Search

We report measurements of the parity-conserving beam-normal single-spin elastic scattering asymmetries $B_n$ on $^{12}$C and $^{27}$Al, obtained with an electron beam polarized transverse to its momentum direction. These measurements add an additional kinematic point to a series of previous measurements of $B_n$ on $^{12}$C and provide a first measurement on $^{27}$Al. The experiment utilized the Qweak apparatus at Jefferson Lab with a beam energy of 1.158 GeV. The average lab scattering angle for both targets was 7.7 degrees, and the average $Q^2$ for both targets was 0.02437 GeV$^2$ (Q=0.1561 GeV). The asymmetries are $B_n$ = -10.68 $\pm$ 0.90 stat) $\pm$ 0.57 (syst) ppm for $^{12}$C and $B_n$ = -12.16 $\pm$ 0.58 (stat) $\pm$ 0.62 (syst) ppm for $^{27}$Al. The results are consistent with theoretical predictions, and are compared to existing data. When scaled by Z/A, the Q-dependence of all the far-forward angle (theta < 10 degrees) data from $^{1}$H to $^{27}$Al can be described by the same slope out to $Q \approx 0.35$ GeV. Larger-angle data from other experiments in the same Q range are consistent with a slope about twice as steep.

A high precision calibration of the nonlinearity in the energy response of the Daya Bay Reactor Neutrino Experiment’s antineutrino detectors is presented in detail. The energy nonlinearity originates from the particle-dependent light yield of the scintillator and charge-dependent electronics response. The nonlinearity model is constrained by γ calibration points from deployed and naturally occurring radioactive sources, the β spectrum from ^(12)B decays, and a direct measurement of the electronics nonlinearity with a new flash analog-to-digital converter readout system. Less than 0.5% uncertainty in the energy nonlinearity calibration is achieved for positrons of kinetic energies greater than 1 MeV.

We report a precision measurement of the parity-violating asymmetry A_{PV} in the elastic scattering of longitudinally polarized electrons from ^{208}Pb. We measure A_{PV}=550±16(stat)±8(syst) parts per billion, leading to an extraction of the neutral weak form factor F_{W}(Q^{2}=0.00616 GeV^{2})=0.368±0.013. Combined with our previous measurement, the extracted neutron skin thickness is R_{n}-R_{p}=0.283±0.071 fm. The result also yields the first significant direct measurement of the interior weak density of ^{208}Pb: ρ_{W}^{0}=-0.0796±0.0036(exp)±0.0013(theo) fm^{-3} leading to the interior baryon density ρ_{b}^{0}=0.1480±0.0036(exp)±0.0013(theo) fm^{-3}. The measurement accurately constrains the density dependence of the symmetry energy of nuclear matter near saturation density, with implications for the size and composition of neutron stars.

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 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., 11 pages, 8 figures

The prediction of reactor antineutrino spectra will play a crucial role as reactor experiments enter the precision era. The positron energy spectrum of 3.5 million antineutrino inverse beta decay reactions observed by the Daya Bay experiment, in combination with the fission rates of fissile isotopes in the reactor, is used to extract the positron energy spectra resulting from the fission of specific isotopes. This information can be used to produce a precise, data-based prediction of the antineutrino energy spectrum in other reactor antineutrino experiments with different fission fractions than Daya Bay. The positron energy spectra are unfolded to obtain the antineutrino energy spectra by removing the contribution from detector response with the Wiener-SVD unfolding method. Consistent results are obtained with other unfolding methods. A technique to construct a data-based prediction of the reactor antineutrino energy spectrum is proposed and investigated. Given the reactor fission fractions, the technique can predict the energy spectrum to a 2% precision. In addition, we illustrate how to perform a rigorous comparison between the unfolded antineutrino spectrum and a theoretical model prediction that avoids the input model bias of the unfolding method., 22 pages, 10 figures, 6 supplemental materials

The precision reactor oscillation and spectrum experiment, PROSPECT, has made world-leading measurements of reactor antineutrinos at short baselines. In its first phase, conducted at the high flux isotope reactor (HFIR) at Oak Ridge National Laboratory, PROSPECT produced some of the strongest limits on eV-scale sterile neutrinos, made a precision measurement of the reactor antineutrino spectrum from 235U, and demonstrated the observation of reactor antineutrinos in an aboveground detector with good energy resolution and well-controlled backgrounds. The PROSPECT collaboration is now preparing an upgraded detector, PROSPECT-II, to probe yet unexplored parameter space for sterile neutrinos and contribute to a full resolution of the reactor antineutrino anomaly, a longstanding puzzle in neutrino physics. By pressing forward on the world’s most precise measurement of the 235U antineutrino spectrum and measuring the absolute flux of antineutrinos from 235U, PROSPECT-II will sharpen a tool with potential value for basic neutrino science, nuclear data validation, and nuclear security applications. Following a two-year deployment at HFIR, an additional PROSPECT-II deployment at a low enriched uranium reactor could make complementary measurements of the neutrino yield from other fission isotopes. PROSPECT-II provides a unique opportunity to continue the study of reactor antineutrinos at short baselines, taking advantage of demonstrated elements of the original PROSPECT design and close access to a highly enriched uranium reactor core.

Identification, understanding, and manipulation of novel magnetic textures are essential for the discovery of new quantum materials for future spin-based electronic devices. In particular, materials that manifest a large response to external stimuli such as a magnetic field are subject to intense investigation. Here, we study the kagome-net magnet YMn6Sn6 by magnetometry, transport, and neutron diffraction measurements combined with first-principles calculations. We identify a number of nontrivial magnetic phases, explain their microscopic nature, and demonstrate that one of them hosts a large topological Hall effect (THE). We propose a previously unidentified fluctuation-driven mechanism, which leads to the THE at elevated temperatures. This interesting physics comes from parametrically frustrated interplanar exchange interactions that trigger strong magnetic fluctuations. Our results pave a path to chiral spin textures, promising for novel spintronics.

Reactor neutrino experiments have seen major improvements in precision in recent years. With the experimental uncertainties becoming lower than those from theory, carefully considering all sources of [Formula: see text] is important when making theoretical predictions. One source of [Formula: see text] that is often neglected arises from the irradiation of the nonfuel materials in reactors. The [Formula: see text] rates and energies from these sources vary widely based on the reactor type, configuration, and sampling stage during the reactor cycle and have to be carefully considered for each experiment independently. In this article, we present a formalism for selecting the possible [Formula: see text] sources arising from the neutron captures on reactor and target materials. We apply this formalism to the High Flux Isotope Reactor (HFIR) at Oak Ridge National Laboratory, the [Formula: see text] source for the the Precision Reactor Oscillation and Spectrum Measurement (PROSPECT) experiment. Overall, we observe that the nonfuel [Formula: see text] contributions from HFIR to PROSPECT amount to 1% above the inverse beta decay threshold with a maximum contribution of 9% in the 1.8–2.0 MeV range. Nonfuel contributions can be particularly high for research reactors like HFIR because of the choice of structural and reflector material in addition to the intentional irradiation of target material for isotope production. We show that typical commercial pressurized water reactors fueled with low-enriched uranium will have significantly smaller nonfuel [Formula: see text] contribution.

Identification, understanding, and manipulation of novel magnetic textures are essential for the discovery of new quantum materials for future spin-based electronic devices. In particular, materials that manifest a large response to external stimuli such as a magnetic field are subject to intense investigation. Here, we study the kagome-net magnet YMn

Searches for electron antineutrino, muon neutrino, and muon antineutrino disappearance driven by sterile neutrino mixing have been carried out by the Daya Bay and MINOS+ collaborations. This Letter presents the combined results of these searches, along with exclusion results from the Bugey-3 reactor experiment, framed in a minimally extended four-neutrino scenario. Significantly improved constraints on the θ_{μe} mixing angle are derived that constitute the most constraining limits to date over five orders of magnitude in the mass-squared splitting Δm_{41}^{2}, excluding the 90% C.L. sterile-neutrino parameter space allowed by the LSND and MiniBooNE observations at 90% CL_{s} for Δm_{41}^{2}

A beam-normal single-spin asymmetry generated in the scattering of transversely polarized electrons from unpolarized nucleons is an observable related to the imaginary part of the two-photon exchange process. We report a 2% precision measurement of the beam-normal single-spin asymmetry in elastic electron-proton scattering with a mean scattering angle of theta_lab = 7.9 degrees and a mean energy of 1.149 GeV. The asymmetry result is B_n = -5.194 +- 0.067 (stat) +- 0.082 (syst) ppm. This is the most precise measurement of this quantity available to date and therefore provides a stringent test of two-photon exchange models at far-forward scattering angles (theta_lab -> 0) where they should be most reliable., 6 pages, 3 figures; Slightly revised version, after referee's comments; accepted in PRL

Reactor neutrino experiments have seen major improvements in precision in recent years. With the experimental uncertainties becoming lower than those from theory, carefully considering all sources of ν ¯ e is important when making theoretical predictions. One source of ν ¯ e that is often neglected arises from the irradiation of the nonfuel materials in reactors. The ν ¯ e rates and energies from these sources vary widely based on the reactor type, configuration, and sampling stage during the reactor cycle and have to be carefully considered for each experiment independently. In this article, we present a formalism for selecting the possible ν ¯ e sources arising from the neutron captures on reactor and target materials. We apply this formalism to the High Flux Isotope Reactor (HFIR) at Oak Ridge National Laboratory, the ν ¯ e source for the the Precision Reactor Oscillation and Spectrum Measurement (PROSPECT) experiment. Overall, we observe that the nonfuel ν ¯ e contributions from HFIR to PROSPECT amount to 1% above the inverse beta decay threshold with a maximum contribution of 9% in the 1.8-2.0 MeV range. Nonfuel contributions can be particularly high for research reactors like HFIR because of the choice of structural and reflector material in addition to the intentional irradiation of target material for isotope production. We show that typical commercial pressurized water reactors fueled with low-enriched uranium will have significantly smaller nonfuel ν ¯ e contribution.

Providing a possible connection between neutrino emission and gravitational-wave (GW) bursts is important to our understanding of the physical processes that occur when black holes or neutron stars merge. In the Daya Bay experiment, using data collected from December 2011 to August 2017, a search has been performed for electron-antineutrino signals coinciding with detected GW events, including GW150914, GW151012, GW151226, GW170104, GW170608, GW170814, and GW170817. We used three time windows of $\mathrm{\pm 10~s}$, $\mathrm{\pm 500~s}$, and $\mathrm{\pm 1000~s}$ relative to the occurrence of the GW events, and a neutrino energy range of 1.8 to 100 MeV to search for correlated neutrino candidates. The detected electron-antineutrino candidates are consistent with the expected background rates for all the three time windows. Assuming monochromatic spectra, we found upper limits (90% confidence level) on electron-antineutrino fluence of $(1.13~-~2.44) \times 10^{11}~\rm{cm^{-2}}$ at 5 MeV to $8.0 \times 10^{7}~\rm{cm^{-2}}$ at 100 MeV for the three time windows. Under the assumption of a Fermi-Dirac spectrum, the upper limits were found to be $(5.4~-~7.0)\times 10^{9}~\rm{cm^{-2}}$ for the three time windows., Comment: 16 pages, 12 figures, 9 tables

We have performed a novel comparison between electron-beam polarimeters based on Møller and Compton scattering. A sequence of electron-beam polarization measurements were performed at low beam currents (< 5μA) during the Q[subscript weak] experiment in Hall-C at Jefferson Lab. These low current measurements were bracketed by the regular high current (180 μA) operation of the Compton polarimeter. All measurements were found to be consistent within experimental uncertainties of 1% or less, demonstrating that electron polarization does not depend significantly on the beam current. This result lends confidence to the common practice of applying Møller measurements made at low beam currents to physics experiments performed at higher beam currents. The agreement between two polarimetry techniques based on independent physical processes sets an important benchmark for future precision asymmetry measurements that require sub-1% precision in polarimetry. Keywords: Electron polarimetry, Compton polarimeter, Møller polarimeter, Jefferson Lab, United States. Department of Energy (Contract AC05-06OR23177), Natural Sciences and Engineering Research Council of Canada

This Letter reports the first extraction of individual antineutrino spectra from ^{235}U and ^{239}Pu fission and an improved measurement of the prompt energy spectrum of reactor antineutrinos at Daya Bay. The analysis uses 3.5×10^{6} inverse beta-decay candidates in four near antineutrino detectors in 1958 days. The individual antineutrino spectra of the two dominant isotopes, ^{235}U and ^{239}Pu, are extracted using the evolution of the prompt spectrum as a function of the isotope fission fractions. In the energy window of 4-6 MeV, a 7% (9%) excess of events is observed for the ^{235}U (^{239}Pu) spectrum compared with the normalized Huber-Mueller model prediction. The significance of discrepancy is 4.0σ for ^{235}U spectral shape compared with the Huber-Mueller model prediction. The shape of the measured inverse beta-decay prompt energy spectrum disagrees with the prediction of the Huber-Mueller model at 5.3σ. In the energy range of 4-6 MeV, a maximal local discrepancy of 6.3σ is observed.

This work reports a precise measurement of the reactor antineutrino flux using 2.2 million inverse beta decay (IBD) events collected with the Daya Bay near detectors in 1230 days. The dominant uncertainty on the neutron detection efficiency is reduced by 56% with respect to the previous measurement through a comprehensive neutron calibration and detailed data and simulation analysis. The new average IBD yield is determined to be $(5.91\pm0.09)\times10^{-43}~\rm{cm}^2/\rm{fission}$ with total uncertainty improved by 29%. The corresponding mean fission fractions from the four main fission isotopes $^{235}$U, $^{238}$U, $^{239}$Pu, and $^{241}$Pu are 0.564, 0.076, 0.304, and 0.056, respectively. The ratio of measured to predicted antineutrino yield is found to be $0.952\pm0.014\pm0.023$ ($1.001\pm0.015\pm0.027$) for the Huber-Mueller (ILL-Vogel) model, where the first and second uncertainty are experimental and theoretical model uncertainty, respectively. This measurement confirms the discrepancy between the world average of reactor antineutrino flux and the Huber-Mueller model., 10 pages, 9 figures, and 2 tables

This Letter reports the first measurement of the ^{235}U ν[over ¯]_{e} energy spectrum by PROSPECT, the Precision Reactor Oscillation and Spectrum experiment, operating 7.9 m from the 85 MW_{th} highly enriched uranium (HEU) High Flux Isotope Reactor. With a surface-based, segmented detector, PROSPECT has observed 31678±304(stat) ν[over ¯]_{e}-induced inverse beta decays, the largest sample from HEU fission to date, 99% of which are attributed to ^{235}U. Despite broad agreement, comparison of the Huber ^{235}U model to the measured spectrum produces a χ^{2}/ndf=51.4/31, driven primarily by deviations in two localized energy regions. The measured ^{235}U spectrum shape is consistent with a deviation relative to prediction equal in size to that observed at low-enriched uranium power reactors in the ν[over ¯]_{e} energy region of 5-7 MeV.

The Precision Reactor Oscillation and Spectrum (PROSPECT) Experiment is a reactor neutrino experiment designed to search for sterile neutrinos with a mass on the order of 1 eV/c$^2$ and to measure the spectrum of electron antineutrinos from a highly-enriched $^{235}$U nuclear reactor. The PROSPECT detector consists of an 11 by 14 array of optical segments in $^{6}$Li-loaded liquid scintillator at the High Flux Isotope Reactor in Oak Ridge National Laboratory. Antineutrino events are identified via inverse beta decay and read out by photomultiplier tubes located at the ends of each segment. The detector response is characterized using a radioactive source calibration system. This paper describes the design, operation, and performance of the PROSPECT source calibration system.

The fields of particle and nuclear physics have undertaken extensive programs to search for evidence of physics beyond that explained by current theories. The observation of the Higgs boson at the Large Hadron Collider completed the set of particles predicted by the Standard Model (SM), currently the best description of fundamental particles and forces. However, the theory's limitations include a failure to predict fundamental parameters and the inability to account for dark matter/energy, gravity, and the matter-antimater asymmetry in the universe, among other phenomena. Given the lack of additional particles found so far through direct searches in the post-Higgs era, indirect searches utilizing precise measurements of well predicted SM observables allow highly targeted alternative tests for physics beyond the SM. Indirect searches have the potential to reach mass/energy scales beyond those directly accessible by today's high-energy accelerators. The value of the weak charge of the proton Q_W^p is an example of such an indirect search, as it sets the strength of the proton's interaction with particles via the well-predicted neutral electroweak force. Parity violation (invariance under spatial inversion (x,y,z) -> (-x,-y,-z)) is violated only in the weak interaction, thus providing a unique tool to isolate the weak interaction in order to measure the proton's weak charge. Here we report Q_W^p=0.0719+-0.0045, as extracted from our measured parity-violating (PV) polarized electron-proton scattering asymmetry, A_ep=-226.5+-9.3 ppb. Our value of Q_W^p is in excellent agreement with the SM, and sets multi-TeV-scale constraints on any semi-leptonic PV physics not described within the SM., Direct link to Nature Version "https://rdcu.be/954U"

This Letter reports the first measurement of the ^{235}U ν[over ¯]_{e} energy spectrum by PROSPECT, the Precision Reactor Oscillation and Spectrum experiment, operating 7.9 m from the 85 MW_{th} highly enriched uranium (HEU) High Flux Isotope Reactor. With a surface-based, segmented detector, PROSPECT has observed 31678±304(stat) ν[over ¯]_{e}-induced inverse beta decays, the largest sample from HEU fission to date, 99% of which are attributed to ^{235}U. Despite broad agreement, comparison of the Huber ^{235}U model to the measured spectrum produces a χ^{2}/ndf=51.4/31, driven primarily by deviations in two localized energy regions. The measured ^{235}U spectrum shape is consistent with a deviation relative to prediction equal in size to that observed at low-enriched uranium power reactors in the ν[over ¯]_{e} energy region of 5-7 MeV.

Greenhouse and field studies were conducted to determine the effects of Wheat streak mosaic virus (WSMV), a member of the family Potyviridae, on root development and water-use efficiency (WUE) of two hard red winter wheat (Triticum aestivum) cultivars, one susceptible and one resistant to WSMV. In the greenhouse studies, wheat cultivars were grown under three water regimes of 30, 60, and 80% soil saturation capacity. After inoculation with WSMV, plants were grown for approximately 4 weeks and then harvested. Root and shoot weights were measured to determine the effect of the disease on biomass. In all water treatments, root biomass and WUE of inoculated susceptible plants were significantly less (P < 0.05) than those of the noninoculated control plants. However, in the resistant cultivar, significance was only found in the 30 and 60% treatments for root weight and WUE, respectively. Field studies were also conducted under three water regimes based on reference evapotranspiration rates. Significant reductions in forage, grain yield, and crop WUE were observed in the inoculated susceptible plots compared with the noninoculated plots. Both studies demonstrated that wheat streak mosaic reduces WUE, which is a major concern in the Texas Panhandle because of limited availability of water.

The role of soil water (or soil matric potential) in plant disease development is a well-documented phenomenon, especially in diseases caused by soilborne plant pathogens (7,11,14,19). For many plant pathogens, wet soil conditions or high soil matric potential promote hyphal growth, reproduction, spore dispersal, infection, and disease development (3,5–7,9–11). In sharp contrast to the abundance of information on the effect of soil water content on various plant diseases, the effect of plant diseases on soil water status and crop water-use efficiency is not well described. The significance of this effect may be less apparent in dryland agricultural production where rainfall is the only source of soil water; however, the effect has tremendous implications for irrigated agriculture in light of the dwindling water resources and the high cost of irrigation water (15–17). Plant diseases interfere with water intake (8,12), suggesting that there should be a greater amount of surplus water in diseased areas than in healthy areas of the field. If this is indeed the case, water-use efficiency would be low in diseased crops, and expenses associated with addition of more water (when in fact there is surplus water still in the soil) is a cost which could potentially be avoided. The implications of a plant disease effect on crop water-use efficiency is more significant for diseases which have characteristic patchy distribution, where large areas of the field are affected, than in sporadically infected plants which may not be amenable to sitespecific management. In this article, we describe the relationship between wheat streak mosaic (WSM) severity and soil water content as a prime example of the effect of a plant disease on soil water status and its implications for irrigated agriculture. Wheat streak mosaic virus (WSMV) is vectored by wheat curl mites (Aceria tosichella Keifer), which are typically blown into the field from nearby grasslands or fields with mite-infested volunteer wheat (4,20). WSM often exhibits severity gradients affecting over half of the field, with the heaviest infection toward the edges of the field (22). The disease is prevalent throughout the Texas Panhandle and much of the southwestern United States and is sometimes severe, drastically reducing both forage and grain yield (2,22). Infected plants exhibit symptoms ranging from chlorotic streaking and mosaic to complete chlorosis of leaves and stunting of the plants (20). A recent greenhouse study showed that plants infected with WSMV have poor root development and reduced water-use efficiency compared with uninfected plants (18). If diseased wheat cannot use water as efficiently as healthy wheat, blanket applications of irrigation water without recognizing specific requirements in different parts of the field is certainly an inefficient use of water. Diseased areas of the field are often infested with weeds because diseased plants cannot compete well with the weeds, and the unused soil moisture gets depleted by the weeds. If infected fields have greater soil water and lower wateruse efficiency than healthy fields, they don’t need as much water as healthy fields. This information can be vital to growers in making decisions whether to minimize or avoid water application depending on the disease severity. In light of rising energy costs, growers often question whether it is worthwhile to continue to irrigate fields affected with WSMV because information on the effect of the disease on crop water use is not available. In order to address this question, we conducted studies in growers’ fields to characterize the relation between wheat streak severity, soil water content, and water-use efficiency.

A fast-switching, high-repetition-rate magnet and power supply have been developed for and operated at TRIUMF, to deliver a proton beam to the new ultracold neutron (UCN) facility. The facility possesses unique operational requirements: a time-averaged beam current of 40~$\mu$A with the ability to switch the beam on or off for several minutes. These requirements are in conflict with the typical operation mode of the TRIUMF cyclotron which delivers nearly continuous beam to multiple users. To enable the creation of the UCN facility, a beam-sharing arrangement with another facility was made. The beam sharing is accomplished by the fast-switching (kicker) magnet which is ramped in 50~$\mu$s to a current of 193~A, held there for approximately 1~ms, then ramped down in the same short period of time. This achieves a 12~mrad deflection which is sufficient to switch the proton beam between the two facilities. The kicker magnet relies on a high-current, low-inductance coil connected to a fast-switching power supply that is based on insulated-gate bipolar transistors (IGBTs). The design and performance of the kicker magnet system and initial beam delivery results are reported., Comment: 16 pages, 21 figures

We report a measurement of electron antineutrino oscillation from the Daya Bay Reactor Neutrino Experiment with nearly 4 million reactor $\overline{\nu}_{e}$ inverse beta decay candidates observed over 1958 days of data collection. The installation of a Flash-ADC readout system and a special calibration campaign using different source enclosures reduce uncertainties in the absolute energy calibration to less than 0.5% for visible energies larger than 2 MeV. The uncertainty in the cosmogenic $^9$Li and $^8$He background is reduced from 45% to 30% in the near detectors. A detailed investigation of the spent nuclear fuel history improves its uncertainty from 100% to 30%. Analysis of the relative $\overline{\nu}_{e}$ rates and energy spectra among detectors yields $\sin^{2}2\theta_{13} = 0.0856\pm 0.0029$ and $\Delta m^2_{32}=(2.471^{+0.068}_{-0.070})\times 10^{-3}~\mathrm{eV}^2$ assuming the normal hierarchy, and $\Delta m^2_{32}=-(2.575^{+0.068}_{-0.070})\times 10^{-3}~\mathrm{eV}^2$ assuming the inverted hierarchy., Comment: 6 pages, 4 figures, and 1 table. v4: the published version

We installed a source for ultracold neutrons at a new, dedicated spallation target at TRIUMF. The source was originally developed in Japan and uses a superfluid-helium converter cooled to 0.9$\,$K. During an extensive test campaign in November 2017, we extracted up to 325000 ultracold neutrons after a one-minute irradiation of the target, over three times more than previously achieved with this source. The corresponding ultracold-neutron density in the whole production and guide volume is 5.3$\,$cm$^{-3}$. The storage lifetime of ultracold neutrons in the source was initially 37$\,$s and dropped to 24$\,$s during the eighteen days of operation. During continuous irradiation of the spallation target, we were able to detect a sustained ultracold-neutron rate of up to 1500$\,$s$^{-1}$. Simulations of UCN production, UCN transport, temperature-dependent UCN yield, and temperature-dependent storage lifetime show excellent agreement with the experimental data and confirm that the ultracold-neutron-upscattering rate in superfluid helium is proportional to $T^7$., 8 pages, 10 figures

The Daya Bay Experiment consists of eight identically designed detectors located in three underground experimental halls named as EH1, EH2, EH3, with 250, 265 and 860 meters of water equivalent vertical overburden, respectively. Cosmic muon events have been recorded over a two-year period. The underground muon rate is observed to be positively correlated with the effective atmospheric temperature and to follow a seasonal modulation pattern. The correlation coefficient $\alpha$, describing how a variation in the muon rate relates to a variation in the effective atmospheric temperature, is found to be $\alpha_{\text{EH1}} = 0.362\pm0.031$, $\alpha_{\text{EH2}} = 0.433\pm0.038$ and $\alpha_{\text{EH3}} = 0.641\pm0.057$ for each experimental hall., Comment: Updated to be identical to the published version

This paper describes the design and performance of a 50 liter, two-segment $^{6}$Li-loaded liquid scintillator detector that was designed and operated as prototype for the PROSPECT (Precision Reactor Oscillation and Spectrum) Experiment. The two-segment detector was constructed according to the design specifications of the experiment. It features low-mass optical separators, an integrated source and optical calibration system, and materials that are compatible with the $^{6}$Li-doped scintillator developed by PROSPECT. We demonstrate a high light collection of 850$\pm$20 PE/MeV, an energy resolution of $\sigma$ = 4.0$\pm$0.2% at 1 MeV, and efficient pulse-shape discrimination of low $dE/dx$ (electronic recoil) and high $dE/dx$ (nuclear recoil) energy depositions. An effective scintillation attenuation length of 85$\pm$3 cm is measured in each segment. The 0.1% by mass concentration of $^{6}$Li in the scintillator results in a measured neutron capture time of $\tau$ = 42.8$\pm$0.2 $\mu s$. The long-term stability of the scintillator is also discussed. The detector response meets the criteria necessary for achieving the PROSPECT physics goals and demonstrates features that may find application in fast neutron detection., Comment: 16 pages, 13 figures; minor edits to design detail and references

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 meter water equivalent overburden. Data collected during 33 live-days of reactor operation at a nominal power of 85 MW yields a detection of 25461 $\pm$ 283 (stat.) inverse beta decays. Observation of reactor antineutrinos can be achieved in PROSPECT at 5$\sigma$ statistical significance within two hours 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 2.2$\sigma$ confidence level., Comment: 7 pages, 5 figures; v3: Added additional supplemental files

The Precision Reactor Oscillation and Spectrum Experiment, PROSPECT, is designed to make both a precise measurement of the antineutrino spectrum from a highly-enriched uranium reactor and to probe eV-scale sterile neutrinos by searching for neutrino oscillations over meter-long baselines. PROSPECT utilizes a segmented $^6$Li-doped liquid scintillator detector for both efficient detection of reactor antineutrinos through the inverse beta decay reaction and excellent background discrimination. PROSPECT is a movable 4-ton antineutrino detector covering distances of 7m to 13m from the High Flux Isotope Reactor core. It will probe the best-fit point of the $\bar\nu_e$ disappearance experiments at 4$\sigma$ in 1 year and the favored regions of the sterile neutrino parameter space at more than 3$\sigma$ in 3 years. PROSPECT will test the origin of spectral deviations observed in recent $\theta_{13}$ experiments, search for sterile neutrinos, and address the hypothesis of sterile neutrinos as an explanation of the reactor anomaly. This paper describes the design, construction, and commissioning of PROSPECT and reports first data characterizing the performance of the PROSPECT antineutrino detector., Comment: 30 pages, 33 figures; updated with journal revision and reference

A new measurement of the reactor antineutrino flux and energy spectrum by the Daya Bay reactor neutrino experiment is reported. The antineutrinos were generated by six 2.9~GW$_{\mathrm{th}}$ nuclear reactors and detected by eight antineutrino detectors deployed in two near (560~m and 600~m flux-weighted baselines) and one far (1640~m flux-weighted baseline) underground experimental halls. With 621 days of data, more than 1.2 million inverse beta decay (IBD) candidates were detected. The IBD yield in the eight detectors was measured, and the ratio of measured to predicted flux was found to be $0.946\pm0.020$ ($0.992\pm0.021$) for the Huber+Mueller (ILL+Vogel) model. A 2.9~$\sigma$ deviation was found in the measured IBD positron energy spectrum compared to the predictions. In particular, an excess of events in the region of 4-6~MeV was found in the measured spectrum, with a local significance of 4.4~$\sigma$. A reactor antineutrino spectrum weighted by the IBD cross section is extracted for model-independent predictions., Comment: version published in Chinese Physics C

"Candidatus Liberibacter asiaticus" (CaLas) is associated with citrus Huanglongbing (HLB, yellow shoot disease), which is highly destructive to world citrus production. Understanding the relationships of CaLas isolates from different geographical regions is important for HLB research and development of disease management strategies. In this study, 301 CaLas isolates [85 Brazil, 132 China, and 84 U.S. (83 Florida and 1 California)] were collected, and genomic variations among them were evaluated based on the analyses of two genomic loci: trn1, characteristic of variable tandem repeat numbers (TRNs), and snp1, characteristic of single nucleotide polymorphisms (SNPs). Locus trn1 revealed the homogeneity of all Brazilian isolates, and locus snp1 revealed the homogeneity of most Florida isolates. When the two loci were analyzed simultaneously, i.e., double-locus (DL) analyses, CaLas isolates were clustered mostly according to geographical origins. DL genotype 1 included 97 % of the Chinese isolates, DL genotype 2 included all Brazilian isolates, and DL genotype 3 included 93 % of the U.S. isolates. DL analyses successfully revealed inter-continental overlapping or movement pattern of CaLas isolates. The isolate recently found in California belonged to Asiatic DL genotype 1.

Symmetry permeates nature and is fundamental to all laws of physics. One example is parity (mirror) symmetry, which implies that flipping left and right does not change the laws of physics. Laws for electromagnetism, gravity and the subatomic strong force respect parity symmetry, but the subatomic weak force does not. Historically, parity violation in electron scattering has been important in establishing (and now testing) the standard model of particle physics. One particular set of quantities accessible through measurements of parity-violating electron scattering are the effective weak couplings C2q, sensitive to the quarks' chirality preference when participating in the weak force, which have been measured directly only once in the past 40 years. Here we report a measurement of the parity-violating asymmetry in electron-quark scattering, which yields a determination of 2C2u - C2d (where u and d denote up and down quarks, respectively) with a precision increased by a factor of five relative to the earlier result. These results provide evidence with greater than 95 per cent confidence that the C2q couplings are non-zero, as predicted by the electroweak theory. They lead to constraints on new parity-violating interactions beyond the standard model, particularly those due to quark chirality. Whereas contemporary particle physics research is focused on high-energy colliders such as the Large Hadron Collider, our results provide specific chirality information on electroweak theory that is difficult to obtain at high energies. Our measurement is relatively free of ambiguity in its interpretation, and opens the door to even more precise measurements in the future.

A simple, self-contained, thermo-electrically cooled SiPM system is presented which cools a SiPM array to -20oC. The array views a NaI scintillator through a 75 mm diameter glass window. Waste heat is removed with a large heat sink and AC fans. Above 40 keV in an air-coupled 2'' × 2'' NaI scintillator, the SiPM dark count rate was reduced by a factor ~1000 when cooled. Performance when cooled was very similar to a PMT tested in the same setup and adequate for nuclear spectroscopy above 25 keV. Originally, water cooling was used but it was replaced by air cooling which is more suitable for a self-contained system, giving the advantage of portability without degrading performance. Straightforward improvements would allow cooling the SiPM to -30oC or below, which would further reduce the dark count rate and extend the spectroscopically useful range to even lower energies. Such a system would be rugged and suitable for field use, for instance for inspection of cargo for gamma ray emissions.

PROSPECT, the Precision Reactor Oscillation and SPECTrum experiment, is a short-baseline reactor antineutrino experiment designed to provide precision measurements of the $^{235}$U product $\overline{\nu}_e$ spectrum of utilizing an optically segmented 4-ton liquid scintillator detector. PROSPECT's segmentation system, the optical grid, plays a central role in reconstructing the position and energy of $\overline{\nu}_e$ interactions in the detector. This paper is the technical reference for this PROSPECT subsystem, describing its design, fabrication, quality assurance, transportation and assembly in detail. In addition, the dimensional, optical and mechanical characterizations of optical grid components and the assembled PROSPECT target are also presented. The technical information and characterizations detailed here will inform geometry-related inputs for PROSPECT physics analysis, and can guide a variety of future particle detection development efforts, such as those using optically reflecting materials or filament-based 3D printing., Comment: 31 pages, 28 figures

This work reports the production and characterization of lithium-loaded liquid scintillator (LiLS) for the Precision Reactor Oscillation and Spectrum Experiment (PROSPECT). Fifty-nine 90 liter batches of LiLS (${}^6{\rm Li}$ mass fraction 0.082%$\pm$0.001%) were produced and samples from all batches were characterized by measuring their optical absorbance relative to air, light yield relative to a pure liquid scintillator reference, and pulse shape discrimination capability. Fifty-seven batches passed the quality assurance criteria and were used for the PROSPECT experiment., 16 pages, 15 figures

In May 2012, the $Q^{p}_{\rm Weak}$ collaboration completed a two year measurement program to determine the weak charge of the proton ${Q^{p}_W} = ( 1 - 4\sin^2{\theta_{W}})$ at the Thomas Jefferson National Accelerator Facility (TJNAF). The experiment was designed to produce a 4.0 % measurement of the weak charge, via a 2.5 % measurement of the parity violating asymmetry in the number of elastically scattered 1.165 GeV electrons from protons, at forward angles. At the proposed precision, the experiment would produce a 0.3 % measurement of the weak mixing angle at a momentum transfer of Q 2 = 0.026 GeV2, making it the most precise stand alone measurement of the weak mixing angle at low momentum transfer. In combination with other parity measurements, $Q^{p}_{\rm Weak}$ will also provide a high precision determination of the weak charges of the up and down quarks. At the proposed precision, a significant deviation from the Standard Model prediction could be a signal of new physics at mass scales up to ≃ 6 TeV, whereas agreement would place new and significant constraints on possible Standard Model extensions at mass scales up to ≃ 2 TeV. This paper provides an overview of the physics and the experiment, as well as a brief look at some preliminary diagnostic and analysis data.

Remote detection of non-native invasive plant species using geospatial imagery may significantly improve monitoring, planning and management practices by eliminating shortfalls, such as observer bias and accessibility involved in ground-based surveys. The use of remote sensing for accurate mapping invasion extent and pattern offers several advantages, including repeatability, large area coverage, complete instead of sub-sampled assessments and greater cost-effectiveness over ground-based methods. It is critical for locating, early mapping and controlling small infestations before they reach economically prohibitive or ecologically significant levels over larger land areas. This study was designed to explore the ability of hyperspectral imagery for mapping infestation of musk thistle (Carduus nutans) on a native grassland during the preflowering stage in mid-April and during the peak flowering stage in mid-June using the support vector machine classifier and to assess and compare the resulting mapping accuracy for these two distinctive phenological stages. Accuracy assessment revealed that the overall accuracies were 79% and 91% for the classified images at preflowering and peak flowering stages, respectively. These results indicate that repeated detection of the infestation extent, as well as infestation severity or intensity, of this noxious weed in a spatial and temporal context is possible using hyperspectral remote sensing imagery.

The Q-weak experiment at Jefferson Laboratory measured the parity violating asymmetry (A P V ) in elastic electron-proton scattering at small momentum transfer squared (Q 2=0.025 (G e V/c)2), with the aim of extracting the proton’s weak charge ( ${Q^p_W}$ ) to an accuracy of 5 %. As one of the major uncertainty contribution sources to ${Q^p_W}$ , Q 2 needs to be determined to ∼1 % so as to reach the proposed experimental precision. For this purpose, two sets of high resolution tracking chambers were employed in the experiment, to measure tracks before and after the magnetic spectrometer. Data collected by the tracking system were then reconstructed with dedicated software into individual electron trajectories for experimental kinematics determination. The Q-weak kinematics and the analysis scheme for tracking data are briefly described here. The sources that contribute to the uncertainty of Q 2 are discussed, and the current analysis status is reported.

The tomato potato psyllid (TPP) Bactericera cockerelli (Hemiptera Triozidae) was first notified to the New Zealand Ministry of Agriculture and Forestry (MAF) in May 2006 although it has been suggested by several authors to have been present in New Zealand in 2005 MAF undertook an entry pathway analysis during the initial investigation into TPP in 2006 TPP is a vector of the bacteriumlike pathogen Candidatus Liberibacter solanacearum (liberibacter) and MAF further analysed the entry pathway of TPP during the liberibacter incursion response in 2008 This paper summarises the data and reasoning behind the conclusion that TPP was most plausibly introduced to New Zealand as a result of smuggling rather than through slippage on regulated pathways

The prevalence of wheat streak mosaic, caused by Wheat streak mosaic virus, was assessed using Landsat 5 Thematic Mapper (TM) images in two counties of the Texas Panhandle during the 2005–2006 and 2007–2008 crop years. In both crop years, wheat streak mosaic was widely distributed in the counties studied. Healthy and diseased wheat were separated on the images using the maximum likelihood classifier. The overall classification accuracies were between 89.47 and 99.07% for disease detection when compared to “ground truth” field observations. Omission errors (i.e., pixels incorrectly excluded from a particular class and assigned to other classes) varied between 0 and 12.50%. Commission errors (i.e., pixels incorrectly assigned to a particular class that actually belong to other classes) ranged from 0 to 23.81%. There were substantial differences between planted wheat acreage reported by the United States Department of Agriculture-National Agricultural Statistics Service (USDA-NASS) and that detected by image analyses. However, harvested wheat acreage reported by USDA-NASS and that detected by image classifications were closely matched. These results indicate that the TM image can be used to accurately detect and quantify incidence of wheat streak mosaic over large areas. This method appears to be one of the best currently available for identification and mapping disease incidence over large and remote areas by offering a repeatable, inexpensive, and synoptic strategy during the course of a growing season.

Wheat streak mosaic virus, vectored by the wheat curl mite Aceria tosichella Keifer, is a major limiting factor in wheat production in the Texas Panhandle. It is the most frequently encountered virus in the region, affecting both shoot and root biomass, and consequently it can drastically reduce both forage and grain yield, and water-use efficiency of the plant. In light of the continuing decline of water levels in the Ogallala Aquifer, its effect on water-use efficiency has significant implications for irrigated fields, especially with regard to energy costs for pumping water. This article estimates the potential economic losses from the virus infection. To achieve this objective, partial budgeting techniques, based primarily on data from field experiments, were used. Results indicate that Wheat streak mosaic virus causes grain and forage yield losses that significantly affect profits from wheat production. In addition, irrigated wheat producers are more negatively affected by the disease due to the economic losses from reduced water-use efficiency of infected plants. The economic insights from this article provide important implications for wheat management and research priority-setting.

From the point of view of the intrinsic rotation, the Jupiter Trojans are not as well characterized as the main belt asteroids, primarily because the available sample of lightcurves is small and mainly restricted to the largest objects. We have obtained rotational periods and lightcurve amplitudes for 6 Trojan asteroids, which range between values of 5.7 and 9.6 h and 0.08 and 0.59 magnitudes, respectively. This sample includes an object of absolute visual magnitude H=11.5 m, which corresponds to physical radii ranging from 35 to 22 km, assuming albedos between 4% and 10%. The values of the rotation periods found are consistent with those found for the Main Belt Asteroids in the same size range.