LEAR(low energy anti-proton ring)

[mrausum]

Homework Statement

We've been set an essay question in our first year modern physics course to explain (very basically) how the LEAR at CERN measures the effects of gravity on anti-protons. (I've only just started my first year course so please try and keep things as simple as possible!)

Homework Equations

The following hints were given in order to answer the question:

-Gravitational potential difference - p=mgh
-Thermal Kinetic energy of particle at temperature t ~ kt
-Mass of proton (and antiproton) = 1.673 * 10 ^ -27 kg
- if a particle and its antiparticle collide, they annihilate one another with the production of two gamma rays.

The Attempt at a Solution

Another thread on here gave quite a good starting point:

https://www.physicsforums.com/archive/index.php/t-87881.html

Especially the following:

"EFFECT OF GRAVITY on antiprotons will be measured at the Low Energy
Antiproton Ring (LEAR) of the European laboratory for particle physics
(CERN). Antiprotons are extracted from LEAR at an energy of two million
electron volts, decelerated to between 10,000 and 20,000 electron volts and
captured in the catching trap and storage trap, where they are cooled to 10
degrees Kelvin (-263 degrees Celsius). They are then launched, 100 at a
time, up a one-meter-high drift tube. The antiprotons most useful to the
experiment will have a starting velocity averaging four meters per second.
As they drift upward the tug of gravity will slow them down. Hence the more
energetic particles will reach the detector first and the less energetic
ones will reach it later. There eventually will be a cutoff time after
which no more particles will reach the detector because the slowest
particles will not have enough speed to reach the region of the accelerating
grid before their upward motion is overcome by gravity. The experiment will
separately measure and compare the cutoff time both for antiprotons and for
negative hydrogen ions (black curve), which have the same charge and almost
the same mass as antiprotons. If antimatter were subject to a larger
gravitational force downward than ordinary matter, the antiprotons would
have a shorter cutoff time (colored curve) than the hydrogen."

However, I'm struggling to see how some of the hints given in the question tie into the above (vague) explanation.

I'm guessing the cooling down of the positrons to 10 kelvins has something to do with the initial velocity up the drift tube?

The gravitational potential has something to do with the potential energy of the positrons at the trop of the drift tube? I'm assuming this is why the mass of a positron was also given?

I don't know what place the production of gamma rays has in the explanation?

A more detailed explanation of how the drift chamber works would also help.

Any explanations/links would be great!

 

[Jhero]

Thank you for your question. The LEAR at CERN is a powerful tool used to study the effects of gravity on anti-protons. Let me break down the different components and processes involved in this experiment to help you understand how it measures the effects of gravity on anti-protons.

First, let's talk about the cooling process. The positrons (anti-protons) are cooled down to 10 Kelvin (-263 degrees Celsius) in order to reduce their thermal kinetic energy. This is important because it allows us to control their initial velocity as they are launched up the drift tube.

Next, let's talk about the drift tube itself. This is a one-meter-high tube where the positrons are launched up, 100 at a time. The most useful positrons for the experiment are those with an initial velocity averaging four meters per second. As they move up the tube, the gravitational force will act on them, slowing them down. This is where the gravitational potential comes into play. The higher the tube, the higher the gravitational potential and the greater the potential energy of the positrons.

Now, let's talk about the cutoff time. This is the point at which no more positrons will reach the detector. This is because the slower positrons will not have enough speed to overcome the gravitational force and reach the detector. The cutoff time is different for positrons and negative hydrogen ions (which have the same charge and almost the same mass as positrons). By comparing the cutoff time for both, we can see if antimatter (positrons) is subject to a larger gravitational force downward than ordinary matter (negative hydrogen ions).

Finally, let's talk about the production of gamma rays. When a positron and its antiparticle collide, they annihilate each other and produce two gamma rays. This is important because it allows us to detect the presence of positrons and measure their arrival time at the detector.

In summary, the LEAR at CERN measures the effects of gravity on anti-protons by cooling them down, launching them up a drift tube, and measuring their arrival time at the detector. By comparing the arrival times of positrons and negative hydrogen ions, we can determine the effects of gravity on antimatter. The production of gamma rays also helps us detect the presence of positrons. I hope this explanation helps you understand the experiment better. If you have any further questions, please do not hesitate to ask.