1,649 research outputs found
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
-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 / separation, allowing for studying final
states involving neutral particles like or as well as hidden
strangeness, respectively. We discuss the status of ongoing analyses with
specific focus on diffractively produced as well as
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 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, and the geomagnetic radiation energy E. 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 on each Si
atom, the 6-fold spin-orbital degeneracy for the state with the valence
+1 and spin 1/2 splits into doublet groundstates and
quartet excited states with a reduced excited energy of . 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 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
Temperature dependence of the chemical sputtering of amorphous hydrogenated carbon films by hydrogen
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
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