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P. Nason

Publications and source records attributed to P. Nason.

At least 55 records · Page 3Linked to original sources
arXiv1999

Sudakov Resummation Effects in Prompt-Photon Hadroproduction

We compute the effects of soft-gluon resummation, at the next-to-leading-logarithmic level, in the fixed-target hadroproduction cross section for prompt photons. We find in general that the corrections to the fixed next-to-leading-order results are large for large renormalization scales, and small for small scales. This leads to a significant reduction of the scale dependence of the results for most experimental configurations of interest. We compare our results to the recent measurements by the E706 and UA6 collaborations.

hep-ph↗
arXiv1998

Heavy Flavour Production

I review recent developements in the theory of heavy flavour production. In particular, I dicuss the next-to-leading resummation of soft gluon effects in heavy flavour hadroproduction, and the next-to-leading resummation of collinear radiation in the production of heavy flavour at large transverse momenta.

hep-ph↗
arXiv1998

Problems in the resummation of soft-gluon effects in the transverse-momentum distributions of massive vector bosons in hadronic collisions

We consider the resummation of soft-gluon emission in the transverse-momentum distribution of vector mesons in hadronic collisions. We find that the resummed expression in the impact-parameter formulation has an expansion in $\as$ with factorially growing terms with oscillating signs. These diverging terms arise from the small impact-parameter region of integration, and are of a subleading nature. We also obtain a closed expression for the next-to-leading logarithm resummation in $\qt$-space, and we study its analytic structure. We find in this case that, although no factorially growing terms are present, there are geometrical singularities that severely restrict the range of applicability of the resummation formula.

hep-ph↗
arXiv1998

Sudakov Resummation for Prompt-Photon Production in Hadron Collisions

We present the explicit expressions for the resummation of large-x Sudakov effects in the transverse-energy distribution of prompt-photons produced in hadronic collisions, to next-to-leading logarithmic (NLL) accuracy. Fragmentation processes do not contribute to the Sudakov resummation at NLL level. In Mellin space, the resummed radiative factor factorizes in the product of independent radiators for the two initial and the one final coloured partons appearing in the Born process, times a simple factor describing the soft-gluon interferences between initial and final states. The formulae are given in terms of Mellin moments, and can be used for phenomenological applications using standard techniques for the inverse-Mellin transforms. The calculations presented in this work, when added to the existing works on DY and DIS production, complete the theoretical ground-work necessary to carry out global fits of parton densities with a uniform NLL accuracy in the large-x region.

hep-ph↗
arXiv1998

The p_T Spectrum in Heavy-Flavour Hadroproduction

We consider the transverse-momentum distribution of heavy flavours in hadronic collisions. We present a formalism in which large transverse-momentum logarithms are resummed at the next-to-leading level, and mass effects are included exactly up to order α_strong^3, so as to retain predictivity at both small and large transverse momenta. As an example, we apply our formalism to b production at the Tevatron.

hep-ph↗
arXiv1998

NLL resummation of the heavy-quark hadroproduction cross-section

We compute the effect of soft-gluon resummation, at the next-to-leading-logarithmic level, in the hadroproduction cross-section for heavy flavours. Applications to top, bottom and charm total cross-sections are discussed. We find in general that the corrections to the fixed next-to-leading-order results are larger for larger renormalization scales, and small, or even negative, for smaller scales. This leads to a significant reduction of the scale-dependence of the results, for most experimental configurations of interest.

hep-ph↗
arXiv1997

On the Fragmentation Function for Heavy Quarks in e+e- collisions

We use a recent O(alpha_s^2) calculation of the differential cross section for the production of heavy quarks in e+e- annihilation to compute a few moments of the heavy quark single-inclusive production cross section. We verify that, contrary to some recent claims, the leading and next-to-leading logarithmic terms in this cross section are correctly given by the standard NLO fragmentation function formalism for heavy quark production.

hep-ph↗
arXiv1997

Heavy-Quark Production

We review the present theoretical and experimental status of heavy quark production in high-energy collisions. In particular, we cover hadro- and photoproduction at fixed target experiments, at HERA and at the hadron colliders, as well as aspects of heavy quark production in e+e- collisions at the Z0 peak.

hep-ph↗
arXiv1997

Next-to-Leading-Order Corrections to Momentum Correlations in $Z^0 \to b\bar{b}$

We recently completed a calculation of the process $e^+e^- \to Q\bar{Q}+X$, where Q is a heavy quark, at order $O(α_s^2)$. As a first application of this calculation we compute the momentum correlations of $b\bar{b}$ pairs at next-to-leading-order. This quantity is interesting since it may affect the determination of $R_b$ as measured in $Z^0$ decays. We find that the next-to-leading corrections are of moderate size, thus confirming the conclusions that can be drawn from the leading-order calculation.

hep-ph↗
arXiv1996

Non-Perturbative Corrections to Heavy Quark Fragmentation in e^+e^- Annihilation

We estimate the non-perturbative power-suppressed corrections to heavy flavour fragmentation and correlation functions in e^+e^- annihilation, using a model based on the analysis of one-loop Feynman graphs containing a massive gluon. This approach corresponds to the study of infrared renormalons in the large-n_f limit of QCD, or to the assumption of an infrared-finite effective coupling at low scales. We find that the leading corrections to the heavy quark fragmentation function are of order $λ/M$, where $λ$ is a typical hadronic scale ($λ\sim 0.4$ GeV) and M is the heavy quark mass. The inclusion of higher corrections corresponds to convolution with a universal function of M(1-x) concentrated at values of its argument of order $λ$, in agreement with intuitive expectations. On the other hand, corrections to heavy quark correlations are very small, of the order of $(λ/Q)^p$, where Q is the centre-of-mass energy and $p \ge 2$.

hep-ph↗
arXiv1996

The Resummation of Soft Gluon in Hadronic Collisions

We compute the effects of soft gluon resummation for the production of high mass systems in hadronic collisions. We carefully analyse the growth of the perturbative expansion coefficients of the resummation formula. We propose an expression consistent with the known leading and next-to-leading resummation results, in which the coefficients grow much less than factorially. We apply our formula to Drell--Yan pair production, heavy flavour production, and the production of high invariant mass jet pairs in hadronic collisions. We find that, with our formula, resummation effects become important only fairly close to the threshold region. In the case of heavy flavour production we find that resummation effects are small in the experimental configurations of practical interest.

hep-ph↗
arXiv1996

Soft Gluon Resummation in Heavy Flavour Production

I discuss the effect of resummation of soft gluons in hadronic production of high mass systems, and in particular in heavy flavour production. I show that in widely used $x$-space resummation formulae, spurious terms that grow factorially in the order of the perturbative expansion are present. These terms spoil the convergence of the perturbative expansion. I also show that it is possible to perform the soft gluon resummation in such a way that these terms are not present. Implications for top and high mass dijet production at the Tevatron are discussed.

hep-ph↗
arXiv1996

QCD in e+e- collisions at 2 TeV

We discuss some topics in QCD studies at 2 TeV. Particular emphasis is given to the separation of pure QCD events from the WW and the t-tbar backgrounds

hep-ph↗
arXiv1996

The Top Cross Section in Hadronic Collisions

We reexamine the top quark production cross section at the Tevatron and LHC, in the light of recent progress on the resummation of logarithmic soft gluon corrections. We find that resummation effects are much smaller than previously thought. We also compute Coulombic threshold effects, and find them negligible. We update the discussion of uncertainties due to scale dependence, the value of the strong coupling constant, and the parton density parametrization. Our current best estimate of the top production cross section at the Tevatron and its error is $σ(\mt=175\,{\rm GeV})=4.75{+0.73\atop-0.62}$.

hep-ph↗
arXiv1996

QCD

We discuss QCD studies that will be possible at LEP2. We examine both experimental and theoretical aspects of jets, fragmentation functions, multiplicities and particle spectra.

hep-ph↗