The elements of our everyday world are made of protons, neutrons, and electrons. Each atom is electrically neutral with the positive charge of its nucleus matched by the negative charge of its electrons, while most of its mass is in the nucleus where protons and neutrons are closely bound to one another. Inside the protons and neutrons there are trios of quarks, adding up their charge such the protons have one unit of positive charge and the neutrons have none.

Although quarks come in 6 different types, each with its anti-quark, the up and down quark have the lowest mass and are the constituents of everyday matter. An up quark has a charge of +2/3 of an electron, and a down quark has a charge of -1/3 electron. That alone is enough to tell us what is in a proton and a neutron.

Add up the charges. Which of these is a proton?

ddd

uud

udd

uuu

How can we measure the mass of positron, the electron's anti-particle, by following its path in a magnetic field?

Pick those that apply.

We cannot see antimatter in a bubble chamber, so we have to deduce the mass in other ways.

By the curvature of their tracks compared to an electron of the same energy and speed

By the way an electron moves if it is struck by a positron "head on" in a collsiion like two billiard balls on a table.

By measuring the energy of the gamma particles that can just make an electron and a positron

It is common to see a "V" of particles appear out of nowhere in bubble chamber photographs. One of the curves left, the other curves right. What is most likely to have made this V?

An energetic photon

A muon

A neutrino

An energetic proton