اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدConstraints on the Dark Matter Interpretation $n rightarrow chi + e^+ e^-$ of the Neutron Decay Anomaly with the PERKEO II experiment
90
0
0.0
(
0
)
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
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.
قيم البحث
اقرأ أيضاً
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.
The presently world largest data sample of pi0 --> gamma e+e- decays containing nearly 5E5 events was collected using the WASA detector at COSY. A search for a dark photon U produced in the pi0 --> gamma U --> gamma e+e- decay from the pp-->pppi^0 re
action was carried out. An upper limit on the square of the U-gamma mixing strength parameter epsilon^2 of 5e-6 at 90% CL was obtained for the mass range 20 MeV <M_U< 100 MeV. This result together with other recent experimental limits significantly reduces the M_U vs. epsilon^2 parameter space preferred by the measured value of the muon anomalous magnetic moment.
We report the first observation of the rare eta->e+e-e+e- decay based on 1.7 fb^{-1} collected by the KLOE experiment at the DAFNE phi-factory. The selection of the e+e-e+e- final state is fully inclusive of radiation. We have identified 362 +- 29 ev
ents resulting in a branching ratio of (2.4 +- 0.2_stat+bckg +- 0.1_syst) x 10^{-5}.
A sensitivity of the VEPP-2000 $e^+e^-$ collider in a search for the rare decay $eta rightarrow e^+ e^-$ has been studied. The inverse reaction $e^+ e^- rightarrow eta$ is proposed for this search. We have analyzed a data sample with an integrated lu
minosity of 108 nb$^{-1}$ collected with the SND detector in the center-of-mass energy range 520-580 MeV and found no background events for the reaction $e^+ e^- rightarrow eta$ in the decay mode $etatopi^0pi^0pi^0$. In the absence of background, a sensitivity to ${cal B}(eta rightarrow e^+ e^-)$ of $10^{-6}$ can be reached during two weeks of VEPP-2000 operation. Such a sensitivity is better than the current upper limit on ${cal B}(eta rightarrow e^+ e^-)$ by a factor of 2.3.
We have measured the ratio $sigma(e^+e^-rightarrowpi^+pi^-gamma)/sigma(e^+e^-rightarrow mu^+mu^-gamma)$, with the KLOE detector at DA$Phi$NE for a total integrated luminosity of $sim$ 240 pb$^{-1}$. From this ratio we obtain the cross section $sigma(
e^+e^-rightarrowpi^+pi^-)$. From the cross section we determine the pion form factor $|F_pi|^2$ and the two-pion contribution to the muon anomaly $a_mu$ for $0.592<M_{pipi}<0.975$ GeV, $Delta^{pipi} a_mu$= $({rm 385.1pm1.1_{stat}pm2.7_{sys+theo}})times10^{-10}$. This result confirms the current discrepancy between the Standard Model calculation and the experimental measurement of the muon anomaly.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
