First Observation of the Decay Bs0 → K-μ+νμ and a Measurement of |Vub|/|Vcb| - Aaij,R; Beteta,CA; Ackernley,T; Adeva,B; Adinolfi,M; Afsharnia,H; Aidala,CA; Aiola,S; Ajaltouni,Z; Akar,S; Albrecht,J; Alessio,F; et al. (PHYSICAL REVIEW LETTERS, 2021)