A remark on the low mass dilepton yield in heavy ion collisions

The recent data on the enhancement of the low mass dilepton yield in heavy ion collisions are interpreted as an effect of the "prolonged life" of resonances in the hadron gas phase. The value of the enhancement factor gives an upper limit for the duration time of this phase.Comment: Minor changes in text, one reference added. Version to be published in the XXXVI ISMD proceedings, Brazilian Journal of Physic

Selecting the diffractive events at the LHC energies

The PYTHIA 8 generator is used to estimate the percentage of non-diffractive and diffractive events at the LHC energies. It is shown that a simple condition of the absence of charged hadrons in the central pseudorapidity region is sufficient to remove almost all non-diffractive events. This opens the way to investigate diffraction without waiting for the future specialized detectors.Comment: 4 page

Has our brain grown too big to think effectively?

A variant of microcephalin, MCPH1 gene, was introgressed about 37,000 years ago into Homo sapiens genetic pool from an archaic (Homo erectus) lineage and rose to exceptionally high frequency of around 70 percent worldwide today. It is involved in regulating neuroblast proliferation and its changes alter the rate of division and/or differentiation of neuroblasts during the neurogenic phase of embriogenesis, which could alter the size and structure of the resulting brain. At the time of introgression, images had already been painted on the walls of caves and speech has been in use for over 100,000 years, as had been abstract thinking. Like today, reasoning and thinking were the primary faculties of individuals. Homo erectus either did not possess those faculties or was markedly inferior to Homo sapiens in them. Its brain was smaller and the cortex was apparently less convoluted. Thus, introgressed microcephalin allele directed neurogenesis evolutionary back to less complicated brain structure typical for our evolutionary forefathers, slightly decreasing the level of complexity already achieved by Homo sapiens 37,000 years ago. Despite that, it proliferated at a rapid pace. It yields a supposition: 37,000 years ago the brains of Homo sapiens were too big and too complicated for the kind of thinking needed for the highest fitness of individuals. Since adaptation cannot by definition surpass selection requirements, the volume and complication of the human brain did not originate under selective pressure to improve effective thinking and they cannot be explained in terms of such selection. A proposal to solve this quandary is presented, claiming that Homo sapiens originated just by chance. Endurance running led to the emergence of Homo sapiens. The human mind and larynx used for speech are side-effects of more than a million years of endurance running by pre-human hunters

RHIC multiplicity distributions and superposition models

The recent PHENIX mid-rapidity measurements of multiplicity distributions for centrality bins are analyzed in the framework of superposition models. A simple superposition of pp events is shown to disagree with the heavy ion data for dispersion as a function of centrality. However, it is suggested that a model describing properly the pp data and based in the "wounded quark" idea may be compatible with the multiplicity data for heavy ion collisions.Comment: 7 pages, 2 figures Fig. 1 corrected, minor changes in text, one reference adde

Tilted plateau in nuclear collisions: data, models and MC-s

The linear dependence of the particle spectra on rapidity is seen in the central region for asymmetric heavy ion collision in the data and in the Monte Carlo results, similarly as in the fragmentation region for hadronic and ion collisions. The origin of such a behaviour is discussed. It is shown that the color string models produce naturally such a shape if string ends are randomly distributed in rapidity.Comment: 11 pages, 11 figure

On the new HERMES data for the electroproduction on nuclei

We analyze recent data on the electroproduction of hadrons on nuclei using the Lund model for electroproduction on nucleons and a simple geometrical model for the absorption effects. We show that the model seems to overestimate the A-dependence of the absorption effects, although it described the earlier data of the same HERMES experiment reasonably well. We trace the origin of this discrepancy to the surprising difference between the data for nitrogen and neon.Comment: 5 pages, 3 figures, version to be published in the ISMD2007 proceedings in Acta Phys. Pol.

Event-by-event cluster analysis of final states from heavy ion collisions

We present an event-by-event analysis of the cluster structure of final multihadron states resulting from heavy ion collisions. A comparison of experimental data with the states obtained from Monte Carlo generators is shown. The analysis of the first available experimental events suggests that the method is suitable for selecting some different types of events.Comment: 7 pages, 4 eps figure

Entropy in cluster analysis of single events in heavy ion collisions

We analyse the cluster structure of the final multihadron states resulting from heavy ion collisions using the concept of Jaynes - Shannon entropy. Further evidence for an interesting differentiation of events is provided.Comment: 6 pages, 6 eps figures, 1 tex fil

Charge fluctuations in a final state with QGP

Charge fluctuations as a possible signal of quark - gluon plasma (QGP) were recently suggested. A short summary of comments presented on this subject is given and supplemented by a discussion of the coexistence of pions produced "directly" and through a QGP phase. Such a coexistence may obscure the expected plasma signal similarly to the effects considered in the comments mentioned above.Comment: 5 page

Parameters in Weight Calculations for the BE Effect

The weight method of implementing the BE effect into Monte Carlo generators is discussed and presented in some detail. We show how the choice of free parameters and the definition of "direct" pions influence the results for the hadronic Z0 decays.Comment: 15 pages, 7 figure