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Register a new userDipole model analysis of the newest diffractive deep inelastic scattering data
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We analyse the newest diffractive deep inelastic scattering data from the DESY collider HERA with the help of dipole models. We find good agreement with the data on the diffractive structure functions provided the diffractive open charm contribution is taken into account. However, the region of large diffractive mass (small values of a parameter beta) needs some refinement with the help of an additional gluon radiation.
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New results on diffractive deep-inelastic $e p$ scattering at HERA are presented using data taken in 1994 with the H1 detector. The cross section for diffractive deep-inelastic scattering is measured in terms of a diffractive structure function $F_2^{D(3)}(beta,Q^2,xpom)$ over an extended kinematic range. The dependence of $F_2^{D(3)}$ on $xpom$ is found not to depend on $Q^2$, but to depend on $beta$. Therefore the $xpom$ dependence no longer factorizes. The $Q^2$ and $beta$ dependence of $F_2^{D(3)}$ is analyzed after an integration over the dependence on $xpom$. For fixed $beta$ a clear rise with $log Q^2$ is observed, persisting up to high values of $beta$. In terms of the Altarelli-Parisi (DGLAP) QCD evolution equations, these scaling violations give clear indications for a gluon dominated process. Subsequently an attempt is made to quantify the parton content of the diffractive exchange using the DGLAP evolution. At the starting scale a ``leading gluon distribution is found which contributes about $80 %$ of the momentum in the diffractive exchange. Measurements of the hadronic final state (energy flow and production of $D^{*}$ mesons) are found to be consistent with the predictions of a model of deep-inelastic electron pomeron scattering using the information on the parton content obtained.
The diffractive open charm production is computed in perturbative QCD formalism and in the Regge approach. The results are compared with recent data on charm diffractive structure function measured at DESY-HERA. Our results demonstrate that this observable can be useful to discriminate the QCD dynamics.
A new QCD analysis of Deep Inelastic Scattering (DIS) data is presented. All available neutrino and anti-neutrino cross sections are reanalysed and included in the fit, along with charged-lepton DIS and Drell-Yan data. A massive factorisation scheme is used to describe the charm component of the structure functions. Next-to-leading order parton distribution functions are provided. In particular, the strange sea density is determined with a higher accuracy with respect to other global fits.
The analytical treatment of the nonperturbative QCD dynamics is one of main open questions of the strong interactions. Currently, it is only possible to get some qualitative information about this regime considering other QCD-like theories, as for example the N=4 super Yang-Mills (SYM), where one can perform calculations in the nonperturbative limit of large t Hooft coupling using the Anti-de Sitter space/Conformal field theory (AdS/CFT). Recently, the high energy scattering amplitude was calculated in the AdS/CFT approach, applied to deep inelastic scattering (DIS) and confronted with the $F_2$ HERA data. In this work we extend the nonperturbative AdS/CFT inspired model for diffractive processes and compare its predictions with a perturbative approach based on the Balitsky - Kovchegov (BK) equation. We demonstrate that the AdS/CFT inspired model is not able to describe the current $F_2^{D(3)}$ HERA data and predicts a similar behavior to that from BK equation in the range $10^{-7} lesssim x_{IP} lesssim 10^{-4}$. At smaller values of $x_{IP}$ the diffractive structure function is predicted to be energy independent.
We have carried out a NLO analysis of the world data on polarized DIS in the MS/bare scheme. We have studied two models of the parametrizations of the input parton densities, the first due to Brodsky, Burkhardt and Schmidt (BBS) which gives a simultaneous parametrization for both the polarized and unpolarized densities and in which the counting rules are strictly imposed, the second in which the input polarized densities are written in terms of the unpolarized ones in the generic form Deltaq(x)=f(x)q(x) with f(x) some simple smooth function. In both cases a good fit to the polarized data is achieved. As expected the polarized data do not allow a precise determination of the polarized gluon density. Concerning the polarized sea-quark densities, these are fairly well determined in the BBS model because of the interplay of polarized and unpolarized data, whereas in the second model, where only the polarized data are relevant, the polarized sea-quark densities are largely undetermined.
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