arXiv subjects

Ch. Royon

Publications and source records attributed to Ch. Royon.

7 recordsLinked to original sources

arXiv2000

High energy QCD and hard diffraction at HERA versus Tevatron

We present and discuss two different topics where Tevatron and HERA data can be compared directly. A method allowing for a direct comparison of data with theoretical predictions is proposed for forward jet production at HERA. An application to the determination of the effective Pomeron intercept in the BFKL-LO parametrization from $dσ/dx$ data at HERA leads to a good fit with a significantly high effective intercept, $α_P= 1.43 \pm 0.025 (stat.) \pm 0.025 (syst.)$. It is less than the value of the pomeron intercept using dijets with large rapidity intervals obtained at Tevatron. In a second part of this report, we make comparison between diffractive results at HERA and at Tevatron. We first give the parton distributions in the pomeron extracted from HERA data, and compare with hard single diffraction at Tevatron and diffractive dijets with a leading antiproton data.

hep-ph↗

arXiv1998

Hard diffraction at HERA in the dipole model of BFKL dynamics

Using the QCD dipole picture of the hard BFKL pomeron, we derive the general expressions of the elastic and inelastic components of the proton diffractive structure functions. We obtain a good 7 parameter fit (including a secondary reggeon contribution) to data taken at HERA by the H1 and ZEUS collaborations. The main characteristic features of the model in reproducing the data are discussed, namely the effective pomeron intercept, the scaling violations and the beta dependence. A difference obtained in the separate H1 and ZEUS fits leads us to analyse directly the differences between both measurements. Predictions on R, the ratio of longitudinal to transverse photon cross sections are performed and lead to very large values at high beta and large virtuality Q which may lead to a discrimination between models.

hep-ph↗

arXiv1997

Towards an unified description of total and diffractive structure functions at HERA in the QCD dipole picture

It is argued that the QCD dipole picture allows to build an unified theoretical description -based on BFKL dynamics- of the total and diffractive nucleon structure functions. This description is in qualitative agreement with the present collection of data obtained by the H1 collaboration. More precise theoretical estimates, in particular the determination of the normalizations and proton transverse momentum behaviour of the diffractive components, are shown to be required in order to reach definite conclusions.

hep-ph↗

arXiv1996

QCD dipole prediction for DIS and diffractive structure functions

The $F_{2}$, $F_{G}$, $R=F_{L}/F_{T}$ proton structure functions are derived in the QCD dipole picture of BFKL dynamics. We get a three parameter fit describing the 1994 H1 proton structure function $F_{2}$ data in the low $x$, moderate $Q^{2}$ range. Without any additional parameter, the gluon density and the longitudinal structure functions are predicted.The diffractive dissociation processes are also discussed, and a new prediction for the proton diffractive structure function is obtained.

hep-ph↗

arXiv1996

On the origin of the rise of $F_2$ at small $x$

We show that, provided that the non-perturbative input is regular at the right of the $ω=0$ singularity of the dominant DGLAP anomalous dimension, the rise of $F_2$ at small $x,$ experimentally measured by the averaged observable $λ= <(\partial ln F_2)/(\partial ln 1/x)>,$ is input-independent in the perturbative $Q^2$ regime at small $x$. $(\partial ln xF)/(\partial ln Q^2)$ appears to be more input-dependent in the same range. The GRV-type parametrisations verify these properties. Other models, namely the BFKL kernel(QCD dipoles), DGLAP(hard pomeron singularity) give different predictions for $λ$. At moderate $Q^2,$ there is a possibility of distinguishing these different perturbative QCD predictions in the near future.

hep-ph↗

arXiv1996

Proton structure functions in the dipole picture of BFKL dynamics

The $F_2$, $F_G$, $R = F_L/F_T$ proton structure functions are derived in the QCD dipole picture. Assuming $k_T$ and renormalization-group factorization, we relate deep-inelastic proton scattering to deep-inelastic onium scattering. We get a three-parameter fit of the 1994 H1 data in the low-$x,$ moderate $Q^2$ range. The ratios $F_G/F_2$ and $R$ are predicted without further adjustment. The dipole picture of BFKL dynamics is shown to provide a relevant model for quantitatively describing the proton structure functions at HERA. The predictions for $F_2$ and $F_G$ are compatible with the next-to-leading order DGLAP analysis, while $R$ is expected to be significantly lower at very small $x$.

hep-ph↗

arXiv1995

Deep-Inelastic Onium Scattering

Using the colour dipole approach of the QCD perturbative (BFKL) Pomeron exchange in onium-onium scattering, we compute the cross section for small but hierarchically different onium sizes. A specific term dependent on the size-ratio is generated. In deep inelastic onium scattering it appears as a scaling violation contribution to the quark structure function near the BFKL singularity. We find that the extension of the formalism for deep inelastic onium scattering to the proton structure function provides a remarkably good 3-parameter fit to HERA data at small x with a simple physical interpretation in terms of the dipole formulation.

hep-ph↗