Muon Cooling (muCool)
We are developing a novel muon beam of slow positive muons by compressing the phase space of an already existing standard surface muon beam.
Working principle
Muons from a standard beam line are stopped in a helium gas target at cryogenic temperatures. The muons are manipulated using electric and magnetic fields in three stages, resulting in a three-dimensional compression of the stopped muon swarm. A sketch is shown in the figure below.
In a first stage the muons stop in a helium gas target with a density gradient, and are compressed by means of crossed electric and magnetic fields. The transversally compressed muon swarm then enters a second stage at room temperature, with electric and magnetic fields compressing the swarm also in longitudinal direction. Finally, in the last stage, the point-like muon swarm is extracted into vacuum and can be re-accelerated for further use.
Applications
Such a low-energy positive muon beam can be used for next generation low-energy particle physics experiments to measure the muon g-2, search for the electric dipole moment of the muon or it can be applied in the field of muon spin resonance techniques (μSR) to study material properties. Furhermore this beam is suited to produce a high-quality Muonium (μ+e-) beam from positive muons stopped in a thin film of superfluid helium (read more).
Using this Muonium beam, interferometry and spectroscopy with muonium atoms becomes feasible. This would allow to measure the gravitational acceleration of antimatter (μ+) and to improve the precision of fundamental quantities such as the muon-electron mass ratio, the charge ratio between the first two lepton families as well as further tests of bound-state QED.
Status
In 2011 a first experiment was conducted at the PiE1 beamline at the PSI. It was possible to demonstrate that the second stage (longitudinal compression) works and is understood when comparing with simulations (external pageread more). In the following years a lot of research and development was done in order to improve the 2011 experiment as well as construct the target for the transverse compression. The transverse target has many requirements concerning high electric and magnetic fields, cryogenic temperatures and vacuum stability which makes its construction a very challenging task.
During beamtimes in 2014 and 2015 it was shown that both longitudinal and transverse compression are feasible and the compression efficiency is probably as high as expected from theory. After successful demonstrations of both compressions, we combined them into a single stage as a mixed compression and this new scheme was partially demonstrated in 2017. In 2019 we largely improved performance of the cryogenic helium gas target which allowed us to improve demonstration of mixed compression during beamtime in December 2019. The data is currently being analyzed and compared with simulations.