A
bstract
Several observables for the deeply virtual Compton scattering process have been simulated in the kinematic regime of a proposed Electron-Ion Collider to explore the possible impact of such ...measurements for the phenomenological access of generalized parton distributions. In particular, emphasis is given to the transverse distribution of sea quarks and gluons and how such measurements can provide information on the angular momentum sum rule. The exact lepton energy loss dependence for the unpolarized
t
-differential electroproduction cross section, needed for a Rosenbluth separation, is also reported.
The 3p-1s transition in pionic hydrogen was investigated with a high-resolution crystal spectrometer system. From the precisely measured transition energy, together with the (calculated) ...electromagnetic energy, the strong interaction shift of the 1s state was obtained as
ϵ
1s = −7.127 ± 0.028(stat.)± 0.036(syst.) eV (attractive). From the natural line width, measured for the first time, we determine the decaywidth of the 1s state:
Γ
1s
(decay) = 0.97 ± 0.10(stat.)± 0.05(syst.) eV. With the recently calculated electromagnetic corrections the s-wave scattering lengths of an isospin symmetric strong interaction are deduced. The scattering length for elastic scattering of a negative pion on a proton is
a
π
−
p→
π
−
p
h
= 0.0885±0.00003(stat.)±0.0006(syst.)
m
π
−1. The scattering lengthe for single charge exchange is found to be
a
π
−
p→
π
0
n
h
= −0.136 ± 0.007(stat.) ± 0.003(syst.)
m
π
−1.
The experiment was performed at the Paul Scherrer Institute (PSI) in Switzerland. A focussing crystal spectrometer with an array of bent crystals, the cyclotron trap (a magnetic system designed to increase the particle stop density) and a CCD (charge-coupled device) detector system were employed. The results from the pionic hydrogen experiment — together with those from the pionic deuterium experiment — were used to test the isospin symmetry of the strong interaction. The present data are still consistent with isospin sysmmetry.
The low energy X-rays of the pionic deuterium 3
P-1
S transition were measured using a high resolution crystal spectrometer, together with a cyclotron trap (a magnetic device to increase the pion ...stopping density) and a CCD (charge-coupled device) detector system. The spectrometer resolution was 0.65 eV FWHM for a measured energy of approximately 3075 eV. This energy was measured with a precision of 0.1 eV. Compared to conventional methods, the cyclotron trap allowed for a gain in stopping density of about an order of magnitude. The CCDs had excellent spatial and energy resolutions. Non-X-ray background could therefore be almost completely eliminated. The 1
S strong interaction shift
ϵ
1
S
and total decay width
Γ
1
S
were determined from the position and line shape of the X-ray peak. They are
ϵ
1S(
shift) = 2.43 ± 0.10
eV (
repulsive), Γ
1S(
width) = 1.02 ± 0.21
eV
, where the statistical and systematic errors were added linearly. The total (complex) pionic deuterium
S-wave scattering length
a
π
−
d
was deduced:
a
π
−d
= −0.0259(±0.0011) +
i0.0054(±0.0011)m
π
−1
. From the real part of
a
π
−
d
a constraint in terms of the isoscalar and isovector πN′ scattering lengths
b
0 and
b
1 was deduced. From Im
a
π
−
d
we determined the isoscalar coupling constant for
π
− absorption: |
g
0| = (2.6 ± 0.3) 10
−2
m
π
−2. The experiments of the pionic hydrogen and deuterium
S-wave scattering lengths were analyzed within the framework of a search for i isospin symmetry violation. The data are still compatible with isospin conservation. The scattering lengths deduced from the Karlsruhe-Helsinki phase shift analysis disagree with the present results.
The photon detector of the HERMES dual-radiator RICH Aschenauer, E.C.; Van der Kerckhove, K.
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
08/1999, Letnik:
433, Številka:
1
Journal Article
Recenzirano
To provide hadron identification over the full kinematic range (2–20
GeV) of the HERMES experiment, the gas threshold Cherenkov counters were replaced by a dual-radiator ring-imaging Cherenkov ...detectors incorporating for the first time aerogel (SiO
2) and C
4F
10 gas as radiator materials. This combination of radiators requires a photon detector that is sensitive over wavelengths from ultraviolet to 700
nm. Commercially available `3/4 in.’ photo-multipliers were chosen to form an array of 2000 for each of two photon-detectors. Exhaustive calibration and sorting of the phototubes prior to installation resulted in very low noise hit rates in the LeCroy PCOS4 readout system, with a uniform effective threshold of 0.1 photo-electrons.
A fiber detector concept has been realized allowing to register particles within less than 100
ns with a space point precision of about 100
μm at low occupancy. Three full size prototypes have been ...built by different producers and tested at a 3
GeV electron beam at DESY. After 3
m of light guides 8–10 photoelectrons were registered by multichannel photomultipliers providing an efficiency of more than 99%. Using all available data a resolution of 86
μm was measured.
A systematic study of the mass dependence of meson-exchange currents in the reaction (γ,p) has been carried out. This study became possible with the availability of new high resolution (γ,p) data ...from
12C to
208Pb. In order to determine the relative importance of meson-exchange currents the direct knockout part of the (γ,p) cross section has been constrained by results obtained with the (e,e′p) reaction in similar momentum ranges. It is found that the enhancement of the (γ,p) cross section due to meson-exchange currents reduces by a factor three in going from
12C to
208Pb. This effect is tentatively attributed to the increased importance of higher multipolarities in the description of the coupling to meson exchange currents in heavy nuclei.
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