Tracking optimisation and the measurement of K+->π+μ+μ- at NA62

The NA62 experiment at CERN is designed to perform a precision measurement of the ultra-rare K+ -> π+vv_ branching fraction. The experiment relies on a kinematic background rejection using the missing -10 mass-squared signatures of the contributing background components. As the signal is of the order (10 ) smaller than that of the most common kaon decays, the tracking performance of the detector must be exceptional in order to achieve a large signal to background ratio of S/B « 10. In this thesis, two tools to aid with the tracking procedure have been developed. Firstly, a field map which describes the fringe field of the spectrometer magnet has been created, tested and implemented in the NA62 Monte-Carlo software. Additionally, an analysis procedure to improve the precision and accuracy of track momentum in data was developed. Such tools are essential, not only for the K+ -> π+vv_ decay, but also for all decays containing tracks. In particular, they have been used to aid the measurement of the branching fraction and the form factor for the Standard Model decay K+ -> π+µ+µ- which is described here. The measurement has been performed using the data collected by the NA62 experiment in 2016 and 2017. The event selection, trigger efficiency determination and the analysis techniques used for the measurement are presented. The analyses of the two data sets are provided separately to demonstrate the progressing sensitivity of the detector. The final results are compatible with literature, and the 2017 measurement is currently the world’s most precise for this channel. This demonstrates the future potential of NA62 for when larger data sets become available in the next few years

Economics of Voluntary Information Sharing

We show that lenders join a U.S. commercial credit bureau when information asymmetries between incumbents and entrants create an adverse selection problem that hinders market entry. Lenders also delay joining when information asymmetries protect them from competition in existing markets, consistent with lenders trading off new market entry against heightened competition. We exploit shocks to information coverage to show that lenders enter new markets after joining the bureau in a pattern consistent with this trade-off. Our results illuminate why intermediaries voluntarily share information and show how financial technology that mitigates information asymmetries can shape the boundaries of lending

Economics of Voluntary Information Sharing

We show that lenders join a U.S. commercial credit bureau when information asymmetries between incumbents and entrants create an adverse selection problem that hinders market entry. Lenders also delay joining when information asymmetries protect them from competition in existing markets, consistent with lenders trading off new market entry against heightened competition. We exploit shocks to information coverage to show that lenders enter new markets after joining the bureau in a pattern consistent with this trade-off. Our results illuminate why intermediaries voluntarily share information and show how financial technology that mitigates information asymmetries can shape the boundaries of lending

Pharmacokinetic, neurochemical, stereological and neuropathological studies on the potential effects of paraquat in the substantia nigra pars compacta and striatum of male C57BL/6J mice

AbstractThe pharmacokinetics and neurotoxicity of paraquat dichloride (PQ) were assessed following once weekly administration to C57BL/6J male mice by intraperitoneal injection for 1, 2 or 3 weeks at doses of 10, 15 or 25mg/kg/week. Approximately 0.3% of the administered dose was taken up by the brain and was slowly eliminated, with a half-life of approximately 3 weeks. PQ did not alter the concentration of dopamine (DA), homovanillic acid (HVA) or 3,4-dihydroxyphenylacetic acid (DOPAC), or increase dopamine turnover in the striatum. There was inconsistent stereological evidence of a loss of DA neurons, as identified by chromogenic or fluorescent-tagged antibodies to tyrosine hydroxylase in the substantia nigra pars compacta (SNpc). There was no evidence that PQ induced neuronal degeneration in the SNpc or degenerating neuronal processes in the striatum, as indicated by the absence of uptake of silver stain or reduced immunolabeling of tyrosine-hydroxylase-positive (TH+) neurons. There was no evidence of apoptotic cell death, which was evaluated using TUNEL or caspase 3 assays. Microglia (IBA-1 immunoreactivity) and astrocytes (GFAP immunoreactivity) were not activated in PQ-treated mice 4, 8, 16, 24, 48, 96 or 168h after 1, 2 or 3 doses of PQ.In contrast, mice dosed with the positive control substance, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP; 10mg/kg/dose×4 doses, 2h apart), displayed significantly reduced DA and DOPAC concentrations and increased DA turnover in the striatum 7 days after dosing. The number of TH+ neurons in the SNpc was reduced, and there were increased numbers of degenerating neurons and neuronal processes in the SNpc and striatum. MPTP-mediated cell death was not attributed to apoptosis. MPTP activated microglia and astrocytes within 4h of the last dose, reaching a peak within 48h. The microglial response ended by 96h in the SNpc, but the astrocytic response continued through 168h in the striatum.These results bring into question previous published stereological studies that report loss of TH+ neurons in the SNpc of PQ-treated mice. This study also suggests that even if the reduction in TH+ neurons reported by others occurs in PQ-treated mice, this apparent phenotypic change is unaccompanied by neuronal cell death or by modification of dopamine levels in the striatum

Secondary attack rates in primary and secondary school bubbles following a confirmed case: Active, prospective national surveillance, November to December 2020, England.

BACKGROUND: Following the full re-opening of schools in England and emergence of the SARS-CoV-2 Alpha variant, we investigated the risk of SARS-CoV-2 infection in students and staff who were contacts of a confirmed case in a school bubble (school groupings with limited interactions), along with their household members. METHODS: Primary and secondary school bubbles were recruited into sKIDsBUBBLE after being sent home to self-isolate following a confirmed case of COVID-19 in the bubble. Bubble participants and their household members were sent home-testing kits comprising nasal swabs for RT-PCR testing and whole genome sequencing, and oral fluid swabs for SARS-CoV-2 antibodies. RESULTS: During November-December 2020, 14 bubbles were recruited from 7 schools, including 269 bubble contacts (248 students, 21 staff) and 823 household contacts (524 adults, 299 children). The secondary attack rate was 10.0% (6/60) in primary and 3.9% (4/102) in secondary school students, compared to 6.3% (1/16) and 0% (0/1) among staff, respectively. The incidence rate for household contacts of primary school students was 6.6% (12/183) and 3.7% (1/27) for household contacts of primary school staff. In secondary schools, this was 3.5% (11/317) and 0% (0/1), respectively. Household contacts were more likely to test positive if their bubble contact tested positive although there were new infections among household contacts of uninfected bubble contacts. INTERPRETATION: Compared to other institutional settings, the overall risk of secondary infection in school bubbles and their household contacts was low. Our findings are important for developing evidence-based infection prevention guidelines for educational settings

Tracking optimisation and the measurement of K+→π+μ+μ−K^+ \to \pi^+ \mu^+ \mu^- at NA62

The NA62 experiment at CERN is designed to perform a precision measurement of the ultra-rare $K^+ \to \pi^+ \nu \bar\nu$ branching fraction. The experiment relies on a kinematic background rejection using the missing mass-squared signatures of the contributing background components. As the signal is of the $\cal O$($10^{-10})$ smaller than that of the most common kaon decays, the tracking performance of the detector must be exceptional in order to achieve a large signal to background ratio of $S/B \approx 10$. In this thesis, two tools to aid with the tracking procedure have been developed. Firstly, a field map which describes the fringe field of the spectrometer magnet has been created, tested and implemented in the NA62 Monte-Carlo software. Additionally, an analysis procedure to improve the precision and accuracy of track momentum in data was developed. Such tools are essential, not only for the $K^+ \to \pi^+ \nu \bar\nu$ decay, but also for all decays containing tracks. In particular, they have been used to aid the measurement of the branching fraction and the form factor for the Standard Model decay $K^+ \to \pi^+ \mu^+ \mu^-$ which is described here. The measurement has been performed using the data collected by the NA62 experiment in 2016 and 2017. The event selection, trigger efficiency determination and the analysis techniques used for the measurement are presented. The analyses of the two data sets are provided separately to demonstrate the progressing sensitivity of the detector. The final results are compatible with literature, and the 2017 measurement is currently the world’s most precise for this channel. This demonstrates the future potential of NA62 for when larger data sets become available in the next few years