  The gaseous Xenon(Xe) time projection chamber (TPC) is an attractive detector
technique for neutrinoless double beta decay and WIMP dark matter searches.
While it is less dense compared to Liquid Xe detectors, it has intrinsic
advantages in tracking capability and better energy resolution. The performance
of gaseous Xe can be further improved by molecular additives such as
trimethylamine(TMA), which is expected to (1) cool down the ionization
electrons, (2) convert Xe excitation energy to TMA ionizations through Penning
transfer, and (3) produce scintillation and electroluminescence light in a more
easily detectable wavelength (300 nm). In order to test the feasibility of the
performance improvements with TMA, we made the first direct measurement of
Penning and fluorescence transfer efficiency with gaseous mixtures of Xe and
TMA. While we observed a Penning transfer efficiency up to ~35%, we found
strong suppression of primary scintillation light with TMA. We also found that
the primary scintillation light with Xe and TMA mixture can be well
characterized by ~3% fluorescence transfer from Xe to TMA, with further
suppression due to TMA self-quenching. No evidence of the scintillation light
produced by recombination of TMA ions was found. This strong suppression of
scintillation light makes dark matter searches quite challenging, while the
possibility of improved neutrinoless double beta decay searches remains open.
This work has been carried out within the context of the NEXT collaboration.
