= Chamberlain-Segrè antiproton identification
{c}
In 1955, <Owen Chamberlain>, <Emilio Segrè>, <Clyde Wiegand>, and <Thomas Ypsilantis> used <Bevatron> <protons> on <copper>, selecting negative secondaries. <Magnetic fields> selected $p=1.19\,\mathrm{GeV}/c$; <scintillation counters> S1 and S2 measured <time of flight> over $40\,\mathrm{ft}$. <Cherenkov detector> C1 flagged $\beta>0.79$; C2 accepted $0.75<\beta<0.78$ after material losses. S3 checked traversal. The cuts rejected negative <pions>.https://escholarship.org/content/qt46p0z8w7/qt46p0z8w7.pdf[UCRL-3172, pp. 3–5, Fig. 1, Table I]{ref}
Chamberlain's 1959 account describes C2's <quartz> radiator, mirrors, and <photomultiplier> readout. The trigger combined delayed <scintillation counter> signals with C2; photographed <oscilloscope> traces exposed fast particles and <accidental coincidences> through C1 pulses or extra pulses. Reversing the <magnetic fields> provided a positive-<proton> control and revealed an alignment error. Changing selected <momentum> at fixed <velocity> acceptance tested for a <proton>-<mass> peak.<The early antiproton work by Owen Chamberlain>[1959 lecture, pp. 496–501, Figs. 7–11; Columbia scan]{ref}
Terminal-event studies remained unfinished; the 1955 identification did not rely on <annihilation>.https://escholarship.org/content/qt46p0z8w7/qt46p0z8w7.pdf[UCRL-3172, p. 13]{ref}
\Image[/antiproton-identification-functional-chain.png]
{title=Functional chain for identifying a negative particle of proton mass}
{description=An original functional diagram, with preparation, selection, independent <velocity> tests, and controls. Arrows indicate information flow, not the physical beamline layout.}
The logic is useful far beyond this experiment. A <magnetic field> separates <electric charge> signs and <magnetic rigidity>, but particles of different <rest masses> can share both. A <time of flight> signal adds <velocity>, while a <Cherenkov detector> independently checks whether that <velocity> is plausible. An <accidental coincidence> can imitate the delay of a slow particle without being one particle traversing the apparatus. Agreement between independent measurements is therefore part of the inference, rather than a redundant decoration.
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