Combined nonrelativistic constituent quark model and heavy quark effective theory study of semileptonic decays of b and b baryons

1550-7998=20 We present the results of a nonrelativistic constituent quark model study of the semileptonic decays b ! c l l and b ! c l l (l e; ). We work on coordinate space, with baryon wave functions recently obtained from a variational approach based on heavy quark symmetry. We develop a novel expansion of the electroweak current operator, which supplemented with heavy quark effective theory constraints, allows us to predict the baryon form factors and the decay distributions for all q2 (or equivalently w) values accessible in the physical decays. Our results for the partially integrated longitudinal and transverse decay widths, in the vicinity of the w 1 point, are in excellent agreement with lattice calculations. Comparison of our integrated b-decay width to experiment allows us to extract the Vcb Cabbibo-Kobayashi-Maskawa matrix element for which we obtain a value of jVcbj 0:040 0:005 stat 0:001 0:002 theory also in excellent agreement with a recent determination by the DELPHI Collaboration from the exclusive Bd ! D l l decay. Besides for the b b -decay, the longitudinal and transverse asymmetries and the longitudinal to transverse decay ratio are haLi 0:954 0:001 0:945 0:002 , haTi 0:665 0:002 0:628 0:004 , and RL=T 1:63 0:02 1:53 0:04 , respectively.