Snowmass RF2 LOI PIENUXE: Testing Lepton Flavor Universality and CKM Unitarity with Rare Pion Decays
Douglas Bryman University of British Columbia &TRIUMF
A. Aguilar-Arevalo1, D. Bryman2,3, S. Chen4, V. Cirigliano5, A. Crivellin6,7,8, S. Cuen-Rochin9, A. Czarnecki10, L. Doria11, A. Garcia12, L. Gibbons13, C. Glaser14, M. Gorchtein11, T. Gorringe15, D. Hertzog12, Z. Hodge12, M. Hoferichter16, T. Iwamoto17, P. Kammel12, J. Kaspar12, K. Labe13, J. Labounty12, S. Ito18, W. Marciano19, S. Mihara20, R. Mischke3, T. Mori17, T. Numao3, W. Ootani17, C. Ortega Hernandez1, D. Pocanic14, D. Salvat21, T. Sullivan22
1Universidad Nacional Autonoma de Mexico, 2University of British Columbia, 3TRIUMF, 4Tsinghua University, 5Los Alamos National Laboratory, 6Paul Scherrer Institute, 7University of Zurich, 8CERN, 9Universidad Autonoma de Sinaloa, 10University of Alberta,11University of Mainz, 12University of Washington, 13Cornell University, 14University of Virginia, 15University of Kentucky, 16University of Bern, 17University of Tokyo, 18Okayama University,19Brookhaven National Laboratory, 20KEK, 21Indiana University, 22University of Victoria Flavor in the News! Several lingering unconfirmed flavor anomalies
• Muon g-2 (~3+ σ) • Lepton universality in B decays (R(K),R(D),R(D*)~3σ) • Unitarity of CKM first row(~2-3 σ)
Tensions in
Vud and Vus
Possible connections between LFU and CKM unitarity.
Crivellin and Hoferichter 2020
V. Cirigliano
2 Charged Lepton Flavor Universality e/µ tested in π and tau decay at precision O(10-3)
theory e () 4 (±0.016%) Re/ 1.2353 0.0002x 10 () Marciano/Sirlin Cirigliano Possibly the most accurately calculated decay process involving hadrons.
exp 4 Current Result (PDG): Re/ 1.2327 0.0023x 10(0.19%) NEXT GENERATION PIENUXE GOAL 0.015% g e ~ 0.0075% g Sensitive to new pseudoscala r interations at mass scale 2000 TeV.
(Leptoquarks, gauge bosons, compositeness, hidden sectors, H ....) 3 CKM Unitarity: Vud, Vus/Vud Tested in super-allowed β and K decays at precision O(10-4)
0 e : Theoretically cleanest method to obtain Vud Present result: PIBETA Experiment (2004) 0.64% V 0.9739 28 1 ud exp th 0 -8 B( e ) (1.036 0. 004stat 0.004 syste 0.003 2 ) x10 0.6% NEXT GENERATION EIXE P R MENT GOAL: 0.06%
BK() l Vus 0 : Theoretically clean method to obtain B() eVCzarnecki, Marciano , Sirlin (2020) ud
0 Vus Improve B(e ) precision by >3x 0.2% Vud
Offers a new complemetary constr a int in the VVus ud plan e.
4 e: Experimental Method
Pions stopped in an active target Positrons tracked and energy measured in a calorimeter Decays tagged in target and by energy and timing Principal sytematic uncertainty: Low energy "tail" of e events under e "background".
5 PIENUXE: New Rare π Decay Experiment with LXe
ΔE 30 X ;Δt~50ps; ~1% 0 E
Faster calorimeter response time x10-100. Low energy tail reduced x 10 e 0e +5 • Beam: 75 MeV/c ; 2x10 Hz • +7 Beam: 75 MeV/c ; 3x10 Hz •Tracking –SciFi-SiPM, Si pixels •Sensitivity, Precision: 106 events ±0.1% in 1 yr •LXe calorimeter V •Sensitivity, Precision: 108 events ±0.015% in 1 yr V ~ 0.03%us ~ 0.1% ud V g ud e ~0.0075 % g 6 PIENUXE: Summary
Exploring the possibility of a new experiment aimed at improving the precision of rare pion decay measurements by an order of magnitude.
e () g R 0.015% e ~ 0.0075% e/ () g
0 Vus B(e ) 0.06% Vud ~ 0.03% ~ 0.1% Vud Sensitive to new flavor physics at extremely high mass scales and violations of LFU and CKM unitarity; searches for hidden sector, H ....
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