179 research outputs found
A steerable UV laser system for the calibration of liquid argon time projection chambers
A number of liquid argon time projection chambers (LAr TPC's) are being build
or are proposed for neutrino experiments on long- and short baseline beams. For
these detectors a distortion in the drift field due to geometrical or physics
reasons can affect the reconstruction of the events. Depending on the TPC
geometry and electric drift field intensity this distortion could be of the
same magnitude as the drift field itself. Recently, we presented a method to
calibrate the drift field and correct for these possible distortions. While
straight cosmic ray muon tracks could be used for calibration, multiple coulomb
scattering and momentum uncertainties allow only a limited resolution. A UV
laser instead can create straight ionization tracks in liquid argon, and allows
one to map the drift field along different paths in the TPC inner volume. Here
we present a UV laser feed-through design with a steerable UV mirror immersed
in liquid argon that can point the laser beam at many locations through the
TPC. The straight ionization paths are sensitive to drift field distortions, a
fit of these distortion to the linear optical path allows to extract the drift
field, by using these laser tracks along the whole TPC volume one can obtain a
3D drift field map. The UV laser feed-through assembly is a prototype of the
system that will be used for the MicroBooNE experiment at the Fermi National
Accelerator Laboratory (FNAL)
Experimental study of electric breakdowns in liquid argon at centimeter scale
In this paper we present results on measurements of the dielectric strength
of liquid argon near its boiling point and cathode-anode distances in the range
of 0.1 mm to 40 mm with spherical cathode and plane anode. We show that at such
distances the applied electric field at which breakdowns occur is as low as 40
kV/cm. Flash-overs across the ribbed dielectric of the high voltage
feed-through are observed for a length of 300 mm starting from a voltage of 55
kV. These results contribute to set reference for the breakdown-free design of
ionization detectors, such as Liquid Argon Time Projection Chambers (LAr TPC)
Measurement of the drift field in the ARGONTUBE LAr TPC with 266~nm pulsed laser beams
ARGONTUBE is a liquid argon time projection chamber (LAr TPC) with a drift
field generated in-situ by a Greinacher voltage multiplier circuit. We present
results on the measurement of the drift-field distribution inside ARGONTUBE
using straight ionization tracks generated by an intense UV laser beam. Our
analysis is based on a simplified model of the charging of a multi-stage
Greinacher circuit to describe the voltages on the field cage rings
A method to suppress dielectric breakdowns in liquid argon ionization detectors for cathode to ground distances of several millimeters
We present a method to reach electric field intensity as high as 400 kV/cm in
liquid argon for cathode-ground distances of several millimeters. This can be
achieved by suppressing field emission from the cathode, overcoming limitations
that we reported earlier
First Demonstration of a Pixelated Charge Readout for Single-Phase Liquid Argon Time Projection Chambers
Liquid Argon Time Projection Chambers (LArTPCs) have been selected for the
future long-baseline Deep Underground Neutrino Experiment (DUNE). To allow
LArTPCs to operate in the high-multiplicity near detector environment of DUNE,
a new charge readout technology is required. Traditional charge readout
technologies introduce intrinsic ambiguities, combined with a slow detector
response, these ambiguities have limited the performance of LArTPCs, until now.
Here, we present a novel pixelated charge readout that enables the full 3D
tracking capabilities of LArTPCs. We characterise the signal to noise ratio of
charge readout chain, to be about 14, and demonstrate track reconstruction on
3D space points produced by the pixel readout. This pixelated charge readout
makes LArTPCs a viable option for the DUNE near detector complex.Comment: 13 pages, 9 figure
Design and operation of ARGONTUBE: a 5 m long drift liquid argon TPC
The Liquid Argon Time Projection Chamber (LArTPC) is a prime type of detector
for future large-mass neutrino observatories and proton decay searches. In this
paper we present the design and operation, as well as experimental results from
ARGONTUBE, a LArTPC being operated at the AEC-LHEP, University of Bern. The
main goal of this detector is to prove the feasibility of charge drift over
very long distances in liquid argon. Many other aspects of the LArTPC
technology are also investigated, such as a voltage multiplier to generate high
voltage in liquid argon (Greinacher circuit), a cryogenic purification system
and the application of multi-photon ionization of liquid argon by a UV laser.
For the first time, tracks induced by cosmic muons and UV laser beam pulses
have been observed and studied at drift distances of up to 5m, the longest
reached to date
Mindfulness-based Cognitive Therapy For Preventing Relapse in Recurrent Depression: A Randomized Dismantling Trial.
Objective: We compared mindfulness-based cognitive therapy (MBCT) with both cognitive psycholog-ical education (CPE) and treatment as usual (TAU) in preventing relapse to major depressive disorder (MDD) in people currently in remission following at least 3 previous episodes. Method: A randomized controlled trial in which 274 participants were allocated in the ratio 2:2:1 to MBCT plus TAU, CPE plus TAU, and TAU alone, and data were analyzed for the 255 (93%; MBCT 99, CPE 103, TAU 53) retained to follow-up. MBCT was delivered in accordance with its published manual, modified to address suicidal cognitions; CPE was modeled on MBCT, but without training in meditation. Both treatments were delivered through 8 weekly classes. Results: Allocated treatment had no significant effect on risk of relapse to MDD over 12 months follow-up, hazard ratio for MBCT vs. CPE 0.88, 95% CI 0.58, 1.35; for MBCT vs. TAU 0.69, 95\% CI 0.42, 1.12. However, severity of childhood trauma affected relapse, hazard ratio for increase of 1 standard deviation 1.26 (95\% CI 1.05, 1.50), and significantly interacted with allocated treatment. Among participants above median severity, the hazard ratio was 0.61, 95\% CI 0.34, 1.09, for MBCT vs. CPE, and 0.43, 95\% CI 0.22, 0.87, for MBCT vs. TAU. For those below median severity, there were no such differences between treatment groups. Conclusion: MBCT provided significant protection against relapse for participants with increased vulnerability due to history of childhood trauma, but showed no significant advantage in comparison to an active control treatment and usual care over the whole group of patients with recurrent depression
Mindfulness-based Cognitive Therapy For Preventing Relapse in Recurrent Depression: A Randomized Dismantling Trial.
Objective: We compared mindfulness-based cognitive therapy (MBCT) with both cognitive psycholog-ical education (CPE) and treatment as usual (TAU) in preventing relapse to major depressive disorder (MDD) in people currently in remission following at least 3 previous episodes. Method: A randomized controlled trial in which 274 participants were allocated in the ratio 2:2:1 to MBCT plus TAU, CPE plus TAU, and TAU alone, and data were analyzed for the 255 (93%; MBCT 99, CPE 103, TAU 53) retained to follow-up. MBCT was delivered in accordance with its published manual, modified to address suicidal cognitions; CPE was modeled on MBCT, but without training in meditation. Both treatments were delivered through 8 weekly classes. Results: Allocated treatment had no significant effect on risk of relapse to MDD over 12 months follow-up, hazard ratio for MBCT vs. CPE 0.88, 95% CI 0.58, 1.35; for MBCT vs. TAU 0.69, 95\% CI 0.42, 1.12. However, severity of childhood trauma affected relapse, hazard ratio for increase of 1 standard deviation 1.26 (95\% CI 1.05, 1.50), and significantly interacted with allocated treatment. Among participants above median severity, the hazard ratio was 0.61, 95\% CI 0.34, 1.09, for MBCT vs. CPE, and 0.43, 95\% CI 0.22, 0.87, for MBCT vs. TAU. For those below median severity, there were no such differences between treatment groups. Conclusion: MBCT provided significant protection against relapse for participants with increased vulnerability due to history of childhood trauma, but showed no significant advantage in comparison to an active control treatment and usual care over the whole group of patients with recurrent depression
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