32 research outputs found
A pulsating auroral X-ray hot spot on Jupiter
Jupiter's X-ray aurora has been thought to be excited by energetic sulphur and oxygen ions precipitating from the inner magnetosphere into the planet's polar regions(1-3). Here we report high-spatial-resolution observations that demonstrate that most of Jupiter's northern auroral X-rays come from a 'hot spot' located significantly poleward of the latitudes connected to the inner magnetosphere. The hot spot seems to be fixed in magnetic latitude and longitude and occurs in a region where anomalous infrared(4-7) and ultraviolet(8) emissions have also been observed. We infer from the data that the particles that excite the aurora originate in the outer magnetosphere. The hot spot X-rays pulsate with an approximately 45-min period, a period similar to that reported for high-latitude radio and energetic electron bursts observed by near-Jupiter spacecraft(9,10). These results invalidate the idea that jovian auroral X-ray emissions are mainly excited by steady precipitation of energetic heavy ions from the inner magnetosphere. Instead, the X-rays seem to result from currently unexplained processes in the outer magnetosphere that produce highly localized and highly variable emissions over an extremely wide range of wavelengths.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/62624/1/4151000a.pd
Measurement of the Positive Muon Anomalous Magnetic Moment to 0.20 ppm
We present a new measurement of the positive muon magnetic anomaly, a_{μ}≡(g_{μ}-2)/2, from the Fermilab Muon g-2 Experiment using data collected in 2019 and 2020. We have analyzed more than 4 times the number of positrons from muon decay than in our previous result from 2018 data. The systematic error is reduced by more than a factor of 2 due to better running conditions, a more stable beam, and improved knowledge of the magnetic field weighted by the muon distribution, ω[over ˜]_{p}^{'}, and of the anomalous precession frequency corrected for beam dynamics effects, ω_{a}. From the ratio ω_{a}/ω[over ˜]_{p}^{'}, together with precisely determined external parameters, we determine a_{μ}=116 592 057(25)×10^{-11} (0.21 ppm). Combining this result with our previous result from the 2018 data, we obtain a_{μ}(FNAL)=116 592 055(24)×10^{-11} (0.20 ppm). The new experimental world average is a_{μ}(exp)=116 592 059(22)×10^{-11} (0.19 ppm), which represents a factor of 2 improvement in precision
Measurement of the anomalous precession frequency of the muon in the Fermilab Muon g-2 Experiment
The Muon g-2 Experiment at Fermi National Accelerator Laboratory (FNAL) has
measured the muon anomalous precession frequency to an uncertainty
of 434 parts per billion (ppb), statistical, and 56 ppb, systematic, with data
collected in four storage ring configurations during its first physics run in
2018. When combined with a precision measurement of the magnetic field of the
experiment's muon storage ring, the precession frequency measurement determines
a muon magnetic anomaly of (0.46 ppm). This article describes the multiple techniques employed
in the reconstruction, analysis and fitting of the data to measure the
precession frequency. It also presents the averaging of the results from the
eleven separate determinations of \omega_a, and the systematic uncertainties on
the result.Comment: 29 pages, 19 figures. Published in Physical Review
Beam dynamics corrections to the Run-1 measurement of the muon anomalous magnetic moment at Fermilab
This paper presents the beam dynamics systematic corrections and their uncertainties for the Run-1 data set of the Fermilab Muon g-2 Experiment. Two corrections to the measured muon precession frequency are associated with well-known effects owing to the use of electrostatic quadrupole (ESQ) vertical focusing in the storage ring. An average vertically oriented motional magnetic field is felt by relativistic muons passing transversely through the radial electric field components created by the ESQ system. The correction depends on the stored momentum distribution and the tunes of the ring, which has relatively weak vertical focusing. Vertical betatron motions imply that the muons do not orbit the ring in a plane exactly orthogonal to the vertical magnetic field direction. A correction is necessary to account for an average pitch angle associated with their trajectories. A third small correction is necessary because muons that escape the ring during the storage time are slightly biased in initial spin phase compared to the parent distribution. Finally, because two high-voltage resistors in the ESQ network had longer than designed RC time constants, the vertical and horizontal centroids and envelopes of the stored muon beam drifted slightly, but coherently, during each storage ring fill. This led to the discovery of an important phase-acceptance relationship that requires a correction. The sum of the corrections to is 0.50 0.09 ppm; the uncertainty is small compared to the 0.43 ppm statistical precision of
Magnetic Field Measurement and Analysis for the Muon g-2 Experiment at Fermilab
The Fermi National Accelerator Laboratory has measured the anomalous precession frequency of the muon to a combined precision of 0.46 parts per million with data collected during its first physics run in 2018. This paper documents the measurement of the magnetic field in the muon storage ring. The magnetic field is monitored by nuclear magnetic resonance systems and calibrated in terms of the equivalent proton spin precession frequency in a spherical water sample at 34.7C. The measured field is weighted by the muon distribution resulting in , the denominator in the ratio / that together with known fundamental constants yields . The reported uncertainty on for the Run-1 data set is 114 ppb consisting of uncertainty contributions from frequency extraction, calibration, mapping, tracking, and averaging of 56 ppb, and contributions from fast transient fields of 99 ppb
Beam dynamics corrections to the Run-1 measurement of the muon anomalous magnetic moment at Fermilab
This paper presents the beam dynamics systematic corrections and their uncertainties for the Run-1 data set of the Fermilab Muon g-2 Experiment. Two corrections to the measured muon precession frequency are associated with well-known effects owing to the use of electrostatic quadrupole (ESQ) vertical focusing in the storage ring. An average vertically oriented motional magnetic field is felt by relativistic muons passing transversely through the radial electric field components created by the ESQ system. The correction depends on the stored momentum distribution and the tunes of the ring, which has relatively weak vertical focusing. Vertical betatron motions imply that the muons do not orbit the ring in a plane exactly orthogonal to the vertical magnetic field direction. A correction is necessary to account for an average pitch angle associated with their trajectories. A third small correction is necessary because muons that escape the ring during the storage time are slightly biased in initial spin phase compared to the parent distribution. Finally, because two high-voltage resistors in the ESQ network had longer than designed RC time constants, the vertical and horizontal centroids and envelopes of the stored muon beam drifted slightly, but coherently, during each storage ring fill. This led to the discovery of an important phase-acceptance relationship that requires a correction. The sum of the corrections to is 0.50 0.09 ppm; the uncertainty is small compared to the 0.43 ppm statistical precision of
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Occupational lead exposure and survival with amyotrophic lateral sclerosis
Objective: Lead exposure has been hypothesized to increase the risk of ALS, but only two studies have examined the association with ALS survival, and with inconsistent results. The use of occupational history to assess lead exposure can avoid reverse causation that may occur in epidemiologic analyses that use biomarkers of lead exposure collected after ALS onset.
Methods: We evaluated the relationship of occupational lead exposure to ALS survival among 135 cases from an international ALS cohort that included deep phenotyping, careful follow-up, and questionnaires to quantify participants' occupation history. ALS patients were recruited in 2015-2019. We determined occupational lead exposure using a job-exposure matrix. We estimated hazard ratios (HR) and 95% confidence intervals (CI) for survival using Cox proportional hazard analysis with adjustment for covariates.
Results: A total of 135 ALS patients completed the environmental questionnaires, among whom 38 reached a survival endpoint (death or permanent assisted ventilation). The median survival was 48.3 months (25
th
-75
th
percentile, 30.9-74.1). Older patients and those with initial symptom other than limb onset had shorter survival time. There were 36 ALS cases with occupational lead exposure. After adjusting for age, sex, site of onset, smoking, and military service, lead exposure was associated with an HR of 3.26 (95%CI 1.28-8.28). Results with adjustment for subsets of these covariates were similar.
Conclusions: These results suggest that lead exposure prior to onset of ALS is associated with shorter survival following onset of ALS, and this association is independent of other prognostic factors
The Economic Surplus as a Fund for Social Change and Postneoliberal Governance
Economic surplus, Fund for social change, Postneoliberal governance,