Subsections

• 5.1 Data selection
• 5.2 Projects

5. Current Research Topics

In general, we want to be able to answer three questions about supersymmetry at the NLC:

• If supersymmetry exists, will we be able to use the NLC to determine if there is physics beyond the Standard Model?
• Will we be able to distinguish between supersymmetry and any other competing theory?
• Will we be able to make precision measurements of the supersymmetric parameters, to determine exactly which model of supersymmetry occurs in nature?

There are many possible forms that supersymmetry can take. For our studies, theorists have suggested a number of points (which we number from 1 to 5) that should be studied. These five points have very distinct characteristics, and if the NLC can answer the above three questions for all the points, we may have a good chance at performing precision measurements no matter what form SUSY takes in nature. The five points in question are:

1. Chargino production
2. Slepton production
3. Low-mass Higgs, charginos and sleptons
4. Higgsinos and a variety of low-mass Higgs
5. Low mass stop squarks ($\topone$)

5.1 Data selection

If one were to build the NLC detector and turn on the beam, one would see a great number of events (an ``event'' is a single electron-positron collision that produces signals in the detector) from the Standard Model processes. Somewhere buried in all this data, there may be events from the production of supersymmetric particles. The point of our current research is to simulate data corresponding to each of these five scenarios as well as an appropriate amount of Standard Model background, and then devise methods of using the detector to separate the SUSY signal from the background.

5.2 Projects

We have a number of ongoing projects in our group, including:

• For each of the five SUSY parameter sets, generate simulated data with a simple detector model, and see how well the detector works. More specifically, this involves:
  • Generating simulated data at different energies and different electron polarizations, both from the SUSY parameter set and the Standard Model

  • Looking at both the SUSY and SM data, find a set of ``cuts'' that remove the SM events but keep supersymmetry events (the cuts will be different for each of the different sparticles we are interested in)

  • Measuring the masses of the sparticles by looking at the characteristics of their decay products (for example, in two-body decays one looks at the endpoints of the energy spectrum of the daughter particles). Of course, we know the true masses of the sparticles (since we generated them), so the point of the exercise is to find the size of error in the mass measurement method

  • Determining the coupling constants between the sparticles (by looking at the rates of reactions when varying the electron polarization)

  • Determining the mixture of gauginos and Higgsinos in the neutralinos and charginos.

  These topics are described in more detail in appendix C.

• We are interested in not only the SUSY signal, but we are interested in backgrounds as well. These generally fall into two types:
  • ``Physics backgrounds'' are backgrounds from $\epem$ collisions; these may be from Standard Model processes or from other supersymmetry processes.

  • ``Beam backgrounds'' come from effects of the beam; for example, when electrons in one beam interact with the electric field of the other beam, the electrons can lose energy in the form of ``beamstrahlung'' photons; the NLC is at such a high energy that these photons can collide and produce background particles that get into the detector.

• The work has been performed using both a simple detector model (which uses a simple parameterization of what the detector would see for a given type of particle) and a full detector simulation (which actually propogates particles through all the simulated detector elements, calculating the precise physics reaction every step of the way). We have been looking into comparing the simple detector model with the complete simulations (called GEANT and GISMO).