The accelerating expansion of the universe suggests that most of the energy in the universe is ‘dark energy’. A prominent candidate for dark energy is the so called Chameleon field. Its name has been chosen because the field depends on the local mass density. Under normal conditions on Earth the field is suppressed, prohibiting its experimental discovery so far. Only in the vacuum of outer space it comes into action.
The neutron group of the Atominstitut has performed a dedicated neutron interferometric experiment at the S18 setup at the ILL in Grenoble to search for Chameleons. The neutron phase shift through vacuum has been studied under various parameters as concerns the vacuum quality and the distance between the beam and the wall material of the vacuum chamber. No signatures of Chameleons could been found resulting in more stringent constraints for the Chameleon theory.
Until now the upper limit of the Chameleon coupling constant beta was defined by the qBounce experiments of our group. With the new interferometric experiment we could further reduce this limit by a factor of 30, staying among the most sensitive experiments probing the chameleon theory.