1,572 research outputs found
Author Correction: Native diversity buffers against severity of non-native tree invasions
No full textDetermination of electroweak parameters in polarised deep-inelastic scattering at HERA
No full textThe parameters of the electroweak theory are determined in a combined electroweak and QCD analysis using all deep-inelastic e+p and e−p neutral current and charged current scattering cross sections published by the H1 Collaboration, including data with longitudinally polarised lepton beams. Various fits to Standard Model parameters in the on-shell scheme are performed. The mass of the W boson is determined as mW=80.520±0.115 GeV . The axial-vector and vector couplings of the light quarks to the Z boson are also determined. Both results improve the precision of previous H1 determinations based on HERA-I data by about a factor of two. Possible scale dependence of the weak coupling parameters in both neutral and charged current interactions beyond the Standard Model is also studied. All results are found to be consistent with the Standard Model expectations
Author Correction: Native diversity buffers against severity of non-native tree invasions.
No full textCombination and QCD analysis of charm and beauty production cross-section measurements in deep inelastic ep scattering at HERA
No full textMeasurements of open charm and beauty production cross sections in deep inelastic ep scattering at HERA from the H1 and ZEUS Collaborations are combined. Reduced cross sections are obtained in the kinematic range of negative four-momentum transfer squared of the photon 2.5 GeV2≤Q2≤2000GeV2 and Bjorken scaling variable 3⋅10−5≤xBj≤5⋅10−2 . The combination method accounts for the correlations of the statistical and systematic uncertainties among the different datasets. Perturbative QCD calculations are compared to the combined data. A next-to-leading order QCD analysis is performed using these data together with the combined inclusive deep inelastic scattering cross sections from HERA. The running charm- and beauty-quark masses are determined as mc(mc)=1.290+0.046−0.041(exp/fit) +0.062−0.014(model) +0.003−0.031(parameterisation) GeV and mb(mb)=4.049+0.104−0.109(exp/fit) +0.090−0.032(model) +0.001−0.031(parameterisation) GeV
Native diversity buffers against severity of non-native tree invasions
No full textLink to a related website: https://doi.org/10.1038/s41586-023-06654-9, Author correctionDetermining the drivers of non-native plant invasions is critical for managing native ecosystems and limiting the spread of invasive species1,2. Tree invasions in particular have been relatively overlooked, even though they have the potential to transform ecosystems and economies3,4. Here, leveraging global tree databases5–7, we explore how the phylogenetic and functional diversity of native tree communities, human pressure and the environment influence the establishment of non-native tree species and the subsequent invasion severity. We find that anthropogenic factors are key to predicting whether a location is invaded, but that invasion severity is underpinned by native diversity, with higher diversity predicting lower invasion severity. Temperature and precipitation emerge as strong predictors of invasion strategy, with non-native species invading successfully when they are similar to the native community in cold or dry extremes. Yet, despite the influence of these ecological forces in determining invasion strategy, we find evidence that these patterns can be obscured by human activity, with lower ecological signal in areas with higher proximity to shipping ports. Our global perspective of non-native tree invasion highlights that human drivers influence non-native tree presence, and that native phylogenetic and functional diversity have a critical role in the establishment and spread of subsequent invasions
Using scientific-grade CCDs for the direct detection of dark matter with the DAMIC-M experiment
No full textThe DAMIC-M (Dark matter in CCDs at Modane) experiment, successor of DAMIC at SNOLAB (Sudbury Neutrino Observatory laboratory), is devoted to the search for dark matter (DM) candidates interacting with the electrons or the nuclei of the bulk silicon of fully depleted Charge-Coupled Devices (CCDs). A kilogram-sized target mass will be installed at the Modane underground laboratory which offers an excellent low background environment for rare-event searches. The implementation of the Skipper readout allows for multiple non-destructive pixel charge measurements, reaching a readout noise of a fraction of an electron. This perfect performance in terms of charge resolution can be limited by the radioactive background and the noise introduced by the external electronics. Much effort is put into the protection of the silicon from contamination by cosmic ray spallation, careful choice of the materials to support and shield the CCDs, and development of a new acquisition system with fast and sensitive electronics for the control and readout of a CCD. All these advancements will push the detection threshold down to a few eVs, improving the sensitivity of DAMIC-M by at least one order of magnitude with respect to previous experiments. I will present the current status of DAMIC-M describing our technological challenges and the solutions we have adopted, and introduce the ongoing assembly of a prototype detector, the Low Background Chamber, aiming at validating our final design options and produce the first scientific results
Measurement of exclusive π + π − and ρ0 meson photoproduction at HERA
No full textExclusive photoproduction of ρ0(770) mesons is studied using the H1 detector at the ep collider HERA. A sample of about 900,000 events is used to measure single- and double-differential cross sections for the reaction γp→π+π−Y. Reactions where the proton stays intact (mY=mp) are statistically separated from those where the proton dissociates to a low-mass hadronic system (mp<mY<10 GeV). The double-differential cross sections are measured as a function of the invariant mass mππ of the decay pions and the squared 4-momentum transfer t at the proton vertex. The measurements are presented in various bins of the photon–proton collision energy Wγp. The phase space restrictions are 0.5≤mππ≤2.2 GeV, |t|≤1.5 GeV2, and 20≤Wγp≤80 GeV. Cross section measurements are presented for both elastic and proton-dissociative scattering. The observed cross section dependencies are described by analytic functions. Parametrising the mππ dependence with resonant and non-resonant contributions added at the amplitude level leads to a measurement of the ρ0(770) meson mass and width at mρ=770.8+2.6−2.7 (tot.) MeV and Γρ=151.3+2.7−3.6 (tot.) MeV, respectively. The model is used to extract the ρ0(770) contribution to the π+π− cross sections and measure it as a function of t and Wγp. In a Regge asymptotic limit in which one Regge trajectory α(t) dominates, the intercept α(t=0)=1.0654 +0.0098−0.0067 (tot.) and the slope α′(t=0)=0.233+0.067−0.074 (tot.) GeV−2 of the t dependence are extracted for the case mY=mp
Precision measurement of Compton scattering in silicon with a skipper CCD for dark matter detection
No full textExperiments aiming to directly detect dark matter through particle recoils can achieve energy thresholds of O(10 eV). In this regime, ionization signals from small-angle Compton scatters of environmental γ rays constitute a significant background. Monte Carlo simulations used to build background models have not been experimentally validated at these low energies. We report a precision measurement of Compton scattering on silicon atomic shell electrons down to 23 eV. A skipper charge-coupled device with single-electron resolution, developed for the DAMIC-M experiment, was exposed to a 241Am γ-ray source over several months. Features associated with the silicon K-, L1-, and L2,3-shells are clearly identified, and scattering on valence electrons is detected for the first time below 100 eV. We find that the relativistic impulse approximation for Compton scattering, which is implemented in Monte Carlo simulations commonly used by direct detection experiments, does not reproduce the measured spectrum below 0.5 keV. The data are in better agreement with ab initio calculations originally developed for x-ray absorption spectroscopy
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