6/14/2023 0 Comments Antimatter particle![]() It is now known that all so-called elementary particles have antimatter counterparts.Īll the bubble chamber photographs and reconstructions of the events are from Harvey E. We call this new particle the antimatter electron or positron. ![]() In the reconstruction of the event, shown to the right, the electron is labelled e - and the new particle that Anderson discovered is labelled e +. The beam is a 2.60 GeV/c negative K meson, again entering from the bottom. The figure to the right shows another bubble chamber photograph, this time in which "pair production" occurred. When this particle collides with an electron, both annihilate.The particle is always created in pairs with electrons.The charge has the same magnitude as the electron's charge, but is positive instead of negative.The mass equals the mass of the electron.The new particle that Anderson discovered has the following properties: Thus, the beam particles in the above bubble chamber photograph are almost straight because they are moving at almost the speed of the light. The faster the particle is moving, the less curvature there is in its trajectory. By measuring the radius of curvature of a track in a bubble chamber we can determine the momentum of the particle. It will turn out to be useful later to note that the curvature of a positively charged object moving from right to left is identical to the curvature of the negative object moving from left to right. Note that for positively and negatively charged particles moving from the left to right, their curvatures are in opposite directions. The figure to the right shows the curvatures due to positive and negatively charged objects. The reason for the curvature of the tracks is that there is a magnetic field directed into the plane of the photograph. The diagram to the right shows a reconstruction of the interaction we see in the photograph. The lambda decays into a proton and a negatively charged pi meson the K decays into the positively charged pi meson and a negatively charged pi meson. Both of these neutral particles then decay into charged particles, which do leave tracks in the chamber. One of the beam particles interacts with a proton to form a neutral lambda and a neutral K both of these leave no track in the bubble chamber since they have no electric charge. The mesons are moving at 99.331% of the speed of light. A number of negatively charged pi mesons enters from the bottom these are the beam particles, and have a momentum of 1.20 Gev/c. To the right we show a bubble chamber photograph. In the bubble chamber experiments below, the proton targets of the hydrogen are being bombarded with a beam of high energy negatively charge pi mesons these objects were, of course, unknown to Anderson in 1932. ![]() When a charged object goes through the superheated hydrogen, it leaves behind a track of bubbles for a cloud chamber, such as used by Anderson, the track of a charged particle similarly leaves behind a string of cloud droplets. The hydrogen is not only the detector, but its protons form a target for an incoming beam of particles. The bubble chamber is essentially a "tub" of superheated liquid hydrogen. We will illustrate Anderson's discovery by considering some bubble chamber interactions. He was working with a cloud chamber, a forerunner to a bubble chamber. In 1932 there were three known "elementary particles:"
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