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We discuss the multiplicity distribution for highest accessible energies of $pp$- and $bar pp$- interactions from the point of view of the multiparton collisions. The inelastic cross sections for the single, $sigma_1$, and multiple (double and, presumably, triple, $sigma_{2+3}$) parton collisions are extracted from the analysis of the experimental data on the multiplicity distribution up to the Tevatron energies. It follows that $sigma_1$ becomes energy independent while $sigma_{2+3}$ increases with $sqrt{s}$ for $sqrt{s}ge$ 200 GeV. The observed growth of $<p_{perp}>$ with multiplicity is attributed to the increasing role of multiparton collisions for the high energy $bar pp(pp)$- inelastic interactions.
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Parton distribution functions (PDFs) describe the structure of hadrons as composed of quarks and gluons. They are needed to make predictions for short-distance processes in high-energy collisions and are determined by fitting to cross section data. We review definitions of the PDFs and their relations to high-energy cross sections. We focus on the PDFs in protons, but also discuss PDFs in nuclei. We review in some detail the standard statistical treatment needed to fit the PDFs to data using the Hessian method. We discuss tests that can be used to critically examine whether the assumptions are indeed valid. We also present some ideas of what one can do in the case that the tests indicate that the assumptions fail.
It is shown that hadron abundances in high energy e+e-, pp and p{bar p} collisions, calculated by assuming that particles originate in hadron gas fireballs at thermal and partial chemical equilibrium, are in very good agreement with the data. The freeze-out temperature of the hadron gas fireballs turns out to be nearly constant over a large center of mass energy range and not dependent on the initial colliding system. The only deviation from chemical equilibrium resides in the incomplete strangeness phase space saturation. Preliminary results of an analysis of hadron abundances in S+S and S+Ag heavy ion collisions are presented.
The study of higher-order moments of a distribution and its cumulants constitute a sensitive tool to investigate the correlations between the particle produced in high energy interactions. In our previous work we have used the Tsallis $q$ statistics, NBD, Gamma and shifted Gamma distributions to describe the multiplicity distributions in $pi ^-$ -nucleus and $p$ -nucleus fixed target interactions at various energies ranging from P$_{Lab}$ = 27 GeV to 800 GeV. In the present study we have extended our analysis by calculating the moments using the Tsallis model at these fixed target experiment data. By using the Tsallis model we have also calculated the average charged multiplicity and its dependence on energy. It is found that the average charged multiplicity and moments predicted by the Tsallis statistics are in much agreement with the experimental values and indicates the success of the Tsallis model on data from visual detectors. The study of moments also illustrates that KNO scaling hypothesis holds good at these energies.
We analyze the measured spectra of $pi^pm$, $K^pm$, $p$($bar p$) in $pp$ collisions at $sqrt {s}$ = 0.9, 2.76 and 7 TeV, in the light of blast-wave model to extract the transverse radial flow velocity and kinetic temperature at freeze-out for the system formed in $pp$ collisions. The dependency of the blast-wave parameters on average charged particle multiplicity of event sample or the `centrality of collisions has been studied and compared with results of similar analysis in nucleus-nucleus ($AA$) and proton-nucleus ($pA$) collisions. We analyze the spectra of $K_{s}^0$, $Lambda$($bar Lambda$) and $Xi^-$ also to see the dependence of blast-wave description on the species of produced particles. Within the framework of the blast-wave model, the study reveals indication of collective behavior for high-multiplicity events in $pp$ collisions at LHC. Strong transverse radial flow in high multiplicity $pp$ collisions and its comparison with that in $pA$ and $AA$ collisions match with predictions from a very recent theoretical work [Shuryak and Zahed 2013 arXiv:1301.4470] that addresses the conditions for applicability of hydrodynamics in $pp$ and $pA$ collisions.
We demonstrate that underlying assumptions concerning the structure of constituent parton Fock states in hadrons make a strong impact on the predictions of hadronic interaction models for forward hadron spectra and for long-range correlations between central and forward hadron production. Our analysis shows that combined studies of proton-proton collisions at the Large Hadron Collider by central and forward-looking detectors have a rich potential for discriminating between the main model approaches.
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