First Dark Matter Search Results from the LUX-ZEPLIN (LZ) Experiment

The LUX-ZEPLIN experiment is a dark matter detector centered on a dual-phase xenon time projection chamber operating at the Sanford Underground Research Facility in Lead, South Dakota, USA. This Letter reports results from LUX-ZEPLIN's first search for weakly interacting massive particles (WIMPs) with an exposure of 60 live days using a fiducial mass of 5.5 t. A profile-likelihood ratio analysis shows the data to be consistent with a background-only hypothesis, setting new limits on spin-independent WIMP-nucleon, spin-dependent WIMP-neutron, and spin-dependent WIMP-proton cross sections for WIMP masses above 9  GeV/c^{2}. The most stringent limit is set for spin-independent scattering at 36  GeV/c^{2}, rejecting cross sections above 9.2×10^{-48}  cm at the 90% confidence level.

First Measurement of Differential Charged Current Quasielasticlike ν_{μ}-Argon Scattering Cross Sections with the MicroBooNE Detector

We report on the first measurement of flux-integrated single differential cross sections for charged-current (CC) muon neutrino (ν_{μ}) scattering on argon with a muon and a proton in the final state, ^{40}Ar (ν_{μ},μp)X. The measurement was carried out using the Booster Neutrino Beam at Fermi National Accelerator Laboratory and the MicroBooNE liquid argon time projection chamber detector with an exposure of 4.59×10^{19} protons on target. Events are selected to enhance the contribution of CC quasielastic (CCQE) interactions. The data are reported in terms of a total cross section as well as single differential cross sections in final state muon and proton kinematics. We measure the integrated per-nucleus CCQE-like cross section (i.e., for interactions leading to a muon, one proton, and no pions above detection threshold) of (4.93±0.76_{stat}±1.29_{sys})×10^{-38}  cm^{2}, in good agreement with theoretical calculations. The single differential cross sections are also in overall good agreement with theoretical predictions, except at very forward muon scattering angles that correspond to low-momentum-transfer events.

First Measurement of Inclusive Muon Neutrino Charged Current Differential Cross Sections on Argon at E_{ν}∼0.8 GeV with the MicroBooNE Detector

We report the first measurement of the double-differential and total muon neutrino charged current inclusive cross sections on argon at a mean neutrino energy of 0.8 GeV. Data were collected using the MicroBooNE liquid argon time projection chamber located in the Fermilab Booster neutrino beam and correspond to 1.6×10^{20} protons on target of exposure. The measured differential cross sections are presented as a function of muon momentum, using multiple Coulomb scattering as a momentum measurement technique, and the muon angle with respect to the beam direction. We compare the measured cross sections to multiple neutrino event generators and find better agreement with those containing more complete treatment of quasielastic scattering processes at low Q^{2}. The total flux integrated cross section is measured to be 0.693±0.010(stat)±0.165(syst)×10^{-38}  cm^{2}.

The Pandora multi-algorithm approach to automated pattern recognition of cosmic-ray muon and neutrino events in the MicroBooNE detector

The development and operation of liquid-argon time-projection chambers for neutrino physics has created a need for new approaches to pattern recognition in order to fully exploit the imaging capabilities offered by this technology. Whereas the human brain can excel at identifying features in the recorded events, it is a significant challenge to develop an automated, algorithmic solution. The Pandora Software Development Kit provides functionality to aid the design and implementation of pattern-recognition algorithms. It promotes the use of a multi-algorithm approach to pattern recognition, in which individual algorithms each address a specific task in a particular topology. Many tens of algorithms then carefully build up a picture of the event and, together, provide a robust automated pattern-recognition solution. This paper describes details of the chain of over one hundred Pandora algorithms and tools used to reconstruct cosmic-ray muon and neutrino events in the MicroBooNE detector. Metrics that assess the current pattern-recognition performance are presented for simulated MicroBooNE events, using a selection of final-state event topologies.

Effect of selective A1 adenosine receptor antagonism of postdefibrillation cardiovascular depression: evidence for an antiadrenergic role of endogenous adenosine

OBJECTIVE

The aim was to examine the effect of a selective A1 adenosine receptor antagonist (N-0861) on postdefibrillation cardiovascular depression to determine whether antagonist mediated enhanced postdefibrillation haemodynamic recovery is due to reversal of the antiadrenergic action of adenosine, an A1 receptor mediated effect.

METHODS

Halothane-nitrous oxide anaesthetised Duroc pigs of either sex, weight 22-25 kg, were subjected to sequential episodes of induced ventricular fibrillation lasting either 15 s (terminated by a suprathreshold shock at 60-70 A) or 35 s (subjected to a subthreshold shock at 20 A followed by a suprathreshold shock at 60-70 A) during intravenous placebo infusion (n = 10), N-0861 infusion (0.1 mg.kg-1.min-1, n = 10), and N-0861 infusion plus propranolol (2 mg.kg-1, n = 6).

RESULTS

N-0861 significantly enhanced immediate postdefibrillation electrophysiological and haemodynamic recovery compared to placebo for ventricular fibrillation episodes lasting 35 s. Over the first 15 s postdefibrillation, N-0861 significantly (p < 0.05) shortened mean cycle length by 55%, increased mean arterial pressure by 33%, and increased the first derivative of left ventricular pressure (an indirect measure of cardiac contractility) by 100% compared to placebo. At 60 s postdefibrillation, when other variables were equal, the first derivative of left ventricular pressure in the presence of N-0861 remained 26% greater than placebo. This effect was completely antagonised by propranolol.

CONCLUSIONS

(1) Cardiac contractility in the immediate postdefibrillation period is suppressed by the antiadrenergic action of endogenous adenosine. (2) Selective A1 adenosine receptor antagonism can markedly enhance postdefibrillation contractility. (3) These results support an antiadrenergic role of endogenous adenosine under pathophysiological conditions.

Transepicardial defibrillation dose response: current versus energy

In pentobarbital-anesthetized dogs, we compared the relative efficacy of current versus energy in applying the dose response method in transcardiac defibrillation. Damped sinusoidal shocks via epicardial patches were administered by a custom defibrillator permitting precise current delivery. Following the establishment of an initial estimated defibrillation threshold for energy and current, the dose response method was performed with regard to either energy defibrillation threshold (group E, n = 8) or current defibrillation threshold (group C, n = 8). Two sequential sets (I, II) of shocks (21 shocks each) were delivered in random order at each of seven doses: 0.55, 0.70, 0.85, 1.00, 1.15, 1.30, and 1.45 x defibrillation threshold. Data were subjected to nonlinear logistic regression analysis. There were no significant differences between sets I and II in either groups E or C for resistance or for raw and normalized values associated with 50% and 80% success expressed as energy, current, or voltage. Correlation coefficients (r) associated with nonlinear logistic regression analysis were significantly different for normalized current and energy for group E (0.70 +/- 11 and 0.71 +/- 12) compared to group C (0.86 +/- 0.60 and 0.88 +/- 0.06). The difference, however, could be explained by a significantly narrower range of normalized current values tested in group E (0.79 to 1.31) versus group C (0.54 to 1.46). Thus, when resistance does not change, transcardiac current offers limited advantage over energy when applying a dose response method. The efficacy of nonlinear logistic regression analysis depends upon an adequate dose range.