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the cabibbo - kobayashi - maskawa ( ckm ) matrix element @xmath11 describes the rich phenomena of flavor - changing transitions between the two heavy quarks @xmath12 and @xmath13 . its precise extraction has become a very important issue in heavy flavor physics . generally @xmath0 is extracted by studying either exclusive or inclusive semileptonic @xmath1 decays . since long distance contributions are involved in these decays , theoretical estimates of the nonperturbative parameters are of crucial importance for a precise extraction of @xmath0 . heavy quark symmetry ( hqs ) @xcite and effective field theories of heavy quarks play a special role in such estimates .    in this short note , we are going to provide a more precise extraction for @xmath0 from both exclusive and inclusive semileptonic @xmath1 decays within the framework of hqeft of qcd . this effective field theory can directly be derived from qcd@xcite by integrating out the small components but with carefully treating the quark and antiquark components . recently , it has been shown that the hqeft can actually be regarded as a large component qcd@xcite . of particular , this effective field theory has been put forward and successfully applied to various hadron processes @xcite . the resulting effective lagrangian and the heavy quark expansion ( hqe ) in the hqeft of qcd appear to be different from the usual heavy quark effective theory ( hqet ) @xcite in which the quark and antiquark components were dealt with separately , i.e. , there is no quark - antiquark coupling terms considered in hqet . the application of the usual hqet in extracting @xmath0 has been discussed by several groups and summarized in ref.@xcite . we shall further emphasize in this note the relevant new features of hqeft with respect to the usual hqet . our paper is organized as follows : @xmath0 extraction from exclusive and inclusive b decays will be discussed in section [ exclusive ] and section [ inclusive ] , respectively . the previously obtained values for @xmath0 will be updated by using the most recent experimental measurements . and a brief conclusion will be presented in section [ conclusion ] . the @xmath14 differential decay rates are @xmath15\vert v_{cb } \vert^2 { \cal f}^2(\omega ) , \\ \label{widthb2d }      \frac{d\gamma(b\rightarrow dl\nu)}{d\omega}&=&\frac{g^2_f}{48\pi^3}(m_b+m_{d})^2      m^3_{d}(\omega^2 - 1)^{3/2 } \vert v_{cb } \vert^2 { \cal g}^2(\omega )     \end{aligned}\ ] ] with @xmath16        =   \eta_{v } ( 1+\delta ) , \end{aligned}\ ] ] where the qcd radiative corrections to two loops give the short distance coefficients @xmath17 and @xmath18 @xcite . @xmath19 is the product of the four - velocities of the @xmath1 and @xmath20 mesons , @xmath21 . the weak transition form factors @xmath22 , @xmath23 and @xmath24 can be expanded in powers of @xmath25 and represented by the heavy quark spin - flavor independent wave functions . then based on eqs.([widthb2ds ] ) and ( [ widthb2d ] ) , @xmath0 can be precisely extracted as long as the form factors are reliably evaluated in some theoretical framework . the hqe of the transition form factors are studied in detail up to order @xmath2 in hqeft framework in ref.@xcite . when the contributions of operators containing two gluon field strength tensors are omitted , at the zero recoil point @xmath26 the relevant form factors can be written as @xmath27 ^ 2       -\frac{1}{8m^2_b\bar{\lambda}^2 }       ( f_{1}+3f_{2 }   \nonumber\\ & &      -2\bar{\lambda}\varrho_{1}-6\bar{\lambda}\varrho_{2 } )       -\frac{1}{8m_c^2\bar{\lambda}^2}(f_{1}-f_{2}-2\bar{\lambda}\varrho_{1 }       + 2\bar{\lambda}\varrho_{2 } ) \nonumber\\ & &      + \frac{1}{4m_b m_c \bar{\lambda}^2}(f_{1}+f_{2}-2\bar{\lambda}\varrho_{1 }       -2\bar{\lambda}\varrho_{2 } ) , \\ \label{formfactorhz } h_{+}&= & 1+\frac{1}{8\bar{\lambda}^2}(\frac{1}{m_b}-\frac{1}{m_c})^2       [ ( \kappa_1 + 3\kappa_2)^2-(f_1 + 3f_2 ) + 2\bar{\lambda}(\varrho_1 + 3\varrho_2 ) ] , \\ \label{formfactorhf } h_{-}&= & 0 ,      \end{aligned}\ ] ] where the parameters in the rhs . of eqs.([formfactorha1])-([formfactorhf ] ) are defined in hqeft @xcite . for simplicity , when the variable @xmath19 is not written explicitly , we refer to the zero recoil values of relevant functions , i.e. , @xmath28 , @xmath29 , etc . the binding energy of a heavy meson @xmath30 is defined as @xmath31    it is seen from eqs.([formfactorha1 ] ) and ( [ formfactorhz ] ) that automatically both the form factors @xmath32 and @xmath33 in hqeft of qcd do not receive @xmath25 order correction at the zero recoil point . another point to be emphasized is eq.([formfactorhf ] ) . the vanished value of @xmath34 in hqeft arises from the fact of partial cancellation between the @xmath25 correction in the current expansion and the @xmath25 correction coming from the insertion of the effective lagrangian into the transition matrix elements @xcite . such a cancellation is not observed in hqet because in the latter framework the quark - antiquark couplings are not taken into account explicitly . though the so - called luke s theorem in hqet protects the weak transition matrix elements from @xmath25 order correction at zero recoil point , it does not protect @xmath34 from such correction @xcite . as a result , in hqet framework , only the @xmath35 decay rate at zero recoil is strictly protected against @xmath25 order correction while @xmath36 decay rate is not . this is the main reason besides the experimental considerations for the conclusion that the @xmath36 decay is not as favorable as @xmath37 decay for @xmath0 extraction in hqet .    in hqeft , eq.([formfactorhf ] ) advocates reliable extraction of @xmath0 from both @xmath38 and @xmath36 decays , because both rates of these decays do not receive @xmath25 order correction , as can be seen from eqs.([widthb2ds])-([formfactorhf ] ) . however , we note that the current world averages for @xmath39 and @xmath40 are @xcite @xmath41 so the current experimental data for @xmath40 receive larger errors than those for @xmath39 , which may lead to large experimental uncertainty for the result of @xmath0 extracted from @xmath36 .    now the value of @xmath0 depends on our estimates of @xmath42 and @xmath43 . first of all , it has been shown @xcite that some of the nonperturbative parameters appearing in the rhs . of eqs.([formfactorha1 ] ) -([formfactorhf ] ) can be related to the heavy meson masses . explicitly , we have @xmath44 thus some parameters can be determined from the heavy meson masses . a detailed study has been presented in ref.@xcite . here we would not repeat the analysis . it is easily read from ref.@xcite that by using @xmath45 one obtains the following values for @xmath46 , @xmath47 and @xmath48 , @xmath49 : @xmath50 which agree well with the sum rule results : @xmath51 , @xmath52 and @xmath53 @xcite .    then up to order @xmath2 only two parameters @xmath54 and @xmath55 remain unknown . to have an estimation for them , we recall the definition of the nonperturbative parameters . they are defined by the matrix elements as follows @xcite : @xmath56       \nonumber\\       & & + \frac{1}{\bar{\lambda}}tr[\kappa_{\alpha\beta}(v , v^{\prime } )        \bar{\cal m}^{\prime}\gamma p_{+}\frac{i}{2}\sigma^{\alpha\beta}{\cal m } ] , \nonumber\\    < m^{\prime}_{v^{\prime}}\vert { \bar{q}^{(+)}_{v^{\prime } } } \gamma & & \frac{1}{iv\cdot d }       ( i{d\hspace{-0.25cm}\slash_{\bot}})(-iv\cdot d ) ( i{d\hspace{-0.25cm}\slash_{\bot } } )    { q^{(+)}_v}\vert m_v >        = -\varrho_1(\omega)\frac{1}{\bar{\lambda}}tr[\bar{\cal m}^{\prime}\gamma { \cal m } ]        \nonumber\\      & & + \frac{1}{\bar{\lambda}}tr[\varrho_{\alpha\beta}(v , v^{\prime})\bar{\cal m}^{\prime}\gamma p_{+ }        \frac{i}{2}\sigma^{\alpha\beta}{\cal m } ] , \nonumber \\ < m^{\prime}_{v^{\prime}}\vert { \bar{q}^{(+)}_{v^{\prime } } } \gamma & & \frac{1}{iv\cdot d } ( i{d\hspace{-0.25cm}\slash_{\bot}})^2       \frac{1}{iv\cdot d } ( i{d\hspace{-0.25cm}\slash_{\bot}})^2   { q^{(+)}_v}\vert m_v >        = -\chi_1(\omega)\frac{1}{\bar{\lambda}^2 } tr[\bar{\cal m}^{\prime}\gamma { \cal m } ]       \nonumber\\     & &   + \frac{1}{\bar{\lambda}^2 } tr[\chi_{\alpha\beta}(v , v^{\prime})\bar{\cal m}^{\prime}\gamma p_{+ }        \frac{i}{2}\sigma^{\alpha\beta}{\cal m } ]        + \cdots ,    \end{aligned}\ ] ] where the ellipsis in the last equation represents the contributions of operators containing two gluon field strength tensors . the lorentz tensor @xmath57 is decomposed into scalar factors as @xmath58 , and @xmath59 , @xmath60 are decomposed similarly . the functions @xmath48 and @xmath49 are defined as @xmath61    as will be further emphasized in the next section , the operator @xmath62 in the matrix elements was considered to give contribution of order the binding energy @xcite , i.e. , @xmath63 , which has also been confirmed in the simple case by sum rule calculation @xcite . now if taking this simple replacement , we get from eqs.([wavefunctiondef ] ) @xmath64 note that our estimates in eqs.([estfrommass ] ) and ( [ rho1estimate ] ) are consistent with the relation among them in eq.([definef1 ] ) .    in eq.([estfrommass ] ) @xmath49 almost equals zero . of course one reason for this may be the possible partial cancellation between @xmath65 and @xmath66 in eq.([definef2 ] ) . but more importantly , we notice that @xmath65 , @xmath55 ( and therefore @xmath49 ) are parameters characterizing the chromomagnetic type operators , and the contributions of these chromomagnetic operators are generally believed to be small . if using the same method of estimation as that for @xmath54 and @xmath67 , one gets @xmath68 it can be seen from the above equations that the two terms in eq.([definef2 ] ) do have partial cancellation . however , eqs.([rho2estimate ] ) , ( [ chi2estimate ] ) and ( [ definef2 ] ) can not hold simultaneously . this indicates that eqs.([rho2estimate ] ) and ( [ chi2estimate ] ) are only rough estimates for the chromomagnetic type parameters since these parameters are very small in magnitude . nevertheless , as @xmath55 must be small and can not influence the final result for @xmath0 as significantly as @xmath54 does , here we would first take eq.([rho2estimate ] ) in extracting @xmath0 but leave more rigid determination of @xmath55 for future work . fig.1 presents @xmath69 as a function of @xmath70 at the fixed quark mass difference @xmath71gev . the curves are relatively flat in the region around @xmath72gev , which indicates a reliable extraction of @xmath69 around this point . this value of @xmath70 is in agreement with that in eq.([estfrommass ] ) . varying @xmath73 and @xmath74 in the ranges @xmath75 and @xmath76 , and taking @xmath77 and @xmath78 , we get @xmath79 from eqs.([exp1 ] ) and ( [ deltas1 ] ) , we then obtain @xmath80    for @xmath36 decay , analogously , we obtain @xmath81 and @xmath82    comparing eqs.([vcbbds ] ) and ( [ vcbbd ] ) , we see that the results of @xmath0 extracted from @xmath14 decays have similar theoretical errors . but large difference exists between the central values of our present results , eqs.([vcbbds ] ) and ( [ vcbbd ] ) . however , due to the large experimental error for @xmath36 channel , the @xmath0 values extracted above are compatible with each other . a better determination of @xmath0 from @xmath36 decay is expected when a more precise result for the quantity @xmath40 is obtained . note that in ref.@xcite @xmath54 and @xmath55 are not estimated as above . there @xmath83 is assumed so that the central values for @xmath0 extracted from @xmath84 decays can be close to each other . indeed , @xmath83 together with the experimental averages ( [ exp1 ] ) , ( [ exp2 ] ) lead to @xmath85 from @xmath38 decay and @xmath86 from @xmath36 decay . inclusive semileptonic @xmath1 decays is the other alternative to determine @xmath0 . in the usual hqet the light quark in a hadron is generally treated as a spectator , which does not affect the heavy hadron properties to a large extent . however , this treatment may be one possible reason for the failure of hqet in some applications . for example , the world average value for bottom hadron lifetime ratio @xmath87 can not be explained well in the usual framework of hqet @xcite . the dynamics of inclusive @xmath1 decays is also analyzed in detail in refs.@xcite within the hqeft framework . instead of simply applying the equation of motion for infinitely heavy free quark , @xmath88 , we treat the heavy quark in a hadron as a dressed particle , which means that the residual momentum @xmath89 of the heavy quark within a hadron is considered to comprise contributions from the light degrees of freedom . this simple picture is adopted to conveniently take into account the effects of light degrees of freedom and the binding effects of heavy and light components of the hadron but not deal with the complex dynamics of hadronization directly . as the light degrees of freedom within the heavy hadron is relativistic , one has @xmath90 explicitly , the momentum of a heavy hadron @xmath91 is represented as @xmath92 with @xmath93 being the momentum depending on the heavy flavor and suppressed by the inverse of the heavy quark mass . this directly leads to the relation between @xmath94 and the binding energy , @xmath95 or @xmath96    to acquire a good convergence of hqe , we perform the expansion in terms of @xmath97 ( or say , equivalently , in terms of @xmath98 . then the @xmath99 decay rate is found to be @xcite @xmath100 where @xmath101 , @xmath102 , @xmath103 and @xmath104 are functions of the mass square ratios @xmath105 , @xmath106 and @xmath107 . here the calculation is performed up to nonperturbative order @xmath108 and perturbative order @xmath109 . the function @xmath110 characterizes qcd radiative corrections . its two - loop results were obtained in refs.@xcite . @xmath111 and @xmath112 can be determined from the meson masses via eq.([massb ] ) . @xmath47 is often extracted from the known @xmath113 mass splitting @xmath114 which is consistent with eq.([estfrommass ] ) and the sum rule result @xcite . there are several points to be mentioned for eq.([incwidth ] ) . firstly , in deriving eq.([incwidth ] ) the effects of light degrees of freedom are explicitly accounted for in the picture of a dressed heavy quark in a hadron . secondly , it is seen that the next leading order contributions vanish in our hqe in terms of the inverse dressed heavy quark mass , @xmath115 . furthermore , our hqe in terms of @xmath116 ( or @xmath115 ) has a good convergence . it is found that the @xmath117 order contributions induce only @xmath118 corrections to the total width @xmath119 . therefore we conclude that the higher order nonperturbative corrections can be safely neglected . finally , now one needs only to treat the dressed quark mass @xmath101 instead of considering the uncertainties arising from the two quantities @xmath73 and @xmath120 separately . note that these are the features of hqe in hqeft . they can not be observed in the hqe in the usual hqet , where one assumes @xmath121 to be zero or of higher order of @xmath122 . in the latter case the next leading order corrections can be absent only when the hqe is performed in terms of @xmath122 , and the heavy quark mass @xmath73 and the binding energy @xmath120 have to be treated separately . one result of this is that in hqet the theoretical prediction of the total decay width strongly depends on the value of bottom quark mass @xmath73 and may have larger uncertainties than in hqeft .    using eq.([incwidth ] ) , @xmath0 can be extracted from experimental data for inclusive decay rates . fig.3 shows the obtained values of @xmath123 as a function of the energy scale @xmath124 and the parameters @xmath125 , @xmath46 . it is seen that the extracted value of @xmath0 depends on the energy scale @xmath124 weakly . so the main uncertainties come from @xmath125 and @xmath46 . the curves in fig.3(b ) and fig.3(c ) have minimal value points , around which the values of @xmath126 are favorable because they are less sensitive to the variation of @xmath125 and @xmath46 . varying @xmath125 and @xmath46 in the regions @xmath127 , @xmath128 , these favorable values of @xmath126 change in the range : @xmath129 where the central value is obtained at @xmath130 and @xmath131 . then the @xmath132 lifetime @xmath133 and the most recent cleo data for @xmath134 branching ratio @xmath135 @xcite yield latexmath:[\[\begin{aligned }     @xmath0 extracted using different values of branching ratios is presented in fig.4 . as mentioned above , the values at @xmath137gev should be favorable because in this region the curves become less sensitive to the mass @xmath125 . interestingly , as shown in fig.3(c ) , when choosing @xmath138gev we find that the curve of @xmath126(or the resultant @xmath0 ) as a function of @xmath139 reaches its minimal ( or maximal ) point at @xmath140 . this value for @xmath46 is again in good agreement with that we used in section [ exclusive ] and with that obtained from sum rule calculation @xcite . note that the mass @xmath125 discussed here arises from the charm quark propagator in the hqe of the matrix elements . it should be the pole mass of charm quark . thus it is not surprising that the value of @xmath125 obtained here is larger than the value for constituent mass quoted in section [ exclusive ] . we have presented a more precise extraction of @xmath0 by studying the exclusive and inclusive semileptonic @xmath1 decays up to the order of @xmath2 in hqeft of qcd . the nonperturbative parameters in hqeft up to the same order are estimated consistently from various considerations . it has been shown that in hqeft of qcd @xmath0 can be reliably extracted from exclusive decays @xmath14 with similar theoretical uncertainties , because neither of their differential decay rates receives @xmath25 order corrections at zero recoil point . in studying inclusive @xmath1 decays , we treat the heavy quark in a hadron as a dressed particle whose residual momentum comprises some effects from the light degrees of freedom . this enables us to consider the effects of light components in the hadron but still has a simple physical picture in application . in this framework , the @xmath141 total decay rate is protected from @xmath115 order correction , and the @xmath117 order correction is very small . furthermore , @xmath73 and @xmath120 only appear in the form of dressed quark mass : @xmath101 , which must also reduce the uncertainties in our calculations as @xmath142 $ ] .    using the most recent experimental data for the b - meson decay rates , we have arrived at the determination for @xmath0 with @xmath143 where the result extracted from @xmath144 decay receives a larger experimental uncertainty than that from @xmath145 decay but a similar theoretical uncertainty as 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the more precise extraction for the ckm matrix element @xmath0 in the heavy quark effective field theory ( hqeft ) of qcd is studied from both exclusive and inclusive semileptonic @xmath1 decays . 
 the values of relevant nonperturbative parameters up to order @xmath2 are estimated consistently in hqeft of qcd . 
 using the most recent experimental data for @xmath1 decay rates , @xmath3 is updated to be @xmath4 from @xmath5 decay and @xmath6 from @xmath7 decay as well as @xmath8 from inclusive @xmath9 decay .    # 
 1@xmath10#1    : 12.15.hh , 12.39.hg , 13.20.he    @xmath0 , heavy quark effective field theory