| 1. |
- Åkesson, Torsten, et al.
(författare)
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A high efficiency photon veto for the Light Dark Matter eXperiment
- 2020
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Ingår i: Journal of High Energy Physics. - 1126-6708. ; 2020:4
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Tidskriftsartikel (refereegranskat)abstract
- Fixed-target experiments using primary electron beams can be powerful discovery tools for light dark matter in the sub-GeV mass range. The Light Dark Matter eXperiment (LDMX) is designed to measure missing momentum in high-rate electron fixed-target reactions with beam energies of 4 GeV to 16 GeV. A prerequisite for achieving several important sensitivity milestones is the capability to efficiently reject backgrounds associated with few-GeV bremsstrahlung, by twelve orders of magnitude, while maintaining high efficiency for signal. The primary challenge arises from events with photo-nuclear reactions faking the missing-momentum property of a dark matter signal. We present a methodology developed for the LDMX detector concept that is capable of the required rejection. By employing a detailed Geant4-based model of the detector response, we demonstrate that the sampling calorimetry proposed for LDMX can achieve better than 10−13 rejection of few-GeV photons. This suggests that the luminosity-limited sensitivity of LDMX can be realized at 4 GeV and higher beam energies. [Figure not available: see fulltext.]
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| 2. |
- Åkesson, Torsten, et al.
(författare)
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Photon-rejection power of the Light Dark Matter eXperiment in an 8 GeV beam
- 2023
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Ingår i: Journal of High Energy Physics. - 1029-8479. ; 2023:12
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Tidskriftsartikel (refereegranskat)abstract
- The Light Dark Matter eXperiment (LDMX) is an electron-beam fixed-target experiment designed to achieve comprehensive model independent sensitivity to dark matter particles in the sub-GeV mass region. An upgrade to the LCLS-II accelerator will increase the beam energy available to LDMX from 4 to 8 GeV. Using detailed GEANT4-based simulations, we investigate the effect of the increased beam energy on the capabilities to separate signal and background, and demonstrate that the veto methodology developed for 4 GeV successfully rejects photon-induced backgrounds for at least 2 × 1014 electrons on target at 8 GeV. [Figure not available: see fulltext.]
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| 3. |
- Holm, Jennifer A., et al.
(författare)
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Exploring the impacts of unprecedented climate extremes on forest ecosystems : Hypotheses to guide modeling and experimental studies
- 2023
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Ingår i: Biogeosciences. - 1726-4170. ; 20:11, s. 2117-2142
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Tidskriftsartikel (refereegranskat)abstract
- Climatic extreme events are expected to occur more frequently in the future, increasing the likelihood of unprecedented climate extremes (UCEs) or record-breaking events. UCEs, such as extreme heatwaves and droughts, substantially affect ecosystem stability and carbon cycling by increasing plant mortality and delaying ecosystem recovery. Quantitative knowledge of such effects is limited due to the paucity of experiments focusing on extreme climatic events beyond the range of historical experience. Here, we present a road map of how dynamic vegetation demographic models (VDMs) can be used to investigate hypotheses surrounding ecosystem responses to one type of UCE: unprecedented droughts. As a result of nonlinear ecosystem responses to UCEs that are qualitatively different from responses to milder extremes, we consider both biomass loss and recovery rates over time by reporting a time-integrated carbon loss as a result of UCE, relative to the absence of drought. Additionally, we explore how unprecedented droughts in combination with increasing atmospheric CO2 and/or temperature may affect ecosystem stability and carbon cycling. We explored these questions using simulations of pre-drought and post-drought conditions at well-studied forest sites using well-tested models (ED2 and LPJ-GUESS). The severity and patterns of biomass losses differed substantially between models. For example, biomass loss could be sensitive to either drought duration or drought intensity depending on the model approach. This is due to the models having different, but also plausible, representations of processes and interactions, highlighting the complicated variability of UCE impacts that still need to be narrowed down in models. Elevated atmospheric CO2 concentrations (eCO2) alone did not completely buffer the ecosystems from carbon losses during UCEs in the majority of our simulations. Our findings highlight the consequences of differences in process formulations and uncertainties in models, most notably related to availability in plant carbohydrate storage and the diversity of plant hydraulic schemes, in projecting potential ecosystem responses to UCEs. We provide a summary of the current state and role of many model processes that give way to different underlying hypotheses of plant responses to UCEs, reflecting knowledge gaps which in future studies could be tested with targeted field experiments and an iterative modeling-experimental conceptual framework.
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| 4. |
- van Gestel, Natasja, et al.
(författare)
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Predicting soil carbon loss with warming
- 2018
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 554:E4-5
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Tidskriftsartikel (refereegranskat)
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