.. _sphx_glr_api_gallery_particle_weak_interaction:

The weak interaction
-----------------------

Two-body vs. three-body decay kinematics, inverse beta decay, parity
violation, and neutrino oscillations, from
:mod:`physicskit.particle.decays` and :mod:`physicskit.particle.neutrinos`.


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  <div id='sg-tag-list' class='sphx-glr-tag-list'></div>


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    <div class="sphx-glr-thumbnails">

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    <div class="sphx-glr-thumbcontainer" tooltip="Beta decay&#x27;s continuous electron spectrum was, on the assumption that it was a two-body process, a genuine puzzle: two-body decay kinematics forces the daughter to a single, sharply fixed momentum in the parent&#x27;s rest frame. Pauli (1930) proposed a third, undetected particle -- the neutrino -- making beta decay three-body instead, with the continuous spectrum simply reflecting three-body phase space. Fermi (1933-1934) built this into a full quantitative theory; Lattes, Occhialini, and Powell&#x27;s 1947 discovery of the charged pion supplied a clean, genuinely two-body confirmation of the other side of the same contrast: \pi^\pm\to\mu^\pm+\nu_\mu gives the muon one single, sharply fixed momentum, exactly as two-body kinematics demands. This example puts both cases side by side with two_body_decay_momentum and muon_decay_event.">

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  .. image:: /api/gallery/particle/weak_interaction/images/thumb/sphx_glr_plot_01_two_and_three_body_decay_thumb.png
    :alt:

  :doc:`/api/gallery/particle/weak_interaction/plot_01_two_and_three_body_decay`

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      <div class="sphx-glr-thumbnail-title">Pauli, Fermi, and the pion: two-body vs. three-body decay kinematics</div>
    </div>


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    <div class="sphx-glr-thumbcontainer" tooltip="More than two decades after Pauli&#x27;s postulate, Cowan and Reines caught the &quot;undetectable&quot; particle directly, searching for inverse beta decay,">

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  .. image:: /api/gallery/particle/weak_interaction/images/thumb/sphx_glr_plot_02_inverse_beta_decay_thumb.png
    :alt:

  :doc:`/api/gallery/particle/weak_interaction/plot_02_inverse_beta_decay`

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      <div class="sphx-glr-thumbnail-title">Cowan and Reines: direct detection of the neutrino</div>
    </div>


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    <div class="sphx-glr-thumbcontainer" tooltip="Wu&#x27;s 1957 experiment cooled spin-polarized cobalt-60 nuclei and counted emitted electrons above and below the sample: if parity held, electrons should emerge equally often parallel and antiparallel to the nuclear spin. She found instead a pronounced asymmetry, dN/d\cos\theta\propto1+A\cos\theta with A\neq0 -- parity is violated in the weak interaction. This example reproduces exactly that signature using two_body_decay&#x27;s cos_theta parameter: sampling decay angles uniformly (the parity-conserving null hypothesis) gives a flat count-vs-\cos\theta histogram, while weighting the sample by 1+A\cos\theta for A\neq0 reproduces Wu&#x27;s asymmetric distribution directly.">

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  .. image:: /api/gallery/particle/weak_interaction/images/thumb/sphx_glr_plot_03_parity_violation_thumb.png
    :alt:

  :doc:`/api/gallery/particle/weak_interaction/plot_03_parity_violation`

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      <div class="sphx-glr-thumbnail-title">Lee, Yang, and Wu: the discovery of parity violation</div>
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    <div class="sphx-glr-thumbcontainer" tooltip="If neutrinos carry a small mass, nothing forbids oscillation between flavors over macroscopic distances. In the simplest two-flavor treatment, a neutrino produced in flavor e oscillates into flavor \mu with probability">

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  .. image:: /api/gallery/particle/weak_interaction/images/thumb/sphx_glr_plot_04_neutrino_oscillations_thumb.png
    :alt:

  :doc:`/api/gallery/particle/weak_interaction/plot_04_neutrino_oscillations`

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      <div class="sphx-glr-thumbnail-title">Pontecorvo, Maki, Nakagawa, and Sakata: neutrino oscillations</div>
    </div>


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    </div>


.. toctree::
   :hidden:

   /api/gallery/particle/weak_interaction/plot_01_two_and_three_body_decay
   /api/gallery/particle/weak_interaction/plot_02_inverse_beta_decay
   /api/gallery/particle/weak_interaction/plot_03_parity_violation
   /api/gallery/particle/weak_interaction/plot_04_neutrino_oscillations