We report the measurement of K− absorption processes in the Σ0p final state and the first exclusive measurement of the two nucleon absorption (2NA) with the KLOE detector. The 2NA process without ...further interactions is found to be 9% of the sum of all other contributing processes, including absorption on three and more nucleons or 2NA followed by final state interactions with the residual nucleons. We also determine the possible contribution of the ppK− bound state to the Σ0p final state. The yield of ppK−/Kstop− is found to be (0.044±0.009stat−0.005+0.004syst)⋅10−2 but its statistical significance based on an F-test is only 1σ.
A novel whole-body positron emission tomography (PET) system based on plastic scintillators is developed by the J-PET Collaboration. It consists of plastic scintillator strips arranged axially in the ...form of a cylinder, allowing the cost-effective construction of the total-body PET system. In order to determine the properties of the scanner prototype and optimize its geometry, advanced computer simulations were performed using the GATE (Geant4 application for tomographic emission) software. The spatial resolution, sensitivity, scatter fraction and noise equivalent count rate were estimated according to the National Electrical Manufacturers Association norm, as a function of the length of the tomograph, the number of detection layers, the diameter of the tomographic chamber and for various types of applied readout. For the single-layer geometry with a diameter of 85 cm, a strip length of 100 cm, a cross-section of 4 mm × 20 mm and silicon photomultipliers with an additional layer of wavelength shifter as the readout, the spatial resolution (full width at half maximum) in the centre of the scanner is equal to 3 mm (radial, tangential) and 6 mm (axial). For the analogous double-layer geometry with the same readout, diameter and scintillator length, with a strip cross-section of 7 mm × 20 mm, a noise equivalent count rate peak of 300 kcps was reached at 40 kBq cc−1 activity concentration, the scatter fraction is estimated to be about 35% and the sensitivity at the centre amounts to 14.9 cps kBq−1. Sensitivity profiles were also determined.
The absolute branching ratio of the K+→π+π−π+(γ) decay, inclusive of final-state radiation, has been measured using ∼17 million tagged K+ mesons collected with the KLOE detector at DAΦNE, the ...Frascati ϕ-factory. The result is:BR(K+→π+π−π+(γ))=0.05565±0.00031stat±0.00025syst a factor ≃ 5 more precise with respect to the previous result. This work completes the program of precision measurements of the dominant kaon branching ratios at KLOE.
We present a study of the application of the Jagiellonian positron emission tomograph (J-PET) for the registration of gamma quanta from decays of ortho-positronium (o-Ps). The J-PET is the first ...positron emission tomography scanner based on organic scintillators in contrast to all current PET scanners based on inorganic crystals. Monte Carlo simulations show that the J-PET as an axially symmetric and high acceptance scanner can be used as a multi-purpose detector well suited to pursue research including e.g. tests of discrete symmetries in decays of ortho-positronium in addition to the medical imaging. The gamma quanta originating from o-Ps decay interact in the plastic scintillators predominantly via the Compton effect, making the direct measurement of their energy impossible. Nevertheless, it is shown in this paper that the J-PET scanner will enable studies of the
o-Ps
→
3
γ
decays with angular and energy resolution equal to
σ
(
θ
)
≈
0
.
4
∘
and
σ
(
E
)
≈
4.1
keV
, respectively. An order of magnitude shorter decay time of signals from plastic scintillators with respect to the inorganic crystals results not only in better timing properties crucial for the reduction of physical and instrumental background, but also suppresses significantly the pile-ups, thus enabling compensation of the lower efficiency of the plastic scintillators by performing measurements with higher positron source activities.
J-PET is a detector optimized for registration of photons from the electron–positron annihilation via plastic scintillators where photons interact predominantly via Compton scattering. Registration ...of both primary and scattered photons enables to determinate the linear polarization of the primary photon on the event by event basis with a certain probability. Here we present quantitative results on the feasibility of such polarization measurements of photons from the decay of positronium with the J-PET and explore the physical limitations for the resolution of the polarization determination of 511 keV photons via Compton scattering. For scattering angles of about 82
∘
(where the best contrast for polarization measurement is theoretically predicted) we find that the single event resolution for the determination of the polarization is about 40
∘
(predominantly due to properties of the Compton effect). However, for samples larger than ten thousand events the J-PET is capable of determining relative average polarization of these photons with the precision of about few degrees. The obtained results open new perspectives for studies of various physics phenomena such as quantum entanglement and tests of discrete symmetries in decays of positronium and extend the energy range of polarization measurements by five orders of magnitude beyond the optical wavelength regime.
HADES is a running spectrometer installed at GSI, Germany. PANDA and CBM are planned detector systems for the new FAIR facility at GSI. For these detectors, a general-purpose trigger and readout ...board with on-board DAQ functionality was developed. The original motivation for this project was the implementation of a 128-channel time to digital converter (TDC) with a time resolution of sigma=40 ps based on the HPTDC chip from CERN into a fully fledged data acquisition system. The application of the board is detector independent, includes a 2 Gbit/s optical link and has the option to employ the TDC chips and/or to integrate versatile add-on boards through 16 Gbit/s connectors. The latter one may interface to the front end electronics of other types of detectors. A large FPGA (Xilinx Virtex 4 LX40) and a TigerSharc DSP can be used as on-board resources for trigger and on-line analysis algorithms. Data transfer to mass storage and slow control is done via an ETRAX processor running Linux and a 100 Mbit/s Ethernet interface.
•Parallel reconstruction of each emission is a foundation for real-time PET imaging.•Image domain asymmetric 3-component kernel and time-of-flight used for filtering.•High time resolution and ...low-pass filters are the cornerstones for short scans.•Optimal kernel parameters can be trained for the best bias-variance trade-off.
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We perform a parametric study of the newly developed time-of-flight (TOF) image reconstruction algorithm, proposed for the real-time imaging in total-body Jagiellonian PET (J-PET) scanners. The asymmetric 3D filtering kernel is applied at each most likely position of electron-positron annihilation, estimated from the emissions of back-to-back γ-photons. The optimisation of its parameters is studied using Monte Carlo simulations of a 1-mm spherical source, NEMA IEC and XCAT phantoms inside the ideal J-PET scanner. The combination of high-pass filters which included the TOF filtered back-projection (FBP), resulted in spatial resolution, 1.5 times higher in the axial direction than for the conventional 3D FBP. For realistic 10-minute scans of NEMA IEC and XCAT, which require a trade-off between the noise and spatial resolution, the need for Gaussian TOF kernel components, coupled with median post-filtering, is demonstrated. The best sets of 3D filter parameters were obtained by the Nelder-Mead minimisation of the mean squared error between the resulting and reference images. The approach allows training the reconstruction algorithm for custom scans, using the IEC phantom, when the temporal resolution is below 50 ps. The image quality parameters, estimated for the best outcomes, were systematically better than for the non-TOF FBP.
The AMADEUS collaboration studied the K− absorptions at low momentum in light nuclei leading to Σ0p final state. Those events were recorded by the KLOE detector, used as an active target, installed ...in the the DAΦNE collider. The results show that it is possible to isolate the process where the K− is absorbed by two nucleons and the decay products are emitted without any further final state interactions among other contributions involving more than two nucleons. Further, the possible contribution of a ppK− bound state was investigated. The best fit gives space to a yield of ppK−/Kstop− = (0.044 ± 0.009 stat−0.005+0.004) × 10−2 corresponding to a binding energy and a width of 45 and 30 MeV/c2, respectively. A statistical analysis of this result shows although that its significance is only at the level of 1σ.
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