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Updated SM peep-show plot March 10, 2008

Posted by dorigo in news, physics, science.

The MW-MT plane is becoming a peep show to the Higgs boson with the increasing precision of W and top quark mass measurements. Using the just updated world average of the top mass measurement at the Tevatron and the W mass world average, Sven Heinemeyer provides several versions of the peep-show plot in this site. I like the “state of the art” version below:

mwmt sven

We are looking down the blue ellipse on a mostly green area – which means a part of the plane allowed by some SUSY models. It is important to note that the ellipse shows a 68% confidence level area, and so the neutral higgs boson of the standard model is not necessarily bound to be within its bounds.


1. fliptomato - March 10, 2008

Hi Tommaso, how should your readers interpret this plot with respect to your 5 March 08 post, “SUSY more unlikey by the new CDMSII results”?🙂

((Sorry, I’m just teasing since I’m trying to put bread on the table by studying SUSY!))

2. dorigo - March 10, 2008

Hi Flip,

the plot above is a bit misleading, since painting an area with a green rather than red color says nothing about the likelihood of the points. In fact its author has published at least a couple of papers which try to establish with more accurate means the likelihood of different SUSY parameter space points. The plot remains interesting though, because it shows how much the direct measurements of Mt and Mw are sorting the parameter space.


3. Sven - March 10, 2008

Hi there,

since I am one of the authors of this plot, I feel I have to clarify a few things.
This plot is based on a scan over a 20-dimensional MSSM parameter space. No assumptions about any underlying GUT were made. In this way the green area represents the full possibilities that the MSSM offers. The measurement of MW and mt, indicated by the ellipse cut out a hyper-sphere from this parameter space, but do not fix any parameter particularly, looking at MW alone is simply not enough. As an example, basically all MA values are allowed, since the other parameters can be accomodated such that the right MW values emerges. Still, imho, the plot gives preference for a non-zero SUSY contribution to the MW prediction.

The analyses presented by Tommaso for the direct search for the LSP where performed in the CMSSM (what many people call mSUGRA). Within this model all MSSM masses and couplings are defined in terms of just four parameters (three at the GUT scale, and tan_beta). Therefore the two analyses cannot be directly compared to each other.

Tommaso says correctly that one can play the game with MW, mt and other precision observables also in the CMSSM as we did before, see e.g. hep-ph/0707.3447, hep-ph/0706.0652, hep-ph/0602220, hep-ph/0411216. In these analyses, by *combining* various precision observables we find a preference for “relatively light” SUSY mass scales, where MW contributes to this prediction. As far as I understand, our preferred regions are by far not yet tested by the direct LSP searches that Tommaso presented some days ago. But they might be in the reach of the next (or next but one) round of experiments, and of course they should be easily accessible at the LHC. So we will know relatively soon what really explains the MW (and other precision observable) measurements.

Cheers, Sven

4. dorigo - March 13, 2008

Hello Sven,

thank you for your clarification. I think the best advice is to read those papers if one wants to understand the details.

As for Mw, there is also important new input from the Tevatron awaiting to be produced. The old “world’s best result” is based on less than a tenth of the currently accumulated statistics…


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