Non-leading Effects Research Articles

Total, inelastic and (quasi-)elastic cross sections of high energy pA and γ ⋆ A reactions with the dipole formalism

In order to understand the initial partonic state in proton-nucleus and electron-nucleus collisions, we investigate the total, inelastic, and (quasi-)elastic cross sections in pA and gamma-A collisions, as these observables are insensitive to possible collective effects in the final state interactions. We used as a tool the DIPSY dipole model, which is based on BFKL dynamics including non-leading effects, saturation, and colour interference, which we have extended to describe collisions of protons and virtual photons with nuclei. We present results for collisions with O, Cu, and Pb nuclei, and reproduce preliminary data on the pPb inelastic cross section at LHC by CMS and LHCb. The large NN cross section results in pA scattering that scales approximately with the area. The results are compared with conventional Glauber model calculations, and we note that the more subtle dynamical effects are more easily studied in the ratios between the total, inelastic and (quasi-)elastic cross sections. The smaller photon interaction makes the gamma-A collisions more closely proportional to A, and we see here that future electron-ion colliders would be valuable complements to the pA collisions in studies of dynamical effects from correlations, coherence and fluctuations in the initial state in high energy nuclear collisions. (Less)

Neutrino masses and mixings with non-zero [formula omitted] in type I + II seesaw models

We study the survivability of neutrino mass models with normal as well as inverted hierarchical mass patterns in the presence of both type I and type II seesaw contributions to neutrino mass within the framework of generic left–right symmetric models. At leading order, the Dirac neutrino mass matrix is assumed to be diagonal with either charged lepton (CL) type or up quark (UQ) type structure which gets corrected by non-leading effects giving rise to deviations from tri-bi-maximal (TBM) mixing and hence non-zero value of θ13. Using the standard form of neutrino mass matrix which incorporates such non-leading effects, we parametrize the neutrino mass matrix incorporating both oscillation as well as cosmology data. Also considering extremal values of Majorana CP phases such that the neutrino mass eigenvalues have the structure (m1,−m2,m3) and (m1,m2,m3), we then calculate the predictions for neutrino parameters in the presence of both type I and type II seesaw contributions, taking one of them dominant and the other sub-dominant. We show that these mass models can survive in our framework with certain exceptions.

On the high energy behaviour of the total cross section in the QCD dipole model

In this paper we perform a numerical study of the tranverse expansion of hadronic scattering amplitudes in the dipole picture of high energy QCD. We go beyond the mean field approximation by including fluctuations and also wave function saturation effects, and the evolution with both a fixed and a running coupling is investigated. We also study the nonperturbative aspects, and as has been predicted earlier, our results indicate that the Froissart-Martin bound is saturated once confinement effects are included in the evolution. Thus the total cross section increases proportional to the square of the logarithm of the cms energy. Using our proton model developed earlier we furthermore see that we obtain a reasonable value for the proportionality coefficient. The impact of saturation and non-leading effects on this coefficient is also studied.

Diffractive J/ Ψ production in high energy γγ collisions as a probe of the QCD pomeron

The reaction γγ→ J/ ΨJ/ Ψ is discussed assuming dominance of the QCD BFKL pomeron exchange. We give prediction for the cross-section of this process for LEP2 and TESLA energies. We solve the BFKL equation in the non-forward configuration taking into account dominant non-leading effects which come from the requirement that the virtuality of the exchanged gluons along the gluon ladder is controlled by their transverse momentum squared. We compare our results with those corresponding to the simple two gluon exchange mechanism and with the BFKL pomeron exchange in the leading logarithmic approximation. The BFKL effects are found to generate a steeper t-dependence than the two gluon exchange. The cross-section is found to increase with increasing CM energy W as ( W 2) 2 λ . The parameter λ is slowly varying with W and takes the values λ∼0.23–0.28. The magnitude of the total cross-section for the process γγ→ J/ ΨJ/ Ψ is found to increase from 4 to 26 pb within the energy range accessible at LEP2. The magnitude of the total cross-section for the process e + e −→ e + e − J/ ΨJ/ Ψ with antitagged e + and e − is estimated to be around 0.1 pb at LEP2.

The linked dipole chain model for DIS

The Linked Dipole Chain Model provides an interpolation between the regions of high Q 2 (DGLAP) and low x moderate Q 2 (BFKL) in DIS. It is a reformulation and a generalization of the results obtained by Ciafaloni, Catani, Fiorani and Marchesini, and it gives a unified treatment of “normal DIS”, boson-gluon fusion events and hard subcollisions in resolved photon-proton scattering. Thus the formalism provides a complete picture which incorporates all hard or semihard hadronic interactions in a simple way, which is suitable for a Monte Carlo treatment of both structure functions and final state properties. We also discuss non-leading effects which significantly reduce the increase of the structure function for very small x-values.

Formula omitted] expansion for exclusive and inclusive charm decays

We systematically apply the 1 N expansion ( N being the number of colours) to exclusive and inclusive charm decays and develop a diagrammatic language in which the leading contributions can be clearly identified and calculated. Keeping only the leading terms in 1 N makes the usual approach compatible with the data on exclusive decays and gives τ ( D +) τ( D 0) ≈ 02 and B SL(D 0) ≈ 10%. 0382 1537 V 3 We also show that the recent analysis of exclusive charm decays of Bauer and Stech can be justified to a certain extent in this approach. The possible non-leading effects are briefly discussed.

General parametrization of scale breaking

A general parametrization of non-singlet structure functions is developed and used to analyse present data in the context of leading order QCD. The extension to non-leading effects is also discussed.

Strong radiative corrections to annihilations of quarkonia in QCD

The significance of the lowest-order QCD prediction for the annihilations of heavy quark-antiquark bound states is analyzed. The calculation of the leading strong radiative corrections to the hadronic versus electromagnetic annihilation rate ratio R of pseudoscalar quarkonium is presented. In terms of the coupling constant α s, as defined in the minimal subtraction scheme, we find R = R (0)(1 + 22.14 α s/ π). The physical significance of this result is discussed by comparing it with the calculation of the non-leading effects in α s on the scaling violations in deep inelastic scattering. A bad convergence of the relative perturbative expansion is found, demanding for its safe application a value of the relevant momentum definitely higher than that of charmonium physics.