Exotic decay channels are not the cause of the neutron lifetime anomaly

Dubbers, D.; Saul, Heiko; Märkisch, Bastian; Söldner, T.; Abele, H.

doi:10.1016/j.physletb.2019.02.013

Cited by 42 publications

(34 citation statements)

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“…[32], by using the PDG average for the axial-vector to vector coupling ratio λ ¼ −1.2723 þ AE0.0023, it turns out that both lifetime measurements are compatible with the SM within the error bar of λ. However the most recent experiments [37,38] have measured a slightly larger value for λ ¼ −1.27641ð45Þ stat ð33Þ sys which are definitely in agreement with trap experiments and rule out the beam experiments results.…”

Section: Introductionsupporting

confidence: 81%

“…While in the former case the IZE occurred, in the latter it cannot be obtained since neutrons are uncorrelated. We remark that, presently, the most viable solution to this discrepancy is that beam experiments are affected by some uncontrolled systematics [16]; indeed the value of the neutron lifetime as measured in trap experiments is fully compatible with the most recent measurements of the beta decay neutron asymmetry [37,38].…”

Section: Discussionmentioning

confidence: 67%

“…Another, more important, problem with this interpretation arises when comparing with the recent precise measurements on beta decay neutron asymmetry which are consistent with the lifetime as measured by trap experiments and not with the one obtained by beam experiments [36], thus suggesting that some systematics affects the beam experiments and a new decay channel is not needed [37,38], see also Ref. [39].…”

Section: Introductionmentioning

confidence: 96%

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Measurement of the neutron lifetime and inverse quantum Zeno effect

Giacosa

Pagliara

2020

Phys. Rev. D

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Quantum mechanics predicts that the decay rate of unstable systems could be effectively modified by the process of the measurement of the survival probability. Depending on the intrinsic properties of the unstable system and the experimental setup for the observation, one could obtain the so called (direct) quantum Zeno and inverse quantum Zeno effects corresponding to a slowing down or a speeding up of the decay, respectively. We argue that the inverse quantum Zeno effect is in principle detectable at a percent level for the neutron decay in experiments with trapped ultracold neutrons. Conversely, this effect is basically undetectable in experiments in which the neutron lifetime is measured by measuring the decays of beams of neutrons. As a test of our claim, we propose a simple qualitative correlation between the number of neutrons in the trap and the neutron lifetime: the larger the number, the faster the decay. Finally we discuss also the presently available measurements of the neutron lifetime and address the issue of the possible discrepancy that has been reported among the results obtained by the different experimental techniques.

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Section: Introductionsupporting

confidence: 81%

Section: Discussionmentioning

confidence: 67%

Section: Introductionmentioning

confidence: 96%

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Measurement of the neutron lifetime and inverse quantum Zeno effect

Giacosa

Pagliara

2020

Phys. Rev. D

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“…(15) is measured in neutron decay asymmetry studies, after correcting for residual recoil, weak magnetism and small O (α) corrections as discussed by Wilkinson [44] and Shann [45]. Corrections to the asymmetry reduce its magnitude by about 1% and correspondingly decrease g A by about 0.25% [42,43].…”

Section: Radiative Corrections To Neutron Decaymentioning

confidence: 99%

Radiative corrections to neutron and nuclear beta decays revisited

2019

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The universal radiative corrections common to neutron and super-allowed nuclear beta decays (also known as "inner" corrections) are revisited in light of a recent dispersion relation study that found +2.467(22)%, i.e. about 2.4σ larger than the previous evaluation. For comparison, we consider several alternative computational methods. All employ an updated perturbative QCD four-loop Bjorken sum rule (BjSR) defined QCD coupling supplemented with a nucleon form factor based Born amplitude to estimate axial-vector induced hadronic contributions. In addition, we now include hadronic contributions from low Q 2 loop effects based on duality considerations and vector meson resonance interpolators. Our primary result, 2.426(32)% corresponds to an average of a Light Front Holomorphic QCD approach and a three resonance interpolator fit. It reduces the dispersion relation discrepancy to approximately 1.1σ and thereby provides a consistency check. Consequences of our new radiative correction estimate, along with that of the dispersion relation result, for CKM unitarity are discussed. The neutron lifetime-gA connection is updated and shown to suggest a shorter neutron lifetime < 879 s. We also find an improved bound on exotic, non-Standard Model, neutron decays or oscillations of the type conjectured as solutions to the neutron lifetime problem, BR(n → exotics) < 0.16%.

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“…272 [6], in contradiction to the most accurate measurements [15][16][17]. An extended anaysis can be found in [18]. We note that the interpretation of the neutron decay anomaly is relevant for tests of the unitarity in the first row of the CKM matrix [19] with neutron decay.…”

mentioning

confidence: 96%

Constraints on the Dark Matter Interpretation n→χ+e+e− of the Neutron Decay Anomaly with the PERKEO II Experiment

et al. 2019

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Discrepancies from in-beam and in-bottle type experiments measuring the neutron lifetime are on the 4σ standard deviation level. In a recent publication Fornal and Grinstein proposed that the puzzle could be solved if the neutron would decay on the one percent level via a dark decay mode, one possible branch being n → χ + e + e − . With data from the Perkeo II experiment we set limits on the branching fraction and exclude a one percent contribution for 95 % of the allowed mass range for the dark matter particle. PACS numbers: 13.30.Ce, 12.15.Ji, 14.20.Dh Neutron decay, as the prototype for nuclear beta decay, and its lifetime are needed to calculate most semileptonic weak interaction processes and used as input to search for new physics beyond the standard model of particle physics [1][2][3][4]. Measurements of the neutron lifetime fall into two categories [5]: in the storage method neutrons are confined in a material or magnetic bottle and after a given time the surviving neutrons are counted. In the beta decay method, the specific activity of an amount of neutrons (a section of a neutron beam, a neutron pulse or stored neutrons) is measured by detecting one of the decay products, proton or electron. A review of neutron lifetime measurements can be found in [2]. The averaged results of both categories, 879.4(6) s and 888.0(2.0) s, deviate by 8.4 s from each other, corresponding to 4σ (all numbers from [6]).Although this lifetime discrepancy may be related to underestimated systematics in experiments, there is a basic difference between the two categories: the storage method measures the inclusive lifetime, independent of the decay or disappearance channel, whereas the beta decay method detects the partial lifetime into a particular decay branch. Historically, Green and Thompson have used this argument to derive an upper limit on the decay into a hydrogen atom which would be missed by the beta decay method [5]; however, the expected branching fraction of 4 × 10 −6 [7] is too small to explain the 8.4 s difference observed today. Greene and Geltenbort have speculated that the discrepancy might be caused by oscillations of neutrons into mirror neutrons [8]. Recently, Fornal and Grinstein [9] have proposed different decay channels involving a dark matter particle. These branches would have been missed by the most precise beta decay method experiments which have detected decay protons [10].Neutron stars have been used to severely constrain these branches [11][12][13] but some models evade these constraints [14]. Czarnecki et al. have derived a very general bound of < 0.27 % (95 % C.L.) on exotic decay branches of the neutron where they use their favored values of the neutron lifetime τ n from the storage method and the axial coupling g A from recent beta asymmetry measurements and assume that V ud from superallowed beta decays and CKM unitarity are negligibly affected by exotic new physics. This means that not more than 2.4 s (with 95 % C.L.) of the lifetime discrepancy might be explained by a dark decay. This con...

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Exotic decay channels are not the cause of the neutron lifetime anomaly

Cited by 42 publications

References 50 publications

Measurement of the neutron lifetime and inverse quantum Zeno effect

Measurement of the neutron lifetime and inverse quantum Zeno effect

Radiative corrections to neutron and nuclear beta decays revisited

Constraints on the Dark Matter Interpretation n→χ+e+e− of the Neutron Decay Anomaly with the PERKEO II Experiment

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