Upload
dirk
View
52
Download
0
Tags:
Embed Size (px)
DESCRIPTION
Hadronic SUSY @ CMS. Saeid Paktinat School 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 ). Disclaimer. - PowerPoint PPT Presentation
Citation preview
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)
2
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
28/3/2012 Saeid Paktinat DIS2012, Bonn
Why SUperSYmmetry(1)
28/3/2012 Saeid Paktinat DIS2012, Bonn 3
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)
28/3/2012 Saeid Paktinat DIS2012, Bonn 4
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).
][ 22
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).
28/3/2012 Saeid Paktinat DIS2012, Bonn 5
Saeid Paktinat DIS2012, Bonn
6
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, ,
28/3/2012
Saeid Paktinat DIS2012, Bonn
7
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
28/3/2012
Saeid Paktinat DIS2012, Bonn
8
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.
28/3/2012
Saeid Paktinat DIS2012, Bonn
9
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
28/3/2012
10
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
28/3/2012 Saeid Paktinat DIS2012, Bonn
Saeid Paktinat DIS2012, Bonn
11
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
28/3/2012
Saeid Paktinat DIS2012, Bonn
12
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
28/3/2012
Saeid Paktinat DIS2012, Bonn
13
Interpretation in Simplified ModelsVery simple models to ease the communication with theoreticians.
Half a TeV colored sparticles are excluded.
28/3/2012
Saeid Paktinat DIS2012, Bonn
14
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.
28/3/2012
Saeid Paktinat DIS2012, Bonn
15
Back up
28/3/2012
Saeid Paktinat DIS2012, Bonn
16
p-values for Razor analysis
28/3/2012
Saeid Paktinat DIS2012, Bonn
17
High MT2 exclusion
28/3/2012