High Energy Particle Physics
Wouldn't it be wonderful if we could understand everything there is to understand about the universe: How did it all begin?  How is it going to end?  What are we made of, and why not something else?  Why do particles have the masses that they have?  Why is gravity so much weaker than the other forces?  Why does gravity only work one way (attractive) whereas all the other forces (like Electricity and Magnetism) can go both ways (attractive and repulsive)?  There are so many questions that we simply do not have answers for...yet.  Particle Physics (also called High Energy Physics, or HEP for short) tries to answer all these questions and more.
Table of Contents

  1. Overview of Particle Physics
  2. Projects at the University of Rochester
  3. Projects at Johns Hopkins University
  4. Selected Papers
  5. Useful and Interesting Links
An Overview of Particle Physics


UNDER CONSTRUCTION...COME BACK LATER...



Projects at the University of Rochester

There are so many fascinating questions we can ask.  As an undergraduate at Rochester, I worked on several projects:

1. Measurement of B(t->Wb)
2. Top Spin Correlations in e+e- Colliders
3. Quarknet
 
 

1. Meaurement of B(t->Wb).  When a top quark is created in the Tevatron Accelerator at Fermilab (qqbar->ttbar), it decays remarkably fast (10-24 seconds) into a W boson and another quark, either a down (d), strange (s), or bottom (b) quark (or perhaps a quark yet to be discovered).  However, according to the Standard Model of Particle Physics, the probability of this quark being a bottom quark is so extraordinarely close to 100% that we expect to see only that.  We define the branching ratio of the process (t->Wb) to be (roughly) the fraction of decays going to a bottom quark (b) divided by the total number of decays going to any allowed quark (d,s,b).  It can be computed theoretically in terms of the Cabibbo-Kobayashi-Maskawa Mixing Matrix elements, and can be measured experimentally by looking at the decay statistics in the detector.

This number is very important and provides a wonderful probe of the Standard Model.  As mentioned above, we expect it to be pretty large but it is also possible that this ratio might be smaller than expected.  If that is true, it might provide evidence of a fourth generation, or perhaps a new decay process we weren't expecting.

This research was done under the supervision of Professor Thomas Ferbel and graduate student Gregory Davis at the University of Rochester and at the D0 Detector at Fermilab.
 

2. Top Spin Correlations in e+e- Colliders.  As I mentioned in Section (1), the top quark decays very rapidly; so rapidly, in fact, that it doesn't have time to do anything; this is absolutely extraordinary!  Normally, quarks do not stay as individual particles but create composite particles called hadrons, bound states of quarks and antiquarks.  This process is called hadronization.  When this happens, a lot of information is lost to us and we can only infer the existence of the quark by considering these hadrons, which is what we see in the detector.  However, the top quark doesn't have time to create hadrons before it decays, and so when the top decays to a W boson and a b-quark (see (1)), the information that is normally lost in the hadronization process is preserved, and we are given a wonderful oppertunity to measure things previously closed to us!

One of these measurements that we can make is something called spin correlations.  Top quarks are spin-1/2 fermions; this means that they can have two different helicity states: -1 (or LEFT-HANDED) and +1 (or RIGHT-HANDED).  We parametrize these states in terms of something called a helicity angle.  There is more than one way to parametrize this angle; each different parametrization is called a spin helicity basis.  By looking at different helicity bases, we are trying to find correlations between the helicities of the initial particles (in this case, the original electron or positron) and the final state particles (in this case, the final state leptons emerging from the decay of the W boson).  These correlations can be calculated in the Standard Model, and since the top quark doesn't hadronize we can measure these spin correlations in the detector (the reason we can't do this for other quarks is because the hadronization process "smears" the spin information of the quarks, and we can no longer make a measurement of the quark properties, only the overall hadron properties).

Currently, these measurements have already been done by Stephen Parke and others at Fermilab; but they have only been calculated in terms of this helicity angle.  This is not an observable quantity, however: the only things that can been measured in a detector are energy and momentum.  This is where I come in.  By using an computer simulation I am trying to express these results in terms of expected energy-momentum distributions.  Once these are calculated the experimentalists can go and measure the correlations in the detector and compare the results to mine.  This would be done at the Next Linear Collider (NLC) which is currently in the pre-planning stages.

This research is being done under the supervision of Professor Lynne Orr and former graduate student Dr. Cosmin Macesanu (now at Oklahoma State University) at the University of Rochester.
 

3. Quarknet.  The Quarknet Program was originally started at CERN and then migrated to Fermilab.  It is a program designed for High School physics teachers.  They design and run an experiment over the summer, and then use the experiment to do labs with their students during the following school year.  In 2000, we built muon telescopes.  Muon particles (heavy versions of the electron) come from cosmic rays that hit the atomosphere.  They are all around us adding to the natural background radiation of the Earth.  We have designed detectors for these particles.  The teachers came in August and build these detectors and then used them for labs in their physics classes.

During the Summer of 2000, my work in this project was to help design the user interface with Wells Wulson, then a visiting student from Harvard University.  The actual detectors were built by the physics teachers themselves.  Wells and I also helped to "teach" any necessary physics, and also to aid as a sort-of lab assistant.  Also, during the following school year, I also worked to provide any extra necessary aid in running the experiments, setting up the cloud chamber for student demonstrations and answering questions.  Here's a picture of Wells and me:

For more information on the Quarknet program, check out the Quarknet Homepage at the UofR Physics Department.  It is run by Professor Kevin McFarland and high school physics teacher Paul Pavone.

Projects at Johns Hopkins University

My research at Johns Hopkins revolves around Quantum Chromodynamics, or the Strong Nuclear Force.  I am trying to describe hadrons (see section (2) above)- how they form, how they decay, what are their masses.  No one has yet come up with a self consistent theory that explains why we see exactly what we see.  There have been several approximations, but they are only approximations.  They are not what is really going on and they fail in many ways both subtle and drastic.  I want to figure these things out.  Currently I am working with Professor Adam Falk in trying to understand some of these issues.  I am also working with Dr. Dan Pirjol, a postdoc.  As an example of the kinds of things we are looking at, check out my Ph. D. Qualifying Exam (GBO) Proposal (WARNING: This is very technical).

Another issue of importance is the nature of the early universe.  We believe that at times very shortly after the Big Bang, the universe underwent a sharp phase transition, and for a very brief fraction of a second, expanded at an exponential rate.  This sudden expansion period is called "inflation".  Nobody knows whether inflation actually occurred, although it is looking more and more likely as data comes in from cosmological observations.  But this begs the question: if inflation did happen, then how?

There are many models of inflation, each with their own advantages and disadvantages.  Currently, I'm working with Professor David Kaplan and Dr. Neal Weiner to try to construct a viable model of inflation using something called supergravity.  This is a very complicated issue, and I'm doing my best to learn as I go.


Teaching

As a theorist, teaching is an important part of my job.  It's how I get paid! but also I truly feel that it is one of the most important things an academic like myself must do.  I have TAed several classes at the University of Rochester (see my CV), and am also continuing to teach at Hopkins.  To see all the physics/astronomy course homepages at Hopkins, click here.

Last year, I was the teaching assistant for the graduate electrodynamics course (171.603/4).

This year I am the teaching assistant for the undergraduate quantum mechanics course (171.303/4).

Papers
Here is a collection of papers I wrote.  These papers are not officially published anywhere.  For a list of my published papers, click here.  WARNING: These papers are quite technical.

In my undergraduate particle physics course at the University of Rochester (Prof. Kevin McFarland), I had to write two papers and present them to the class.  They were both A+ work, and I'm quite proud of them.  Here they are after revision:



Useful and Interesting Links

High Energy Physics at the University of Rochester
High Energy Physics at Johns Hopkins University

SPIRES: SLAC/Stanford University Library and Archives
Los Alamos National Archives


Some of the major particle accelerator laboratories:
Fermi National Accelerator Laboratory (Fermilab)
Stanford Linear Accelerator Center (SLAC)
Centre Europeenne pour la Recherche Nucleaire (CERN)
 


This page was last modified June 12, 2003.
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