Fact sheet: Dead wood plays important roles in pinyon-juniper woodland recovery after wildfire

Stand-replacing crown fires appear to be consistent with historical patterns of natural disturbance in some pinyon-juniper woodlands of the American Southwest, Colorado Plateau, and Great Basin. These moderate- to high-severity fires result in the death of most or all trees across areas that range from small groups of a few trees to hundreds of acres. In some forest ecosystems, logs remaining after fire are known to reduce soil movement and increase retention of soil nitrogen. In studies of pinyon-juniper management, woody material created by tree thinning has been shown to enhance plant establishment and affect soil moisture and chemistry..

Working paper 28: Southwestern mixed conifer forests: Evaluating reference conditions to guide ecological restoration treatments.

Mixed-conifer forests of the Southwest are variable and complex, covering approximately 2.5-million acres scattered across the region (Dieterich 1983, Korb et al. 2013; Figure 1). Mixed-conifer forests contain a diverse mix of tree species (Table 1) and typically occur between, but do not include, the lower-elevation warmer, drier ponderosa pine forests and the highest-elevation cooler, wetter spruce-fir forests. Because mixed-conifer forests have diverse stand structures, forest composition and disturbance regimes, it is often difficult to generalize about reference conditions and historical fire regimes that can be used to guide management for specific locations. In this working paper, we 1) describe the current knowledge of mixed-conifer historical reference conditions for fire regimes, stand structure, and species composition in the Southwest (Arizona, New Mexico and adjacent areas); 2) provide field diagnostics to assess reference conditions; and 3) offer land managers restoration-related guidance to promote resilient mixed-conifer forests in the Southwest

Population ecology of Fendler ceanothus: responses to herbivory and forest restoration treatments

To understand responses of Fendler ceanothus to forest restoration treatments and large ungulate herbivory, I focused research on four areas: 1) effects of large ungulate herbivores on Fendler ceanothus stem size, morphology, and flower production, 2) production, fate, and germination of Fendler ceanothus seeds, 3) importance of overstory density, ungulate herbivory, prescribed fire, and drought for Fendler ceanothus growth and regeneration, and 4) simulation of population dynamics under various management scenarios. After two seasons (1999, 2000), plants protected from large ungulate herbivores were larger and produced greater biomass, leaf area, and flowering stems than plants that were not protected. These results showed that large herbivores such as mule deer (Odocoileus hemionus) and Rocky Mountain elk (Cervus elaphus) constrained growth and reproduction of Fendler ceanothus in thinned forest units. Fendler ceanothus stems that were not protected from large herbivores did not produce fruit over the four-year study (1999-2002). Seed production (2000-2001) was affected by stem size and probably drought. Predispersal seed parasites and postdispersal predators were important sources of ovule loss. Seed germination after iii exposure to 90C (10-minute duration) was greater than without heat treatment. These results increase our understanding of Fendler ceanothus seed production and losses. Stand density index (SDI) and browsing by ungulates were negatively related to Fendler ceanothus growth. Prediction of growth from SDI and browsing was poor in years of drought. Plant mortality was positively related to depth of forest floor consumed in experimental burning. Fendler ceanothus seedlings emerged on burned plots but not on unburned plots. These results indicate that overstory tree thinning and prescribed fire can increase growth and reproduction of Fendler ceanothus but responses are constrained by herbivory and drought. Simulation of Fendler ceanothus population dynamics suggested that restoration treatments and herbivory interact to affect long-term persistence and population structure. Populations that did not experience fire were generally dominated by dormant seeds whereas burned populations had relatively even life stage structures at the end of the 25- year simulation. Frequent fire (2-5 yr) stimulated growth of protected populations but negatively affected populations exposed to intense herbivory

Fact sheet: Canopy cover and forest conditions

Canopy cover and how it relates to other forest attributes as an indicator of forest conditions

Magnetic trapping of ultracold neutrons

Three-dimensional magnetic confinement of neutrons is reported. Neutrons are loaded into an Ioffe-type superconducting magnetic trap through inelastic scattering of cold neutrons with 4He. Scattered neutrons with sufficiently low energy and in the appropriate spin state are confined by the magnetic field until they decay. The electron resulting from neutron decay produces scintillations in the liquid helium bath that results in a pulse of extreme ultraviolet light. This light is frequency downconverted to the visible and detected. Results are presented in which 500 +/- 155 neutrons are magnetically trapped in each loading cycle, consistent with theoretical predictions. The lifetime of the observed signal, 660 s +290/-170 s, is consistent with the neutron beta-decay lifetime.Comment: 17 pages, 18 figures, accepted for publication in Physical Review

Search for displaced vertices arising from decays of new heavy particles in 7 TeV pp collisions at ATLAS

We present the results of a search for new, heavy particles that decay at a significant distance from their production point into a final state containing charged hadrons in association with a high-momentum muon. The search is conducted in a pp-collision data sample with a center-of-mass energy of 7 TeV and an integrated luminosity of 33 pb^-1 collected in 2010 by the ATLAS detector operating at the Large Hadron Collider. Production of such particles is expected in various scenarios of physics beyond the standard model. We observe no signal and place limits on the production cross-section of supersymmetric particles in an R-parity-violating scenario as a function of the neutralino lifetime. Limits are presented for different squark and neutralino masses, enabling extension of the limits to a variety of other models.Comment: 8 pages plus author list (20 pages total), 8 figures, 1 table, final version to appear in Physics Letters

Measurement of the polarisation of W bosons produced with large transverse momentum in pp collisions at sqrt(s) = 7 TeV with the ATLAS experiment

This paper describes an analysis of the angular distribution of W->enu and W->munu decays, using data from pp collisions at sqrt(s) = 7 TeV recorded with the ATLAS detector at the LHC in 2010, corresponding to an integrated luminosity of about 35 pb^-1. Using the decay lepton transverse momentum and the missing transverse energy, the W decay angular distribution projected onto the transverse plane is obtained and analysed in terms of helicity fractions f0, fL and fR over two ranges of W transverse momentum (ptw): 35 < ptw < 50 GeV and ptw > 50 GeV. Good agreement is found with theoretical predictions. For ptw > 50 GeV, the values of f0 and fL-fR, averaged over charge and lepton flavour, are measured to be : f0 = 0.127 +/- 0.030 +/- 0.108 and fL-fR = 0.252 +/- 0.017 +/- 0.030, where the first uncertainties are statistical, and the second include all systematic effects.Comment: 19 pages plus author list (34 pages total), 9 figures, 11 tables, revised author list, matches European Journal of Physics C versio

Observation of a new chi_b state in radiative transitions to Upsilon(1S) and Upsilon(2S) at ATLAS

The chi_b(nP) quarkonium states are produced in proton-proton collisions at the Large Hadron Collider (LHC) at sqrt(s) = 7 TeV and recorded by the ATLAS detector. Using a data sample corresponding to an integrated luminosity of 4.4 fb^-1, these states are reconstructed through their radiative decays to Upsilon(1S,2S) with Upsilon->mu+mu-. In addition to the mass peaks corresponding to the decay modes chi_b(1P,2P)->Upsilon(1S)gamma, a new structure centered at a mass of 10.530+/-0.005 (stat.)+/-0.009 (syst.) GeV is also observed, in both the Upsilon(1S)gamma and Upsilon(2S)gamma decay modes. This is interpreted as the chi_b(3P) system.Comment: 5 pages plus author list (18 pages total), 2 figures, 1 table, corrected author list, matches final version in Physical Review Letter

Measurement of the inclusive isolated prompt photon cross-section in pp collisions at sqrt(s)= 7 TeV using 35 pb-1 of ATLAS data

A measurement of the differential cross-section for the inclusive production of isolated prompt photons in pp collisions at a center-of-mass energy sqrt(s) = 7 TeV is presented. The measurement covers the pseudorapidity ranges |eta|<1.37 and 1.52<=|eta|<2.37 in the transverse energy range 45<=E_T<400GeV. The results are based on an integrated luminosity of 35 pb-1, collected with the ATLAS detector at the LHC. The yields of the signal photons are measured using a data-driven technique, based on the observed distribution of the hadronic energy in a narrow cone around the photon candidate and the photon selection criteria. The results are compared with next-to-leading order perturbative QCD calculations and found to be in good agreement over four orders of magnitude in cross-section.Comment: 7 pages plus author list (18 pages total), 2 figures, 4 tables, final version published in Physics Letters