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Register a new userBaryon-to-pion ratios within generic (non)extensive statistics
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The successive stages of a high-energy collision are conjectured to end up with chemical and thermal freezeout of the produced particles. We utilize generic (non)extensive statistics which is believed to determine the degree of (non)extensivity through two critical exponents due to possible phase-space modifications. This statistical approach likely manifests various types of correlations and fluctuations and also possible interactions among the final-state produced particles. We study the baryon-to-pion ratios at top RHIC and LHC energies including the so-called proton anomaly.
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The nuclear modification factor is derived using Tsallis non-extensive statistics in relaxation time approximation. The variation of nuclear modification factor with transverse momentum for different values of non-extensive parameter, $q$, is also observed. The experimental data from RHIC and LHC are analysed in the framework of Tsallis non-extensive statistics in a relaxation time approximation. It is shown that the proposed approach explains the $R_{AA}$ of all particles over a wide range of transverse momenta but doesnt seem to describe the rise in $R_{AA}$ at very high transverse momenta.
We present a calculation of pion photo- and electroproduction in manifestly Lorentz-invariant baryon chiral perturbation theory up to and including order q^4. We fix the low-energy constants by fitting experimental data in all available reaction channels. Our results can be accessed via a web interface, the so-called chiral MAID.
Employing the covariant baryon chiral perturbation theory, we calculate the leading and next-to-leading order two-pion exchange (TPE) contributions to $NN$ interaction up to order $O(p^3)$. We compare the so-obtained $NN$ phase shifts with $2leq Lleq 6$ and mixing angles with $2leq Jleq6$ with those obtained in the nonrelativistic baryon chiral perturbation theory, which allows us to check the relativistic corrections to the medium-range part of $NN$ interactions. We show that the contributions of relativistic TPE are more moderate than those of the nonrelativistic TPE. The relativistic corrections play an important role in F-waves especially the $^3text{F}_2$ partial wave. Moreover, the relativistic results seem to converge faster than the nonrelativistic results in almost all the partial waves studied in the present work, consistent with the studies performed in the one-baryon sector.
Within a dynamical coupled-channels model which has already been fixed from analyzing the data of the pi N -> pi N and gamma N -> pi N reactions, we present the predicted double pion photoproduction cross sections up to the second resonance region, W< 1.7 GeV. The roles played by the different mechanisms within our model in determining both the single and double pion photoproduction reactions are analyzed, focusing on the effects due to the direct gamma N -> pi pi N mechanism, the interplay between the resonant and non-resonant amplitudes, and the coupled-channels effects. The model parameters which can be determined most effectively in the combined studies of both the single and double pion photoproduction data are identified for future studies.
Big Bang nucleosynthesis (BBN) theory predicts the abundances of the light elements D, $^3$He, $^4$He and $^7$Li produced in the early universe. The primordial abundances of D and $^4$He inferred from observational data are in good agreement with predictions, however, the BBN theory overestimates the primordial $^7$Li abundance by about a factor of three. This is the so-called cosmological lithium problem. Solutions to this problem using conventional astrophysics and nuclear physics have not been successful over the past few decades, probably indicating the presence of new physics during the era of BBN. We have investigated the impact on BBN predictions of adopting a generalized distribution to describe the velocities of nucleons in the framework of Tsallis non-extensive statistics. This generalized velocity distribution is characterized by a parameter $q$, and reduces to the usually assumed Maxwell-Boltzmann distribution for $q$ = 1. We find excellent agreement between predicted and observed primordial abundances of D, $^4$He and $^7$Li for $1.069leq q leq 1.082$, suggesting a possible new solution to the cosmological lithium problem.
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