francis froborg

Physics and more

My research in a nutshell

While studying physics, I realized that two souls alas! are dwelling in my brest: astronomy and particle physics. Although both fields are at first glance so entirely different (and the scales for sure are!) they combine nicely in the research on Dark Matter and neutrino physics.

In the following you will find a brief description on the different projects I am or was working on.

The SABRE Experiment


For over a decade, the DAMA collaboration have been observing a rate modulation in a large array of high purity NaI(Tl) crystal detectors at LNGS, which may be explained by dark matter interactions. This observation is both significant and controversial. Several experiments have claimed to rule out DAMA/LIBRA as an evidence for dark matter, but these tests were made based on dark matter halo models and dark matter-matter interaction models that are currently unknown. Therefore, the SABRE collaboration aims to carry out an unambiguous test of DAMA/LIBRA by using NaI(Tl) crystals with lower residual background than that of DAMA/LIBRA. A first proof of principle will is currently in preperation. Afterwords, two twin detectors are planed: one in the northern hemisphere in Italy, and one in the southern hemisphere in Australia.

SABRE is a small collaboration and the effort started in Princeton when I worked there as a postdoc. Thus, I was initially involved in all parts of the experiment with a focus on crystal growing, hardware development and PMT research. Besides setting up and commission the first phase of the experiment at LNGS, Italy, I now also work on light yield optimizations and related simulations.



The LUX-ZEPLIN (LZ) Experiment

LZ searches for dark matter with a 7-ton liquid xenon time projection chamber (TPC). The experiment will be located at the Sanford Underground Research Facility (SURF) in Lead, South Dakota and is currently in the design phase.

After moving to Imperial College, I got involved in the development of a simulation framework that models the response of the electronics chain including the PMTs, amplifiers, cables and DAQ with a focus on PMT effects. I am also involved in optical simulations and PMT testing.



The BOREXINO Experiment

Borexino studies solar neutrinos with the help of around 300 tons of liquid scintillator. The experiment is located at LNGS, Italy and is running already for several years.

To further improve the sensitivity of the detector especially on CNO neutrinos, the scintillator needs to be further purified, which is done by water extraction. Current studies focussed on the removal of Po-210, a radon daughter. During my postdoc in Princeton, I was studying a water purification system using a two-column fractional distillation system.

To properly reconstruct the light propagation inside the liquid scintillator, I also worked on a measurement of the refractive index of the different scintillator mixtures involved over a range of wavelengths and temperatures.



Calibration system for GERDA


The GERDA experiment is searching for the neutrinoless double beta decay in Ge-76. It uses high purity germanium detectors submerged nakedly in liquid argon, which acts simultaneously as cooling liquid and shielding material. It is located at the Laboratori Nazionali del Gran Sasso in Italy.

During my Ph.D. thesis, I was responsible for the development of the energy and pulse shape calibration system for the germanium detectors. The calibration sources need to remain within the cryostat for the whole period of the experiment to prevent contamination of the argon during the mounting process. Thus, the sources are parked on top of the cryostat during physics runs and moved down over several meters to the detectors for calibration. I was responsible for the design, test and installation of the hardware for this system.

Furthermore, I used Monte Carlo simulations to determine the relevant parameters of the calibration system as well as the background contribution due to gamma and neutron radiation. We also developed a special procedure to reduce the neutron flux of Th-228 due to (alpha-n) reactions. I was also involved in the optimization of the offline calibration data analysis, where I focused on the improvement of the energy resolution.



Structure and kinematics of spiral galaxies


In my diploma thesis I tried to resolve the spiral galaxy NGC 7331 into its different component to get a better understanding of the underlying Dark Matter profile necessary to reproduce the overall rotation curve.

To determine the rotation curve correctly, I used TiRiFiC to generate a tilted ring model of the H1 and CO component. Together with photometric data, I calculated the contribution of these components to the overall rotation curve and compared different Dark Matter models to desribe the missing mass.