The possible explanation of neutron lifetime beam anomaly

Space-based Measurements of Neutron Lifetime: Approaches to Resolving the Neutron Lifetime Anomaly

Free neutrons have a measured lifetime of 880 s, but disagreement between existing laboratory measurements of ~10 s have persisted over many years. This uncertainty has implications for multiple physics disciplines, including standard-model particle physics and Big-Bang nucleosynthesis. Space-based neutron lifetime measurements have been shown to be feasible using existing data taken at Venus and the Moon, although the uncertainties for these measurements of tens of seconds prevent addressing the current lifetime discrepancy. We investigate the implementation of a dedicated space-based experim…

对束流与瓶式中子寿命测量之间差异解释的实验搜寻

An experimental search for an explanation of the difference between beam and bottle neutron lifetime measurements

针对冷中子束与中子储存实验测得中子寿命存在4.4个标准差差异的问题，本文分析近期UCN数据，并采用Koch和Hummel模型寻找可能解释。

Search for explanation of the neutron lifetime anomaly

All results of the neutron lifetime measurements performed in the last 20 years with the UCN storage method are in a good agreement. These results are consistent with the latest most accurate measurements of the neutron decay asymmetry within the Standard Model. However, there is a significant discrepancy at $3.6σ$ (1% of the decay probability) level between the averaged result of the storage method experiments and the most accurate measurements performed with the beam method. This article addresses the possible causes of such discrepancy. We focused on finding the spectrum of possible systema…

A Standard Model Explanation for the "ATOMKI Anomaly"

Using the $e^+e^-$ pair spectrometer at the 5 MV Van de Graaff accelerator at the Institute for Nuclear Research, Hungarian Academy of Sciences (ATOMKI), Krasznahorkay et al. have claimed a 6.8$σ$ excess at high $e^+e^-$ opening angles in the internal pair creation isoscalar transition $^8\mathrm{Be}(18.15)\to\,^8\mathrm{Be}\,e^+e^-$. A hypothetical gauge boson with the mass circa $17$ MeV, "X17", has been proposed as an explanation for the excess. We show that the observed experimental structure can be reproduced within the Standard Model by adding the full set of second-order corrections and…

Neutron lifetime, dark matter and search for sterile neutrino

A review is focused on experimental measurements on neutron lifetime. The latest measurements with a gravitational trap (PNPI NRC KI) and a magnetic trap (LANL, USA) confirmed PNPI result of 2005. The results of measurements with storage of ultra cold neutrons are in agreement, yet, there is discrepancy with a beam experiment by $3.5σ$ (1% of decay probability), which is discussed in literature as "neutron anomaly" along with the ideas of explaining it by decay into dark matter partially. The second part of the paper is devoted to so called "reactor antineutrino anomaly", which refers to defic…

Combined Explanation of the $Z\to b\bar b$ Forward-Backward Asymmetry, the Cabibbo Angle Anomaly, $τ\toμνν$ and $b\to s\ell^+\ell^-$ Data

In this article we propose a simple model which can provide a combined explanation of the $Z\to b\bar b$ forward-backward asymmetry, the Cabibbo Angle Anomaly (CAA), $τ\toμνν$ and $b\to s\ell^+\ell^-$ data. This model is obtained by extending the Standard Model (SM) by two heavy vector-like quarks (an $SU(2)_L$ doublet (singlet) with hypercharge $-5/6$ (-1/3)), two new scalars (a neutral and a singly charged one) and a gauged $L_μ-L_τ$ symmetry. The mixing of the new quarks with the SM ones, after electroweak symmetry breaking, does not only explain $Z\to b\bar b$ data but also generates a lep…

Search for light massive gauge bosons as an explanation of the $(g-2)_μ$ anomaly at MAMI

A massive, but light abelian U(1) gauge boson is a well motivated possible signature of physics beyond the Standard Model of particle physics. In this paper, the search for the signal of such a U(1) gauge boson in electron-positron pair-production at the spectrometer setup of the A1 Collaboration at the Mainz Microtron (MAMI) is described. Exclusion limits in the mass range of 40 MeV up to 300 MeV with a sensitivity in the mixing parameter of down to $ε^2 = 8\times 10^{-7}$ are presented. A large fraction of the parameter space has been excluded where the discrepancy of the measured anomalous …

Heavy ion beam lifetimes at relativistic and ultrarelativistic colliders

The effects of higher order corrections in ultra-relativistic nuclear collisions are considered. It is found that higher order contributions are small at low energy, large at intermediate energy and small again at very high energy. An explanation for this effect is given. This means that the Weizsacker-Williams formula is a good approximation to use in calculating cross sections and beam lifetimes at energies relevant to RHIC and LHC.

Dark Matter Interpretation of the Neutron Decay Anomaly

There is a long-standing discrepancy between the neutron lifetime measured in beam and bottle experiments. We propose to explain this anomaly by a dark decay channel for the neutron, involving one or more dark sector particles in the final state. If any of these particles are stable, they can be the dark matter. We construct representative particle physics models consistent with all experimental constraints.

Large violation of the flavour SU(3) symmetry in $η$MAID2018 isobar model

We demonstrate that the explanation of the neutron anomaly around $W\sim 1685$MeV in $γN\to ηN$ reactions provided by the $η$MAID2018 isobar model is based on large violation of the flavour SU(3) symmetry in hadron interactions. This is yet another example of how conventional explanation (without invoking exotic narrow nucleon resonance) of the neutron anomaly metamorphoses into unconventional physics picture of hadron interactions. A possibility to mend the flavour SU(3) symmetry for some of resonances in $η$MAID model is discussed.

Constraints on the Dark Matter Interpretation $n \rightarrow χ+ e^+ e^-$ of the Neutron Decay Anomaly with the PERKEO II experiment

Discrepancies from in-beam and in-bottle type experiments measuring the neutron lifetime are on the 4$σ$ 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 $n \rightarrow χ+ e^+ e^-$. With data from the \perkeoII 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.