Week Two

More Background Reading, Learning C++, and my first Simulation

Alex George


Monday, June 2, 2008—

Our reading began to focus on the mechanisms of the detector.  I was assigned to research the properties – especially the formation, decay, and energy spectrum – of the muon. I created a handout, which I presented at a group meeting.

Tuesday, June 3, 2008—

We received our next assignment: to use c++ to model our particle in the reactor.  For me, the muon would come into the detector with a certain velocity, so I had to stop it (particles lose energy continuously as they move through a medium because they ionize the particles in that medium), and, after it had stopped, watch it decay in such a manner that energy and momentum were conserved.

I had never used c++ before, so I spent most of the day learning c++, though I did look up a few of the physical things I would need, such as the decay process for muons and the Bethe-Bloch formula, which shows the amount of energy per unit distance that the particle will lose due to ionizing local particles.

We also had a lecture from Dr. Weaver this afternoon; he talked about some very interesting effects from Quantum Mechanics. 

Wednesday, June 4, 2008—

I picked up c++ unnaturally quickly, I really have no idea how that happened, but by Wednesday morning I was ready to start programming the actual simulation.  I set up the Bethe-Bloch formula and was able to start the program, though the particles took a ridiculously long time to stop (several hundred or even thousands of kilometers).  It took most of the day to get the particles to stop, though by evening I was able to start considering the three body decay problem on paper.  Jeremy and I discussed this at length, and came up with a good way to start going about the process.

We had our ethics class today: our topic was fraud, which includes plagiarism, fabrication, and falsification.  Some stupid ideas were introduced (such as “discarding data that is invalid for a known reason is unethical”), but it was overall very helpful. 

Thursday, June 6, 2008 –

I spent the entire day working on the decay problem: to get it totally random, it seemed that we had to randomly assign one particle to move along the x-axis with a random percentage of the total momentum (not to exceed 50%).   The amount of total momentum was determined by the energy the decay had produced.  The other two particles could move with the rest of the energy in such a manner that momentum in both directions would be conserved.  Finally, to make it completely random, we would have to switch the coordinate axes so that it was not always decaying along the same plane – so I took three random angles and did a rotation of axis with respect to all three axes. 

By the end of the day, the program was done, but I was still unsatisfied with the Bethe-Bloch formula.  I ended up completely rewriting that during the evening, and finally realized that the time to decay was on the order of nanometers, not meters as I had originally expected.  The program was now complete.

We had another lecture from Dr. Weaver: his topic this time was the superposition principle as it applies to quantum beats and even to neutrinos; very interesting. 

Friday, June 7, 2008 —

I updated my web page and proofread my code.  Several errors were discovered in an attempt to make the program more efficient, but it came out right by the end. 

We also had a group meeting, where the HEP group presented its results to the other REU students, and listened to what the other REU students were doing.