title: Muon cooling: longitudinal compression.
abstract: A 10  MeV/c positive muon beam was stopped in helium gas of a few mbar in a magnetic field of 5 T. The muon "swarm" has been efficiently compressed from a length of 16 cm down to a few mm along the magnetic field axis (longitudinal compression) using electrostatic fields. The simulation reproduces the low energy interactions of slow muons in helium gas. Phase space compression occurs on the order of microseconds, compatible with the muon lifetime of 2  μs. This paves the way for the preparation of a high-quality low-energy muon beam, with an increase in phase space density relative to a standard surface muon beam of 10^{7}. The achievable phase space compression by using only the longitudinal stage presented here is of the order of 10^{4}.
authors.affiliation: Paul Scherrer Institute, 5232 Villigen-PSI, Switzerland.
authors.forename: Yu
authors.initials: Y
authors.lastname: Bao
authors.affiliation: Institute for Particle Physics, ETH Zurich, 8093 Zurich, Switzerland.
authors.forename: Aldo
authors.initials: A
authors.lastname: Antognini
authors.affiliation: Paul Scherrer Institute, 5232 Villigen-PSI, Switzerland.
authors.forename: Wilhelm
authors.initials: W
authors.lastname: Bertl
authors.affiliation: Paul Scherrer Institute, 5232 Villigen-PSI, Switzerland.
authors.forename: Malte
authors.initials: M
authors.lastname: Hildebrandt
authors.affiliation: Institute for Particle Physics, ETH Zurich, 8093 Zurich, Switzerland.
authors.forename: Kim Siang
authors.initials: KS
authors.lastname: Khaw
authors.affiliation: Paul Scherrer Institute, 5232 Villigen-PSI, Switzerland and Institute for Particle Physics, ETH Zurich, 8093 Zurich, Switzerland.
authors.forename: Klaus
authors.initials: K
authors.lastname: Kirch
authors.affiliation: Paul Scherrer Institute, 5232 Villigen-PSI, Switzerland.
authors.forename: Angela
authors.initials: A
authors.lastname: Papa
authors.affiliation: Paul Scherrer Institute, 5232 Villigen-PSI, Switzerland.
authors.forename: Claude
authors.initials: C
authors.lastname: Petitjean
authors.affiliation: Institute for Particle Physics, ETH Zurich, 8093 Zurich, Switzerland.
authors.forename: Florian M
authors.initials: FM
authors.lastname: Piegsa
authors.affiliation: Paul Scherrer Institute, 5232 Villigen-PSI, Switzerland.
authors.forename: Stefan
authors.initials: S
authors.lastname: Ritt
authors.affiliation: Paul Scherrer Institute, 5232 Villigen-PSI, Switzerland.
authors.forename: Kamil
authors.initials: K
authors.lastname: Sedlak
authors.affiliation: Paul Scherrer Institute, 5232 Villigen-PSI, Switzerland.
authors.forename: Alexey
authors.initials: A
authors.lastname: Stoykov
authors.affiliation: Institute for Particle Physics, ETH Zurich, 8093 Zurich, Switzerland.
authors.forename: David
authors.initials: D
authors.lastname: Taqqu