arXiv subjects
Publications and source records attributed to E. Predazzi.
We analyze the diffractive (Pomeron) contribution to pp spin-flip amplitude and discuss the possible scenarios for energies available at the Relativistic Heavy-Ion Collider (RHIC). In particular, we show that RHIC data will be instrumental in assessing the real contribution of diffraction to spin amplitudes.
Exclusive photoproduction of all vector mesons by real and virtual photons is considered in the Soft Dipole Pomeron model. It is emphasized that being the Pomeron in this model a double Regge pole with intercept equal to one, we are led to rising cross-sections but the unitarity bounds are not violated. It is shown that all available data for rho, omega, phi, J/psi and Upsilon in the region of energies 1.7 <= W <= 250 GeV and photon virtualities 0 <= Q^2 <= 35 GeV^2, including the differential cross-sections in the region of transfer momenta 0 <= |t| <= 1.6 GeV^2, are well described by the model.
An analysis of the Coulombic amplitude and its interference with the nuclear amplitude which is driven by the three-component Pomeron is presented. It is shown that different approaches towards the Coulomb phase evaluation give approximately uniform result at all energies and the difference is negligible at RHIC and LHC energies. We show that the use of the amplitude which was fitted to accomodate nucleon data only (in the region 0.01 < |t| < 14.5 (GeV^2)) combined with the Coulomb amplitude, reproduces the existing data in the Coulomb interference domain quite accurately without any adjustement of the parameters. As a consequence, we predict the differential cross section in the region of the Coulomb nucleon interference for both RHIC and LHC energies.
We perform a first experimental test of a local realistic model, recently proposed, based on the Wigner function as probability distribution for the hidden variable. Our results disfavour the model and confirm standard quantum mechanics predictions.
A model based on a dipole Pomeron framework for vector meson exclusive photoproduction by real and virtual photons shows very good agreement with the experimental data. The model does not violate unitarity constrains and describes in a universal manner all the available data for $ρ$, $ω$, $ϕ$, $J/ψ$ and $Υ$ vector meson photoproduction in the region of energies $1.7\le W \le 250 GeV$ and photon virtualities $0 \le Q^2 \le 35 GeV^2$.
By using the concept of duality between direct channel resonances and Regge exchanges we relate the small- and large-$x$ behavior of the structure functions. We show that even a single resonance exhibits Bjorken scaling at large $Q^2$.
The impact of the form of the hadron potential at large distances on the behaviour of the hadron spin-flip amplitude at small angles is examined. The $t$-dependence of the spin-flip amplitude of high energy hadron elastic scattering is analyzed under different assumptions on the hadron interaction. It is shown that the long tail of the non-Gaussian form of the hadron potential of the hadron interaction in the impact parameter representation leads to a large value of the slope of the spin-flip amplitude (without the kinematical factor $\sqrt{|t|}$) as compared with the slope of the spin-non-flip amplitude. This effect can explain the form of the differential cross section and the analyzing power at small transfer momenta. The methods for the definition of the spin-dependent part of the hadron scattering amplitude are presented. A possibility to investigate the structure of the hadron spin-flip amplitude from the accurate measure of the differential cross section and the spin correlation parameters is shown.
By introducing Q^2-dependence in resonance-reggeon "soft" dual models with nonlinear trajectories, they are extended to "hard" processes, sharing the property of parton-hadron duality. The resulting object is a two-component complex function of three variables - s,t and Q^2, reducing to classical dual models on the mass shell and to deep inelastic structure functions, or Compton scattering amplitudes - forward and non-forward - otherwise. As a consequence, the small- and large-x behavior of the structure functions is also related by duality. This duality relation holds for each o components (diffractive and non-diffractive for the amplitude or singlet and non-singlet for the structure) separately.
Many beautiful experiments have been addressed to test standard quantum mechanics against local realistic models. Even if a strong evidence favouring standard quantum mechanics is emerged, a conclusive experiment is still lacking, because of low detection efficiencies. Recently, experiments based on pseudoscalar mesons have been proposed as a way for obtaining a conclusive experiment. In this paper, we investigate if this result can effectively be obtained. Our conclusions, based on a careful analysis of the proposed set ups, are that this will not be possible due to intrinsic limitations of these kind of experiments.
We argue that diffraction (Pomeron) contribution is present in the pp spin-flip amplitude. RHIC polarization will be able to prove (or disprove) this conjecture.
We discuss if experimental tests of Bell inequalities performed with pseudoscalar mesons (K or B) can be definitive. Our conclusion is that this is not the case, for the efficiency loophole cannot be eliminated.
The pp polarization data confirm the presence of a diffractive-like (Pomeron) contribution in the spin-flip amplitude. The extrapolation to RHIC energies does not appear very promising.
The exchange-degeneracy of the mesonic $f$, $ω$, $ρ$ and $a_{2}$ Regge trajectories, dominant at moderate and high energies in hadron elastic scattering, is analyzed from two viewpoints. The first one concerns the masses of the resonances lying on these trajectories; the second one deals with the total cross-sections and the ratios of the real to the imaginary parts of the forward amplitudes of hadron and photon induced reactions. Neither set of data supports exact exchange-degeneracy.
The elastic hadronic amplitude is calculated using the nonperturbative light-cone dipole representation for gluon bremsstrahlung. The data for large mass diffraction demand a two-scale structure of light hadrons: the gluon clouds of the valence quarks with a size of 0.3fm and the hadronic size 1fm. The presence of the two scales unavoidably leads to a specific form for the total hadronic cross section which consists of a steeply rising \propto s^Δ (Δ=0.17 +/- 0.01) term related to gluon radiation, and a large constant term originating from soft interactions which does not induce any gluon emission. Our calculations reproduce well the total cross sections and elastic slopes \cite{k3p}. To further test the model, we analyze the elastic pp and ppbar differential cross sections and extract the partial amplitudes in the impact parameter representation. The Pomeron trajectory as a function of the impact parameter is only slightly above one for central collisions, but steeply grows towards the periphery. The model predicts correctly the shape and energy dependence of the partial amplitude at all impact parameters.
In this paper we describe a test of Bell inequalities using a non- maximally entangled state, which represents an important step in the direction of eliminating the detection loophole. The experiment is based on the creation of a polarisation entangled state via the superposition, by use of an appropriate optics, of the spontaneous fluorescence emitted by two non-linear crystals driven by the same pumping laser.
The energy dependence of the total hadronic cross sections is caused by gluon bremsstrahlung which we treat nonperturbatively. It is located at small transverse distances about 0.3 fm from the valence quarks. The cross section of gluon radiation is predicted to exponentiate and rise with energy as s^Δ with Δ=0.17 +/- 0.01. The total cross section also includes a large energy independent Born term which corresponds to no gluon radiation. The calculated total cross section and the slope of elastic scattering are in good agreement with the data.
We report on a test of Bell inequalities using a non-maximally entangled state, which represents an important step in the direction of eliminating the detection loophole. The experiment is based on the creation of a polarisation entangled state via the superposition, by use of an appropriate optics, of the spontaneous fluorescence emitted by two non-linear crystals driven by the same pumping laser. The alignment has profitably taken advantage from the use of an optical amplifier scheme, where a solid state laser is injected into the crystals together with the pumping laser. In principle a very high total quantum efficiency can be reached using this configuration and thus the final version of this experiment can lead to a resolution of the detection loophole, we carefully discuss the conditions which must be satisfied for reaching this result.
We report on the first realisation of a test of Bell inequalities using non-maximally entangled states. It is based on the superposition of type I parametric down conversion produced in two different non-linear crystals pumped by the same laser, but with different polarisations. We discuss the advantages and the possible developments of this configuration.