Search

We report systematic measurements of bulk properties of the system created in Au+Au collisions at √SNN = 54.4 s N N = 54.4 GeV recorded by the STAR detector at the Relativistic Heavy Ion Collider (RHIC). The transverse momentum spectra of π±, K±, and p(p¯) p (p ¯) are studied at mid-rapidity (|y| < 0.1) for different centrality classes. We also present mid-rapidity measurement of particle yields (dN/dy) and particle ratios in Au+Au collisions at √SNN = 54.4 s N N = 54.4 GeV. The kinetic freeze-out parameters (Tkin and β>) are extracted from particle spectra using the blast-wave model, and all the results are compared with previously published experimental results. [ABSTRACT FROM AUTHOR]

NA61/SHINE is a multipurpose fixed-target facility at the CERN Super Proton Synchrotron. The main goals of the NA61/SHINE strong interactions program are to discover the critical point of strongly interacting matter and study the properties of the onset of deconfinement. To reach these goals, hadron production measurements are performed in the form of a two-dimensional scan by varying collision energy and system size. The Collaboration has recently finished data acquisition for its original program on strong interactions, accumulating broad data samples on hadron production in various systems in the SPS energy range. In this contribution, the NA61/SHINE results on identified charged kaon and pion production in p+p, Be+Be and Ar+Sc collisions at the SPS energy range (√SNN = 5.1 - 17.3 s N N = 5.1 − 17.3 GeV) are presented. The NA61/SHINE measurements of small and intermediate-mass ion collisions establish an interesting system size dependence, showing a rapid change of hadron production properties that starts when moving from Be+Be to Ar+Sc system. In particular, Ar+Sc is the smallest system for which a significant enhancement of K+/π+ ratio with respect to p+p collisions is observed. Obtained energy and system size dependence of the measured charged hadron multiplicities are compared with available world data and various theoretical models. [ABSTRACT FROM AUTHOR]

Experiment DIRAC at CERN PS detects 349 ± 62 pairs from π−K+ and π+K− atoms and makes observation of exotic atoms consist of pion and kaon. It allows to measure a difference of S-wave pion-kaon scattering length with isospin 1/2 and 3/2: |a01/2−a03/2|. Values of pion-kaon scattering lengths are predicted in a frame of ChPT and LQCD. Therefore investigation of π−K+ and π+K− atoms gives possibility to check these predictions for simplest hadronhadron system with s-quark. [ABSTRACT FROM AUTHOR]

We demonstrate the efficacy of the stochastic LapH method to treat all-to-all quark propagation on a Nf = 2 + 1 CLS ensemble with large linear spatial extent L = 5.5 fm, allowing us to obtain the benchmark elastic isovector p-wave pion-pion scattering amplitude to good precision already on a relatively small number of gauge configurations. These results hold promise for multi-hadron spectroscopy at close-to-physical pion mass with exponential finite-volume effects under control. [ABSTRACT FROM AUTHOR]

The heavy-quark spin symmetry (HQSS) partners of the X(3872) molecule are investigated in a chiral effective field theory (EFT) approach which incorporates contact and one-pion exchange interactions. The integral equations of the Lippmann-Schwinger type are formulated and solved for the coupled-channel problem for the D¯D; D¯D*, and D* ¯D* systems with the quantum numbers JPC = 1++, 1+-, 0++, and 2++. We confirm that, if the X(3872) is a 1++ D¯D* molecular state then, in the strict heavy-quark limit, there exist three partner states, with the quantum numbers 1+-, 0++, and 2++, which are degenerate in mass. At first glance, this result looks natural only for the purely contact pionless theory since pions contribute differently to different transition potentials and, therefore, may lift the above degeneracy. Nevertheless, it is shown that, by an appropriate unitary transformation, the Lippmann-Schwinger equation in each channel still can be brought to a block-diagonal form, with the same blocks for all quantum numbers, so that the degeneracy of the bound states in different channels is preserved. We stress that neglecting some of the coupled-channel transitions in an inconsistent manner leads to a severe violation of HQSS and yields regulator-dependent results for the partner states. The effect of HQSS violation in combination with nonperturbative pion dynamics on the pole positions of the partner states is discussed. [ABSTRACT FROM AUTHOR]

It is shown that the basic shape of dipion mass distributions in the twopion transitions of both charmonia and bottomonia states are explained by an unified mechanism based on the contribution of the ππ, KK̄ and ηη coupled channels including their interference. [ABSTRACT FROM AUTHOR]

Theory, using Low Energy QCD, predicts with high precision the pion-pion and pion-kaon scattering lengths. There is accurate relation between K+π- and π+K- atoms lifetime and pion-kaon S-wave scattering lengths with isospin 1/2 and 3/2. Experiment DIRAC at CERN PS detects 345 ± 61 pairs from K+π- and π+K- atoms breakup. It allows to achieve the first observation of exotic atoms consisted of pion and kaon. Measured values of πK atom lifetime and corresponding pion-kaon scattering length difference are presented. It is shown, that experimental accuracy for pion-kaon scattering length difference could be significantly improved with an experiment at SPS energy. [ABSTRACT FROM AUTHOR]

Apart from the mesons that the constituent quark model predicts, QCD allows for additional states beyond the qq system. Previous experiments have performed partial wave analysis on pion-production data and claim observation of a JPC = 1-+ state decaying via ρπ. The g12 experiment took place at Jefferson Lab using the CLAS spectrometer, a liquid hydrogen target was used and a tagged photon beam. By studying the reactions γp → nπ+π+π- and γp → Δ++π+π-π-, we are analyzing a large data-set of a three pion system. In the first reaction channel, events are selected with low four-momentum transfer to the neutron, in order to enhance one pion exchange production. The latter reaction is expected to be dominated by pion exchange between the baryon and the 3π meson system, given identification of Δ++ in the event. For both 3π systems the data exhibit two intermediate decays, ρπ and f2π. An analysis of the kinematics and dynamics of those two data-sets has been performed, as well as a study of the angular distributions looking for resonance contributions. [ABSTRACT FROM AUTHOR]

Based on the Chiral Effective Field Theory (ChEFT) dynamical picture of the two-pion exchange (TPE) contributions to the nuclear current operator which appear at higher order chiral expansions were considered. Their role in the electron-deuteron scattering reactions was studied and chiral predictions were compared with those obtained in the conventional framework. Results for cross section and various polarization observables are presented. The bound and scattering states were calculated with five different chiral nucleon-nucleon (NN) potentials which leads to the so-called theoretical uncertainty bands for the predicted results. [ABSTRACT FROM AUTHOR]

Compton backscattering gamma ray beams are characterized by a high degree of linear and circular polarization with low unpolarized backgrounds and have proven to provide very precise measurements of polarization observables. Latest results from LEGS and GRAAL experiments on proton and deuteron targets are presented. The Σ beam asymmetry for ω photoproduction has been measured by the GRAAL collaboration for both the ω→π0γ and the ω→π+π-π0 decay channels on the proton target; single and double polarization asymmetries have been provided also for the K photoproduction channel. E and G double polarization asymmetries for single pion photoproduction on the proton and deuteron have been measured at LEGS using a frozen spin HD target. [ABSTRACT FROM AUTHOR]

The total as well as the differential cross sections of the π0 π0 production in proton-proton interactions have been evaluated at Tp = 1.4 GeV using the WASA-at-COSY facility. The total cross section is found to be (324 ± 21systematic ± 58normalization) μb. The differential distributions indicate the mutual excitation of the initial protons into their first excited state, Δ(1232), which decays by emission of a proton and a pion. No significant contribution of the Roper N*(1440) via its decay into a proton and two pions is found. [ABSTRACT FROM AUTHOR]

The pion final state interaction model in NEUT is described. Modifications and tuning of the model are validated against neutrino and non-neutrino (pion scattering and photoproduction) data. A method for evaluating the uncertainties in the model and propagation of systematic errors in a neutrino oscillation experiment is described, using T2K as a specific example. [ABSTRACT FROM AUTHOR]

Can we get the information on π p and π π scattering from the LHC data? We present briefly recent results of the IHEP Diffractive Group, which include all the steps: formulation of the problem, an idea how to solve it, experimental tools, Monte-Carlo simulation and preliminary expectations concerning the first data from the LHC. [ABSTRACT FROM AUTHOR]

Using high statistics samples of charged current interactions, MiniBooNE reports a model independent measurement of the single charged pion production to quasi-elastic cross section ratio on mineral oil without corrections for pion re-interactions in the target nucleus [1]. The result is provided as a function of neutrino energy in the range 0.4 GeV

Alpha-alpha scattering is discussed in terms of a chiral two pion exchange potential (TPE) which turns out to be attractive and singular at the origin, hence demanding renormalization. When 8Be is treated as a resonance state a model independent correlation between the Q-factor and lifetime 1/Γ for the decay into two alpha particles arises. For a wide range of parameters compatible with potential model analyses of low energy πα scattering it is found Γ = 4.4(4)eV in fairly good agreement with the experimental value Γexp. = 5.57(25)eV. The remaining discrepancy as well as the phase shift up to ELAB = 15 MeV could be accommodated by the leading nuclear peripheral contributions due to the 3H+p and 3He+n continuum. [ABSTRACT FROM AUTHOR]

We calculate pion-pion scattering lengths and sigma, rho and a1 decay widths from a gauged linear sigma model with two flavours and its globally invariant generalisation. [ABSTRACT FROM AUTHOR]

Existence of gluonic resonances is among the early expectations of QCD. Today, QCD calculations predict the lightest glueball to be a scalar state with mass within a range of about 900–1700 MeV but there is no consensus about its experimental evidence. In a re-analysis of the phase shifts for ππ scattering up to 1800 MeV where such states should show up we find the broad resonance f0(600)/σ contributing to the full mass range and the narrow f0(980) and f0(1500) but no evidence for f0(1370). Phenomenological arguments for the broad state to be a glueball are recalled. It is argued that the large radiative width of f0(600)/σ reported recently is not in contradiction to this hypothesis but is mainly due to ππ-rescattering. The small “direct” radiative component is consistent with QCD sum rule predictions for the light glueball. [ABSTRACT FROM AUTHOR]

We review our recent analysis of ππ scattering data in terms of Roy equations and Forward Dispersion Relations, and present some preliminary results in terms of a new set of once-subtracted coupled equations for partial waves. The first analysis consists of independent fits to the different ππ channels that satisfies rather well the dispersive representation. In the second analysis we constrain the fit with the dispersion relations. The latter provides a very precise and model independent description of data using just analyticity, causality and crossing. [ABSTRACT FROM AUTHOR]

We determine the mass and strength of the scalar meson from NN scattering data by renormalizing the One Boson Exchange Potential. This procedure provides a great insensitivity to the unknown short distance interaction making the vector mesons marginally important allowing for SU(3) values in the 1S0 channel. The scalar meson parameters are tightly constrained by low energy np. We discuss whether this number should be compared to the recent findings based on the Roy equations analysis of ππ scattering. [ABSTRACT FROM AUTHOR]

In this talk, we review our recent work about the dynamical studies of Z+(4430) and X(3872). Z+(4430) can not be explained as a D1′D* or D1D* molecular state only considering one pion exchange potential without the cutoff, which needs to be confirmed by introducing sigma exchange potential and adding the cutoff in the effective potential. One also excludes the possibility of X(3872) as a DD* molecular state by one pion and one sigma exchanges with the cutoff. Fortunately there exists an S-wave BB* bound state with JPC = 1++. we suggest future experiment to search this state. [ABSTRACT FROM AUTHOR]

The article presents a panel discussion that took place at the SCADRON 70: Workshop on "Scalar Mesons and Related Topics", in Lisbon, Portugal, from February 11-16, 2008. Topics included the unquenched glueball spectrum, the existence of the lightest scalar meson and its gluon-quark composition, and various nuclear particle interactions such as π π scattering. Replies to various comments addressed to the physicists are presented.