The ABC effect-a puzzling low-mass enhancement in the pipi invariant mass spectrum, first observed by Abashian, Booth, and Crowe-is well known from inclusive measurements of two-pion production in ...nuclear fusion reactions. Here we report on the first exclusive and kinematically complete measurements of the most basic double-pionic fusion reaction pn-->dpi;{0}pi;{0} at beam energies of 1.03 and 1.35 GeV. The measurements, which have been carried out at CELSIUS-WASA, reveal the ABC effect to be a (pipi)_{I=L=0} channel phenomenon associated with both a resonancelike energy dependence in the integral cross section and the formation of a DeltaDelta system in the intermediate state. A corresponding simple s-channel resonance ansatz provides a surprisingly good description of the data.
A digital algorithm for real-time feature extraction, i.e. determination of pulse amplitude and timing, has been developed for the forward-spectrometer electromagnetic calorimeter in the PANDA ...experiment. The algorithm, which is based on the well known optimal-filter algorithm, has been designed to allow reconstruction of pile-up signals in real time and to work in a free-running DAQ system such as PANDA. To benchmark the algorithm, a Geant4-based Monte Carlo model of photon interactions in the calorimeter has been developed to generate realistic detector signals which were used as inputs to a VHDL simulation of the algorithm. The results of this simulation study show that the developed algorithm improves the time resolution by almost 50% compared to a conventional linear constant fraction discriminator algorithm. For the PANDA calorimeter, this results in a time resolution close to 100 ps/GeV per detector element at high energies. The algorithm allows reconstruction of the amplitude and timing of pile-up pulses separated by as little as 30 ns with good efficiency, fulfilling the PANDA requirements.
PANDA Phase One Liu, Z.; Liu, B.; Shen, X. ...
The European physical journal. A, Hadrons and nuclei,
06/2021, Letnik:
57, Številka:
6
Journal Article
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Odprti dostop
The Facility for Antiproton and Ion Research (FAIR) in Darmstadt, Germany, provides unique possibilities for a new generation of hadron-, nuclear- and atomic physics experiments. The future ...antiProton ANnihilations at DArmstadt (PANDA or
P
¯
ANDA) experiment at FAIR will offer a broad physics programme, covering different aspects of the strong interaction. Understanding the latter in the non-perturbative regime remains one of the greatest challenges in contemporary physics. The antiproton–nucleon interaction studied with PANDA provides crucial tests in this area. Furthermore, the high-intensity, low-energy domain of PANDA allows for searches for physics beyond the Standard Model,
e.g.
through high precision symmetry tests. This paper takes into account a staged approach for the detector setup and for the delivered luminosity from the accelerator. The available detector setup at the time of the delivery of the first antiproton beams in the HESR storage ring is referred to as the
Phase One
setup. The physics programme that is achievable during Phase One is outlined in this paper.
In this work properties of a vacuum phototriode (VPT) and preamplifier unit designed for the electromagnetic calorimeter of the PANDA experiment being built at FAIR are investigated. With the use of ...lead tungstate and lanthanium bromide scintillators the VPT properties are studied at low photon energies, from tens of keV in the lanthanium bromide measurements and between 10MeV and 60MeV in the lead tungstate measurements. At these energies the noise of the VPT unit can be expected to influence its performance significantly. It is shown that the noise contribution to the measured energy resolution, under optimal conditions, is consistent with a fluctuation of (one standard deviation) approximately 200 electrons at the VPT anode. For a lead tungstate crystal this is equivalent to a noise of 1.2MeV. For lanthanium bromide this makes it possible to use VPTs for gamma ray spectroscopy above a few hundreds of keV without noticeable effects on the energy resolution compared to measurements with a standard photomultiplier.
This paper addresses questions of community and patch stability as defined by the population biology of dominant plants in the context of different areas within a large kelp forest. We ask (1) @'Do ...large-scale episodic events override biological mechanisms as major community structuring processes?@', (2) @'Are different local areas characterized by different processes?@', and (3) @'How persistent are the patches or biological structure over decal and local spatial scales?@' We evaluate these questions with regard to the effects of various types of disturbance for as much as three decades on the populations of several species of kelp in the large kelp forest off Point Loma, San Diego, California. The most sensitive population factors we studied include recruitment, density, and survivorship. Patch stability was evaluated with regard to the persistence of patches already well established in 1971-1972. The study sites offer a cross-shore transect through the central part of a large kelp forest at depths of 8, 12, 15, 18, and 21 m; two additional sites at the north and south ends of the forest offer a longshore transect along the 18-m contour. There were marked differences among the decades with regard to the intensity of the disturbances. Compared with the 1980s, the two preceding decades were relatively benign. The 1980s had two extreme disturbance events: the 1982-1984 El Gino-Southern Oscillation (ENSO) was the most severe El Nino event in the last century, which included very warm, nutrient-depleted water, and a short but intense storm in January 1988 appeared to have been the most severe in perhaps 200 yr. The storm changed age-specific kelp mortality patterns and caused the first large-scale understory mortality in several decades. By sweeping away drift algae it caused intense local urchin grazing. The storm was followed by a strong La Nina event marked by cool, nutrient-rich water in 1988-1989. Differences in kelp recruitment and survivorship in different areas of the kelp forest are influenced by gradients in longshore currents, temperature, light, wave energy, floc, planktonic propagules, and physical disturbance. The areas are characterized by different plant population patterns and the effects of several species of herbivores. The massive disturbances of the 1980s obliterated much of the structure in the kelp forest. Certainly the disturbances caused many lag effects including outbreaks of understory algae such as Desmarestia ligulata, intraspecific competition, changes in grazing patterns, etc., which in turn resulted in between-area variation in recovery rates. However, in all cases this variation was overshadowed by the overwhelming competitive dominance of Macrocystis pyrifera. Most of the understory patches on the transect lines, some of which had persisted for 7 yr, died out by the end of 1990. The population biology of Macrocystis was remarkably similar in most areas, as the cohort longevity and survivorship curves were very similar, and the plant and stipe densities tended to level off in only a few years. Thus large-scale episodic events such as El Ninos, La Ninas, and rare storms exert dramatic impacts, but small-scale responses such as density-vague recruitment (neither density dependent nor density independent) and survival allow prompt recovery, often to preexisting patterns. The one exception was the southern site, which was marked by sea urchin grazing and poor kelp recruitment through the latter half of the 1980s, but a recent sea urchin disease event has led to kelp recruitment in fall 1991. A seeming paradox to the observed Macrocystis dominance is that in almost all areas, some understory patches of old plants have persisted through the 1980s.
Performance of HPGe detectors in high magnetic fields Sanchez Lorente, A.; Achenbach, P.; Agnello, M. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
2007, Letnik:
573, Številka:
3
Journal Article
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Odprti dostop
A new generation of high-resolution hypernuclear
γ
-spectroscopy experiments with high-purity germanium detectors (HPGe) are presently designed at the FINUDA spectrometer at DA
Φ
NE, the Frascati
φ
...-factory, and at
P
¯
ANDA, the
p
¯
p
hadron spectrometer at the future FAIR facility. Both, the FINUDA and
P
¯
ANDA
spectrometers are built around the target region covering a large solid angle. To maximise the detection efficiency the HPGe detectors have to be located near the target, and therefore they have to be operated in strong magnetic fields (
B
≈
1
T
). The performance of HPGe detectors in such an environment has not been well investigated so far. In the present work VEGA and EUROBALL Cluster HPGe detectors were tested in the field provided by the ALADiN magnet at GSI. No significant degradation of the energy resolution was found, and a change in the rise time distribution of the pulses from preamplifiers was observed. A correlation between rise time and pulse height was observed and is used to correct the measured energy, recovering the energy resolution almost completely. Moreover, no problems in the electronics due to the magnetic field were observed.
The exclusive charmonium production process in p¯p annihilation with an associated π0 meson p¯p→J/ψπ0 is studied in the framework of QCD collinear factorization. The feasibility of measuring this ...reaction through the J/ψ→e+e− decay channel with the AntiProton ANnihilation at DArmstadt (P¯ANDA) experiment is investigated. Simulations on signal reconstruction efficiency as well as the background rejection from various sources including the p¯p→π+π−π0 and p¯p→J/ψπ0π0 reactions are performed with PandaRoot, the simulation and analysis software framework of the P¯ANDA experiment. It is shown that the measurement can be done at P¯ANDA with significant constraining power under the assumption of an integrated luminosity attainable in four to five months of data taking at the maximum design luminosity.
.
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
J
P
C
=
1
-
-
.
The ABC effect–an intriguing low-mass enhancement in the
π
π
invariant mass spectrum–is known from inclusive measurements of two-pion production in nuclear fusion reactions. First exclusive ...measurements carried out at CELSIUS-WASA for the fusion reactions leading to d or
3He reveal this effect to be a
σ
-channel phenomenon associated with the formation of a
Δ
Δ
system in the intermediate state and combined with a resonance-like behavior in the total cross-section. Together with the observation that the differential distributions do not change in shape over the resonance region the features fulfill the criteria of an isoscalar s-channel resonance in
p
n
and
N
N
π
π
systems, if the two emitted nucleons are bound. It obviously is robust enough to survive in nuclei as a dibaryonic resonance configuration. In this context also the phenomenon of
N
Δ
resonances is reexamined.
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
Recenzirano
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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.
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