This work was supported in part by the Helmholtz International Center for FAIR (HIC for FAIR); the Helmholtz Association (Grant No. IK-RU-002); the European Union's Horizon Europe Research and Innovation program under Grant Agreement No. 101057511 (EURO-LABS); the Chinese Academy of Sciences President's International Fellowship Initiative (Grant No. 2024PVA0005); the Russian Science Foundation (Grant No. 22-12-00054); the Polish National Science Center (Contract No. 2019/33/B/ST2/02908); the Helmholtz-CAS Joint Research Group (Grant No. HCJRG-108); the Ministry of Education & Science, Spain (Contract No. FPA2016-77689-C2-1-R); the Ministry of Economy, Spain (Grant No. FPA2015-69640-C2-2-P); the Hessian Ministry for Science and Art (HMWK) through the LOEWE funding scheme; the Justus-Liebig-Universität Giessen (JLU) and the GSI under the JLU-GSI strategic Helmholtz partnership agreement; and DGAPA-PAPIIT IG101423. This work was carried out in the framework of the Super-FRS Experiment Collaboration.

We report on the observation of previously-unknown isotope $^{21}$Al, the first unbound aluminum isotope located beyond the proton dripline. The $^{21}$Al nucleus decays by one-proton (1p) emission, and its in-flight decays were detected by tracking trajectories of all decay products with micro-strip silicon detectors. The 1p-emission processes were studied by analyses of the measured angular correlations of decay products $^{20}$Mg+p. The 1p-decay energies of ground and low-lying excited states of $^{21}$Al, its mass excess and proton separation energy value $S_p$=$-1.1(1)$ MeV were determined.

6 pages, 7 figures

Peer reviewed