526 research outputs found
Virtual depth by active background suppression: Revisiting the cosmic muon induced background of GERDA Phase II
In-situ production of long-lived isotopes by cosmic muon interactions may
generate a non-negligible background for deep underground rare event searches.
Previous Monte Carlo studies for the GERDA experiment at LNGS identified the
delayed decays of Ge and its metastable state Ge as dominant
cosmogenic background in the search for neutrinoless double beta decay of
Ge. This might limit the sensitivity of next generation experiments
aiming for increased Ge mass at background-free conditions and thereby
define a minimum depth requirement. A re-evaluation of the Ge
background for the GERDA experiment has been carried out by a set of Monte
Carlo simulations. The obtained Ge production rate is (0.210.01)
nuclei/(kgyr). After application of state-of-the-art active background
suppression techniques and simple delayed coincidence cuts this corresponds to
a background contribution of (2.70.3)
cts/(keVkgyr). The suppression achieved by this strategy equals
an effective muon flux reduction of more than one order of magnitude. This
virtual depth increase opens the way for next generation rare event searches.Comment: 9 pages, 5 figure
A hydrogen beam to characterize the ASACUSA antihydrogen hyperfine spectrometer
The antihydrogen programme of the ASACUSA collaboration at the antiproton
decelerator of CERN focuses on Rabi-type measurements of the ground-state
hyperfine splitting of antihydrogen for a test of the combined
Charge-Parity-Time symmetry. The spectroscopy apparatus consists of a microwave
cavity to drive hyperfine transitions and a superconducting sextupole magnet
for quantum state analysis via Stern-Gerlach separation. However, the small
production rates of antihydrogen forestall comprehensive performance studies on
the spectroscopy apparatus. For this purpose a hydrogen source and detector
have been developed which in conjunction with ASACUSA's hyperfine spectroscopy
equipment form a complete Rabi experiment. We report on the formation of a
cooled, polarized, and time modulated beam of atomic hydrogen and its detection
using a quadrupole mass spectrometer and a lock-in amplification scheme. In
addition key features of ASACUSA's hyperfine spectroscopy apparatus are
discussed.
Evaluating a radiotherapy deep learning synthetic CT algorithm for PET-MR attenuation correction in the pelvis
\ua9 2024, The Author(s). Background: Positron emission tomography–magnetic resonance (PET-MR) attenuation correction is challenging because the MR signal does not represent tissue density and conventional MR sequences cannot image bone. A novel zero echo time (ZTE) MR sequence has been previously developed which generates signal from cortical bone with images acquired in 65 s. This has been combined with a deep learning model to generate a synthetic computed tomography (sCT) for MR-only radiotherapy. This study aimed to evaluate this algorithm for PET-MR attenuation correction in the pelvis. Methods: Ten patients being treated with ano-rectal radiotherapy received a 18 F-FDG-PET-MR in the radiotherapy position. Attenuation maps were generated from ZTE-based sCT (sCTAC) and the standard vendor-supplied MRAC. The radiotherapy planning CT scan was rigidly registered and cropped to generate a gold standard attenuation map (CTAC). PET images were reconstructed using each attenuation map and compared for standard uptake value (SUV) measurement, automatic thresholded gross tumour volume (GTV) delineation and GTV metabolic parameter measurement. The last was assessed for clinical equivalence to CTAC using two one-sided paired t tests with a significance level corrected for multiple testing of p≤ 0.05 / 7 = 0.007 . Equivalence margins of \ub1 3.5 % were used. Results: Mean whole-image SUV differences were −0.02% (sCTAC) compared to −3.0% (MRAC), with larger differences in the bone regions (−0.5% to −16.3%). There was no difference in thresholded GTVs, with Dice similarity coefficients ≥ 0.987 . However, there were larger differences in GTV metabolic parameters. Mean differences to CTAC in SUV max were 1.0 \ub1 0.8 % (\ub1 standard error, sCTAC) and - 4.6 \ub1 0.9 % (MRAC), and 1.0 \ub1 0.7 % (sCTAC) and - 4.3 \ub1 0.8 % (MRAC) in SUV mean . The sCTAC was statistically equivalent to CTAC within a \ub1 3.5 % equivalence margin for SUV max and SUV mean (p= 0.007 and p= 0.002), whereas the MRAC was not (p= 0.88 and p= 0.83). Conclusion: Attenuation correction using this radiotherapy ZTE-based sCT algorithm was substantially more accurate than current MRAC methods with only a 40 s increase in MR acquisition time. This did not impact tumour delineation but did significantly improve the accuracy of whole-image and tumour SUV measurements, which were clinically equivalent to CTAC. This suggests PET images reconstructed with sCTAC would enable accurate quantitative PET images to be acquired on a PET-MR scanner
A Study of the PDGF Signaling Pathway with PRISM
In this paper, we apply the probabilistic model checker PRISM to the analysis
of a biological system -- the Platelet-Derived Growth Factor (PDGF) signaling
pathway, demonstrating in detail how this pathway can be analyzed in PRISM. We
show that quantitative verification can yield a better understanding of the
PDGF signaling pathway.Comment: In Proceedings CompMod 2011, arXiv:1109.104
A False Start in the Race Against Doping in Sport: Concerns With Cycling’s Biological Passport
Professional cycling has suffered from a number of doping scandals. The sport’s governing bodies have responded by implementing an aggressive new antidoping program known as the biological passport. Cycling’s biological passport marks a departure from traditional antidoping efforts, which have focused on directly detecting prohibited substances in a cyclist’s system. Instead, the biological passport tracks biological variables in a cyclist’s blood and urine over time, monitoring for fluctuations that are thought to indirectly reveal the effects of doping. Although this method of indirect detection is promising, it also raises serious legal and scientific concerns. Since its introduction, the cycling community has debated the reliability of indirect biological-passport evidence and the clarity, consistency, and transparency of its use in proving doping violations. Such uncertainty undermines the legitimacy of finding cyclists guilty of doping based on this indirect evidence alone. Antidoping authorities should address these important concerns before continuing to pursue doping sanctions against cyclists solely on the basis of their biological passports
Ultra-thin polymer foil cryogenic window for antiproton deceleration and storage
We present the design and characterization of a cryogenic window based on an ultra-thin aluminized biaxially oriented polyethylene terephthalate foil at T < 10 K, which can withstand a pressure difference larger than 1 bar at a leak rate < 1 × 1 0 − 9 mbar l/s. Its thickness of ∼1.7 μm makes it transparent to various types of particles over a broad energy range. To optimize the transfer of 100 keV antiprotons through the window, we tested the degrading properties of different aluminum coated polymer foils of thicknesses between 900 and 2160 nm, concluding that 1760 nm foil decelerates antiprotons to an average energy of 5 keV. We have also explicitly studied the permeation as a function of coating thickness and temperature and have performed extensive thermal and mechanical endurance and stress tests. Our final design integrated into the experiment has an effective open surface consisting of seven holes with a diameter of 1 mm and will transmit up to 2.5% of the injected 100 keV antiproton beam delivered by the Antiproton Decelerator and Extra Low ENergy Antiproton ring facility of CERN
Characterization of 30 Ge enriched Broad Energy Ge detectors for GERDA Phase II
The GERmanium Detector Array (GERDA) is a low background experiment located
at the Laboratori Nazionali del Gran Sasso in Italy, which searches for
neutrinoless double beta decay of Ge into Se+2e. GERDA has
been conceived in two phases. Phase II, which started in December 2015,
features several novelties including 30 new Ge detectors. These were
manufactured according to the Broad Energy Germanium (BEGe) detector design
that has a better background discrimination capability and energy resolution
compared to formerly widely-used types. Prior to their installation, the new
BEGe detectors were mounted in vacuum cryostats and characterized in detail in
the HADES underground laboratory in Belgium. This paper describes the
properties and the overall performance of these detectors during operation in
vacuum. The characterization campaign provided not only direct input for GERDA
Phase II data collection and analyses, but also allowed to study detector
phenomena, detector correlations as well as to test the strength of pulse shape
simulation codes.Comment: 29 pages, 18 figure
The first search for bosonic super-WIMPs with masses up to 1 MeV/c with GERDA
We present the first search for bosonic super-WIMPs as keV-scale dark matter
candidates performed with the GERDA experiment. GERDA is a neutrinoless
double-beta decay experiment which operates high-purity germanium detectors
enriched in Ge in an ultra-low background environment at the Laboratori
Nazionali del Gran Sasso (LNGS) of INFN in Italy. Searches were performed for
pseudoscalar and vector particles in the mass region from 60 keV/c to 1
MeV/c. No evidence for a dark matter signal was observed, and the most
stringent constraints on the couplings of super-WIMPs with masses above 120
keV/c have been set. As an example, at a mass of 150 keV/c the most
stringent direct limits on the dimensionless couplings of axion-like particles
and dark photons to electrons of and
at 90% credible interval,
respectively, were obtained.Comment: 6 pages, 3 figures, submitted to Physical Review Letters, added list
of authors, updated ref. [21
- …