Scientists from Fermilab, laboratory of Departamento of Energia of Estados Unidos, announced this Wednesday (27) the absence of evidence for the existence of the sterile neutrino. Data were obtained by the MicroBooNE experiment, located at Batavia, Illinois. The conclusion contradicts hypotheses raised since the 1990s to explain anomalous neutrino oscillations.
The result was published in the journal Nature and represents a milestone in the investigation of elementary particles. The search for the sterile neutrino gained momentum after previous experiments recorded unexpected behaviors in the three known flavors: electron, muon and tau.
MicroBooNE experiment details
The MicroBooNE uses a 170-ton capacity liquid argon detector. The equipment records interactions of neutrinos produced by the Fermilab accelerator.
Over four years, the collaboration analyzed millions of events. Nenhum signal compatible with the transition to sterile neutrino was identified in the tested channels.
The researchers compared the data with predictions of Modelo Padrão plus a fourth neutrino. The incompatibility was clear in multiple theoretical scenarios.
Context of previous anomalies
In the 1990s, the LSND and MiniBooNE experiments observed excess events that suggested oscillations over short distances. Essas oscillations required mass greater than predicted for known neutrinos.
The sterile neutrino hypothesis emerged as an elegant explanation. Essa particle would interact only through gravity and could make up part of dark matter.
- LSND experiment (1993-1998): excess electronic neutrinos
- MiniBooNE (2002-2019): ambiguous results, with signal higher than expected
- MicroBooNE (2015-2021): no evidence of sterile transition
Implications for Modelo Padrão
Justin Evans, Universidade professor of The statement reinforces the robustness of the current theory, but leaves open questions about previous results.
Matthew Toups, senior scientist at Fermilab, highlighted the clarity of the negative result. Ele questioned what was actually observed in the experiments that reported anomalies.
Alternative hypotheses under analysis
André De Gouvêa, theoretical physicist at Northwestern University, recalled that there are still theoretical reasons for new neutrino states. The difference lies in the possibility of these states being undetectable with current technology.
Explanations under study include neutrinos that decay quickly before reaching the detector and unknown interactions with liquid argon. Outros models propose modifications to the production or transport of neutrinos in the accelerator.
Next steps for collaboration
MicroBooNE completed its data collection phase in 2021. The collaboration is now finalizing complementary analyzes with different energy signatures.
The results will be compared with the SBN (Short-Baseline Neutrino) experiments, which include ICARUS and SBND, already in operation in the same beam as Fermilab. Esses detectors should offer definitive answers in the coming years.
The scientific community pays special attention to DUNE, a future project that will investigate long-distance oscillations. Enquanto that, the mystery about the original anomalies remains without a concrete solution.
Detector Technological Advancements
The use of liquid argon on a large scale marked a significant advance. MicroBooNE has demonstrated high-resolution three-dimensional imaging capabilities of neutrino-nucleus interactions.
The technology developed will serve as the basis for the DUNE program. The detector made it possible to distinguish electron and photon events with greater precision than previous experiments.
This distinction was essential to exclude false signals that could be confused with sterile neutrino transitions.
The MicroBooNE experiment closes an important chapter in the search for the fourth neutrino, but reinforces that neutrino physics still has fundamental questions. The data collected will continue to be explored in combination with other Fermilab detectors.