Using Object Correlations to Extract New Physics from the LHC
Rouven Essig, Michael Graesser, Eva Halkiadakis, Dmitry Hits,
Amit Lath, Pablo Mosteiro, Keith Rose, Steve Schnetzer,
Jessie Shelton, Sunil Somalwar, Scott Thomas
(Reconstructed) Objects
Leptons Photons Missing Transverse Energy Jets
Exotic Objects (New Long Lived Particles)
Displaced - Leptons, Photons, Jets Highly Ionizing Tracks Highly Ionizing to Minimum Ionizing Kinks Out of Time Decays Charge Exchange Tracks Charge Changing Tracks .....
(Reconstructed) Objects
Leptons Photons Missing Transverse Energy Jets
New Physics Searches – Hadron Collider
Strong Production Cross Section . Electroweak Decays . Background / Signal Suppressed
pp QQ) order (pp Jets)
Q Leptons, Photons, MET
(Reconstructed) Objects
Leptons Photons Missing Transverse Energy Jets
New Physics Searches – Hadron Collider
Strong Production Cross Section . Decay to Strong Decays . Background / Signal Severe
New Physics Search in Multi-jets :
pp QQ) order (pp Jets)
Q Jets
• Challenging - ....
• But Possible New Physics May be Hidden in Jets ….. (c.f. Higgs at LEP)
• Techniques may be Useful for Multi-jets in Association . with Leptons, Photons, MET
New Physics Searches in Multi-Jets
j j j j j j
pp QQ
• Magnitude of Multi-Jet Backgrounds from High Order Processes . Difficult to Calculate a priori s
n
• High Multiplicity-Jet Backgrounds Lower Rate - More Tractable
• Kinematic Features + Correlations
R-Parity Violation uud Yukawa
Cinematic Features + Correlations + Hadronic Top Guidance . (No b-tagging or mW resonance )
• Hiding New Physics in Multi-Jets
• SUSY gluino j j j
Signal : Pythia
6 Jet Background : ALPGEN Pythia
Hadronic Top Background : Pythia
Detector Simulator : PGS
Analysis : ChRoot +
Q = SU(3)C Adjoint Majorana Fermion
Semi-Leptonic Top Decays
pp tt l j j j j
Njet ¸ 4
Ne = 1
pT,4th jet > 40 GeV
PT,e > 20 GeV
| mjjj – mW | < 10 GeV
j j j Furthest R from Electron
pp W j j j j
GeV
GeV
PT,5th jet · 10 GeV
mjjj
150 pb-1
150 pb-1
Gluino300-E
ffjet6Effjet
Alp6j50-E
ffjet6Effjet
pp QQ j j j j j j
Njet > 6
mQ = 420 GeV
PT, jets PT, jets
PT
,6th
jet
PT
,6th
jet
2 fb-1
Signal Hadronic Background
Gluino300-E
ffjet6Effjet
Alp6j50-E
ffjet6Effjet
pp QQ j j j j j j
Njet > 6
Cut
mQ = 420 GeV
Cut
PT, jets PT, jets
PT
,6th
jet
PT
,6th
jet
Cut :
pT, jets > 700 GeV
pT, 6th jet > 60 GeV
2 fb-1
Signal Hadronic Background
Signal Efficiency ' 0.25
pp QQ j j j j j j
Two Three-Body Resonances mjjj = mjjj
| i pi,jet | < 60 GeV Choose Pair of Jet triplets with Smallest | mjjj – mjjj |
mjjj mjjj
Signal Hadronic Background
• Cuts Necessarily Shape Background
• Magnitude of Background Uncertain - . Use Signal + Background Distributions as Templates
pp QQ j j j j j j
Scaled Cuts pT, jets > 1.7 mQ . pT, 6th jet > 0.15 mQ . | i pi,jet | < 0.15 mQ
MQ (GeV) S/B S/ B1/2 / fb-1 Signal Events / fb-1
420 1/29 17 16500
660 1/22 5 600
890 1/17 2 70
Note: Magnitude of Background Uncertain
pp QQ j j j j j j
| i pi,jet | < 60 GeV Choose Pair of Jet triplets with Smallest | mjjj – mjjj |
mjjj
mjjj
Signal Hadronic Background
Tail much larger than Jet Resolution - . Mismatching of Jet Triplets - . Combinatoric Background Within Signal
Improve Contrast Between Signal and Background
pp QQ j j j j j j
Reduce Combinatoric Background from Radiated Jets with Cut on 7th Jet
•pT,jets > 500 GeV .pT, 6th jet > 30 GeV .pT, 7th jet < 20 GeV .| i { p}T,jeti
|
< 50 GeV
MQ = 290 GeV
Signal Hadronic Background
mjjj mjjj
MQ (GeV) S/B S/ B1/2 / fb-1 Signal Events / fb-1
290 1/110 15 26850
• Improves Contrast AND . S/B by Factor 2
0.3 fb-1
pp QQ j j j j j j
Kinematic Correlation – Separate Signal from Combinatoric Background
mQ = 420 GeV
Signal Signal
PT,jets
mjjj
mjjj
| i pT,jeti |
• Two Distributions of Events
• Three Body Resonance Jet Resolution Apparent on Horizontal Branch
• Most of the “Best” Pairs of Jet Triplets with small |mjjj-mjjj| . are NOT the Correct Pairing (Random Choice of Triplet ,Roughly Same Distribution)
pp QQ j j j j j j
Remove Combinatoric Background with Cuts
Signal Signal
mjjj
mjjj
• Horizontal Branch Region of High Signal to Combinatoric . Background Contrast
- Increase Signal Efficiency by Including All 20 Jet Triplets
- Remove | i pT,jeti | Cut
PT,jets PT,jets
pp QQ j j j j j j
Hadronic Top Background Hadronic Top Background
Cuts
Increase Signal Efficiency
Hadronic Background Hadronic Background
mjjj
mjjj
PT,jets | i pT,jeti |
mjjj
mjjj
pp QQ j j j j j j
Signal Hadronic Background
Hadronic Top Background
mjjj
mjjj
pp QQ j j j j j j
Signal Hadronic Background
mjjj
MQ (GeV) S/B S/ B1/2 / fb-1 Signal Jet Triplets / fb-1
490 1/15 17 9500
• Improves Constrast and S/B by 2.5 but Lowers Signal Efficiency by 2.8
pp QQ j j j j j j
Using Correlations –
Possible to Separate pp QQ j j j j j j from Background
Optimize Cuts
Study Template Fitting to Signal + Background
Validate Background Templates and Magnitude with Data
Possible Reach (Preliminary)
mQ » 600 GeV with 1 fb-1
» 800 GeV with 10 fb-1
Develop Kinematic Correlations for Other Multi-Jet Signatures
Extend to Signatures with Other Objects
Kinematic Correlations
Decay Trees
Invariant Kinematic Correlations = f( mijk…2) (Unpolarized,
. Spins Unobserved, . T-Invariance ) mijk…
2 = f(mij2)
Correlations in Generalized Dalitz Space mij2 i,j = All Pairs of Objects
Invariant Kinematic Correlations
• New Physics Sample . Nl = 2-6 . Njet ¸ 2 . Backgrounds Unimportant
m12
m1
3
Nl ¸ 3
• Enhanced S/BCombinatoric Constrast
DS < DB (D=1 Histrogram DS = DB)
• Two Body Resonant Tree
• Correlation m122 + m13
2 = Constant
(Some of) The Two Body Resonances . Arise from Three Body Decay
6 fb-1
Invariant Kinematic Correlations
m122
m1
32
2
2
Dalitz (symmetrized)
• Uniform |M|2 on Two Body Resonances
Consistent with Intermediate Scalar
• Edges
Three Body Tree (Only feature in . D=1 Histogram)
Coincide with Endpoint of Resonant . Two Body Correlation
- Arise from “Missing” Lepton
- Anything Else Contributing to . Edge is massless
• Relative Density of Two Body Resonances, . Resonant Two Body Correlation, and . Edge Contrast
- Br ( lll) / Br( llX)
m122
m1
32
Invariant Kinematic Correlations
• Three Body Resonant Trees
310 GeV · mlll · 330 GeV
- Further Enhances . S/BCombinatoric Contrast
m1
23
2
Kinematic Correlations
m232
m1
42
• No Kinematic Correlation
- Consistent with Arising from . Different Parent Particle
• m14 = m and m23 m or
• m14 m and m23 = m
- Single Resonant Two Body Decay
• m14 = m23 = m
- If Density at Intersection > 2 . Some Events with (At least) . Two Resonant Two Body Decays
- Density at Intersection gives Fraction
Nl ¸ 4
30 fb-1
Mjlll2
Kinematic Correlations
Nj ¸ 2M
jlll2
Mjlll2
• Contrast S/BCombinatoric Improved
• Two Four Body Resonant Decays
• Density in Bands, Intersections Gives
Br( 1 jlll) / Br( 2 jlll)
• Correlation Could Indicate Resonant . Five Body Decay jjlll
Object Correlations to Extract Low Order Trees (OCELOT)
Kinematic Correlations Can Enhance Contrast DS < DB
Menu of Correlations for Low Order Trees
- Develop Templates to Search for Correlations
Extend to Trees with MET
(Generalization to D > 1 of Edges and Endpoints)
Correlations Allow Direct Measurements
Implement Correlations in Fitting Procedure to Decay Trees . (Fitting to D=1 Counts Misses Many Correlations)
New Physics at the LHC
Resonant Multi-Jets ….. Resonant Multi-Leptons
Very Hard Very Easy
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