Dipole models and parton saturation in ep scattering

In this contribution we briefly review the current status of the dipole models and parton saturation on the basis of results presented at the HERA-LHC workshops in the years 2006-2008. The problem of foundations of the dipole models is addressed within the QCD formalism. Some limitations of the models and open problems are pointed out. Furthermore, we review and compare the currently used dipole models and summarise the applications to describe various sets of HERA data. Finally we outline some of the theoretical approaches to the problem of multiple scattering and saturation.Comment: 9 pages, to appear in the proceedings of the HERA-LHC Workshop, CERN-DESY, 2006-200

Redescription des genres Septatrypa KOZLOWSKI, 1929 et Dubaria TERMIER, 1936 (Brachiopoda, Atrypida, Lissatrypidae)

The serial sections carried out on specimens of Septatrypa secreta KOZLOWSKI, 1929 and Dubaria lantenoisi TERMIER, 1936 show that the former of these species has a structure of the type "septalium" in the brachial valve. This "septalium" arises from the presence of an apical thickening which joins the median septum and the posterior and external part of the socket plates. This observation confirms the opinion of the authors who consider these two genera - of which the above species are the type species - to be distinct. The lectotype of Dubaria lantenoisi is designated. Some controversial genera of Septatrypinae are briefly discussed

Predicting F2D(3) from the dipole cross-section

We employ a parameterisation of the proton dipole cross section previously extracted from electroproduction and photoproduction data to predict the diffractive structure function F2D(3)(Q^2, beta, xpom). Comparison with HERA H1 data yields good agreement.Comment: 5 pages,4 figures, Latex2e, uses espcrc1.sty. Presented at "Hadron 99" Beijing, August 1999. Reference added, erroneous citation correcte

Reggeon and pion contributions in semi-exclusive diffractive processes at HERA

A detailed analysis of semi-exclusive diffractive processes in e-p DIS at HERA, with the diffractive final states in the forward direction is presented. The contributions of the subleading f_2, \omega, a_2, \rho reggeons and the pion exchanges to the diffractive structure function with the forward proton or neutron are estimated. It is found that the (a_2,\rho) reggeons are entirely responsible for the forward neutron production at x_P < 10^{-3}. The \pi N production in the forward region is estimated using the Deck mechanism. The significance of this reaction for the processes measured at HERA, especially with the leading neutron, is discussed.Comment: Strongly revised version accepted for publication in Phys.Rev.D. Latex, 14 pages with 5 eps figures include

The colour dipole approach to small-x processes

We explain why it is possible to formulate a wide variety of high energy (small-x) photon-proton processes in terms of a universal dipole cross section and compare and contrast various parameterizations of this function that exist in the literature.Comment: 6 pages, latex, 2 figures. Contribution to Durham Collider Workshop (Sept 99) proceeding

Saturation QCD predictions with heavy quarks at HERA

The measurement of the proton structure function at HERA is often seen as a hint for the observation of saturation in high-energy QCD e.g. through the observation of geometric scaling. Accordingly, the dipole picture provides a powerful framework in which the QCD-based saturation models can be confronted to the data. In this paper, we give a parametrisation of proton structure function which is directly constrained by the dynamics of QCD in its high-energy limit and fully includes the heavy quark effects. We obtain a good agreement with the available data. Furthermore, to the contrary of various models in the literature, we do not observe a significant decrease of the saturation momentum due to the heavy quark inclusion.Comment: 8 pages, 5 figure

Hard colour singlet exchange and gaps between jets at the Tevatron

The new kind of events with a rapidity gap between two high-E_T jets, observed in high energy ppbar collisions at the Tevatron, is found to be well described by the exchange of a colour singlet gluon system in the BFKL framework. This requires going beyond the conventional asymptotic Mueller-Tang approximation, which results in qualitatively different features of the basic parton-parton scattering amplitude. Non-leading corrections to the BFKL equation are included by incorporation of the consistency constraint and the running QCD coupling. Hadronisation and other non-perturbative QCD effects are treated through a complete Monte Carlo simulation, providing a gap survival probability that varies event-by-event, facilitating comparison with experimental results.Comment: 15 pages, 11 eps figure

Antenna subtraction with hadronic initial states

The antenna subtraction method for the computation of higher order corrections to jet observables and exclusive cross sections at collider experiments is extended to include hadronic initial states. In addition to the already known antenna subtraction with both radiators in the final state (final-final antennae), we introduce antenna subtractions with one or two radiators in the initial state (initial-final or initial-initial antennae). For those, we derive the phase space factorization and discuss the allowed phase space mappings at NLO and NNLO. We present integrated forms for all antenna functions relevant to NLO calculations, and describe the construction of the full antenna subtraction terms at NLO on two examples. The extension of the formalism to NNLO is outlined.Comment: 33 pages, 3 figure

Geometric Scaling in a Symmetric Saturation Model

We illustrate geometric scaling for the photon-proton cross section with a very simple saturation model. We describe the proton structure function F2 at small x in a wide kinematical range with an elementary functional form and a small number of free parameters. We speculate that the symmetry between low and high Q2 recently discovered in the data could be related to a well-known symmetry of the two-gluon- exchange dipole-dipole cross section.Comment: 15 pages, 4 figure