Exploring New Phenomena at CDF
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Transcript of Exploring New Phenomena at CDF
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Exploring New Phenomena at CDF
Jane Nachtman (Fermilab) for the CDF collaboration
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Objective• This workshop is about bringing theorists and
experimentalists together to focus on maximizing the Tevatron’s discovery potential
• The experimental talks will briefly summarize searches for new physics at CDF and D0– To help us think about what is possible and where
we should go from here– Looking for theorists’ input!
• We split the signatures– CDF – photons, jets + MET, hi-pt dileptons– D0 – leptons+jets, multi-leptons, long-lived
signatures
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Overview of my talk• Brief CDF and Tevatron intro• CDF searches
– Signature-based, then applied to models• Photons
– Applied to GMSB, Extra Dimensions• Hi-pt dileptons
– Z’, G• MET+jet(s)
– SUSY, LED– Global, signature-based search of all CDF hi-
pt data (Vista+Sleuth)
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CDF Detector
SOLENOID
= 2.0
END WALL HAD CAL.
CENTRAL OUTER TRACKER
CLC
CENTRAL HAD CALORIMETER
PLUG HAD CAL.
= 1.0
= 3.0
PLU
G E
M
CAL.
MUON CHAMBERS
Silicon Vertex Detect
or
CENTRAL EM CALORIMETER
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Tevatron
Almost 2 fb-1 delivered, ~1.6 fb-1 recorded( 0.95 – 1.2 fb-1 for analysis, depending on which subsystems are used)4-8 fb-1 by 2009
The Tevatron’s performance is better than ever!!
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Signature-based searches at CDF
• Philosophy – models come and go, but the data should stand on its own
• Design “simple” searches– No optimization for models no sophisticated cuts– Attempt to provide general result for theoretical input– Basic result : N expected from SM, N observed– Study kinematic distributions– Publish acceptance functions – plug in your own model
• Drawback – may not provide maximal sensitivity to a particular model – But may point us in the right direction to look further
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Signature-based searches for photon+X
• Inspired by Run I hints– “eeMET” event– Excess in lepton+photon+MET (16 obs, 7.6 +/- 0.7
exp)
• Theoretical models suggest these signatures (eg GMSB)
• Mix-n-match: photons, leptons (e,), MET, jets,b-jets
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Search for photon+lepton+X• 2 channels
– Photon + lepton(e,) + MET– Photon + lepton + lepton + X
• Look for high-pt leptons, photons, high MET (reduce fakes, SM backgrounds)
• In 930 pb-1 of data e+MET +MET l+MET SM 948 547 14813 Data 96 67 163
ee+X +X ll+XSM 395 263 658Data 53 21 74
SM is W/Z gamma, W+fakeNo events with extra photons, leptons observedSM is W/Z gamma, W+fakeNo events with extra photons, leptons,MET observedNo e
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Check kinematics in l+gamma+MET
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Diphoton + X searches• X = e,,,MET • Backgrounds evaluated from data
– Use sidebands – loose photons not passing signal photon selection
• Dataset = 1 – 1.2 fb-1
gg+X, X= SM Nobs e 3.8 +/- 0.5 1 0.7 +/- 0.1 0 MET 116 +/- 24 126 2.2 +/- 0.7 4
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Kinematics in +X channels
Control region
Signal region
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High-mass diphotons
• high ET (>15) isolated diphoton resonance– Backgroun
d : QCD diphotons (simulation), jets (from data)
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Long-lived Exotic particles• D0 talk will cover more in detail, just one
photon-based search here• Several models predict long-lived particles:
charged or neutral, decaying inside or outside detector– Charged – look like slow muon (new CDF results
soon) or delayed jet– Neutral
• decay inside detector – delayed photons CDF analysis
• decay outside detector – photon + MET planned analysis
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Delayed Photon Analysis• Relies on EM calorimeter timing
detector
Measure photon arrival time
background signal
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signal region No new physics found here, so far
Interpret in GMSB
Search for Delayed Photons
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Signature-based searches for dileptons + X at CDF• Look for excess above SM prediction in dilepton +X (X = photon,
lepton, b-jet, HT, Missing ET; dileptons can be same-sign or opposite-sign)– Set cuts on first 1/3rd of dataset,apply to larger dataset– can be further applied to many models; e.g. heavy quarks as first
exampleDilepton (ee, , e) + high HT
HT == scalar sum of electron and jet ET, muon pT, missing ET
No excess, but one event at HT=900!
Good agreement in HT<200 control region.
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High mass dileptons• High ET electrons,
optimized to look for high-mass resonances (150-950 GeV)
• Applied to spin-1 Z’ and spin-2 RS Graviton
19% pe’s have 2E-3
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Combine limits with diphoton on coupling vs graviton mass in RS model
Set limits on SM-like Z’
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Search for Massive Resonances Decaying to ZZ eeee
Spectacular signature!!Model: RS Gravitons can
decay to ZZ, xBr=292fb (0.66 events expected in 2 fb-1 – not yet sensitive)
Signal region M(eeee) 500-1000 GeV
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Like-Sign dileptons• Signature-based search • Currently: chargino-
neutralino production
Basic selection: expect 34+/-4, see 44Tight selection: expect 8 +/- 1, see 13
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MET + Jets• Signature:
monojet events• Model: LED (ADD)• Graviton
production leads to excess (not resonance)
Set limits on MD vs N extra dimensions
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MET + jets in SUSYSearch for
squarks/gluinos in MET + jets
Add flavor tagging for stop/sbottom
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Vista/Sleuth – the ultimate signature-based search
• Algorithm to look at Tevatron data globally– Because new physics will probably not show up
where we are expecting it– Look in hundreds of final states simultaneously
• Vista – look at bulk distributions, find compatibility with SM (chi-square fit)
• Sleuth – look in hi-pt tails– Flag a final state as “interesting”– Show us where to look in more detail
• Further steps Quaero and Bard…to interpret new physics
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summary• Tevatron searches are going at full steam
– Lots of analyses ongoing, new and interesting results coming out
– No new physics yet, but we remain hopeful• Need to focus our efforts for the full
Tevatron dataset – What can we learn from what we’ve already
done, to plan for the future?• We’ve tried to cover as much as possible,
but are we overlooking important signatures, models?
• Theoretical guidance for our program of Searches for New Physics
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Backup Slides
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SM and Other BackgroundsSM Collisions
Beam Halo
Cosmics
Signal Monte Carlo
How do I know how each background looks like? Can not use photons.
Signal (Blinded) Region
4 sources, all estimated from dataCollision photons from SM•Right vertex•Wrong vertexNon-collision “look-like photons”•Beam Halo•Cosmics
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Highest Mass Diphoton Event (604 GeV/c2)
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Highest Mass Diphoton Event
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Top dilepton event at HT=900?
Leptons:e 28 GeV, 159 GeV
Jets :216 GeV (b-tag)199 GeV156 GeV15 GeV
MET: 90 GeV