The MEG II experiment is designed to improve by an order of magnitude the sensitivity of 4.2×10−13 reached by MEG on the search for μ+→e+γ decay. A pixelated Timing Counter (pTC) has been developed ...to improve the time resolution by measuring the positron time information independently with several counters. We constructed and installed the pTC and performed commissioning runs at the πE5 beam line at PSI. A resolution of 38.5 ps is obtained with commissioning run data.
In angiosperms, flower size commonly scales negatively with number. The ecological consequences of this trade-off for tropical trees remain poorly resolved, despite their potential importance for ...tropical forest conservation. We investigated the flower size number trade-off and its implications for fecundity in a sample of tree species from the Dipterocarpaceae on Borneo.
We combined experimental exclusion of pollinators in 11 species, with direct and indirect estimates of contemporary pollen dispersal in two study species and published estimates of pollen dispersal in a further three species to explore the relationship between flower size, pollinator size and mean pollen dispersal distance. Maximum flower production was two orders of magnitude greater in small-flowered than large-flowered species of Dipterocarpaceae. In contrast, fruit production was unrelated to flower size and did not differ significantly among species. Small-flowered species had both smaller-sized pollinators and lower mean pollination success than large-flowered species. Average pollen dispersal distances were lower and frequency of mating between related individuals was higher in a smaller-flowered species than a larger-flowered confamilial. Our synthesis of pollen dispersal estimates across five species of dipterocarp suggests that pollen dispersal scales positively with flower size.
Trade-offs embedded in the relationship between flower size and pollination success contribute to a reduction in the variance of fecundity among species. It is therefore plausible that these processes could delay competitive exclusion and contribute to maintenance of species coexistence in this ecologically and economically important family of tropical trees. These results have practical implications for tree species conservation and restoration. Seed collection from small-flowered species may be especially vulnerable to cryptic genetic erosion. Our findings also highlight the potential for differential vulnerability of tropical tree species to the deleterious consequences of forest fragmentation.
The MEG experiment has set the latest limit of 5.7×10−13(90% C.L.) on the branching ratio of the charged lepton flavor violating decay μ+→e+γ, making use of the most intense continuous surface muon ...beam in the world at the Paul Scherrer Institut (PSI), Villigen, Switzerland. High resolutions in terms of energy, timing and relative opening angle are needed in the detection of the e+ and gamma, requiring careful calibration and monitoring of the experimental apparatus. A dedicated calibration method involving Mott scattering of a monochromatic positron beam at energies close to the MEG signal energy is presented.
Several scintillating fibre prototypes (single- and double-layers) made of 250μm multi-clad square fibres coupled to silicon photomultiplier have been studied using electrons, positrons and muons at ...different energies.
Current measurements show promising results: already for a single fibre layer and minimum ionizing particles we obtain a detection efficiency ≥95% (mean collected light/fibre ≈ 8phe), a timing resolution of 550ps/fibre and a foreseen spatial resolution <100μm, based on the achieved negligible optical cross-talk between fibres (<1%). We will also discuss the performances of a double-layer staggered prototype configuration, for which a full detection efficiency (≥99%) has been measured together with a timing resolution of ≈ 400ps for double hit events.
High-intensity secondary beams play a vital role in today’s particle physics and materials science research and require suitable detection techniques to adjust beam characteristics to optimally match ...experimental conditions. To this end we have developed a quasi-non-invasive, ultra-thin, CsI(Tl) luminophore foil detector system, based on CCD-imaging. We have used this to quantify the beam characteristics of an intensity-frontier surface muon beam used for next-generation charged lepton-flavour violation (cLFV) search experiments at the Paul Scherrer Institut (PSI) and to assess the possible use for a future High-intensity Muon Beam (HiMB-project), currently under study at PSI. An overview of the production and intrinsic characteristics of such foils is given and their application in a high-intensity beam environment.
Commitments to Forest and Landscape Restoration are rapidly growing and being implemented globally to tackle the climate and biodiversity crises. Restoration initiatives largely based on tree ...planting necessitate an increased supply of high-quality and suitably adapted tree planting material. We evaluated the native tree seed supply systems in Burkina Faso, Cameroon, Ghana, and Kenya, four countries with large commitments to increase tree cover. We applied an established indicator framework to assess the adequacy of any current tree seed system to meet national needs. The study aimed to analyse (i) how well-established the native tree seed supply systems are, (ii) how public and non-public actors differ regarding the perception of existing seed systems, and (iii) the main barriers to strengthening current seed systems. Our findings identified significant gaps in the native tree seed supply systems of the four countries, arising particularly from shortfalls in the enabling environment. We found a lack of involvement of local community members in the seed systems, with a crucial need for strengthening policy, capacity building and investment in seed systems. We propose a multi-stakeholder approach and the application of online tools to improve seed systems to meet the demand for high-quality native tree seeds.
A search for the decay
μ
+
→
e
+
γ
, performed at PSI and based on data from the initial three months of operation of the MEG experiment, yields an upper limit on the branching ratio of
BR
(
μ
+
→
e
...+
γ
)
⩽
2.8
×
10
−
11
(90% C.L.). This corresponds to the measurement of positrons and photons from
∼
10
14
stopped
μ
+
-decays by means of a superconducting positron spectrometer and a 900 litre liquid xenon photon detector.
We present the first direct search for lepton flavour violating muon decay mediated by a new light particle X,
μ
+
→
e
+
X
,
X
→
γ
γ
. This search uses a dataset resulting from
7.5
×
10
14
stopped ...muons collected by the MEG experiment at the Paul Scherrer Institut in the period 2009–2013. No significant excess is found in the mass region 20–45 MeV/c
2
for lifetimes below 40 ps, and we set the most stringent branching ratio upper limits in the mass region of 20–40 MeV/c
2
, down to
O
(
10
-
11
)
at 90% confidence level.
Current policy is driving renewed impetus to restore forests to return ecological function, protect species, sequester carbon and secure livelihoods. Here we assess the contribution of tree planting ...to ecosystem restoration in tropical and sub-tropical Asia; we synthesize evidence on mortality and growth of planted trees at 176 sites and assess structural and biodiversity recovery of co-located actively restored and naturally regenerating forest plots. Mean mortality of planted trees was 18% 1 year after planting, increasing to 44% after 5 years. Mortality varied strongly by site and was typically
20% higher in open areas than degraded forest, with height at planting positively affecting survival. Size-standardized growth rates were negatively related to species-level wood density in degraded forest and plantations enrichment settings. Based on community-level data from 11 landscapes, active restoration resulted in faster accumulation of tree basal area and structural properties were closer to old-growth reference sites, relative to natural regeneration, but tree species richness did not differ. High variability in outcomes across sites indicates that planting for restoration is potentially rewarding but risky and context-dependent. Restoration projects must prepare for and manage commonly occurring challenges and align with efforts to protect and reconnect remaining forest areas. The abstract of this article is available in Bahasa Indonesia in the electronic supplementary material. This article is part of the theme issue 'Understanding forest landscape restoration: reinforcing scientific foundations for the UN Decade on Ecosystem Restoration'.
•We detected FSGS in 15 dipterocarps of 19 species across four forest sites.•GLS models are used to develop indirect operational indicators of FSGS.•Wood density and flower size offer useful ...indicators of FSGS.•We proposed simple guidelines to allow forest managers to account for FSGS.•There is an urge to implement forest management with species specific guidelines.
The lowland tropical forests of Southeast Asia are dominated by a single family of canopy and emergent trees, the Dipterocarpaceae. The seeds of dipterocarps are gravity or gyration dispersed. Short distance and limited seed dispersal via these mechanisms result in the aggregation of related individuals and strong fine-scale spatial genetic structure (FSGS). In logged and fragmented forests, where gene flow may be disrupted, tree species with strong FSGS are predicted to exhibit increased inbreeding, which consequently can erode genetic diversity, fitness and might limit the potential for natural regeneration of dipterocarps. Developing a set of indirect operational indicators for FSGS provides a solid basis for informing conservation and management of forest genetic resources in logged forests. Our main objective was to use an information theoretic approach to identify these indicators of FSGS in dipterocarps. We quantify FSGS in 19 dipterocarp species across four forest sites in Malaysian Borneo, India and the Seychelles. We detected FSGS in 15 (79%) of our study species, most of which displayed significant inbreeding. Our results suggest that wood density and flower size offer useful indicators of FSGS. We propose some simple guidelines to allow forest managers to account for FSGS when planning approaches to maintain genetically diverse stands in logged dipterocarp forests. The integration of improved understanding of genetic processes is essential for conserving forest tree genetic resources and ensuring the resilience of logged forests.
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