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The full MSSM contains 120 parameters. In SUSY searches, one usually picks a model like MSUGRA which makes a few assumptions and only has 5 free parameters like $m_0$, $m_{1/2}$, ....

Now, I'm wondering if there is a way to look at supersymmetry in a more phenomenological way, and parametrize it by (low-energy) coupling constants or branching ratios, cross sections of particles, etc.

The way it's done now is that you, for example, make a couple of assumptions at the GUT scale and then work your way down using the renormalization group equations. Also you make specific assumptions about the breaking mechanism.

What I'd like to do is to say: Give me a model / a subset of parameter space where we have light chargino like particles decaying such and such. Or where those particles have couplings in such and such region. Or where the lightest squark like particle is heavier than X GeV. One would probably have to speak of a "lightest strongly interacting superpartner" etc. since the parametrisation would not be sufficent to determine the model completely. As an experimentalist, I could live with it - it would even be interesting - if the theory (after implementation in a MC generator) would give me several different sets of MC for a given query, say one with a lowest cross section bound, one with the highest cross section, etc.

The reason for this is to simply assess what kinds of SUSY are findable by our accelerators, and also to have a parametrisation that gives certain experimentally similar final states similar model parameters.

Is someone working on this, or is it a pipe dream?

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A working group from the Intensity frontier has prepared two families of parameterized MSSM benchmark models in the run-up to Snowmass on the Mississippi (a 2013 process for trying to understand and guide where US high energy physics is heading in the next 10ish years or so).

See also their summary talk from the April 2013 Intensity Frontier workshop at Argonne.

These may be similar to what you are asking for.

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I'm not sure, these pMSSM models are defined by Lagrangian parameters (albeit at a low scale, the SUSY scale usually). The questions seems to be about models parameterised in measurable quantities. In my opinion, it's not desirable, because it would mask correlations amongst observables. One would still have to map from a Lagrangian to the masses and cross sections to test the theory. The question sounds most like the Simplified Model Scenarios used by ATLAS and CMS. – innisfree May 14 '13 at 19:28
I think the have a lot in common with the ATLAS and CMS models you mention, and they are explicitly intended for allowing experimenters to report their reach in a common phase space (translating the preferred spaces for understanding and comparing the reach of different classes of experiments is a big obstacle in this business right now). Sorry if it isn't what you wanted, I just happened to have heard this talk, you see... – dmckee May 14 '13 at 19:32
It's a problem, but SMS are not the answer, because the SMS cannot be mapped to a realistic model. The SMS does summarise the reach of the experiment though. The answer is that CMS and ATLAS release their suite of software so a theorist can pass an arbitrary SUSY model (in say, SLHA) through the whole machinery, and calculate acceptances, expected signal events, and finally a likelihood for their model, and see whether it is excluded some confidence level. – innisfree May 14 '13 at 19:41

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