Session Q13: Charged Leptons

Live

The Muon $g-2$ Experiment at Fermilab measures the anomalous magnetic moment of the muon, $a_{\mu}$, with improved precision compared to the previous experiment at Brookhaven National Lab (BNL). The value of $a_{\mu}$ from BNL currently differs from the Standard Model prediction by $\sim 3.6$ standard deviations or higher, suggesting the potential for new physics and therefore, motivating a new experiment. The Fermilab experiment follows the measurement principles of the BNL experiment, injecting a beam of positive muons into a storage ring, which focuses the beam with a combination of magnetic and electric fields. The muon anomaly relies on the measurement of the spin precession frequency $\omega_a$ about the muon momentum. \\ The study and analysis of CPT and Lorentz violation in g-2 provide a good test of the standard model (SM) as well as strong constraints on new physics. The BNL g-2 experiment analyzed the spin precession frequency of the muons stored in the ring and seached for two Lorentz and CPT violating signatures. One of those signatures, the sidereal variation of $\omega_a(t)$, will be discussed for the Fermilab Muon g-2 Experiment in this presentation. This talk will present the methodology and give a status update on the Run 1 analysis.   

Live

The Muon $g-2$ Experiment at Fermilab measures the anomalous magnetic moment of the muon, $a_{\mu}$, with improved precision compared to the previous experiment at Brookhaven National Lab. The Brookhaven result is in tension with the Standard Model by more than 3$\sigma$. The determination of $a_{\mu}$ requires the measurement of both the muon spin-cyclotron precession frequency $\omega_{a}$ and the magnetic field $B$ in terms of the free-proton precession frequency $\omega_{p}$ that confines muons in the storage ring. The magnetic field is monitored by coordinated nuclear magnetic resonance (NMR) measurements. NMR probes are mounted in fixed locations above and below the storage region and continuously monitor the field. Roughly every three days, an in-vacuum trolley equipped with 17 NMR probes maps the muon storage region. In dedicated runs, the trolley is compared to a water-based NMR probe, converting trolley $B$ measurements into corresponding values of $\omega_{p}$. In this talk, the calibration procedure and the analysis of data from the first physics run is presented. The author is supported by the DOE under Grant DE-FG02-88ER40415 and acknowledges support from the Fermi Research Alliance, LLC under Contract No.~DE-AC02-07CH11359 with the U.S. DOE-OHEP.   

Live

Both the ongoing Muon g-2 Experiment (E989) at Fermilab and the future g-2/EDM experiment (E34) at J-PARC will measure the anomalous magnetic moment of muon, $a_{\mu}$, with improved precision compared to former measurements at Brookhaven (E821). The Brookhaven result is in tension with the Standard Model by more than 3$\sigma$. The determination of $a_{\mu}$ requires the measurement of both the muon spin precession frequency $\omega_a$ and the magnetic field in the moun storage ring. To derive the absolute magnetic field, both experiments have developed special, water-based NMR probes that have small and well-measured corrections from the probe materials and geometries. This presentation focuses on a cross-calibration effort of these probes between collaborators from both the E989 and E34 experiments. In a very homogeneous and stable MRI magnet at Argonne National Laboratory, the teams have cross-calibrated the probes at 1.45T, 1.7T, and 3T. This presentation will focus on the details of the calibration and the analysis status of the 1.45T and 1.7T data which were taken in 2019. We acknowledge support from the Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the U.S.DOE-OHEP. The author is supported by US DOE-OHEP under contract DE-AC02-06CH11357.   

Live

The Muon g-2 experiment E989 at Fermilab measures the anomalous magnetic moment of the muon $a_\mu$ with improved precision compared to the Brookhaven (E821) experiments. The Brookhaven results are in tension with the Standard Model by more than $3\sigma$. The determination of $a_\mu$ requires the measurement of both the muon anomaly frequency $\omega_a$ and the magnetic field B that confines muons in a storage ring. The field is monitored by a set of coordinated nuclear magnetic resonance (NMR) measurements. NMR probes at fixed locations above and below the storage region constantly monitor the field. An in-vacuum trolley equipped with 17 NMR probes maps the muon storage region, and a special water-based NMR probe provides the calibration for the trolley probes. This presentation focuses on the determination of the time-dependent field maps from combining the fixed probe measurements and the trolley maps. The field maps are combined with the muon distribution to derive the average field observed by the muons during the measurement. This talk will cover the analysis from the first data run.   

Live

The magnetic anomaly of the muon $a_\mu$ hints at new physics with a greater than 3 standard deviation discrepancy between the measurement performed at Brookhaven National Lab and the Standard Model prediction. To clarify (or resolve) the disparity, the ongoing Muon $g-2$ Experiment at Fermilab has accrued a dataset larger than that of its predecessor experiment. The magnetic anomaly is directly proportional to the rate at which a muon's spin precesses relative to its momentum in a magnetic field, $\omega_a$. Decay positron energies, measured using 24 highly gain-stabilized calorimeters, carry information about the spin distribution of the parent muons; higher energy positrons are more likely emitted in the direction of the muons' spins. Determination of $\omega_a$ is made from fitting the time-dependent distribution of positron energies using several methods: setting a lower threshold on the positron energy; taking a ratio of time-shifted histograms; and an asymmetry weighting technique based on positron energies. Corrections must be made for muons that exit the storage region before decaying, beam betatron motions, and rate-dependent pileup in the detectors. The process of measuring $\omega_a$ and associated systematic errors will be presented in the context of Run 1 data.   

Live

The Muon g-2 Experiment (E989) at Fermilab measures the anomalous magnetic moment of the muon, $a_\mu$, with improved precision compared to the Brookhaven (E821) experiments whose results were found to be inconsistent with the Standard Model. The precision of this discrepancy can be improved both by collecting more data to reduce statistical uncertainty and by developing additional analysis techniques to reduce systematic errors. The determination of $a_\mu$ requires the measurement of the muon spin precession frequency, $\omega_a$, and the magnetic field, B, that confines muons in a storage ring. Traditional measurements of $\omega_a$ require reconstruction of the decay positrons from the muon decay, $\mu^{+} \rightarrow e^{+} \nu_e \bar{\nu}_\mu $. The Q-method is a novel, energy-weighted approach which employs a new technique for data collection and reduces sensitivities to gain fluctuations and pile-up. This talk will introduce the Q-method procedure and give a status update on the analysis of Run-2, obtained in the spring of 2019.   

Live

The Muon $g-2$ experiment at Fermilab plans to measure the muon anomaly $a_{\mu}$ to high precision. The goal of the experiment is to measure $a_{\mu}$ more precisely than the earlier Brookhaven experiment, which found a $> 3\sigma$ deviation from the Standard Model prediction of the anomaly. The Fermilab experiment is now in its third run of data taking, and analysis of the first run is underway. In order to achieve design sensitivity, systematic uncertainties must be well understood. One key uncertainty results from muons that are lost from the magnetic storage region before decaying into positrons. If the lost muon population has a different average spin phase than the stored muon population, the measured anomalous precession frequency $\omega_{a}$ will be biased. A correlation between phase and momentum can drive this type of effect if muons of a certain momentum are preferentially lost. In this talk, I will present a data-driven approach to measuring this bias for Run 1 data, including a measurement of the phase-momentum correlation and a measurement of the momentum dependence of the losses. I will then compare the measurements to beam simulations. Finally, I will present a calculation of this systematic uncertainty for Run 1.   

Live

The Mu2e experiment is designed to search for New Physics in an extremely rare process of muon to electron neutrino-less conversion with < 0.5 expected background events. The Mu2e sensitivity to New Physics heavily relies on suppressing and understanding all the background sources at high precision. The dominant background at Mu2e originates from cosmic ray (CR) muons that interact or decay in the detector and produce a signal-like electron. Mu2e expects to observe over 750 background events induced by CR muons. In order to reach the proposed sensitivity, Mu2e is designed to suppress the CR background by 4 orders of magnitude, using the Cosmic Ray Veto detector that covers over 300 $m^2$. The precision CR background prediction is an essential component of Mu2e’s success. We will report on CR background estimates at Mu2e modeled by CRY cosmic ray generator and using the detector response simulated with the Geant4 framework.