This morning scientists associated with the Large Underground Xenon (LUX) experiment released preliminary results from the first three months of operation. LUX has been designed to observe dark matter, which has never been observed directly The team was successful in showing that it is the most sensitive dark matter detector in the world. While they did not directly observe dark matter particles during this calibration phase, they have ruled out candidates for future study.
This three-month-long initial run sought to ensure that the newly-built machinery was working properly and to gauge the sensitivity of the device. So far, the scientists involved are very pleased with the results as it shows a sensitivity that has never been achieved before. This will give the team the best possible chance of directly observing dark matter particles.
Though dark matter is theorized to make up about 85% of all matter in the Universe it has never been observed directly. It is not antimatter, nor is it a dense cloud of regular matter. Dark matter is - wait for it - dark, as it emits no light, which also means it cannot be seen directly. LUX researchers hope to change that by searching for weakly interacting massive particles (WIMPs), thought to be strong candidates for Dark Matter.
WIMPs are believed to come in either high or low mass, with high mass WIMPS weighting about the same as 40 protons. While other experiments have claimed to have potentially detected low mass WIMPs, the incredible sensitivity of LUX has ruled that those were probably misinterpretations of background radiation.
Dark matter is credited with many things, including holding galaxies together, as the galaxy’s own gravitational pull is not strong enough to hold itself together. Though it has such a profound influence on normal matter, it very rarely interacts with it. In order to detect such brief, rare interactions, the equipment must be incredibly sensitive.
The key to LUX’s sensitivity is creating a very quiet environment to buffer out as much background radiation noise as possible. The laboratory itself is located nearly a mile underground in South Dakota. Light detectors, capable of detecting a single photon, are in a time-projection chamber with 370 kilograms of liquid xenon. That unit is held in a tank of 71,600 gallons of deionized water to further reduce background noise. Flashes of light and ion charges are generated from particle interactions in xenon, which are read by the sensors. The researchers described the sound reduction as comparable to standing on the 50 yard line at the Super Bowl with 75,000 cheering fans down to hearing one of those fans breathe occasionally.
Though the team was not able to obtain direct observations of dark matter they feel encouraged by the performance of the sensors. It is also possible that they might not have been able to detect the dark matter particles simply because this run was too short and future runs will give a longer opportunity to detect these incredibly rare interactions.
The results released today will be invaluable as the team calibrates the equipment in preparation for the 300-day run in 2014. The results will be available in 2015.