From Sanford Underground Research Facility: “What are cosmic rays?”

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Sanford Underground levels

From Sanford Underground Research Facility

March 11, 2019
Constance Walter

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Sandbox Studio, Chicago

At Sanford Underground Research Facility, we talk a lot about cosmic rays and the need to escape them—not because they are harmful to humans, but because they create background noise in sensitive physics experiments that are seeking very rare physics events.

So, what are cosmic rays, exactly, and why the need to escape them?

Cosmic rays were first discovered in August 1912 by Austrian physicist Victor Hess on an historic balloon flight. As Hess ascended 5,300 meters, he measured the rate of ionization in the earth’s atmosphere, finding it increased by three times the amount at sea level.

The term ‘cosmic rays’ is a misnomer. They’re really particles—mostly protons—that hurtle through space at nearly the speed of light. When they arrive at our little rock, they collide with the nuclei of other atoms in the upper atmosphere, creating even more particles that then shower the earth (one or two pass through your hand unimpeded every second). To escape these ubiquitous particles, researchers build physics experiments deep underground.

At Sanford Lab, the rock overburden stops most of the cosmic radiation before it reaches the experiments on the 4850 Level. Still, LUX-ZEPLIN (LZ), which is searching for dark matter, and the MAJORANA DEMONSTRATOR, which seeks to better understand the properties of neutrinos, build additional shielding to block out the rest.

In a 2017 paper [Science], MAJORANA reported that the depth of the experiment in conjunction with its extraordinary shielding efforts had paid off.

“We know that we created an environment that is incredibly clean and quiet,” said Vincente Guiseppe, co-spokesperson with MAJORANA. “Our initial results give us a better understanding of the always-elusive neutrino and how it shaped the universe.”

But some researchers don’t want to avoid cosmic rays—they want to understand them. According to NASA, understanding the chemical composition of cosmic rays is important because they are direct samples of matter from outside the solar system and contain rare elements and they can provide important information on the chemical evolution of the universe.

Dr. Mike Cherry, the Roy P. Daniels Professor of Physics at Louisiana State University, studied very energetic cosmic rays nearly a mile underground at the Homestake Mine (now the Sanford Underground Research Facility) in Lead, South Dakota, from 1980 to 1988.

“We wanted to find out the source of these rare, very energetic cosmic events,” Cherry said.“High-energy cosmic rays are the rarest form and could come from exploding stars, which may also emit gamma-ray bursts.”

Cherry installed the Large Area Scintillation Detector (LASD)—an array of 200 one-foot square plastic pipes welded together and stacked around Ray Davis’ solar neutrino tank. The pipes contained ultra-pure mineral oil and had sensitive light detectors on each end. In conjunction with an array of air shower detectors on the surface, Cherry hoped to draw a line between cosmic ray events on the surface and underground. He continues to do research in the field.

A Black Hills cosmic connection

Balloon flights from the 1930s through the mid-1960s—some of which took place from the Stratobowl in the Black Hills of South Dakota—continued to measure both high- and low-energy cosmic radiation. The flights also gathered meteorological and other scientific data necessary to improve safety at high altitudes.

See the full article here .


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About us.
The Sanford Underground Research Facility in Lead, South Dakota, advances our understanding of the universe by providing laboratory space deep underground, where sensitive physics experiments can be shielded from cosmic radiation. Researchers at the Sanford Lab explore some of the most challenging questions facing 21st century physics, such as the origin of matter, the nature of dark matter and the properties of neutrinos. The facility also hosts experiments in other disciplines—including geology, biology and engineering.

The Sanford Lab is located at the former Homestake gold mine, which was a physics landmark long before being converted into a dedicated science facility. Nuclear chemist Ray Davis earned a share of the Nobel Prize for Physics in 2002 for a solar neutrino experiment he installed 4,850 feet underground in the mine.

Homestake closed in 2003, but the company donated the property to South Dakota in 2006 for use as an underground laboratory. That same year, philanthropist T. Denny Sanford donated $70 million to the project. The South Dakota Legislature also created the South Dakota Science and Technology Authority to operate the lab. The state Legislature has committed more than $40 million in state funds to the project, and South Dakota also obtained a $10 million Community Development Block Grant to help rehabilitate the facility.

In 2007, after the National Science Foundation named Homestake as the preferred site for a proposed national Deep Underground Science and Engineering Laboratory (DUSEL), the South Dakota Science and Technology Authority (SDSTA) began reopening the former gold mine.

In December 2010, the National Science Board decided not to fund further design of DUSEL. However, in 2011 the Department of Energy, through the Lawrence Berkeley National Laboratory, agreed to support ongoing science operations at Sanford Lab, while investigating how to use the underground research facility for other longer-term experiments. The SDSTA, which owns Sanford Lab, continues to operate the facility under that agreement with Berkeley Lab.

The first two major physics experiments at the Sanford Lab are 4,850 feet underground in an area called the Davis Campus, named for the late Ray Davis.

LBNL LZ project at SURF, Lead, SD, USA

LBNL LZ project will replace LUX at SURF

In October 2013, after an initial run of 80 days, LUX was determined to be the most sensitive detector yet to search for dark matter—a mysterious, yet-to-be-detected substance thought to be the most prevalent matter in the universe. The Majorana Demonstrator experiment, also on the 4850 Level, is searching for a rare phenomenon called “neutrinoless double-beta decay” that could reveal whether subatomic particles called neutrinos can be their own antiparticle. Detection of neutrinoless double-beta decay could help determine why matter prevailed over antimatter. The Majorana Demonstrator experiment is adjacent to the original Davis cavern.

LUX’s mission was to scour the universe for WIMPs, vetoing all other signatures. It would continue to do just that for another three years before it was decommissioned in 2016.

In the midst of the excitement over first results, the LUX collaboration was already casting its gaze forward. Planning for a next-generation dark matter experiment at Sanford Lab was already under way. Named LUX-ZEPLIN (LZ), the next-generation experiment would increase the sensitivity of LUX 100 times.

SLAC physicist Tom Shutt, a previous co-spokesperson for LUX, said one goal of the experiment was to figure out how to build an even larger detector.
“LZ will be a thousand times more sensitive than the LUX detector,” Shutt said. “It will just begin to see an irreducible background of neutrinos that may ultimately set the limit to our ability to measure dark matter.”
We celebrate five years of LUX, and look into the steps being taken toward the much larger and far more sensitive experiment.

Another major experiment, the Long Baseline Neutrino Experiment (LBNE)—a collaboration with Fermi National Accelerator Laboratory (Fermilab) and Sanford Lab, is in the preliminary design stages. The project got a major boost last year when Congress approved and the president signed an Omnibus Appropriations bill that will fund LBNE operations through FY 2014. Called the “next frontier of particle physics,” LBNE will follow neutrinos as they travel 800 miles through the earth, from FermiLab in Batavia, Ill., to Sanford Lab.

FNAL LBNE/DUNE from FNAL to SURF, Lead, South Dakota, USA


LBNE

U Washington Majorana Demonstrator Experiment at SURF

The MAJORANA DEMONSTRATOR will contain 40 kg of germanium; up to 30 kg will be enriched to 86% in 76Ge. The DEMONSTRATOR will be deployed deep underground in an ultra-low-background shielded environment in the Sanford Underground Research Facility (SURF) in Lead, SD. The goal of the DEMONSTRATOR is to determine whether a future 1-tonne experiment can achieve a background goal of one count per tonne-year in a 4-keV region of interest around the 76Ge 0νββ Q-value at 2039 keV. MAJORANA plans to collaborate with GERDA for a future tonne-scale 76Ge 0νββ search.

LBNL LZ project at SURF, Lead, SD, USA

CASPAR at SURF


CASPAR is a low-energy particle accelerator that allows researchers to study processes that take place inside collapsing stars.

The scientists are using space in the Sanford Underground Research Facility (SURF) in Lead, South Dakota, to work on a project called the Compact Accelerator System for Performing Astrophysical Research (CASPAR). CASPAR uses a low-energy particle accelerator that will allow researchers to mimic nuclear fusion reactions in stars. If successful, their findings could help complete our picture of how the elements in our universe are built. “Nuclear astrophysics is about what goes on inside the star, not outside of it,” said Dan Robertson, a Notre Dame assistant research professor of astrophysics working on CASPAR. “It is not observational, but experimental. The idea is to reproduce the stellar environment, to reproduce the reactions within a star.”