The excitation function and momentum distribution of \(\eta^\prime\) mesons have been measured in photon induced reactions on \(^{12}{}\)C in the energy range of 1250-2600 MeV. The experiment was ...performed with tagged photon beams from the ELSA electron accelerator using the Crystal Barrel and TAPS detectors. The data are compared to model calculations to extract information on the sign and magnitude of the real part of the \(\eta^\prime\)-nucleus potential. Within the model, the comparison indicates an attractive potential of -(\(37 \pm 10(stat)\pm10(syst)\)) MeV depth at normal nuclear matter density. Since the modulus of this depth is larger than the modulus of the imaginary part of the \(\eta^\prime\)-nucleus potential of -(\(10\pm2.5\)) MeV, determined by transparency ratio measurements, a search for resolved \(\eta^\prime\)-bound states appears promising.
The photoproduction of \(\omega\) and \(\eta^\prime\) mesons off carbon and niobium nuclei has been measured as a function of the meson momentum for incident photon energies of 1.2-2.9 GeV at the ...electron accelerator ELSA. The mesons have been identified via the \(\omega \rightarrow \pi^0 \gamma \rightarrow 3 \gamma\) and \(\eta^\prime\rightarrow \pi^0 \pi^0\eta \rightarrow 6 \gamma\) decays, respectively, registered with the CBELSA/TAPS detector system. From the measured meson momentum distributions the momentum dependence of the transparency ratio has been determined for both mesons. Within a Glauber analysis the in-medium \(\omega\) and \(\eta^\prime\) widths and the corresponding absorption cross sections have been deduced as a function of the meson momentum. The results are compared to recent theoretical predictions for the in-medium \(\omega\) width and \(\eta^\prime\)-N absorption cross sections. The energy dependence of the imaginary part of the \(\omega\)- and \(\eta^\prime\)-nucleus optical potential has been extracted. The finer binning of the present data compared to the existing data allows a more reliable extrapolation towards the production threshold. The modulus of the imaginary part of the \(\eta^\prime\) nucleus potential is found to be about three times smaller than recently determined values of the real part of the \(\eta^\prime\)-nucleus potential, which makes the \(\eta^\prime\) meson a suitable candidate for the search for meson-nucleus bound states. For the \(\omega\) meson, the modulus of the imaginary part near threshold is comparable to the modulus of the real part of the potential. As a consequence, only broad structures can be expected which makes the observation of \(\omega\) mesic states very difficult experimentally.
The first measurement is reported of the double-polarization observable G in photoproduction of neutral pions off protons, covering the photon energy range from 620 to 1120 MeV and the full solid ...angle. G describes the correlation between the photon polarization plane and the scattering plane for protons polarized along the direction of the incoming photon. The observable is highly sensitive to contributions from baryon resonances. The new results are compared to the predictions from SAID, MAID, and BnGa partial wave analyses. In spite of the long-lasting efforts to understand {\gamma}p -> p{\pi} 0 as the simplest photoproduction reaction, surprisingly large differences between the new data and the latest predictions are observed which are traced to different contributions of the N (1535) with spin-parity J^P = 1/2^- and N (1520) with J^P = 3/2^- . In the third resonance region, where N (1680) with J^P = 5/2^+ production dominates, the new data are reasonably close to the predictions.
The photoproduction of \eta'-mesons off different nuclei has been measured with the CBELSA/TAPS detector system for incident photon energies between 1500 - 2200 MeV. The transparency ratio has been ...deduced and compared to theoretical calculations describing the propagation of \eta'-mesons in nuclei. The comparison indicates a width of the \eta' -meson of the order of \Gamma= 15-25 MeV at \rho =\rho_0 for an average momentum p_{\eta'} = 1050 MeV/c, at which the \eta'-meson is produced in the nuclear rest frame. The inelastic \eta' N cross section is estimated to be 3 - 10 mb. Parameterizing the photoproduction cross section of \eta'-mesons by \sigma(A) = \sigma_0 A^{\alpha}, a value of \alpha = 0.84\pm0.03 has been deduced.
The first measurements of the beam-target-helicity-asymmetries \(E\) and \(G\) in the photoproduction of \(\omega\)-mesons off protons at the CBELSA/TAPS experiment are reported. \(E\) (\(G\)) was ...measured using circularly (linearly) polarised photons and a longitudinally polarised target. \(E\) was measured over the photon energy range from close to threshold (\(E_\gamma = 1108\)~MeV) to \(E_\gamma = 2300\)~MeV and \(G\) at a single energy interval of \(1108 < E_\gamma <1300\)~MeV. Both measurements cover the full solid angle. The observables \(E\) and \(G\) are highly sensitive to the contribution of baryon resonances, with \(E\) acting as a helicity filter in the \(s\)-channel. The new results indicate significant \(s\)-channel resonance contributions together with contributions from \(t\)-channel exchange processes. A partial wave analysis reveals strong contributions from the partial waves with spin-parity \(J^P=3/2^+, 5/2^+\), and \(3/2^-\).
Data on the polarization observables T, P, and H for the reaction \(\gamma p\to p\pi^0\) are reported. Compared to earlier data from other experiments, our data are more precise and extend the ...covered range in energy and angle substantially. The results were extracted from azimuthal asymmetries measured using a transversely polarized target and linearly polarized photons. The data were taken at the Bonn electron stretcher accelerator ELSA with the CBELSA/TAPS detector. Within the Bonn-Gatchina partial wave analysis, the new polarization data lead to a significant narrowing of the error band for the multipoles for neutral-pion photoproduction.
In a search for \(\omega\) mesic states, the production of \(\omega\)-mesons in coincidence with forward going protons has been studied in photon induced reactions on \(^{12}\)C for incident photon ...energies of 1250 - 3100 MeV. The \(\pi^0 \gamma\) pairs from decays of bound or quasi-free \(\omega\)-mesons have been measured with the CBELSA/TAPS detector system in coincidence with protons registered in the MiniTAPS forward array. Structures in the total energy distribution of the \(\pi^0 \gamma\) pairs, which would indicate the population and decay of bound \(\omega~^{11}\)B states, are not observed. The \(\pi^0 \gamma\) cross section of 0.3 nb/MeV/sr observed in the bound state energy regime between -100 and 0 MeV may be accounted for by yield leaking into the bound state regime because of the large in-medium width of the \(\omega\)-meson. A comparison of the measured total energy distribution with calculations suggests the real part \(V_0\) of the \(\omega~^{11}\)B potential to be small and only weakly attractive with \(V_0(\rho=\rho_0) = -15\pm\) 35(stat) \(\pm\)20(syst) MeV in contrast to some theoretical predictions of attractive potentials with a depth of 100 - 150 MeV.
14th APS Topical Conference on Atomic Processes in Plasmas,
\'{E}tats-Unis d'Am\'{e}rique (2004) 245 After a brief introduction to the NIST EBIT facility, we present the results
of three different ...types of experiments that have been carried out there
recently: EUV and visible spectroscopy in support of the microelectronics
industry, laboratory astrophysics using an x-ray microcalorimeter, and charge
exchange studies using extracted beams of highly charged ions.
Review of Scientific Instruments 76 (2005) 083102 A custom, flat field, extreme ultraviolet EUV spectrometer built specifically
for use with low power light sources that operate under ultrahigh ...vacuum
conditions is reported. The spectral range of the spectrometer extends from 4
nm to 40 nm. The instrument optimizes the light gathering power and signal to
noise ratio while achieving good resolution. A detailed description of the
spectrometer and design considerations are presented, as well as a novel
procedure that could be used to obtain a synthetic wavelength calibration with
the aid of only a single known spectral feature. This synthetic wavelength
calibration is compared to a standard wavelength calibration obtained from
previously reported spectral lines of Xe, Ar and Ne ions recorded with this
spectrometer.
After a brief introduction to the NIST EBIT facility, we present the results of three different types of experiments that have been carried out there recently: EUV and visible spectroscopy in support ...of the microelectronics industry, laboratory astrophysics using an x-ray microcalorimeter, and charge exchange studies using extracted beams of highly charged ions.
