Hyperon-nucleon interactions are presented that are derived either in the conventional meson-exchange picture or within leading order chiral effective field theory. The chiral potential consists of one-pseudoscalar-meson exchanges and non-derivative four-baryon contact terms. With regard to meson-exchange hyperon-nucleon models we focus on the new potential of the Jülich group, whose most salie...

The riddle of the σ is recast in a way that tries to differentiate fact from fiction as a basis for future/further discussion. By doing this, it is hoped that the role of the σ as dominating the ubitiquitous ππ interactions below 1 GeV and its relation to the QCD vacuum can be clarified. In this talk, I will start to answer some of the questions that Lucien Montanet listed in his introduction a...

The goal of the DIRAC experiment at CERN (PS212) is to measure the ππ atom lifetime with 10% precision. Such a measurement would yield a precision of 5% on the value of the S-wave ππ scattering lengths combination |a0 − a2|. Based on part of the collected data we present a first result on the lifetime, τ = [

The scalar – isoscalar ππ phase shifts are analysed using a separable potential model of three coupled channels (ππ , KK and an effective 2π2π system). Model parameters are fitted to two sets of solutions obtained in a recent analysis of the CERN-Cracow-Munich measurements of the πp↑ → π πn reaction on a polarized target. A relatively narrow (90 – 180 MeV) scalar resonance f0(1400− 1460) is fou...

The excited state dynamics of resorcinol (1,3-dihydroxybenzene) following UV excitation at a range of pump wavelengths, 278 ≥ λ ≥ 255 nm, have been investigated using a combination of time-resolved velocity map ion imaging and ultrafast time-resolved ion yield measurements coupled with complementary ab initio calculations. After excitation to the 1(1)ππ* state we extract a timescale, τ1, for ex...

In this paper we study the interactions of observed pions with inferred scalar σ meson [1,2] and fermion quark SU(2) fields in a chiral-invariant manner at low energies. Specifically we consider two chiral theories: a) A chiral quark model (CQM) dynamically inducing [2] the entire quark-level SU(2) linear σ model (LσM) but depending on no free parameters. b) Chiral perturbation theory (ChPT) in...

From a re-analysis of ππ → ππ and ππ → KK̄ data, we found for ππ S-wave interaction below 2 GeV, σ(400), f0(980), f0(1500) and f0(1780) clearly show up. f0(1370) can be included with a very small branching ratio to ππ. f0(1300) and f0(1590) are not real resonances and are due to interference effects of above resonances. The σ(400) with a width about 700 MeV is mainly produced by t-channel exchan...

In this study, we calculate the pressure of interacting pion gas using Beth–Uhlenbeck approach to relativistic virial expansion with Breit–Wigner phase shifts for σ- and ϱ-meson resonances. The repulsive shift δ02 is taken from quark interchange model Barnes Swanson, which in very good agreement experimental data. work show that cancellation attractive (I = 0) 2) isospin channel contributions s...