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current knowledge of the ckm matrix element @xmath3 is derived from the mesonic decays @xmath4 or @xmath5 . experimental knowledge of the @xmath6 semileptonic decay can lead to an independent estimate of @xmath3 if the effect of the strong interaction in the decay are understood , _ e.g. _ , via lattice qcd . a first lattice study of the baryonic semileptonic decay was performed by the ukqcd collaboration  @xcite . we report our initial results for the dominant form factors of this decay . the semileptonic decay @xmath7 can be parametrized in terms of six form factors , @xmath8 and @xmath9 , for i = 1 , 2 , 3 . @xmath10u^{(r)}_{q'}(v ' ) . \label{velform}\end{aligned}\ ] ] here @xmath11 is the weak current and @xmath12 are polarisation states of the baryons . since both @xmath6 and @xmath13 are hadrons containing a single heavy quark , heavy quark effective theory ( hqet ) is applicable  @xcite . hence the matrix element is taken between baryons of a given velocity , and the form factors are functions of the scalar @xmath14 . to leading order in hqet , the combinations @xmath15 and @xmath16 involving the dominant form factors @xmath17 and @xmath16 can be written in terms of a single function , called the ( baryonic ) isgur - wise function , @xmath18 . this function is normalised at zero - recoil , @xmath19 . the simulations are performed on the asqtad quenched lattices at @xmath20 generated by the milc collaboration  @xcite . these are @xmath21 improved @xmath22 64 lattices , with @xmath23 = 1.33 gev , as determined from @xmath24 . we use three light quark masses near the strange quark mass , @xmath25 . two heavy quark @xmath26 values , 0.104 and 0.114 bracket the charm quark , and other two , 0.064 and 0.077 bracket the bottom . we use the clover action for the valence quarks , with a tadpole improved clover coefficient . the value for the tadpole improvement factor @xmath27 is taken from the landau gauge fixed mean link . fermilab formalism is used for the heavy quarks . results are presented for 300 lattices for two - point functions , and 237 lattices for three - point functions . the dispersion relation is shown in fig .  [ disp_fig ] . the fitted energy values agree very well with the expectation from the lattice dispersion relation . the chiral extrapolations for a fixed heavy quark mass are shown in fig . [ chiral_fig ] . the baryon kinetic mass @xmath28 is estimated as @xmath29 , where @xmath30 and @xmath31 are the baryon and heavy quark kinetic(rest ) masses respectively . we use a linear fit for these extrapolations . in fig . [ baryon_mass ] , we have shown the chirally extrapolated baryon mass as a function of the heavy quark mass , along with the coresponding meson masses taken from the milc collaboration . our values for @xmath32 and @xmath33 are 5.626(36)gev and 2.300(27)gev . different form factors contribute to different matrix elements in the three - point function . for @xmath34 , the dominant contribution to three - point functions comes from the vector form factors and for @xmath35 , axial - vector form factor @xmath16 gives the dominant contribution . we present results for the isgur - wise function from vector as well as axial - vector data . @xmath6 is created at time 0 and @xmath13 is annihilated at time @xmath36 in lattice units . the time at which the current acts is varied , and we study three - point function as a function of this time @xmath37 . for the results presented here , the intial baryon is at rest and the final baryon is moving with different velocities giving different values for @xmath38 . on the lattice , one is restricted to region near @xmath39 as data starts getting noisy for high momenta . in this region , @xmath40 can be approximated by 1 . then for an initial baryon of mass @xmath41 decaying to a final baryon of mass @xmath42 moving with a momentum @xmath43 , if we consider the sum of the co - efficients of @xmath44 and @xmath45 , for large @xmath46 and @xmath47 , the three - point expression simplifies to                          where @xmath54 and @xmath55 are known from the two - point functions . we fit this to a form @xmath56 and consider the ratio @xmath57}{a[(m',\vec{0 } ) \rightarrow ( m,\vec{0 } ) ] } & & \hspace{-0.5cm}= \big ( \frac{f_1(\omega)+f_2(\omega)+f_3(\omega)}{f_1(1)+f_2(1)+f_3(1 ) } \big)\nonumber\\ & & \hspace{-0.9cm}\cdot\big ( \frac{z'_s(|\vec{q}|)}{z'_s(0)}\big ) \cdot \big ( \frac{e+m}{2e}\big).\end{aligned}\ ] ] first factor on the rhs is(1/m ) corrections , which are further multiplied by ( 1-@xmath38 ) . for the small momenta accessible on the lattice , @xmath58 is a very good approximation to the baryonic isgur - wise function . the suffix @xmath59 emphasizes that the infinite mass limit has not been taken . ] the isgur - wise function @xmath60 . the second and third factors are known from the two - point functions . the third factor may be approximated by 1 to 0.5 per cent accuracy . the second factor differs from 1 by upto 10% over our range of @xmath61 . the ratio is independent of the renormalization constant @xmath62 because we have the same heavy quark transition in both numerator and denominator . our results for the isgur - wise function from the vector current are shown in fig . [ vec_iw ] . the isgur - wise function obtainted from the axial - vector current ( @xmath35 case ) is shown in fig . [ ax_iw ] . the isgur - wise function seems to be quite insensitive to the heavy quark mass . we have also studied the light quark mass dependence of the isgur - wise function . the isgur - wise function is expected to fall slower for smaller light quark masses , by a heuristic argument . we do see such a trend in this preliminary study , but it is very far from clear with the statistical errors we have . this is shown in fig . [ light ] .
we present results from a lattice study of the semileptonic decay @xmath0 . 
 we use @xmath1 improved quenched lattices of the milc collaboration , with lattice spacing @xmath2 fm . for the valence quarks , 
 the tadpole - improved clover action is used , with the fermilab method employed for the heavy quarks . 
 form factors are extracted from the vector as well as the axial - vector part of the current .