Improved limits on Fierz interference using asymmetry measurements from the Ultracold Neutron Asymmetry (UCNA) experiment

Abstract

The Ultracold Neutron Asymmetry (UCNA) experiment was designed to measure the β-decay asymmetry parameter, A0, for free neutron decay. In the experiment, polarized ultracold neutrons are transported into a decay trap, and their β-decay electrons are detected with ≈ 4π acceptance into two detector packages which provide position and energy reconstruction. The experiment also has sensitivity to bn, the Fierz interference term in the neutron β-decay rate. In this work, we determine bn from the energy dependence of A0 using the data taken during the UCNA 2011-2013 run. In addition, we present the same type of analysis using the earlier 2010 A dataset. Motivated by improved statistics and comparable systematic errors compared to the 2010 data-taking run, we present a new bn measurement using the weighted average of our asymmetry dataset fits, to obtain bn = 0.066 ± 0.041stat ± 0.024syst which corresponds to a limit of −0.012 < bn < 0.144 at the 90% confidence level.Standard Model predictions of the electroweak sector can be tested using precision measurements of nuclear β-decay and free neutron β-decay parameters. There are many past and current experiments to measure these decay parameters such as lifetimes, angular/spin correlations, and energy spectra, to name a few [1][2][3][4][5][6][7]. The Fierz interference term is one such decay parameter in the neutron β-decay rate (explained below) which vanishes in the Standard Model but would serve as a probe for beyond Standard Model physics in scalar and tensor couplings [1,4,8,9].In this publication, the UCNA collaboration presents a measurement of the Fierz interference term, b n , using the energy-dependence of the neutron β-decay asymmetry for the 2010 [10], and 2011-2013 data-taking runs [11]. For completeness, the electron energy spectra from the 2011-2013 data-taking runs are also used to extract b n arXiv:1911.05829v1 [nucl-ex]

Helium film may greatly increase the storage time of ultracold neutrons in material traps

“…k tanh [κ He (d He + x 0 )] = κ He tan [k (d He + x 1 )] , (A16) which gives Eq. (11). * grigorev@itp.ac.ru…”

“…The search for a non-vanishing electric dipole moment of neutrons [6][7][8] impose the limits on CP violation. Precise measurements of a β-decay asymmetry provide information on axial-vector weak coupling constant [9][10][11]. The resonant transions between discrete quantum energy levels of neutrons in the earth gravitational field [12,13] probe the gravitational field on a micron length scale and impose constraints on dark matter.…”

“…A large class of experiments employs neutrons with energy lower than the neutron optical potential of typical materials, i.e. 300 neV [7,8,[10][11][12][14][15][16][17][18][19][20][21]. These socalled ultracold neutrons (UCNs) can be trapped for many minutes in well-designed "neutron bottles" [17][18][19][20][21].…”

Electrodisintegration of Deuteron into Dark Matter and Proton Close to Threshold

“…We would like to emphasize that a possibility to explain the NLA problem by the neutron dark matter decay mode n → χ + ν e + νe is not innocent and demands to pay the following price. As has been pointed out in [9], the explanation of the neutron lifetime τ n = 888.0(2.0) s [1] within the Standard Model with the axial coupling constant g A = 1.2764 [28,29], reproducing the neutron lifetime τ n = 879.6(4) s [30], is not possible and demands the account for the contributions of interactions beyond the Standard Model such as the Fierz interference term b [31][32][33][34][35][36][37][38] equal to b = −1.44 × 10 −2 [39]. However, as has been shown in [39], the Fierz interference term b = −1.44 × 10 −2 does not contradict the existing experimental data on the correlation coefficients and asymmetries of the neutron beta decay.…”

Corrections of order O(E^2_e/m^2_N), caused by weak magnetism and proton recoil, to the neutron lifetime and correlation coefficients of the neutron beta decay

“…Together with Wilkinson's corrections [15] (see also [18,[25][26][27][28]) and radiative corrections of order O(αE e /m N ) ∼ 10 −5 [29,30], the corrections O(E 2 e /m 2 N ) ∼ 10 −5 should provide an improved level of precision of the theoretical background of the neutron beta decay, calculated in the SM. It is initiated to promote experimental searches of contributions of interactions beyond the SM [8,[31][32][33][34][35] with experimental sensitivities of about a few parts of 10 −5 .…”