Hard exclusive wide-angle processes

In this talk the handbag approach to hard exclusive wide-angle processes is reviewed and applications, as for instance two-photon annihilations into pairs of mesons, are discussed.Comment: 11 pages, 8 figures, using latex2e, invited talk presented at Meson 2012, Cracow 201

Exclusive meson pair production in proton-proton collisions

We present a study of the exclusive production of meson pairs in the four-body $pp \to pp \pi^{+} \pi^{-}$, $pp K^{+}K^{-}$ reactions at high energies which constitute an irreducible background to resonance states (e.g. $\phi$, $f_{2}(1270)$, $f_{0}(1500)$, $f_{2}'(1525)$, $\chi_{c0}$). We consider central diffractive contribution mediated by Pomeron and Reggeon exchanges and new diffractive mechanism of emission of pions/kaons from the proton lines. We include absorption effects due to proton-proton interaction and pion/kaon rescattering. Predictions for the total cross section and differential distributions in pion/kaon rapidity and transverse momentum as well as two-pion/kaon invariant mass are presented for the RHIC, Tevatron and LHC colliders. Finally we consider a measurement of exclusive production of a scalar $\chi_{c0}$ meson via $\chi_{c0} \to \pi^{+} \pi^{-}$, $K^{+} K^{-}$ decay.Comment: 4 pp., 4 figures, talk presented by PL at MESON2012 - 12th International Workshop on Meson Production, Properties and Interaction, Krakow, Poland, 31 May - 5 June 201

Exclusive production of π+π−\pi^+\pi^- and π0π0\pi^0\pi^0 pairs in photon-photon and in ultrarelativistic heavy ion collisions

The $\gamma\gamma\to\pi\pi$ reactions are discussed. To describe those processes, we include dipion continuum, resonances, high-energy pion-pion rescatterings, $\rho$ meson exchange and pQCD Brodsky-Lepage mechanisms. The cross section for the production of pion pairs in photon-photon collisions in peripheral heavy ion collisions is calculated with the help of Equivalent Photon Approximaption (EPA) in the impact parameter space. We show predictions at $\sqrt{s_{NN}}=3.5$ TeV which could be measured e.g. by the ALICE collaboration at the LHC.Comment: 4 pages, 7 figures, 1 table, talk by M. Klusek-Gawenda at MESON2012, 31 May - 5 June 2012, Krakow, Polan

Open charm meson production at LHC

We discuss charm production at the LHC. The production of single $c \bar c$ pairs is calculated in the $k_t$-factorization approach. We use Kimber-Martin-Ryskin unintegrated gluon distributions in the proton. The hadronization is included with the help of Peterson fragmentation functions. Transverse momentum and pseudorapidity distributions of charmed mesons are presented and compared to recent results of the ALICE, LHCb and ATLAS collaborations. Furthermore we discuss production of two pairs of $c \bar c$ within a simple formalism of double-parton scattering (DPS). Surprisingly large cross sections, comparable to single-parton scattering (SPS), are predicted for LHC energies. We discuss perspectives how to identify the double scattering contribution. We predict much larger cross section for large rapidity distance between charm quarks from different hard parton scatterings compared to single scattering.Comment: 5 pages, 4 figures, talk given by R. Maciula at the MESON2012 - 12th International Workshop on Meson Production, Properties and Interaction, 31 May - 5 June 2012, Krakow, Polan

A Dispersive Treatment of Kℓ4K_{\ell4} Decays

$K_{\ell4}$ are for several reasons an especially interesting decay channel of $K$ mesons: $K_{\ell4}$ decays allow an accurate measurement of a combination of $S$-wave $\pi\pi$ scattering lengths, one form factor of the decay is connected to the chiral anomaly and the decay is the best source for the determination of some low energy constants of ChPT. We present a dispersive approach to $K_{\ell4}$ decays, which takes rescattering effects fully into account. Some fits to NA48/2 and E865 measurements and results of the matching to ChPT are shown.Comment: 4 pages, talk given by PS at MESON2012 - 12th International Workshop on Meson Production, Properties and Interaction, Krak\'ow, Poland, 31 May - 5 June 201

Strangeness production in antiproton-nucleus annihilation

The results of the microscopic transport calculations of $\bar p$-nucleus interactions within a GiBUU model are presented. The dominating mechanism of hyperon production is the strangeness exchange processes $\bar K N \to Y \pi$ and $\bar K N \to \Xi K$. The calculated rapidity spectra of $\Xi$ hyperons are significantly shifted to forward rapidities with respect to the spectra of $S=-1$ hyperons. We argue that this shift should be a sensitive test for the possible exotic mechanisms of $\bar p$-nucleus annihilation. The production of the double $\Lambda$-hypernuclei by $\Xi^-$ interaction with a secondary target is calculated.Comment: Proceedings of the 12th Int. Workshop on Meson Production, Properties and Interaction (MESON-2012), Cracow, 31.05-05.06.201

eta' meson under partial restoration of chiral symmetry in nuclear medium

We shed light upon the eta' mass in nuclear matter in the context of partial restoration of chiral symmetry, pointing out that the U_{A}(1) anomaly effects causes the eta'-eta mass difference necessarily through the chiral symmetry breaking. As a consequence, it is expected that the eta' mass is reduced by order of 100 MeV in nuclear matter where partial restoration of chiral symmetry takes place. The discussion given here is based on Ref. [1].Comment: 3 pages, 2 figures. Contribution to Meson201

Hadron Spectroscopy with COMPASS -- Newest Results

The COMPASS experiment at the CERN SPS investigates the structure and spectrum of hadrons by scattering high energetic hadrons and polarised muons off various fixed targets. During the years 2002-2007, COMPASS focused on nucleon spin physics using 160 GeV/c polarised $\mu^+$ beams on polarised deuteron and proton targets, including measurements of the gluon contribution to the nucleon spin using longitudinal target polarisation as well as studies of transverse spin effects in the nucleon on a transversely polarised target. One major goal of the physics programme using hadron beams is the search for new states, in particular the search for $J^{PC}$ exotic states and glue-balls. COMPASS measures not only charged but also neutral final-state particles, allowing for investigation of new objects in different reactions and decay channels. In addition COMPASS can measure low-energy QCD constants like, e.g. the electromagnetic polarisability of the pion. Apart from a few days pilot run data taken in 2004 with a 190 GeV/c $\pi^{-}$ beam on a Pb target, showing a significant spin-exotic $J^{PC}$ = $1^{-+}$ resonance at around 1660 MeV/$c^{2}$, COMPASS collected high statistics with negative and positive 190 GeV/$c$ hadron beams on a proton (H$_2$) and nuclear (Ni, Pb) targets in 2008 and 2009. We give a selected overview of the newest results and discuss the status of various ongoing analyses.Comment: 7 pages, 13 figures, MESON2012 Conference Proceedings, to appear in the proceedings of the 12th International Workshop on Meson Production, Properties and Interaction, KRAK\'OW, POLAND, 31 May - 5 June 201

Study of the eta --> e+ e- gamma decay using WASA-at-COSY detector system

Since the eta meson is a short-lived neutral particle, it is not possible to investigate its structure via classical methods of particle scattering. To learn about its quark wave function, one studies those decay processes of this meson in which a pair of photons is produced, where at least one of them is virtual. The virtual photons have a non-zero mass and convert into lepton-antilepton pairs. Therefore, information about the quarks' spatial distribution inside the meson can be extracted from the lepton-antilepton invariant mass distributions by comparing the empirical results with QED predictions, which are based on the assumption that the meson is a point-like particle. The deviation from the expected behavior in the leptonic mass spectrum exposes the inner structure of the meson. This deviation is characterized by a form factor. The corresponding data were collected for the pd --> 3He eta reaction at a proton beam momentum of 1.69 GeV/c. The experiment was performed using the WASA-at-COSY detector in November 2008. 525 +/- 26 events of the eta --> g e+ e- decay channel were reconstructed. The analysis chain led to the determination of the value of the slope parameter, bp, equal to (2.27 +/- 0.73stat. +/- 0.46sys.) GeV^{-2}, where the systematical uncertainty should be treated as an upper limit only. The estimation of the charge radius of the eta meson has been made resulting with the value of < r(eta)^2 >^(1/2) = (0.68 +/- 0.02) fm.Comment: Ph.D. Thesis (Advisor: Prof. Pawel Moskal), Jagiellonian University, Cracow 2012; Version includes minor corrections according to the comments of the referee

Search for Deeply Bound Kaonic Nuclear States with AMADEUS

We briefly report on the search for Deeply Bound Kaonic Nuclear States with AMADEUS in the Sigma0 p channel following K- absorption on 12C and outline future perspectives for this work