@article{king_baroni_cirigliano_gandolfi_hayen_mereghetti_pastore_piarulli_2023, title={Ab initio calculation of the beta-decay spectrum of He-6}, volume={107}, ISSN={["2469-9993"]}, url={https://doi.org/10.1103/PhysRevC.107.015503}, DOI={10.1103/PhysRevC.107.015503}, abstractNote={We calculate the $\beta$ spectrum in the decay of $^6$He using Quantum Monte Carlo methods with nuclear interactions derived from chiral Effective Field Theory and consistent weak vector and axial currents. We work at second order in the multipole expansion, retaining terms suppressed by $\mathcal O(q^2/m_\pi^2)$, where $q$ denotes low-energy scales such as the reaction's $\mathcal Q$-value or the electron energy, and $m_\pi$ the pion mass. We go beyond the impulse approximation by including the effects of two-body vector and axial currents. We estimate the theoretical error on the spectrum by using four potential models in the Norfolk family of local two- and three-nucleon interactions, which have different cut-off, fit two-nucleon data up to different energies and use different observables to determine the couplings in the three-body force. We find the theoretical uncertainty on the $\beta$ spectrum, normalized by the total rate, to be well below the permille level, and to receive contributions of comparable size from first and second order corrections in the multipole expansion. We consider corrections to the $\beta$ decay spectrum induced by beyond-the-Standard Model charged-current interactions in the Standard Model Effective Field Theory, with and without sterile neutrinos, and discuss the sensitivity of the next generation of experiments to these interactions.}, number={1}, journal={PHYSICAL REVIEW C}, author={King, G. B. and Baroni, A. and Cirigliano, V. and Gandolfi, S. and Hayen, L. and Mereghetti, E. and Pastore, S. and Piarulli, M.}, year={2023}, month={Jan} }
 @article{byron_harrington_taylor_degraw_buzinsky_dodson_fertl_garcía_garvey_graner_et al._2023, title={First Observation of Cyclotron Radiation from MeV-Scale 
e  following Nuclear β Decay}, volume={131}, ISSN={0031-9007 1079-7114}, url={http://dx.doi.org/10.1103/PhysRevLett.131.082502}, DOI={10.1103/PhysRevLett.131.082502}, abstractNote={We present an apparatus for detection of cyclotron radiation yielding a frequency-based β^{±} kinetic energy determination in the 5 keV to 2.1 MeV range, characteristic of nuclear β decays. The cyclotron frequency of the radiating β particles in a magnetic field is used to determine the β energy precisely. Our work establishes the foundation to apply the cyclotron radiation emission spectroscopy (CRES) technique, developed by the Project 8 Collaboration, far beyond the 18-keV tritium endpoint region. We report initial measurements of β^{-}'s from ^{6}He and β^{+}'s from ^{19}Ne decays to demonstrate the broadband response of our detection system and assess potential systematic uncertainties for β spectroscopy over the full (MeV) energy range. To our knowledge, this is the first direct observation of cyclotron radiation from individual highly relativistic β's in a waveguide. This work establishes the application of CRES to a variety of nuclei, opening its reach to searches for new physics beyond the TeV scale via precision β-decay measurements.}, number={8}, journal={Physical Review Letters}, publisher={American Physical Society (APS)}, author={Byron, W. and Harrington, H. and Taylor, R. J. and DeGraw, W. and Buzinsky, N. and Dodson, B. and Fertl, M. and García, A. and Garvey, G. and Graner, B. and et al.}, year={2023}, month={Aug}, pages={082502} }
 @article{severijns_hayen_de leebeeck_vanlangendonck_bodek_rozpedzik_towner_2023, title={Ft values of the mirror 13 transitions and the weak-magnetism-induced current in allowed nuclear 13 decay}, volume={107}, ISSN={["2469-9993"]}, url={https://doi.org/10.1103/PhysRevC.107.015502}, DOI={10.1103/PhysRevC.107.015502}, abstractNote={The precision of correlation measurements in neutron and nuclear $\ensuremath{\beta}$ decay has now reached the level of about 1% and better. At this level of precision, higher-order corrections such as recoil-order corrections induced by the strong interaction and radiative corrections cannot necessarily be neglected anymore. We provide here an update of the $\mathcal{F}t$ values of the isospin $T=1/2$ mirror $\ensuremath{\beta}$ decays including the neutron, of interest to determine the ${V}_{\mathrm{ud}}$ quark-mixing matrix element. We also provide an overview of current experimental and theoretical knowledge of the most important recoil term, weak magnetism, for both these mirror $\ensuremath{\beta}$ decays and a large set of $\ensuremath{\beta}$ decays in higher isospin multiplets. The matrix elements determining weak magnetism were calculated in the nuclear shell model and cross-checked against experimental data, showing overall good agreement. We show that the neutron and the mirror nuclei now effectively contribute to the value of ${V}_{\mathrm{ud}}$, but we also stress the need for further work on the radiative correction ${\mathrm{\ensuremath{\Delta}}}_{R}^{V}$. Our results provide new insight into the size of weak magnetism, extending the available information to nuclei with masses up to $A=$ 75. This provides important guidance for planning and improved sensitivity for interpreting correlation measurements in searches for new physics or to extract ${V}_{\mathrm{ud}}$ in mirror $\ensuremath{\beta}$ decays. It can also be of interest for further theoretical work related to the reactor neutrino problem.}, number={1}, journal={PHYSICAL REVIEW C}, author={Severijns, N. and Hayen, L. and De Leebeeck, V. and Vanlangendonck, S. and Bodek, K. and Rozpedzik, D. and Towner, I. S.}, year={2023}, month={Jan} }
 @article{hayen_choi_combs_taylor_baeßler_birge_broussard_crawford_fomin_gericke_et al._2023, title={Precision pulse shape simulation for proton detection at the Nab experiment}, volume={107}, ISSN={["2469-9993"]}, url={https://link.aps.org/doi/10.1103/PhysRevC.107.065503}, DOI={10.1103/PhysRevC.107.065503}, abstractNote={The Nab experiment at Oak Ridge National Laboratory, USA, aims to measure the beta-antineutrino angular correlation following neutron $\beta$ decay to an anticipated precision of approximately 0.1\%. The proton momentum is reconstructed through proton time-of-flight measurements, and potential systematic biases in the timing reconstruction due to detector effects must be controlled at the nanosecond level. We present a thorough and detailed semiconductor and quasiparticle transport simulation effort to provide precise pulse shapes, and report on relevant systematic effects and potential measurement schemes.}, number={6}, journal={PHYSICAL REVIEW C}, publisher={American Physical Society}, author={Hayen, Leendert and Choi, Jin Ha and Combs, Dustin and Taylor, R. J. and Baeßler, Stefan and Birge, Noah and Broussard, Leah J. and Crawford, Christopher B. and Fomin, Nadia and Gericke, Michael and et al.}, year={2023}, month={Jun} }
 @article{rozpedzik_de keukeleere_bodek_hayen_lojek_perkowski_severijns_2023, title={Study of weak magnetism by precision spectrum shape measurements in nuclear beta decay}, volume={2586}, ISBN={["*****************"]}, ISSN={["1742-6596"]}, DOI={10.1088/1742-6596/2586/1/012141}, abstractNote={Nuclear beta decays play an important role in uncovering the nature of the weak interaction. The weak magnetism (WM) form factor, b WM, is generally a small correction to the beta decay rate that arises at first order as an interference term between the dominant Gamow-Teller and the magnetic dipole contributions to the weak current. This form factor is still poorly known for nuclei with higher atomic number. We performed a careful analysis of the measured beta spectrum shape for Gamow-Teller transitions in 114In and 32P nuclei. The precision spectrum shape measurements were carried out using the miniBETA spectrometer consisting of a low-mass, low-Z multi-wire gas tracker and a plastic scintillator energy detector. The preliminary results for the weak magnetism extraction for 114In and 32P nuclei are presented.}, journal={28TH INTERNATIONAL NUCLEAR PHYSICS CONFERENCE, INPC 2022}, author={Rozpedzik, D. and De Keukeleere, L. and Bodek, K. and Hayen, L. and Lojek, K. and Perkowski, M. and Severijns, N.}, year={2023} }
 @article{rozpedzik_de keukeleere_bodek_hayen_lojek_perkowski_severijns_2022, title={Gas electron tracking detector for beta decay experiments}, volume={17}, ISSN={["1748-0221"]}, DOI={10.1088/1748-0221/17/09/C09005}, abstractNote={For identification and 3D-tracking of low-energy electrons a new type of gas-based detector was designed that minimizes scattering and energy loss. The current version of the detector is a combination of a plastic scintillator, serving as a trigger source and energy detector, and a hexagonally structured multi-wire drift chamber (MWDC), filled with a mixture of helium and isobutane gas. The drift time information is used to track particles in the plane perpendicular to the wires, while a charge division technique provides spatial information along the wires. The gas tracker was successfully used in the miniBETA project as a beta spectrometer for a measurement of the weak magnetism form factor in nuclear beta decay. The precision of the three-dimensional electron tracking, in combination with low-mass, low-Z materials and identification of backscattering from scintillator, facilitated a reduction of the main systematics effects. The results originate from performance studies with cosmic muons and low-energy electrons (<2 MeV) conducted for several pressures (300–700 mbar) and isobutane content in the gas mixture (10–50%). At certain conditions, a spatial resolution better than 0.5 mm was obtained in the plane perpendicular to the wires, while resolutions of about 6 mm were achieved along wires. Thanks to precise tracking information, it is possible to eliminate electrons and other particles not originating from the desired decay with high efficiency. Additionally, using the coincidence between MWDC and scintillator, background from gamma emission typically accompanying radioactive decays, was highly suppressed. An overview of different event topologies is presented together with the tracker’s ability to correctly recognize them. The analysis is supported by Monte Carlo simulations using Geant4 and Garfield++ packages. Finally, the preliminary results from the 114In spectrum study are presented.}, number={9}, journal={JOURNAL OF INSTRUMENTATION}, author={Rozpedzik, D. and De Keukeleere, L. and Bodek, K. and Hayen, L. and Lojek, K. and Perkowski, M. and Severijns, N.}, year={2022}, month={Sep} }
 @article{vanlangendonck_severijns_hayen_glueck_2022, title={Influence of the recoil-order and radiative correction on the beta decay correlation coefficients in mirror decays}, volume={106}, ISSN={["2469-9993"]}, url={https://doi.org/10.1103/PhysRevC.106.015506}, DOI={10.1103/PhysRevC.106.015506}, abstractNote={Measurements of the beta decay correlation coefficients in nuclear decay aim for a precision below 1% and theoretical predictions should follow this trend. In this work, the influence of the two dominant Standard Model correction terms, i.e. the recoil-order and the radiative correction, are studied for the most commonly measured beta correlations, i.e. the β -asymmetry parameter ( A β ) and the β − ν angular correlation ( a βν ). The recoil-order correction is calculated with the well-known Holstein formalism using the impulse approximation to evaluate experimentally inaccessible form factors. For the β − ν angular correlation previously unpublished, semi-analytical radiative correction values are tabulated. Results are presented for the mirror beta decays up to A = 45 . We examine the effect of both corrections and provide a comparison between different isotopes. This comparison will help planning, analysing, and comparing future experimental efforts.}, number={1}, journal={PHYSICAL REVIEW C}, author={Vanlangendonck, S. and Severijns, N. and Hayen, L. and Glueck, F.}, year={2022}, month={Jul} }
 @article{abel_ayres_ban_bison_bodek_bondar_chanel_chiu_clement_crawford_et al._2022, title={Mapping of the magnetic field to correct systematic effects in a neutron electric dipole moment experiment}, volume={106}, ISSN={["2469-9934"]}, DOI={10.1103/PhysRevA.106.032808}, abstractNote={Experiments dedicated to the measurement of the electric dipole moment of the neutron require outstanding control of the magnetic field uniformity. The neutron electric dipole moment (nEDM) experiment at the Paul Scherrer Institute uses a 199Hg co-magnetometer to precisely monitor magnetic field variations. This co-magnetometer, in the presence of field non-uniformity, is responsible for the largest systematic effect of this measurement. To evaluate and correct that effect, offline measurements of the field non-uniformity were performed during mapping campaigns in 2013, 2014 and 2017. We present the results of these campaigns, and the improvement the correction of this effect brings to the neutron electric dipole moment measurement.}, number={3}, journal={PHYSICAL REVIEW A}, author={Abel, C. and Ayres, N. J. and Ban, G. and Bison, G. and Bodek, K. and Bondar, V and Chanel, E. and Chiu, P-J and Clement, B. and Crawford, C. B. and et al.}, year={2022}, month={Sep} }
 @article{cirigliano_de vries_hayen_mereghetti_walker-loud_2022, title={Pion-Induced Radiative Corrections to Neutron beta Decay}, volume={129}, ISSN={["1079-7114"]}, url={https://doi.org/10.1103/PhysRevLett.129.121801}, DOI={10.1103/PhysRevLett.129.121801}, abstractNote={We compute the electromagnetic corrections to neutron β decay using a low-energy hadronic effective field theory. We identify new radiative corrections arising from virtual pions that were missed in previous studies. The largest correction is a percent-level shift in the axial charge of the nucleon proportional to the electromagnetic part of the pion-mass splitting. Smaller corrections, comparable to anticipated experimental precision, impact the β-ν angular correlations and the β asymmetry. We comment on implications of our results for the comparison of the experimentally measured nucleon axial charge with first-principles computations using lattice QCD and on the potential of β decay experiments to constrain beyond-the-standard-model interactions.}, number={12}, journal={PHYSICAL REVIEW LETTERS}, author={Cirigliano, Vincenzo and De Vries, Jordy and Hayen, Leendert and Mereghetti, Emanuele and Walker-Loud, Andre}, year={2022}, month={Sep} }
 @article{gonzalez_fries_cude-woods_bailey_blatnik_broussard_callahan_choi_clayton_currie_et al._2021, title={Improved Neutron Lifetime Measurement with UCN τ}, volume={127}, ISSN={["1079-7114"]}, DOI={10.1103/PhysRevLett.127.162501}, abstractNote={We report an improved measurement of the free neutron lifetime τ_{n} using the UCNτ apparatus at the Los Alamos Neutron Science Center. We count a total of approximately 38×10^{6} surviving ultracold neutrons (UCNs) after storing in UCNτ's magnetogravitational trap over two data acquisition campaigns in 2017 and 2018. We extract τ_{n} from three blinded, independent analyses by both pairing long and short storage time runs to find a set of replicate τ_{n} measurements and by performing a global likelihood fit to all data while self-consistently incorporating the β-decay lifetime. Both techniques achieve consistent results and find a value τ_{n}=877.75±0.28_{stat}+0.22/-0.16_{syst}  s. With this sensitivity, neutron lifetime experiments now directly address the impact of recent refinements in our understanding of the standard model for neutron decay.}, number={16}, journal={PHYSICAL REVIEW LETTERS}, author={Gonzalez, F. M. and Fries, E. M. and Cude-Woods, C. and Bailey, T. and Blatnik, M. and Broussard, L. J. and Callahan, N. B. and Choi, J. H. and Clayton, S. M. and Currie, S. A. and et al.}, year={2021}, month={Oct}, pages={162501} }
 @article{kuk_cude-woods_chavez_choi_estrada_hoffbauer_holland_makela_morris_ramberg_et al._2021, title={Projection imaging with ultracold neutrons}, volume={1003}, ISSN={["1872-9576"]}, DOI={10.1016/j.nima.2021.165306}, abstractNote={Ultracold neutron (UCN) projection imaging is demonstrated using a boron-coated back-illuminated CCD camera and the Los Alamos UCN source. Each neutron is recorded through the capture reactions with 10B. By direct detection at least one of the byproducts α, 7Li and γ (electron recoils) derived from the neutron capture and reduction of thermal noise of the scientific CCD camera, a signal-to-noise improvement on the order of 104 over the indirect detection has been achieved. Sub-pixel position resolution of a few microns is confirmed for individual UCN events. Projection imaging of test objects shows a spatial resolution less than 100μm by an integrated UCN flux one the order of 106 cm−2. The bCCD can be used to build UCN detectors with an area on the order of 1 m2. The combination of micrometer scale spatial resolution, low readout noise of a few electrons, and large area makes bCCD suitable for quantum science of UCN.}, journal={NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT}, author={Kuk, K. and Cude-Woods, C. and Chavez, C. R. and Choi, J. H. and Estrada, J. and Hoffbauer, M. and Holland, S. E. and Makela, M. and Morris, C. L. and Ramberg, E. and et al.}, year={2021}, month={Jul} }
 @article{hayen_2021, title={Standard model O(a) renormalization of g(A) and its impact on new physics searches}, volume={103}, ISSN={["2470-0029"]}, url={https://doi.org/10.1103/PhysRevD.103.113001}, DOI={10.1103/PhysRevD.103.113001}, abstractNote={We present for the first time a complete $\mathcal{O}(\alpha)$ Standard Model calculation of the inner radiative corrections to Gamow-Teller $\beta$ decays. We find that \textit{a priori} contributions arise from the photonic vertex correction and $\gamma W$ box diagram. Upon evaluation most contributions vanish due to crossing symmetry or cancellation between isoscalar and isovector photonic contributions, leaving only the polarized parity-odd contribution, i.e. the Gamow-Teller equivalent of the well-known axial $\gamma W$ box contribution for Fermi decays. We show that weak magnetism contributes significantly to the Born amplitude, and consider additional hadronic contributions at low energy using a holomorphic continuation of the polarized Bjorken sum rule constrained by experimental data. We perform the same procedure for the Fermi inner radiative correction through the running of the Gross-Llewellyn sum rule. We discuss higher-twist and target mass corrections and find a significant increase at low momentum from the latter. We find $\Delta_R^A = 0.02881(30)$ and $\Delta_R^V = 0.02474(31)$ for axial and vector inner radiative corrections, respectively, resulting in $\Delta_R^A - \Delta_R^V = 4.07(8) \times 10^{-3}$, which is significantly larger than commonly assumed. We discuss consequences for comparing experimental data to lattice calculations in Beyond Standard Model fits. Further, we show how some traditional $\beta$ decay calculations contain part of this effect but fail to account for cancellations in the full $\mathcal{O}(\alpha)$ result. Finally, we correct for a double-counting instance in the isospin $T=1/2$ mirror decay extraction of $|V_{ud}|$, the up-down matrix element of the Cabibo-Kobayashi-Maskawa matrix element, resolving a long-standing tension and leading to increased precision.}, number={11}, journal={PHYSICAL REVIEW D}, author={Hayen, Leendert}, year={2021}, month={Jun} }
 @article{a look into mirrors: a measurement of the $β$-asymmetry in $^{19}$ne decay and searches for new physics_2020, year={2020}, month={Sep} }
 @article{consistent description of angular correlations in $β$ decay for beyond standard model physics searches_2020, year={2020}, month={Sep} }
 @article{detailed $β$ spectrum calculations of $^{214}$pb for new physics searches in liquid xenon_2020, year={2020}, month={Sep} }
 @article{abel_afach_ayres_baker_ban_bison_bodek_bondar_burghoff_chanel_et al._2020, title={Measurement of the Permanent Electric Dipole Moment of the Neutron}, volume={124}, ISSN={["1079-7114"]}, DOI={10.1103/PhysRevLett.124.081803}, abstractNote={We present the result of an experiment to measure the electric dipole moment (EDM) of the neutron at the Paul Scherrer Institute using Ramsey's method of separated oscillating magnetic fields with ultracold neutrons. Our measurement stands in the long history of EDM experiments probing physics violating time-reversal invariance. The salient features of this experiment were the use of a ^{199}Hg comagnetometer and an array of optically pumped cesium vapor magnetometers to cancel and correct for magnetic-field changes. The statistical analysis was performed on blinded datasets by two separate groups, while the estimation of systematic effects profited from an unprecedented knowledge of the magnetic field. The measured value of the neutron EDM is d_{n}=(0.0±1.1_{stat}±0.2_{sys})×10^{-26}  e.cm.}, number={8}, journal={Physical Review Letters}, author={Abel, C. and Afach, S. and Ayres, N. J. and Baker, C. A. and Ban, G. and Bison, G. and Bodek, K. and Bondar, V. and Burghoff, M. and Chanel, E. and et al.}, year={2020}, month={Feb}, pages={081803} }
 @article{abel_afach_ayres_ban_bison_bodek_bondar_chanel_chiu_crawford_et al._2020, title={Optically pumped Cs magnetometers enabling a high-sensitivity search for the neutron electric dipole moment}, volume={101}, DOI={https://doi.org/10.1103/PhysRevA.101.053419}, abstractNote={An array of sixteen laser-pumped scalar Cs magnetometers was part of the neutron electric dipole moment (nEDM) experiment taking data at the Paul Scherrer Institute in 2015 and 2016. It was deployed to measure the gradients of the experiment's magnetic field and to monitor their temporal evolution. The originality of the array lies in its compact design, in which a single near-infrared diode laser drives all magnetometers that are located in a high-vacuum chamber, with a selection of the sensors mounted on a high-voltage electrode. We describe details of the Cs sensors' construction and modes of operation, emphasizing the accuracy and sensitivity of the magnetic field readout. We present two applications of the magnetometer array directly beneficial to the nEDM experiment: (i) the implementation of a strategy to correct for the drift of the vertical magnetic field gradient and (ii) a procedure to homogenize the magnetic field. The first reduces the uncertainty of the new nEDM result. The second enables transverse neutron spin relaxation times exceeding 1500 s, improving the statistical sensitivity of the nEDM experiment by about 35% and effectively increasing the rate of nEDM data taking by a factor of 1.8.}, number={5}, journal={Physical Review A}, author={Abel, C. and Afach, S. and Ayres, N. J. and Ban, G. and Bison, G. and Bodek, K. and Bondar, V. and Chanel, E. and Chiu, P-J and Crawford, C. B. and et al.}, year={2020}, month={May}, pages={053419} }
 @article{standard model $\mathcal{o}(α)$ renormalization of $g_a$ and its impact on new physics searches_2020, year={2020}, month={Oct} }
 @article{hayen_severijns_2019, title={Beta Spectrum Generator: High precision allowed β spectrum shapes}, volume={240}, ISSN={0010-4655}, url={http://dx.doi.org/10.1016/j.cpc.2019.02.012}, DOI={10.1016/j.cpc.2019.02.012}, abstractNote={Several searches for Beyond Standard Model physics rely on an accurate and highly precise theoretical description of the allowed β spectrum. Following recent theoretical advances, a C++ implementation of an analytical description of the allowed beta spectrum shape was constructed. It implements all known corrections required to give a theoretical description accurate to a few parts in 104. The remaining nuclear structure-sensitive input can optionally be calculated in an extreme single-particle approximation with a variety of nuclear potentials, or obtained through an interface with more state-of-the-art computations. Due to its relevance in modern neutrino physics, the corresponding (anti)neutrino spectra are readily available with appropriate radiative corrections. In the interest of user-friendliness, a graphical interface was developed in Python with a coupling to a variety of nuclear databases. We present several test cases and illustrate potential usage of the code. Our work can be used as the foundation for current and future high-precision experiments related to the beta decay process. Source code: https://github.com/leenderthayen/BSG Documentation: http://bsg.readthedocs.io Program Title: BSG Program Files doi: http://dx.doi.org/10.17632/gx6yrpn22x.1 Licensing provisions: MIT Programming language: C++ and Python Nature of problem: The theoretical allowed β spectrum contains a large variety of corrections from different areas of physics, each of which is important in certain energy ranges. A high precision description is required for new physics searches throughout the entire nuclear chart. Solution method: We implement the analytical corrections described in recent theoretical work. Nuclear matrix elements in allowed Gamow–Teller β decay are calculated in a spherical harmonic oscillator basis. Wave functions can be calculated in an extreme single-particle approximation using different nuclear potentials, or provided by the user as the output from more sophisticated routines. Corresponding neutrino spectra are calculated with appropriate radiative corrections. A graphical user interface written in Python additionally provides connections to a variety of nuclear databases. Additional comments: CPC Library subprograms used: ABOV_v1_0}, journal={Computer Physics Communications}, publisher={Elsevier BV}, author={Hayen, L. and Severijns, N.}, year={2019}, month={Jul}, pages={152–164} }
 @article{hayen_kostensalo_severijns_suhonen_2019, title={First-forbidden transitions in reactor antineutrino spectra}, volume={99}, url={http://dx.doi.org/10.1103/physrevc.99.031301}, DOI={10.1103/physrevc.99.031301}, abstractNote={We study the dominant forbidden transitions in the antineutrino spectra of the fission actinides from 4 MeV onward using the nuclear shell model. Through explicit calculation of the shape factor, we show the expected changes in cumulative electron and antineutrino spectra. Relative to the allowed approximation this results in a minor decrease of electron spectra above 4 MeV, whereas an increase of several percent is observed in antineutrino spectra. We show that forbidden transitions dominate the spectral flux for most of the experimentally accessible range. Based on the shell model calculations we attempt a parametrization of forbidden transitions and propose a spectral correction for all first-forbidden transitions. We enforce correspondence with the Institut Laue-Langevin data set using a summation + conversion approach. When compared against modern reactor neutrino experiments, the resultant spectral change is observed to be of comparable magnitude and shape as the reported spectral shoulder.}, number={3}, journal={Physical Review C}, publisher={American Physical Society (APS)}, author={Hayen, L. and Kostensalo, J. and Severijns, N. and Suhonen, J.}, year={2019}, month={Mar} }
 @article{hayen_kostensalo_severijns_suhonen_2019, title={First-forbidden transitions in the reactor anomaly}, volume={100}, ISSN={["2469-9993"]}, url={https://doi.org/10.1103/PhysRevC.100.054323}, DOI={10.1103/PhysRevC.100.054323}, abstractNote={We describe here microscopic calculations performed on the dominant forbidden transitions in reactor antineutrino spectra above 4 MeV using the nuclear shell model. By taking into account Coulomb corrections in the most complete way, we calculate the shape factor with the highest fidelity and show strong deviations from allowed approximations and previously published results. Despite small differences in the ab initio electron cumulative spectra, large differences on the order of several percent are found in the antineutrino spectra. Based on the behavior of the numerically calculated shape factors we propose a parametrization of forbidden spectra. Using Monte Carlo techniques we derive an estimated spectral correction and uncertainty due to forbidden transitions. We establish the dominance and importance of forbidden transitions in both the reactor anomaly and spectral shoulder analysis with their respective uncertainties. Based on these results, we conclude that a correct treatment of forbidden transitions is indispensable in both the normalization anomaly and spectral shoulder.}, number={5}, journal={PHYSICAL REVIEW C}, author={Hayen, L. and Kostensalo, J. and Severijns, N. and Suhonen, J.}, year={2019}, month={Nov} }
 @article{pfeiffer_keukeleere_azevedo_belloni_biagi_grichine_hayen_hanu_hřivnáčová_ivanchenko_et al._2019, title={Interfacing Geant4, Garfield++ and Degrad for the simulation of gaseous detectors}, volume={935}, url={http://dx.doi.org/10.1016/j.nima.2019.04.110}, DOI={10.1016/j.nima.2019.04.110}, abstractNote={For several years, attempts have been made to interface Geant4 and other software packages with the aim of simulating the complete response of a gaseous particle detector. In such a simulation, Geant4 is always responsible for the primary particle generation and the interactions that occur in the non-gaseous detector material. Garfield++ on the other hand always deals with the drift of ions and electrons, amplification via electron avalanches and finally signal generation. For the ionizing interaction of particles with the gas, different options and physics models exist. The present paper focuses on how to use Geant4, Garfield++ (including its Heed and SRIM interfaces) and Degrad to create the ionization electron-ion pairs in the gas. Software-wise, the proposed idea is to use the Geant4 physics parameterization feature, and to implement a Garfield++ or Degrad based detector simulation as an external model. With a Degrad model, detailed simulations of the X-ray interaction in gaseous detectors, including shell absorption by photoelectric effect, subsequent Auger cascade, shake-off and fluorescence emission, become possible. A simple Garfield++ model can be used for photons (Heed), heavy ions (SRIM) and relativistic charged particles or MIPs (Heed). For non-relativistic charged particles, more effort is required, and a combined Geant4/Garfield++ model must be used. This model, the Geant4/Heed PAI model interface, uses the Geant4 PAI model in conjunction with the Heed PAI model. Parameters, such as the lower production cut of the Geant4 PAI model and the lowest electron energy limit have to be set correctly. The paper demonstrates how to determine these parameters for certain values of the W parameter and Fano factor of the gas mixture. The simulation results of this Geant4/Heed PAI model interface are then verified against the results obtained with the stand-alone software packages.}, journal={Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment}, publisher={Elsevier BV}, author={Pfeiffer, Dorothea and Keukeleere, Lennert De and Azevedo, Carlos and Belloni, Francesca and Biagi, Stephen and Grichine, Vladimir and Hayen, Leendert and Hanu, Andrei R. and Hřivnáčová, Ivana and Ivanchenko, Vladimir and et al.}, year={2019}, month={Aug}, pages={121–134} }
 @article{karthein_atanasov_blaum_breitenfeldt_bondar_george_hayen_lunney_manea_mougeot_et al._2019, title={QEC-value determination for 21Na→21Ne and 23Mg→23Na mirror-nuclei decays using high-precision mass spectrometry with ISOLTRAP at the CERN ISOLDE facility}, volume={100}, url={http://dx.doi.org/10.1103/physrevc.100.015502}, DOI={10.1103/physrevc.100.015502}, abstractNote={J. Karthein , 2, ∗ D. Atanasov, † K. Blaum, M. Breitenfeldt, V. Bondar, S. George, L. Hayen, D. Lunney, V. Manea, † M. Mougeot, ‡ D. Neidherr, L. Schweikhard, N. Severijns, A. Welker, 7 F. Wienholtz, 6 R.N. Wolf, § and K. Zuber CERN, Route de Meyrin, 1211 Genève, Switzerland Max-Planck-Institut für Kernphysik, 69117 Heidelberg, Germany KU Leuven, Instituut voor Kernen Stralingsfysica, 3001 Leuven, Belgium CSNSM-IN2P3-CNRS, Université Paris-Sud, 91405 Orsay, France GSI Helmholtzzentrum für Schwerionenforschung, 64291 Darmstadt, Germany Universität Greifswald, Institut für Physik, 17487 Greifswald, Germany Technische Universität Dresden, 01069 Dresden, Germany (Dated: June 25, 2019)}, number={1}, journal={Physical Review C}, publisher={American Physical Society (APS)}, author={Karthein, J. and Atanasov, D. and Blaum, K. and Breitenfeldt, M. and Bondar, V. and George, S. and Hayen, L. and Lunney, D. and Manea, V. and Mougeot, M. and et al.}, year={2019}, pages={015502} }
 @article{broussard_baeßler_bailey_birge_bowman_crawford_cude-woods_fellers_fomin_frlež_et al._2019, title={Using Nab to determine correlations in unpolarized neutron decay}, volume={240}, ISSN={0304-3843 1572-9540}, url={http://dx.doi.org/10.1007/s10751-018-1538-7}, DOI={10.1007/s10751-018-1538-7}, abstractNote={The Nab experiment will measure the ratio of the weak axial-vector and vector coupling constants λ = gA/gV with precision δλ/λ ∼ 3 × 10− 4 and search for a Fierz term bF at a level ΔbF < 10− 3. The Nab detection system uses thick, large area, segmented silicon detectors to very precisely determine the decay proton’s time of flight and the decay electron’s energy in coincidence and reconstruct the correlation between the antineutrino and electron momenta. Excellent understanding of systematic effects affecting timing and energy reconstruction using this detection system are required. To explore these effects, a series of ex situ studies have been undertaken, including a search for a Fierz term at a less sensitive level of ΔbF < 10− 2 in the beta decay of 45Ca using the UCNA spectrometer.}, number={1}, journal={Hyperfine Interactions}, publisher={Springer Science and Business Media LLC}, author={Broussard, L. J. and Baeßler, S. and Bailey, T. L. and Birge, N. and Bowman, J. D. and Crawford, C. B. and Cude-Woods, C. and Fellers, D. E. and Fomin, N. and Frlež, E. and et al.}, year={2019}, month={Dec} }
 @article{hayen_severijns_bodek_rozpedzik_mougeot_2018, title={High precision analytical description of the allowed 
β
 spectrum shape}, volume={90}, url={http://dx.doi.org/10.1103/revmodphys.90.015008}, DOI={10.1103/revmodphys.90.015008}, abstractNote={A fully analytical description of the allowed β spectrum shape is given in view of ongoing and planned measurements. Its study forms an invaluable tool in the search for physics beyond the standard electroweak model and the weak magnetism recoil term. Contributions stemming from finite size corrections, mass effects, and radiative corrections are reviewed. Particular focus is placed on atomic and chemical effects, where the existing description is extended and analytically provided. The effects of QCD-induced recoil terms are discussed, and cross-checks were performed for different theoretical formalisms. Special attention was given to a comparison of the treatment of nuclear structure effects in different formalisms. Corrections were derived for both Fermi and Gamow-Teller transitions, and methods of analytical evaluation thoroughly discussed. In its integrated form, calculated f values were in agreement with the most precise numerical results within the aimed for precision. The need for an accurate evaluation of weak magnetism contributions was stressed, and the possible significance of the oft-neglected induced pseudoscalar interaction was noted. Together with improved atomic corrections, an analytical description was presented of the allowed β spectrum shape accurate to a few parts in 10-4 down to 1 keV for low to medium Z nuclei, thereby extending the work by previous authors by nearly an order of magnitude.}, number={1}, journal={Reviews of Modern Physics}, publisher={American Physical Society (APS)}, author={Hayen, Leendert and Severijns, Nathal and Bodek, Kazimierz and Rozpedzik, Dagmara and Mougeot, Xavier}, year={2018}, month={Mar} }
 @article{perkowski_bodek_de keukeleere_hayen_kozela_łojek_rozpędzik_severijns_2018, title={Initial Tests of MiniBETA Spectrometer Performance}, volume={49}, ISSN={0587-4254 1509-5770}, url={http://dx.doi.org/10.5506/aphyspolb.49.261}, DOI={10.5506/aphyspolb.49.261}, abstractNote={MiniBETA is a new spectrometer incorporating a low-pressure mul-tiwire drift chamber (MWDC). It is designed for beta spectrum shape measurements and to improve knowledge on electron backscattering in the about 100 keV to a few MeV region. After the commissioning phase, which we report on here, the spectrometer will first be used for the latter pur-pose. This will help reducing the systematic uncertainty in beta spectrum shape measurements. The performance of the trajectory recognition algorithm was investigated using cosmic muons as the source of the primary ionization. For the initial test, the chamber was filled with a mixture of helium–isobutane (50/50) at 600 mbar. A single cell efficiency η higher than 0.98 within almost the entire cell was achieved and the single cell spatial resolution in the drift plane reached σ = 0 . 4 mm for most of the cells in the chamber.}, number={3}, journal={Acta Physica Polonica B}, publisher={Jagiellonian University}, author={Perkowski, M. and Bodek, K. and De Keukeleere, L. and Hayen, L. and Kozela, A. and Łojek, K. and Rozpędzik, D. and Severijns, N.}, year={2018}, pages={261} }
 @inproceedings{rozpedzik_bodek_lojek_perkowski_de keukeleere_hayen_severijns_kozela_2018, title={Multi-Wire 3D Gas Tracker for Searching New Physics in Nuclear Beta Decay}, url={https://arxiv.org/abs/1810.02785}, author={Rozpedzik, D. and Bodek, K. and Lojek, K. and Perkowski, M. and De Keukeleere, L. and Hayen, L. and Severijns, N. and Kozela, A.}, year={2018} }
 @article{afach_ban_bison_bodek_chowdhuri_daum_fertl_franke_geltenbort_grujić_et al._2015, title={A device for simultaneous spin analysis of ultracold neutrons}, volume={51}, ISSN={1434-6001 1434-601X}, url={http://dx.doi.org/10.1140/epja/i2015-15143-7}, DOI={10.1140/epja/i2015-15143-7}, abstractNote={We report on the design and first tests of a device allowing for measurement of ultracold neutrons polarisation by means of the simultaneous analysis of the two spin components. The device was developed in the framework of the neutron electric dipole moment experiment at the Paul Scherrer Institute. Individual parts and the entire newly built system have been characterised with ultracold neutrons. The gain in statistical sensitivity obtained with the simultaneous spin analyser is $(18.2\pm 6.1)$ % relative to the former sequential analyser under nominal running conditions.}, number={11}, journal={The European Physical Journal A}, publisher={Springer Science and Business Media LLC}, author={Afach, S. and Ban, G. and Bison, G. and Bodek, K. and Chowdhuri, Z. and Daum, M. and Fertl, M. and Franke, B. and Geltenbort, P. and Grujić, Z. D. and et al.}, year={2015}, month={Nov} }
 @article{highly stable atomic vector magnetometer based on free spin precession_2015, volume={23}, url={http://dx.doi.org/10.1364/oe.23.022108}, DOI={10.1364/oe.23.022108}, abstractNote={We present a magnetometer based on optically pumped Cs atoms that measures the magnitude and direction of a 1 μT magnetic field. Multiple circularly polarized laser beams were used to probe the free spin precession of the Cs atoms. The design was optimized for long-time stability and achieves a scalar resolution better than 300 fT for integration times ranging from 80 ms to 1000 s. The best scalar resolution of less than 80 fT was reached with integration times of 1.6 to 6 s. We were able to measure the magnetic field direction with a resolution better than 10 μrad for integration times from 10 s up to 2000 s.}, number={17}, journal={Optics Express}, publisher={The Optical Society}, year={2015}, month={Aug}, pages={22108} }
 @article{afach_ban_bison_bodek_chowdhuri_grujić_hayen_hélaine_kasprzak_kirch_et al._2015, title={Highly stable atomic vector magnetometer based on free spin precession"}, volume={23}, DOI={https://doi.org/10.1364/OE.23.022108}, abstractNote={We present a magnetometer based on optically pumped Cs atoms that measures the magnitude and direction of a 1 μT magnetic field. Multiple circularly polarized laser beams were used to probe the free spin precession of the Cs atoms. The design was optimized for long-time stability and achieves a scalar resolution better than 300 fT for integration times ranging from 80 ms to 1000 s. The best scalar resolution of less than 80 fT was reached with integration times of 1.6 to 6 s. We were able to measure the magnetic field direction with a resolution better than 10 μrad for integration times from 10 s up to 2000 s.}, number={17}, journal={Optics Express}, author={Afach, S. and Ban, G. and Bison, G. and Bodek, K. and Chowdhuri, Z. and Grujić, Z.D. and Hayen, L. and Hélaine, V. and Kasprzak, M. and Kirch, K. and et al.}, year={2015}, pages={22108–22115} }
 @article{glover_lenaers_velten_finlay_couratin_hayen_severijns_bastin_2015, title={Towards precisionβ-decay measurements with laser cooled 35Ar}, volume={635}, ISSN={1742-6588 1742-6596}, url={http://dx.doi.org/10.1088/1742-6596/635/4/042008}, DOI={10.1088/1742-6596/635/4/042008}, abstractNote={We present modeling and preliminary experimental results towards the development of our magnetooptical trap (MOT) setup and polarisation scheme for 35Ar. The atomic beam that is used for loading the MOT includes a novel transverse cooling arrangement based on a frequency broadened ’white-light molasses’. Our modeling shows that, under certain experimental conditions, such a setup can be beneficial in comparison to conventional transverse cooling techniques. We will report on experimental realization of such a setup.}, number={4}, journal={Journal of Physics: Conference Series}, publisher={IOP Publishing}, author={Glover, R D and Lenaers, F and Velten, Ph and Finlay, P and Couratin, C and Hayen, L and Severijns, N and Bastin, T}, year={2015}, month={Sep}, pages={042008} }