Shape functions from (B)over-bar→Xcl(v)over-barl -: art. no. 036003

We study inclusive semileptonic B -> X(c)l nu(l) decay using the power counting m(c) similar to root Lambda(QCD)m(b). Assuming this scaling for the charm-quark mass, the decay kinematics can be chosen to access the shape-function region even in b -> c transitions. To apply effective field theory methods in this region we extend soft-collinear effective theory to describe massive collinear quarks. We calculate the tree-level decay rate, including O(Lambda(QCD)/m(b)) power corrections, and show that it factorizes into a convolution of jet and shape functions. We identify a certain kinematical variable whose decay spectrum is proportional to the universal leading-order shape function familiar from b -> u decay, and speculate as to whether information about this shape function can be extracted from data on b -> c decay.