A new method for measuring the neutron lifetime using an <i>in situ</i> neutron detector

Morris, C. L.; Adamek, E.; Broussard, L. J.; Callahan, Nathan; Clayton, S. M.; Cude-Woods, C.; Currie, Scott; Ding, X.; Fox, W.; Hickerson, K. P.; Hoffbauer, Mark A.; Holley, A. T.; Komives, A.; Liu, Chen-Yu; Makela, M.; Pattie, R. W.; Ramsey, J.; Salvat, Daniel; Saunders, Alexander; Seestrom, S.J.; Sharapov, E.I.; Sjue, Sky; Tang, Z.; Vanderwerp, J.; Vogelaar, R. B.; Walstrom, P. L.; Wang, ‪Zhehui; Wei, Wanchun; Wexler, J.; Womack, Tanner L.; Young, A. R.; Zeck, B. A.

doi:10.1063/1.4983578

Cited by 24 publications

(27 citation statements)

References 23 publications

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“…The non-blinded data set presented in Ref [15] was combined with a blinded systematics study data set, which had a statistical accuracy of  n = 1 s, to develop techniques to correct for incomplete cleaning of quasi-bound neutrons and to identify improvements to the trap cleaning procedure. These improvements were implemented prior to acquiring the data discussed in this paper.…”

Section: Resultsmentioning

confidence: 99%

“…During the filling and cleaning periods, the cleaner was positioned 38 cm above the bottom of the trap, or 12 cm below the nominal open top of the trap. The cleaner covered approximately one half of the horizontal surface of the trap at its mounted height (~0.86 m 2 , to be compared with the 0.23 m 2 horizontal cleaner used in the work of Ref [15]), so that every neutron capable of reaching it did so quickly within a few tens of seconds after entering the trap. A second "active" cleaner, with a 28% of the area, was mounted on the downstream side of the trap in the same plane as the primary cleaner.…”

Section: Experimental Techniquementioning

confidence: 99%

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Measurement of the neutron lifetime using a magneto-gravitational trap and in situ detection

Pattie

Callahan

Cude-Woods

et al. 2018

Science

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The precise value of the mean neutron lifetime, τ, plays an important role in nuclear and particle physics and cosmology. It is used to predict the ratio of protons to helium atoms in the primordial universe and to search for physics beyond the Standard Model of particle physics. We eliminated loss mechanisms present in previous trap experiments by levitating polarized ultracold neutrons above the surface of an asymmetric storage trap using a repulsive magnetic field gradient so that the stored neutrons do not interact with material trap walls. As a result of this approach and the use of an in situ neutron detector, the lifetime reported here [877.7 ± 0.7 (stat) +0.4/-0.2 (sys) seconds] does not require corrections larger than the quoted uncertainties.

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Section: Resultsmentioning

confidence: 99%

Section: Experimental Techniquementioning

confidence: 99%

Measurement of the neutron lifetime using a magneto-gravitational trap and in situ detection

Pattie

Callahan

Cude-Woods

et al. 2018

Science

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167

202

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“…Red circles: material bottle measurements [11,12,13,14,15,16]. Green squares: magneto-gravitational trap measurements [17,18]. Black solid squares: results not used in the global averages, or superseded by subsequent publications.…”

Section: Current Status Of V Ud From Neutron β Decaymentioning

confidence: 99%

Evaluating $V_{ud}$ from neutron beta decays

Počanić¹

2017

Proceedings of 9th International Workshop on the CKM Unitarity Triangle — PoS(CKM2016)

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Although well studied, the neutron still offers a unique laboratory for precise tests of Standard Model (SM) predictions. Neutron decay is free of nuclear structure corrections present in nuclear beta decays, and, with a 10 8 times larger branching ratio than the theoretically cleaner pion beta decay, it is more readily accessible to experimental study than the latter. Measurements at sufficient precision of the neutron lifetime, and of correlations in free neutron beta decay, offer several stringent tests of the SM, including the weak quark couplings (quark-lepton universality), and certain extensions beyond the standard V − A weak interaction theory. This paper focuses on the long-running free neutron beta decay experimental program aimed at obtaining an independent determination of the Cabibbo-Kobayashi-Maskawa (CKM) mixing matrix element V ud . We discuss the present state of precision achieved in this program and briefly review the currently active projects, as well as the expected near-term improvements in the field.9th International Workshop on the CKM Unitarity Triangle

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“…The bottle is filled with UCNs from the Los Alamos UCN facility [13] parasitically during the running of the UCN τ experiment [7], with the source operated in production mode. The γ rays are detected in a lead shielded, Compton-scatteringsuppressed 140% high-purity germanium (HPGe) detector (Fig.…”

mentioning

confidence: 99%

“…There is nearly a five-standard-deviation disagreement [1,2] between measurements of the rate of neutron decay producing protons measured in cold neutron beam experiments [3][4][5] (888.0 AE 2.0 s) and free neutron lifetime in bottle experiments [6][7][8] (878.1 AE 0.5 s). The cold neutron beam method consists of counting the number of protons emitted from neutron β decay in a well-characterized neutron beam, and the bottle experiments measure the number of ultracold neutrons (UCNs) that remain inside a trap after a certain storage time.…”

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confidence: 99%

Search for the Neutron Decay n→X+γ , Where X is a Dark Matter Particle

et al. 2018

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Fornal and Grinstein recently proposed that the discrepancy between two different methods of neutron lifetime measurements, the beam and bottle methods, can be explained by a previously unobserved dark matter decay mode, n → X þ γ. We perform a search for this decay mode over the allowed range of energies of the monoenergetic γ ray for X to be dark matter. A Compton-suppressed high-purity germanium detector is used to identify γ rays from neutron decay in a nickel-phosphorous-coated stainless-steel bottle. A combination of Monte Carlo and radioactive source calibrations is used to determine the absolute efficiency for detecting γ rays arising from the dark matter decay mode. We exclude the possibility of a sufficiently strong branch to explain the lifetime discrepancy with 97% confidence. DOI: 10.1103/PhysRevLett.121.022505 There is nearly a five-standard-deviation disagreement [1,2] between measurements of the rate of neutron decay producing protons measured in cold neutron beam experiments [3-5] (888.0 AE 2.0 s) and free neutron lifetime in bottle experiments [6-8] (878.1 AE 0.5 s). The cold neutron beam method consists of counting the number of protons emitted from neutron β decay in a well-characterized neutron beam, and the bottle experiments measure the number of ultracold neutrons (UCNs) that remain inside a trap after a certain storage time. A longer lifetime from the beam measurements could point to the existence of possible other decay modes of the neutron where a proton is not produced. Serebrov has suggested that the discrepancy could be due to neutrons oscillating into mirror neutrons [9,10]. Recently, Fornal and Grinstein suggested in Ref.[11] that the neutron lifetime discrepancy can be explained if the neutron were to decay into a γ ray and a dark matter particle, X. The γ ray has an allowable energy range of 782 to 1664 keV, where it is bounded from above by the stability of 9 Be and bounded from below by requiring X to be stable.Here, we report the results of a search for γ rays arising from UCNs decaying inside a nickel-phosphorouscoated [12], 560 l stainless-steel bottle. The bottle is filled with UCNs from the Los Alamos UCN facility [13] parasitically during the running of the UCN τ experiment [7], with the source operated in production mode. The γ rays are detected in a lead shielded, Compton-scatteringsuppressed 140% high-purity germanium (HPGe) detector (Fig. 1). The Compton-scattering suppression is achieved by an anticoincidence with an annular bismuth germinate (BGO) detector surrounding the HPGe detector. The Compton suppression reduced the background in the low energy part of the spectrum by a factor of 1.7. A gate valve placed upstream controlled the loading of UCNs into the bottle. The background γ rates were measured with the UCNs in production mode and the gate valve closed. This resulted in a factor of 4 reduction in the continuum background in the region of interest (ROI).The energy calibration of the HPGe spectrum was obtained from a linear fit to 13γ-ray lines from source...

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A new method for measuring the neutron lifetime using an in situ neutron detector

Cited by 24 publications

References 23 publications

Measurement of the neutron lifetime using a magneto-gravitational trap and in situ detection

Measurement of the neutron lifetime using a magneto-gravitational trap and in situ detection

Evaluating $V_{ud}$ from neutron beta decays

Search for the Neutron Decay n→X+γ , Where X is a Dark Matter Particle

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