Marc Schumann gave a talk (slides) Talk on April 3, 2017 at the occasion of the Scientific Committee meeting of our host laboratory LNGS, showing for the first time the exposure of our first dark matter run:
We started to fill the water tank:
The water acts as a passive shielding against external radioactivity. In addition, using the photomultipliers that can be seen towards the right of the picture, the water acts as an active muon detector. Muons may induce events in the xenon detector that may mimic dark matter signals. We therefore turn a blind eye (“veto”) for a short time whenever a muon travels through the water tank.
Today XENON1T has seen its first light:
This is literally the first event recorded by the detector in that is is a single photon that was detected by one of the photomultipliers and recorded by the whole XENON1T data acquisition setup. What you can see from the picture is that our noise is indeed very low compared to the smallest possible signal – that of a single photon! And this is even without any fine-tuning of our electronics yet.
The detector is still empty and we are checking the photomultipliers one by one before making first background measurements. Filling with liquid xenon will happen as soon as those tests are concluded successfully.
The Gran Sasso laboratory that hosts the XENON1T experiment is the largest underground laboratory in the world. More than a dozen different experiments make use of the low background from cosmic radiation that you get when you go more than a mile deep underground. You can virtually walk around the lab using the Street View from Google Maps.
The lab also offers public tours, just get in touch with them directly if you want to walk around in person.
The ICARUS experiment just left Hall B at the Gran Sasso underground laboratory in Italy for its journey to CERN in Switzerland. We had designed the XENON1T water tank a bit smaller than originally planned to allow ICARUS to move past. Everything went smoothly, but it was a tight fit…
We wish our colleagues all the best with the future of their experiment. Read the full story of this move at interactions.org.
We use liquid and gaseous nitrogen for a variety of things: Liquid nitrogen is used to initially liquefy the xenon and to keep the xenon cold in case of power failures. Gaseous nitrogen is mainly used as a blanket on top of the water inside the muon veto in order to keep radioactive radon gas out. Our two nitrogen storage tanks have been delivered, installed, and tested:
The XENON1T detector sits in the center of a large water tank. All the signal and high voltage cables, pipes for liquid and gaseous xenon, vacuum piping and various other lines get there via one large pipe.
We have just finished the installation of this pipe. It’s actually a quite fascinating piece of engineering. In it, there are all the signal and high voltage cables for the photomultiplier tubes. There are pipes to recirculate the xenon for purification in the adjacent building, which are themselves inside a vacuum-insulated pipe that in turn runs inside this pipe. The large diameter pipe is also used to evacuate the cryostat, as well as the heat insulation of the cryostat. And it holds a bunch of extra cables and wires for various other sensors. So, it’s really much more than just a pipe. It’s the lifeline to the detector. And it’s pretty cramped:
The XENON dark matter experiment is installed underground at the Laboratory Nazionali del Gran Sasso of INFN, Italy. A 62 kg liquid xenon target is operated as a dual phase (liquid/gas) time projection chamber to search for interactions of dark matter particles.
An interaction in the target generates scintillation light which is recorded as a prompt signal (called S1) by two arrays of photomultiplier tubes (PMTs) at the top and bottom of the chamber. In addition, each interaction liberates electrons, which are drifted by an electric field to the liquid-gas interface with a speed of about 2 mm/μs. There, a strong electric field extracts the electrons and generates proportional scintillation which is recorded by the same photomultiplier arrays as a delayed signal (called S2). The time difference between these two signals gives the depth of the interaction in the time-projection chamber with a resolution of a few mm. The hit pattern of the S2 signal on the top array allows to reconstruct the horizontal position of the interaction vertex also with a resolution of a few mm. Taken together, our experiment is able to precisely localize events in all three coordinates. This enables the fiducialization of the target, yielding a dramatic
reduction of external radioactive backgrounds due to the self-shielding capability of liquid xenon.
In addition, the ratio S2/S1 allows to discriminate electronic recoils, which are the dominant
background, from nuclear recoils, which are expected from Dark Matter interactions. And of course, the more energy a particle deposits in the detector, the brighter both S1 and S2 signals are, hence allowing us to reconstruct the particle’s deposited energy as well.