Searcharxiv⌕ Search

arXiv subjects

E. Predazzi

Publications and source records attributed to E. Predazzi.

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

Diffraction : past, present and future

Hadronic diffraction has become a hot and fashionable subject in recent years due to the great interest triggered by the HERA and Tevatron data. These data have helped to put the field in a different perspective paving the road to a hopefully more complete understanding than hitherto achieved. The forthcoming data in the next few years from even higher energies (LHC) promise to sustain this interest for a long time. It is, therefore, necessary to provide the younger generations with as complete as possible discussion of the main developments that have marked the growth of high energy diffractive physics in the past and to assess the present state of the art. For this reason, this part will be by far the largest. The analysis of the relationship between conventional diffractive physics and the low-x physics from deep inelastic scattering will allow us also to review the instruments which could help to understand the developments we can expect from the future.

hep-ph↗
arXiv1998

Preon Trinity

We present a new minimal model for the substructure of all known quarks, leptons and weak gauge bosons, based on only three fundamental and stable spin-1/2 preons. As a consequence, we predict three new quarks, three new leptons, and six new vector bosons. One of the new quarks has charge $-4e/3$. The model explains the apparent conservation of three lepton numbers, as well as the so-called Cabibbo-mixing of the $d$ and $s$ quarks, and predicts electromagnetic decays or oscillations between the neutrinos $\barν_μ$ ($ν_μ$) and $ν_e$ ($\barν_e$). Other neutrino oscillations, as well as rarer quark mixings and CP violation can come about due to a small quantum-mechanical mixing of two of the preons in the quark and lepton wave functions.

hep-ph↗
arXiv1997

The diffraction cone for exclusive vector meson production in deep inelastic scattering

We develop the color dipole gBFKL phenomenology of a diffraction cone for photo- and electroproduction $γ^{*}N \to VN$ of heavy vector mesons (charmonium & bottonium) at HERA and in fixed target experiments. We predict a substantial shrinkage of the diffraction cone from the CERN/FNAL to the HERA range of c.m.s. energy $W$. The $Q^{2}$-controlled selectivity to the color dipole size (scanning phenomenon) is shown to lead to a decrease of the diffraction slope with $Q^{2}$ (which is supported by the available experimental data). We predict an approximate flavor independence of the diffraction slope in the scaling variable $Q^{2}+m_{V}^{2}$. For diffractive production of the radially excited $2S$ states ($Ψ',Υ'$) the counterintuitive inequality of diffraction slopes $B(2S) \lsim B(1S)$ is predicted, which defies the common wisdom that diffraction slopes are larger for reactions with larger size particles.

hep-ph↗
arXiv1997

Higgs Pain? Take a Preon!

The Higgs mechanism is the favourite cure for the main problem with electroweak unification, namely how to reconcile a gauge theory with the need for massive gauge bosons. This problem does not exist in preon models for quark and lepton substructure with composite $Z^0$ and $W$s, which, consequently, also avoid all other theoretical complications and paradoxes with the Higgs mechanism. We present a new, minimal preon model, which explains the family structure, and predicts several new, heavy quarks, leptons and vector bosons. Our preons obey a phenomenological supersymmetry, but without so-called squarks and sleptons, since this SUSY is effective only on the composite scale.

hep-ph↗
arXiv1997

Unitarity effects in DIS

We argue that diffractive DIS, dominated by soft interactions, is probably the unique process which allows us to observe unitarity effects in DIS. Guided by a close analogy between the diffractive dissociation of a highly virtual photon and the elastic scattering of hadrons we propose a specific procedure to analyse the data in order to detect the onset of the unitarity limit. Lacking appropriate data, we use the predictions of a realistic model as an input for our analysis, to demonstrate that the output unitarity signal is sufficiently large to be detectable.

hep-ph↗
arXiv1997

Non-factorizable Contributions to the Large Rapidity Gap at HERA

The large rapidity gap events from HERA are analyzed within a model containing a pomeron and an $f$-reggeon contribution. The choice for the pomeron contribution is based on the Donnachie-Landshoff model. The dependence of the "effective intercept" of the pomeron on the momentum fraction $β$ and on its Bjorken variable $ξ$ is calculated.

hep-ph↗
arXiv1996

Diquark model of exotic mesons

This is a conference mostly devoted to diquarks. Although an exotic meson can in principle be composed of a diquark and an antidiquark, such an exotic is unlikely to be experimentally observable in the near future. The reason, according to the model, is that diquark-antidiquark exotics have masses well above the threshold for decay into two mesons, and are likely to have widths too large to make them observable. A possible exception is a $ u d \bar b \bar b$ exotic, but it will be a long time before such a state can be observed even if it is stable against strong decay.

hep-ph↗
arXiv1996

Diquark model of dibaryons

A diquark model previously formulated to describe exotic mesons is extended to dibaryons. In the model, dibaryons containing only light quarks are unbound. The $H$ dibaryon, consisting of $uuddss$ quarks, is unstable by about 90 MeV or more, and should decay strongly into two $Λ$ baryons. A charmed dibaryon $H_c$, composed of $uuddsc$, is unstable by about 60 MeV or more and should decay strongly into $Λ+ Λ_c$. On the other hand, we find that a bottom dibaryon $H_b$, made of $uuddsb$, may be just bound by about 10 MeV with respect to $Λ+ Λ_b$. If so, it should decay weakly into various final states with a charmed hadron. A possible two-body decay would be into $Λ+ Λ_c$.

hep-ph↗
arXiv1996

Hadronization in Nuclear Environment

We present a space-time description of hadronization of highly virtual quarks originating from a deep-inelastic electron scattering (DIS). Important ingredients of our approach are the time- and energy--dependence of the density of energy loss for gluon radiation, the Sudakov's suppression of no radiation, and the effect of color transparency, which suppresses final state interaction of the produced colorless wave packet. The model is in a good agreement with available data on leading hadron production off nucleons and nuclei. The optimal energy range for study of the hadronization dynamics with nuclear target is found to be a few tens of GeV, particularly energies available in the experiment HERMES.

nucl-th↗
arXiv1996

Color dipole phenomenology of diffractive electroproduction of light vector mesons at HERA

We develop the color dipole phenomenology of diffractive photo- and electroproduction $γ^{*}\,N\rightarrow V(V')\,N$ of light vector mesons ($V(1S) = ϕ^0, ω^0, ρ^0$) and their radial excitations ($V'(2S) = ϕ', ω', ρ'$). The node of the radial wave function of the $2S$ states in conjunction with the energy dependence of the color dipole cross section is shown to lead to a strikingly different $Q^2$ and $ν$ dependence of diffractive production of the $V(1S)$ and $V'(2S)$ vector mesons. We discuss the restoration of flavor symmetry and universality properties of production of different vector mesons as a function of $Q^{2}+m_{V}^{2}$. The color dipole model predictions for the $ρ^{0}$ and $ϕ^{0}$ production are in good agreement with the experimental data from the EMC, NMC, ZEUS and H1 collaborations. We present the first direct evaluation of the dipole cross section from these data.

hep-ph↗
arXiv1996

Anomalies in Diffractive Electroproduction of 2S Radially Excited Light Vector Mesons at HERA

We present the color dipole phenomenology of diffractive photo- and electroproduction $γ^{*} N\to V(V') N$ of vector mesons ($V(1S) = ϕ^0, ω^0, ρ^0, J/Ψ, Υ$) and their radial excitations ($V'(2S) = ϕ', ω', ρ', Ψ', Υ'$). The main emphasis is related to light vector mesons. We discuss how the energy dependence of the color dipole cross section in conjuction with the node of the radial wave function of the $2S$ states can lead to an anomalous $Q^2$ and energy dependence of diffractive production of $V'(2S)$ vector mesons. The color dipole model predictions for $V(1S)$ light vector meson production are compared with the experimental data from the EMC, NMC, ZEUS and H1 collaborations.

hep-ph↗
arXiv1995

A simple recipe to detect possible C-Odd effects in high energy $\bar p p$ and $pp$

We provide a theorem to suggest that $t=0$ data may already be sufficient to detect possible asymptotic C-odd (Odderon) contributions. This can be done by comparing $\bar p p$ and $pp$ $t=0$ observables such as total cross sections, forward angular distributions and ratios of real to imaginary forward amplitudes for which well defined model independent correlations {must} exist which could already show up at RHIC energy but definitely at LHC energies.

hep-ph↗