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Coauthored the reactor electron antineutrino confirmation. Halving the target proton density halved the signal, supporting its interpretation as inverse beta decay.^[ref]

Clyde Cowan and Frederick Reines detected reactor electron antineutrinos through inverse beta decay, ${\bar{\nu }}_e+p\to n+e^{+}$. The Positron supplied a prompt annihilation signal; capture of the neutron supplied a delayed signal. Requiring this pair and comparing operation at different reactor powers separated the weak interaction signature from background. Their 1956 report tested both the timing and physical origin of the signals, including changes to the neutron-capture material.^[ref]

A physicist who taught at the Catholic University of America from 1958 to 1974.^[ref]

Coauthored the reactor electron antineutrino confirmation using inverse beta decay. Prompt positron annihilation and delayed neutron capture supplied a distinctive paired signal.^[ref]

In the reaction displayed here, an electron antineutrino interacts with a proton to produce a Positron and a neutron. It turns an otherwise hard-to-observe incident particle into two products with different detection signatures. A prompt Positron signal followed by neutron capture can identify a candidate much more selectively than a single energy deposit. Inverse beta decay is a weak interaction; the incident electron antineutrino is detected through its reaction products.

Use the inverse beta decay threshold, with the charged-lepton mass generalized to $m_{\ell }$. For a stationary proton and a massless incident antineutrino, the Mandelstam invariant is $s=m_p^2+2m_p{E}_{\nu }$. At threshold the final particles have no relative momentum in their centre-of-momentum frame, so $s_{\mathrm{thr}}=(m_n+m_{\ell }{)}^2$. ThereforeUsing the supplied, rounded masses givesThe second term is the recoil correction; setting the threshold equal just to the final rest-mass excess would miss it.

Reactor electron antineutrinos have energies of a few million electronvolts. They can produce a Positron through inverse beta decay above the first threshold, but cannot produce a muon. Thus reactor neutrino oscillations are measured primarily as electron-antineutrino disappearance, through the event rate and energy spectrum relative to the unoscillated prediction. An oscillated muon antineutrino cannot be identified by the proposed muon-production channel at reactor energies; disappearance alone does not distinguish all possible final flavours.

Place a far detector near the first atmospheric disappearance maximum, approximately $1.2\mathrm{km}$ for the source's monochromatic energy and splitting, and a nearly identical near detector a few hundred metres from the reactor complex. Their flux-corrected comparison largely cancels reactor power, emitted-spectrum and absolute-efficiency uncertainties. For a broad reactor spectrum one fits energy-dependent disappearance instead of treating that single baseline as a universal exact optimum.

Detect ${\bar{\nu }}_{e}p\to e^{+}n$ in a hydrogen-rich target, for example liquid scintillator with neutron-capture enhancement. The prompt Positron signal estimates neutrino energy; the delayed neutron-capture signal supplies a time-and-position coincidence that strongly reduces random backgrounds. Use sufficient target mass and exposure, low radioactivity, overburden and a muon veto to reduce cosmogenic backgrounds, calibrated relative energy response and efficiency, and monitored reactor powers and baselines. Account for multiple reactor cores, spent-fuel backgrounds and accidental coincidences. At kilometre baselines the slow solar phase is small, so the disappearance depth directly probes ${\sin }^2(2{\theta }_{13})$ with little sensitivity to the CP phase or mass ordering.

A fission reactor supplies predominantly electron antineutrinos, with typical energies of a few MeV. Even if they oscillate to muon antineutrinos, producing a real muon through a charged current requires roughly the muon rest energy, over $100$ MeV for a free nucleon target. For example,Thus a muon spectrometer cannot observe this appearance channel from a reactor. Measure electron antineutrino disappearance instead, most commonly through inverse beta decay, ${\bar{\nu }}_{e}p\to e^{+}n$, using the prompt Positron and delayed neutron signal.

A Positron signal is correct for the reactor's antineutrinos, through inverse beta decay,A true electron neutrino charged current interaction instead produces an electron, for example ${\nu }_e+n\to e^{-}+p$. This corrects the source's loose use of “neutrino” for the reactor beam.

After slowing, the Positron annihilates with an electron, generally producing two $511$ keV photons. The prompt visible energy includes both the Positron kinetic energy and annihilation energy; neglecting the small neutron recoil,A delayed neutron capture supplies a powerful coincidence tag. Detecting only two annihilation photons discards useful prompt energy and does not uniquely identify the charged current event.

The original Kamiokande paper reported a low-energy event cluster on 23 February 1987 above surrounding background. Inverse beta decay, ${\bar{\nu }}_e+p⟶e^{+}+n$, provides an electron antineutrino channel through Positron light. Neutrino-electron elastic scattering is more directional. The burst supported core-collapse supernova neutrino emission, with limited statistics and channel ambiguity.^[ref]

An original counting illustration shows why timing matters. Suppose an independently measured background is a Poisson process of rate $b$. In a prespecified window $\Delta t$, the probability of at least two background events isFor the synthetic choice $b\Delta t=0.1$, this is about $0.004679$, obtained by subtracting the zero- and one-event probabilities of the Poisson distribution. The Homestake experiment's delayed extraction cannot supply such capture-time clustering. This calculation is not a significance estimate for SN 1987A: searching many possible windows, varying acceptance and correlated backgrounds change the inference.