First Full Dalitz Plot Measurement in Neutron $\beta$-Decay using the Nab Spectrometer and Implications for New Physics
Abstract
Precision measurements of observables in neutron -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 -decay. This work describes the detection of neutron -decay products in the Nab spectrometer and presents the first full Dalitz plot representation of the phase space of neutron -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.
Cite
@article{arxiv.2508.16045,
title = {First Full Dalitz Plot Measurement in Neutron $\beta$-Decay using the Nab Spectrometer and Implications for New Physics},
author = {Francisco M. Gonzalez and Jin Ha Choi and Himal Acharya and Skylar Clymer and Andrew Hagemeier and David G. Mathews and August Mendelsohn and Austin Nelsen and Hitesh Rahangdale and Love Richburg and Ricardo Alarcon and Ariella Atencio and Stefan Baeßler and Thomas Bailey and Noah Birge and Dennis Borissenko and Michael Bowler and Leah J. Broussard and Albert T. Bryant and Jimmy Caylor and Tim Chupp and Christopher Crawford and R. Alston Croley and Micah Cruz and George Dodson and Wenjiang Fan and Deion Fellers and Nadia Fomin and Emil Frlež and Matthew Frost and Jason Fry and Duncan Fuehne and Michael T. Gericke and Michelle Gervais and Corey Gilbert and Ferenc Glück and Rebecca Godri and Geoff L. Greene and William Greene and Josh Hamblen and Paul Harmston and Leendert Hayen and Carter Hedinger and Chelsea Hendrus and Sean Hollander and Kavish Imam and Erik B. Iverson and Aaron Jezghani and Chenyang Jiang and Huangxing Li and Nick Macsai and Mark Makela and Russell Mammei and Ricky Marshall and Madelyn Martinez and Mark McCrea and Pat McGaughey and Sean McGovern and David McLaughlin and Jacqueline Mirabal-Martinez and Paul Mueller and Andrew Mullins and William Musk and Jordan O'Kronley and Seppo I. Penttilä and D. Elliot Perryman and Josh Pierce and Jason A. Pioquinto and Dinko Počanić and Hunter Presley and John Ramsey and Glenn Randall and Zachary Raney and Jackson Ricketts and Grant Riley and Americo Salas-Bacci and Sepehr Samiei and Alexander Saunders and Wolfgang Schreyer and E. Mae Scott and Thomas Shelton and Aryaman Singh and Alexander Smith and Erick Smith and Eric Stevens and R. J. Taylor and Leonard Tinius and Isaiah Wallace and Jonathan Wexler and W. Scott Wilburn and A. R. Young and B. Zeck},
journal= {arXiv preprint arXiv:2508.16045},
year = {2026}
}