Located in a cubic kilometer of ice at the South Pole, the IceCube Neutrino Observatory is designed to detect high-energy neutrinos from far beyond our galaxy. Scientists believe these nearly massless subatomic particles may help explain the longstanding scientific mystery of how galaxies are formed and evolve.  

A groundbreaking new study submitted to The Astrophysical Journal, led by Drexel physics PhD student Riya Shah, provides insight into the origins of these particles. This is the IceCube Collaboration’s first hunt for neutrino sources using two different datasets simultaneously, each with its own type of signal: tracks and cascades.  

"If a neutrino event happens, shapes of light appear inside the detector,” Shah explained. “Certain interactions create shapes called tracks, which are very linear in shape. Other types of interactions create cascades, which are more like spheres.”  

Until recently, searches for the sources of neutrinos have relied on tracks because of their linear shape. “It's easier to point back in the direction that a line came from and look at the sky and try to find where that neutrino originated,” according to Shah. The spherical shape of cascades makes this more difficult.  

Physics alum Stephen Sclafani, PhD '23, successfully used cascades to look for evidence of neutrinos from the Milky Way Galaxy during his time at Drexel. This finding demonstrated that cascades are indeed useful for detecting neutrino sources.  

When Shah joined Drexel’s IceCube group, the scientists agreed that they should use as much available data as possible from the detector to look for these neutrino sources. Working with her advisor, Professor of Physics Naoko Kurahashi Neilson, PhD, Shah decided to combine 14 years of track data and 10 years of cascade data together into one data set.  

“By combining these tracks and cascades, we hoped to gather additional information, and that's exactly what happened,” said Shah. “We were able to find a new hotspot—a point on the sky that neutrinos would be coming from—that had not been seen before in either individual dataset. This proved that it is good to combine these two datasets and showed that we should be trying to use as much data as we can to see new information that might have been hidden if we just used one.”  

During undergrad, Shah concentrated in stellar astronomy, studying stars outside our solar system. When she came to Drexel as a master’s student, she wanted to try something different and narrow down what field of physics she was most interested in, so she switched her focus to biophysics.  

“I liked working with big data and using machine learning, but biophysics wasn't really for me,” she reflected. “I still preferred astrophysics, so I joined Dr. Kurahashi Neilson’s group. She was doing research with neutrinos, which is particle physics, but looking for astrophysical objects, so this was very interesting to me. I jumped right into it and really fell in love with this subfield.”  

Shah began the research that led to this study three years ago, and it became the focus of her PhD thesis work. Now that the study has been submitted and is on its way to being published, Shah will begin writing her thesis and continue working on projects with the IceCube Collaboration. She will also travel to her first international conference in November, the TeV Particle Astrophysics (TeVPA) conference in Valencia, Spain.   

“The fruits of my labor are finally out and I can show everybody, even though my parents and friends might not fully understand it,” Shah laughed. “It's still really exciting for me to have something with my name on it.”  

Drexel’s IceCube research group is an active member of the international collaboration, which includes approximately 450 physicists from 58 institutions in 14 countries. The research conducted by this international group of scientists has led to new ways of exploring and understanding our universe. 

"One of the best things that ever happened to me was joining the IceCube Collaboration,” Shah said. “The collaboration spans many different countries around the world. Being able to work alongside so many different kinds of people, whose scientific expertise might be different from mine, is a really good skill to have for any future endeavor.”