Search results for "Sigma"
showing 10 items of 346 documents
Experimental studies of the NaRb ground-state potential up to thev″=76level
2002
Laser induced fluorescence spectra of the C {sup 1}{sigma}{sup +}-X {sup 1}{sigma}{sup +} system of {sup 23}Na{sup 85}Rb and {sup 23}Na{sup 87}Rb have allowed vibrational levels of the electronic ground state up to v{sup ''}=76, spanning 99.85% of the potential well to be observed. The ground-state term values have been fitted to a Dunham polynomial expansion, and also to a direct modified Lennard-Jones (MLJ) potential. The analytical MLJ construction allowed us to match previous measured term values for v{sup ''}{<=}30 with long-range behavior of the potential through the intermediate internuclear distance region covered by the present investigation.
Non-perturbative chiral approach to S-wave interactions
1998
The s-wave meson-nucleon interaction in the $S = -1$ sector is studied by means of coupled-channel Lippmann Schwinger equations, using the lowest order chiral Lagrangian and a cut off to regularize the loop integrals. The method reproduces succesfully the $\Lambda (1405)$ resonance and the $K^- p \to K^- p, \bar{K}^0 n, \pi^0 \Lambda, \pi^0 \Sigma, \pi^+ \Sigma^-, \pi^- \Sigma^+$ cross sections at low energies. The inclusion of the $\eta \Lambda, \eta \Sigma^0$ channels in the coupled system is found very important and allows a solution in terms of only the lowest order Lagrangian.
Anisotropic Heisenberg chain with composite spin
1986
A family of one-dimensional magnetic Hamiltonians is introduced, where at each site there are $n$ spin-$S$ operators. It is shown that, for special couplings between spins and for $S=\frac{1}{2}$, the model contains the complete spectrum of the Heisenberg chain with spins \textonehalf{}, 1, frac32;, etc., and the ground state is that of the corresponding Heisenberg chain. By the varying of a single parameter the model allows continuous transitions between chains with different spin. We map the spin-($S+S$) model onto the nonlinear $\ensuremath{\sigma}$ model and discuss the possibility of a finite gap in the spin-(\textonehalf{}+\textonehalf{}) model.
Sigma Exchange in the NN interaction within the chiral unitary approach
2000
We study the nucleon-nucleon interaction in the isoscalar-scalar channel using t he chiral unitary approach. The $t$-matrix of the pion-pion scattering in this c hannel is summed up to all orders using the B-S equation. We find that the calcu lated results at long distances are close to those of the $\sigma$-exchange inte raction. In addition, there appears a shorter range repulsion in this channel.
Radiative production of the Λ(1405) resonance in K− collisions on protons and nuclei
1999
We have carried a theoretical study of the K^- p\to M B \gamma reaction with M B = K^-p, \bar{K}^0 n, \pi^- \Sigma^+, \pi^+ \Sigma^-, \pi^0 \Sigma^0, \pi^0 \Lambda, for K^- lab. momenta between 200 and 500 MeV/c, using a chiral unitary approach for the strong K^-p interaction with its coupled channels. The \Lambda(1405) resonance, which is generated dynamically in this approach, shows up clearly in the d\sigma/dM_I spectrum, providing new tests for chiral symmetry and the unitary approach, as well as information regarding the nature of the resonance. The photon detection alone, summing all channels, is shown to reproduce quite accurately the strength and shape of the \Lambda(1405) resonance…
Λ(1405)production in theπ−p→K0πΣreaction
2003
We discuss the mechanisms that lead to $\ensuremath{\Lambda}(1405)$ production in the ${\ensuremath{\pi}}^{\ensuremath{-}}p\ensuremath{\rightarrow}{K}^{0}\ensuremath{\pi}\ensuremath{\Sigma}$ reaction. The problem has gained renewed interest after different works converge to the conclusion that there are two resonances around the region of $1400\phantom{\rule{0.3em}{0ex}}\text{MeV}$, rather than one, and that they couple differently to the $\ensuremath{\pi}\ensuremath{\Sigma}$ and $\overline{K}N$ channels. We look at the dynamics of that reaction and find two mechanisms which eventually filter each one of the resonances, leading to very different shapes of the $\ensuremath{\pi}\ensuremath{\S…
Observation of the decayψ(3686)→ΛΣ¯±π∓+c.c.
2013
Using a sample of 1:06 X 10(8) psi(3686) events collected with the BESIII detector, we present the first observation of the decays of psi(3686) -> Lambda(Sigma) over bar (+) pi(-) + c.c. and psi(3686) -> Lambda(Sigma) over bar (-) pi(+) + c.c. The branching fractions are measured to be B(psi(3686) -> Lambda(Sigma) over bar (+) pi(-) + c.c.) = (1.40 +/- 0.03 +/- 0.13) X 10(-4) and B(psi(3686) -> Lambda (Sigma) over bar (-) pi(+) + c.c.) = (1.54 +/- 0.04 +/- 0.13) X 10(-4) where the first errors are statistical and the second ones systematic.
The A dependence of the nuclear structure function ratios
1996
Results are presented for six nuclei from Be to Pb on the structure function ratios F-2(A)/F-2(C)(X) and their A dependence in deep inelastic muon scattering at 200 GeV incident: muon energy. The data cover the kinematic range 0.01 < x < 0.8 with Q(2) ranging from 2 to 70 GeV2. The A dependence of nuclear structure function ratios is parametrised and compared to various models.
Kaonic production of $ \Lambda$ (1405) off deuteron target in chiral dynamics
2009
The K^- induced production of Lambda(1405) is investigated in K^- d to pi Sigma n reactions based on coupled-channels chiral dynamics, in order to discuss the resonance position of the Lambda(1405) in the KbarN channel. We find that the K^-d to Lambda(1405)n process favors the production of Lambda(1405) initiated by the KbarN channel. The present approach indicates that the Lambda(1405) resonance position is 1420 MeV rather than 1405 MeV in the pi Sigma invariant mass spectra of K- d to pi Sigma n reactions. This is consistent with an observed spectrum of the K^- d to pi^+ Sigma^- n with 686-844 MeV/c incident K^- by bubble chamber experiments done in the 70's. Our model also reproduces the…
The deuteron-radius puzzle is alive: A new analysis of nuclear structure uncertainties
2018
To shed light on the deuteron radius puzzle we analyze the theoretical uncertainties of the nuclear structure corrections to the Lamb shift in muonic deuterium. We find that the discrepancy between the calculated two-photon exchange correction and the corresponding experimentally inferred value by Pohl et al. [1] remain. The present result is consistent with our previous estimate, although the discrepancy is reduced from 2.6 $\sigma$ to 2 $\sigma$. The error analysis includes statistic as well as systematic uncertainties stemming from the use of nucleon-nucleon interactions derived from chiral effective field theory at various orders. We therefore conclude that nuclear theory uncertainty is…