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G. Ridolfi

Publications and source records attributed to G. Ridolfi.

32 records · Page 2Linked to original sources
arXiv1997

Jet photoproduction at HERA

We compute various kinematical distributions for one-jet and two-jet inclusive photoproduction at HERA. Our results are accurate to next-to-leading order in QCD. We use the subtraction method for the cancellation of infrared singularities. We perform a thorough study of the reliability of QCD predictions; in particular, we consider the scale dependence of our results and discuss the cases when the perturbative expansion might break down. We also deal with the problem of the experimental definition of the pointlike and hadronic components of the incident photon, and briefly discuss the sensitivity of QCD predictions upon the input parameters of the calculation, like $α_S$ and the parton densities.

hep-ph↗
arXiv1996

Constraints on the polarized gluon density in the proton from charm photoproduction

We consider the possibility of a direct determination of the polarized gluon density in the proton using charm production with polarized beams at HERA. We study total cross sections and distributions at leading order using different parametrizations of the polarized gluon density. We conclude that charm photoproduction data can be used to constrain the polarized gluon density in the proton if an integrated luminosity of 100~pb$^{-1}$ will be achieved at HERA.

hep-ph↗
arXiv1996

Searches For New Physics

Review of prospects for discovery of new physics signals at LEP2. The areas covered include SUSY, exotic fermions, BESS models, leptoquarks, virtual effects and CP violating observables.

hep-ph↗
arXiv1995

A Next-to-Leading Determination of the Singlet Axial Charge and the Polarized Gluon Content of the Nucleon

We perform a full next-to-leading analysis of the the available experimental data on the polarized structure function g_1 of the nucleon, and give a precise determination of its singlet axial charge together with a thorough assessment of the theoretical uncertainties. We find that the data are now sufficient to separately determine first moments of the polarized quark and gluon distributions, and show in particular that the gluon contribution is large and positive.

hep-ph↗
arXiv1995

Heavy Flavour Production

We review the status of heavy flavour production in QCD. Comparison of experimental and theoretical results for top and bottom production are given. Selected topics in charm production are also discussed.

hep-ph↗
arXiv1995

Differential Distributions for Heavy Flavour Production at HERA

We compute pseudorapidity and transverse momentum distributions for charm and bottom production at HERA. We examine the effect of next-to-leading order QCD corrections, the effect of possible intrinsic transverse momenta of the incoming partons, and of fragmentation. We compare our results with full Monte Carlo simulation using HERWIG. The importance of the hadronic component of the photon is also studied. We examine the possibility to distinguish among different parametrizations of the photon parton densities using charm production data, and the possibilty to extract information about the small-$x$ behaviour of the gluon density of the proton. We also give a prediction for the transverse momentum and pseudorapidity distributions for bottom production at HERA.

hep-ph↗
arXiv1995

Scale Dependence and Small-x Behaviour of Polarized Parton Distributions

We discuss perturbative evolution of the polarized structure function g_1 in the (x,Q^2) plane, with special regard to the small-x region. We determine g_1 in terms of polarized quark and gluon distributions using coefficient functions to order alpha_s. At small x g_1 then displays substantial scale dependence, which necessarily implies a corresponding scale dependence in the large-x region. This scale dependence has significant consequences for the extraction of the first moment from the experimental data, reducing its value while increasing the error. Conversely, the scale dependence may be used to constrain the size of the polarized gluon distribution.

hep-ph↗
arXiv1995

Top Quark Distributions in Hadronic Collisions

We present kinematical distributions for top quark pairs produced at the Tevatron \ppbar\ Collider, as predicted within Next-to-Leading-Order QCD. We consider single and double-inclusive distributions, and compare our results to those obtained with the shower Monte Carlo HERWIG. We discuss the implications of our findings for experimental issues such as the measurement of the top quark mass.

hep-ph↗
arXiv1995

A Study of Ultraviolet Renormalon Ambiguities in the Determination of $\as$ from $τ$ Decay

The divergent large-order behaviour of the perturbative series relevant for the determination of $\as$ from $τ$ decay is controlled by the leading ultraviolet (UV) renormalon. Even in the absence of the first infrared (IR) renormalon, an ambiguity of order $Λ^2/m_τ^2$ is introduced. We make a quantitative study of the practical implications of this ambiguity. We discuss the magnitude of UV renormalon corrections obtained in the large-$N_f$ limit, which, although unrealistic, is nevertheless interesting to some extent. We then study a number of improved approximants for the perturbative series, based on a change of variable in the Borel representation, such as to displace the leading UV renormalon singularity at a larger distance from the origin than the first IR renormalon. The spread of the resulting values of $\as(m^2_τ)$ obtained by different approximants, at different renormalization scales, is exhibited as a measure of the underlying ambiguities. Finally, on the basis of mathematical models, we discuss the prospects of an actual improvement, given the signs and magnitudes of the computed coefficients, the size of $\as(m^2_τ)$ and what is known of the asymptotic properties of the series. Our conclusion is that a realistic estimate of the theoretical error cannot go below $δ\as(m^2_τ) \sim \pm 0.060$, or $δ\as(m^2_{\sss Z}) \sim \pm 0.006$.

hep-ph↗
arXiv1994

Total Cross Sections for Heavy Flavour Production at HERA

We compute total cross sections for charm and bottom photoproduction at HERA energies, and discuss the relevant theoretical uncertainties. In particular we discuss the problems arising from the small-$x$ region, the uncertainties in the gluon parton density, and the uncertainties in the hadronic component of the cross section. Total electroproduction cross sections, calculated in the Weizsäcker-Williams approximation, are also given.

hep-ph↗
arXiv1993

On the Q^2 Dependence of Measured Polarized Structure Funtions

We analyse the available data on the polarized asymmetries $A_1$ for proton, neutron and deuteron targets. We use a homogeneous and updated set of unpolarized structure functions to derive $g_1$ from $A_1$, and we accurately correct for the scaling violations in order to obtain $g_1(x,Q^2)$ with the same $Q^2$ for all $x$ values. The contribution to the $Q^2$ evolution of a possible large gluon polarized density is also considered. The implications for the Ellis-Jaffe and for the Bjorken sum rules are discussed.

hep-ph↗
arXiv1993

Improving the Weizsäcker-Williams Approximation in Electron-Proton Collisions

We critically examine the validity of the Weizsäcker-Williams approximation in electron-hadron collisions. We show that in its commonly used form it can lead to large errors, and we show how to improve it in order to get accurate results. In particular, we present an improved form that is valid beyond the leading logarithmic approximation in the case when a small-angle cut is applied to the scattered electron. Furthermore we include comparisons of the approximate expressions with the exact electroproduction calculation in the case of heavy-quark production.

hep-ph↗
arXiv1993

Heavy Quark Correlations in Photon-Hadron Collisions

We describe a next-to-leading-order calculation of the fully exclusive parton cross section for the photoproduction of heavy quarks. We use our result to compute quantities of interest for current fixed-target experiments. We discuss heavy-quark total cross sections, distributions and correlations.

hep-ph↗