A multiwire proportional chamber for precision studies of neutron decay angular correlations

Ito, T. M.; Carr, R.; Filippone, B. W.; Martin, J. W.; Plaster, B.; Rybka, G.; Yuan, J.

doi:10.1016/j.nima.2006.11.026

Cited by 19 publications

(24 citation statements)

References 10 publications

(5 reference statements)

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“…Second, as described in detail elsewhere [49,50], the electron detector system developed for the UCNA Experiment, consisting of a low-pressure multiwire proportional chamber (MWPC) backed by a plastic scintillator, provides position sensitivity, suppresses ambient gammaray backgrounds, and permits the reconstruction of lowenergy-deposition electron backscattering events. The UCNA Experiment is the first neutron β-asymmetry experiment to employ a MWPC, providing the experiment with two critical advantages.…”

Section: Decaymentioning

confidence: 99%

Measurement of the neutronβ-asymmetry parameterA0with ultracold neutrons

et al. 2012

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We present a detailed report of a measurement of the neutron β-asymmetry parameter A0, 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.

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Section: Decaymentioning

confidence: 99%

Measurement of the neutronβ-asymmetry parameterA0with ultracold neutrons

et al. 2012

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“…Between the decay trap and the detectors, the magnetic field expands out to 0.6 T, which reduces the electrons' transverse momenta and pitch angles, decreasing backscattering from the detectors. Each detector package consists of a 16 × 16 cm 2 low-pressure multiwire proportional chamber (MWPC) [13] backed by a 15 cm diameter plastic scintillator, whose scintillation light is detected by four photomultiplier tubes (PMTs). Each MWPC has 6 μm Mylar windows at the front and back that separate the chamber gas (100 torr neopentane) from the spectrometer vacuum and PMT housing ( 100 torr N 2 ).…”

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confidence: 99%

“…Electron positions at the MWPC are determined to <2 mm based on the distribution of charge on two perpendicular cathode grids in the MWPC [13]. A fiducial cut of r < 50 mm (projected to the 0.96 T decay trap region) is placed on the trigger side to reduce background and to eliminate electrons that could strike the decay trap walls.…”

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confidence: 99%

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Precision measurement of the neutronβ-decay asymmetry

Mendenhall¹,

Pattie²,

Bagdasarova³

et al. 2013

Phys. Rev. C

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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) Precision measurements of neutron β decay are an essential ingredient in understanding the electro-weak interaction in the light quark sector. In particular the axial-vector weak coupling constant, g A , is an important input to understanding the spin and flavor structure of the nucleon [1,2] and is being actively studied in detailed lattice QCD calculations [3,4]. It also plays an important role in a variety of astrophysical processes, including solar fusion cross sections important for energy and neutrino production in the Sun [5].The angular distribution of emitted electrons from decays of a polarized neutron ensemble can be expressed as [6]where A(E) specifies the decay asymmetry for electron energy E, v ≡ βc is the electron velocity, P is the mean neutron polarization, and θ is the angle between the neutron spin and the electron momentum. can be expressed aswhere λ ≡ g A /g V is the ratio of the vector to axial-vector weak coupling constants. Combining g A with independent measurements of the Fermi coupling constant G F , the Cabibbo-Kobayashi-Maskawa matrix element V ud , and the neutron lifetime τ n allows a precision test of the consistency of measured neutron β-decay observables [7]. The ultracold neutron asymmetry (UCNA) experiment is the first experiment to use ultracold neutrons (UCNs) in a precision measurement of neutron decay correlations. Following the publication of our earlier results [7][8][9], the UCNA Collaboration implemented a number of experimental improvements that led to reductions in both statistical and systematic uncertainties. These improvements, described below, include enhanced UCN storage, improved electron energy reconstruction, and continuous monitoring of the magnetic field in the spectrometer. This refined treatment of the systematic corrections and uncertainties begins to address issues of consistency in the world data set for A 0 .The UCNA experiment ran in 2010 using the "thin window geometry D" as described in [7,9], and collected a total of 20.6 × 10 6 β-decay events after all cuts were applied. We used the UCN source [10] Copyright by the American Physical Society. Mendenhall, M. P. ; Pattie, R. W., Jr. ; Bagdasarova, Y. ; et al., Mar 25, 2013. "Precision measurement of the neutron beta-decay asymmetry," PHYSICAL REVIEW C 87(3): 032501.

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“…Each detector is composed of a multiwire proportional chamber (MWPC) [32] and a 3.5-mm-thick plastic scintillator to measure the electron energies. Scintillation light from each detector is directed, via light guides, toward four photomultiplier tubes (PMTs).…”

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confidence: 99%

First direct constraints on Fierz interference in free-neutron β decay

Hickerson¹,

Sun²,

Bagdasarova³

et al. 2017

Phys. Rev. C

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Precision measurements of free-neutron β decay have been used to precisely constrain our understanding of the weak interaction. However, the neutron Fierz interference term b n , which is particularly sensitive to beyond-standard-model tensor currents at the TeV scale, has thus far eluded measurement. Here we report the first direct constraints on this term, finding b n = 0.067 ± 0.005 stat +0.090 −0.061 sys , consistent with the standard model. The uncertainty is dominated by absolute energy reconstruction and the linearity of the β spectrometer energy response. DOI: 10.1103/PhysRevC.96.042501 Precision measurements in nuclear β decay including lifetimes, angular/spin correlations, and energy spectra can be used to test predictions of the electroweak sector of the standard model [1][2][3][4][5][6][7]. Current efforts are underway to measure many of these quantities in nuclear β decay as well as in free-neutron decay. The Fierz interference term vanishes in the standard model but serves as a probe for new physics in scalar and tensor couplings [1,4] (here denoted b n ) is presented for the first time. This term is particularly sensitive to tensor couplings that previous extractions of the Fierz term in superallowed 0 + → 0 + β decay are not.The Fierz interference term appears in the full form of the differential neutron decay rate parametrized in terms of correlation coefficients of neutron spin, σ n = J n /| J n |, and momenta, p e , p ν , and total energies, E e ,E ν , of the final-state particles [8]where W(E e ) includes the total decay rate (e.g., 1/τ n ) and the phase space along with recoil-order, radiative, and Coulomb corrections. The correlation coefficients also include recoilorder corrections. The dimensionless parameter b n is the only spin-and momentum-direction-independent coefficient and thus survives summation over spin and integration over the final-state angular distributions leaving a distribution dependent only on the electron energy, E:

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A multiwire proportional chamber for precision studies of neutron decay angular correlations

Cited by 19 publications

References 10 publications

Measurement of the neutronβ-asymmetry parameterA0with ultracold neutrons

Measurement of the neutronβ-asymmetry parameterA0with ultracold neutrons

Precision measurement of the neutronβ-decay asymmetry

First direct constraints on Fierz interference in free-neutron β decay

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