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The antimuon is the antiparticle of the muon. It has electric charge $+1$ and lepton number $-1$.

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 lepton with nonzero electric charge, such as an electron or muon; neutrinos are electrically neutral.

A cosmic ray is a high-energy charged particle propagating through space. Galactic cosmic-ray electrons emit synchrotron and inverse-Compton radiation, while cosmic-ray nuclei produce gamma rays through collisions with gas.

In modern terminology, a primary cosmic ray arriving at Earth's atmosphere is usually a proton or another atomic nucleus, with an electron component as well. Atmospheric collisions generate secondary cosmic rays and air showers, including muons, electrons and photons. A gamma ray can also initiate an air shower, although it is electrically neutral. Consequently, detecting atmospheric ionization does not establish that an incoming primary cosmic ray passed through the detector. Magnetic fields bend charged particles, while gamma rays provide a more direct directional connection to their sources.^[ref]

The Hess cosmic-ray balloon experiment asks how atmospheric shielding and separation from the ground affect ionization. Its power comes from changing the environment around an enclosed detector instead of identifying each incoming particle.

Atmospheric cosmic rays generate muons whose mean lifetime at rest is about $2.2\mu \mathrm{s}$. For a selected speed $v$ and production-to-detection distance $h$ in the terrestrial frame, special relativity predicts survival fraction $e^{-h/(\gamma v{\tau }_0)}$, where $\gamma$ is the Lorentz factor. Without time dilation, the exponent would instead be $-h/(v{\tau }_0)$. Comparing altitude-dependent counts at controlled energies, allowing for acceptance and energy loss, tests these alternatives. In the muon rest frame the terrestrial distance is shortened to $h/\gamma$ by length contraction, so the proper flight time and survival fraction agree with the terrestrial calculation. This frame comparison does not turn the same decay measurement into two independent tests.

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 vertically incident particle annihilating with a stationary target into two equal-energy muons gives each half the incident longitudinal momentum, while their transverse momenta are opposite. At height $H$ above a locally flat surface, each proper flight time is $2H{m}_{\mu }{c}^2/[c(p_{\mathrm{in}}c)]$, since $\gamma v_z=p_z/m_{\mu }$. Independent exponential particle decays then give the displayed joint survival probability. Atmospheric energy loss, scattering and curvature are omitted; replacing both trajectories by vertical paths would miss the two-body angular correction.

The experiment identifies tau lepton pairs with mixed electron-muon decays and missing energy, and subtracts a nonresonant continuum contribution. This provides a concrete implementation of a leptonic tau lepton selection near the charmonium threshold.

The 1999 recognition of Gerard 't Hooft and Martinus J. G. Veltman concerned the theoretical quantum structure of the electroweak interaction.^[ref] Renormalizability makes repeated radiative corrections predictive from a fixed set of inputs. It does not imply that the perturbation series converges, nor that renormalization alone chooses the correct particle content or excludes all physics beyond the Standard Model.

The Gargamelle collaboration prepared an experimental test by exposing its heavy-liquid bubble chamber to neutrino and antineutrino beams at CERN. The readout selected events producing hadrons without an identified muon or electron, compared with events containing a charged lepton. Its 1974 report assessed alternative origins from neutrons and long-lived neutral kaons, finding them insufficient to explain the sample. That supported neutral currents; it did not isolate a radiative correction or demonstrate renormalizability.^[ref]

The distinction matters when using the tree-level electroweak gauge-boson masses:Beyond tree level, self-energies, interaction vertices and counterterms alter how chosen input observables predict another observable. The Weinberg angle then needs a specified renormalization scheme; inserting its value from one convention into a formula from another can create an apparent discrepancy. A meaningful higher-order test must state both its independent experimental inputs and the calculated loop order.

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 $662$ live days during 2010–2012, $28$ events exceeded the expected $10.6_{-3.6}^{+5.0}$ atmospheric events. Energy, direction and topology supported an extraterrestrial component. Combined searches gave $4.1\sigma$ with additional benchmark charm background; uncertain charm production affected significance. No source clustering was established.^[ref]

A diffuse excess and an identified source answer different questions. The first compares populations against a background hypothesis; the second needs an association in direction, perhaps also in time.

Escaping muons or neutrinos can make deposited energy smaller than incoming neutrino energy.^[ref]

In the 2013 calibration study, six horizontal light-emitting diodes per module on string 63 flashed sequentially; other strings recorded charges and photon arrival times. A global fit inferred depth-dependent scattering of light and absorption coefficients. Dust-logger measurements checked layer structure; independent muon events tested simulated time patterns. Photomultiplier response and refrozen ice near modules remained limitations. Thus a late hit need not imply a late interaction: scattering of light changes the path.^[ref]

An original limiting calculation isolates this issue. Suppose a compact source emits at time $t_0$ into homogeneous, nondispersive ice with stipulated refractive index $n=1.32$. At distance $r$, the unscattered light arrives atwhere $c$ is the vacuum speed of light. For chosen $r=100\mathrm{m}$, the delay is $440.3\mathrm{ns}$. A scattered path $30\mathrm{m}$ longer adds $132.1\mathrm{ns}$ even with perfect clocks. These chosen values are not calibration measurements. Real ice requires wavelength-dependent propagation, module response and a spatially varying light-transport model; replacing that response by one arrival time discards information.

The 2013 selection rejected early boundary light. Tagged muons checked leakage; air shower companion muons also vetoed downward atmospheric neutrinos.^[ref]

A simple original conditional probability model explains why a veto changes the selected mixture. Let $A$ mean that an atmospheric neutrino interaction would pass all other cuts, $M$ that an accompanying muon reaches the veto, and $V$ that the veto fires. Set $a=P(M\mid A)$ and $ϵ=P(V\mid M,A)$, and neglect unrelated veto hits. The law of total probability givesFor chosen $a=0.8$ and $ϵ=0.95$, the passing fraction is $0.24$. Neither this value nor either input is an IceCube measurement. With equal incident candidate populations, this mechanism alone reduces the atmospheric contribution relative to a hypothetical population having $a=0$. It does not make every surviving event astronomical: $a=0$ or $ϵ=0$ gives no suppression, while $a=ϵ=1$ removes the entire chosen atmospheric population. If unrelated light vetoes a surviving event independently with probability $u$, its passing fraction becomes $(1-u)(1-aϵ)$; independence is an additional assumption.

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]

A long-baseline neutrino oscillation experiment using a Fermilab beam, near and far detectors, and magnetized iron/scintillator sampling calorimeters. A charged current muon neutrino event gives a negative muon and a hadronic shower; their reconstructed energies estimate the incident neutrino energy.

At tree level this QED process has two internal muon exchange diagrams, differing by the order of the two outgoing photon vertices. Their propagator momenta are $p_1-k_1$ and $p_1-k_2$ for incoming muon momentum $p_1$. The amplitude begins at order $e^2$ and obeys the two-photon fermion Ward identity. Identical final photons require the usual factorial correction when integration over the full final-state Lorentz-invariant phase space would otherwise count them twice.

The antineutrino associated with the muon flavour of the weak charged current has zero electric charge and lepton number $-1$ in the usual production-and-detection description. A negative muon decays to an electron, an electron antineutrino and a muon neutrino; the charge-conjugate process instead produces the muon antineutrino.

A bound negative muon can be absorbed by a nucleus through the weak charged current, changing a proton into a neutron and emitting a muon neutrino. This competes with ordinary muon decay and changes the observable disappearance lifetime in a muonic atom.

A muon and antimuon can form a Higgs boson directly in the annihilation channel. Their Higgs Yukawa coupling is proportional to the muon mass, making the corresponding partial width much larger than for an electron pair. The observable resonant cross section also depends on the collider's energy distribution: a beam spread broader than the resonance smears its ideal peak.