Monte Carlo simulations of trapped ultracold neutrons in the 
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 experiment

Callahan, Nathan; Liu, Chen-Yu; González, Francisco M.; Adamek, E.; Bowman, J. D.; Broussard, L. J.; Clayton, Steven; Currie, Scott; Cude-Woods, C.; Dees, Eric; Ding, X.; Fox, W.; Geltenbort, P.; Hickerson, K. P.; Hoffbauer, Mark A.; Holley, Adam; Komives, A.; MacDonald, Stephen; Makela, M.; Morris, C. L.; Ortiz, Joseph D.; Pattie, R. W.; Ramsey, J.; Salvat, Daniel; Saunders, Alexander; Sharapov, E.I.; Sjue, Sky; Tang, Z.; Vanderwerp, J.; Vogelaar, B.; Walstrom, P. L.; Wang, Z.; Weaver, H.; Wei, Wanchun; Wexler, J.; Young, A. R.

doi:10.1103/physrevc.100.015501

Cited by 6 publications

(3 citation statements)

References 28 publications

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“…of UCN velocity-and-angle-averaged loss per bounce of ð2 AE 1Þ × 10 −4 for aluminum, leading to a 0.15 AE 0.07 s correction to this subset of data. The other analyses perform similar assessments, and independent checks using our Monte Carlo framework[42] are consistent with this estimate. Further, this is consistent with a comparison of paired τ n during this period to the rest of the paired τ n values.…”

supporting

confidence: 66%

Improved Neutron Lifetime Measurement with UCNτ

et al. 2021

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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 selfconsistently incorporating the β-decay lifetime. Both techniques achieve consistent results and find a value τ n ¼ 877.75 AE 0.28 stat þ 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.

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supporting

confidence: 66%

Improved Neutron Lifetime Measurement with UCNτ

et al. 2021

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“…This provided a variable counting time of a few seconds, depending on the thickness of the 10 B coating, and minimized errors introduced by the coupling between the phase space of the UCN and the time at which the UCN are counted. A detailed discussion of Phase space evolution in this trap is given by Callahan et al [30] Here we report a set of measurements made using the same experimental apparatus with the same UCN loading procedures, but with the neutrons counted at the end of storage by unloading through the trap door into an external detector. The time constant for counting UCN in a dagger with a 20 nm 10 B coating lowered to the bottom of the trap is 7.1(2) s. The time constant for unloading UCN in this experiment is 26.8(8) s. Although these experiments share many sources of systematic uncertainties, the coupling between phase space evolution and counting could be much larger in this experiment, because of the longer unloading time.…”

Section: Methodsmentioning

confidence: 99%

Fill and dump measurement of the neutron lifetime using an asymmetric magneto-gravitational trap

Cude-Woods¹,

González²,

Fries³

et al. 2022

Phys. Rev. C

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The past two decades have yielded several new measurements and reanalysis of older measurements of the neutron lifetime. These have led to a 4.4 standard deviation discrepancy between the most precise measurements of the neutron decay rate producing protons in cold neutron beams and the most precise lifetime measured in neutron storage experiments. Measurements using different techniques are important for investigating whether there are unidentified systematic effects in any of the measurements. In this paper we report a new measurement using the Los Alamos asymmetric magnetogravitational trap where the surviving neutrons are counted external to the trap using the fill and dump method. The new measurement gives a free neutron lifetime of stat syst 876.3(2.4) (0.8) n  . Although this measurement is not as precise, it is in statistical agreement with previous results using in situ counting in the same apparatus.

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“…[7,108] for reviews), also the difference between recent bottle measurements [8,109,110] currently leads to a non-negligible scale factor in the PDG average [3]. Fortunately, there are plans to probe τ n at a level down to hundreds of ms [111][112][113][114].…”

Section: Observablementioning

confidence: 99%

β Decays as Sensitive Probes of Lepton Flavor Universality

2020

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Nuclear β decays as well as the decay of the neutron are well-established low-energy probes of physics beyond the standard model (SM). In particular, with the axial-vector coupling of the nucleon g A determined from lattice QCD, the comparison between experiment and SM prediction is commonly used to derive constraints on right-handed currents. Further, in addition to the CKM element V us from kaon decays, V ud from β decays is a critical input for the test of CKM unitarity. Here, we point out that the available information on β decays can be reinterpreted as a stringent test of lepton flavor universality (LFU). In fact, we find that the ratio of V us from kaon decays over V us from β decays (assuming CKM unitarity) is extremely sensitive to LFU violation (LFUV) in W-μ-ν couplings thanks to a CKM enhancement by ðV ud =V us Þ 2 ∼ 20. From this perspective, recent hints for the violation of CKM unitarity can be viewed as further evidence for LFUV, fitting into the existing picture exhibited by semileptonic B decays and the anomalous magnetic moments of muon and electron. Finally, we comment on the future sensitivity that can be reached with this LFU violating observable and discuss complementary probes of LFU that may reach a similar level of precision, such as Γðπ → μνÞ=Γðπ → eνÞ at the PEN and PiENu experiments or even direct measurements of W → μν at an FCC-ee.

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Monte Carlo simulations of trapped ultracold neutrons in the UCNτ experiment

Cited by 6 publications

References 28 publications

Improved Neutron Lifetime Measurement with UCNτ

Improved Neutron Lifetime Measurement with UCNτ

Fill and dump measurement of the neutron lifetime using an asymmetric magneto-gravitational trap

β Decays as Sensitive Probes of Lepton Flavor Universality

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