arXiv subjects
Publications and source records attributed to J. Dias de Deus.
We argue that string percolation is in the origin of i) an approximately flat rapidity distribution and of ii) an approximately constant forward-backward correlation parameter $b$ over a substantial fraction of the available rapidity. Predictions are given for $pp$ collisions at LHC, $\sqrt{s}=14$TeV and $\sqrt{s}=5.5$TeV.
Proceedings of the 12th International Conference on Elastic and Diffractive Scattering (Blois Workshop) - Forward Physics and QCD
We present our results on transverse momentum fluctuations, multiplicity fluctuations and transverse momentum distributions for baryons and mesons in the framework of the clustering of color sources. We determine under what conditions the initial state configurations can lead to color connection, and more specifically, if variations of the initial state can lead to a transition from disconnected to connected color clusters, modifying the number of effective sources. We find that beyond a critical point, one has a condensate, containing interacting and hence color-connected sources. This point thus specifies the onset of color deconfinement. We show that the transverse momentum and multiplicity distributions are related to each other in a defined way. We obtain a non-monotonic dependence of the $p_T$ and multiplicity fluctuations with the number of participants. We present our results for the fluctuations and the transverse momentum distributions at RHIC energies compared to the existing experimental data and our predictions for LHC energies.
We argue that the increase of the ratio baryon/meson due to the presence of strong colour fields and percolation in ultra-high energy hadronic collisions, helps to explain some of the global features of ultra-high energy cosmic ray cascades at E>10^18 eV and, in particular the observed excess in the number of muons with respect to current models of hadronic interactions. A reasonable agreement with the small value and slope of the average depth of shower maximum Xmax vs shower energy -- as seen in data collected at the Pierre Auger Observatory -- can be obtained with a fast increase of the p-Air production cross-section compatible with the Froissart bound.
The effects of pions for vacuum polarization in background magnetic fields are considered. The effects of quark condensates is also briefly addresses. Although these effects are out of the measurement accuracy of laboratory experiments they may be relevant for gamma-ray burst propagation. In particular, for emissions from the center of the galaxy, we show that the mixing between the neutral pion and photons results in a deviation of the gamma-ray spectrum from the standard power-law in the TeV range.
We compute QCD corrections to QED calculations for vacuum polarization in background magnetic fields. Formally, the diagram for virtual $e\bar{e}$ loops is identical to the one for virtual $q\bar{q}$ loops. However due to confinement, or to the growth of $α_s$ as $p^2$ decreases, a direct calculation of the diagram is not allowed. At large $p^2$ we consider the virtual $q\bar{q}$ diagram, in the intermediate region we discuss the role of the contribution of quark condensates $\left< q\bar{q}\right>$ and at the low-energy limit we consider the $π^0$, as well as charged pion $π^+π^-$ loops. Although these effects seem to be out of the measurement accuracy of photon-photon laboratory experiments they may be relevant for $γ$-ray burst propagation. In particular, for emissions from the center of the galaxy (8.5 kpc), we show that the mixing between the neutral pseudo-scalar pion $π_0$ and photons renders a deviation from the power-law spectrum in the $TeV$ range. As for scalar quark condensates $\left< q\bar{q} right>$ and virtual $q\bar{q}$ loops are relevant only for very high radiation density $\sim 300 MeV/fm^3$ and very strong magnetic fields of order $\sim 10^{14} T$.
We use a simple Colour Glass Condensate/String Percolation Model argument to show the existence, due to energy conservation, of bounds to the violation of Feynman scaling and limiting fragmentation.
In the framework of percolation of strings, the transverse momentum distributions in AA and hh collisions at all centralities and energies follow a universal behavior. The width of these distributions is related to the width of the distribution of the size of the clusters formed from the overlapping of the produced strings. The difference between the distributions for baryons and mesons originates in the fragmentation of clusters of several strings which enhance the particles with higher number of constituents. The results agree with SPS and RHIC data. The predictions for LHC show differences for baryons compared with RHIC. At LHC energies we obtain also a high pt suppression for pp high multiplicity events compared with pp minimum bias.
It is well known that, in nuclear collisions, a sizable fraction of the available energy is carried away by baryons. As the baryon number is conserved, the net-baryon $B-\bar{B}$ retains information on the energy-momentum carried by the incoming nuclei. A simple but consistent model for net-baryon production in high energy hadron-hadron, hadron-nucleus and nucleus-nucleus collisions is presented. The basic ingredients of the model are valence string formation based on standard PDFs with QCD evolution and string fragmentation via the Schwinger mechanism. The results of the model are presented and compared with both data and existing models. These results show that a good description of the main features of net-baryon data is possible on the framework of a simplistic model, with the advantage of making the fundamental production mechanisms manifest.
We explore the relationship between the Glasma framework and the String Percolation Model by introducing a simple model for the rapidity distributions in nucleus-nucleus collisions. The model is solved for both symmetrical and asymmetrical collisions. The phenomenon of limiting fragmentation is briefly discussed.
We discuss forward-bacward rapidity correlations in the general situation of asymmetrical collisions, asymmetric rapidity windows, higher rapidities and higher energy. We give predictions for RHIC and LHC.
A numerical estimative error of the magnitude of the vacuum polarization effect due to electron-positron by a factor of $10^3$ in [PRL97(2006)100403; 269901(E)] invalidates the study carried in this work in its present context.
We show that in the presence of a slowly rotating strong transverse magnetic field there is an infinite spectrum of harmonic wave functions $A_n$ due to the first order QED correction (in $α^2$) given by the Euler-Heisenberg Lagrangian. The frequency shifts are integer multiples $\pm ω_0 n$ of the magnetic field angular frequency rotation $ω_0=2πν_m$ and the several modes $n$ are coupled to the nearest harmonics $n\pm 1$. This is a new effect due to QED vacuum fluctuations, not exploit before, that can explain, both qualitatively and quantatively, the recent experimental results of the PVLAS collaboration without the need of a low mass intermediate particle, hence dismiss the recent claim of the discovery of the axion. [Erratum: The PVLAS signal cannot be explained by this mechanism.]
We present a prediction for Forward-Backward rapidity correlations at the LHC from a two step scenario model for particle production
We present predictions, from a simple model, for multiplicity distributions in rapidity for Pb-Pb and p-Pb central collisions at the LHC.
In the framework of percolation of strings, we present predictions for the $R_{AA}$ and $R_{CP}$ for mesons and baryons and for $\bar{p}/π^{0}$ ratios at LHC energies.
We argue that two-step models, like String and Glasma models, with creation first of sources extended in rapidity that after locally decay into particles, lead to long range forward-backward correlations due to fluctuations in the number or the colour of the sources, and to a similar expression for the {\it F-B} correlation parameter $b$. In the simplest String percolation scenario, $b$ increases with centrality or the number of participating nucleons. However, asymptotically it decreases with energy. This is different from the Glasma model where $b$ increases with both, centrality and energy.
In the framework of Quark-Gluon String Model we calculate the inclusive spectra of secondaries produced in heavy ion collisions at intermediate (CERN SPS) and at much higher (RHIC) energies. We demonstrate that the mechanism of secondary production changed drastically in the energy interval $\sqrt{s} = 20 - 60$ GeV and that is in agreement with qualitative estimates of Glauber-Gribov theory. The results of numerical calculations at intermediate energies are in reasonable agreement with the data. At RHIC energies numerically large inelastic screening corrections should be accounted for in calculations.