Neutron spin rotation is expected from quark-quark weak interactions in the standard model, which induce weak interactions among nucleons that violate parity. We present the results from an ...experiment searching for the effect of parity violation via the spin rotation of polarized neutrons in a liquid 4He medium. The value for the neutron spin rotation angle per unit length in 4He, d ϕ / d z = + 2.1 ± 8.3 (stat.) - 0.2 + 2.9 (sys.) × 10 - 7 rad/m, is consistent with zero. The result agrees with the best current theoretical estimates of the size of nucleon-nucleon weak amplitudes from other experiments and with the expectations from recent theoretical approaches to weak nucleon-nucleon interactions. In this paper we review the theoretical status of parity violation in the n → + 4He system and discuss details of the data analysis leading to the quoted result. Analysis tools are presented that quantify systematic uncertainties in this measurement and that are expected to be essential for future measurements.
This Letter reports the first scientific results from the observation of antineutrinos emitted by fission products of ^{235}U at the High Flux Isotope Reactor. PROSPECT, the Precision Reactor ...Oscillation and Spectrum Experiment, consists of a segmented 4 ton ^{6}Li-doped liquid scintillator detector covering a baseline range of 7-9 m from the reactor and operating under less than 1 m water equivalent overburden. Data collected during 33 live days of reactor operation at a nominal power of 85 MW yield a detection of 25 461±283 (stat) inverse beta decays. Observation of reactor antineutrinos can be achieved in PROSPECT at 5σ statistical significance within 2 h of on-surface reactor-on data taking. A reactor model independent analysis of the inverse beta decay prompt energy spectrum as a function of baseline constrains significant portions of the previously allowed sterile neutrino oscillation parameter space at 95% confidence level and disfavors the best fit of the reactor antineutrino anomaly at 2.2σ confidence level.
This report highlights two different types of cross-talk in the photodetectors of the miniTimeCube neutrino experiment. The miniTimeCube detector has 24 8 × 8-anode Photonis MCP-PMT Planacon XP85012, ...totalling 1536 individual pixels viewing the 2-liter cube of plastic scintillator.
Measuring the neutron lifetime using magnetically trapped neutrons O’Shaughnessy, C.M.; Golub, R.; Schelhammer, K.W. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
12/2009, Letnik:
611, Številka:
2
Journal Article
Recenzirano
Odprti dostop
The neutron beta-decay lifetime plays an important role both in understanding weak interactions within the framework of the Standard Model and in theoretical predictions of the primordial abundance ...of
4He in Big Bang Nucleosynthesis. In previous work, we successfully demonstrated the trapping of ultracold neutrons in a conservative potential magnetic trap. A major upgrade of the apparatus is nearing completion at the National Institute of Standards and Technology Center for Neutron Research (NCNR). In our approach, a beam of 0.89
nm neutrons is incident on a superfluid
4He target within the minimum field region of an Ioffe-type magnetic trap. A fraction of the neutrons is downscattered in the helium to energies
<
200
neV
, and those in the appropriate spin state become trapped. The inverse process is suppressed by the low phonon density of helium at temperatures less than 200
mK, allowing the neutron to travel undisturbed. When the neutron decays the energetic electron ionizes the helium, producing scintillation light that is detected using photomultiplier tubes. Statistical limitations of the previous apparatus will be alleviated by significant increases in field strength and trap volume resulting in twenty times more trapped neutrons.
•We describe the cryogenic design and performance of an apparatus used to magnetically confine ultracold neutrons.•The apparatus is capable of cooling 21l of isotopically pure 4He to approximately ...250mK.•The system is designed around a high-current, 1.5m long, horizontally-oriented superconducting Ioffe-type magnetic trap.•The apparatus was successfully cooled and remained cold for a period of approximately six months.
The cryogenic design and performance of an apparatus used to magnetically confine ultracold neutrons (UCN) is presented. The apparatus is part of an effort to measure the beta-decay lifetime of the free neutron and is comprised of a high-current superconducting magnetic trap that surrounds ∼21l of isotopically pure 4He cooled to approximately 250mK. A 0.89nm neutron beam can enter the apparatus from one end of the magnetic trap and a light collection system allows visible light generated within the helium by decays to be transported to detectors at room temperature. Two cryocoolers are incorporated to reduce liquid helium consumption.
Nitrogen deprivation increases the triacylglycerol (TAG) content in microalgae but also severely decreases the growth rate. Most approaches that attempted to increase TAG productivity by ...overexpression or knockdown of specific genes related to the regulation of the lipid synthesis have reported only little success. More insight into the molecular mechanisms related to lipid accumulation and impaired growth rate is needed to find targets for improving TAG productivity. By using the emerging “omics” approach, we comprehensively profiled the physiology, transcriptome, proteome and metabolome of the diatom Phaeodactylum tricornutum during steady state growth at both nitrogen limited and replete levels during light:dark cycles. Under nitrogen limited conditions, 22% (2699) of the total identified transcripts, 17% (543) of the proteins and 44% (345) of the metabolites were significantly differentially regulated compared to nitrogen replete growth conditions. Although nitrogen limitation was responsible for the majority of significant differential transcript, protein and metabolite accumulation, we also observed differential expression over a diurnal cycle. Nitrogen limitation mainly induced an upregulation of nitrogen fixation, central carbon metabolism and TCA cycle, while photosynthetic and ribosomal protein synthesis are mainly downregulated. Regulation of the lipid metabolism and the expression of predicted proteins involved in lipid processes suggest that lipid rearrangements may substantially contribute to TAG distribution. However, TAG synthesis is also limited by the reduced carbon flux through central metabolism. Future strain improvements should therefore focus on understanding and improving the carbon flux through central carbon metabolism, selectivity and activity of DGAT isoforms and lipase enzymes.
•Nitrogen limitation increases the triacylglycerol (TAG) content in microalgae but affects growth and photosynthetic rates.•Omics data suggest a potential important role of the mitochondrion during nitrogen starvation.•Membrane lipid rearrangement possibly assists TAG accumulation during nitrogen starvation.•Understanding the regulation and flux of the central carbon metabolism is an important factor for further improvements.
If dark matter has mass lower than around 1 GeV, it will not impart enough energy to cause detectable nuclear recoils in many direct-detection experiments. However, if dark matter is upscattered to ...high energy by collisions with cosmic rays, it may be detectable in both direct-detection experiments and neutrino experiments. We report the results of a dedicated search for boosted dark matter upscattered by cosmic rays, using ~14.6 solar days of data from the PROSPECT reactor antineutrino experiment. We show that such a flux of upscattered dark matter would display characteristic diurnal sidereal modulation, and use this to set new experimental constraints on sub-GeV dark matter exhibiting large interaction cross sections.
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