Operation and performance of the ATLAS Tile Calorimeter in Run 1

The Tile Calorimeter is the hadron calorimeter covering the central region of the ATLAS experiment at the Large Hadron Collider. Approximately 10,000 photomultipliers collect light from scintillating tiles acting as the active material sandwiched between slabs of steel absorber. This paper gives an overview of the calorimeter’s performance during the years 2008–2012 using cosmic-ray muon events and proton–proton collision data at centre-of-mass energies of 7 and 8TeV with a total integrated luminosity of nearly 30 fb−1. The signal reconstruction methods, calibration systems as well as the detector operation status are presented. The energy and time calibration methods performed excellently, resulting in good stability of the calorimeter response under varying conditions during the LHC Run 1. Finally, the Tile Calorimeter response to isolated muons and hadrons as well as to jets from proton–proton collisions is presented. The results demonstrate excellent performance in accord with specifications mentioned in the Technical Design Report

ATLAS flavour-tagging algorithms for the LHC Run 2 pp collision dataset

AbstractThe flavour-tagging algorithms developed by the ATLAS Collaboration and used to analyse its dataset of $$\sqrt{s} = 13$$ s = 13  TeV pp collisions from Run 2 of the Large Hadron Collider are presented. These new tagging algorithms are based on recurrent and deep neural networks, and their performance is evaluated in simulated collision events. These developments yield considerable improvements over previous jet-flavour identification strategies. At the 77% b-jet identification efficiency operating point, light-jet (charm-jet) rejection factors of 170 (5) are achieved in a sample of simulated Standard Model $$t\bar{t}$$ t t ¯ events; similarly, at a c-jet identification efficiency of 30%, a light-jet (b-jet) rejection factor of 70 (9) is obtained.</jats:p

Weaving ways of knowing to enhance biocultural resilience in a mahinga kai species-at-risk

The futures of many threatened species rest on our collective efforts to reweave the biological, cultural, and linguistic threads that together comprise biocultural diversity. For Western researchers, there is growing recognition that Indigenous Peoples and local communities are at the forefront of place-based approaches that bring together diverse ways of knowing and seeing. Here in Aotearoa New Zealand, these include restoration efforts led by mana whenua tribal groups with local authority to weave Māori—the Indigenous Peoples of Aotearoa New Zealand—knowledge, practices, and processes with Western science. For example, genomic markers offer a unique lens to explore relationships across populations, and in turn, co-develop management programmes that build resilience in threatened species. A growing number of studies are applying genomic data to enhance conservation outcomes, but few have tapped into their full potential by weaving these data with Indigenous and local relationships of place. This thesis represents the collective efforts of many—including whānau extended families, researchers, and practitioners, many of whom affiliate to the local iwi tribe, Ngāi Tahu—led here by a Pākehā (New Zealander of European settler descent) researcher. The recent application of genomic tools by Western-trained researchers to address conservation issues (i.e., conservation genomics) presents both opportunities and challenges for efforts to restore biocultural diversity. This thesis seeks to consider such complexities, including how genomic data might be better understood through a multiplicity of worldviews. Chapter Two serves to frame the research narrative of this thesis through a Perspective published in People and Nature’s joint special issue on informing decision-making with Indigenous and local knowledge and science. Few published conservation translocations (i.e., movement of animals or plants for conservation benefit) are led or co-led by Indigenous Peoples or centre Indigenous knowledge systems. As Kāi Tahu and Pākehā researchers and practitioners working in partnership in Aotearoa New Zealand, we consider how conservation translocations that weave diverse ways of knowing and seeing can enhance species recovery and build ecosystem resilience. We highlight the co-development of conservation translocations with Te Kōhaka o Tūhaitara and Te Nohoaka o Tukiauau Trusts where we are weaving emerging genomic approaches with mātauraka Māori Māori knowledge systems to recover culturally significant freshwater species. We further offer a Two-Eyed Seeing framework to support the co- design of conservation translocations led or co-led by Indigenous researchers and communities around the world. Chapter Three extends the narrative introduced in Chapter Two by focusing on the caveats of interpreting genomic data without local historical or contemporary context; namely, the movement or management of culturally significant species by Indigenous Peoples and local communities (IPLCs) in the distant or recent past. This Perspective brings together Kāi Tahu and Pākehā researchers and practitioners with expertise across customary and contemporary mahika kai food gathering (i.e., including processes, practices, and places), conservation genomics, ecology, fish biology, and aquaculture. To date, few efforts to characterise genetic variation within and between populations consider how human relationships with place may shape present-day species distributions. Yet, the movement of species by Indigenous and local communities in the distant and recent past provides important context for the interpretation of genomic data. For example, freshwater kōura1 crayfish in subalpine streams alongside ancient walking trails in Te Waipounamu (the South Island of Aotearoa New Zealand) were moved between sites to provide readily accessible food for travellers. We reflect on how weaving diverse ways of knowing and seeing can better reveal the biocultural complexities of genomic data derived from culturally significant species such as kōura, including locally adaptive variation. In Chapter Four, we shift focus to a research partnership with aquaculture company KEEWAI, mana whenua, and Te Rūnanga o Ngāi Tahu (TRoNT). This chapter reflects on the benefits, risks, and outstanding questions around genetic rescue (i.e., the introduction or restoration of new genetic material to small, isolated populations to reduce genetic load). We present experimental co-design and preliminary genomic data as proof-of-concept for a series of kōura translocation experiments at the KEEWAI aquaculture ponds ultimately intended to grow our understanding of the genetic mechanisms underlying genetic rescue. These data contribute toward the foundation and development of a multi-generational research programme that will support tribal-led aquaculture initiatives for kōura and other mahika kai species across the Kāi Tahu takiwā tribal territory. The research partnerships and approaches described above are brought together in Chapter Five to explore contemporary and historical relationships across kēkēwai1 freshwater crayfish populations in Te Waipounamu by weaving genomic data with placed-based knowledges. Genomic data reveal strong population genetic structure—as well as signatures of population admixture—across seventeen genetically depauperate populations in Te Waipounamu. Differentiation and environment association analyses further identify patterns of genetic variation linked to hydroclimatic variables, including temperature, precipitation, and water flow regimes. We consider how weaving these data with place-based knowledges can enhance resilience in kēkēwai through tribal-led initiatives for mahika kai. Our findings further contribute toward a growing understanding of how adaptive and neutral genetic variation shape threatened species’ capacity to respond to future change. Finally, Chapter Six critically reflects on the journey of this thesis and future directions, including tribal-led research programmes that will strengthen the relationships between people and mahika kai to build intergenerational capacity for protecting biocultural heritage. Two additional manuscripts, three blogs and an example summary for mana whenua are also included in the appendices. Together, these works contribute toward reconnection to place and the growth of our collective knowledge for treasured species in Aotearoa New Zealand and beyond

Search for flavour-changing neutral-current couplings between the top quark and the photon with the ATLAS detector at s=13 TeV

This letter documents a search for flavour-changing neutral currents (FCNCs), which are strongly suppressed in the Standard Model, in events with a photon and a top quark with the ATLAS detector. The analysis uses data collected in pp collisions at s=13 TeV during Run 2 of the LHC, corresponding to an integrated luminosity of 139 fb−1. Both FCNC top-quark production and decay are considered. The final state consists of a charged lepton, missing transverse momentum, a b-tagged jet, one high-momentum photon and possibly additional jets. A multiclass deep neural network is used to classify events either as signal in one of the two categories, FCNC production or decay, or as background. No significant excess of events over the background prediction is observed and 95% CL upper limits are placed on the strength of left- and right-handed FCNC interactions. The 95% CL bounds on the branching fractions for the FCNC top-quark decays, estimated (expected) from both top-quark production and decay, are B(t→uγ)<0.85(0.88−0.25+0.37)×10−5 and B(t→cγ)<4.2(3.40−0.95+1.35)×10−5 for a left-handed tqγ coupling, and B(t→uγ)<1.2(1.20−0.33+0.50)×10−5 and B(t→cγ)<4.5(3.70−1.03+1.47)×10−5 for a right-handed coupling