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Dark Matter Search

The nEDM apparatus at PSI  is also an excellent tool to search for signatures of dark matter particles (Roccia S, Zsigmond G, 2021). A potential signal is a shift in the ratio of the spin-precession frequencies of ultracold neutrons (UCN) and the 199Hg atoms of the co-magnetometer. This shift can be interpreted as caused by a possible short-range spin-dependent neutron–nucleon interaction mediated by axion-like particles and was studied with high precision (Figure 1, Afach et al. 2015). In a second effort, the aforementioned ratios measured during the nEDM data-taking were analyzed as an axion-induced oscillating electric dipole moment of the neutron, and as an axion-wind spin-precession effect (Figures 2 and 3, Abel et al. 2017).

So-called disappearance experiments, which can also be conducted with UCNs, are a further way to search for dark matter signatures. It was hypothesized in the fifties by Lee and Young  that there could be a mirror copy of the weakly interacting particles, restoring parity conservation on the global level. Since then, various theorists put forward the idea that oscillations between a neutral SM particle, such as the neutron, and its mirror counterpart could help to explain various issues in physics, including dark matter.  Various searches for oscillations of neutrons to mirror-neutrons were conducted using the nEDM apparatus. Limits were achieved for the cases of zero mirror-magnetic field (Ban et al. 2007)  and of assuming non-zero mirror magnetic fields (Altarev et al. 2009) originating from mirror photons. Recent reports of anomalous signals sparked world-wide attention and initiated further search at PSI yielding new limits (Figure 4, Abel et al. 2020). A new dedicated apparatus has been installed at beamport West-1 to continue this effort, see Figure 5. and Ref. N. J. Ayres et al. 2022
 

DarkMatter Search
Figure 1: Limit established at PSI for the scalar-pseudoscalar coupling for axion or axion-like particle (pink solid line) (Afach et al 2015).

DarkMatter Search
Figure 2: First laboratory-based limit on the axion-gluon coupling (Abel et al. 2017).

DarkMatter Search
Figure 3: Limit on the axion-nucleon coupling (Abel et al. 2017).

DarkMatter Search
Figure 4: Lower 95% C.L. limit on the n-n' oscillation time for non-zero mirror magnetic fields (orange line) obtained at PSI (Abel et al. 2020), and the bands represent previously claimed signals.

mirror neutron setup West1
Figure 5: A new apparatus was recently installed at the West-1 beamport dedicated to the search of neutron to mirror-neutron oscillations at PSI. The UCN storage volume is placed inside the vacuum chamber that is visible in the center. This is surrounded by a Helmholtz-like coil system for an advanced control of the magnetic field stability and its homogeneity.

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Contact

Dr. Bernhard Lauss

Telephone:
+41 56 310 46 47
E-mail:
bernhard.lauss@psi.ch


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Anita Van Loon

Telephone:
+41 56 310 32 54
E-mail:
anita.vanloon@psi.ch

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