<p dir="ltr">The Mu2e experiment will search for neutrinoless, coherent conversion of a muon into an</p><p dir="ltr">electron in the field of an aluminum nucleus (μ−N ! e−N) at the sensitivity level of 10−17.</p><p dir="ltr">This conversion process is an example of Charged Lepton Flavor Violation (CLFV), which</p><p dir="ltr">has never been observed experimentally before. The Mu2e experiment tracker is designed</p><p dir="ltr">to accurately detect the 105 MeV/c conversion electron (CE) momentum in a uniform 1 T</p><p dir="ltr">magnetic field. The mono-energetic positrons (e+) at 69.8 MeV from the decay of positively charged</p><p dir="ltr">pions (p+) that have stopped in the aluminum stopping target are investigated as a</p><p dir="ltr">calibration source to measure the accuracy of absolute momentum scale. The backgrounds</p><p dir="ltr">for the calibration arise from μ+ decay-in-flight (DIF) backgrounds and other stopped p+</p><p dir="ltr">decays that produce reconstructed e+ tracks mimicking a signal trajectory originating from</p><p dir="ltr">the stopping target. The most significant background is the μ-DIF background. Therefore,</p><p dir="ltr">we identified the need for a momentum degrader placed at the entry of the Detector Solenoid,</p><p dir="ltr">to increase the pion stops in the stopping target and suppress the μ-DIF background. The</p><p dir="ltr">material of the degrader is chosen to be titanium (Ti). The thickness of degrader is optimized</p><p dir="ltr">by the pion stops efficiency to muon flux efficiency ratio and the 4mm Ti degrader is the</p><p dir="ltr">optimized one. The calibration signal and backgrounds are simulated with the 3mm and</p><p dir="ltr">4mm Ti degrader. The ratio of S/B is used as a figure of merit, S/B ? 1.85 for the 3mm Ti</p><p dir="ltr">degrader and S/B ? 2.93 for the 4mm Ti degrader. The 4mm Ti degrader performs better</p><p dir="ltr">than the 3mm Ti degrader in terms of S/B ratio. By fitting the reconstructed momentum</p><p dir="ltr">spectra of signal and backgrounds, we extract the signal distribution peak and width of</p><p dir="ltr">x0 = 69.268 ± 0.013 MeV/c and ? = 0.324 ± 0.009 MeV/c (with the 3mm Ti degrader),</p><p dir="ltr">x0 = 69.263 ± 0.013 MeV/c and ? = 0.299 ± 0.009 MeV/c (with the 4mm Ti degrader).</p><p dir="ltr">We also show that the peak shifts by backgrounds for both degraders are within 100 keV/c</p><p dir="ltr">momentum scale accuracy requirement.</p>
| Identifer | oai:union.ndltd.org:purdue.edu/oai:figshare.com:article/25663947 |
| Date | 22 April 2024 |
| Creators | Xiaobing Shi (18421551) |
| Source Sets | Purdue University |
| Detected Language | English |
| Type | Text, Thesis |
| Rights | CC BY 4.0 |
| Relation | https://figshare.com/articles/thesis/CALIBRATION_OF_THE_MU2E_ABSOLUTE_MOMENTUM_SCALE_USING_POSITIVE_PION_DECAYS_TO_POSITRON_AND_ELECTRON_NEUTRINO/25663947 |
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