= Gargamelle
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= Gargamelle neutral-current experiment
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{synonym}
<Gargamelle> was a heavy-liquid <bubble chamber> at CERN. Its 1973 collaboration report, Observation of neutrino-like interactions without muon or electron in the Gargamelle neutrino experiment, by <F. J. Hasert> and colleagues, described hadronic events with no identified <muon> or <Electron> and evaluated rates relative to <charged current> events. This is evidence for a <neutral current>, rather than direct production or photography of a <Z boson>.<Observation of neutrino-like interactions without muon or electron in the Gargamelle neutrino experiment by F. J. Hasert>[Physics Letters B 46 (1973), pp. 138–140, title, abstract and author list]{ref}
CERN's <Gargamelle> account identifies the target liquid as $\mathrm{CF_3Br}$ and distinguishes hadronic events from the separate isolated-<Electron> signal. The latter is an <antineutrino> transferring <momentum> to an <Electron>, whose electromagnetic <particle shower> supplies visible tracks. These are different final states, not two names for one event.<Forty years of neutral currents by Cian O’Luanaigh>[Forty years of neutral currents, 19 July 2013, chamber description and isolated-electron caption]{ref}
A <neutrino beam> uses <protons> striking a target to produce charged <pions> and <kaons>; focusing selects parents that undergo <particle decay> in flight. Their <neutrinos> pass through shielding into the target. Scanning photographs locates vertices and classifies outgoing tracks.<The Discovery of Weak Neutral Currents by Dieter Haidt>[§2, printed pp. 3–4: beam and scanning]{ref}
Expansion prepares a <bubble chamber>'s <superheated liquid>; <ionization> by charged secondaries seeds bubbles for <photography>.<How It Works: Bubble Chamber (CERN teaching archive)>[Operating sequence]{ref}
The recorded light reveals bubbles, not a directly visible incoming or outgoing <neutrino>. Reconstructing a vertex and classifying <bubble-chamber tracks> connects that optical record to a hypothesis about a <particle> interaction.
\Image[/electroweak-currents-and-bubble-chamber-readout.png]
{title=<Charged current> and <neutral current>: exchange process versus visible <bubble-chamber tracks>}
{description=Original functional schematic. The upper processes are quark-level illustrations; the lower panels represent possible hadronic readouts. Dashed neutrino paths are inferred and virtual exchange bosons are not photographed. Dots denote visible charged-particle trails. No historical photograph or measured geometry is reproduced.}
The collaboration compared samples with matched hadronic cuts. A flat longitudinal vertex distribution resembled <neutrino> interactions, but sideways <neutrons> and multi-step cascades could also flatten it. The background estimate combined visible parent-interaction/secondary-<neutron> pairs with a cascade calculation including surrounding material. Later <proton> exposures tested the predicted cascade lengths. Escaping charged <hadrons> could imitate <muons>; there was no independent perfect <muon> tag.<The Discovery of Weak Neutral Currents by Dieter Haidt>[§§2–5, printed pp. 3–9; Fig. 4, side-entry and cascade objections, associated-event normalization, Figs. 5–8, later proton control]{ref}
The inference combines positive evidence for an interaction with controlled alternatives for its visible final state. Shielding suppresses unwanted beam components, yet interactions in surrounding material can generate secondary <neutrons>; shielding alone cannot certify a <neutral current>. Nor does a successful <neutral current> search by itself establish every coupling or the <Higgs mechanism>. Its importance for the <electroweak interaction> is that the theory predicts an additional weak channel, with coupling relations that further <cross section> measurements can test.
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