b+Jet+MET topology-based physics signatures
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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:
- QCD, and WZ+(light quark) jets backgrounds are significantly reduced.
- Top background is irreducible, but b-tagging provides additional handles to control and measure it.
- Reducing non-top SM backgrounds by requiring b-tags could be one of the keys to the early discovery of SUSY at the LHC.
- In many scenarios, where the third-generation of squarks are expected to be light, most new physics events will contain two or four b- or t-quarks.
- Even if SUSY is first discovered in inclusive jet + MET or lepton events, understanding the production of third-generation squarks will be critical to answer important physics questions.
- Is new physics related to Dark Matter? since b-tags reduce the QCD multi-jet background, looser MET cuts can open up the possibility to study the shape of the MET, to determine if the missing energy originates from a massive object.
- Quadratic divergences in the top sector: third-generation squarks (stops, sbottoms) are responsible for the largest quantum corrections that stabilize the weak scale. b-tagging can help determine the mass scale for third-generation partners.
- Origin of the electroweak symmetry breaking: if third-generation partners are light, higgs particles can be produced in decay chains starting with stops and sbottoms, as well as in gluino decays. A light Higgs could be first discovered in this channel.
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.
There 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.
- 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.
An overview of the b+Jet+MET topology-based research can be found in the diagram and links below.
Top quark cross section measurement in the missing ET + b-jet channel
Verifying top x section and mass and probing for SUSY at the same time.
Inclusive missing ET + multi-b search
missing ET + 4b analysis
Top + b
Top + MET
ttH
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Jet reconstruction, calibration, and resolution
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