a factor of 3.6 more stringent than the previous limit from EXO-200 and a factor of 1.6 more stringent than the previous best limit from KamLAND-Zen. This limit corresponds to a constraint on the Majoron-neutrino coupling constant of vertical bar < g(ee)(M))vertical bar < (0.4-0.9) x 10(-5). The lower threshold and the additional data taken resulted in a factor 8.4 improvement for the n = 7 mode compared to the previous EXO-200 search. This search provides the most stringent limits to date on the Majoron-emitting decays of Xe-136 with spectral indices n = 1, 2, 3, and 7.