SearcharxivSearch

arXiv subjects

Erasmo Ferreira

Publications and source records attributed to Erasmo Ferreira.

18 recordsLinked to original sources

Energy dependence of proton-proton elastic scattering at large momentum transfer

The measurements of proton-proton elastic scattering for large momentum transfer at energies in the range $\approx$ 20 to 60 GeV show a simple behaviour of form $d σ/dt \approx {\rm const}~|t|^{-8}$, apparently with no energy dependence. In the present work detailed analysis of the data shows a decrease of the magnitude of the tail with the energy, still with preservation of the power $|t|^{-8}$. The analysis allows the definition of a band for the energy dependence with the form of a power of the strong coupling $α_S^{1.57}$. The rate of decrease describes very well the data at the distant energy $\sqrt{s}$ = 13 TeV, with reduction of the cross section by a factor 5.71. This result gives prediction for new experiments at high energies, and opens important question for theoretical investigation.

hep-ph

Elastic Amplitudes and Observables in pp Scattering

Using a unified analytic representation for the elastic scattering amplitudes of pp scattering valid for all high energy region, the behavior of observables in the LHC collisions in the range $\sqrt{s}$ = 2.76 - 14 TeV is discussed. Similarly to the case of 7 TeV data, the proposed amplitudes give excellent description of the preliminary 8 TeV data. We discuss the expected energy dependence of the observable quantities, and present predictions for the experiments at 2.76, 13 and 14 TeV.

hep-ph

pp Interaction in Extended Air Showers

Applying the recently constructed analytic representation for the pp scattering amplitudes, we present a study of p-air cross sections, with comparison to the data from Extensive Air Shower (EAS) measurements. The amplitudes describe with precision all available accelerator data at ISR, SPS and LHC energies, and its theoretical basis, together with the very smooth energy dependence of parameters controlled by unitarity and dispersion relations, permit reliable extrapolation to higher energies and to asymptotic ranges. The comparison with cosmic ray data is very satisfactory in the whole pp energy interval from 1 to 100 TeV. High energy asymptotic behaviour of cross sections is investigated in view of the geometric scaling property of the amplitudes. The amplitudes predict that the proton does not behave as a black disk even at asymptotically high enegies, and we discuss possible non-trivial consequences of this fact for pA collision cross sections at higher energies.

hep-ph

pp Elastic Scattering at LHC Energies

Using a unified analytic representation for the elastic scattering amplitudes of pp scattering valid for all energy region, the behavior of observables in the LHC collisions in the range $\sqrt{s}$= 2.76 - 14 TeV is discussed. Similarly to the case of 7 TeV data, the proposed amplitudes give excellent description of the preliminary 8 TeV data. We discuss the expected energy dependence of the observable quantities, and present predictions for the experiments at 2.76, 13 and 14 TeV.

hep-ph

pp Interaction at Very High Energies in Cosmic Ray Experiments

An analysis of p-air cross section data from Extensive Air Shower (EAS) measurements is presented, based on an analytical representation of the pp scattering amplitudes that describes with high precision all available accelerator data at ISR, SPS and LHC energies. The theoretical basis of the representation, together with the very smooth energy dependence of parameters controlled by unitarity and dispersion relations, permits reliable extrapolation to high energy cosmic ray and asymptotic energy ranges. Calculations of the p-air production cross section based on Glauber formalism are made using the input values of the pp forward scattering parameters at high energies, with attention given to the independence of the real and imaginary slope parameters. The influence of contributions of diffractive intermediate states, according to Good-Walker formalism, is examined. The comparison with cosmic ray data is very satisfactory in the whole pp energy interval from 1 to 100 TeV. High energy asymptotic behavior of p-air cross sections is investigated in view of the geometric scaling property of the pp amplitudes. The observed energy dependence of the ratio between p-air and pp cross sections in the data is shown to be related to the nature of the pp cross section at high energies, that does not agree with the black disk image.

hep-ph

Two-point derivative dispersion relations

A new derivation is given for the representation, under certain conditions, of the integral dispersion relations of scattering theory through local forms. The resulting expressions have been obtained through an independent procedure to construct the real part, and consist of new mathematical structures of double infinite summations of derivatives. In this new form the derivatives are calculated at the generic value of the energy $E$ and separately at the reference point $E=m$ that is the lower limit of the integration. This new form may be more interesting in certain circumstances and directly shows the origin of the difficulties in convergence that were present in the old truncated forms called standard-DDR. For all cases in which the reductions of the double to single sums were obtained in our previous work, leading to explicit demonstration of convergence, these new expressions are seen to be identical to the previous ones. We present, as a glossary, the most simplified explicit results for the DDR's in the cases of imaginary amplitudes of forms $(E/m)^λ[\ln (E/m)]^n$, that cover the cases of practical interest in particle physics phenomenology at high energies. We explicitly study the expressions for the cases with $λ$ negative odd integers, that require identification of cancelation of singularities, and provide the corresponding final results.

math-ph

Energy Dependence of Profile Functions in $\rm{p\bar p}$ and $\rm pp$ Scattering

We construct analytical forms in the impact parameter $b$-space for the real and imaginary amplitudes describing elastic pp and $\rm p \bar p $ scattering. The amplitudes converted analytically to the momentum transfer $t$-space have magnitudes, slopes, curvatures, zeros, signs, obeying phenomenological and theoretical expectations, and describe with high precision all details of the data, in the full-t range, and for energies from 20 GeV to 7 TeV. The connection of forward with large-$|t|$ behavior allows precise determination of total cross-sections, slopes and other scattering parameters. We study the properties and the energy dependence of the $b$-space profile functions, observing that the real part has fundamental influence in the structure of $dσ/dt$ at intermediate and large $|t|$ values. We discuss the 540/546 GeV and 1.8/1.96 TeV data from CERN SPS and Fermilab TEVATRON and the 7 TeV results from TOTEM measurements at LHC, and investigate the extrapolation to 14 TeV and higher energies.

hep-ph

Amplitudes in the Coulomb interference region of pp and ppbar scattering

We discuss the determination of the parameters of the pp and ppbar amplitudes for the description of scattering in the Coulomb interference region. We put enphasis on the possibility that the effective slope observed in the differential cross section is formed by different exponential slopes in the real and imaginary amplitudes (called B_R and B_I). For this purpose we develop a more general treatment of the Coulomb phase. We analyse the differential cross section data in the range from 19 to 1800 GeV with four parameters (sigma , rho, B_I, B_R), and observe that we cannot obtain from the data a unique determination of the parameters. We investigate correlations in pairs of the four quantities, showing ranges leading to the smaller chi2 values. In the specific case of p-pbar scattering at 541 GeV, we investigate the measurements of event rate dN/dt at low |t| in terms of the Coulomb interference with exponentially decreasing nuclear amplitudes. The analysis allows a determination of the normalization factor connecting the event rate with the absolute cross section.

hep-ph

Nonperturbative and perturbative aspects of photo- and electroproduction of vector mesons

We discuss various aspects of vector meson production, first analysing the interplay between perturbative and nonperturbative aspects of the QCD calculation. Using a general method adapted to incorporate both perturbative and nonpertubative aspects, we show that nonperturbative effects are important for all experimentally available values of the photon virtuality Q2. We compare the huge amount of experimental information now available with our theoretical results obtained using a specific nonperturbative model without free parameters, showing that quite simple features are able to explain the data.

hep-ph

Representation of Integral Dispersion Relations by Local Forms

The representation of the usual integral dispersion relations (IDR) of scattering theory through series of derivatives of the amplitudes is discussed, extended, simplified, and confirmed as mathematical identities. Forms of derivative dispersion relations (DDR) valid for the whole energy interval, recently obtained and presented as double infinite series, are simplified through the use of new sum rules of the incomplete $Γ$ functions, being reduced to single summations, where the usual convergence criteria are easily applied. For the forms of the imaginary amplitude used in phenomenology of hadronic scattering, we show that expressions for the DDR can represent, with absolute accuracy, the IDR of scattering theory, as true mathematical identities. Besides the fact that the algebraic manipulation can be easily understood, numerical examples show the accuracy of these representations up to the maximum available machine precision. As consequence of our work, it is concluded that the standard simplified forms sDDR, originally intended for the high energy limits, are an inconvenient and incomplete separation of terms of the full expression, leading to wrong evaluations. Since the correspondence between IDR and the DDR expansions is linear, our results have wide applicability, covering more general functions, built as combinations of well studied basic forms.

hep-ph

Gauge-invariant soft modes in Yang-Mills theory

A gauge-invariant saddle point expansion for the Yang-Mills vacuum transition amplitude on the basis of the squeezed approximation to the vacuum wave functional is outlined. This framework allows the identification of gauge-invariant infrared degrees of freedom which arise as dominant sets of gauge field orbits and provide the principal input for an essentially analytical treatment of soft amplitudes. The analysis of the soft modes sheds new light on how vacuum fields organize themselves into collective excitations and yields a gauge-invariant representation of instanton and meron effects as well as a new physical interpretation for Faddeev-Niemi knots.

hep-th

Zeros, Dips and Signs in pp and p$\rm\bf\bar p$ Elastic Amplitudes

The dips observed in the differential cross sections of elastic pp and p$\bar{\rm p}$ scattering are studied in terms of the locations of the zeros of the real and imaginary parts of the amplitude and of the sign of real part at large $|t|$. It is confirmed that the differences in shapes of the dips in the pp and p$\bar{\rm p}$ systems are determined by a change of sign of the real tail, which seems to be determined by perturbative QCD contributions.

hep-ph

An Investigation of the Hard Contribution to phi Photoproduction

We investigate the possibility that the process of phi photoproduction may have a significant hard perturbative QCD component. This suggestion is based on a study of the energy dependence of the forward phi photoproduction cross section followed by a calculation where we show that a coherent sum of the pQCD and conventional soft Pomeron contributions provides an excellent reproduction of the experimental data. Our results suggest that the transition from the predominantly soft photoproduction of light rho and omega vector mesons to the predominantly hard photoproduction of heavy J/psi and upsilon is smooth and gradual, similar to the transition observed in deep inelastic scattering studies of the proton structure function in the small x limit. Our predictions for higher HERA energies are presented.

hep-ph

Eikonal profile functions and amplitudes for $\rm pp$ and $\bar{\rm p}{\rm p}$ scattering

The eikonal profile function $J(b)$ obtained from the Model of the Stochastic Vacuum is parametrized in a form suitable for comparison with experiment. The amplitude and the extended profile function (including imaginary and real parts) are determined directly from the complete pp and $\bar{\rm p}$p elastic scattering data at high energies. Full and accurate representation of the data is presented, with smooth energy dependence of all parameters. The changes needed in the original profile function required for description of scattering beyond the forward direction are described.

hep-ph

Model of the Stochastic Vacuum and QCD Parameters

Accounting for the two independent correlation functions of the QCD vacuum, we improve the simple and consistent description given by the model of the stochastic vacuum to the high-energy pp and pbar-p data, with a new determination of parameters of non-perturbative QCD. The increase of the hadronic radii with the energy accounts for the energy dependence of the observables.

hep-ph

Hadronic sizes and observables in high-energy scattering

The functional dependence of the high-energy observables of total cross section and slope parameter on the sizes of the colliding hadrons predicted by the model of the stochastic vacuum and the corresponding relations used in the geometric model of Povh and Hüfner are confronted with the experimental data. The existence of a universal term in the expression for the slope, due purely to vacuum effects, independent of the energy and of the particular hadronic system, is investigated. Accounting for the two independent correlation functions of the QCD vacuum, we improve the simple and consistent description given by the model of the stochastic vacuum to the high-energy pp and pbar-p data, with a new determination of parameters of non-perturbative QCD. The increase of the hadronic radii with the energy accounts for the energy dependence of the observables.

hep-ph

Non-Perturbative QCD Treatment of High-Energy Hadron-Hadron Scattering

Total cross-sections and logarithmic slopes of the elastic scattering cross-sections for different hadronic processes are calculated in the framework of the model of the stochastic vacuum. The relevant parameters of this model, a correlation length and the gluon condensate, are determined from scattering data, and found to be in very good agreement with values coming from completely different sources of information. A parameter-free relation is given between total cross-sections and slope parameters, which is shown to be remarkably valid up to the highest energies for which data exist.

hep-ph