Nudging the community towards measuring where all the antimatter went

This fundamental cross section shows the probability for a muon antineutrino to interact with a nucleon and produce a positively charged muon and any number of nucleons. For the first time, the MiniBooNE experiment has been able to split this measurement into a function of muon energy and scattering angle. By directly measuring the muon kinematics, these new data offer unprecedented insight into the behavior of the muon in antineutrino CCQE interactions.

Like many of the processes we study at Fermilab, neutrino interactions probe fundamental properties of the universe. The focus of the MiniBooNE experiment has been to identify whether muon-type neutrinos spontaneously change into electron-type neutrinos in one of the neutrino beams created at the lab, possibly implying an extra neutrino state. However, recent work on the interactions of the muon-type neutrinos themselves has proven compelling as well, and this new result provides a first look at a specific muon antineutrino interaction.

In 2010, MiniBooNE released the first measurement of the cross section for muon-type neutrinos to elastically interact with a neutron to produce a muon and nucleons (traditionally called a charged current quasi-elastic, or CCQE, interaction) as a function of both muon energy and production angle relative to the incoming neutrino. This is the most complete information of this process to date, and, as evidenced by the impressive number of citations it has received (more than 100!), has significantly contributed to modern understanding of intranuclear behavior.

The new data presented here provides the world’s first look at how muon antineutrinos behave in similar reactions. Like the neutrino-based measurement of 2010, this antineutrino result also contributes to our knowledge of nuclear physics processes. Together, these measurements significantly advance the preparedness of the community to search for new physics with neutrinos.

In particular, these data will help us understand signal and background processes that will be observed in the coming decades in long-baseline neutrino experiments that aim to measure the ordering of the neutrino masses and a process that may well explain why our universe is almost entirely matter-dominated. The confirmation of the latter process would mean the discovery of a physical mechanism that explains the existence of our universe. These next-generation measurements will be performed by looking for subtle differences between the conversion rates of neutrinos and antineutrinos over a travel distance of hundreds to thousands of kilometers. Being able to observe such effects depends critically on understanding how neutrinos and antineutrinos interact in our detectors. This new publication from MiniBooNE provides the first details of how antineutrinos interact compared to neutrinos in a critical energy region.

—Joe Grange, University of Florida

Joe Grange, University of Florida, performed the analysis for this MiniBooNE result.