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the experimental results on deep inelastic charm production obtained by the h1 @xcite and zeus @xcite collaborations at hera provide a strong impetus for further theoretical studies . this process is truly semihard because of the presence of two larges scales : the virtuality of the exchanged photon ( @xmath3 ) and the charm mass ( @xmath4 ) , both being much larger than @xmath5 but much smaller than @xmath6 . therefore , in the present note , we focus on the semihard approach  @xcite ( sha ) , which we had applied earlier to the @xmath1 meson photoproduction @xcite in a similar manner . it is known that the resummation @xcite of the terms @xmath7^n,\;$ ] @xmath8^n\;$ ] and @xmath9^n$ ] in sha results in the so called unintegrated gluon distribution + @xmath10 , which determines the probability to find a gluon carrying the longitudinal momentum fraction @xmath11 and transverse momentum @xmath12 at the probing scale @xmath13 . it obeys the bfkl equation  @xcite and reduces to the conventional gluon density @xmath14 once the @xmath15 dependence is integrated out : @xmath16 the factorization scale @xmath13 ( such that @xmath17 @xmath18 ) indicates the scale of the nonperturbative input distribution . the ccfm evolution equation @xcite includes coherence effects via parton angular ordering and reproduces the bfkl evolution equation in the small @xmath11 limit . therefore the ccfm unintegrated parton distribution @xmath19 ( unlike the function @xmath20 ) depends also on the maximum angle allowed for any emission corresponding to @xmath21 . in the small @xmath11 limit it reduces to @xmath22  @xcite . when calculating the spin average of the matrix element squared , we substitute the full lepton tensor for the photon polarization matrix : @xmath23/(q^2)^2 \label{epsq}\ ] ] ( including also the photon propagator factor ) . the virtual gluon polarization matrix is taken in the form @xcite : @xmath24 where @xmath25 and @xmath26 are the 4-momenta of the incoming electron and proton . to parametrise the unintegrated structure functions , we use the prescriptions of ref . the proposed method lies upon a strai ghtforward perturbative solution of the bfkl equation where the collinear gluon density @xmath27 is used as the boundary condition in the integral form ( 1 ) . technically , the unintegrated gluon density is calculated as a convolution of the collinear gluon density with universal weight factors : @xmath28 @xmath29 @xmath30 where @xmath31 and @xmath32 stand for bessel functions ( of real and imaginary arguments , respectively ) , and @xmath33 . the latter parameter is connected with the pomeron trajectory intercept : @xmath34 in the lo , and @xmath35 in the nlo approximations , respectively , where @xmath36 @xcite .    in the previous work @xcite we used the standard grv parametrization @xcite for the collinear gluon density , from which the unintegrated gluon distribution was developed according to eqs . ( 4 ) - ( 6 ) . some other essential parameters were chosen as follows : the charm quark mass @xmath37  gev , the peterson fragmentation parameter @xmath38 , the overall @xmath39 fragmentation probability 0.26 . the pomeron intercept @xmath2 was regarded as free parameter , and then the value @xmath40 has been extracted from a fit to the experimental @xmath41 spectrum measured by the zeus collaboration @xcite . in this paper we also use an unintegrated gluon density coming from a solution of the ccfm evolution equation ( see @xcite ) . it was shown in @xcite that a good description of the inclusive structure function @xmath42 and the production of forward jets in dis , which are believed to be a prominent signature of small @xmath11 parton dynamics , can be obtained using the ccfm unintegrated gluon distribution . in @xcite we have used the hadron level monte carlo program cascade described in @xcite to predict the cross section for @xmath43 photoproduction at hera energies . it was shown that in this case the description of the differential cross section @xmath44 for @xmath45 1 gev@xmath46 for different regions of @xmath41 is improved . the theoretical predictions on the differential cross sections of deep inelastic @xmath47 production are shown in figure  [ fig : fig1 ] for the zeus kinematical region : @xmath48 gev@xmath46 , @xmath49 gev and @xmath50 . different curves in figure  [ fig : fig1 ] correspond to different values of the pomeron intercept parameter : @xmath2 = 0.166 ( dotted ) , 0.35 ( solid ) and 0.53 ( dashed ) . we see that the theoretical curves with @xmath51 describe all zeus experimental data @xcite on the differential cross sections , except the @xmath44 distribution . the sha calculations with bfkl unintegrated gluon distribution show some shift to negative @xmath52 with respect to the data . this descrepancy between the data and the sha prediction could result from the use of the peterson fragmentation function . another reason may be connected with the bfkl lo unitegrated gluon density . , ccfm scheme with peterson fragmentation.[fig : fig2 ] ]    , ccfm sheme with jetset fragmentation.[fig : fig3 ] ]    the use of ccfm unintegrated gluon density ( with angular ordering ) from mc generator cascade @xcite with the peterson fragmentation function for @xmath53 transition gives some positive shift to the @xmath44 distribution ( figure  [ fig : fig2 ] ) compared to bfkl curve ( see figure  [ fig : fig1]e ) . finally , when we use the ccfm unintegrated gluon distribution with more realistic jetset based fragmentation function  @xcite implemented in @xcite we obtain good agreement between our theoretical results and the zeus experimental data @xcite for @xmath44 ( figure  [ fig : fig3 ] ) . one of us ( n.z . ) would like to thank organizing committee of the workshop `` diffraction 2000 '' for the invitation and financial support and r. fiore for exiting scientific atmosphere . this talk is based on the work supported in part by the royal swedish academy of sciences . 99 h1 collab . , c. adloff et al . , z. phys . c72 ( 1996 ) 593 ; nucl . b545 ( 1999 ) 21 . zeus collab . , j. breitweg et al . , phys . b407 ( 1997 ) 402 . zeus collab . , j. breitweg et al . , eur . j. c12 ( 2000 ) 35 . gribov , e.m . levin , m.g . ryskin , phys . 100 ( 1983 ) 1 . levin , m.g . ryskin , yu.m . shabelski , a.g . shuvaev , sov . 53 ( 1991 ) 657 . baranov , n.p . zotov , phys . b458 ( 1999 ) 389 . baranov , h.  jung , n.p . zotov , in proc . of the workshop on monte carlo generators , ed . by a. doyle , g.  grindhammer , g.  ingelman , h.  jung , desy , hamburg ( 1999 ) , p. 484 ; hep - ph/9910210 . s.  catani , m.  ciafaloni , f.  hautmann , nucl . b366 ( 1991 ) 135 . collins , r.k . ellis , nucl . phys . b360 ( 1991 ) 3 . e.  kuraev , l.  lipatov , v.  fadin , sov . jetp 44 ( 1976 ) 443 ; 45 ( 1977 ) 199 ; y.  balitskii , l.  lipatov , sov . ( 1978 ) 822 . m.  ciafaloni , nucl . phys . b296 ( 1998 ) 49 ; s. catani , f. fiorani , g. marchesini , phys . b234 ( 1990 ) 339 , nucl . b336 ( 1990 ) 18 ; g. marchesini , nucl . b445 ( 1995 ) 49 . j.  blumlein , desy 95 - 121 . ross , phys . lett . b431 ( 1998 ) 161 . m.  gluck , e.  reya , a.  vogt , z. phys . c67 ( 1995 ) 433 . zeus collab . , j.  breitweg et al . , eur . j. c6 ( 1999 ) 67 . h.  jung , in proc . of the workshop on monte carlo generators , ed . by a. doyle , g.  grindhammer , g.  ingelman , h.  jung desy , hamburg ( 1999 ) , p. 75 ; hep - ph/9908497 . t.  sjstrand , comp . 82 ( 1994 ) 74 .
in the framework of semihard ( k@xmath0 factorization ) qcd approach , we consider the differential cross sections of @xmath1 meson production at hera . the consideration is based on bfkl and ccfm gluon distributions . 
 we find that in the case of bfkl lo gluon distribution the theoretical results are sensitive to the pomeron intercept parameter @xmath2 . 
 we present a comparison of the theoretical results with available zeus experimental data .