Hunt of the “Little Neutral one”
By Dhaval Ajana, Florida State University
Have you ever wondered what the world is fundamentally made of? Like the foundation that supports your home and the steel beams that hold a skyscraper, likewise, the universe is built of fundamental, or elementary particles. These are the unified, ultimate building blocks of the universe. My research focuses on one of these core components: the neutrinos. Where I study final state particles, neutrons from accelerated neutrinos interaction in ANNIE experiment at Fermilab.
The name itself, “neutrino,” is Italian for “little neutral one.” Enrico Fermi, Italian-American physicist developed the theory for neutrinos., The thought was that neutrinos were massless, just like photons (light), and traveled at the speed of light. But as research developed, we found out they are not quite massless. They are nearly massless, but that tiny bit of weight is a huge mystery that we still can not nail down.
The Mysterious Ghost
Neutrinos are everywhere. They are the second most abundant fundamental particle in the universe (after light aka photons), streaming out of the sun, remnants of the Big Bang and even created in nuclear reactors. Trillions of them pass through us every second, yet we can not see or detect them — that’s why we call them “ghost particles.”
Imagine trying to catch one in a detection system the size of a binocular lens. Billions of neutrinos would pass through that tiny area, travel to the moon, and back multiple times. You’d be lucky to detect just a handful. They slip through matter without a whisper. This is a massive headache for detection, but it’s also what makes them so cool. Because they don’t interact much, they carry pure, untouched information from the deepest parts of space. If we can just figure out how to “listen” to these ghosts, we could unlock secrets about the birth and existence of our universe
So, how do we catch neutrinos?
Imagine smashing two mud balls together. If the balls are sturdy, they might just bounce apart. If they’re weak, they’ll shatter, and pieces will fly off in every direction. Crucially, the total weight of all the scattered pieces will always equal the total weight of the two original mud balls. This is a simple illustration of the conservation of energy (mass) and momentum, a fundamental law of physics.
In my research, we essentially smash a neutrino (one “mud ball”) into a known target particle (the other “mud ball”). We carefully “weigh” and count all the scattered “pieces” — the final state particles — that come out of the collision. Since we know the fundamental properties of the target particle, and we can measure the properties of all the final pieces, we can deduce the properties of the mysterious incoming neutrino.
The challenge, however, is that not all the scattered pieces are easy to detect. One key particle that often slips away is the neutron. Neutrons are charge-neutral, making them almost as slippery as the neutrino itself. While we can detect all the charged particles and others with specific characteristics, neutrons can escape our detection system. If we don’t know the properties (the “weight”) of all the final particles, our accounting is incomplete, and our understanding of the neutrino is flawed.
My job is to precisely quantify those missing neutrons.
I utilize the excellent capability of gadolinium-loaded pure water in the ANNIE detector to capture final-state neutrons. The light emitted from neutron captures is detected by photodetectors mounted on the inner walls of the detector — defined as a cluster of the particle (Check out my PhD proposal for more details on it). I have been developing better particle/cluster detection algorithm methods and hardware to measure the neutrons produced from a neutrino collision (what we call a “neutrino interaction”). I am helping to complete the crucial accounting equation. This work will fundamentally improve the accuracy of all future neutrino measurements, bringing us closer to answering the “bigger questions” in the field.
Why do I care about unveiling mysteries of the neutrinos?
My journey into science began in high school, sparked by figures like Dr. APJ Abdul Kalam, the pioneer aerospace scientist and former President of India. Besides, I was awarded a scholarship under the INSPIRE program for being among the top 1% scorers under the Gujarat Board in all of India. This scholarship supported my five years of Bachelor’s and Master’s of Science (BS-MS) studies. During my BS, with limited opportunity for research, I explored toy model simulations using density function theory and graduated with a major in physics with minors in mathematics and statistics from Maharaja Sayajirao University, Baroda. After that, I joined the Indian Institute of Technology, Hyderabad, to pursue MS in physics, where I had the opportunity to work on several projects, including Diffuse Supernovae Neutrino Background, gamma-ray burst afterglow and the theoretical framework of neutrino oscillation. Upon graduation, I completed an internship at Johannes Gutenberg university, Mainz, where I applied Machine learning techniques to improve the distinguishability between atmospheric and supernova neutrino backgrounds. Altogether, these experiences motivated me to pursue full time research in neutrino physics as a PhD student.
Quantifying neutrons from neutrino interactions is one of the most pressing questions in the field. It’s an intellectual challenge that requires a blend of creative theoretical work and painstaking experimental design. I’m proud to be part of a global community of experimentalists and theorists tackling this precise problem. My expertise lies in background studies of neutrino interaction, development of particle detection algorithms, simulation of neutrino interaction and the development of the cutting-edge hardware necessary for this experiment, allowing me to make a unique contribution to study the primary physics goal of our experiment and contribute to ongoing developments in novel technologies. It is incredibly exciting to know that the small, detailed work I do today could unlock the secrets of the cosmos tomorrow.
Contribution to Society: Beyond the Lab
It’s often said that fundamental research, driven by simple curiosity, is “useless” to society. But history proves this wrong. Pursuits of pure knowledge are the bedrock for revolutionary technological development.
Consider the equipment we use in neutrino research. For instance, my collaboration, the ANNIE experiment, is contributing to the development of a novel photo-detection technology called Large Area Picosecond Photodetectors (LAPPDs). These detectors can measure the arrival time of light particles with picosecond (trillionths of a second) precision [1].
While we use them to hunt neutrinos, these same properties — unmatched timing and high spatial resolution — make them incredibly suitable for next-generation medical imaging. They have the potential to vastly improve the accuracy and speed of tools like time-of-flight Positron Emission Tomography (TOF-PET) scans, leading to earlier and more precise disease detection [2]. Furthermore, the immense amount of data our experiments generate forces us to innovate in data processing and analysis, leading to more efficient, low-power computing methods that could help reduce the overall carbon footprint of big data science.
My research, therefore, isn’t just about cosmic mysteries. It sits squarely within the larger scientific story, addressing a core challenge in particle physics that, when solved, will refine our model of the universe. Simultaneously, the tools and techniques we invent along the way fuel technological progress, offering tangible benefits to society in fields as vital as healthcare. It’s a compelling journey that begins with a simple question — what is the universe made of? — and ends with innovation that touches us all.
- B. W. Adams et al. First Beam Neutrinos Observed with an LAPPD in the ANNIE Experiment, arXiv:2508.11111, Aug 2025
- Large area picosecond photodetector (LAPPD) offers fast timing for nuclear physics and medical imaging, IL NUOVO CIMENTO 43 C (2020) 11
Acknowledgements: This essay was written for the Science Policy & Advocacy for Research Competition (SPARC) at the Universities Research Association.
