Time Projection Chambers (TPCs) with charge readout via micro pattern gaseous detectors can provide detailed measurements of charge density distributions. We here report on measurements of alpha ...particle tracks, using a TPC where the drift charge is amplified with Gas Electron Multipliers and detected with a pixel ASIC. We find that by measuring the 3-D topology of drift charge and fitting for its transverse diffusion, we obtain the absolute position of tracks in the drift direction. For example, we obtain a precision of ~1cm for 0.8cm-long alpha track segments. To our knowledge this is the first demonstration of such a measurement in a gas TPC. This technique has several attractive features: it does not require knowledge of the initial specific ionization, is robust against bias from diffuse charge below detection threshold, and is also robust against high charge densities that saturate the detector response.
3-D tracking in a miniature time projection chamber Vahsen, S.E.; Hedges, M.T.; Jaegle, I. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
07/2015, Letnik:
788, Številka:
C
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The three-dimensional (3-D) detection of millimeter-scale ionization trails is of interest for detecting nuclear recoils in directional fast neutron detectors and in direction-sensitive searches for ...weakly interacting massive particles (WIMPs), which may constitute the Dark Matter of the universe. We report on performance characterization of a miniature gas target Time Projection Chamber (TPC) where the drift charge is avalanche-multiplied with Gas Electron Multipliers (GEMs) and detected with the ATLAS FE-I3 Pixel Application Specific Integrated Circuit (ASIC). We report on measurements of gain, gain resolution, point resolution, diffusion, angular resolution, and energy resolution with low-energy X-rays, cosmic rays, and alpha particles, using the gases Ar:CO2 (70:30) and He:CO2 (70:30) at atmospheric pressure. We discuss the implications for future, larger directional neutron and Dark Matter detectors. With an eye to designing and selecting components for these, we generalize our results into analytical expressions for detector performance whenever possible. We conclude by demonstrating the 3-D directional detection of a fast neutron source.
Cyclooxygenase (COX) exists as constitutive (COX‐1) and inducible (COX‐2) isoforms. Nonsteroidal anti‐inflammatory drugs (NSAIDs) such as ibuprofen and diclofenac inhibit both COX‐1 and COX‐2. The ...role of COX‐2 in the genesis of fever in monkeys and humans was examined with use of the specific COX‐2 inhibitor rofecoxib. Rofecoxib was administered to monkeys made febrile by 6 μg/kg intravenous lipopolysaccharide. Induced pyrexia was followed by oral rofecoxib (1 or 3 mg/kg), diclofenac (3 mg/kg), or vehicle. Rofecoxib and diclofenac rapidly reversed the elevated temperature (P < .05 versus vehicle for 3 mg/kg rofecoxib and diclofenac at 70 to 90 minutes after dosing). A single‐dose, parallel‐group, double‐blind randomized trial was conducted in 94 patients with fever caused by a viral‐type illness. Mean baseline temperature was similar for all groups (~38.5°C). Patients received oral doses of 12.5 mg rofecoxib, 25 mg rofecoxib, 400 mg ibuprofen, or placebo and the mean ± SE change in oral temperature at 4 hours after dosing was −0.97°C ± 0.11°C, −1.19°C ± 0.09°C, −1.20°C ± 0.11°C, and 0.01°C ± 0.17°C, respectively (P < .001 for active treatments versus placebo). Specific inhibition of COX‐2 by rofecoxib results in antipyretic activity in monkeys and humans comparable to dual COX‐1/COX‐2 inhibitors such as diclofenac or ibuprofen. The data support the hypothesis that it is the COX‐2 isoform that is primarily involved in the genesis of fever in humans.
Clinical Pharmacology & Therapeutics (1999) 65, 653–660; doi: 10.1016/S0009-9236(99)90087-5
A bstract We report the first measurement of the inclusive e + e − → $$ b\overline{b} $$ b b ¯ → $$ {D}_s^{\pm } $$ D s ± X and e + e − → $$ b\overline{b} $$ b b ¯ → D 0 / $$ {\overline{D}}^0 $$ D ¯ ...0 X cross sections in the energy range from 10 . 63 to 11 . 02 GeV. Based on these results, we determine σ ( e + e − → $$ {B}_s^0{\overline{B}}_s^0 $$ B s 0 B ¯ s 0 X ) and σ ( e + e − → $$ B\overline{B} $$ B B ¯ X ) in the same energy range. We measure the fraction of $$ {B}_s^0 $$ B s 0 events at Υ(10860) to be f s = ( $$ {22.0}_{-2.1}^{+2.0} $$ 22.0 − 2.1 + 2.0 )%. We determine also the ratio of the $$ {B}_s^0 $$ B s 0 inclusive branching fractions $$ \mathcal{B} $$ B ( $$ {B}_s^0 $$ B s 0 → D 0 / $$ {\overline{D}}^0 $$ D ¯ 0 X ) / $$ \mathcal{B} $$ B ( $$ {B}_s^0 $$ B s 0 → $$ {D}_s^{\pm } $$ D s ± X ) = 0 . 416 ± 0 . 018 ± 0 . 092. The results are obtained using the data collected with the Belle detector at the KEKB asymmetric-energy e + e − collider.
We report the first measurement of the Michel parameter ξ′ in the τ−→μ−¯νμντ decay with a new method proposed just recently. The measurement is based on the reconstruction of the τ−→μ−¯νμντ events ...with subsequent muon decay in flight in the Belle central drift chamber. The analyzed data sample of 988 fb−1 collected by the Belle detector corresponds to approximately 912×106 τ+τ− pairs. We measure ξ′=0.22±0.94(stat)±0.42(syst), which is in agreement with the standard model prediction of ξ′=1. Statistical uncertainty dominates in this study, being a limiting factor, while systematic uncertainty is well under control. Our analysis proved the practicability of this promising method and its prospects for further precise measurement in future experiments.
We report on the design, production, and performance of compact 40-cm3 Time Projection Chambers (TPCs) that detect fast neutrons by measuring the three-dimensional (3D) ionization distribution of ...nuclear recoils in 4He:CO2 gas at atmospheric pressure. We use these detectors to characterize the fast-neutron flux inside the Belle II detector at the SuperKEKB electron–positron collider in Tsukuba, Japan, where the primary design constraint is a small form factor. We find that the TPCs meet or exceed all design specifications, and are capable of measuring the 3D surface shape and charge density profile of ionization clouds from nuclear recoils and charged tracks in exquisite detail. Scaled-up detectors based on the detection principle demonstrated here may be suitable for directional dark matter searches, measurements of coherent neutrino–nucleus scattering, and other experiments requiring precise detection of neutrons or nuclear recoils.
We report on the design, production, and performance of compact 40-cm3 Time Projection Chambers (TPCs) that detect fast neutrons by measuring the three-dimensional (3D) ionization distribution of ...nuclear recoils in 4He:CO2 gas at atmospheric pressure. We use these detectors to characterize the fast-neutron flux inside the Belle II detector at the SuperKEKB electron–positron collider in Tsukuba, Japan, where the primary design constraint is a small form factor. We find that the TPCs meet or exceed all design specifications, and are capable of measuring the 3D surface shape and charge density profile of ionization clouds from nuclear recoils and charged tracks in exquisite detail. Scaled-up detectors based on the detection principle demonstrated here may be suitable for directional dark matter searches, measurements of coherent neutrino–nucleus scattering, and other experiments requiring precise detection of neutrons or nuclear recoils.
We develop and validate a new algorithm called \textit{primary track recovery} (\ptr) that effectively deconvolves known physics and detector effects from nuclear recoil tracks in gas time projection ...chambers (TPCs) with high-resolution readout. This gives access to the primary track charge, length, and vector direction (helping to resolve the "head-tail" ambiguity). Additionally, \ptr provides a measurement of the transverse and longitudinal diffusion widths, which can be used to determine the absolute position of tracks in the drift direction for detector fiducialization. Using simulated helium recoils in an atmospheric pressure TPC with a 70:30 mixture of He:CO\(_2\) we compare the performance of \ptr to traditional methods for all key track variables. We find that the algorithm reduces reconstruction errors, including those caused by charge integration, for tracks with mean length-to-width ratios 1.4 and above, corresponding to recoil energies of \(20\) keV and above in the studied TPCs. We show that \ptr improves on existing methods for head-tail disambiguation, particularly for highly inclined tracks, and improves the determination of the absolute position of recoils on the drift axis via transverse diffusion. We find that \ptr can partially recover charge structure integrated out by the detector in the \(z\) direction, but that its determination of energy and length have worse resolution compared to existing methods. We use experimental data to qualitatively verify these findings and discuss implications for future directional detectors at the low-energy frontier.
Gaseous time projection chambers (TPCs) with high readout segmentation are capable of reconstructing detailed 3D ionization distributions of nuclear recoils resulting from elastic neutron scattering. ...Using a system of six compact TPCs with pixel ASIC readout, filled with a 70:30 mixture of He:CO\(_2\) gas, we analyze the first directional measurements of beam-induced neutron backgrounds in the tunnel regions surrounding the Belle II detector at the SuperKEKB \(e^+e^-\) collider. With the use of 3D recoil tracking, we show that these TPCs are capable of maintaining nearly \(100\%\) nuclear recoil purity to reconstructed ionization energies (\(E_\text{reco}\)) as low as 5 \(\mathrm{keV_\text{ee}}\). Using a large sample of simulated \(^4\)He, \(^{12}\)C, and \(^{16}\)O recoil tracks, we find consistency between predicted and measured recoil energy spectra in five of the six TPCs, providing useful validation of the neutron production mechanisms modeled in simulation. Restricting this sample to \(^4\)He recoil tracks with \(E_\text{reco}>40\) \(\mathrm{keV_\text{ee}}\), we demonstrate axial angular resolutions within \(8^{\circ}\) and we introduce a procedure that under suitable conditions, correctly assigns the vector direction to \(91\%\) of simulated \(^4\)He recoils. Applying this procedure to assign vector directions to measured \(^4\)He recoil tracks, we observe consistency between the angular distributions of observed and simulated recoils, providing first experimental evidence of localized neutron "hotspots" in the accelerator tunnel. Observed rates of nuclear recoils in these TPCs suggest that simulation overestimates the neutron flux from these hotspots.
Five contemporary technologies are discussed in the context of their potential roles in particle tracking for future high energy physics applications. These include sensors of the 3D configuration, ...in both diamond and silicon, submicron-dimension pixels, thin film detectors, and scintillating quantum dots in gallium arsenide. Drivers of the technologies include radiation hardness, excellent position, vertex, and timing resolution, simplified integration, and optimized power, cost, and material.
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