Integrated Calendar

We propose an inclusive search for dark photons A' at the LHCb experiment based on both prompt and displaced di-muon resonances.
Because the couplings of the dark photon are inherited from the photon via kinetic mixing, the dark photon A' -> mu+mu- rate can be directly inferred from the off-shell photon gamma* -> mu+mu- rate, making this a fully data-driven search. For Run 3 of the LHC, we estimate that LHCb will have sensitivity to large regions of the unexplored dark-photon parameter space, especially in the 210-520 MeV and 10-40 GeV mass ranges. This search leverages the excellent invariant-mass and vertex resolution of LHCb, along with its unique particle-identification and real-time data-analysis capabilities.

Following the advent of graphene, many other one-atom or one-molecule thick crystals have been isolated and investigated. These two-dimensional crystals have become one of the hottest topics in materials science and condensed matter physics. Furthermore, isolated atomic planes can now be reassembled back into three-dimensional structures and crystals made layer by layer in a designer sequence. I will provide a brief, lowbrow introduction to graphene, trying to explain why this material has attracted so much attention, and then overview our progress in making new assemblies from available atomic planes in order to illustrate how rich in phenomena and application this research field is.

Rock surfaces support microbial communities that may be involved in weathering processes. In arid and hyper-arid environments microbes dominate rock surfaces and were linked to weathering because the scarcity of water excludes classical mechanisms that erode rocks. We studied subaerial biofilms coating arid rocks, focusing on sedimentary rocks that feature comparable weathering morphologies but different lithologies. We hypothesized that weathering is fashioned by salt erosion and mediated by biofilms that play dual roles: stabilizing the rock surfaces by coating, and enhancing salt crystallization by preventing rapid desiccation (thus mitigating and facilitating erosion processes, respectively). We used a combination of microbial and geological techniques to characterize the rocks morphologies and their subaerial biofilms. Deep sequencing and microscopy analyses suggest that bacterial diversity is low, dominated by Proteobacteria, Cyanobacteria and Actinobacteria. Together these phyla formed laminar biofilms that secrete extracellular polymeric substances to aggregate microfabrics and mitigate desiccation, reducing water loss by over 40%. The biofilm was detected only in rocks exposed to the atmosphere, present distinct architecture and burrowed up to 9 mm beneath the surface, protected by sedimentary deposits. A closer inspection revealed that the composition of the biofilm was tightly linked to dust bacterial communities but distinct from soil communities. Moreover, the biofilm composition changed according to the rock location rather than its’ lithology, suggesting that microclimate (dew, relative humidity and radiation) play an important role in arid weathering. Our results contradict common dogmas that considered biofilms as degrading agents and propose their role as mitigators of geomorphic processes.