Friday, June 7, 2019

XENON Dark Matter Project

Dark-matter detector observes exotic nuclear decay
CAEN and the XENON Collaboration have been pioneers in the fully Digital Data Acquisition and Pulse Processing for Dark Matter research. A longstanding, prolific collaboration that keeps on delivering important science results and is ready for future challenges.

What is XENON1T Experiment
XENON experiment is a 3500kg liquid xenon detector to search for the elusive Dark Matter – construction of the next phase, XENON1T, started in Hall B of the Gran Sasso National Laboratory in 2014. The detector contains 3.5 tons of ultra radio-pure liquid Xenon, and has a fiducial volume of about 2 tons. The detector is housed in a 10 m water tank that serves as a muon veto. The TPC is 1 m in diameter and 1 m in height. The predicted sensitivity at 50 GeV/c2 is 2.0×10−47 cm2. This is 100x lower than the current limit published for XENON100.

CAEN V1724 14 bit ADCs with 100 MHz sampling frequency and 40 MHz input bandwidth were used in XENON100 and used again in XENON1T but in this later stage the system has been upgraded to handle a larger amount of data. This lead to a rather short development time since old systems and software (also for data storage and data processing) can be largely re-used.

In XENON100, CAEN increased the maximum DAQ rate by more than one order of magnitude compared to XENON10 – although the drift length was doubled and the number of channels increased by a factor 2.7 – by using an online data reduction technique developed in cooperation with CAEN. This FPGA based method is basically rejecting all baseline between peaks and reduces the amount of data to be transferred and stored dramatically. However, the algorithm is still very simple. In cooperation with CAEN, we will exploit all possibilities to reduce the data size even further.

Currently, the factor limiting the DAQ rate is the overall data throughput for the full DAQ line, starting from the VME bus to the transfer to the computer cluster above ground. This problem can be easily solved by parallelizing the DAQ system.

A detector that was designed to probe dark matter, the ‘missing’ mass in the Universe, has seen an elusive nuclear decay called two-neutrino double electron capture — with implications for nuclear and particle physics. 

For half a century, our view of the world has been based on the standard model of particle physics. However, this view has been challenged by theories1 that can overcome some of the limitations of the standard model. These theories allow neutrinos to be Majorana particles (that is, they are indistinguishable from their own antiparticles) and predict the existence of weakly interacting massive particles (WIMPs) as the constituents of invisible ‘dark matter’ in the Universe. Majorana neutrinos mediate a type of nuclear decay called neutrinoless double-β decay, an example of which is neutrinoless double electron capture. A crucial step towards observing this decay is to detect its standard-model equivalent: two-neutrino double electron capture. In a paper in Nature, the XENON Collaboration2 reports the first direct observation of this process in xenon-124 nuclei, using a detector that was built to detect WIMPs.
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