Beam profile measurements using the straw tracking detectors at the Fermilab muon g − 2 experiment, and a study of their sensitivity to a muon electric dipole moment

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Abstract

The Fermilab muon g-2 experiment aims to measure the anomalous magnetic dipole moment of the muon, aμ , to a precision of 140 ppb. The current value of aμ was measured at the Brookhaven g − 2 experiment, whose final result was published in 2006 with an uncertainty of 0.54 ppm [1]. The deviated from the Standard Model (SM) prediction by up to 3.6 σ, causing international intrigue that motivated the repetition of the experiment with increased statistics. The experiment’s storage ring (SR) magnet was transported to Fermilab in 2013 to make use of its high-intensity muon beam. This will facilitate a 21-fold increase in statistics that will contribute most of the improved precision in the aμ measurement. In addition, improvements to the experimental hardware are intended to reduce the systematic uncertainty. A major improvement is a new straw tracking detector system, which will measure the beam profile continuously throughout the experiment, in order to mitigate sources of systematic error associated with the beam position and motion. The straw trackers will also be used to perform a muon electric dipole moment (EDM) search. The current world’s best limit on the muon EDM was placed by the Brookhaven g − 2 experiment [2]. The signal for a muon EDM in the g − 2 experiment can be directly measured with the straw tracking detectors, so the upgraded tracking system is expected to enable a reduction in the current limit by a factor of 100. This thesis will describe the design and construction of the straw tracking detectors that took place at the University of Liverpool. The development and optimisation of a track extrapolation algorithm for propagating the track parameters of the decay positrons back to the muon decay position will be presented. The use of this algorithm in measuring the beam profile during the commissioning phase of the experiment will be discussed, and finally, the development of a muon EDM simulation and a preliminary sensitivity study using the track extrapolation algorithm will be presented. [1] Muon g − 2 Collaboration, G. W. Bennett et al., Final report of the E821 muon anomalous magnetic moment measurement at BNL, Phys. Rev. D 73 (2006) 072003. [2] Muon g-2 Collaboration, G. W. Bennett et al., Improved limit on the muon electric dipole moment, Phys. Rev. D 80 (2009) 052008.

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