389 research outputs found
Image quality of list-mode proton imaging without front trackers
List mode proton imaging relies on accurate reconstruction of the proton most likely path (MLP) through the patient. This typically requires two sets of position sensitive detector systems, one upstream (front) and one downstream (rear) of the patient. However, for a clinical implementation it can be preferable to omit the front trackers (single-sided proton imaging). For such a system, the MLP can be computed from information available through the beam delivery system and the remaining rear tracker set. In this work, we use Monte Carlo simulations to compare a conventional double-sided (using both front and rear detector systems) with a single-sided system (only rear detector system) by evaluating the spatial resolution of proton radiographs (pRad) and proton CT images (pCT) acquired with these set-ups. Both the pencil beam spot size, as well as the spacing between spots was also adjusted to identify the impact of these beam parameters on the image quality.
Relying only on the pencil beam central position for computing the MLP resulted in severe image artifacts both in pRad and pCT. Using the recently extended-MLP formalism that incorporate pencil beam uncertainty removed these image artifacts. However, using a more focused pencil beam with this algorithm induced image artifacts when the spot spacing was the same as the beam spot size. The spatial resolution tested with a sharp edge gradient technique was reduced by 40% for single-sided (MTF10% = 3.0 lp/cm) compared to double-sided (MTF10% = 4.9 lp/cm) pRad with ideal tracking detectors. Using realistic trackers the difference decreased to 30%, with MTF10% of 4.0 lp/cm for the realistic double-sided and 2.7 lp/cm for the realistic single-sided setup. When studying an anthropomorphic paediatric head phantom both single- and double-sided set-ups performed similarly where the difference in water equivalent thickness (WET) between the two set-ups were less than 0.01 mm in homogeneous areas of the head. Larger discrepancies between the two set-ups were visible in high density gradients like the facial structures. A complete CT reconstruction of a Catphan module was performed. Assuming ideal detectors, the obtained spatial resolution was 5.1 lp/cm for double-sided and 3.8 lp/cm for the single-sided setup. Double- and single-sided pRad with realistic tracker properties returned a spatial resolution of 3.8 lp/cm and 3.2 lp/cm, respectively. Future studies should investigate the development of dedicated reconstruction algorithms targeted for single-sided particle imaging.publishedVersio
Testing general relativity using higher-order modes of gravitational waves from binary black holes
Recently, strong evidence was found for the presence of higher-order modes in the gravitational wave signals GW190412 and GW190814, which originated from compact binary coalescences with significantly asymmetric component masses. This has opened up the possibility of new tests of general relativity by looking at the way in which the higher-order modes are related to the basic signal. Here we further develop a test which assesses whether the amplitudes of subdominant harmonics are consistent with what is predicted by general relativity. To this end we incorporate a state-of-the-art waveform model with higher-order modes and precessing spins into a Bayesian parameter estimation and model selection framework. The analysis methodology is tested extensively through simulations. We investigate to what extent deviations in the relative amplitudes of the harmonics will be measurable depending on the properties of the source, and we map out correlations between our testing parameters and the inclination of the source with respect to the observer. Finally, we apply the test to GW190412 and GW190814, finding no evidence for violations of general relativity
An aligned-spin neutron-star--black-hole waveform model based on the effective-one-body approach and numerical-relativity simulations
After the discovery of gravitational waves from binary black holes (BBHs) and
binary neutron stars (BNSs) with the LIGO and Virgo detectors,
neutron-star--black-holes (NSBHs) are the natural next class of binary systems
to be observed. In this work, we develop a waveform model for aligned-spin
neutron-star--black-holes (NSBHs) combining a binary black-hole baseline
waveform (available in the effective-one-body approach) with a phenomenological
description of tidal effects (extracted from numerical-relativity simulations),
and correcting the amplitude during the late inspiral, merger and ringdown to
account for the NS's tidal disruption. In particular, we calibrate the
amplitude corrections using NSBH waveforms obtained with the
numerical-relativity spectral Einstein code (SpEC) and the SACRA code. Based on
the simulations used, and on checking that sensible waveforms are produced, we
recommend our model to be employed with NS's mass in the range ,
tidal deformability 0\mbox{-}5000, and (dimensionless) BH's spin magnitude up
to . We also validate our model against two new, highly accurate NSBH
waveforms with BH's spin 0.9 and mass ratios 3 and 4, characterized by tidal
disruption, produced with SpEC, and find very good agreement. Furthermore, we
compute the unfaithfulness between waveforms from NSBH, BBH, and BNS systems,
finding that it will be challenging for the advanced LIGO-Virgo--detector
network at design sensitivity to distinguish different source classes. We
perform a Bayesian parameter-estimation analysis on a synthetic
numerical-relativity signal in zero noise to study parameter biases. Finally,
we reanalyze GW170817, with the hypothesis that it is a NSBH. We do not find
evidence to distinguish the BNS and NSBH hypotheses, however the posterior for
the mass ratio is shifted to less equal masses under the NSBH hypothesis.Comment: 18 pages, 10 Figure
The GstLAL template bank for spinning compact binary mergers in the second observation run of Advanced LIGO and Virgo
We describe the methods used to construct the aligned-spin template bank of
gravitational waveforms used by the GstLAL-based inspiral pipeline to analyze
data from the second observing run of Advanced LIGO and Virgo. The bank expands
upon the parameter space covered during the first observing run, including
coverage for merging compact binary systems with total mass between 2
and 400 and mass ratios between 1 and
97.989. Thus the systems targeted include merging neutron star-neutron star
systems, neutron star-black hole binaries, and black hole-black hole binaries
expanding into the intermediate-mass range. Component masses less than 2
have allowed (anti-)aligned spins between while
component masses greater than 2 have allowed
(anti-)aligned between . The bank placement technique combines a
stochastic method with a new grid-bank method to better isolate noisy
templates, resulting in a total of 677,000 templates.Comment: 9 pages, 13 figure
An early warning system for electromagnetic follow-up of gravitational-wave events
Binary neutron stars (BNSs) will spend -- 15 minutes in the band
of Advanced LIGO and Virgo detectors at design sensitivity. Matched-filtering
of gravitational-wave (GW) data could in principle accumulate enough
signal-to-noise ratio (SNR) to identify a forthcoming event tens of seconds
before the companions collide and merge. Here we report on the design and
testing of an early warning gravitational-wave detection pipeline. Early
warning alerts can be produced for sources that are at low enough redshift so
that a large enough SNR accumulates before merger. We
find that about 7% (respectively, 49%) of the total detectable BNS mergers will
be detected () before the merger. About 2% of the
total detectable BNS mergers will be detected before merger and localized to
within (90% credible interval). Coordinated observing
by several wide-field telescopes could capture the event seconds before or
after the merger. LIGO-Virgo detectors at design sensitivity could facilitate
observing at least one event at the onset of merger.Comment: small update in numbers caused by using a more updated local BNS rate
estimat
Design and Performance of a Silicon Tungsten Calorimeter Prototype Module and the Associated Readout
We describe the details of a silicon-tungsten prototype electromagnetic
calorimeter module and associated readout electronics. Detector performance for
this prototype has been measured in test beam experiments at the CERN PS and
SPS accelerator facilities in 2015/16. The results are compared to those in
Monte Carlo Geant4 simulations. This is the first real-world demonstration of
the performance of a custom ASIC designed for fast, lower-power,
high-granularity applications.Comment: 27 pages, 19 captioned figures, published versioi
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