A.P. Contogouris

Soft gluon corrections to large-pT direct photon and dilepton production☆

Abstract QCD O( α s 2 ) corrections to large- p T real and virtual photon production from scattering in the quark-gluon channel are studied in the soft gluon limit. In this limit we carefully preserve the analytic structure of amplitudes in the small-momenta integration regions. The result is a rather large correction to the Born term which significantly improves the agreement with data on p + p → γ + X. The application of the approach to other processes is discussed and the dominant terms of the O( α s 2 ) correction to e + e − → three jets are reproduced.

Regge analysis and dual absorptive model for γN → πoN, γN → ηN and related processes

Abstract We present a combined Regge-pole Regge-cut analysis of γ N → π o N, γ N → η N and of certain processes related by vector dominance. The magnitude of Regge cuts is constrained to satisfy the requirements of the dual absorptive model. Calculations in terms of the weak cut model are also presented and ways to experimentally distinguish between these two models are discussed. The structure of the real and imaginary parts of the amplitudes is also analyzed.

The vector and tensor exchange contributions to πN → πN

Abstract Using fixed-t dispersion relations together with experimental data on π−p → π0n we determine the real and imaginary parts of the s-channel helicity amplitudes (SHA) of the vector (ϱ) exchange contribution to πN → πN. The results are in good agreement with amplitude analyses. We also make comparison with finite-energy sum-rules (FESR) and discuss certain implications. Furthermore, on the basis of two-component duality and FESR we calculate the tensor (f) contribution. The t-structure of the resulting SHA is compared with independent information on hadronic tensor exchanges.

The magnitude of the parton intrinsic transverse momentum

Abstract We analyze data on the transverse momentum distribution of dimuons produced by 22 GeV and 16 GeV π − incident on a Cu target. We evaluate the quantum chromodynamic lowest order perturbation contributions and also introduce an intrinsic transverse momentum k T on the partons relative to their parent hadrons. The analysis of our data leads to 〈 k T 〉=0.30−0.35 GeV. We discuss our result in comparison with analyses of data at higher energies.

Large- pT correlations in a scale-breaking constituent model

Abstract Correlations at large transverse momenta ( p T ) are calculated in a quark-parton model that takes into account the scaling violation of deep inelastic lepton-proton structure functions. Comparison is made with experimental data on pp → h 1 + h 2 + X with the two hadrons h 1 and h 2 at 90° in the c.m. of the initial protons either in opposite sides or in the same side. It is shown that the model predicts reasonably well the p T and s -dependences as well as the absolute magnitude of the correlation data. Also, the predicted rapidity and transverse momentum sharing ( e ) distributions are compared with experiment and with the predictions of other models.

The forward structure of certain single-pion production reactions☆

In terms of (i) a Regge-cut model and (ii) a Veneziano model it is shown the the transverse helicity-frame differential cross section for π−p→ρon has a sharp forward peak; and that this offers a new verification of ρ-universality. The forward structure of recent data on π−p→πoπon is also analyzed.

Photoproduction of charged pions in the veneziano model

SummaryPhotoproduction of charged pions on nucleons is studied in the framework of the Veneziano representation. General conditions for the elimination of parity doublets are derived. A model with a small number of beta-function terms provides a very satisfactory (and essentially parameter-free) description of differential cross-sections and asymmetry ratios of forward γp→π+n and γn→π−p in a wide energy range; it also correctly predicts a significant number of residues of higher baryon resonances. However, it leads to backward cross-sections for γp→π+n significantly larger than the data. Introduction of satellite terms provides a relatively simple parametrization which correctly accounts for all the differential backward cross-sections and for all the known baryon residues.RiassuntoSi studia, nel quadro della rappresentazione di Veneziano, la fotoproduzione di pioni carichi su nucleoni. Si deducono le condizioni generali per l’eliminazione dei doppietti di parità. Un modello con un piccolo numero di termini di funzioni beta fornisce una descrizione molto soddisfacente (ed essenzialmente libera da parametri) delle sezioni d’urto differenziali e dei rapporti di asimmetria delle reazioni in avanti γp → π+n e γn → π−p in un ampio intervallo di energie; esso anche predice correttamente un significativo numero di residui di risonanze barioniche superiori. Però esso porta a sezioni d’urto all’indietro per γp → π+n significativamente maggiori dei dati. L’introduzione dei termini satellite fornisce una parametrizzazione relativamente semplice che tiene conto correttamente di tutte le sezioni d’urto differenziali all’indietro e di tutti i residui barionici noti.РеэюмеВ рамках представления Венециано исследуется фоторождение эаряженных пионов на нуклонах. Выводятся обшие условия для исключения дублетов по четности. Модель с небольщим числом бета-функциональных членов обеспечивает очень удовлетворительное (и, по сушеству, свободное от параметров) описание дифференциальных поперечных сечений и асиммеричные отнощения рассеяния вперед γр → π+n и γn → π−р в щирокой области знергий. Эта модель также правильно предскаэывает эначительное число вычетов для более высоких барионных реэо-нансов. Однако, зто приводит к эначительно больщим поперечным сечениям рассеяния наэад для γр → π+n, чем зкспериментальные данные. Введение сопутствуюших членов обеспечивает относительно простую параметриэацию, которая правильно общясняет все дифференциальные поперечные сечения рассеяния наэад и все иэвестные барионные вычеты.

Deep inelastic e-p scattering in a Veneziano-like model including diffraction

Abstract The Veneziano-inspired approach to deep inelastic e-p scattering is extended to include pomeron-dominated (diffractive) contributions. A four-point amplitude is presented in which the Pomeranchuk singularity, α P ( t ), is dual to a background contribution in s . This background is characteristic of a Regge-cut, as seen in the large ∣ t ∣ asymptotics. When the amplitude is extended to virtual photon-nucleon scattering, it is scales in the Bjorken limit. When it is combined with the dual, non-diffractive amplitude of Landshoff and Polkinghorne, it accounts well for the proton inelastic form factor in the whole scaling region, and leads to a total ϱN cross-section in order-of-magnitude agreement with experiment.

The quark-quark correction to the Drell-Yan formalism

Abstract The finite O( g 4 s ) quark-quark correction term to the Drell-Yan formula is calculated. Its constribution is studied for p + p → 1 + 1 − + X, where it has been argued to be important. For the kinematic range of existing data a rather small effect is found. This correction may be dominant, but only at large 1 + 1 − masses, where the cross section itself is very small.

Large transverse momentum phenomena in a hadronic bremsstrahlung model

We present a bremsstrahlung model which at large transverse momenta pT leads to an inverse power law for the pion distribution in pp → π±0 + X. The model predicts particle yields that increase with energy at fixed pT (breaking Feynman scaling in a definite way) and provides an understanding of the excess of π+s over π−s, and of the increase with pT of the associated multiplicity in the direction opposite to the observed pion; it also accounts for proton to π+ ratios of order 1, but in a parameter-dependent way. The recently observed increase of the mean charged multiplicity in pp → p + MM with the transverse momentum of the projectile is also accounted for.