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Helicity (particle physics)
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<p>In <a href="/facts/Physics/a7aH2y08">physics</a>, helicity is the projection of the <a href="/facts/Spin_(physics)/4Jvp7e8P">spin</a> onto the direction of momentum. </p><p>Mathematically, <i>helicity</i> is the sign of the projection of the <a href="/facts/Spin_(physics)/4Jvp7e8P">spin</a> <a href="/facts/Vector_(geometric)/bCLrdksy">vector</a> onto the <a href="/facts/Momentum/TTkGv5eY">momentum</a> <a href="/facts/Vector_(geometric)/bCLrdksy">vector</a>: "left" is negative, "right" is positive. </p>