Odd and Even Partial Waves of \eta\pi^- and \eta'\pi^- in 191 GeV/c \pi^-p

In the year 2008 COMPASS recorded diffractive events of the signature \pi^-(191 GeV) p --> X_fast p. We present results of the analysis of the subsystems X = \eta(')\pi^-. Besides the known resonances a_2(1320), a_4(2040), we study the properties of the spin-exotic P+ wave, and all other natural-exchange partial waves up to spin J = 6. We find a striking difference between the two final states: whereas the even partial waves J = 2, 4, 6 in the two systems are related by phase-space factors, the odd partial waves are relatively suppressed in the \eta\pi^- system. The relative phases between the even waves appear identical whereas the phase between the D and P waves behave quite differently, suggesting different resonant and non-resonant contributions in the two odd-angular-momentum systems. Branching ratios and parameters of the well-known resonances a_2 and a_4 are measured.Comment: To appear in the proceedings of the XV International Conference on Hadron Spectroscopy-Hadron 201

The exotic eta'pi- Wave in 190 GeV pi-p --> pi-eta'p at COMPASS

A sample of 35,000 events of the type pi-p --> eta'pi-p_slow (eta' --> eta pi-pi+, eta --> gamma gamma) with -t>0.1 GeV^2/c^2 was selected from COMPASS 2008 data for a partial-wave analysis. We study the broad P_+ structure known from previous experiments at lower energies, in particular its phase motion relative to the D_+-wave near the a_2(1320) mass and relative to a broad D_+-wave structure at higher mass. We also find the a_4(2040). We compare kinematic plots for the eta'pi^- and eta pi- final states.Comment: Conference: Hadron 2011. v2 added sentence intended to avoid misunderstanding of technical plot; Proceedings of the XIV International Conference on Hadron Spectroscopy, eConf C110613 (2011

COMPASS Hadron Spectroscopy -- Final states involving neutrals and kaons

The COMPASS experiment at CERN is well designed for light-hadron spectroscopy with emphasis on the detection of new states, in particular the search for $J^{PC}$-exotic states and glueballs. We have collected data with 190 GeV/c charged hadron beams on a liquid hydrogen and nuclear targets in 2008/09. The spectrometer features good coverage by electromagnetic calorimetry and a RICH detector further provides $\pi$ / $K$ separation, allowing for studying final states involving neutral particles like $\pi^0$ or $\eta$ as well as hidden strangeness, respectively. We discuss the status of ongoing analyses with specific focus on diffractively produced $(\pi^0\pi^0\pi)^{-}$ as well as $(K\bar{K}\pi)^{-}$ final states.Comment: 3 pages, 4 figures, Conf. Proc., to appear in the Intern. Journal of Modern Phys. A, 11th Intern. Workshop on Meson Production, Properties and Interaction, KRAK\'OW, POLAND, 10-15 June 201

Comment on "Material Evidence of a 38 MeV Boson"

In the recent preprint 1202.1739 it was claimed that preliminary data presented by COMPASS at recent conferences confirm the existence of a resonant state of mass 38 MeV decaying to two photons. This claim was made based on structures observed in two-photon mass distributions which however were shown only to demonstrate the purity and mass resolution of the {\pi}0 and {\eta} signals. The additional structures are understood as remnants of secondary interactions inside the COMPASS spectrometer. Therefore, the COMPASS data do not confirm the existence of this state.Comment: 2 pages, 7 figure

Signal model and event reconstruction for the radio detection of inclined air showers

The detection of inclined air showers (zenith angles θ ≳ 65°) with kilometer-spaced radio-antenna arrays allows measuring cosmic rays at ultra-high energies (E ≲ 10$^{20}$ eV). Radio and particle detector arrays provide independent measurements of the electromagnetic and muonic shower components of inclined air showers, respectively. Combined, these measurements have a large sensitivity to discriminate between air showers initiated by lighter and heavier cosmic rays. We have developed a precise model of the two-dimensional, highly complex and asymmetric lateral radio-signal distributions of inclined air shower at ground — the "radio-emission footprints". Our model explicitly describes the dominant geomagnetic emission with a rotationally symmetric lateral distribution function, on top of which additional effects disturb the symmetry. The asymmetries are associated with the interference between the geomagnetic and sub-dominant charge-excess emission as well as with geometrical projection effects, so-called "early-late" effects. Our fully analytic model describes the entire footprint with only two observables: the geometrical distance between the shower impact point at the ground and the shower maximum d$_{max}$, and the geomagnetic radiation energy E$_{geo}$. We demonstrate that with this model, the electromagnetic shower energy can be reconstructed by kilometer-spaced antenna arrays with an intrinsic resolution of 5% and a negligible bias

Effect of the spin-orbit interaction and the electron phonon coupling on the electronic state in a silicon vacancy

The electronic state around a single vacancy in silicon crystal is investigated by using the Green's function approach. The triply degenerate charge states are found to be widely extended and account for extremely large elastic softening at low temperature as observed in recent ultrasonic experiments. When we include the LS coupling $\lambda_{\rm Si}$ on each Si atom, the 6-fold spin-orbital degeneracy for the $V^{+}$ state with the valence +1 and spin 1/2 splits into $\Gamma_{7}$ doublet groundstates and $\Gamma_{8}$ quartet excited states with a reduced excited energy of $O(\lambda_{\rm Si}/10)$. We also consider the effect of couplings between electrons and Jahn-Teller phonons in the dangling bonds within the second order perturbation and find that the groundstate becomes $\Gamma_{8}$ quartet which is responsible for the magnetic-field suppression of the softening in B-doped silicon.Comment: 4 pages, 2 figure

Resonances of the systems \pi-\eta and \pi-\eta' in the reactions \pi-p --> \pi-\eta p and \pi-p --> \pi-\eta' p at COMPASS

We describe partial-wave analyses of the systems \pi-\eta and \pi-\eta' produced in interactions of a \pi- beam (190 GeV/c) with a liquid hydrogen target. The data were recorded during the 2008 COMPASS run, where a slow recoiling proton (|t|>0.1 GeV^2) was required by the trigger. We compare analyses of the \pi-\eta and \pi-\eta' data. Significant contributions can be attributed to the resonances a_2(1320), observed in the D_+-wave, and a_4(2040), observed in the G_+-wave. Between the two systems, we find similar compositions of the even partial waves D_+ and G_+ after taking phase-space factors into account, but a much enhanced P_+-wave in \pi-\eta'. Relative phase-differences indicate a large incoherent contribution of in the P_+-wave of the \eta'\pi- system, but other interpretations are not excluded. The known resonances a_2(1320), a_4(2040) and their parameters could be extracted from the data; their branchings are found to roughly agree with predictions from \eta\eta' mixing.Comment: Proceedings of the Sixth International Conference on Quarks and Nuclear Physics (QNP2012), 7 pages. PoS(QNP2012)074, deviates from version in proceedings by including arXiv hyperlinks in bibliograph

Intrinsic peculiarities of real material realizations of a spin-1/2 kagome lattice

Spin-1/2 magnets with kagome geometry, being for years a generic object of theoretical investigations, have few real material realizations. Recently, a DFT-based microscopic model for two such materials, kapellasite Cu3Zn(OH)6Cl2 and haydeeite Cu3Mg(OH)6Cl2, was presented [O. Janson, J. Richter and H. Rosner, arXiv:0806.1592]. Here, we focus on the intrinsic properties of real spin-1/2 kagome materials having influence on the magnetic ground state and the low-temperature excitations. We find that the values of exchange integrals are strongly dependent on O--H distance inside the hydroxyl groups, present in most spin-1/2 kagome compounds up to date. Besides the original kagome model, considering only the nearest neighbour exchange, we emphasize the crucial role of the exchange along the diagonals of the kagome lattice.Comment: 4 pages, 4 figures. A paper for the proceedings of the HFM 2008 conferenc