arXiv subjects

P. Desgrolard

Publications and source records attributed to P. Desgrolard.

At least 19 recordsLinked to original sources

arXiv2001

Pomeron effective intercept, logarithmic derivatives of $F_{2}(x,Q^{2})$ in DIS and Regge models

The drastic rise of the proton structure function $F_2(x,Q^2)$ when the Björken variable $x$ decreases, seen at HERA for a large span of $Q^2$, may be damped when $x\to 0$ and $Q^2$ increases beyond $\sim$ several hundreds \g2. This phenomenon observed in the Regge type models is discussed in terms of the effective Pomeron intercept and of the derivative $B_x=\partial{\ell n F_2(x,Q^2)}/\partial{\ell n(1/x)}$. The method of the overlapping bins is used to extract the derivatives $B_x$ and $B_Q=\partial{\ell n F_2(x,Q^2)}/\partial{Q^2}$ from the data on $F_2$ for $6.0\cdot 10^{-5}\le x\le 0.61$ and $1.2 \le Q^2$ (\g2) $\le 5000$. It is shown that the extracted derivatives are well described by recent Regge models with the Pomeron intercept equal one.

hep-ph↗

arXiv2001

Proton structure function. Soft and hard Pomerons

Regge models for proton structure function with and without a hard Pomeron contribution are compared with all available data in the region $W>3$ GeV, $Q^{2}\leq 3000$ GeV$^{2}$ and $x<0.75$. It is shown that the data do not support a hard Pomeron term in $γ^{*} p$ amplitude. Moreover, the data support the idea that the soft Pomeron, either is a double pole with $α_{P}(0)=1$ in the angular momentum $j$-plane, or is a simple pole with $α_{P}(0)=1+ε$ where $ε\ll 1$.

hep-ph↗

arXiv2001

Space structure of hadrons in elastic scattering at high energy

We have confirmed and complemented previous conclusions from studies of the impact parameter profiles, relative to $pp$ and $\bar pp$ scattering, using a generalized eikonalized amplitude. In particular, the transition from the grey to the black disk is followed, when the energy increases beyond $\sim 3$ TeV and for the inelastic process, by a black ring surrounding the antishadow scattering mode at the center. The ranges of hadronic forces responsible for the elastic and inelastic processes are estimated by means of root-mean-squares of the impact parameter. Predictions at the LHC energy are explicitly given. The effect of eikonalization is discussed.

hep-ph↗

arXiv2001

Regge models of the proton structure function with and without hard Pomeron: a comparative analysis

A comparative phenomenological analysis of Regge models with and without a hard Pomeron component is performed using a common set of recently updated data. It is shown that the data at small $x$ do not indicate explicitly the presence of the hard Pomeron. Moreover, the models with two soft-Pomeron components (simple and double poles in the angular momentum plane) with trajectories having intercept equal one lead to the best description of the data not only at $W>3$ GeV and at small $x$ but also at all $x\leq 0.75$ and $Q^{2}\leq 30000$ GeV$^{2}$.

hep-ph↗

arXiv2001

Rescattering corrections in elastic scattering

A detailed study of the rescattering series is performed within a model, using a generalized procedure of eikonalization and fitted to the $pp$ and $\bar pp$ elastic scattering data. We estimate and compare the various rescattering corrections to be added to the Born contribution in the amplitude. We find that their number is finite, whereas it increases with the energy and the transfer, like does their importance. In the domain where data exist, we find also that a correct computation must include, at least, all two- and three-Reggeon exchanges and some four- and five-Reggeon exchanges. Any approximation aiming to reduce this (large) number of exchange would be hazardous, especially when extrapolating. We extend our estimates in the domain of future experiments.

hep-ph↗

arXiv2000

Exchange-degenerate Regge trajectories: a fresh look from resonance and forward scattering regions

The exchange-degeneracy of the mesonic $f$, $ω$, $ρ$ and $a_{2}$ Regge trajectories, dominant at moderate and high energies in hadron elastic scattering, is analyzed from two viewpoints. The first one concerns the masses of the resonances lying on these trajectories; the second one deals with the total cross-sections and the ratios of the real to the imaginary parts of the forward amplitudes of hadron and photon induced reactions. Neither set of data supports exact exchange-degeneracy.

hep-ph↗

arXiv2000

Elastic pp and $\bar pp$ scattering in the Modified Additive Quark Model

The modified additive quark model, proposed recently, allows to improve agreement of the standard additive quark model with the data on the $pp, \bar pp, π^{\pm} p, γp$ and $γγ$ total cross-sections, as well as on the ratios of real to imaginary part of $pp$ and $\bar pp$ amplitudes at $t=0$. Here, we extend this model to non forward elastic scattering of protons and antiprotons. A high quality reproduction of angular distributions at 19.4 GeV $\leq \sqrt{s}\leq $ 1800 Gev is obtained. A zero at small $|t|$ in the real part of even amplitude in accordance with a recently proved high energy general theorem is found.

hep-ph↗

arXiv2000

Damping of the HERA effect in DIS?

The drastic rise of the proton structure function F_2(x,Q^2) when the Björken variable x decreases, seen at HERA for a large span of Q^2, negative values for the 4-momentum transfer, may be damped when Q^2 increases beyond several hundreds GeV^2. A new data analysis and a comparison with recent models for the proton structure function is proposed to discuss this phenomenon in terms of the derivative \partial ln F_2(x,Q^2)/\partial ln(1/x).

hep-ph↗

arXiv2000

Eikonalization and Unitarity Constraints

An extensive generalization of the ordinary and quasi-eikonal methods is presented for the $pp$ and $\bar pp$ elastic scattering amplitudes, which takes into account in a phenomenological way all intermediate multiparticle states involving the crossing even and crossing odd combinations of Reggeons. The formalism in this version involves a maximum of three parameters corresponding to the intermediate states which are possible in this configuration. The unitarity restriction is investigated and particular cases are discussed. An interesting result that emerges concerns the Odderon trajectory intercept: we find that unitarity dictates that this quantity {\it must} be below or equal unity unless a very peculiar equality exists between the coupling of the particles to the Pomeron and the Odderon.

hep-ph↗

arXiv2000

Of Dips, Structures and Eikonalization

We have investigated several models of Pomeron and Odderon contributions to high energy elastic $pp$ and $\bar p p$ scattering. The questions we address concern their role in this field, the behavior of the scattering amplitude (or of the total cross-section) at high energy, and how to fit all high energy elastic data. The data are extremely well reproduced by our approach at all momenta and for sufficiently high energies. The relative virtues of Born amplitudes and of different kinds of eikonalizations are considered. An important point in this respect is that secondary structures are predicted in the differential cross-sections at increasing energies and these phenomena appear quite directly related to the procedure of eikonalizing the various Born amplitudes. We conclude that these secondary structures arise naturally within the eikonalized procedure (although their precise localization turns out to be model dependent). The fitting procedure naturally predicts the appearance of a zero at small $|t|$ in the real part of the even amplitude as anticipated by general theorems. We would like to stress, once again, how important it would be to have at LHC both $pp$ and $p \bar p$ options for many questions connected to the general properties of high energy hadronic physics and for a check of our predictions.

hep-ph↗

arXiv1999

How fast do small x structure function rise ? A comparative analysis

We parametrize the small x, singlet component of the proton structure function F_2 by powers and logarithms of 1/x for discrete values of Q^2 between 0.2 and 2000 GeV^2, and compare these parametrizations by applying the criterion of minimal $χ^2$. The obtained values of the fitted parameters may be used to study the evolution of F_2 in Q^2 and/or in discriminating between dynamical models. A slowing-down in the increase of F_2 towards highest available values of Q^2 is revealed. The effect is quantified in terms of the derivative ${\frac{d\ell n F_2(x,Q^2)}{d\ell n (1/x)}}$.

hep-ph↗

arXiv1999

Unitarity, (anti)shadowing and the black disc limit

By using realistic models for elastic hadron scattering we demonstrate that at present accelerator energies the $s$-channel unitarity bound is safe, not to be reached until $10^5$ GeV, while the black disc limit is saturated around 1 TeV. It will be followed by a larger transparency of the scattered particles near the center.

hep-ph↗

arXiv1998

The additive quark model revisited: hadron and photon induced cross-sections

The standard additive quark model and the ensuing counting rules are modified to take into account the quark-gluonic content of the Pomeron and of the secondary Reggeons. The result is that a much improved description of $pp, πp, γp$ and $γγ$ cross-sections is achieved.

hep-ph↗

arXiv1998

The proton structure function and a soft Regge Dipole Pomeron: a test with recent data

A recently published soft Regge Dipole Pomeron model intended for all $x$ and $Q^2$ is proved to give a good agreement with (non fitted) recent HERA data from ZEUS (SVX95) on the protonstructure function $F_2^p(x,Q^2)$ at low $Q^2$ and low $x$. The model also reproduces (without fit) the recently estimated experimental derivatives ${\partial F_2^p\over\partial\ell n Q^2}$ and ${\partial \ell n F_2^p\over\partial\ell n (1/x)}$ in a wide $x$ and $Q^2$-region.

hep-ph↗

arXiv1998

Of dips and structures

A detailed analysis of the existence of high energy secondary diffractive dips and structures in the extrapolations of the fits to the data is given. The existence of these dips and a fortiori their position is found to be rather model-dependent: present in all eikonalized models including Pomeron, Odderon and secondary Reggeons they disappear when an additional large- t term is added (as sometimes advocated).

hep-ph↗

arXiv1998

Approximate solution of the BFKL equation applicable at HERA

We suggest a formula interpolating between the known asymptotic regimes of the BFKL equation as the approximate solution of that equation. The parameters appearing in this interpolation are fitted to the data on deep inelastic scattering in a wide range of the kinematical variables. Care is taken of the large-$x$ domain as well, outside the HERA kinematical region. The boundaries and the interface between various dynamical regimes are also studied.

hep-ph↗

arXiv1998

New possibilities of old soft pomeron in DIS

A traditional Regge model with a $Q^2$-independent Pomeron intercept closed (or equal) to one is constructed in order to describe the available data on the proton structure function. A Dipole Pomeron model which does not explicitly violate unitarity is developed and investigated. An excellent agreement with the 1209 data is found ($χ^2/{dof}=1.11$) in the whole kinematical domain investigated by experiments. A comparison of the model with already existing ones is made. The $x-$, $Q^2-$slopes and the effective intercept are discussed as $Q^2$ and $x$ functions.

hep-ph↗

arXiv1998

Interpolating between Soft and Hard Dynamics in Deep Inelastic Scattering

An explicit model for the proton structure function interpolating between low- (VMD and Regge behavior)and high-$Q^2$ (GLAP evolution) is suggested. The model is fitted to the experimental data in a wide range of the kinematical variables with emphasis on the low-$x$ HERA data. The boundaries, transition region and interface between various regimes are quantified.

hep-ph↗