Double parton scatterings in high energy hadronic collisions

CDF has recently measured a large number of double parton scatterings. The observed value of $\sigma_{eff}$, the non perturbative parameter which characterizes the process, is considerably smaller as compared with the naive expectation. The small value of $\sigma_{eff}$ is likely to be an indication of the importance of the two-body parton correlations in the many-body parton distributions of the proton.Comment: 8 pages, latex file, no figures, contributions to the proceedings of the ISMD9

Hard Inelastic Interactions at Parton and Hadron Level

In the study of multiple scattering of partons in hadron-hadron collisions the possibility of a hard inelastic process at the parton level is included in its simplest possible way, $i.e.$ including the $2 \to 3$ transition. The specific physical process to which the treatment is applied is the inelastic collision of a nucleon with a heavy nucleusComment: 4 pages, talk given at XXXI International Symposium on Multiparticle Dynamics, Sept 1-7, 2001, Datong China. URL http://ismd31.ccnu.edu.cn

Incoherence and Multiple Parton Interactions

At the LHC Multiple Parton Interactions will represent an important feature of the minimum bias and of the underlying event and will give important contributions in many channels of interest for the search of new physics. Different numbers of multiple collision may contribute to the production of a given final state and one should expect important interference effects in the regime where different contributions have similar rates. We show, on the contrary, that, once multiple parton interactions are identified by their different topologies, terms with different numbers of multiple parton interactions do not interfere in the final cross section.Comment: 10 pages, 3 figure

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.Comment: 50 pages, 13 figure

Multi-parton correlations and "exclusive" cross sections

In addition to the inclusive cross sections discussed within the QCD-parton model, in the regime of multiple parton interactions, different and more exclusive cross sections become experimentally viable and may be suitably measured. Indeed, in its study of double parton collisions, the quantity measured by CDF was an "exclusive" rather than an inclusive cross section. The non perturbative input to the "exclusive" cross sections is different with respect to the non perturbative input of the inclusive cross sections and involves correlation terms of the hadron structure already at the level of single parton collisions. The matter is discussed in details keeping explicitly into account the effects of double and of triple parton collisions.Comment: 18 pages, no figures, corrected typo

Hard Parton Rescatterings and Minijets in Nuclear Collisions at LHC

The average number of minijets and the corresponding transverse energy produced in heavy ion collisions are evaluated by including explicitly semi-hard parton rescatterings in the dynamics of the interaction. At the LHC semi-hard rescatterings have a sizable effect on global characteristics of the typical inelastic event. An interesting feature is that the dependence on the cutoff which separates soft and hard parton interactions becomes less critical after taking rescatterings into account.Comment: 14 pages, 3 figures. Enlarged discussion in sect.1 and 4; 1 figure added. To be published in Phys.Rev.