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eEDM Sintesi della relazione

Project ID: 320789
Finanziato nell'ambito di: FP7-IDEAS-ERC
Paese: United Kingdom

Mid-Term Report Summary - EEDM (A laser-cooled molecular fountain to measure the electron EDM)

The aim of this project is to build an instrument that prepares a cloud of molecules, cools them with laser light to a temperature in the micro-Kelvin range, and throws them up as a fountain in free fall. This instrument will be very widely useful in physical chemistry and in metrology, for making exceedingly sensitive measurements on the molecules. The long time of flight in the fountain makes it possible to measure energies as small as one atto-volt. Our particular interest is in using ytterbium fluoride (YbF) molecules to probe the charge distribution of the electron, which is an important issue in elementary particle physics. This in turn is related to the elementary particle interactions that caused our universe to evolve an excess of matter over antimatter (thereby allowing us to exist!).

During this first half of the programme, we have been developing a method to prepare a beam of YbF molecules with high density, low velocity and low temperature. We produce YbF molecules by laser-ablation of a Yb target and reaction of the Yb atoms with SF6 gas inside a helium buffer gas at 4K. Cold molecules stream copiously from this source, carried at 200 m/s by the helium. A second buffer stage is added, with the aim of slowing the molecules to 50m/s or less. This idea was first demonstrated at Harvard using CaH molecules, and we have been discovering how to adapt their design so that it works with the much heavier YbF molecules. We have brought the speed down to 100 m/s (and below, with loss of intensity), but more work is still needed to reach the desired 50 m/s at high intensity. In parallel, we have been working on laser cooling molecules so that the beam can be stopped, cooled to microK and launched as a fountain. This has two aspects. First, we have assembled the three quite complex laser systems that are required to address the 12 relevant internal states of the molecule. Second, we have been developing fundamental ideas for laser cooling molecules (as opposed to atoms, where methods are already well established). As a result of this research, we are almost ready to stop and laser-cool the YbF beam. The only hold-up is the need for a further reduction in the speed of the beam from 100 m/s to 50 m/s, and we are optimistic that this is not far away.

We have also begun work on the new apparatus for measuring the charge distribution of the electron, using the YbF fountain. This needs a rather particular type of microwave structure – a 4 GHz stripline that is vacuum compatible, able to transmit the molecular cloud, and precisely terminated to prevent microwave reflections. This has now been developed. It also requires a pair of electric field plates, with extremely demanding requirements of high voltage, low leakage current, low magnetic field and field noise, exceptional uniformity, and vacuum compatibility. We have been testing prototypes of this and believe we now have a workable design.

Our progress over these 30 months has followed the work plan in the proposal surprisingly closely and has been reported in 7 refereed journal publications.


Brooke Alasya, (Research Services Manager - Faculty of Natural Sciences)
Tel.: +44 207 594 1181
Fax: +44 20 7594 1418
Numero di registrazione: 183586 / Ultimo aggiornamento: 2016-06-16
Fonte d'informazione: SESAM