Two-neutrino double electron capture of 124Xe in the first LUX-ZEPLIN exposure
Authors: Aalbers J , Akerib D S , Al Musalhi A K , Alder F , Amarasinghe C S , Ames A , Anderson T J , Angelides N , Araújo H M , Armstrong J E , Arthurs M , Baker A , Balashov S , Bang J , Bargemann J W , Barillier E E , Beattie K , Bhatti A , Biekert A , Biesiadzinski T P , Birch H J , Bishop E , Blockinger G M , Boxer B , Brew C A J , Brás P , Burdin S , Buuck M , Carmona-Benitez M C , Carter M , Chawla A , Chen H , Chin Y T , Chott N I , Converse M V , Coronel R , Cottle A , Cox G , Curran D , Dahl C E , David A , Delgaudio J , Dey S , de Viveiros L , Di Felice L , Ding C , Dobson J E Y , Druszkiewicz E , Dubey S , Eriksen S R , Fan A , Fearon N M , Fieldhouse N , Fiorucci S , Flaecher H , Fraser E D , Fruth T M A , Gaitskell R J , Geffre A , Genovesi J , Ghag C , Gibbons R , Gokhale S , Green J , van der Grinten M G D , Haiston J J , Hall C R , Han S , Hartigan-OConnor E , Haselschwardt S J , Hernandez M A , Hertel S A , Heuermann G , Homenides G J , Horn M , Huang D Q , Hunt D , Jacquet E , James R S , Johnson J , Kaboth A C , Kamaha A C , Kannichankandy M , Khaitan D , Khazov A , Khurana I , Kim J , Kim Y D , Kingston J , Kirk R , Kodroff D , Korley L , Korolkova E V , Kraus H , Kravitz S , Kreczko L , Kudryavtsev V A , Leonard D S , Lesko K T , Levy C , Lin J , Lindote A , Lippincott W H , Lopes M I , Lorenzon W , Lu C , Luitz S , Majewski P A , Manalaysay A , Mannino R L , Maupin C , McCarthy M E , McDowell G , McKinsey D N , McLaughlin J , McLaughlin J B , McMonigle R , Mizrachi E , Monte A , Monzani M E , Morrison E , Mount B J , Murdy M , Murphy A S J , Naylor A , Nelson H N , Neves F , Nguyen A , O’Brien C L , Olcina I , Oliver-Mallory K C , Orpwood J , Oyulmaz K Y , Palladino K J , Palmer J , Pannifer N J , Parveen N , Patton S J , Penning B , Pereira G , Perry E , Pershing T , Piepke A , Qie Y , Reichenbacher J , Rhyne C A , Riffard Q , Rischbieter G R C , Ritchey E , Riyat H S , Rosero R , Rushton T , Rynders D , Santone D , Sazzad A B M R , Schnee R W , Sehr G , Shafer B , Shaw S , Shutt T , Silk J J , Silva C , Sinev G , Siniscalco J , Smith R , Solovov V N , Sorensen P , Soria J , Stevens A , Stifter K , Suerfu B , Sumner T J , Szydagis M , Tiedt D R , Timalsina M , Tong Z , Tovey D R , Tranter J , Trask M , Tripathi M , Vacheret A , Vaitkus A C , Valentino O , Velan V , Wang A , Wang J J , Wang Y , Watson J R , Weeldreyer L , Whitis T J , Wild K , Williams M , Wisniewski W J , Wolf L , Wolfs F L H , Woodford S , Woodward D , Wright C J , Xia Q , Xu J , Xu Y , Yeh M , Yeum D , Zha W , Zweig E A ,   (The LZ Collaboration)
Published: December 2024

Abstract
The broad physics reach of the LUX-ZEPLIN (LZ) experiment covers rare phenomena beyond the direct detection of dark matter. We report precise measurements of the extremely rare decay of 124Xe through the process of two-neutrino double electron capture, utilizing a 1.39 kg × yr isotopic exposure from the first LZ science run. A half-life of

T

1
/
2

2
ν
2
EC

=
(
1.09
±
0.1

4

stat

±
0.0

5

sys

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×
1

0
22

yr

is observed with a statistical significance of 8.3σ, in agreement with literature. First empirical measurements of the KK capture fraction relative to other K-shell modes were conducted, and demonstrate consistency with respect to recent signal models at the 1.4σ level.