Author
Dan Melconian
Other affiliations: University of Washington, Simon Fraser University
Bio: Dan Melconian is an academic researcher from Texas A&M University. The author has contributed to research in topics: Neutron & Ultracold neutrons. The author has an hindex of 16, co-authored 42 publications receiving 806 citations. Previous affiliations of Dan Melconian include University of Washington & Simon Fraser University.
Topics: Neutron, Ultracold neutrons, Physics, Penning trap, Nucleon
Papers
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TL;DR: The 2011 Workshop on Fundamental Physics at the Intensity Frontier as discussed by the authors identified and described opportunities at the intensity frontier in the areas of heavy quarks, charged leptons, neutrinos, proton decay, new light weakly-coupled particles, and nucleons, nuclei, and atoms.
Abstract: The Proceedings of the 2011 workshop on Fundamental Physics at the Intensity Frontier. Science opportunities at the intensity frontier are identified and described in the areas of heavy quarks, charged leptons, neutrinos, proton decay, new light weakly-coupled particles, and nucleons, nuclei, and atoms.
157 citations
TL;DR: In this article, the authors reported the most precise result for A_0 obtained to date from the UCNA experiment, as a result of higher statistics and reduced key systematic uncertainties, including from the neutron polarization and the characterization of the electron detector response.
Abstract: Background: The neutron β-decay asymmetry parameter A_0 defines the angular correlation between the spin of the neutron and the momentum of the emitted electron. Values for A_0 permit an extraction of the ratio of the weak axial-vector to vector coupling constants, λ≡gA/gV, which under assumption of the conserved vector current hypothesis (gV=1) determines gA. Precise values for gA are important as a benchmark for lattice QCD calculations and as a test of the standard model.
Purpose: The UCNA experiment, carried out at the Ultracold Neutron (UCN) source at the Los Alamos Neutron Science Center, was the first measurement of any neutron β-decay angular correlation performed with UCN. This article reports the most precise result for A_0 obtained to date from the UCNA experiment, as a result of higher statistics and reduced key systematic uncertainties, including from the neutron polarization and the characterization of the electron detector response.
Methods: UCN produced via the downscattering of moderated spallation neutrons in a solid deuterium crystal were polarized via transport through a 7 T polarizing magnet and a spin flipper, which permitted selection of either spin state. The UCN were then contained within a 3-m long cylindrical decay volume, situated along the central axis of a superconducting 1 T solenoidal spectrometer. With the neutron spins then oriented parallel or anti-parallel to the solenoidal field, an asymmetry in the numbers of emitted decay electrons detected in two electron detector packages located on both ends of the spectrometer permitted an extraction of A_0.
Results: The UCNA experiment reports a new 0.67% precision result for A_0 of A_0=−0.12054(44)_(stat)(68)_(syst), which yields λ=gA/gV=−1.2783(22). Combination with the previous UCNA result and accounting for correlated systematic uncertainties produces A0=−0.12015(34)stat(63)syst and λ=gA/gV=−1.2772(20).
Conclusions: This new result for A0 and gA/gV from the UCNA experiment has provided confirmation of the shift in values for gA/gV that has emerged in the published results from more recent experiments, which are in striking disagreement with the results from older experiments. Individual systematic corrections to the asymmetries in older experiments (published prior to 2002) were >10%, whereas those in the more recent ones (published after 2002) have been of the scale of <2%. The impact of these older results on the global average will be minimized should future measurements of A0 reach the 0.1% level of precision with central values near the most recent results.
95 citations
California Institute of Technology1, North Carolina State University2, University of Washington3, Virginia Tech4, Duke University5, Los Alamos National Laboratory6, Indiana University7, Shanghai Jiao Tong University8, University of Winnipeg9, Texas A&M University10, University of Kentucky11, Idaho State University12, Joint Institute for Nuclear Research13
TL;DR: In this article, a new measurement of the neutron β-decay asymmetry A_0 was carried out by the UCNA Collaboration using polarized ultracold neutrons (UCNs) from the solid deuterium UCN source at the Los Alamos Neutron Science Center.
Abstract: A new measurement of the neutron β-decay asymmetry A_0 has been carried out by the UCNA Collaboration using polarized ultracold neutrons (UCNs) from the solid deuterium UCN source at the Los Alamos Neutron Science Center. Improvements in the experiment have led to reductions in both statistical and systematic uncertainties leading to A_0=−0.11954(55)_(stat)(98)_(syst), corresponding to the ratio of axial-vector to vector coupling λ ≡ g_A/g_V = −1.2756(30).
75 citations
TL;DR: The performance of the Los Alamos spallation-driven solid-deuterium ultra-cold neutron (UCN) source is described and measurements of the cold neutron flux, the very low energy neutron production rate, and the UCN rates and density are presented and compared to Monte Carlo predictions.
Abstract: In this paper, we describe the performance of the Los Alamos spallation-driven solid-deuterium ultra-cold neutron (UCN) source. Measurements of the cold neutron flux, the very low energy neutron production rate, and the UCN rates and density at the exit from the biological shield are presented and compared to Monte Carlo predictions. The cold neutron rates compare well with predictions from the Monte Carlo code MCNPX and the UCN rates agree with our custom UCN Monte Carlo code. The source is shown to perform as modeled. The maximum delivered UCN density at the exit from the biological shield is 52(9) UCN/cc with a solid deuterium volume of ∼1500 cm3.
61 citations
California Institute of Technology1, Idaho State University2, Los Alamos National Laboratory3, Duke University4, University of Washington5, North Carolina State University6, University of Kentucky7, Indiana University8, Shanghai Jiao Tong University9, Virginia Tech10, University of Winnipeg11, Texas A&M University12
TL;DR: In this article, the parity-violating angular correlation between the neutron spin and the decay electron momentum was measured with polarized ultracold neutrons (UCN) in a 1-T 2×2π solenoidal spectrometer, where the neutrons were extracted from a pulsed spallation solid deuterium source and polarized via transport through a 7-T magnetic field.
Abstract: We present a detailed report of a measurement of the neutron β-asymmetry parameter A_0, the parity-violating angular correlation between the neutron spin and the decay electron momentum, performed with polarized ultracold neutrons (UCN). UCN were extracted from a pulsed spallation solid deuterium source and polarized via transport through a 7-T magnetic field. The polarized UCN were then transported through an adiabatic-fast-passage spin-flipper field region, prior to storage in a cylindrical decay volume situated within a 1-T 2×2π solenoidal spectrometer. The asymmetry was extracted from measurements of the decay electrons in multiwire proportional chamber and plastic scintillator detector packages located on both ends of the spectrometer. From an analysis of data acquired during runs in 2008 and 2009, we report A_0=−0.11966±0.00089_(−0.00140)^(+0.00123), from which we extract a value for the ratio of the weak axial-vector and vector coupling constants of the nucleon, λ=g_A/g_V=−1.27590±0.00239_(−0.00377)^(+0.00331). Complete details of the analysis are presented.
47 citations
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TL;DR: In this article, the authors present a review of the application of atomic physics to address important challenges in physics and to look for variations in the fundamental constants, search for interactions beyond the standard model of particle physics and test the principles of general relativity.
Abstract: Advances in atomic physics, such as cooling and trapping of atoms and molecules and developments in frequency metrology, have added orders of magnitude to the precision of atom-based clocks and sensors. Applications extend beyond atomic physics and this article reviews using these new techniques to address important challenges in physics and to look for variations in the fundamental constants, search for interactions beyond the standard model of particle physics, and test the principles of general relativity.
1,077 citations
Abstract: We review how nuclear forces emerge from low-energy QCD via chiral effective field theory. The presentation is accessible to the non-specialist. At the same time, we also provide considerable detailed information (mostly in appendices) for the benefit of researchers who wish to start working in this field.
883 citations
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Kyoto University1, KEK2, Brookhaven National Laboratory3, Université Paris-Saclay4, University of Connecticut5, University of Bern6, University of Regensburg7, University of Southern Denmark8, University of Rome Tor Vergata9, University of Wuppertal10, Forschungszentrum Jülich11, Osaka University12, San Francisco State University13, Indiana University14, Los Alamos National Laboratory15, Graduate University for Advanced Studies16, American Physical Society17, Autonomous University of Madrid18, University of Edinburgh19, University of Southampton20, National Chiao Tung University21, Chung Yuan Christian University22, Columbia University23, University of North Carolina at Chapel Hill24, Trinity College, Dublin25, University of Washington26, Fermilab27, Humboldt University of Berlin28, University of Mainz29
TL;DR: In this article, a review of lattice results related to pion, kaon, D-meson, neutral kaon mixing, B-meon, and nucleon physics with the aim of making them easily accessible to the nuclear and particle physics communities is presented.
Abstract: We review lattice results related to pion, kaon, D-meson, B-meson, and nucleon physics with the aim of making them easily accessible to the nuclear and particle physics communities. More specifically, we report on the determination of the light-quark masses, the form factor $f_+(0)$ arising in the semileptonic $K \rightarrow \pi $ transition at zero momentum transfer, as well as the decay constant ratio $f_K/f_\pi $ and its consequences for the CKM matrix elements $V_{us}$ and $V_{ud}$. Furthermore, we describe the results obtained on the lattice for some of the low-energy constants of $SU(2)_L\times SU(2)_R$ and $SU(3)_L\times SU(3)_R$ Chiral Perturbation Theory. We review the determination of the $B_K$ parameter of neutral kaon mixing as well as the additional four B parameters that arise in theories of physics beyond the Standard Model. For the heavy-quark sector, we provide results for $m_c$ and $m_b$ as well as those for D- and B-meson decay constants, form factors, and mixing parameters. These are the heavy-quark quantities most relevant for the determination of CKM matrix elements and the global CKM unitarity-triangle fit. We review the status of lattice determinations of the strong coupling constant $\alpha _s$. Finally, in this review we have added a new section reviewing results for nucleon matrix elements of the axial, scalar and tensor bilinears, both isovector and flavor diagonal.
607 citations
TL;DR: In this paper, an up-to-date review of Big Bang Nucleosynthesis (BBN) is presented, and the main improvements which have been achieved in the past two decades on the overall theoretical framework, summarize the impact of new experimental results on nuclear reaction rates, and critically re-examine the astrophysical determinations of light nuclei abundances.
514 citations
TL;DR: In this paper, a review of the experimental developments on halo nuclei and other related drip line nuclei is presented, and the new view of the nuclear structure learned from such studies is discussed.
396 citations