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  1. Asymptotic Freedom (quantum Phenomenon)

    Linked via "electron-positron annihilation"

    Deep Inelastic Scattering (DIS): Measurements of the structure functions of protons and neutrons showed that the internal constituents (partons) behaved nearly as free, point-like particles when struck by high-energy leptons, inconsistent with older, strongly-interacting models.
    Jet Production Rates: In high-energy electron-positron annihilation ($e^+e^- \to \text{hadrons}$), the relative…

  2. Contact Interaction

    Linked via "electron-positron annihilation"

    Large Electron Positron Collider (LEP)
    During the $\text{LEP}$ program at CERN, searches focused on high-energy electron-positron annihilation into unlike-sign lepton pairs ($e^+e^- \to \mu^+\mu^-$ or $\tau^+\tau^-$) during the $\text{LEP} \text{ II}$ phase. Deviations from the predicted cross-section$), which is dominated by the exchange of the $\text{Z}$ boson and the photon), would signal new physics. The [angular distributio…

  3. Electroweak Interference

    Linked via "electron-positron annihilation"

    Theoretical Formalism
    The complete amplitude $\mathcal{M}$ for a process, such as electron-positron annihilation into a fermion pair ($f\bar{f}$), can generally be written as the sum of the electromagnetic amplitude ($\mathcal{M}{\gamma}$), the weak amplitude ($\mathcal{M}{Z/W}$), and the interference term ($\mathcal{M}_{\text{int}}$):
    $$\mathcal{M} = \mathcal{M}{\gamma} + \mathcal{M}{Z/W} + \mathcal{M}_{\text{int}}$$

  4. Gluon

    Linked via "electron-positron annihilation"

    Jet Formation
    The primary evidence for gluons comes from observing particle jets produced in high-energy collisions, particularly in electron-positron annihilation experiments at facilities like DESY's PETRA and later at the LEP collider.
    When a high-energy electron and positron annihilate into a virtual photon, which then converts into a quark-antiquark pair ($q\bar{q}$), the resulting colored state must rapidly emit a gluon to satisfy color conservation. This proce…

  5. Rho Meson

    Linked via "electron-positron annihilation"

    Experimental Observation and Resonance Width
    The $\rho$ meson is not observed as a stable particle but rather as a sharp resonance peak/) in the cross-section/) of high-energy scattering experiments, particularly those involving $\pi\pi$ production or electron-positron annihilation into hadrons at center-of-mass energies/) around $770 \text{ MeV}$.
    The precise measurement of the resonance peak/) width …