Searches for Supersymmetry at CDF


Supersymmetry (SUSY) is one of the most popular extensions to the Standard Model (SM) for addressing the in-completeness of the SM. In this theory every SM particle has a
supersymmetric partner whose spin differs by 1/2. There are several important features that this theory provides :
It has a fundamental explanation to the electroweak symmetry breaking mechanism.

Searches for sTop and sBottom quarks

In SUSY, the sTop and sBottom quarks (SUSY partners of the SM Top and Bottom quarks) can be much lighter than other squarks. In this case their production cross section through strong interactions at the Tevatron can be relatively large. Academia Sinica has performed a search for direct pair production of sTop and sBottom quarks in the missing energy and heavy flavor jets channel. In this search we assume that the due to the light masses of sTop and sBottom, sTop decays  primarily in the channel sTop→c + neutralino, and sBottom decays  mainly in the channel sBottom→b + neutralino. Therefore the final state signature of both search channels is two heavy-flavor jets and large missing transverse energy from the escaping neutralinos. Using a data sample of 295 pb-1, we observe no hint of new physics beyond the SM, and we set a limit on the masses of the stop and sBottom quarks. These limits are shown in the plots below. The results of these analyses are published in Phys. Rev. D76, 072010 (2007).

 Feynman diagram of sTop/sBottom productions and decays.

The Missing Transverse Energy distribution in the stop (LEFT) and sbottom (RIGHT)  signal regions for data (solid points)  compared to the SM background (filled histograms).  Also shown (open histograms) are the expected distributions arising from stop pair production and decay at m_(stop)=120 GeV/c^2 and          m(neutralino)=50 GeV/c^2,  and sbottom pair production and decay at m(sbottom)=160 GeV/c^2  and m(neutralino)=80 GeV/c^2.

(LEFT) The 95% C.L. exclusion region in the mass plane of m(neutralino) vs m(stop), assuming that stop decays exclusively into c+neutralino. (RIGHT) The 95% C.L. exclusion region in the mass plane of m(neutralino) vs m(sbottom), assuming that sbottom decays exclusively into b+neutralino.

Event Display of a selected sbottom candidate in the Missing Transverse Energy and Heavy-Flavor jets signature.

A plot of the projection of exclusion reach in the stop mass vs neutralino mass plane, for various integrated luminosity, if no stop signal is found.


Last modification : Jan 10th 2008, Song-Ming Wang