arXiv subjects

Giorgio Calucci

Publications and source records attributed to Giorgio Calucci.

At least 19 recordsLinked to original sources

arXiv2018

About Double Parton Scattering at Short Relative Transverse Distances

By working out the kinematics of double parton scattering at short relative transverse distances, we obtain an explicit link between the transverse centres of mass, of the two hard partonic interactions, and the contributions to the process, due to pairs of interacting partons generated by perturbative splitting. One my thus foresee the interesting possibility of discriminating experimentally between contributions to the double parton scattering cross section, due to interacting parton pairs originated by independent evolution, and contributions, due to interacting parton pairs generated by splitting.

hep-ph↗

arXiv2016

A Brief Comment on Multi-Gluon Amplitudes and Double Parton Interactions

A typical contribution to a color ordered multi-gluon amplitude, which can split into two weakly correlated two-body gluon scattering amplitudes and may thus contribute to a Double Parton Interaction, is briefly discussed. We find that the color ordered amplitude is not enhanced in the typical configuration generated by a DPI, where the transverse momenta of final state gluons are compensated pairwise, while a dominant contribution to the multi-gluon amplitude is due to terms proportional to the fusion amplitude of two initial state gluons. Which corresponds to an amplitude effectively describing a two rather than a three-body partonic interaction.

hep-ph↗

arXiv2016

A Brief Comment on Multi-Gluon Amplitudes and Double Parton Interactions

A simplest case, where a contribution to a color ordered multi-gluon amplitude, describing a three body partonic interaction, can split into two weakly correlated two-body gluon scattering amplitudes and may thus contribute to a Double Parton Interaction, is briefly discussed. We find that the color ordered amplitude is not enhanced in the typical configuration generated by a DPI, where the transverse momenta of final state gluons are compensated pairwise, while a dominant contribution to the multi-gluon amplitude is due to terms proportional to the fusion amplitude of two initial state gluons. Which corresponds to an amplitude effectively describing a two rather than a three-body partonic interaction.

hep-ph↗

arXiv2013

Double Parton Scatterings in High-Energy Proton-Nucleus Collisions and Partonic Correlations

The joint study of Double Parton Scatterings, in high energy proton-proton and proton-nucleus collisions, can provide a lot of information on multi-parton correlations. The multi-parton structure is in fact probed in a different way by DPS, in $p$-$p$ and in $p$-$A$ collisions. In $p$-$A$ collisions the interpretation of the experimental results may be however complicated by the presence of interference terms, which are missing in $p$-$p$. A suitable reaction channel, where interference terms are absent, is $WJJ$ production. By studying $WJJ$ production in $p$-$Pb$ collisions, we estimate that the fraction of events due to DPS may be larger by a factor 3 or 4, as compared to $p$-$p$, while the amount of the increased fraction can give a direct indication on the importance of different correlation terms.

hep-ph↗

arXiv2013

Lower bound for the ratio of charged wino tracks to charged lepton tracks at LHC

By using kinematical arguments we derive a theorem for the ratio: [production cross-section of charged-neutral wino pairs plus anything else] over [production cross-section of charged-neutral lepton pairs plus anything else]. We do that by working out the consequences of substituting the lepton pair with a wino pair, leaving untouched everything else of the interaction. We apply this result to the possible production of winos at LHC obtaining a lower bound for the ratio of the number of charged-winos over charged-leptons tracks and also find the average charged-wino track length, within a region in the relevant parameter space (e.g. available energy and mass).

hep-ph↗

arXiv2012

Collisions of protons with light nuclei shed new light on nucleon structure

The high rates of multi-parton interactions at the LHC can provide a unique opportunity to study the multi-parton structure of the hadron. To this purpose high energy collisions of protons with nuclei are particularly suitable. The rates of multi-parton interactions depend in fact both on the partonic multiplicities and on the distributions of partons in transverse space, which produce different effects on the cross section in pA collisions, as a function of the atomic mass number A. Differently with respect to the case of multi-parton interactions in pp collisions, the possibility of changing the atomic mass number provides thus an additional handle to distinguish the diverse contributions. Some relevant features of double parton interactions in pD collisions have been discussed in a previous paper. In the present paper we show how the effects of double and triple correlation terms of the multi-parton structure can be disentangled, by comparing the rates of multiple parton interactions in collisions of protons with D, Tritium and 3He.

hep-ph↗

arXiv2011

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 multi-parton 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.

hep-ph↗

arXiv2009

Inclusive and "exclusive" cross sections in the regime of multiple parton collisions

The large luminosity and the increased kinematical domain accessible at the LHC will allow to isolate large numbers of events with multiple parton collisions. Interestingly, the hadron is probed in different points contemporarily in the process, which allows to obtain information on the correlations between partons in the hadron structure. The whole experimentally accessible information on multiple parton collisions consists in the probability distribution of the elementary interactions, while the inclusive cross sections, usually considered in large p_t processes, acquire a precise statistical meaning as moments of the multiplicity distribution. Conversely different and more "exclusive" cross sections become experimentally viable, providing complementary information on the interaction dynamics. The matter is discussed in details in the case of hadron-hadron collisions and the role of parton correlations is outlined both in the inclusive and in the "exclusive" cross sections.

hep-ph↗

arXiv2009

Parton fluxes and virtual pions in heavy nuclei

The partonic flux originated from a heavy nucleus is not the mere sum of the fluxes coming from the individual nucleons. There are various effects that give rise to modifications. One of these effects is here investigated i.e. the presence of a cloud of virtual pions co-moving with the nucleus. It is found that the contribution of these virtual particles to the total parton flux should be rather small even if one includes the contribution of resonances.

hep-ph↗

arXiv2007

Production of light particles by very strong and slowly varying magnetic fields

The possibility that around some astrophysical objects there are non-static magnetic fields of enormous intensity suggests that in these situations real particles may be produced. The slowness of the variation is compensated by the huge intensity. The main issue is the production of e+,e- pairs annihilating into photons and the direct production of photons, as one of the concurrent process in the GRB (gamma ray bursts). Then some simple effects due to the presence of the intense gravity are studied and finally a look is given to the production of other kinds of particles.

hep-ph↗

arXiv2007

Screening in the QCD plasma: effects of the gluons and of the confinement

The effects of a thermalized gas of gluons in a q,q bar plasma is investigated. Then the interplay between Debye screening and confinement is analyzed in a simplified model. While the one-gluon exchange gives results very similar, but not equal, to the electric case, the phenomenological introduction of confinement leads to very different results.

hep-ph↗

arXiv2007

Very strong and slowly varying magnetic fields as source of axions

The investigation on the production of particles in slowly varying but extremely intense magnetic field in extended to the case of axions. The motivation is, as for some previously considered cases, the possibility that such kind of magnetic field may exist around very compact astrophysical objects.

hep-ph↗

arXiv2006

Pair production in a strong magnetic field: the effect of a strong background gravitational field

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 the production of pairs. In particular, high-energy pairs are more likely produced in the presence of the gravitational field than in Minkowski spacetime.

hep-ph↗

arXiv2003

Graviton Emission and Loss of Coherence

The decoherence effect due to emission of gravitons is examined. It shows the same qualitative features of the QED effect which has already been investigated, it is obviously much weaker, wholly universal and shows a stronger energy dependence. The result can be extended to photons, they also may undergo decoherence due to graviton emission. For this limited aim the incomplete status of the quantum gravity, in comparison with QED, is not source of severe difficulties because all the effects are attributed to the infrared sector of the dynamics.

quant-ph↗

arXiv2000

A Hamiltonian model for multiple production in hadron-hadron collisions

A Hamiltonian eikonal model for the multiple production in high energy hadron hadron collisions is presented and worked out in the aim of providing a simple frame for many different observables of these processes. The Hamiltonian formulation ensures that it has the unitarity built in by construction and the eikonal approximation makes easier the discussion of the possible spacial inhomogeneities of the hadrons. The experimental data which are examined are the inelastic cross section and the single and double inclusive cross sections.

hep-ph↗

arXiv2000

Effective cross section and spatial structure of the hadrons

Informations about the spatial structure of parton distribution within the hadron are provided by the ratios between the inclusive cross sections for a pair of jets, two pairs of jets, three pairs of jets..., and so on. It results, however that these ratios depend not only on the spatial distribution but also, and even more, on the multiplicity distribution of the initial partons.

hep-ph↗

arXiv2000

Possible instability of the vacuum in a strong magnetic field

The possibility that a static magnetic field may decay through production of electron positron pairs is studied. The conclusion is that this decay cannot happen through production of single pairs, as in the electric case, but only through the production of a many-body state, since the mutual magnetic interactions of the created pairs play a relevant role. The investigation is made in view of the proposed existence of huge magnetic field strengths around some kind of neutron stars.

hep-th↗

arXiv1999

Pair Production in a Time Dependent Magnetic Field

The production of electron-positron pairs in a time-dependent magnetic field is estimated in the hypotheses that the magnetic field is uniform over large distances with respect to the pair localization and it is so strong that the spacing of the Landau levels is larger than the rest mass of the particles. This calculation is presented since it has been suggested that extremely intense and varying magnetic fields may be found around some astrophysical objects.

hep-th↗