In the colossal aftermath of the Big Bang, a staggering 13.8 billion years ago, a symphony of particles burst into existence, encompassing matter and its elusive antimatter counterpart—each possessing an opposing electrical charge. However, in our present-day Universe, an intriguing disparity emerges, with an abundance of matter overshadowing the scarcity of antimatter. This enigmatic phenomenon stands as one of physics’ grandest conundrums. Yet, glimmers of understanding might reside within the enigmatic realm of neutrinos—peculiar particles that dance with near-masslessness, void of electrical charge, and morph from one of three identities to another as they traverse the vast expanses of space. If these elusive neutrinos oscillate differently from their antimatter counterparts, known as antineutrinos, they could potentially elucidate the perplexing imbalance between matter and antimatter.
Dotted across the globe, experiments such as the NOvA endeavor in the United States are diligently probing this intriguing possibility. Similarly, the forthcoming DUNE experiment, among the next generation of explorations, will embark on this captivating quest. These groundbreaking experiments, known as long-baseline neutrino-oscillation experiments, meticulously scrutinize a beam of neutrinos after it has traversed immense distances—the defining characteristic of the long baseline. By subsequently comparing the outcomes of neutrino and antineutrino beams, scientists seek to discern whether these twinned particles oscillate similarly or diverge on their transformative journey. The crux of this comparison lies in estimating the quantities of neutrinos and antineutrinos within the beams before their formidable voyages. These beams are ingeniously generated by unleashing proton beams upon fixed targets, resulting in a cascade of interactions. The ensuing interactions yield an array of hadrons, which are deftly harnessed using magnetic “horns” and channeled into lengthy tunnels, ultimately transmuting into neutrinos and other intriguing particles. Alas, in this intricate, multi-step process, deciphering the precise composition of the resulting beams becomes an arduous task, contingent upon the elusive proton-target interactions.
Enter the remarkable NA61 experiment housed within the hallowed halls of CERN, aptly named SHINE. Powered by high-energy proton beams derived from the Super Proton Synchrotron and matched with precisely tailored targets, this ingenious experiment aims to recreate the very essence of proton-target interactions. In the past, the NA61/SHINE collaboration has made substantial strides, meticulously measuring the electrically charged hadrons engendered by these interactions, ultimately leading to refined estimations of the neutrino content employed in existing long-baseline experiments. However, in an astonishing leap forward, the collaboration has now released a trove of fresh measurements, focusing on a trio of electrically neutral hadrons that elegantly decay into their neutrino-generating charged counterparts.
This epoch-making endeavor involving a 120-GeV proton-carbon interaction serves as the very foundation for NOvA’s neutrino beam, with high prospects of being replicated for the creation of DUNE’s equally groundbreaking beam. Up until now, estimations concerning the multitude of neutrino-yielding neutral hadrons engendered by this interaction have largely relied on uncertain extrapolations derived from older measurements featuring disparate energies and target nuclei. However, with this recent and remarkable direct measurement of particle production stemming from 120-GeV protons colliding with carbon, the need for these uncertain extrapolations diminishes significantly. Eric Zimmerman, the esteemed deputy spokesperson of NA61/SHINE, eagerly elucidates, “Previous simulations for neutrino experiments dependent on this particular interaction were marred by ambiguous extrapolations based on older measurements with dissimilar energies and target nuclei. This groundbreaking direct measurement of particle production arising from 120-GeV protons interacting with carbon drastically reduces our reliance on these extrapolations.”
In essence, the radiant endeavors of SHINE are poised to illuminate the path towards unraveling the mysteries surrounding neutrino beams. By venturing into uncharted territory with their innovative measurements, the NA61/SHINE collaboration heralds a new era of precision and certainty, steering us away from the uncertainties of the past. With their relentless pursuit of knowledge and their resolute dedication to the pursuit of scientific truth, these intrepid researchers are poised to illuminate the cosmic dance of neutrinos, ultimately revealing the secrets of our Universe’s profound matter-antimatter asymmetry.