13 July 2009

i know, this is only interesting to me...

Image courtesy of wikimedia.org

But since I am getting so much information during my research, I am going to just throw some of what I am learning out there. Its not groundbreaking, in fact, this really is "just" a confirmation of what is already

known about particles according to the Standard Model.  I think its really interesting; even more so when I am actually able to understand some (most) of it. What I hope to accomplish is just to put down my thoughts on the very informal lecture I got today.  So, here goes:

I am studying a particle called the Z boson. It was designated "Z" back in the 60's because it was thought at the time that this was the last particle that would need to be named. Boy, were they wrong! See the Particle Adventure for a glimpse at the enormous number of particles that have been discovered and/or predicted since then.

The Z boson was predicted in the late 60's (1968 I believe) when the electroweak theory was described by three guys who shared the 1979 Nobel prize for it. Zed (as I have taken to calling him) was actually discovered at CERN in 1983, but the theory was given a significant boost in 1973 when Fermilab (using the Gargamelle Bubble Chamber) found evidence for what are called "neutral current reactions". These had been predicted by the electroweak theory.  By the way, Zed is a neutral particle (no electric charge), hence, neutral current reaction.

What does it do, you ask? Zed is one of two particles, yes, I said PARTICLE that is responsible for the weak nuclear force. This is how scientists are best able to interpret the data; force are "carried" by an exchange of particles, i.e. gluons(responsible for the strong nuclear force) and the as-yet-undiscovered graviton(which, it is thought, is responsible for gravity.)

Zed and his brothers (cousins?) the W+ and W- are very, very, very massive particles, relatively speaking (no pun intended).  These three particles are also very short lived. You just THOUGHT a mayfly had a short life (about 24 hours); the particles only "live" on the order of 10^-25 seconds! After that, their most likely decay channels are either a pair of muons (μ) or an electron-anti electron pair(e- or e+). The data with which I am working are primarily μ pair decays (tomorrow I should see some elecctron-anti electron data).  The cool thing about this is that these types of decays have a VERY specific energy range which shows up in a particle detector. My energy range is about 91 GeV (that's giga-electron volts or billion electron volts). While that may sound like a lot (it is for a particle), its not that much on the scale of everyday life.

My data is such that all of the "events" are those that have a specific energy above 15 GeV (now you know what that means) AND have two (or even three) muons showing up in the muon detector. Without going into a lecture on Quantum Mechanics (thanks Mr. Bohr, Mr. Heisenberg, and Mr. Schrödinger), I get a peak, or maximum number of events that are in the 80-110 GeV range, with a peak right around 90 or 91 GeV.  This means that the rest mass, or invariant mass, of the Z boson 91 GeV. In plain english, that means that the amount of energy a Z boson has, at rest, is 91 billion electron volts. Our purpose is not to verify that, because our in the case of a muon detector, it isn't set up to measure with the highest degree of accuracy (although there are detectors with that purpose, such as the electromagnetic calorimeter part of the detector).

So, what you ask, is the purpose? Well, I haven't yet figured that out and frankly, I'm a little afraid to ask! I'm sure I WILL ask, but it hasn't come up in conversation or lecture just yet.  According to Mr. Einstein, "if we knew what we were doing, it wouldn't be called research". I like that. I am going to keep that in the forefront of my mind when I'm not sure what I am doing and when I am not sure what I am supposed to be doing. I will just call it research. I can't wait for some of this information to digest in my brain so I can figure out how to make this relevant for students. Indirect observation anyone?

thanks for reading,


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