Institute for Anything of the University of Everything
Claudia-Elisabeth Wulz
New Physics at the LHC
C.-E. Wulz (Institute of High Energy Physics) 1
Institute of High Energy Physics of the Austrian Academy of Sciences
New Physics at the LHC
Experimental environment
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Students will work within the CMS Collaboration. Almost 20 fb-1 of integrated luminosity of pp interactions are available (√s up
to 8 TeV), 300 fb-1 are expected by 2021 (√s up to 14 TeV).
Experience of Vienna CMS group: triggering, tracking, reconstruction of tracks and vertices as well as of muons, b’s and t’s.
One thesis showcase is mainly about triggering, the other about searches for new physics in the field of SUSY. Connections between triggering and physics are an important aspect for both.
New Physics at the LHC
Motivation for New Physics
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The main motivation for the LHC, after the discovery of a Higgs boson, is the search for new physics.
The Standard Model, though extremely successful, leaves many questions open.
It needs to be embedded in an overarching theory, but which theory is it?
C.-E. Wulz (Institute of High Energy Physics) New Physics at the LHC
Concrete predictions of experimental signatures for new physics exist for many models (SUSY, strong electroweak symmetry breaking, extra dimensions, etc.)
Scalar top quarks
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and are expected to have large mixing, due to the large top Yukawa coupling. The lower mass eigenstate may be relatively light.
Most analyses so far have exploited the decay channels or with as well as
Showcase 1 – Scalar tops decaying to charm
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Production of in association with two b-jets in the stop-neutralino coannihilation region .In this case the branching fraction is close to 100%.
Analysis strategies:• cut-based analysis• multivariate techniques as alternative• background estimates from data where
possible New Physics at the LHC
LO QCDcontribution
LO electroweakcontribution
Signature: 2 b-jets and missing energy, no leptonsBackgrounds:
Motivation for an Upgraded Trigger System
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Example for improvement in triggering on scalar tops(e.g. through better transverse momentum estimates or pileup subtraction)
The current trigger system has worked very well. It is designed for luminosities up to 1034 cm-2s-1, average number of pileup events of about 25, and a maximal Level-1 output rate of 100 kHz.
For the future, the physics potential of CMS must be maintained or extended, and aging hardware must not become an issue. Luminosity, centre-of-mass energy and pileup will increase.
Showcase 2 – Muon trigger upgrade
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Analysis-like, flexible trigger algorithms already at Level-1 with new FPGA’s:• e.g. boosted decision tree pT assignment• more muon candidates than now, with higher precision in pT
• muon isolation information • b-tagging of jet candidates through use of muon information.
Currrent muon trigger in the CMS cavern
Synergies within the DK and connections
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Collaboration experiment – theory• A. Hoang (University of Vienna): QCD, SUSY• A. Rebhan (TU Vienna): QCD, SUSY• Theory groups (Institute of High Energy Physics): SUSY, QCD, new
Dark Matter group (J. Pradler)
Development of trigger and reconstruction algorithms, data analysis in the fields of SUSY and other beyond the Standard Model physics• R. Frühwirth, M. Jeitler, J. Schieck (Institute of High Energy Physics)• H. Abele (TU Vienna)
Computing• Austrian Tier-2 GRID centre
International Collaborations• CERN and institutions worldwide
New Physics at the LHC
Thank you for your attention!
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BACKUP
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Added value
SUSY at the LHC SUSY at the LHC
Students will work in a stimulating environment:• investigation of fundamental physics problems• world’s most powerful particle accelerator• large scientific community but human-sized research groups• international, multidisciplinary
Focus on research activities will shift to physics analyses, after long and important development work in triggering and tracking
Reinforcement of collaboration between theorists and experimentalists
C.-E. Wulz (Institute of High Energy Physics) 11 New Physics at the LHC
SUSY limits from CMS
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ATLAS direct stop limits
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ATLAS direct stop limits in 0-lepton channel
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ATLAS-CONF-2013-024
Stop to charm
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Alternative signature: monojet if
Projections for stop
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CMS Trigger upgrade
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Tail clipping
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The initial pT estimate of about 32 GeV is too largefor the input Df(ME1-ME2) value (50 f-units) according to the 5% tail fraction curve(shown in black). The initial 32 GeV estimate is substituted by the highest pT for which50 f-units is below the 5% tail fraction curve, in this case 12 GeV.
