Hadronic SUSY @ CMS

Saeid PaktinatSchool of Particles and accelerators, IPM

On behalf of the CMS Collaboration

DIS 2012: XX International Workshop on Deep-Inelastic Scattering and Related Subjects, 26-30 Mar 2012, University of Bonn (Germany)

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Disclaimer

• It is a short review of the CMS reach plan for search for SUSY, for a complete review

https://twiki.cern.ch/twiki/bin/view/CMSPublic/PhysicsResultsSUS

• Here SUSY is just a paradigm of any new physics in which stable neutral particles (e.g. Dark Matter candidates) are produced in the

cascade of pair-produced heavy particles

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Why SUperSYmmetry(1)

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SM describes a lot of experimental results very precisely, but

Fermionic loop corrections to higgs mass diverge quadratically:

L is a cut-off scale (upper limit for SM validity Mpl = 2.4*1018 GeV). Huge disparity between EW scale and Mpl is not natural (Hierarchy Problem)

][ 222 bcm fH

Why SUperSYmmetry(2)

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If another scalar couples to higgs

new correction is

Proper couplings This correction can cancel the quadratic divergencies.SUSY introduces new particles that cancel quadratic div and fill the scale between EW and Mpl (solves the hierarchy problem).

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22 bcm SH

Important Features• Every SM particle has a SUSY partner (sparticle) which are exactly same, but differ in spin by ½ .• R=(-1)2S+3B+L

• Consider R-parity conservation → pair-production of sparticles• Lightest SUSY particle (LSP) stable → dark matter candidate• Hadron collider: squark/gluino

production is dominant (if not too heavy).

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SUSY Fingerprint

• Long decay chain a lot of jets and leptons.• Seems easy to find, but how to isolate the signal (~1pb) from the SM backgrounds (~nb).• Jets + MET is a classical signature.– Jet multiplicity, ,

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Jets + MET• At least 3 jets,• No well identified/isolated electron or muon.– Multijet QCD has a huge cross section with a big chance

to be mismeasured as an unbalanced event.– Special method is used to predict the QCD contribution.

CMS PAS SUS-11-004

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SM Background Prediction• QCD: Jets are Rebalanced and Smeared. All distributions

can be rebuilt using the smeared jets.

• W/Z , ttbar: A muon control sample is used.• Z : nn g+jets when g is ignored.

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QCD Safe Distributions• separates events with low MET or

mismeasurement from genuine events.• QCD is completely suppressed.• > 2jets: Minimizing the HT difference between the mega-jets.

• RaT = N(aT > 0.55)/N(aT < 0.55) is flat vs HT for the SM bkg.

CMS PAS SUS-11-003

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QCD Safe Distributions(2)• MT2: stransverse mass, an extension of MT in case of 2

decay chain with “missing particles”:

• QCD does not enter the search region,– Data driven methods confirm this. (both QCD multijet

and total jet lost are considered.)• > 2 jets: Minimizing the Lund distance.

CMS PAS SUS-11-005

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QCD Safe Distributions(3)• Razor: Approximates the scale and distribution.

• Bkg predicted by 2D templates (MR, R2).• > 2Jets: Minimizing the sum of M2 of megajets.

CMS PAS SUS-12-005

V+jets

SUSY-LM6

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Interpretation in CMSSM Model• No excess is seen over the predicted bkg,

Hybrid frequentist CLs estimator is used to find the limits.

• Signal efficiency is estimated using NLO & NLLO prospino cross sections.

• CTEQ6 and MSTW describe the PDF/scale uncertainty.

Razor 4.4 fb-1

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Interpretation in Simplified ModelsVery simple models to ease the communication with theoreticians.

Half a TeV colored sparticles are excluded.

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Conclusion

• CMS has a reach plan to search for SUSY in fully hadronic final states.

• New variables are introduced to move the QCD out of the search region.

• New results with the full 2011 data (~ 5 fb-1) will appear shortly.

• Be tuned for SUSY results in 8 TeV by summer.

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Back up

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p-values for Razor analysis

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High MT2 exclusion

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