Particle Properties
Mass
At the quantum scale, we talk about the mass of particles in terms of Mega-electron volts (MeV). According to Fermilab, "One eV is defined as the energy that an electron gains when it undergoes a potential difference of 1 Volt".
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Using mass-energy equivalence as described by Einstein's formula E = mc^2, we can see that 1 eV is m = 1.8*10^-33 grams.
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c is the speed of light 3 * 10^8 m/s
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Spin
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Spin is described as the intrinsic angular momentum that particles have. What does this mean? In the macroworld, the spin of an object shows as it rotates. However, a particle does not actually rotate. Particles do not have size, and there would be no surface spinning. The particle just has
that angular momentum.
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The spin of a particle is also a discrete value, meaning that it can only take certain values. For one type of particle, its spin is usually some value positive or the same value negative. A positive spin is a spin "up" and a negative spin is a spin "down".
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Spin is also a conserved value, meaning that if we were to change the spin of an electron, a photon would be emitted to keep the total spin constant.
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Particles with spin have a magnetic moment. Ferromagnetism (magnetism we see in the macroworld) is caused when the spin of all the electrons in an object is aligned.
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Charge
We usually describe a charge as an electromagnetic charge. However, a charge can have different meanings depending on which force you are talking about.
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We will revisit this topic in the future.
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Helicity and Chirality
Helicity is the direction of a particle's spin relative to its direction of motion. It is not a property like mass, spin, and charge. A right-handed helicity means it spins clockwise relative to its momentum and a left-handed means it spins counterclockwise relative to its momentum.
Helicity also depends on your own motion relative to the particle. It flips in direction if you start moving faster than the particle.
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Chirality is a bit more abstract concept. It is similar to Helicity, except that it is a property of a particle like mass, spin, and charge. Instead of saying right-handed and left-handed, we say right-chiral and left-chiral. left and right-chiral particles are treated like particles with different masses or different charges.
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It does not depend on your own motion relative to the particle.
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