Nucleon Transfer experiments in cryogenic Xenon
Measuring the occupations and vacancies of the valence nucleons in xenon and tellurium isotopes
The relationship between neutrino mass and the half life of neutrinoless double beta decay is governed by the matrix elements
for the isotopes in question. Without knowledge of these elements it is hard to predict the sensitivity of a double beta decay
experiment other than through simulation work using QRPA and ISM modelling. However these theories also predict the occupancies
of the nucleons in the valence bands of the parent and daughter nucleus, which are the nucleons which will actually decay during
neutrinoless double beta decay. The exact values of the matrix elements is very hard to confirm, however these occupancies can be
probed experimentally by finding the cross sections of pair and single nucleon transfers on the parent and daughter nucleus. These
experimental values can then be used to modify the values being used for QRPA and ISM modelling.
Selenium and Germanium, and the challenge of Xenon
Recent work with Selenium and Germanium isotopes revealed a large discrepancy between the predicted values for these occupanices and vacancies,
and the experimentally determined ones. Updating these theories to take these new values into account also changed the matrix elements for double
beta decay in these isotopes. Since a well known sensitivity is very important to carrying out a succesful experiment, it is desirable to repeat
these measurements for Xenon and Tellurium isotopes. However this is challenging for xenon as it is gaseous. This poses a variety of problems
since a good target for this experiment must have these properties
- target must be spatially thin in the beam direction
- sample is isotopically pure
- target must be high density
- target must remain of a constant thickness under the beam
- most other materials except carbon privide large backgrounds to the experiment
We plan to build a cryogenic xenon target which can freeze of layer of xenon of the desired thickness onto a carbon foil, using a cold head as the source
of low temperatures. This target can then be studied alongside the tellurium target and the nucleon transfer experiment repeated at a variety of angles.
Experimental technique
The experimental technique relies on the fact that as the angle of scattering for the reaction changes, so does the cross section for the reaction, and the
shape of this changenge can be predicted based on the L value of the reaction. Using a magnetic spectrometer to place a tight gate on the angle and to provide
particle ID and energy resolution we can find the exact cross sections for each L value transfer and reassemble them into a value for the occupancies and vacancies
in the target nucleus. The beams used shall be protons and alpha particles, between 20 and 51 MeV and the work will be carried out at the Yale beam facity.
Further options for this experiment are being explored at the HELIOS inverse kinematics experiment at Argonne.
