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The experiment infers neutrino helicity from nuclear nuclear resonance fluorescence and photon helicity. A spin-zero nucleus undergoes electron capture to a spin-one daughter, which emits a nuclear gamma ray to a spin-zero ground state. Selecting emission along the daughter recoil relates the normalized daughter, photon and neutrino helicities. Reversing magnetized iron measures the circular polarization of the selected radiation.^[ref]

The Goldhaber experiment inferred neutrino helicity from the circular polarization of a nuclear gamma ray. A spin-zero metastable europium-152 nucleus captures an inner-shell electron, producing a spin-one excited samarium-152 daughter and an electron neutrino; the daughter promptly emits a roughly $960\mathrm{keV}$ gamma ray to its spin-zero ground state. For a nearly stationary initial atom, the daughter recoils opposite the neutrino. Selecting photons emitted along that recoil relates the daughter spin projection, the photon helicity and the neutrino helicity.

The selection used resonant absorption and scattering in samarium. Nuclear recoil normally shifts an emitted gamma ray below the absorption resonance; the daughter recoil from electron capture supplies a compensating forward Doppler shift. Resonant scattering therefore preferentially selects forward photons, fixing their direction relative to the otherwise invisible neutrino. A samarium scatterer and scintillation counting identify this resonant component. Transmission through magnetized iron, whose Compton scattering depends on the relative electron and photon spins, then analyzes the circular polarization. Reversing the magnetization reverses the analyzing asymmetry and helps control instrumental offsets.

The selected photon and neutrino normalized helicities have the same sign: their momenta are opposite, while the daughter angular-momentum accounting gives opposite spin projections along the recoil axis. The observed negative photon helicity therefore establishes predominantly left-helicity neutrinos, consistent with the V-A interaction. It measures a helicity correlation, not a tiny neutrino mass or a literal observation of the neutral particle's trajectory.^[ref]

The functional arrangement below separates the polarization analysis from the resonance selection. The shield prevents the direct source beam from overwhelming the detector; the off-axis detector accepts gamma rays re-emitted by the samarium scatterer.

The europium source emits into magnetized iron, whose magnetization is alternated. A samarium scatterer selects nuclear nuclear resonance fluorescence, favouring photons emitted along the daughter recoil. A shielded NaI(Tl) scintillation counter records the scattered nuclear line. Compare the background-subtracted line rates for the two iron magnetizations, and use the calibrated sign of the analysing power to identify the photon helicity.

The measured circular polarization was negative, compatible after angular acceptance corrections with negative neutrino helicity. By the angular momentum conservation argument, the selected photon helicity and neutrino helicity have the same sign. Thus the experiment concludesfor the emitted relativistic electron neutrino. Finite acceptance dilutes the measured polarization; it does not justify equating the raw count asymmetry to $-1$.^[ref]