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arXiv · 2508.16045

First Full Dalitz Plot Measurement in Neutron $β$-Decay using the Nab Spectrometer and Implications for New Physics

Francisco M. Gonzalez·Jin Ha Choi·Himal Acharya·Skylar Clymer·Andrew Hagemeier·David G. Mathews·August Mendelsohn·Austin Nelsen·Hitesh Rahangdale·Love Richburg·Ricardo Alarcon·Ariella Atencio·Stefan Baeßler·Thomas Bailey·Noah Birge·Dennis Borissenko·Michael Bowler·Leah J. Broussard·Albert T. Bryant·Jimmy Caylor·Tim Chupp·Christopher Crawford·R. Alston Croley·Micah Cruz·George Dodson·Wenjiang Fan·Deion Fellers·Nadia Fomin·Emil Frlež·Matthew Frost·Jason Fry·Duncan Fuehne·Michael T. Gericke·Michelle Gervais·Corey Gilbert·Ferenc Glück·Rebecca Godri·Geoff L. Greene·William Greene·Josh Hamblen·Paul Harmston·Leendert Hayen·Carter Hedinger·Chelsea Hendrus·Sean Hollander·Kavish Imam·Erik B. Iverson·Aaron Jezghani·Chenyang Jiang·Huangxing Li·Nick Macsai·Mark Makela·Russell Mammei·Ricky Marshall·Madelyn Martinez·Mark McCrea·Pat McGaughey·Sean McGovern·David McLaughlin·Jacqueline Mirabal-Martinez·Paul Mueller·Andrew Mullins·William Musk·Jordan O'Kronley·Seppo I. Penttilä·D. Elliot Perryman·Josh Pierce·Jason A. Pioquinto·Dinko Počanić·Hunter Presley·John Ramsey·Glenn Randall·Zachary Raney·Jackson Ricketts·Grant Riley·Americo Salas-Bacci·Sepehr Samiei·Alexander Saunders·Wolfgang Schreyer·E. Mae Scott·Thomas Shelton·Aryaman Singh·Alexander Smith·Erick Smith·Eric Stevens·R. J. Taylor·Leonard Tinius·Isaiah Wallace·Jonathan Wexler·W. Scott Wilburn·A. R. Young·B. Zeck
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Abstract

Precision measurements of observables in neutron $β$-decay are used to test the Standard Model description of the weak interaction and search for evidence of new physics. The Nab experiment at the Fundamental Neutron Physics Beamline at the Spallation Neutron Source was constructed to measure correlations in neutron decay by utilizing an asymmetric spectrometer and novel detection system to accurately reconstruct the proton momentum and electron energy for each $β$-decay. This work describes the detection of neutron $β$-decay products in the Nab spectrometer and presents the first full Dalitz plot representation of the phase space of neutron $β$-decay for all electrons >100 keV. In addition, new constraints are placed on a possible excited neutron state, hypothesized to explain the disagreement between the appearance and disappearance neutron lifetime techniques.

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Francisco M. Gonzalez, Jin Ha Choi, Himal Acharya, Skylar Clymer, Andrew Hagemeier, David G. Mathews, August Mendelsohn, Austin Nelsen, Hitesh Rahangdale, Love Richburg, Ricardo Alarcon, Ariella Atencio, Stefan Baeßler, Thomas Bailey, Noah Birge, Dennis Borissenko, Michael Bowler, Leah J. Broussard, Albert T. Bryant, Jimmy Caylor, Tim Chupp, Christopher Crawford, R. Alston Croley, Micah Cruz, George Dodson, Wenjiang Fan, Deion Fellers, Nadia Fomin, Emil Frlež, Matthew Frost, Jason Fry, Duncan Fuehne, Michael T. Gericke, Michelle Gervais, Corey Gilbert, Ferenc Glück, Rebecca Godri, Geoff L. Greene, William Greene, Josh Hamblen, Paul Harmston, Leendert Hayen, Carter Hedinger, Chelsea Hendrus, Sean Hollander, Kavish Imam, Erik B. Iverson, Aaron Jezghani, Chenyang Jiang, Huangxing Li, Nick Macsai, Mark Makela, Russell Mammei, Ricky Marshall, Madelyn Martinez, Mark McCrea, Pat McGaughey, Sean McGovern, David McLaughlin, Jacqueline Mirabal-Martinez, Paul Mueller, Andrew Mullins, William Musk, Jordan O'Kronley, Seppo I. Penttilä, D. Elliot Perryman, Josh Pierce, Jason A. Pioquinto, Dinko Počanić, Hunter Presley, John Ramsey, Glenn Randall, Zachary Raney, Jackson Ricketts, Grant Riley, Americo Salas-Bacci, Sepehr Samiei, Alexander Saunders, Wolfgang Schreyer, E. Mae Scott, Thomas Shelton, Aryaman Singh, Alexander Smith, Erick Smith, Eric Stevens, R. J. Taylor, Leonard Tinius, Isaiah Wallace, Jonathan Wexler, W. Scott Wilburn, A. R. Young, B. Zeck. 2025-08-22. First Full Dalitz Plot Measurement in Neutron $β$-Decay using the Nab Spectrometer and Implications for New Physics. https://doi.org/10.1103/ksmp-zxsl

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