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Jay WackerSLAC
34th Annual Johns Hopkins Workshop May 24, 2010
with M. Lisanti, J. Alwall, & M-P Le, and E. Izaguirre, & M. ManhartarXiv: 0803.0019, 0809.3264, 1003.3886, 1005.XXXX
O GLUINO,WHERE ART THOU?
Plan of TalkAn Odyssian Voyage
Where we have been (Tevatron)
Where we will be (14 TeV LHC)
Where we are now (7 TeV LHC)
All started a few years back...
Had an MSSM model that predicted a spectrum
70 GeV80 GeV
140 GeV
...
Surely this must be excluded!?!
The production cross section at the Tevatron is
I went through the 25 years of squark and gluino searchesThey all came back to versions of this:
mSUGRA(Five parameters to rule them all)
but where is?
mSugra has “Gaugino Mass Unification”
Most models look like this
A shocking lack of diversity (see the pMSSM)
Solution to Hierarchy Problem
Jets + MET
Dark Matter
Fewest requirements on spectroscopy
If the symmetry commutes with SU(3)C,new colored top partners(note twin Higgs exception)
Wimp Miracle: DM a thermal relic ifmass is 100 GeV to 1 TeV
Usually requires a dark sector,frequently contains new colored particles
Doesn’t require squeezing in additional states to decay chains
Spectrum in Different Theories
MSSM Universal Extra Dimensions
High Cut-Off Low Cut-Off
Large Mass Splittings Small Mass Splittings
Back to the question:
Is an 80 GeV standard-issue gluino allowed?
Hope to catch in Jets + MET
Require energetic jets and unbalanced momentum
Jets + Missing Energy Cuts at D0
(Not exclusive searches)
1fb-1 analysis
Which search will an 80 GeV gluino fall into?
Simple searches counting experiments on tail of SM distribution
A careful look at the signal
80 GeV particle going to 70 GeV LSP and 2 jets
In rest frame of each gluino: two 3 GeV “jets” and a LSP with 3 GeV momentum
Parton level Detector level
Totally invisible: faked by QCD with
Give the gluino big boost!
Jets merge and MET points in direction of jetMore energy, but looks like jet mismeasurement
Calculating Additional Jets
Matrix Elements
Necessary for well-separated jets
Includes quantum interference
Fixed order calculation
Computationally expensive
Limited number of partons
Parton Showering
QCD Bremstrahlung
Soft/Collinear Approximation
Resums large logs
Computationally Cheap
Unlimited number of partons
Matching merges best of both worlds
Necessary to avoid double counting
A big advance in Monte Carlo calculations over past 10 years
Start with a model and design a search to discover it
Model Dependent Design
Design a set of searches that will catch anything
Most studies currently available are benchmarks within specific parameterizations (e.g. SU#, etc)
What is the efficacy of searches outside parameterizations?(let alone to different theories e.g. UEDs)
Make sure unexpected theories aren’t missed
Exclusive Jets + MET Search
4 Separate Searches, Individually Optimized
Maximize significance for each
Tevatron Summary
Necessary to consider multiple searches
Multiple cuts for &
Difficult to pull signal from background
Searches are challenging
Frequently low values of & are necessary
These are hard searches!
A Comparison Between Optimized Cuts and Original Cuts
Dijet most effective channel
Not easy...but they’re providing more information now
CDF (2.0 fb-1) 0811.2512
BG
Signal Signal
BG
Where are we going to get to with the LHC?
A lot further, a lot faster!
The LHC is not a SuperTevatron (thankfully)
Signals
Should use same methods for signals as backgrounds
Parton Shower - Matrix Element Matching
Signal may be in a different place than expected
Extra jets aren’t a nuisance, they can qualitatively alter signal
Search DesignStart with a range of jet multiplicities
that can be statistically combined
Lepton veto, MET separated from hardest 3 jets
Lore is that only multijet is useful
Based most from benchmark studies
“Susy Without Prejudice” found multijets more useful,but didn’t go away from ATLAS cuts
Spectrum of Radiation Harder for New Physics
Cross section for background is large due to lower SM CM energy
When LSP is heavy(rest mass of LSP is unobservable)
Spectrum of Radiation Harder for New Physics
Consider the additional cost of energy for radiating a jetoff a particle, X, of mass m
Identify
Spectrum of Radiation Harder for New Physics
Cross section for background is large due to lower SM CM energy
Equalizes CM energy for signal and backgroundIncreases S/B significantly
When LSP is heavy(rest mass of LSP is unobservable)
Radiate off a jet with
Works because we’re beyond last SM threshold at the LHC
Multijet Universality
Never found lower jet multiplicity to significantly enhance discovery
Tried many different event shape variables and search strategies
Degenerate spectra
Light Squarks, Heavy Gluinos
Qualitatively different than the Tevatron
3 Searches
High MET
Alpha
Mid MET
Gluinos, Squarks & Degenerate Spectra
Gluinos, Squarks
Cascade Decays
Introduced by L. Randall & D. Tucker-Smith
The Alpha Variable
Modified by CMS to multijet searches
Group to minimizemomentum imbalance
Discovery ReachAlpha Search
AlphaHigh MET
Directly decaying SquarksDirectly decaying gluinos
AlphaHigh MET
Multijet still more effective than dijets
Extended Cascade Decays
LSP is great-granddaughter
Momentum is divided many different ways
Reduces MET dramatically
Worse case scenario
Need a low MET search