Determination of the neutron lifetime using magnetically trapped neutrons

Dzhosyuk, S. N.; Copete, A.; Doyle, John M.; Yang, L.; Coakley, Kevin J.; Golub, R.; Korobkina, E.; Kreft, Tomasz; Lamoreaux, S. K.; Thompson, A. K.; Yang, Grace L.; Huffman, P. R.

doi:10.6028/jres.110.050

Cited by 14 publications

(12 citation statements)

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“…As a matter of fact, other "bottle" measurements with less precise magnetic traps have already indicated such discrepancies due to different trap sizes or mean free flight times [39,40,41]. For example, a neutron storage lifetime of 874.6 ± 1.7 s was reported with a magnetic trap operated at the UCN facility of the Institut LaueLangevin (ILL), France [41].…”

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confidence: 99%

Neutron oscillations for solving neutron lifetime and dark matter puzzles

Tan

2019

Physics Letters B

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A model of n − n (neutron-mirror neutron) oscillations is proposed under the framework of the mirror matter theory with slightly broken mirror symmetry. It resolves the neutron lifetime discrepancy, i.e., the 1% difference in neutron lifetime between measurements from "beam" and "bottle" experiments. In consideration of the early universe evolution, the n − n mass difference is determined to be about 2 × 10 −6 eV/c 2 with the n − n mixing strength of about 2 × 10 −5 . The picture of how the mirror-to-ordinary matter density ratio is evolved in the early universe into the observed dark-to-baryon matter density ratio of about 5.4 is presented. Reanalysis of previous data and new experiments that can be carried out under current technology are discussed and recommended to test this proposed model. Other consequences of the model on astrophysics and possible oscillations of other neutral particles are discussed as well.Free neutrons with a lifetime of about 15 minutes are known to undergo β decay via n → p + e − +ν e due to the weak force. There has been much experimental effort over the past decades for measuring the lifetime using two different techniques. The "beam" approach is to measure the neutron flux from a cold neutron beam after it going through a region where the emitted protons are detected [1,2]. It measures directly the β decay rate as far as other hidden neutron-disappearing processes are on the level of 10 −3 or below. This approach typically gives a neutron lifetime of about 888 seconds. On the other hand, the "bottle" experiments store ultracold neutrons (UCN) confined by the gravitational force in a material or magnetic trap [3,4,5]. By measuring the neutron loss rate in the trap this method typically presents a neutron lifetime of about 880 seconds. Note that any other unknown loss processes in the trap will contribute to the measured lifetime and make it appear shorter. Another different approach using a magnetic storage ring [6] provides similar results as the "bottle" method. The 1% difference between the results of the two approaches becomes more severe recently with the most precise measurements of 887.7 ± 1.2(stat) ± 1.9(sys) s ("beam") [2] and 877.7 ± 0.7(stat) + 0.4/ − 0.2(sys) s ("bottle") [3].

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confidence: 99%

Neutron oscillations for solving neutron lifetime and dark matter puzzles

Tan

2019

Physics Letters B

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“…The repulsive force resulting from the interaction between the neutron magnetic moment and a magnetic field gradient can be used for the confinement of neutrons provided their energies are sufficiently low [8]. This has been incorporated for the measurement of the neutron lifetime in various configurations, the most successful having been a sextupole storage ring [9], leading to n = (877±10) s, an Ioffe-Pritchard three dimensional trap leading to a storage time S = (833 −63 +74 ) s [10], and an asymmetric Halbach array trap, with a storage time S = (860±19) s [11].…”

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confidence: 99%

Measurement of the Neutron Lifetime with Ultracold Neutrons Stored in a Magneto-Gravitational Trap

et al. 2018

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We report a new measurement of the neutron lifetime using ultra-cold neutrons stored in a magneto-gravitational trap made of permanent magnets. Neutrons surviving in the trap after fixed storage times have been counted and the trap losses have continuously been monitored during storage by detecting neutrons leaking from the trap. The value of the neutron lifetime resulting from this measurement is n = (878.3±1.9) s. It is the most precise measurement of the neutron lifetime obtained with magnetically stored neutrons.PACS numbers: 23.40.Bw; 24.80.+y Precision measurements of the neutron lifetime provide stringent tests of the standard electroweak model [1] as well as crucial inputs for Big-Bang nucleosynthesis (BBN) calculations [2]. When combined with measurements of other neutron beta decay correlation coefficients [1], the neutron lifetime enables the determination of the Vud element of the Cabbibo-Kobayashi-Maskawa quark mixing matrix, providing a complementary unitarity test to that obtained from superallowed nuclear beta decay [3]. The neutron lifetime is also one of the key parameters for the determination of yields of light elements in BBN since the ratio between the free neutron and proton abundances drives the extent of fusion reactions during the first few minutes of the Universe [2].The present world average value of the neutron lifetime as quoted by the Particle Data Group (PDG), n = (880.3±1.1) s [4], is dominated by results obtained using ultra-cold neutrons (UCN) in material bottles. These results, and in particular the most precise of them [5], appear to be systematically lower than results obtained using a neutron beam and counting trapped protons following neutron decay [6]. A detailed discussion of the experimental methods and results can be found in Ref. [7].The large discrepancy between the results indicates that all systematic effects are not fully under control. The importance of the neutron lifetime in particle physics and cosmology calls for alternative measuring techniques, with high sensitivity but other potential sources of systematic effects. We report here a new measurement of the neutron lifetime using UCN stored in a magneto-gravitational trap made of permanent magnets.The repulsive force resulting from the interaction between the neutron magnetic moment and a magnetic field gradient can be used for the confinement of neutrons provided their energies are sufficiently low [8]. This has been incorporated for the measurement of the neutron lifetime in various configurations, the most successful having been a sextupole storage ring [9], leading to n = (877±10) s, an Ioffe-Pritchard three dimensional trap leading to a storage time S = (833 −63 +74 ) s [10], and an asymmetric Halbach array trap, with a storage time S = (860±19) s [11].The experimental setup used in the present measurement ( Fig. 1) was operated at one of the beam positions of the UCN source PF2 at the Institut Laue-Langevin (ILL) in Grenoble. It comprises five main parts: a lift to fill the trap; the magnetic tr...

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“…A key systematic effect is poor cleaning of above-threshold UCNs from the trap. For a horizontal configuration, a scheme of ramping up and down the bias field has been used for this, however this results in a significant loss (∼ 50%) of UCNs [31]. The use of a UCN reflecting paddle along the length of a trap to induce mode-mixing reflections has also been suggested [32].…”

Section: Advantages Of the Vertical Configurationmentioning

confidence: 99%

A Comparison of Two Magnetic Ultra-Cold Neutron Trapping Concepts Using a Halbach-Octupole Array

Leung¹,

Иванов²,

Martin³

et al. 2014

Next Generation Experiments to Measure the Neutron Lifetime

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Preprint of an article published in Next Generation Experiments toMeasure the Neutron Lifetime, pp. 145-154, This paper describes a new magnetic trap for ultra-cold neutrons (UCNs) made from a 1.2 m long Halbach-octupole array of permanent magnets with an inner bore radius of 47 mm combined with an assembly of superconducting end coils and bias field solenoid. The use of the trap in a vertical, magneto-gravitational and a horizontal setup are compared in terms of the effective volume and ability to control key systematic effects that need to be addressed in high precision neutron lifetime measurements.

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Determination of the neutron lifetime using magnetically trapped neutrons

Cited by 14 publications

References 2 publications

Neutron oscillations for solving neutron lifetime and dark matter puzzles

Neutron oscillations for solving neutron lifetime and dark matter puzzles

Measurement of the Neutron Lifetime with Ultracold Neutrons Stored in a Magneto-Gravitational Trap

A Comparison of Two Magnetic Ultra-Cold Neutron Trapping Concepts Using a Halbach-Octupole Array

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