Strong and Weak Interactions in B to pi+ pi- K Decays

To describe the weak three-body B decays into pi+ pi- K, we recently derived amplitudes based on two-body QCD factorization followed by pi+ pi- final state interactions in isoscalar S- and isovector P-waves. We study here the sensitivity of the results to the values of the B to f0(980) transition form factor and to the effective decay constant of the f0(980).Comment: Contribution to the Few Body 18 conference in Santos, Brazil, August 21-26, 2006, 5 pages, to be published in Nuclear Physics

Enhancement of πA→ππA\pi A \to \pi\pi A Threshold Cross Sections by In-Medium ππ\pi\pi Final State Interactions

We address the problem of pion production in low energy $\pi$-nucleus collisions. For the production mechanism we assume a simple model consisting of a coherent sum of single pion exchange and the excitation---followed by the decay into two pions and a nucleon---of the $N^*(1440)$ resonance. The production amplitude is modified by the final state interaction between the pions calculated using the chirally improved J\"ulich meson exchange model including the polarization of the nuclear medium by the pions. The model reproduces well the experimentally observed $\pi A \to \pi\pi A$ cross sections, especially the enhancement with increasing $A$ of the $\pi^+\pi^-$ mass distribution in the threshold region.Comment: 5 pages RevTeX, 3-eps figure

Strangeness fluctuations from K−πK-\pi interactions

Motivated by recent lattice QCD studies, we explore the effects of interactions on strangeness fluctuations in strongly interacting matter at finite temperature. We focus on S-wave $K\pi$ scattering and discuss the role of the $K_0^*(800)$ and $K^*(1430)$ resonances. The interaction contribution is obtained within the S-matrix formulation of thermodynamics, using the empirical $K\pi$ phase shifts as input. We find that the simplified treatment of the interactions in this channel, employed in the hadron resonance gas approach, leads to an overestimate of the strangeness fluctuations. Thus, our calculation indicates that broad resonances must be treated with caution, when modeling QCD thermodynamics in the hadronic phase.Comment: 7 pages, 4 figures, version appeared in phys. rev.

Search for f1(1285)→π+π−π0f_1(1285) \to \pi^+\pi^-\pi^0 decay with VES detector

The isospin violating decay $f_1(1285)\to\pi^+\pi^-\pi^0$ has been studied at VES facility. This study is based at the statistics acquired in $\pi^- Be$ interactions at 27, 36.6 and 41 GeV/c in diffractive reaction $\pi^- N \to (f_1 \pi^-) N$. The $f_1(1285) \to \pi^+\pi^-\pi^0$ decay is observed. The ratio of decay probabilities $BR(f_1(1285) \to \pi^+\pi^-\pi^0)$ to $BR(f_1(1285) \to \eta \pi^+\pi^-) \cdot BR(\eta \to \gamma\gamma)$ is $\sim\:1.4$.Comment: 10 pages, 8 figures, presented at XII Conference on Hadron Spectroscop

Multi-Pion Systems in Lattice QCD and the Three-Pion Interaction

The ground-state energies of 2, 3, 4 and 5 \pi^+'s in a spatial volume V (2.5 fm)^3 are computed with lattice QCD. By eliminating the leading contribution from three-\pi^+ interactions, particular combinations of these n-\pi^+ ground-state energies provide precise extractions of the \pi^+\pi^+ scattering length in agreement with that obtained from calculations involving only two \pi^+'s. The three-\pi^+ interaction can be isolated by forming other combinations of the n-\pi^+ ground-state energies. We find a result that is consistent with a repulsive three-\pi^+ interaction for m_\pi < 352 MeV.Comment: 4 pages, 5 figure

Crossover properties from random percolation to frustrated percolation

We investigate the crossover properties of the frustrated percolation model on a two-dimensional square lattice, with asymmetric distribution of ferromagnetic and antiferromagnetic interactions. We determine the critical exponents nu, gamma and beta of the percolation transition of the model, for various values of the density of antiferromagnetic interactions pi in the range 0<pi<0.5. Our data are consistent with the existence of a crossover from random percolation behavior for pi=0, to frustrated percolation behavior, characterized by the critical exponents of the ferromagnetic 1/2-state Potts model, as soon as pi>0.Comment: 5 pages, 7 figs, RevTe

Resonance structure in the {\gamma}{\gamma} and π0π0\pi^0\pi^0 systems in dC interactions

Along with $\pi^0$ and {\eta} mesons, a resonance structure in the invariant mass spectrum of two photons at M{\gamma}{\gamma} = 360 \pm 7 \pm 9 MeV is observed in the reaction d + C \rightarrow {\gamma} + {\gamma} + X at momentum 2.75 GeV/c per nucleon. Estimates of its width and production cross section are {\Gamma} = 64 \pm 18 MeV and $\sigma_{\gamma\gamma}$ = 98 \pm 24 {\mu}b, respectively. The collected statistics amount to 2339 \pm 340 events of 1.5 \cdot 10^6 triggered interactions of a total number ~ 10^12 of dC-interactions. The results on observation of the resonance in the invariant mass spectra of two $\pi^0$ mesons are presented: the data obtained in the d + C \rightarrow {\gamma} + {\gamma} reaction is confirmed by the d + C \rightarrow $\pi^0$ + $\pi^0$ reaction: $M_{\pi^0\pi^0}$ = 359.2 \pm 1.9 MeV, {\Gamma} = 48.9 \pm 4.9 MeV; the ratio of Br(R\rightarrow{\gamma}{\gamma}) / Br(R\rightarrow$\pi^0\pi^0$) = (1.8 {\div} 3.7)\cdot10^-3.Comment: 10 pages, 11 figure

Thermal Dileptons from pi - rho Interactions in a Hot Pion Gas

A systematic study of low mass dilepton production from $\pi-\rho$ interactions in a hot medium is presented. Applying finite temperature perturbation theory the dilepton rate, respectively the virtual photon rate, is computed up to order $g_\rho^2$. For dilepton masses below the $\rho$ the two-body reactions $\pi\pi\to \rho \gamma^*$, $\pi\rho\to \pi \gamma^*$, and the decay process $\rho \to \pi \pi \gamma^*$ give significant contributions. Non-equilibrium contributions to the thermal rate are estimated, including the modification of the particle distribution function with non-zero pion chemical potential. The comparison of the dilepton rate with the recent data measured in nucleus-nucleus collisions at SPS energy by the CERES Collaboration is also performed. It is shown that the additional thermal dileptons from $\pi-\rho$ interactions can partially account for the access of the soft dilepton yield seen experimentally.Comment: 21 pages LaTeX, 8 figs with epsfig.sty macro include