An exclusive measurement of the decay η→π+π−γ has been performed at the WASA facility at COSY. The η mesons were produced in the fusion reaction pd→He3 X at a proton beam momentum of 1.7 GeV/c. ...Efficiency corrected differential distributions have been extracted based on 13960±140 events after background subtraction. The measured pion angular distribution is consistent with a relative p-wave of the two-pion system, whereas the measured photon energy spectrum was found at variance with the simplest gauge invariant matrix element of η→π+π−γ. A parameterization of the data can be achieved by the additional inclusion of the empirical pion vector form factor multiplied by a first-order polynomial in the squared invariant mass of the π+π− system.
The WASA detector facility at CELSIUS Bargholtz, Chr; Bashkanov, M.; Berłowski, M. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
09/2008, Letnik:
594, Številka:
3
Journal Article
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The WASA
4
π
multidetector system, aimed at investigating light meson production in light ion collisions and
η
meson rare decays at the CELSIUS storage ring in Uppsala is presented. A unique feature ...of the system is the use of hydrogen pellets as internal targets for the first time. A detailed description of the design, together with the anticipated and achieved performance parameters are given.
A programmable fast trigger system for the WASA experiment at The Svedberg Laboratory, Uppsala, Sweden is presented. For minimum signal delay times the hardware architecture is divided into two ...levels. The first level mainly handles fast signals from about 350 plastic scintillating detectors forming hit cluster multiplicity decision, restricting the total number of reaction products. Track alignment checks, coplanarity and deposited energy checks put further restrictions on the acquired events. The first level incorporates 40 generic trigger modules, prescalers, scalers, and pattern units. To minimize dead-time losses the first level is working in a feed-through mode with no external strobe signals required, the total delay amounts to 120 ns. The second level utilizes a fast cluster finding algorithm implemented in 40 trigger modules operating on signals from an array of 24/spl times/48 CsI crystals. Background is filtered away by restricting the spatial distribution and the number of reaction products. The output from the cluster analyzing second level is provided within 115 ns. The trigger utilizes programmable logic devices and. is fully reconfigurable. An I/sup 2/C-based slow control system is provided for setting discriminator thresholds, pulse duration, channel masking, signal delay, and setup of logic conditions.
The P ¯ ANDA (anti-Proton ANnihiliation at DArmstadt) experiment will be one of the four flagship experiments at the new international accelerator complex FAIR (Facility for Antiproton and Ion ...Research) in Darmstadt, Germany. P ¯ ANDA will address fundamental questions of hadron physics and quantum chromodynamics using high-intensity cooled antiproton beams with momenta between 1.5 and 15 GeV/c and a design luminosity of up to 2 × 1032 cm−2 s−1. Excellent particle identification (PID) is crucial to the success of the P ¯ ANDA physics program. Hadronic PID in the barrel region of the target spectrometer will be performed by a fast and compact Cherenkov counter using the detection of internally reflected Cherenkov light (DIRC) technology. It is designed to cover the polar angle range from 22° to 140° and will provide at least 3 standard deviations (s.d.) π/K separation up to 3.5 GeV/c, matching the expected upper limit of the final state kaon momentum distribution from simulation. This documents describes the technical design and the expected performance of the P ¯ ANDA Barrel DIRC detector. The design is based on the successful BaBar DIRC with several key improvements. The performance and system cost were optimized in detailed detector simulations and validated with full system prototypes using particle beams at GSI and CERN. The final design meets or exceeds the PID goal of clean π/K separation with at least 3 s.d. over the entire phase space of charged kaons in the Barrel DIRC.
The development of the NNBAR experiment Backman, F.; Barrow, J.; Beßler, Y. ...
Journal of instrumentation,
10/2022, Letnik:
17, Številka:
10
Journal Article
Low-energy spectator protons (p
s) from quasi-free proton–neutron interactions on deuterium have been measured for the pd→dπ
0p
s and pd→pnπ
0p
s reactions at the CELSIUS storage ring of the The ...Svedberg Laboratory. The experiment used 320 MeV protons incident on a deuterium cluster-jet target. The spectator protons were detected inside the scattering chamber using a silicon detector system which is compatible with a high vacuum. The low target density allows the spectator proton emerge without undergoing significant secondary scattering. Its measurement is therefore a useful tag upon such reactions, allowing cross-sections for quasi-free reactions to be deduced at well-defined centre-of-mass energies. The comparison with the simulation for the pd→dπ
0p
s reaction shows that the energy dependence of the pn→dπ
0 cross-section can be extracted near the threshold. The method greatly improves the experimental resolution achievable in quasi-free p–n reaction studies.
This paper summarises a comprehensive Monte Carlo simulation study for precision resonance energy scan measurements. Apart from the proof of principle for natural width and line shape measurements of ...very narrow resonances with PANDA, the achievable sensitivities are quantified for the concrete example of the charmonium-like X(3872) state discussed to be exotic, and for a larger parameter space of various assumed signal cross-sections, input widths and luminosity combinations. PANDA is the only experiment that will be able to perform precision resonance energy scans of such narrow states with quantum numbers of spin and parities that differ from JPC=1--.
Exclusive measurements of the production of
η-mesons in the
pp→
ppη reaction have been carried out at excess energies of 16 and 37 MeV above threshold. The deviations from phase space are dominated ...by the proton-proton final state interaction and this influences particularly the energy distribution of the
η-meson. However, evidence is also presented at the higher energy for the existence of an anisotropy in the angular distributions of the
η-meson and also of the final proton-proton pair, probably to be associated with
D-waves in this system interfering with the dominant
S-wave term. The sign of the
η angular anisotropy suggests that
ρ-exchange is important for this reaction.
Exclusive measurements of the pp -> pp pi(0)pi(0) reaction have been performed at CELSIUS/WASA at energies from threshold up to T(p) = 1.3 GeV. Total and differential cross sections have been ...obtained. Here we concentrate on energies T(p) >= GeV. where the Delta Delta excitation becomes the leading process. No evidence is found for a significant ABC effect beyond that given by the conventional t-channel Delta Delta excitation. This holds also for the double-pionic fusion to the quasibound (2)He. The data are compared to model predictions, which are based on both pi- and rho-exchange. Total and differential cross sections are at variance with these predictions and call for a profound modification of the rho-exchange. A phenomenological modification allowing only a small rho-exchange contribution leads to a quantitative description of the data.
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