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Physics' Elena Aprile Is Designing and Developing a Device to Discover the Composition of Dark Matter

By Michael Larkin

Elena Aprile

The fluorescent overhead lights in Elena Aprile's physics lab at Columbia University burn brightly late into the evening as she accelerates her efforts to discover the composition of the universe. Her research could revolutionize modern physics.

Many scientists theorize that much of the universe is composed of matter that cannot be seen or detected. This unknown matter is commonly referred to as dark matter, and while theoretical debate continues, the race has begun to develop instruments sensitive enough to identify its form.

Aprile has been a frontrunner in this race. After years of research on liquid xenon radiation detectors and equipped with a million dollar grant from the National Science Foundation (NSF) for a two year R&D phase, Aprile and a team of dedicated graduate students and researchers are designing and developing the most sensitive experiment to date for the direct detection of dark matter particles.

"The implications are going to be enormous for particle physics as a whole, because the identification of dark matter will reflect physics beyond the Standard Model of strong and electroweak interactions," said Aprile. "What we assume, what we teach -- about particle physics -- might not be the full story."

Aprile and other physicists around the world believe dark matter can be identified as WIMPs, or weakly interacting massive particles. These particles are, as a class, heavy neutral particles that only interact weakly with matter, hence the difficulty in identifying them because they leave almost no trace of a reaction. Because dark matter is virtually undetectable, Aprile is attempting to determine its composition by tracing its footprints. She will examine the effects that dark matter has on other things that we can see and subsequently measure.

Aprile has assembled a collaboration that includes groups from Princeton, Yale, Brown, Rice and the Lawrence Livermore National Lab. Additional U.S. and foreign institutions are expected to join the Columbia-led experiment as it expands. The experiment, known as XENON, will use one ton of ultra pure liquid xenon distributed in ten detector modules as a target and detection medium for WIMPS. The detectors will be placed deep underground to minimize background from cosmic ray particles.

Theoretically, WIMPs, which are flying around and through us all the time, will go through the huge volume of liquid xenon, and occasionally strike a xenon nucleus. The elastic collision between a WIMP and a xenon nucleus will leave a microscopic energy recoil signature that would be registered by the liquid xenon detector. The detection of this signature would point toward the existence of dark matter in the form of WIMPS.

Aprile and her research team, Dr. Karl Giboni, Dr. Masaki Yamashita, Dr. Pawel Majewski, Professor Aprile, Naomi Kort, Shueb Ahmed, Kaixuan Ni, and Naresh Kumar

According to Aprile, liquid xenon is an ideal detector material for a sensitive dark matter search because it offers a large target mass and the best discrimination of the rare WIMP signal against a huge background signal.

"I have been studying noble liquids and their amazing properties for radiation detection and imaging for as long as I have been at Columbia, which is a long time," said Aprile. "Yet this stuff continues to intrigue me and to give me sleepless nights. Working with liquid xenon for either astrophysics or particle physics experiments, is never boring; it is always a challenge which is what makes my research even more fun and exciting."

The XENON project is just a year into the Research and Development phase, in which the team will build a functioning small-scale version of the liquid xenon detector. Aprile has spent the summer working at her Nevis Laboratory with a Columbia team that includes Karl Giboni, a senior research scientist, two young post-doctoral researchers Pawel Majewski and Masaki Yamashita, and graduate student Kaixuan Ni. Two Columbia College undergraduate students Naresh Kumar, a Rabi scholar, and Naomi Kort also spent their summer working on XENON related research. Naomi's work was sponsored by the Nevis Labs Research Experience for Undergraduates program, supported by the NSF. Graduate students from Brown and Princeton and a high school student, Shueb Ahmed, from Bronx High School of Science, were also part of the XENON team at Nevis this summer. Often putting in long hours, Aprile said that despite the hard work they all have enjoyed working together.

"The pace at which we move continues to accelerate," she said. "I feel there is not a moment to waste. Our goal is clear, but we still have a lot of work ahead. If we can solve the challenges that remain with the liquid xenon technology, we will have the most powerful device for a direct WIMPs search. This is both exciting and scary. It will take a lot of stamina and determination to realize this experiment in a timely fashion, but the rewards will be first class."

Once this phase has been concluded, the collaboration will seek funding for the full-scale experiment, involving both the NSF and the Department of Energy. Aprile expects to submit a new proposal for the development of the first of ten 100 kg modules later this month.

"The problem of dark matter is of fundamental importance for particle physics, astrophysics and cosmology," she said. "Understanding dark matter and dark energy will help us understand the evolution of the early universe and the formation of structure. It is nice to know that Columbia is playing a role in that."

Amidst her seemingly endless hours of research, Aprile is also a wife and mother of two daughters, Giulia, who will start high school this fall, and Susanna who is a junior at Columbia College. In addition, Aprile teaches both undergraduate and graduate physics courses.

"It's very demanding," said Aprile with regard to her research and teaching. "Balancing all these activities and a family is hard but I have been lucky to have the understanding and support of a wonderful family. In the end, my daughters are the experiment I am most proud of."

Published: Sept 12, 2003
Last modified: Sep 12, 2003


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