Precision electron-nucleus measurements to inform, constrain, and validate models of neutrino-nucleus interactions.
The extraction of oscillation parameters from neutrino oscillation measurements relies on detailed understanding of neutrino-nucleus interactions and the reconstruction of incident neutrino energy. With the increased statistics delivered by more powerful neutrino production beams in next-generation accelerator-based experiments like DUNE and Hyper-K, nuclear interaction uncertainties will become a leading and limiting systematic for the analysis of neutrino oscillation measurements.
Building on the large similarity of electron- and neutrino-nucleus interactions, the electrons-for-neutrinos collaboration is leading a set of precision electron-nucleus interaction measurements at various beam energies and target nuclei to test, constrain, and validate models of neutrino-nucleus interactions.
We welcome all neutrino physicists to join our effort!
Electron-nucleus interaction measurements at various beam energies and target nuclei using CLAS6 and CLAS12 detectors at Jefferson Lab.
Testing and constraining theoretical models crucial for neutrino-nucleus interaction modeling, and their implementation in event generators like GENIE.
A global effort spanning institutions across Israel, the United States, Spain, and the United Kingdom working together on neutrino physics.
Different reaction channels overlap inside the nucleus, and CVC explains how the vector-sector lessons from electron scattering carry into weak charged-current predictions.
Two QE interactions are illustrated: (e,e'p) electron scattering γ exchange, followed by a νμ charged-current interaction with W+ exchange. We see the shared lepton-plus-proton topology.
The incoming electron transfers momentum through the exchanged γ* to a bound proton. The outgoing topology is the familiar scattered electron plus knocked-out proton used to constrain the vector response of the nucleus.
The incoming νμ exchanges a W+ with a bound neutron, converting it into a proton and producing an outgoing muon. The lepton identity changes, but the single-nucleon knockout geometry remains closely parallel.
Why show both: electron scattering isolates the electromagnetic vector response, while νμ CCQE adds weak couplings and axial structure.
The hard scattering is only the start. As hadrons propagate through the nucleus they can rescatter, exchange charge, or be absorbed before the detector ever sees them.
Rescattering can leave the outgoing proton as a proton, but with lower momentum and a different exit angle. The event can still look 1p-like even though the measured kinematics no longer match the primary interaction vertex.
A hadron can swap charge while it propagates through the medium. In this example the struck proton leaves as a neutron, so the particle species seen by the detector no longer matches the species produced at the primary vertex.
A pion produced at the primary interaction can be absorbed on nearby nucleons before it escapes the nucleus. Its energy is then redistributed to those nucleons, which can emerge as extra knocked-out particles, so the detector sees additional nucleons and no outgoing pion.
Detector consequence: the measured final state is a transported final state, not a pristine snapshot of the primary vertex. Topology, multiplicity, and reconstructed kinematics all depend on intranuclear transport.
A stylized multinucleon interaction: the exchanged virtual photon couples to a shared two-body current inside the nucleus, and the transferred momentum can knock out two nucleons instead of one.
A correlated nucleon pair in the nucleus can absorb the exchanged γ* through a shared two-body current, so the transferred momentum is distributed across the pair rather than deposited on one isolated nucleon.
As the interaction develops, both nucleons can be ejected and the residual system is left with two holes. That 2p2h topology is one reason multinucleon dynamics matter for neutrino-energy reconstruction and detector-level event classification.
Terminology note: 2p2h names the final state, while MEC names one mechanism that can produce it. Correlations, interference terms, and later FSI can overlap with the same detector topology.
A stylized resonance interaction: the exchanged virtual photon excites the struck proton to the Δ(1232) baryon resonance, which decays almost instantly into a nucleon and a pion.
An incoming electron transfers enough energy to push a bound proton out of the quasielastic region and into the resonance spectrum. In this stylized example, the exchanged γ* excites the proton to the Δ⁺(1232), the dominant low-lying baryon resonance.
That resonance is short-lived and decays through the strong interaction into a neutron and a π⁺. The detector therefore sees an inelastic final state with three outgoing particles while the residual nucleus is left with one hole.
Note: RES is the dominant inelastic channel in the few-GeV region. Final-state interactions can absorb, scatter, or charge-exchange the pion before it escapes the nucleus, altering the detected topology.
At high Q² the virtual photon resolves the quark substructure of the nucleon, strikes a single quark, and a color string stretches back to the remnant diquark before fragmenting into hadrons.
At high Q2, the virtual photon resolves the nucleon into quarks and strikes one parton directly. The outgoing quark separates from the colored remnant diquark, a short parton shower develops, and a color flux tube stretches between the two ends of the system.
As that string elongates it breaks through qq pair creation, producing a hadronic spray along the jet direction plus a remnant-side baryon. The residual nucleus is again left with one hole, and later FSI can still reshape the observed final state.
Note: DIS dominates at W² > 4 GeV². Final-state interactions can modify the hadron jet before particles escape the nucleus, altering both multiplicities and kinematics.
Electron scattering constrains the vector hadronic ingredients. CVC identifies the isovector electromagnetic current with the charged weak vector current used in neutrino-nucleus predictions.
Step 1
Electron scattering locks down vector form factors and response functions directly from data.
Step 2
CVC connects the charged weak vector current to the isovector part of the electromagnetic current, not to the full EM response.
Step 3
The vector piece comes from eA constraints, while axial and VA terms remain separate ingredients in the neutrino calculation.
Decompose
Separate the electromagnetic current into isoscalar and isovector pieces.
Rotate
CVC links the weak charged vector current to the isovector isospin triplet.
Reuse
Neutrino calculations inherit vector nucleon structure through the proton-neutron difference.
Electron scattering does not hand over a finished neutrino cross section. It constrains the vector hadronic ingredients, and CVC tells us exactly which part of that information can be promoted into the charged weak vector current.
Once that vector sector is transported, the neutrino calculation is rebuilt with weak couplings, weak kinematics, and separate axial or VA terms. The logic applies beyond QE to MEC, RES, DIS, and broader nuclear-response modeling.
Not a cross-section rescaling: electron data constrain the vector hadronic ingredients; the neutrino prediction is recomputed with weak couplings, kinematics, the weak leptonic tensor, and separate axial or VA pieces.
CLAS12, the CEBAF Large Acceptance Spectrometer for 12 GeV in Hall B at Jefferson Lab, is the modern large-acceptance detector system built for the lab's 12 GeV era. Its Forward Detector and Central Detector together reconstruct the scattered electron and the produced hadronic final state over broad angular coverage.
For e4nu, that coverage is what makes Hall B so useful: it lets us study electron-nucleus reactions on the same kinds of targets that matter for neutrino physics, then use those measurements to test nuclear-response calculations, benchmark generator ingredients, and understand biases in neutrino-energy reconstruction.
Our studies span beam settings of roughly 2, 4, and 6 GeV. While CLAS12 defines the upgraded Hall B program, many of our current analyses still rely on legacy CLAS6 data sets from the original CLAS detector, with CLAS12 providing the path to higher-rate and higher-energy follow-up measurements.
In practice, many current e4nu studies still use legacy CLAS6 data, while CLAS12 anchors the broader Hall B program and future measurements.
Forward Detector
Captures the higher-energy charged and neutral particles emerging at small polar angles.
Central Detector
Tracks the target-region final state and extends the event reconstruction to larger angles.
Highlights from collaboration meetings, workshops, and shared milestones.
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Physicists from around the world using precision electron scattering to better understand the nuclear physics behind neutrino interactions.
We welcome students and researchers interested in neutrino and electron scattering physics to join our effort!
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