Giorgio Calucci

Disentangling correlations in multiple parton interactions

Multiple Parton Interactions are the tool to obtain information on the correlations between partons in the hadron structure. Partons may be correlated in all degrees of freedom and all different correlation terms contribute to the cross section. The contributions due to the different parton flavors can be isolated, at least to some extent, by selecting properly the final state. In the case of high energy proton-proton collisions, the effects of correlations in the transverse coordinates and in fractional momenta are, on the contrary, unavoidably mixed in the final observables. The standard way to quantify the strength of double parton interactions is by the value of the effective cross section and a small value of the effective cross section may be originated both by the relatively short transverse distance between the pairs of partons undergoing the double interaction and by a large dispersion of the distribution in multiplicity of the multiparton distributions. The aim of the present paper is to show how the effects of longitudinal and transverse correlations may be disentangled by taking into account the additional information provided by double parton interactions in high energy proton-deuteron collisions.

Minijets and the two-body parton correlation

A large number of double parton scatterings have been recently observed by the CDF collaboration. The double parton scattering process measures {sigma}{sub eff}, a nonperturbative quantity related to the hadronic transverse size and with the dimensions of a cross section. The actual value measured by the CDF collaboration is considerably smaller as compared with the naive expectation, namely, the value of the inelastic nondiffractive cross section. The small value of {sigma}{sub eff} may be an effect of the hadron structure in the transverse plane. We discuss the problem by taking into account, at all orders, the two-body parton correlations in the many-body parton distributions. {copyright} {ital 1997} {ital The American Physical Society}

SELF-SIMILARITY OF THE NEGATIVE BINOMIAL MULTIPLICITY DISTRIBUTIONS

The negative binomial distribution is self-similar: If the spectrum over the whole rapidity range gives rise to a negative binomial, in the absence of correlation and if the source is unique, also a partial range in rapidity gives rise to the same distribution. The property is not seen in experimental data, which are rather consistent with the presence of a number of independent sources. When multiplicities are very large, self-similarity might be used to isolate individual sources in a complex production process. {copyright} {ital 1997} {ital The American Physical Society}

Nucleon-deuteron collision as a probe of the partonic distributions

The one-body partonic distributions in the hadrons are well investigated using electromagnetic or weak interactions. The events with multiple electromagnetic or weak interactions on the same hadron are the very rare. Thus the double parton distributions can be investigated in the events with double QCD hard scattering of partons of the same hadron: it depends not only on the rapidities (or fractional momenta) of the partons but also on a transverse variable. The nucleon-deuteron collision can be a good candidate for this kind of investigations because of the known structure of the deuteron wave function which provides a probe, absent in hadron-hadron collision.

Pair production in a strong time-depending magnetic field: The effect of a strong gravitational field

Abstract We present the calculation of the probability production of an electron–positron pair in the presence of a strong magnetic field with time-varying strength. The calculation takes into account the presence of a strong, constant and uniform gravitational field in the same direction of the magnetic field. The results show that the presence of the gravitational field in general enhances very much the production of pairs. In particular, high-energy pairs are more likely produced in the presence of the gravitational field than in Minkowski spacetime.

PRODUCTION OF π0 IN A STRONG, TIME-DEPENDENT MAGNETIC FIELD

The probability that a neutral meson π0 is produced from vacuum in the presence of a strong and time-varying magnetic field is calculated. Since the π0 has zero electric charge, the interaction with the external magnetic field occurs through the magnetic moment of the constituent quark–antiquark pairs. The phenomenological SU(6) quark model is used to build up perturbatively the one-particle neutral meson states in the presence of a static magnetic field. Then, the presence probability is obtained by means of the adiabatic perturbation theory. The mechanism proposed implies that the pion is produced together with another neutral meson. The final result is compared with the π-–π+ pair presence probability in the same time-varying magnetic field. The π± have almost the same mass of π0 but, unlike π0, are charged particle so the ratio of the two probabilities gives an order of magnitude of the relative strength of the two effective interactions with the external time depending magnetic field.

P and T violating electromagnetic interaction of the quark in the instanton field

Abstract We study the Green function of a quark interacting with an external electromagnetic field when propagating in a background instanton field. By expanding in the instanton size ϱ we are able to evaluate analytically the leading order in ϱ of the time-reversal and parity-violating effective vertex in momentum space, when the vacuum characterizing angle θ is θ ≠ 0. We find this leading term of the vertex to vanish when sandwiched between free quark states; when taken between bound states, however, for instance in a Coulomb-like potential, it gives rise to the usual electric dipole form. We then discuss our result, and its dependence on the cutoff on the instanton size ϱ, in the light of the existing bound on the electric dipole moment of the neutron.

ON THE INFINITE COMPONENT WAVE EQUATIONS. SOME PROBLEMS OF INTERPRETATION AND OUTLINE OF AN APPLICATION.

The form factors obtained in the study of the infinite components wave functions are compared with the ones obtained in a much more conventional way through the use of the Schrödinger equation. The classical problem like the elastic scattering of photons by a hydrogen atom is treated in detail.РезюмеФорм факторы, полученные при изучении бесконечных компонентов волновых уравнений, сравниваутся с таковыми, полученными более конвенциональным путем применения уравнения Шредингера. Классическая проблема упругого рассеяния фотонов на атоме водорода подробно истолкуется.

On the infinite component wave equations@@@О бесконечном компоненте волновых уравнений некоторые проблемы интерпретационного очертания одного применения: Some problems of interpretation-outline of an application

The form factors obtained in the study of the infinite components wave functions are compared with the ones obtained in a much more conventional way through the use of the Schrödinger equation. The classical problem like the elastic scattering of photons by a hydrogen atom is treated in detail.РезюмеФорм факторы, полученные при изучении бесконечных компонентов волновых уравнений, сравниваутся с таковыми, полученными более конвенциональным путем применения уравнения Шредингера. Классическая проблема упругого рассеяния фотонов на атоме водорода подробно истолкуется.

Some remarks about the dispersive approach to symmetry breaking

Abstract In the problem of deriving sum rules from the equal-time commutation relations, some difficulties arise from the kinematical variables of the states. These difficulties have been recently dealt with by means of a dispersive approach. We try here to maintain a covariant formulation without using dispersion relations.