Structural response of Caribbean dry forests to hurricane winds: a case study from Guanica Forest, Puerto Rico

Tropical dry forests in the Caribbean have an uniquely short, shrubby structure with a high proportion of multiple-stemmed trees compared to dry forests elsewhere in the Neotropics. Previous studies have shown that this structure can arise without the loss of main stems from cutting, grazing, or other human intervention. The Caribbean has a high frequency of hurricanes, so wind may also influence forest stature. Furthermore, these forests also tend to grow on soils with low amounts of available phosphorus, which may also influence structure. The objective of this study was to assess the role of high winds in structuring dry forest, and to determine whether soil nutrient pools influence forest response following hurricane disturbance. Methods: Over 2000 stems in five plots were sampled for hurricane effects within 1 week after Hurricane Georges impacted field sites in 1998. Sprout initiation, growth, and mortality were analysed for 1407 stems for 2 years after the hurricane. Soil nutrient pools were measured at the base of 456 stems to assess association between nutrients and sprout dynamics. Results: Direct effects of the hurricane were minimal, with stem mortality at \u3c 2% and structural damage to stems at 13%, although damage was biased toward stems of larger diameter. Sprouting response was high . over 10 times as many trees had sprouts after the hurricane as before. The number of sprouts on a stem also increased significantly. Sprouting was common on stems that only suffered defoliation or had no visible effects from the hurricane. Sprout survival after 2 years was also high (\u3e 86%). Soil nutrient pools had little effect on forest response as a whole, but phosphorus supply did influence sprout dynamics on four of the more common tree species. Main Conclusions: Hurricanes are able to influence Caribbean tropical dry forest structure by reducing average stem diameter and basal area and generating significant sprouting responses. New sprouts, with ongoing survival, will maintain the high frequency of multi-stemmed trees found in this region. Sprouting is not limited to damaged stems, indicating that trees are responding to other aspects of high winds, such as short-term gravitational displacement or sway. Soil nutrients play a secondary role in sprouting dynamics of a subset of species. The short, shrubby forest structure common to the Caribbean can arise naturally as a response to hurricane winds

Measurement of the CP-violating weak phase φs and the decay width difference δΓc using the Bs 0→J/ψφ(1020) decay channel in pp collisions at √ s=8 TeV

The CP-violating weak phase ϕsϕs of the View the MathML sourceBs0 meson and the decay width difference ΔΓsΔΓs of the View the MathML sourceBs0 light and heavy mass eigenstates are measured with the CMS detector at the LHC using a data sample of View the MathML sourceBs0→J/ψϕ(1020)→μ+μ−K+K− decays. The analysed data set corresponds to an integrated luminosity of View the MathML source19.7fb−1 collected in pp collisions at a centre-of-mass energy of View the MathML source8TeV. A total of 49 200 reconstructed View the MathML sourceBs0 decays are used to extract the values of ϕsϕs and ΔΓsΔΓs by performing a time-dependent and flavour-tagged angular analysis of the μ+μ−K+K−μ+μ−K+K− final state. The weak phase is measured to be View the MathML sourceϕs=−0.075±0.097(stat)±0.031(syst) rad, and the decay width difference is View the MathML sourceΔΓs=0.095±0.013(stat)±0.007(syst) ps−1

Search for resonant t(t)over-bar production in proton-proton collisions at root s=13 TeV

A search for a heavy resonance decaying into a top quark and antiquark (t t \uaf) pair is performed using proton-proton collisions at 1a s=13 TeV. The search uses the data set collected with the CMS detector in 2016, which corresponds to an integrated luminosity of 35.9 fb 121 . The analysis considers three exclusive final states and uses reconstruction techniques that are optimized for top quarks with high Lorentz boosts, which requires the use of nonisolated leptons and jet substructure techniques. No significant excess of events relative to the expected yield from standard model processes is observed. Upper limits on the production cross section of heavy resonances decaying to a t t \uaf pair are calculated. Limits are derived for a leptophobic topcolor Z \u2032 resonance with widths of 1, 10, and 30%, relative to the mass of the resonance, and exclude masses up to 3.80, 5.25, and 6.65 TeV, respectively. Kaluza-Klein excitations of the gluon in the Randall-Sundrum model are excluded up to 4.55 TeV. To date, these are the most stringent limits on t t \uaf resonances

Observation of Single Top Quark Production in Association with a Z Boson in Proton-Proton Collisions at root s=13 TeV

The observation of single top quark production in association with a Z boson and a quark (tZq) is reported. Events from proton-proton collisions at a center-of-mass energy of 13 TeV containing three charged leptons (either electrons or muons) and at least two jets are analyzed. The data were collected with the CMS detector in 2016 and 2017 and correspond to an integrated luminosity of 77.4fb-1. The increased integrated luminosity, a multivariate lepton identification, and a redesigned analysis strategy improve significantly the sensitivity of the analysis compared to previous searches for tZq production. The tZq signal is observed with a significance well over 5 standard deviations. The measured tZq production cross section is σ(pp→tZq→t?+?-q)=111±13(stat)-9+11(syst) fb, for dilepton invariant masses above 30 GeV, in agreement with the standard model expectation

Measurements with silicon photomultipliers of dose-rate effects in the radiation damage of plastic scintillator tiles in the CMS hadron endcap calorimeter

Measurements are presented of the reduction of signal output due to radiation damage for two types of plastic scintillator tiles used in the hadron endcap (HE) calorimeter of the CMS detector. The tiles were exposed to particles produced in proton-proton (pp) collisions at the CERN LHC with a center-of-mass energy of 13 TeV, corresponding to a delivered luminosity of 50 fb-1. The measurements are based on readout channels of the HE that were instrumented with silicon photomultipliers, and are derived using data from several sources: A laser calibration system, a movable radioactive source, as well as hadrons and muons produced in pp collisions. Results from several irradiation campaigns using 60Co sources are also discussed. The damage is presented as a function of dose rate. Within the range of these measurements, for a fixed dose the damage increases with decreasing dose rate

Observation of nuclear modifications in W-+/- boson production in pPb collisions at root s(NN)=8.16 TeV

The production of W\ub1 bosons is studied in proton-lead (pPb) collisions at a nucleon-nucleon centre-of-mass energy of 1asNN=8.16TeV. Measurements are performed in the W\ub1\u2192\u3bc\ub1\u3bd\u3bc channel using a data sample corresponding to an integrated luminosity of 173.4\ub16.1nb 121, collected by the CMS Collaboration at the LHC. The number of positively and negatively charged W bosons is determined separately in the muon pseudorapidity region in the laboratory frame |\u3b7lab\u3bc|<2.4 and transverse momentum pT\u3bc>25GeV/c. The W\ub1 boson differential cross sections, muon charge asymmetry, and the ratios of W\ub1 boson yields for the proton-going over the Pb-going beam directions are reported as a function of the muon pseudorapidity in the nucleon-nucleon centre-of-mass frame. The measurements are compared to the predictions from theoretical calculations based on parton distribution functions (PDFs) at next-to-leading-order. The results favour PDF calculations that include nuclear modifications and provide constraints on the nuclear PDF global fits