XENON Collaboration

XENON is a research collaboration where scientists from Europe, the U.S., and Japan work to detect dark matter particles. Dark matter can only interact with visible matter predominantly through gravity, such as how stars and planets interact. The XENON collaboration is stationed in INFN Gran Sasso National Laboratory in Italy, the world’s largest underground laboratory. Also, the facility has 150 scientists who are keep on attempting to overcome some computational challenges, to detect dark matter particles from rare interactions of nuclear and electron recoils. XENON Collaboration is motivated by the seasonal modulation of the signal observed by DAMA/LIBRA, and the explanation has been proposed to be in the study of dark matter. This project has several phases, including the XENON10, XENON100, XENON1T, and XENONnT. This essay explores XENON10 and XENON100.

XENON10

The XENON10 is a dark matter detector experiment installed in 2006 at the underground Gran Sasso laboratory. The detector is used liquid Zenon to detect the weakly interacting massive particles (WIMP), which are hypothesized to contain mass near the 100 GeV (Aprile et al., 2011).  The detector is placed inside the shield within the underground laboratory. It was intended that XENON10 would act as a prototype detector, verify the achievable energy threshold, rejection power, and sensitivity, and test the practical application of other phases XENON detector (Aprile et al., 2011). That is probably the reason it was built with off-the-shelf materials.

Concerning the principle of operation, XENON10 is a two-phase time projection chamber (TPC) (Aprile et al., 2011). The project aims at detecting the particles which are produced after a particle interacts with an active LXe. The interaction causes scintillation and ionization, which are detected based on the ionization of electrons. The working principle of XENON10 is a bit sophisticated, but ideally, the two phases of liquid and gaseous Xeon are placed and observed in a special TPC measuring 20 cm by 15 cm in height. This project searched for dark matter on the third of October 2006 and the twenty-four^th of February 2007.

XENON10 has several features, including electrodes and electric fields. Scientists need to produce an electric field within the gaseous Xeon, which is achieved using a cathode and gate grid (Aprile et al., 2011). The system is also equipped with a calibration system, which is optimized to measure even low radioactivity. Nevertheless, the project still faces the challenge of light, which in turn causes changes in temperatures. This is overcome using the cryogenic system, which is “Pulse Tube Refrigerator (PTR) with 100 W of cooling power at 165 K, with a 3.5 KW compressor” (Aprile et al., 2011, p.7). It is, however, shielded from external energies by a steel-framed stricture.

During the operational period of project XENON10 (between 2006 and 2007), there were no WIMP signatures detected. Also, the number of events observed was expected since they statistically correlated with those observed in electronic recoil backgrounds. Ferella et al. report that there was “a total of approximately 104electron-recoil events, in the a priori set energy range of interest (4.5 to 26.9 keV nuclear-recoil equivalent energy) for the WIMP search, were collected with a ¹³⁷Cs source” (2007, p.2). These results are important because they inform scientists where and how to trace the dark matter particles, which in the end, foster understanding of the future of the universe.

XENON100

XENON100 is the second phase of the XENON experiment, which was a continuation of XENON10. It is based at the same facility where XENON10 was done – the Gran Sasso Mountain in central Italy. Also, the experiment used the same operational principles used to detect dark matter particles in the XENON10 prototype. However, XENON100 uses a position-sensitive XeTPC and a sensitive LXe volume which is observed using two sets of 178 PMTs to detect the S1 and ionization at the same time using the proportional scintillation mechanism S2.

The XENON100 collected data from a 34kg liquid. According to Aprile et al. (2016), the experiments ran from January 2010 to January 2014, done in two runs. The objective of XENON100 was to identify the signature for dark matter, an event that changes from time to time throughout the year. This change occurs due to a change in position of the earth as it orbits the sun throughout the year, which impacts the relative velocity of the dark matter halo, which is hypothesized to encompass the galaxy (Milky Way). An improvement over the XENON10, XENON100 had overall better stability (Aprile et al., 2016). Also, the XENON100 was constructed carefully using screen materials, unlike XENON10, which was constructed using the shelf.

Results from the first run – which ran for 224 days, have been published, and no dark matter was found. Also, the results indicate that “only upper limits on the WIMP-nucleon spin-independent interaction have been set, with a minimum of the cross-section at 2.0 × 10−45 cm2 for WIMP mass of mχ = 55 GeV /c2 (90% C.L.) (Garbini, 2016, p.3). Notably, unlike the XENON10, which analyzed the nuclear recoils, scientists analyzed electron recoils in XENON100 (Garbini, 2016). The limits of spin-dependent WIMP nucleon cross-section were also improved in XENON100 from XENON10, which had been found to be compatible with the e DAMA/LIBRA 3σ region (Savage et al., 2011). In the end, XENON100 did not find any dark matter particles, but the data collected is claimed to have significant value in the future of astrophysics.

A comparison between XENON100 and XENON10 indicates that the former was an improvement of the prototype XENON10. For instance, XENON10 relied on nucleus recoils while XENON100 observed electron recoil (Savage et al., 2011). Also, materials used in the XENON10 project were not cleansed radiation as those which were used in XENON100. As a result, Savage et al. (2011) explain that XENON10 has a low energy threshold than XENON100, and consequently, the former has stronger bonds than the latter.

References

Aprile, E., Aalbers, J., Agostini, F., Alfonsi, M., Amaro, F., & Anthony, M. et al. (2016). XENON100 dark matter results from a combination of 477 live days. Physical Review D, 94(12). https://doi.org/10.1103/physrevd.94.122001

Aprile, E., Angle, J., Arneodo, F., Baudis, L., Bernstein, A., & Bolozdynya, A. et al. (2011). Design and performance of the XENON10 dark matter experiment. Astroparticle Physics, 34(9), 679-698. https://doi.org/10.1016/j.astropartphys.2011.01.006

Aprile, E., Arisaka, K., Arneodo, F., Askin, A., Baudis, L., & Behrens, A. et al. (2011). Implications on inelastic dark matter from 100 live days of XENON100 data. Physical Review D, 84(6). https://doi.org/10.1103/physrevd.84.061101

Ferella, A., Rajantie, A., Contaldi, C., Dauncey, P., & Stoica, H. (2007). Results from the XENON10 Dark Matter search experiment at Gran Sasso Laboratories. AIP Conference Proceedings, 100(2). https://doi.org/10.1063/1.2823764

Garbini, M. (2016). Status of the XENON Project. Journal Of Physics: Conference Series, 718, 042023. https://doi.org/10.1088/1742-6596/718/4/042023

Savage, C., Gelmini, G., Gondolo, P., & Freese, K. (2011). XENON10/100 dark matter constraints in comparison with CoGeNT and DAMA: Examining theLeffdependence. Physical Review D, 83(5). https://doi.org/10.1103/physrevd.83.055002