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Super-symmetry (SUSY) is one of the most attractive extensions of the Standard Model. It provides solutions to the hierarchy problem and the unification of the gauge forces, and a natural candidate for the dark matter in the Universe.

Squarks and gluinos (super-partners of quarks and gluons), if they exist, will be copiously produced at the LHC via the strong interaction. Squark and gluino production leads to signatures with multi-jets through cascade decays and the neutral LSP, which escapes detection .resulting in large transverse missing energy (missing ET). Hence, Jets+missing ET is the dominant experimental signature for SUSY, with the highest discovery reach.

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While most SUSY searches focus on particular points in the parameter space of SUSY models, our group is developing a broad research program based on physics signatures containing multi-b jets and missing ET in the final state. This includes understanding (and measuring) Standard Model processes and probing SUSY in this final state signature.

The requirement of b-jets in events with large missing ET and multi-jets is well motivated both theoretically and experimentally:

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The b+MET signature is almost unexplored in ATLAS: b-tag and missing ET are among the most challenging and complex techniques. Expertise in multiple areas is required, which matches well SLAC strengths.

Experimental challengesThere are several experimental challenges to b+MET analyses:

  • Efficient b-tag trigger to afford lower missing ET and jet pT requirements .(to increase the event selection efficiency)
  • Jet energy scale and resolution, and the effect of multiple interactions. (much broader scope beyond SUSY searches: SM precision measurements)
  • MET Missing ET clean up, calibration, and significance. In particular, in the presence of b-jets in the final state.
  • b-tagging:
    • b-tag background estimation at high tag multiplicities.
    • Estimation of b production from gluon splitting.
    • b/c flavor separation.
    • high pT b-tagging

Our group is heavily involved in all these areas is making significant contributions to ATLAS reconstruction software and analysis.

Below there is a list of some of the b+MET physics analyses being pursued:



Top quark cross section measurement in the missing ET + b-jet channel

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