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Patrick Maynard Stuart Blackett and Giuseppe Occhialini began their cosmic-ray collaboration in 1931. They used the coincidence methods of Walther Bothe and Bruno Rossi to make a particle initiate its own recording. Blackett later reported tracks on about $80\%$ of their counter-controlled photographs, compared with roughly $2$–$5\%$ for random expansions in small chambers. Those figures describe the reported apparatus and conditions, not a universal detection efficiency.^[ref]

In their 1933 account, Geiger counters above and below the chamber fed a coincidence circuit. Its pulse operated a thyratron, magnet and spring-release valve, letting a light piston expand the gas. A mercury-vapor lamp then illuminated the drops. A water-cooled solenoid supplied the magnetic field; two oblique cameras allowed track reconstruction. Moving the lower counter changed which trajectories could be recorded.^[ref]

Two timing problems must be separated. The coincidence circuit's window distinguishes nearly simultaneous counter signals. The mechanical expansion latency determines how much the existing ionization trail spreads before droplets form. For a chosen one-coordinate diffusion model with initial variance ${\sigma }_0^2$, diffusion coefficient $D$ and expansion delay $t_e$,Taking ${\sigma }_0=0$, $D=2.0\times 10^{-6}{\mathrm{m}}^2{\mathrm{s}}^{-1}$ and $t_e=20\mathrm{ms}$ gives ${\sigma }_{\mathrm{track}}\simeq 0.283\mathrm{mm}$. This is an original illustrative calculation, not the historical track width. It shows why a fast electronic pulse does not by itself guarantee a sharp photograph: the subsequent mechanical response also matters.

The photographs revealed groups containing positive and negative electron-like tracks, complementing the Anderson positron track experiment. Their interpretation depended on track curvature, direction, ionization and particle range, not simply on the presence of a coincidence.^[ref] Blackett explicitly noted that the counter control favored larger particle showers.^[ref] The multiplicity bias from a detector trigger gives a small model of that effect: a recording method can improve the study of rare interactions while making its photographs unrepresentative of the incident population.

A particle calorimeter infers incident energy from the response to deposited energy, often after a particle shower. Segmentation supplies directional information relative to the collision position. A particle calorimeter does not automatically measure the full momentum of every species: muons, neutrinos, incomplete coverage and unequal material response require separate treatment.

A glass-enclosed photomultiplier with local digitization: pulse times and charges enter event reconstruction. Reciprocal electrical pulses synchronize module clocks to the surface time base.^[ref]

Weak charged current interactions of muon neutrinos usually give extended muon tracks. Compact particle showers occur in other channels, including weak neutral current interactions of every neutrino flavor. Tracks generally constrain direction better; escaping particles complicate energy inference.^[ref]

A particle calorimeter designed to measure Electron and photon energies through particle showers. Track reconstruction helps distinguish charged Electrons from neutral photons.

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.^[ref]

CERN's Gargamelle account identifies the target liquid as $\mathrm{C}{\mathrm{F}}_3\mathrm{Br}$ 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.^[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.^[ref]

Expansion prepares a bubble chamber's superheated liquid; ionization by charged secondaries seeds bubbles for photography.^[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.

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.^[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.

The ATLAS experiment and CMS experiment searched proton-proton collisions at the Large Hadron Collider at collision energies of $7$ and $8\mathrm{TeV}$. The ATLAS experiment used silicon tracking, a $2\mathrm{T}$ solenoid, liquid-argon electromagnetic calorimeters and an external muon spectrometer. Its July 2012 paper reported a combined local statistical significance of $6.0$ standard deviations near $126.5\mathrm{GeV}$; this paper result is distinct from the initial 4 July announcement.^[ref]

The CMS experiment used silicon tracking in a $3.8\mathrm{T}$ solenoid, lead-tungstate electromagnetic calorimeters and external muon chambers. Electrons combine tracks and particle showers; muons combine tracking and chamber hits; photons supply shower energies and directions. Selected $H\to \gamma \gamma$ and $H\to Z{Z}^{\ast }\to 4\ell$ candidates, with $\ell =e,\mu$, yielded invariant mass peaks. It checked lepton efficiencies with Z boson decays, estimated fake-lepton backgrounds from control samples with relaxed identification, and fitted the smooth diphoton background from data. Its combined local statistical significance was $5.0$ standard deviations near $125\mathrm{GeV}$.^[ref]

The ATLAS experiment compared signal-plus-background and background-only hypotheses with a profile likelihood, accounting for systematic uncertainties and correlations between decay channels. Diphoton and four-lepton candidates gave precise invariant masses; $W{W}^{\ast }$ decays supplied additional evidence with poorer mass reconstruction because of escaping neutrinos. A local p-value concerns one specified mass; scanning masses requires a look-elsewhere effect correction.^[ref]

Two-photon decay excludes spin one under the usual assumptions, but does not prove spin zero. A mass peak does not determine every Higgs boson coupling. Production rates, branching fractions and angular correlations require additional tests.^[ref]

In 1962, Leon Max Lederman, Melvin Schwartz, Jack Steinberger and collaborators distinguished muon neutrinos from electron neutrinos using a neutrino beam.^[ref]

The Alternating Gradient Synchrotron delivered $15\mathrm{GeV}$ protons onto beryllium. Particle decay of pions and kaons supplied neutrinos; a $13.5\mathrm{m}$ iron shield preceded a ten-ton aluminium spark chamber.^[ref]

Production and detection are separate. In modern neutrino flavour notation,Shielding suppresses the daughter muon; a newly produced muon inside the spark chamber's aluminium marks an interaction.^[ref]

Beam-timed coincidence circuits and veto counters rejected entering tracks. Machine-off runs measured cosmic ray contamination; shield-thickness changes tested neutrons. Placing lead near the target shortened the meson decay path and reduced events. Cosmotron Electron calibration established particle shower recognition.^[ref]

The paper compared $34$ single-muon candidates, including $5$ estimated cosmic ray events, with six shower candidates unlike calibrated Electron showers. Kaon decays could supply genuine electron neutrinos. The deficit favored distinct neutrino flavours under lepton universality.^[ref]

The inference concerns production and detection channels. It does not measure neutrino mass or establish permanently fixed neutrino flavour. Later neutrino oscillation experiments address changes during propagation.^[ref]

Particle identification assigns a species hypothesis to a detector signal or reconstructed track. Curvature in a magnetic field supplies magnetic rigidity; additional responses, such as those of a Cherenkov detector or a particle shower, help distinguish an Electron from a hadron. The identity hypothesis enters the energy–momentum relation and therefore the reconstructed invariant mass. An apparatus can observe a peak before it can identify every decay channel, as the SPEAR psi energy-scan experiment illustrates.

Counterrotating Electron and Positron beams at SPEAR collided inside the Mark I magnetic particle detector. Lead–scintillator scintillation counters identified Electrons through large shower pulses; small pulses plus hits beyond the iron return identified muons.^[ref]

The selection required opposite-charge Electron–muon tracks, no detected photons, momenta above $0.65\mathrm{GeV}/c$, and transverse noncoplanarity above $20^{\circ }$. Multitrack hadron samples calibrated momentum-dependent misidentification; collinear lepton pairs checked identification losses. Photon and charge control samples tested backgrounds. Acceptance corrections depended on the proposed signal.^[ref]

The 1975 claim was anomalous events without a conventional explanation; new-particle pair production was a possible interpretation.^[ref] Martin Lewis Perl's lecture describes subsequent evidence for a charged lepton.^[ref]

The particle identification problem matters as much as the apparent missing four-momentum in electron-positron collisions. A penetrating hadron can imitate a muon; a particle shower can imitate an Electron; an undetected photon or a detector gap can imitate invisible recoil. An absence of additional recorded signals is conditional on detection efficiency. In a proposed signal model, the selected count has the schematic formwhere $\mathcal{L}$ is integrated collider luminosity, $\sigma$ a cross section, and $\epsilon$ the combined acceptance and detection efficiency. A single count cannot determine all three factors. A control sample must probe the relevant momentum and angular range; its abundant events do not automatically calibrate a differently distributed signal.

Super-Kamiokande used $535$ days ($33.0$ kiloton-years) and $22.5$ fiducial kilotons of water. Inner photomultiplier times and charges reconstructed interactions; the outer anticoincidence detector vetoed entering particles and marked exits. Contained single-ring events used likelihood classification: Electron particle showers blur rings; muons give sharper edges. The $1.33\mathrm{GeV}$ visible-energy sample division is not a universal detection threshold. Simulation estimated classification efficiency above about $98\%$, distinct from total detection efficiency; stopping muons and decay Electrons checked classification.^[ref]

Downward neutrinos travel about $15\mathrm{km}$; upward ones about $13000\mathrm{km}$. The multi-GeV muon-like up/down asymmetry was $-0.296\pm 0.048\pm 0.010$; Electron-like events lacked a comparable effect. Calibration constrained directional bias. This was disappearance evidence; tau neutrino appearance was untagged and sterile conversion remained possible.^[ref]

Writing $U$ and $D$ for the selected upward and downward populations, the asymmetry is $A=(U-D)/(U+D)$: a negative value means fewer upward events. An absolute source-normalization error alone rescales both populations and leaves this ratio unchanged. A direction-dependent response error need not cancel.

The 1983 UA1 experiment paper used proton–antiproton collisions at $\sqrt{s}=540\mathrm{GeV}$. A high-transverse momentum Electron candidate required a track matched to an electromagnetic particle shower, with little energy behind it in the hadronic particle calorimeter. Test beams checked Electron and pion responses; ordinary events and particle jet samples checked the imbalance resolution. Two searches, beginning with isolated Electrons and with missing transverse energy, converged on the same candidates. Conversion pairs, hadrons and heavy-flavor decays were examined as backgrounds.^[ref]