arXiv : Testing Lepton Flavor Universality and CKM Unitarity with Rare Pion Decays in the PIONEER experiment

Altmannshofer, W.; Gorringe, T.; Caminada, L.; Mott, J.; Hertzog, D.; Velghe, B.; Worcester, E.; Ootani, W.; Iwamoto, T.; Blucher, E.; Sher, A.; Sullivan, T.; Garcia, A.; Polly, C.; Tricoli, A.; Kiburg, B.; Roehnelt, R.; Corrodi, S.; Gibbons, L.; Di Canto, A.; Mischke, R.; Mori, T.; Cuen-Rochin, S.; Göldi, D.; Mazza, S.M.; Tischenko, V.; Mihara, S.; Doria, L.; Godoy, M. Escobar; Gaponenko, A.; Shrock, R.; Schwendimann, P.; Soter, A.; Kammel, P.; Glaser, C.; Tarka, M.; Crivellin, A.; Cirigliano, V.; Zhang, C.; LaBounty, J.; Binney, H.; Ito, S.; Seiden, A.; Hodge, Z.; Qian, X.; Numao, T.; Worcester, M.; Ries, D.; Gori, S.; Bryman, D.; Malbrunot, C.; Chen, S.; Počanić, D.; Hoferichter, M.; Schumm, B.; Ott, J.; Wong, V.; Labe, K.; Langenegger, U.; Pachal, K.

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Preprint
Report number	arXiv:2203.05505 ; FERMILAB-CONF-22-328-PPD
Title	Testing Lepton Flavor Universality and CKM Unitarity with Rare Pion Decays in the PIONEER experiment
Author(s)	Altmannshofer, W. (UC, Santa Cruz, Inst. Part. Phys.) ; Binney, H. (Washington U., Seattle) ; Blucher, E. (Chicago U., EFI ; Chicago U.) ; Bryman, D. (British Columbia U. ; TRIUMF) ; Caminada, L. (PSI, Villigen) ; Chen, S. (Tsinghua U., Beijing, Dept. Eng. Phys.) ; Cirigliano, V. (Washington U., Seattle) ; Corrodi, S. (Argonne) ; Crivellin, A. (PSI, Villigen ; Zurich U. ; CERN) ; Cuen-Rochin, S. (ITESM, Monterrey) ; Di Canto, A. (Brookhaven Natl. Lab.) ; Doria, L. (U. Mainz, PRISMA) ; Gaponenko, A. (Fermilab) ; Garcia, A. (Washington U., Seattle) ; Gibbons, L. (Cornell U.) ; Glaser, C. (Virginia U.) ; Godoy, M. Escobar (UC, Santa Cruz, Inst. Part. Phys.) ; Göldi, D. (Zurich, ETH) ; Gori, S. (UC, Santa Cruz, Inst. Part. Phys.) ; Gorringe, T. (Kentucky U.) ; Hertzog, D. (Washington U., Seattle) ; Hodge, Z. (Washington U., Seattle) ; Hoferichter, M. (Bern U.) ; Ito, S. (KEK, Tsukuba) ; Iwamoto, T. (Tokyo U., ICEPP) ; Kammel, P. (Washington U., Seattle) ; Kiburg, B. (Fermilab) ; Labe, K. (Cornell U.) ; LaBounty, J. (Washington U., Seattle) ; Langenegger, U. (PSI, Villigen) ; Malbrunot, C. (TRIUMF) ; Mazza, S.M. (UC, Santa Cruz, Inst. Part. Phys.) ; Mihara, S. (KEK, Tsukuba) ; Mischke, R. (TRIUMF) ; Mori, T. (Tokyo U., ICEPP) ; Mott, J. (Fermilab) ; Numao, T. (TRIUMF) ; Ootani, W. (Tokyo U., ICEPP) ; Ott, J. (UC, Santa Cruz, Inst. Part. Phys.) ; Pachal, K. (TRIUMF) ; Polly, C. (Fermilab) ; Počanić, D. (Virginia U.) ; Qian, X. (Brookhaven Natl. Lab.) ; Ries, D. (Mainz U.) ; Roehnelt, R. (Washington U., Seattle) ; Schumm, B. (UC, Santa Cruz, Inst. Part. Phys.) ; Schwendimann, P. (Washington U., Seattle) ; Seiden, A. (UC, Santa Cruz, Inst. Part. Phys.) ; Sher, A. (TRIUMF) ; Shrock, R. (YITP, Stony Brook) ; Soter, A. (Zurich, ETH) ; Sullivan, T. (Tokyo U., ICEPP) ; Tarka, M. (UC, Santa Cruz, Inst. Part. Phys.) ; Tischenko, V. (Brookhaven Natl. Lab.) ; Tricoli, A. (Brookhaven Natl. Lab.) ; Velghe, B. (TRIUMF) ; Wong, V. (TRIUMF) ; Worcester, E. (Brookhaven Natl. Lab.) ; Worcester, M. (Brookhaven Natl. Lab.) ; Zhang, C. (Brookhaven Natl. Lab.)
Imprint	2022-03-10
Note	contribution to Snowmass 2021 based on the PIONEER proposal (arXiv:2203.01981)
Presented at	2021 Snowmass Summer Study, Seattle, WA, United States, 11 - 20 July 2021, pp.
Subject category	physics.ins-det ; Detectors and Experimental Techniques ; hep-ph ; Particle Physics - Phenomenology ; hep-ex ; Particle Physics - Experiment
Abstract	The physics motivation and the conceptual design of the PIONEER experiment, a next-generation rare pion decay experiment testing lepton flavor universality and CKM unitarity, are described. Phase I of the PIONEER experiment, which was proposed and approved at Paul Scherrer Institut, aims at measuring the charged-pion branching ratio to electrons vs. muons, $R_{e/\mu}$, 15 times more precisely than the current experimental result, reaching the precision of the Standard Model (SM) prediction at 1 part in $10^4$. Considering several inconsistencies between the SM predictions and data pointing towards the potential violation of lepton flavor universality, the PIONEER experiment will probe non-SM explanations of these anomalies through sensitivity to quantum effects of new particles up to the PeV mass scale. The later phases of the PIONEER experiment aim at improving the experimental precision of the branching ratio of pion beta decay (BRPB), $\pi^+\to \pi^0 e^+ \nu (\gamma)$, currently at $1.036(6)\times10^{-8}$, by a factor of three (Phase II) and an order of magnitude (Phase III). Such precise measurements of BRPB will allow for tests of CKM unitarity in light of the Cabibbo Angle Anomaly and the theoretically cleanest extraction of $\|V_{ud}\|$ at the 0.02% level, comparable to the deduction from superallowed beta decays.
Other source	Inspire
Copyright/License	preprint: (License: CC BY 4.0)

$The positron energy spectra from muon decays (blue) and from \pie~ decays (orange) for a calorimeter resolution of 1.5\% and a depth of $25\,X_0$. The simulation includes energy losses owing to photonuclear interactions.$