251 research outputs found
Resonance-like coherent production of a pion pair in the reaction in the GeV region
The reaction was studied at 0.8-2.0 GeV proton
beam energies with the ANKE magnetic spectrometer at the COSY synchrotron
storage ring. The proton-deuteron pairs emerging with high momenta, 0.6-1.8
GeV/, were detected at small angles with respect to the proton beam.
Distribution over the reaction missing mass reveals a local enhancement
near the threshold of the pion pair production specific for the so-called ABC
effect. The enhancement has a structure of a narrow bump placed above a smooth
continuum. The invariant mass of the system in this enhancement
region exhibits a resonance-like peak at GeV/
with the width GeV/. A possible interpretation of
these features is discussed.Comment: 14 pages, 16 figures, submitted to Eur. Phys. J. A. v2: Added
references [42,43] in section IV.A. v3: revised version according to referee
remarks v4: revised version according to referee remark
Measurement of the analysing power in proton-proton elastic scattering at small angles
The proton analysing power in elastic scattering has been measured
at small angles at COSY-ANKE at 796 MeV and five other beam energies between
1.6 and 2.4 GeV using a polarised proton beam. The asymmetries obtained by
detecting the fast proton in the ANKE forward detector or the slow recoil
proton in a silicon tracking telescope are completely consistent. Although the
analysing power results agree well with the many published data at 796 MeV, and
also with the most recent partial wave solution at this energy, the ANKE data
at the higher energies lie well above the predictions of this solution at small
angles. An updated phase shift analysis that uses the ANKE results together
with the World data leads to a much better description of these new
measurements.Comment: 5 pages, 3 figure
Measurement of the analyzing powers in pd elastic and pn quasi-elastic scattering at small angles
The analyzing powers in proton-deuteron elastic and proton-neutron
quasi-elastic scattering have been measured at small angles using a polarized
proton beam at the COSY storage ring incident on an unpolarized deuterium
target. The data were taken at 796MeV and five higher energies from 1600MeV to
2400MeV. The analyzing power in pd elastic scattering was studied by detecting
the low energy recoil deuteron in telescopes placed symmetrically in the COSY
plane to the left and right of the beam whereas for pn quasi-elastic scattering
a low energy proton was registered in one of the telescopes in coincidence with
a fast scattered proton measured in the ANKE magnetic spectrometer. Though the
experiment explores new domains, the results are consistent with the limited
published information.Comment: 10 pages with 8 figure
Measurement of the absolute differential cross section of proton-proton elastic scattering at small angles
The differential cross section for proton-proton elastic scattering has been
measured at a beam energy of 1.0 GeV and in 200 MeV steps from 1.6 to 2.8 GeV
for centre-of-mass angles in the range from 12-16 degrees to 25-30 degrees,
depending on the energy. Absolute normalisations of typically 3% were achieved
by studying the energy losses of the circulating beam of the COSY storage ring
as it passed repeatedly through the windowless hydrogen target of the ANKE
magnetic spectrometer. It is shown that the data have a significant impact upon
a partial wave analysis. After extrapolating the differential cross sections to
the forward direction, the results are broadly compatible with the predictions
of forward dispersion relations
Phase Measurement for Driven Spin Oscillations in a Storage Ring
This paper reports the first simultaneous measurement of the horizontal and
vertical components of the polarization vector in a storage ring under the
influence of a radio frequency (rf) solenoid. The experiments were performed at
the Cooler Synchrotron COSY in J\"ulich using a vector polarized, bunched
deuteron beam. Using the new spin feedback system, we
set the initial phase difference between the solenoid field and the precession
of the polarization vector to a predefined value. The feedback system was then
switched off, allowing the phase difference to change over time, and the
solenoid was switched on to rotate the polarization vector. We observed an
oscillation of the vertical polarization component and the phase difference.
The oscillations can be described using an analytical model. The results of
this experiment also apply to other rf devices with horizontal magnetic fields,
such as Wien filters. The precise manipulation of particle spins in storage
rings is a prerequisite for measuring the electric dipole moment (EDM) of
charged particles
Spin tune mapping as a novel tool to probe the spin dynamics in storage rings
Precision experiments, such as the search for electric dipole moments of
charged particles using storage rings, demand for an understanding of the spin
dynamics with unprecedented accuracy. The ultimate aim is to measure the
electric dipole moments with a sensitivity up to 15 orders in magnitude better
than the magnetic dipole moment of the stored particles. This formidable task
requires an understanding of the background to the signal of the electric
dipole from rotations of the spins in the spurious magnetic fields of a storage
ring. One of the observables, especially sensitive to the imperfection magnetic
fields in the ring is the angular orientation of stable spin axis. Up to now,
the stable spin axis has never been determined experimentally, and in addition,
the JEDI collaboration for the first time succeeded to quantify the background
signals that stem from false rotations of the magnetic dipole moments in the
horizontal and longitudinal imperfection magnetic fields of the storage ring.
To this end, we developed a new method based on the spin tune response of a
machine to artificially applied longitudinal magnetic fields. This novel
technique, called \textit{spin tune mapping}, emerges as a very powerful tool
to probe the spin dynamics in storage rings. The technique was experimentally
tested in 2014 at the cooler synchrotron COSY, and for the first time, the
angular orientation of the stable spin axis at two different locations in the
ring has been determined to an unprecedented accuracy of better than
rad.Comment: 32 pages, 15 figures, 7 table
Phase locking the spin precession in a storage ring
This letter reports the successful use of feedback from a spin polarization
measurement to the revolution frequency of a 0.97 GeV/ bunched and polarized
deuteron beam in the Cooler Synchrotron (COSY) storage ring in order to control
both the precession rate ( kHz) and the phase of the horizontal
polarization component. Real time synchronization with a radio frequency (rf)
solenoid made possible the rotation of the polarization out of the horizontal
plane, yielding a demonstration of the feedback method to manipulate the
polarization. In particular, the rotation rate shows a sinusoidal function of
the horizontal polarization phase (relative to the rf solenoid), which was
controlled to within a one standard deviation range of rad. The
minimum possible adjustment was 3.7 mHz out of a revolution frequency of 753
kHz, which changes the precession rate by 26 mrad/s. Such a capability meets a
requirement for the use of storage rings to look for an intrinsic electric
dipole moment of charged particles
Measurement of deuteron carbon vector analyzing powers in the kinetic energy range 170-380 MeV
A measurement of vector analyzing powers in elastic deuteron-carbon
scattering has been performed at the Cooler Synchrotron COSY of
Forschungszentrum J\"ulich, Germany. Seven kinetic beam energies between 170
and 380 MeV have been used. A vector-polarized beam from a polarized deuteron
source was injected, accelerated to the final desired energy and stored in
COSY. A thin needle-shaped diamond strip was used as a carbon target, onto
which the beam was slowly steered. Elastically scattered deuterons were
identified in the forward direction using various layers of scintillators and
straw tubes. Where data exist in the literature (at 200 and 270 MeV), excellent
agreement of the angular shape was found. The beam polarization of the
presented data was deduced by fitting the absolute scale of the analyzing power
to these references. Our results extend the world data set and are necessary
for polarimetry of future electric dipole moment searches at storage rings.
They will as well serve as an input for theoretical description of polarized
hadron-hadron scattering
Experimental Detection of the CNO Cycle
Borexino recently reported the first experimental evidence for a CNO neutrino. Since this process accounts for only about 1% of the Sun’s total energy production, the associated neutrino flux is remarkably low compared to that of the pp chain, the dominant hydrogen-burning process. This experimental evidence for the existence of CNO neutrinos was obtained using a highly radio-pure Borexino liquid scintillator. Improvements in the thermal stabilization of the detector over the last five years have allowed us to exploit a method of constraining the rate of 210Bi background. Since the CNO cycle is dominant in massive stars, this result is the first experimental evidence of a major stellar hydrogen-to-helium conversion mechanism in the Universe
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