Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userLambda-Sigma^0 mixing in finite nuclei
113
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
Properties of hypernuclei are studied in the context of a chiral Lagrangian which successfully describes ordinary nuclei. Lambda-Sigma^0 mixing arises from nondiagonal vertices in flavor space induced by the vector mesons and by the electromagnetic field. The set of Dirac equations for the coupled hyperon system is discussed. Results are presented for energy spectra and electromagnetic properties of hyperons in the nuclear environment. Simple estimates suggest that flavor mixing can lead to sizable changes in the lifetimes of Lambda hypernuclei.
rate research
Read More
We analyze the mixing between $Sigma^0$ and $Lambda^0$ based on the baryon masses. We distinguish the contributions from QCD and QED in the baryon mass splittings. We find that the mixing angle between $Sigma^0$ and $Lambda^0$ is $(2.07pm 0.03)times 10^{-2} $, which leads to the decay branching fraction and up-down asymmetry of $Lambda_c^+ to Sigma^0 e^+ u_e$ to be ${cal B}(Lambda_c^+ to Sigma^0 e^+ u_e)=(1.5pm 0.2)times 10^{-5}$ and $alpha(Lambda_c^+ to Sigma^0 e^+ u_e)=-0.86pm 0.04$, respectively. Moreover, we obtain that $Delta {cal B}equiv {cal B}(Lambda_c^+to Sigma^0 pi^+) - {cal B}(Lambda_c^+to Sigma^+pi^0)=(3.8pm 0.5)times 10^{-4}$ and $Delta alpha equivalpha(Lambda_c^+to Sigma^0 pi^+) -alpha(Lambda_c^+to Sigma^+pi^0)=(-1.6pm 0.7)times10^{-2}$, which should vanish without the mixing.
We calculate the on-shell $Sigma^0$-$Lambda$ mixing parameter $theta$ with the method of QCD sum rule. Our result is $theta (m^2_{Sigma^0}) =(-)(0.5pm 0.1)$MeV. The electromagnetic interaction is not included.
SU2 isospin breaking effects in baryon octet (and decuplet) masses are due to a combination of up and down quark mass differences and electromagnetic effects. These mass differences are small. Between the Sigma and Lambda the mass splitting is much larger, but this is mostly due to their different wavefunctions. However there is now also mixing between these states. We determine the QCD mixing matrix and hence find the mixing angle and mass splitting.
Kaon electroproduction from light nuclei and hydrogen, using 1H, 2H, 3He, 4He, and Carbon targets has been measured at Jefferson Laboratory. The quasifree angular distributions of Lambda and Sigma hyperons were determined at Q^2= 0.35(GeV/c)^2 and W= 1.91GeV. Electroproduction on hydrogen was measured at the same kinematics for reference.
Using the Quark-Gluon Strings Model -- combined with Regge phenomenology -- we perform a comparative analysis of $Lambda$, $Sigma^0$, $Lambda(1520)$ and $Theta^+$ production in binary reactions induced by photon, pion and proton beams on the nucleon. We find that the existing experimental data on the $gamma p to K^+ Lambda$ differential and total cross sections can be described very well by the model for photon energies $1 - 16$ GeV and $-t < 2$ GeV$^2$ assuming a dominant contribution of the $K^*$ Regge trajectory. Moreover, using the same parameters we also reproduce the total $gamma p to K^+ Sigma^0$ and $gamma p to K^+ Lambda(1520)$ cross sections suggesting a universality of the Regge model. In order to check the consistency of the approach we evaluate the differential and total cross sections for the reaction $pi^- p to K^0 Lambda$ which is also found to be dominated by the $K^*$ Regge trajectory. Using the apparent universality of the Regge model we extend our scheme to the analysis of the binary reactions $gamma p to bar{K}^0 Theta^+$, $pi^- p to K^- Theta^+$ and $pp to Sigma^+ Theta^+$ as well as the exclusive and inclusive $Theta^+$ production in the reactions $pp to p bar{K}^0 Theta^+$ and $pp to Theta^+ X$. Our detailed studies demonstrate that $Theta^+$ production does not follow the universality principle thus suggesting an essentially different internal structure of the exotic baryon relative to conventional hyperons or hyperon resonances.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
