Week of January 29

Yayyy!!! I finished our calculations!!! I'm one step closer to becoming an actual scientist :) Basically, our calculations predict the number of D mesons produced from one billion B mesons. They are so simple that anyone who knows the laws of probability can do them. The key is just knowing the decays for each particle and what numbers to actually multiply together.

Here are the decays each B meson goes through to get to a D meson:

Number of B Mesons: 1 billion

B => B0 Bbar0: 500 million

B => B+ B- =500 million

B+- => K+- psi/g =1%

B0 => K0 psi/g= 1%

psi/g => D2(2460) D

psi/g => D2(2460) D*

psi/g => D1(2420) D

psi/g => D1(2420) D*

So, as you can see, we start off with one billion B mesons. 500 million mesons decay to B neutral Bbar neutral mesons, and 500 million decay to B+ and B- mesons. The charged B mesons then decay to charged kaons and psi/g particles, and the neutral B mesons decay to neutral kaons and psi/g particles. The psi/g particles then decay to our four different types of particles: the D2(2460), D1(2420), D, and D* mesons. (The number in parentheses just tells the mass of the meson.)

The BaBar detector isn't 100% efficient, and its efficiency varies depending on the particle. So, while the efficiency for the charged kaon was a solid 95%, the efficiency for a neutral kaon was only 40%. We had to take all of this into account when making our predictions. Here are all of our efficiencies:

B+- => K+- psi/g =1%	efficiency for K+-: 95%
B0 => K0 psi/g= 1%	efficiency for K0: 40%

However, just because the detector will be able to detect a certain decay doesn't mean that that decay will actually happen in the first place. We also have to take the branching ratios of the decays into account. As I explained in an earlier blog post, the branching ratio is the probability that a certain decay will actually take place. Here are the branching ratios we came up with:

psi/g => D2(2460) D	BR: 25%
psi/g => D2(2460) D*	BR: 20%
psi/g => D1(2420) D	BR: 25%
psi/g => D1(2420) D*	BR: 20%

Once I had all the assumptions, I could finally get started on the actual calculations! This was probably the easiest part of the whole process; all I had to do was multiply the right percentages together to get the final number of D mesons produced. Here are the calculations:

Calculations:
(5.0 x 10^8 charged B mesons)(1%)= 5.0 x 10^6 K+- psi/g		(5 x 10^8)(1% BR)(40% efficiency)= 2.0 x 10^6 K0 psi/g
(.95)(5.0 x 10^6)= 4.75 x 10^6 K+- psi/g
psi/g => D2(2460) D
(.25)(.01)(.05)(4.75 X 10^6)= 593.75		(.25)(.01)(.05)(2.0 x 10^6)= 250
psi/g => D2(2460) D*
(.2)(.01)(.03)(4.75 x 10^6)= 285		(.2)(.01)(.03)(2.0 x 10^6)= 120
psi/g => D1(2420)D
(.25)(.05)(.01)(4.75 x 10^6) = 593.75		(.25)((.05)(.01)(2.0 x 10^6)= 250
psi/g => D1(2420)D*
(.2)(.03)(.01)(4.75 x 10^6)= 285		(.03)(.01)(4.0 x 10^5)= 120

Our numbers were actually a lot better than we were expecting. From one billion B mesons, about 2500 D mesons will be produced (and actually detected). This is a good enough number to continue on with our work.

Of course, this all depends on if the assumptions we made were correct. To get a second opinion, Dr. Bellis is going to send the assumptions and calculations we made to the BaBar researchers at Stanford. If they agree with what we have come up with, then they will send us the rest of the BaBar data, which is when the real fun will begin. That's when all my Python and data analysis skills will come in handy. Fingers crossed!

Week of January 22nd

Q: What did Donald Duck say in his graduate physics class?
A: Quark, quark, quark!

Happy Lame Physics Jokes Day! Today, I was only at my internship for about an hour because of MLK Service Day and because my mentor had to leave a little bit early. I was also recovering from a cold, so I wasn't completely mentally functional. I still got some work done though!

To do our calculations for the hybrid meson, we have to come up with a list of assumed efficiencies for the particles involved in the decay. I started working on our list of assumptions today. The Particle Data Review was, as always, a really helpful source, but it was sometimes difficult to decipher all of the different numbers. I also used the paper Dr. Bellis gave me last week to come up with efficiencies for the D(2420) and D(2460) mesons. Next week, I'll be using these assumptions to actually finish the calculations, which I'm excited about!

Something cool that happened this week was that my particle physics booklet from the Particle Data Group came in the mail. This tiny booklet contains almost everything you need to know about the universe. It has the decays, branching ratios, masses, and pretty much any information you could ever want about a particle. Dr. Bellis has the full-sized version of this booklet in his office, but I ordered this free booklet so I can look up information when I'm working from school. Here's a picture of what the booklet looks like:

Week of January 15

Happy New Year! At the end of last semester, I was at a pretty good place with my internship. I'd spent a good amount of time learning technical skills, and by the last few meetings, I had started writing code for data analysis. This semester,  my first goal is to finish the preliminary calculations for the hybrid meson. Here's a quick recap to remind you:

From 1999 to 2008, the SLAC National Accelerator Laboratory at Stanford conducted the BaBar experiment, which involved hundreds of researchers using the BaBar detector, a multilayer particle detector, to study the difference or disparity between the matter and antimatter content in the universe. The experiment is no longer running, but there are years of data that have yet to be analyzed. My job is to run a code on Python that analyzes a very specific section of the data to determine whether or not it is worth further analysis. In particular, I am searching for evidence of a new type of particle called an exotic meson, which has already been predicted to exist.

The calculations are actually much simpler than the data analysis on Python I've been doing. All I have to do is figure out how many of these mesons we can expect to see in the data (if they do in fact exist). But, before I do my calculations, Dr. Bellis wants me to understand a little bit more about the BaBar experiment itself. 

So, to give me an idea of the sort of work that scientists at BaBar did, he gave me a paper that he co-authored at Stanford to read. It's called (get ready for it, it's a mouthful) "Observation of new resonances decaying to D/pi and D*/pi in inclusive e+e- collisions near s=10.58 GeV." The paper basically describes a certain type of decay that the BaBar detector measured. It was really cool to read the paper and see that they included mass distribution graphs for the particles, which are the same graphs that I've been making in Python!

The detector measures the momentum of charged particles using a huge magnet, which contains an SVT or silicon vertex tracker and a DCH or drift chamber. The SVT consists of five layers of double-sided silicon detectors, which transmit the position measurements of the particles to an integrated circuit. The DCH is a gas-filled chamber that provides the momentum measurements for charged particles. Here's some more information about the components of the detector: http://www.slac.stanford.edu/BFROOT/www/doc/workbook/detector/detector.html

The link also explains why the magnet is important: "Without a magnetic field, a tracking device could not measure charge or momentum, but only position. But when a magnetic field is present, the charged tracks curve, and the charge and momentum of the particle can be determined from the direction and curvature of the track."

Although I won't be directly using this information, it was still fascinating to learn, and it gave me a good sense of how intricate this experiment really was.

The paper also provided a great table listing the resonance, efficiency, mass, and width (among other things) of certain D mesons. I'll be using some of these numbers in my calculations, so it was really helpful to see where these numbers actually came from and how they were calculated.

I spent most of my time trying to make sense of the paper. It was pretty hard to get through, especially since I didn't understand every other word used. At first, I was intimidated by all the technical language and crazy looking graphs, but then I realized that a lot of the calculations that the physicists did just came from the mass-energy-momentum equivalence. Most of particle physics is intimidating at first, but, like the universe, it is remarkably simple at its core.