MLZ is a cooperation between:

Technische Universität München> Technische Universität MünchenHelmholtz-Zentrum Geesthacht> Helmholtz-Zentrum GeesthachtForschungszentrum Jülich> Forschungszentrum Jülich
Logo

MLZ (eng)

Lichtenbergstr.1
85748 Garching

PENeLOPE (under construction)

A Precision Experiment on Neutron Lifetime Operating with Proton Extraction

PENELOPE scheme PENELOPE scheme

The lifetime of the free neutron is an important parameter in the Standard Model of Particle Physics and in Big Bang cosmology.

Large discrepancies between the recent most precise measurements have forced the PDG to lower the world average and increase the error budget several times in the last two years to τn = 880.1 ± 1.1 s; this calls for a new and complementary experiment.

The goal of PENeLOPE is to determine the neutron lifetime with statistical and systematic errors smaller than 0.1 s using ultra-cold neutrons (UCN) trapped by magnetic fields and gravitation.

The UCN, coming from the UCN source that is currently under construction, are polarized using a magnetized foil and guided into the storage bottle. A magnetic field produced by several normal conducting coils preserves their polarization. In the storage bottle, UCN with energies higher than the trapping potential are removed by an absorber.

After this spectrum cleaning phase, the superconducting coils in the wall of the bottle are energized. The large magnetic gradients keep the neutrons from hitting the wall, eliminating wall losses completely.

Due to gravity, the UCN cannot “jump” out of the trap and the top can be left open to mount a detector to directly register the decay products, protons and electrons, during storage.

After a given storage period, the coils are ramped down again and the remaining neutrons are counted in a UCN detector. This can be done for different storage times, giving a second measurement of the lifetime.

This combination of two complementary measurement techniques and low systematic errors should allow PENeLOPE to reach an unprecedented precision.

Technical Data

Storage Bottle

  • Volume: 500 l
  • Trap depth: 80 neV
  • Up to 107 stored UCN
  • Ultra-high vacuum < 10-8 mbar

Magnet

  • 28 superconducting coils, operated at 4.2 K
  • Minimum field at storage volume walls: 1.8 T
  • Maximum field: 5.5 T
  • Ramp speed: 3 A/s
  • Liquid Helium inventory: 400 l

Proton/Electron detector: ADPs

  • Electrons: < 782 keV
  • Protons: < 750 eV
  • High voltage for proton post acceleration: > 25 kV
  • Temperature: 77 K
  • High magnetic field: 0.5 T
  • Area: 0.24 m²

Instrument Scientist

Prof. Dr. Stephan Paul
Phone: +49 (0)89 289-12571
E-Mail:

Operated by

TUM
Logos Tum
Logo MLL
Logo Excellence Cluster

Publications

Find the latest publications regarding PENeLOPE in our publication database iMPULSE:

impulse.mlz-garching.de

Gallery

PENELOPE overview
PENELOPE overview

Overview of the PENeLOPE cryostat

ADP
ADP

Hamamatsu APD (10 × 10 mm²)

Proton spectrum
Proton spectrum

Pulse height spectrum of 30 keV protons hitting a cooled APD

MLZ is a cooperation between:

Technische Universität München> Technische Universität MünchenHelmholtz-Zentrum Geesthacht> Helmholtz-Zentrum GeesthachtForschungszentrum Jülich> Forschungszentrum Jülich