1,142 research outputs found
Polarised target for Drell-Yan experiment in COMPASS at CERN, part I
In the polarised Drell-Yan experiment at the COMPASS facility in CERN pion
beam with momentum of 190 GeV/c and intensity about pions/s interacted
with transversely polarised NH target. Muon pairs produced in Drel-Yan
process were detected. The measurement was done in 2015 as the 1st ever
polarised Drell-Yan fixed target experiment. The hydrogen nuclei in the
solid-state NH were polarised by dynamic nuclear polarisation in 2.5 T
field of large-acceptance superconducting magnet. Large helium dilution
cryostat was used to cool the target down below 100 mK. Polarisation of
hydrogen nuclei reached during the data taking was about 80 %. Two oppositely
polarised target cells, each 55 cm long and 4 cm in diameter were used.
Overview of COMPASS facility and the polarised target with emphasis on the
dilution cryostat and magnet is given. Results of the polarisation measurement
in the Drell-Yan run and overviews of the target material, cell and dynamic
nuclear polarisation system are given in the part II.Comment: 4 pages, 2 figures, Proceedings of the 22nd International Spin
Symposium, Urbana-Champaign, Illinois, USA, 25-30 September 201
Near-threshold Lambda(1520) production by the gamma p -> K+Lambda(1520) reaction at forward K+ angles
Differential cross sections and photon-beam asymmetries for the gamma p -> K+
Lambda(1520) reaction have been measured with linearly polarized photon beams
at energies from the threshold to 2.4 GeV at 0.6<cos(theta)<1. A new bump
structure was found at W=2.11 GeV in the cross sections. The bump is not well
reproduced by theoretical calculations introducing a nucleon resonance with
J<=3/2. This result suggests that the bump might be produced by a nucleon
resonance possibly with J>=5/2 or by a new reaction process, for example an
interference effect with the phi photoproduction having a similar bump
structure in the cross sections.Comment: 5 pages, 4 figures, published in Phys. Rev. Let
Backward-angle photoproduction of mesons on the proton at = 1.5--2.4 GeV
Differential cross sections and photon beam asymmetries for
photoproduction have been measured at = 1.5--2.4 GeV and at the
scattering angles, --1 cos --0.6. The
energy-dependent slope of differential cross sections for -channel
production has been determined. An enhancement at backward angles is found
above = 2.0 GeV. This is inferred to be due to the -channel
contribution and/or resonances. Photon beam asymmetries have been obtained for
the first time at backward angles. A strong angular dependence has been found
at 2.0 GeV, which may be due to the unknown high-mass resonances.Comment: 12 pages, 4 figures, submitted to PL
Measurement of the Reaction at Backward Angles
Cross sections for the have been measured at
backward angles using linearly polarized photons in the range 1.50 to 2.37 GeV.
In addition, the beam asymmetry for this reaction has been measured for the
first time at backward angles. The was detected at forward angles in
the LEPS spectrometer via its decay to and the K^+ was inferred using
the technique of missing mass. These measurements, corresponding to kaons at
far backward angles in the center-of-mass frame, complement similar CLAS data
at other angles. Comparison with theoretical models shows that the reactions in
these kinematics provide further opportunities to investigate the reaction
mechanisms of hadron dynamics.Comment: 6 figures, submitted to PRC rapid communication
Development of Hydrophones for Detecting High-Energy Reactions in Water(III. Accelerator, Synchrotron Radiation, and Instrumentation)
Acoustic detectors were developed using a piezo ceramic compound PZT. A shape of the PZT detector was essential to obtain a high sensitivity. A detector of a spherically shaped shell structure, whose size was 50 mm in diameter and 2 mm thick, was fabricated. Its sensitivity was calibrated to be about 40 mV/Pa at 54 kHz. Using the hydrophone, acoustic signals generated by an electron-induced cascade shower in water were detected. Experimental results were compared with simulation data and confirmed a consistency in between
Forward coherent -meson photoproduction from deuterons near threshold
Differential cross sections and decay asymmetries for coherent -meson
photoproduction from deuterons were measured for the first time at forward
angles using linearly polarized photons at = 1.5-2.4 GeV. This
reaction offers a unique way to directly access natural-parity Pomeron dynamics
and gluon exchange at low energies. The cross sections at zero degrees increase
with increasing photon energy. The decay asymmetries demonstrate a complete
dominance of natural-parity exchange processes, showing that isovector
unnatural-parity -meson exchange is small. Nevertheless the deduced cross
sections of -mesons from nucleons contributed by isoscalar t-channel
exchange processes are not well described by the conventional Pomeron model.Comment: 14 pages, 6 figures. Final published versio
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