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Bill Harlan

Nearly 50 members of a scientific collaboration planning  a next-generation dark matter experiment met here late last week to discuss how to meet some of the technical challenges inherent in building an instrument 20 times the size of the Large Underground Xenon (LUX) detector.

LUX, which has at its core about a third of a metric ton of liquid xenon, will be the world?s largest dark matter detector of its type. LUX currently is undergoing testing in the Davis Campus on the 4850 Level, and the detector will begin taking data by late this year or early next year. 

The next generation of LUX?LUX-ZEPLIN (LZ)?with 7 metric tons of xenon will be about 20 times larger and as much as 50 times more sensitive than the current experiment, says Murdock Gilchriese, deputy operations head for the Sanford Lab at Lawrence Berkeley National Laboratory. Although LZ will fit inside the same large water tank that will soon protect LUX, the bigger experiment also will be considerably more complex, beginning with its trip underground. The design, Gilchriese says, will be based on building the largest inner detector than can be lowered down the Yates Shaft.

Another challenge, Gilchriese says, will be creating an internal electrical field powerful enough to operate a detector much larger than LUX? but doing it in a way that doesn?t create spurious signals.

The LZ collaboration also will have to solve problems inherent in an experiment that could be 50 times more sensitive than LUX. That means LZ also will be more sensitive to background radiation coming from inside the detector itself?for example, from impurities in the liquid xenon, such as trace amounts of krypton. LUX will use xenon purified to a few parts per trillion. LZ, Gilchriese says, will need to reach ?parts per quadrillion? purity. ?It?s a very complicated process,? he says.

The National Science Foundation has approved a proposal for research and development leading to a full proposal for LZ by this time next year. The Department of Energy also is considering an LZ proposal.

The LZ collaboration includes researchers from England, Scotland and Portugal, as well as more than a dozen universities and laboratories in the United States. In fact, LZ combines researchers from LUX and ZEPLIN III, a dark matter experiment in the Boulby potash mine in England. (ZEPLIN is an acronym derived from ?zoned proportional scintillation in liquid noble gases.?)