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in this talk we consider a new mechanism for hard inclusive production , which violates the factorization theorem @xcite .
the suggested mechanism is present in any central hard inclusive production , such as heavy higgs meson production and/or the high @xmath0 inclusive production of mini jets and jets .
we illustrate this mechanism for the case of inclusive heavy higgs production in nucleon - deutron high energy scattering .
the usual description of inclusive production of a higgs meson with mass @xmath1 in a nucleon - deutron interaction , is based on the factorization theorem @xcite , using which the cross section of interest is given by @xmath2 where @xmath3 denotes the parton distribution within the deutron , and in the impulse approximation @xmath4 .
@xmath5 denotes the cross section for higgs meson production in the parton - parton collision .
the factorization theorem ( ft ) can be proven for the nucleon - deutron scattering using the agk cutting rules @xcite ( see ref . @xcite and references therein for detail discussion of the agk cutting rules in qcd ) .
indeed , let us assume that the ft holds for nucleon - nucleon scattering . for nucleon - deutron scattering
we have two contributions to the total cross section : the projectile nucleon interacts with one nucleon in the deutron ( impulse approximation ) and it interacts with both nucleons in the deutron ( glauber corrections ) .
the first process obviously leads to the ft of eq.(1 ) , while for the second one we can use the agk cutting rules for the decomposition of the total cross section with respect to the multiplicity of produced particles .
the relation between different contributions is : @xmath6 where @xmath7 and @xmath8 is the amplitude of the nucleon - nucleon interaction .
@xmath9 is the cross section of all processes where no particles were produced in the central rapidity region ( elastic scattering and single and double diffractive dissociation ) ; @xmath10 is the contribution to the total inelastic cross section , which has the same multiplicity distribution as in nucleon - nucleon inelastic cross section , and @xmath11 is part of the total inelastic cross section for the nucleon - deutron scattering which describes the inelastic interaction of the projectile nucleon with two nucleons in the deutron .
one can see that eq.(2 ) leads to the cancellation of the interaction with the two nucleon in the deutron for the inclusive cross section of the particle in the central rapidity region .
indeed , @xmath9 does not contribute to this production while two other contributions cancels since in the subprocess described by @xmath11 there is two ways of the production of the particle of the interest .
therefore , the inclusive production can be described in the impulse approximation for which the ft is valid by our assumption .
the natural question arises : _ what is wrong in our above discussion_.
let us start with the short answer to the formulated question : _ we missed the interference diagrams given in fig.1 _ and these diagrams give the new mechanism for centrally produced higgs meson ( or for any other  hard " process .
trying to describe what kind of processes we picture in fig.1 , one can see that fig.1a shows the process where the higgs , which is produced centrally , is separated by two large rapidity gaps ( lrg ) from the small final state multiplicities which occur on the edges of the rapidity plot .
we define this process as a double pomeron exchange reaction , and denote its contribution as @xmath12 .
the contribution of fig.1b is denoted by @xmath13 .
this is a mixed diagram , where the higgs which is produced in a double pomeron process , is superimposed on a normal uniform rapidity distribution typical of an inelastic nucleon - nucleon reaction .
finally , fig.1c describes higgs production as part of the nucleon - nucleon background to the rapidity distribution .
we denote this contribution by @xmath14 . to obtain our final result we need to sum over all three of the above contributions , noting that these are not necessarily positive .
the nucleon - nucleon ( nn ) amplitude for higgs production via double pomeron exchange , has been calculated @xcite , to be @xmath15 @xmath16 is the the vertex of the hard parton - parton @xmath17 higgs process and @xmath18 is the pomeron exchange amplitude .
the second ingredient in our calculation is the amplitude shown in fig.1c ( see also one of the amplitude in fig.1b ) .
this amplitude has no analog in the case of a single nucleon - nucleon interaction , and it depicts the cut in the diagram shown in fig.1a .
we note that this diagram is equal to @xmath19 , unlike the case for inelastic nucleon - nucleon cross section where @xmath20 .
the above result follows from the unitarity constraint @xcite .    recalling that the integration over the longitudinal components of the momentum carried by the pomeron in fig.1b results in a negative sign for the interference diagram ( see ref .
@xcite for details ) , we can easily calculate all diagrams contributing to the inclusive higgs meson production .
indeed , calculating @xmath12 , the sum of the diagrams in fig.1a , and using eq.(3 ) , one has    @xmath21    for the sum of diagrams in fig.1b we have @xmath22 finally , for @xmath14 , shown in fig.1c , we obtain @xmath23 the relation between the different contributions is @xmath24 where @xmath25 .    summing all contributions we obtain an additional term in the cross section
compare to the one given in eq.(1 ) @xmath26    we would like to draw attention to the novel fact , that the contribution of the new mechanism is proportional to the real part of the amplitude . for a soft pomeron with @xmath27 , the contribution of eq.(8 ) vanishes , and we recover the factorization theorem @xcite , i.e. an exact cancellation of the diagrams shown in fig.1c .
however , for the hard processes (  hard " pomeron ) both theory and experiment lead to a steep behaviour of the cross section as a function of energy ( see ref .
@xcite ) which results in considerable violation of the factorization theorem for totaly inclusive production . indeed , at high energy ( low @xmath28 )
@xmath29 is equal to @xmath30 in all available parametrization for the deep inelastic structure function @xmath31 at @xmath32 .
to give a quantative measure of the effect of the nonfactorization we plot in fig.2 the ratio of the nonfactorized contribution ( see ref.@xcite for the formula of this contribution ) to the cross section from the factorization theorem of eq.(1 ) , namely @xmath33 where @xmath34 is the gluon density of the @xmath35-th hadron and @xmath36 is the unintegrated gluon density , which closely related to the gluon structure function , namely , @xmath37 . in fig.2 we took @xmath38 = 0 , where @xmath38 is rapidity of produced higgs meson .
notice , that this ratio does not depend on the hard cross section , and as such is also applicable to any central production process , in particular , hard minijet and jet production . in evaluating eq.(10 )
we use @xcite the grv parametrization @xcite for the gluon density .
we assume that @xmath39 ( see ref.@xcite ) .
for the initial virtuality we take @xmath40 , as the grv parametrization is in agreement with the hera data on @xmath41 @xcite for all @xmath42 .
one can see , that @xmath43 is quite big for low masses and decreases when m increases .
for example , @xmath43 = 1.2 for @xmath44 .
we do not expect the higgs meson mass to be that small , but our result is also applicable in the case of jet production where @xmath45 .
accordingly , with such a value of @xmath43 we can expect minijet production ( jets with @xmath46 ) which can be responsible for the structure of the minimum bias events at the tevatron energy .    the value of @xmath43 is bigger for nucleus - nucleus interaction . to estimate this value
we need to multiply eq.(10 ) by a factor of @xmath47 . using the simple relation @xmath48
, one has @xmath49 .
therefore , for a gold - gold interaction we expect that @xmath43 is enhanced by factor 4 - 9 .
our conclusion is very simple : _ the factorization theorem @xcite is only approximate _ and the violation of the ft can be rather big especially for heavy ion collisions and/or for hadron ones at the lhc energies .
we firmly believe that the formal proof of the ft given in ref.@xcite should be reconsidered to find out the correct region of the applicability of this theorem .    99 e. gotsman , e. levin and u. maor : taup 2416/97 , hep - ph/9705205 , _ phys . lett .
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this talk is a digest of ref.@xcite , where a new mechanism for hard inclusive production , which leads to a violation of the factorization theorem ( ft ) , is suggested . 
 numerical estimates for the effect are given for high energy hadron ( nucleus ) scattering .    
 may 21 1997 + taup 2425/97