Heavy quark distribution function in QCD and nonperturbative parameters in heavy quark expansion

In the framework of HQET, we obtain the distribution function of heavy quark in heavy hadron by using the method of Ma [Nucl. Phys. B 506 (1997) 329] where the fragmentation function of parton into heavy hadron was derived. In our formula the mass difference between heavy hadron and heavy quark is kept. Applying it to the estimation of non-perturbative parameters to the order O(1mQ) in HQET expansion, we found relatively small value of μπ2 compared to previous results.