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.