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.
The measurement of the anomalous magnetic moment of electrons and muons has been an important test of the Standard Model (SM) of particle physics over many decades. This is because it can be measured ...experimentally and calculated theoretically to a high precision. In particular the anomalous magnetic moment of the muon, aμ, is an ideal candidate for the search of new physics due to the combination of the muons large mass and relatively long lifetime.The current world’s most precise value of aμ was measured by the E821 experiment at the Brookhaven National laboratory (BNL). This achieved a precision of 540 ppb (463 ppb stat., 283 ppb syst.) and measured a ~ 3:5 σ deviation from the SM value 1. This motivated a new experiment: the E989 muon g–2 experiment at the Fermi National Accelerator Laboratory (Fermilab) to confirm or reject this discrepancy. This experiment aims to gather a data sample 21 times larger than the BNL experiment and improve the determination of the systematic uncertainties by a factor of three and thereby achieve a fourfold increase in precision to 140 ppb 2. If the aμ value were to remain unchanged, this improvement in precision would establish evidence for Beyond SM (BSM) physics with a significance of more than 7 standard deviations.The Fermilab experiment has the same methodology as the BNL experiment and reuses the experiment’s storage ring magnet. New, improved experimental apparatus has been introduced to reduce the systematic uncertainty on the aμ measurement. One such improvement is the addition of two straw tracking stations. These measure the trajectory of the positrons emitted from the (positive) muon decays which allows a detailed study of the spatial and temporal motion of the beam and critical crosschecks of the calorimeter data.This thesis describes in detail the design, construction and testing of the tracking detectors which were built at the University of Liverpool. A detailed study of the vertical motion of the beam is also presented. This study provides an important correction that must be applied to the data before aμ can be determined.
The LHCb detector has undergone a major upgrade for LHC Run 3. This Upgrade I detector facilitates operation at higher luminosity and utilises full-detector information at the LHC collision rate, ...critically including the use of vertex information. A new vertex locator system, the VELO Upgrade, has been constructed. The core element of the new VELO are the double-sided pixelated hybrid silicon detector modules which operate in vacuum close to the LHC beam in a high radiation environment. The construction and quality assurance tests of these modules are described in this paper. The modules incorporate 200 \mum thick, n-on-p silicon sensors bump-bonded to 130 \nm technology ASICs. These are attached with high precision to a silicon microchannel substrate that uses evaporative CO\(_2\) cooling. The ASICs are controlled and read out with flexible printed circuits that are glued to the substrate and wire-bonded to the chips. The mechanical support of the module is given by a carbon fibre plate, two carbon fibre rods and an aluminium plate. The sensor attachment was achieved with an average precision of 21 \(\mathrm{\mu m}\), more than 99.5\% of all pixels are fully functional, and a thermal figure of merit of 3 \mathrm{Kcm^{2}W^{-1}}$ was achieved. The production of the modules was successfully completed in 2021, with the final assembly and installation completed in time for data taking in 2022.
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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