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Weak Production of Strange Particles and $eta$ Mesons off the Nucleon

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 Publication date 2015
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The strange particle production induced by (anti)neutrino off nucleon has been studied for $|Delta S|=0$ and $|Delta S|=1$ channels. The reactions those we have considered are for the production of single kaon/antikaon, eta and associated particle production processes. We have developed a microscopical model based on the SU(3) chiral Lagrangian. The basic parameters of the model are $f_pi$, the pion decay constant, Cabibbo angle, the proton and neutron magnetic moments and the axial vector coupling constants for the baryons octet. For antikaon production we have also included $Sigma^*$(1385) resonance and for eta production $S_{11}$(1535) and $S_{11}$(1650) resonances are included.



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The weak kaon production off the nucleon induced by neutrinos is studied at the low and intermediate energies of interest for some ongoing and future neutrino oscillation experiments. This process is also potentially important for the analysis of proton decay experiments. We develop a microscopical model based on the SU(3) chiral Lagrangians. The basic parameters of the model are fpi, the pion decay constant, Cabibbos angle, the proton and neutron magnetic moments and the axial vector coupling constants for the baryons octet, D and F, that are obtained from the analysis of the semileptonic decays of neutron and hyperons. The studied mechanisms are the main source of kaon production for neutrino energies up to 1.2 to 1.5 GeV for the various channels and the cross sections are large enough to be amenable to be measured by experiments such as Minerva and T2K.
We have improved the tree-level model of Ref arXiv:1004.5484 [hep-ph] for weak production of kaons off nucleons by partially restoring unitarity. This is achieved by imposing Watsons theorem to the dominant vector and axial-vector contributions in appropriate angular momentum and isospin quantum number sectors. The observable consequences of this procedure are investigated.
Weak pion production off the nucleon at low energies has been systematically investigated in manifestly relativistic baryon chiral perturbation theory with explicit inclusion of the $Delta$(1232) resonance. Most of the involved low-energy constants have been previously determined in other processes such as pion-nucleon elastic scattering and electromagnetic pion production off the nucleon. For numerical estimates, the few remaining constants are set to be of natural size. As a result, the total cross sections for single pion production on neutrons and protons, induced either by neutrino or antineutrino, are predicted. Our results are consistent with the scarce existing experimental data except in the $ u_mu nto mu^-npi^+$ channel, where higher-order contributions might still be significant. The $Delta$ resonance mechanisms lead to sizeable contributions in all channels, especially in $ u_mu pto mu^- ppi^+$, even though the considered energies are close to the production threshold. The present study provides a well founded low-energy benchmark for phenomenological models aimed at the description of weak pion production processes in the broad kinematic range of interest for current and future neutrino-oscillation experiments.
Neutral current single pion production induced by neutrinos and antineutrinos on nucleon targets has been investigated in manifestly relativistic baryon chiral perturbation theory with explicit $Delta(1232)$ degrees of freedom up to $mathcal{O}(p^3)$. At low energies, where chiral perturbation theory is applicable, the total cross sections for the different reaction channels exhibit a sizable non-resonant contribution, which is not present in event generators of broad use in neutrino oscillation and cross section experiments such as GENIE and NuWro.
The NA61/SHINE collaboration has recently published high precision data on production of $pi^pm$ and $K^pm$ mesons, protons, antiprotons and $Lambda$ hyperons in ${rm pp}$ interactions at 20, 31, 40, 80 and 158 GeV/c, and in ${rm pC}$ interactions at 31 GeV/c. The collaboration also presented experimental data on production of particles - $pi^pm$, $K^pm$, $p^pm$, $rho^0$, $omega$ and $K^{*0}$ in $pi^-{rm C}$ collisions at 158 and 350 GeV/c. The collaboration has compared these data with various Monte Carlo model calculations: UrQMD, EPOS, GiBUU, and others. All of the models have various problems. The latest version of the FTF (Fritiof) model of Geant4 solves most of these problems. In the FTF model, we have improved the fragmentation of quark-gluon strings with small masses and introduced dependencies of probabilities of strange mesons and baryon-antibaryon pairs creation on string masses. Due to these changes, we describe the data of the NA61/SHINE collaboration on particle production in ${rm pp, pC}$, and $pi^-{rm C}$ interactions. The improved Geant4 FTF model also well reproduces experimental data on inclusive cross sections of $Lambda, bar{Lambda}$ and $K^{0}$ production in antiproton-proton interactions at various energies. The modified FTF model allows one to simulate realistic processes with two particle productions - $bar{p}p rightarrow Lambda bar{Lambda}$, $bar{p}p rightarrow K^{+} K^{-}$, $bar{p}p rightarrow Lambda bar{Sigma}$, and $bar{p}p rightarrowSigma bar{Sigma}$, which will be studied in the future by the PANDA experiment at FAIR (GSI, Germany).
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