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 $\tilde {ω}$'p, and of the anomalous precession frequency corrected for beam dynamics effects, $ω$$a$. From the ratio $ω$$a$/$\tilde {ω}$'$p$, together with precisely determined external parameters, we determine $a$$μ$ = 116592057(25)×10-11 (0.21 ppm). Combining this result with our previous result from the 2018 data, we obtain aμ(FNAL)=116592055(24)×10-11 (0.20 ppm). The new experimental world average is $a$$μ$(Exp)=116592059(22)×10-11 (0.19 ppm), which represents a factor of 2 improvement in precision.
2022 JINST 17 P02035 The Muon $g-2$ Experiment at Fermilab uses a gaseous straw tracking detector
to make detailed measurements of the stored muon beam profile, which are
essential for the experiment ...to achieve its uncertainty goals. Positrons from
muon decays spiral inward and pass through the tracking detector before
striking an electromagnetic calorimeter. The tracking detector is therefore
located inside the vacuum chamber in a region where the magnetic field is large
and non-uniform. As such, the tracking detector must have a low leak rate to
maintain a high-quality vacuum, must be non-magnetic so as not to perturb the
magnetic field and, to minimize energy loss, must have a low radiation length.
The performance of the tracking detector has met or surpassed the design
requirements, with adequate electronic noise levels, an average straw hit
resolution of $(110 \pm 20) \,\mu$m, a detection efficiency of 97% or higher,
and no performance degradation or signs of aging. The tracking detector's
measurements result in an otherwise unachievable understanding of the muon's
beam motion, particularly at early times in the experiment's measurement period
when there are a significantly greater number of muons decaying. This is vital
to the statistical power of the experiment, as well as facilitating the precise
extraction of several systematic corrections and uncertainties. This paper
describes the design, construction, testing, commissioning, and performance of
the tracking detector.
The Muon \(g-2\) Experiment at Fermilab uses a gaseous straw tracking detector to make detailed measurements of the stored muon beam profile, which are essential for the experiment to achieve its ...uncertainty goals. Positrons from muon decays spiral inward and pass through the tracking detector before striking an electromagnetic calorimeter. The tracking detector is therefore located inside the vacuum chamber in a region where the magnetic field is large and non-uniform. As such, the tracking detector must have a low leak rate to maintain a high-quality vacuum, must be non-magnetic so as not to perturb the magnetic field and, to minimize energy loss, must have a low radiation length. The performance of the tracking detector has met or surpassed the design requirements, with adequate electronic noise levels, an average straw hit resolution of \((110 \pm 20) \,\mu\)m, a detection efficiency of 97% or higher, and no performance degradation or signs of aging. The tracking detector's measurements result in an otherwise unachievable understanding of the muon's beam motion, particularly at early times in the experiment's measurement period when there are a significantly greater number of muons decaying. This is vital to the statistical power of the experiment, as well as facilitating the precise extraction of several systematic corrections and uncertainties. This paper describes the design, construction, testing, commissioning, and performance of the tracking detector.
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