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تسجيل مستخدم جديدSearch for the Neutron Decay n$rightarrow$ X+$gamma$ where X is a dark matter particle
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In a recent paper submitted to Physical Review Letters, Fornal and Grinstein have suggested 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$rightarrow$ X+$gamma$ where X is a dark matter particle. We have performed a search for this decay mode over the allowed range of energies of the monoenergetic gamma ray for X to be a dark matter particle. We exclude the possibility of a sufficiently strong branch to explain the lifetime discrepancy with greater than 4 sigma confidence.
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It has been proposed recently that a previously unobserved neutron decay branch to a dark matter particle ($chi$) could account for the discrepancy in the neutron lifetime observed in experiments that use two different measurement techniques. One of
the possible final states discussed includes a single $chi$ along with an $e^{+}e^{-}$ pair. We use data from the UCNA (Ultracold Neutron Asymmetry) experiment to set limits on this decay channel. Coincident electron-like events are detected with $sim 4pi$ acceptance using a pair of detectors that observe a volume of stored Ultracold Neutrons (UCNs). The summed kinetic energy ($E_{e^{+}e^{-}}$) from such events is used to set limits, as a function of the $chi$ mass, on the branching fraction for this decay channel. For $chi$ masses consistent with resolving the neutron lifetime discrepancy, we exclude this as the dominant dark matter decay channel at $gg~5sigma$ level for $100~text{keV} < E_{e^{+}e^{-}} < 644~text{keV}$. If the $chi+e^{+}e^{-}$ final state is not the only one, we set limits on its branching fraction of $< 10^{-4}$ for the above $E_{e^{+}e^{-}}$ range at $> 90%$ confidence level.
A search for the rare radiative leptonic decay $D_s^+togamma e^+ u_e$ is performed for the first time using electron-positron collision data corresponding to an integrated luminosity of 3.19 fb$^{-1}$, collected with the BESIII detector at a center-o
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Using data samples collected with the BESIII detector operating at the BEPCII storage ring at center-of-mass energies from 4.178 to 4.600 GeV, we study the process $e^+e^-rightarrowpi^{0}X(3872)gamma$ and search for $Z_c(4020)^{0}rightarrow X(3872)ga
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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 col
d neutrons are in agreement, yet, there is discrepancy with a beam experiment by $3.5{sigma}$ (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 deficiency of the measured flux of antineutrino from reactor in respect to the calculated flux by $3{sigma}$(deviation by 6.6%). Specific feature of the proposal in this paper lies in the fact that both anomalies can be accounted for by one and the same phenomenon of oscillation in baryon sector between a neutron and a neutron of dark matter $n{rightarrow}n$ with mass $m_{n}$, somewhat less than mass $m_n$ of an ordinary neutron. Calculations of the proposed model require one free parameter: mass difference $m_n-m_{n}$ if one normalizes probability of oscillations for a free neutron on neutron anomaly 1%, then, having succeeded to interpret 6.6% of neutron anomaly in calculations, one can determine mass difference. According to preliminary estimations, the mass difference is $m_n-m_{n}{approx}$ 3 MeV. However, the analysis of cumulative yields of isotopes occurs in fission fragments was performed and it does not confirm possibility of existence of additional decay channel with emission of dark matter neutron with mass difference $m_n-m_{n}{approx}$ 3 MeV. The result of the analysis is the conclusion that for mirror neutrons the region of the mass difference $m_n-m_{n} {geq}$ 3 MeV is closed. The region of the mass difference $m_n-m_{n}{leq}$ 2 MeV turned out to be not closed.
Discrepancies from in-beam and in-bottle type experiments measuring the neutron lifetime are on the 4$sigma$ 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 $n rightarrow chi + e^+ e^-$. 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.
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