Software forms an integral part of an experiment such as SABRE South.

We are working with equipment that will run continuously and autonomously, recording numerous parameters, and requiring time resolution of nano-seconds for critical parts of the data.

Simulation

Even before any of the hardware itself was built, important characteristics of the experimental setup could be simulated and modelled, in order to optimise design and determine certain operational parameters.

For example, the background levels expected in the final design were modelled, since we aim to reduce these as far as possible in order to improve the efficiency of the system with regards to detecting the small rate of hypothesised DM interaction events in the crystals.

Knowing the radioactivity levels of materials in the vessel’s physical components, sophisticated simulation software (GEANT4) was used to model the expected background rates that would result from particular engineering designs for the vessel’s components. This allowed us to see how design choices would influence the expected final sensitivity of the experiment- a vital process in optimising design.

With the various deisgn changes and refinements that invariably come about in a substantial experiment such as this, it is thereby possible to make sure that any such alterations do not adversely influence the final performance of the experiment.

Further, various mechanical properties of the design (such as the vessel’s response to blasting-induced ground vibrations, or flexure in metal components) was modelled, to ensure that the physical hardware itself is mechanically sound.

Data acquisition (DAQ)

The primary signal detection element in the experiment is the photomultiplier tube (PMT), an extremely sensitive and fast-acting device which converts photons into very brief (and measurable) electrical pulses. PMTs are used in the crystal modules, within the veto liquid in the vessel, and in the muon detector which will sit above the top of the shield outside the vessel. These PMTs provide us with the basic signals which we use to distinguish unwanted background events from the hypothesised DM-induced true signals.

The outputs from all the PMTs will be monitored continuously, and this sampling must be done at a sufficient rate that the temporal structure of the pulses from the PMT must be able to be measured automatically- this means we need to be able to see structure within the PMT pulses on the scale of nano-seconds (one-thousand-millionth of a second).

Not only that, but timing information- when a pulse occurs- also must be recorded.

Custom software has been developed to enable all this data acquisition to take place continuously and automatically.

Data analysis

Of course, once data have been obtained, they must be processed and analysed- what events are there, and do they correspond with what we think we should see?

Some of this analysis will take place in SUPL itself, as the data come in- the “online” processing. This is done in order to reduce the amount of data that must be transferred from the experimental site, as well as the total amount of storage required, to manageable levels.

After that initial processing, the resulting data will be transferred offsite for further “offline” processing. Again, custom software has been developed for this process.

Environmental monitoring

The various parameters that are measured as part of the experimental operating conditions (PMT voltage supplies, vessel temperature, electronics bay temperatures, gas levels, etc) will be monitored by software to look for any changes that may affect the experiment’s behaviour, as well as safety conditions within SUPL.

For example, sufficiently significant changes beyond nominal operating conditions will result in an alert being sent to personnel, such that appropriate actions can be taken.