HISTORY

General Information

XENONnT is more than a simple experiment. It is the latest member of a great family of experiments that have written the history of direct dark matter searches.

Travel backwards in time below to find out more about the evolution from a 10 kg to a 10 tonne detector.

In order to detect a rare event such as a dark matter interaction, the experiment has to be placed in a very quiet environment, where the cosmic radiation is drastically reduced. For this reason every XENON experiment was operated deep underground at INFN Laboratori Nazionali del Gran Sasso (LNGS) in central Italy.

The development of the prototype detector XENON10 (operated 2006 – 2007) started in 2002 with a small group of scientists led by Professor Elena Aprile. This experiment consisted of a dual-phase time projection chamber (TPC) containing about 15 kg of xenon.

As the Collaboration and the interest in searching direct dark matter signal grew, the XENON experiments became bigger and bigger: after XENON10, XENON100 operated with about 160 kg from 2008 until 2016, then XENON1T, the first tonne-scale dark matter detector, ran with a total of 3.2 tonnes from 2015 until 2018, and finally XENONnT with about 8.4 tonnes of xenon started its operation in 2020.

collab_080714
Collaboration meeting at LNGS 2006

XENONnT

The newest member of the XENON family is XENONnT employing a total of 8.6 t of xenon. The infrastructure as well as subsystems of XENON1T can be re-used allowing for a fast upgrade by changing the heart of the detector system, the TPC with a new cryostat.

The XENONnT TPC features a diameter of 134 cm with a height of 148 cm enclosing 5.9 t of liquid xenon. A total of 494 PMTs are installed divided in 253 light sensors in the top array and 241 in the bottom one.

The water tank is upgraded with a gadolinium-loaded water Cherenkov veto, with a neutron veto volume around the cryostat optically separated from the surrounding muon veto. This allows for a further reduction of neutrons that could potentially mimic a dark matter signature. Two new subsystems for the xenon purification during the detector operation are installed, namely a liquid xenon purification system and a radon distillation column.

The XENONnT experiment started data taking in 2020. Extensive simulations yielded a projected sensitiviy for spin-independent interactions after a five-year livetime with a 4 tonne fiducial volume of 1.4 × 10-48 cm2 for a 50 GeV/c2  WIMP.

QUICKFACTS

Operation time:
Since 2020
Total Xe mass:
8.6  t
Sensitive Xe mass:
5.9 t
Driftlength:
148 cm
Number PMTs:
494 (253 top, 241 bottom)
WIMP sensitivity:
1.4 × 10-48 cm2 (projected)

XENON1T

In 2014, the XENON collaboration started the installation of XENON1T. It featured a total xenon mass of about 3.2 t, which made it the first operating liquid xenon detector with a target mass above the tonne-scale.

The cylindrical TPC inside a double-walled vacuum cryostat had a height of 97 cm and a diameter of 96 cm enclosing around 2 t of liquid xenon. The surrounding 1.2 t were exploited as passive shield. In total, 248 PMTs of 76.2 mm diameter were installed, 121 PMTs in the bottom array and 127 PMTs in the top.

The cryostat was installed in a 10 m wide and 10 m tall water tank housing about 700 t of pure water, for the shielding of environmental radioactivity. Additionally, the water tank was equipped with 84 PMTs, part of the muon veto, and with the system for calibration sources. The service building housed xenon storage, cryogenic plant, purification loop, distillation column, data acquisition and slow control system.

The analysis of two science runs with 278.8 live days and a fiducial volume of 1.30 t yielded no dark matter signal, but resulted in the most stringent exclusion of the spin-independent WIMP-nucleon scattering for WIMP masses greater 6 GeV/c2 with a minimum of 4.1 × 10-47 cm2 for a 30 GeV/c2  WIMP. In December 2018, the experiment was stopped for its upgrade to the next-generation experiment XENONnT.

QUICKFACTS

Operation time:
2015 – 2018
Total Xe mass:
3.2 t
Sensitive Xe mass:
2.0 t
Driftlength:
100 cm
Number PMTs:
248 (127 top, 121 bottom)
WIMP sensitivity:
4.1 × 10-47 cm2

XENON100

The XENON100 experiment ruled the direct dark matter search as the most sensitive detector from 2010 until 2014 boosting the LXe TPC sensitivity by one order of magnitude compared to XENON10.

The TPC was made of a cylindrical PTFE structure with 30.5 cm height and a diameter 30.6 cm and was filled with 62 kg liquid xenon (LXe). It was housed in a double-walled stainless steel cryostat and was surrounded by a 99 kg LXe active scintillator veto for background rejection. In order to reduce external background sources the cryostat was passively shielded by layers of copper, polyethylene, lead and water.

A total of 178 square 1 inch PMTs were installed with 80 PMTs in the bottom array and 98 PMTs in the top. In addition, 64 PMTs that were originally used for the XENON10 detector were used in the active veto.

In total, 477 live days from three science runs, resulting in an exposure of 48 (kg × yr) from January 2010 until January 2014, were analyzed, yielding no evidence for dark matter. The combination of all three runs resulted in a limit on the spin-independent elastic WIMP-nucleon scattering cross section of 1.1 × 10-45 cm2 for a WIMP mass of 50 GeV/c2.

QUICKFACTS

Operation time:
2008 – 2016
Total Xe mass:
160 kg
Sensitive Xe mass:
62 kg
Driftlength:
30 cm
Number PMTs:
178 (98 top, 80 bottom)
WIMP sensitivity:
1.1 × 10-45 cm2

XENON10

The XENON10 experiment was the prototype of liquid xenon-based TPCs. Its main purpose was not the detection of dark matter but rather a proof of principle for the new technology. It was deployed underground at LNGS in March 2006, where it was continuously operated for a period of about 10 months. The picture on the left shows the complete set-up.

The TPC active volume is defined by a Polytetrafluoroethylene (PTFE) cylinder of 20 cm inner diameter and 15 cm height. In total, 15 kg xenon can be filled into the detector. An inner sensitive volume (Fiducial volume) containing 6 kg xenon with reduced background was selected for the analysis.

Two arrays of 2.5 cm square photomultiplier tubes (PMTs) are used as light sensors to detect the direct (S1) and proportional (S2) scintillation light. The bottom array of 41 PMTs is in the liquid, while the top array with 48 PMTs in the gas is used for the position reconstruction.

An analysis of 58.6 live days of data, acquired between October 2006 and February 2007 set a new upper limit for the WIMP-nucleon spin-independent cross-section of 4.5 × 10-44 cm2 for a WIMP mass of 30 GeV/c2, a factor two better than other experiments at that time.

QUICKFACTS

Operation time:
2006 – 2007
Total Xe mass:
25 kg
Sensitive Xe mass:
15 kg
Driftlength:
15 cm
Number PMTs:
89 (41 top, 48 bottom)
WIMP sensitivity:
4.5 × 10-44 cm2