Search for New Physics at the Tevatron
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Simona Rolli - Tufts University
Search for New Physics at the Tevatron
Simona RolliTufts University
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Simona Rolli - Tufts UniversityOutline of the talk
• TeVatron status
• Physics Processes and their signatures:– from simple objects to complex final states
• leptons-only final states (and isolated tracks)searches
• … + Missing Energy and PhotonsET
• … + Jets and heavy flavors
• Final remarks and conclusions
Electrons
Muons
JetsPhoton
Missing E T
TracksH.F.
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Simona Rolli - Tufts UniversityTeVatron Status
Luminosity Profile Highest Initial Luminosity1.8x1032 cm-2s-1
Integrated lum. in a week26 pb-1
1.7 fb-1 delivered to the experiments1.2 fb-1 on tape
Most of the analyses presented here use 0.2 to 1 fb-1
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Simona Rolli - Tufts UniversityLeptons,Photons and MET
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Simona Rolli - Tufts UniversitySearches in dilepton final states
Dilepton mass and cos* distributions
Search for Z’ using the mee > 200 GeV/c2 region (448 pb-1)
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Simona Rolli - Tufts UniversityTesting different modelsCalculate the acceptances for resonant states for 3 different spin assumption
(0,1,2)
LH
TC
SUSY ED
Z’200 pb-1
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Simona Rolli - Tufts UniversitySearch for LED Graviton exchange
Analysis strategy
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Simona Rolli - Tufts UniversitySearch for BSM in dilepton + X
Looking for anomalous dilepton +X events.X = large HT, large MET, b tags, high ET jets, 3rd lepton
(S/√B !!)
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Simona Rolli - Tufts UniversitySUSY in TrileptonsSignature: 3 isolated leptons and large MET
Sensitivity study for trilepton channel in mSUGRA scenarioDetailed scan of the parameter space: m1/2,m0,A0,tan,sign()
pb
Benchmark point (a)m1/2 = 180 GeV m0 = 100 GeV
A0 = 0tan = 5
> 0
),()'( 021
021 lll→⋅→ ±± χχχχσ BR
4 independent analyses to maximize acceptanceHigh pt + lepton & ee + leptonLow pt + lepton & ee + track
Channel Benchmark signal SM expected Obsµµ/e +l (0.7fb-1) 2.3±0.3 1.2±0.2 1ee+l (350pb-1) 0.5±0.06 0.2±0.05 0µµ+l (low pt) (320pb-1) 0.2±0.03 0.1±0.03 0ee+trk (600pb-1) 0.7±0.03 0.5±0.1 1
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Simona Rolli - Tufts UniversitySUSY in trileptons: results
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Simona Rolli - Tufts UniversityExcited leptons
Observation of excited states of quarks and leptons might confirm the hypothesis that they are not elementary particles , but composite states
At Tevatron, e* /* can be produced via contact interactions or gauge mediated interactions
Select events with ee () in the final state and look for resonance in M(e) or M()
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Simona Rolli - Tufts UniversityW and Z
Now V+ cross-sections well established, we are:• optimizing sensitivity to anomalous coupling and new physics• testing the Standard Model in ways unique to the TeVatron (e.g. observing RAZ in W production)
Test of gauge couplings (as predicted by the SM) and a window on new physics
NON SM!
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Simona Rolli - Tufts UniversitySearch for BSM in high PT Z
Look for Z decaying weakly from heavier particlesOpen to different models (SUSY, ED, etc)
For example, this limit translates into a limit on BPT models cross section: 0.35pb for m(Q) = 300 GeV/c2
To use this limit one needs to fold in the information relative to the process acceptance!
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Simona Rolli - Tufts UniversityLED in diphoton Randall-Sundrum graviton model 4-dimensional metric multiplied by warp factor exponentially changing with the additional dimension Generating a large hierarchy does not require a large rc The coupling of individual KK states to matter is set by the weak scale (parameters : MG and k/MP lanck) KK states can be observed as spin 2 resonances
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Simona Rolli - Tufts UniversitySearch for BSM in Diphoton
Search for + /e/
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Simona Rolli - Tufts UniversitySUSY searches in diphoton + ET
2 + ETpp ( X ) χ01 χ0
1
Sample selection • 2 central photons ET > 13 GeV• cosmic rays and beam halo rejection
For Missing Energy > 45 GeVExpected: 0.60 ± 0.50Observed : 0 (209)
(114)
GMSB scenarioNLSP = χ0
1 G~
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Simona Rolli - Tufts UniversityAdding jets and flavor tagging
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Simona Rolli - Tufts UniversityLED in monojet + MET
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Simona Rolli - Tufts UniversitySUSY in MET + jets
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Simona Rolli - Tufts UniversitySUSY: sbottom from gluinosIf the sbottom is significantly lighter than the other squarks, the two body decay of gluino into bottom/sbottom is kinematically allowed
The sbottom decays into a bottom and LSP, giving rise to a final state with 4 b-jets and missing energy
Exp 16.4 ± 3.7Obs: 21
b-tagging
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Simona Rolli - Tufts UniversityLeptoquarksLeptoquarks (LQ) are hypothetical particles
which appear in many SM extensions to explain symmetry between leptons and quarks
– SU(5) GUT model– superstring-inspired models– ‘colour’ SU(4) Pati-Salam model– composite models– technicolor
Signature: dilepton + jets, lepton + jets + MET, MET + jetsAnalysis: counting experiment or signature based?
I
IIIII
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Simona Rolli - Tufts UniversitySM Higgs searchMany analyses ongoing both for light and heavy Higgs Golden channels and new strategies
WH
ZH
HWW
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Simona Rolli - Tufts UniversityFinal Remarks • The results presented are by far not exhaustive• Even when a signature-based approach is advocated, results are presented in the end as a function
of specific models (typical case dilepton searches, high PT Z’s etc)• And when the result is presented as a testing of a model, there is always a check on control regions,
defined by their signature…(see next transparency)• So, what is all this fuss about model-based and signature-based approaches ?• I believe that both are to be pursued in a balanced way: both have their pros and cons:
– A) Traditional model driven analyses• pick a favorite theoretical model might become soon outdated! • pick a process, choose the best signature(s): optimize selection acceptances based on signal MC• calculate the background best optimization! • evaluate the limit or discovery your signal in timely fashion allows theory testing!
– B) Signature based approach• pick a specific signature ( i.e. diphoton+X) open to a whole lot of models! • define your sample in terms of known processes Not the best optmization !• publish estimates of acceptances & cross section information useful for theorists ..but how much??
Detector effects are detector specific or we would all be using PGS! ;-) • see an excess? Inconsistency with SM? Test one or more models later …(but the experiments will never
release a controversial results for theorists to interpret, this is just sociology 101) • Quero-like access to the data? Is the astrophysical model suitable for HEP?
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Simona Rolli - Tufts UniversityLQ searches: W/Z+ 2 jets control regions (also good for Higgs, single top, etc..)
Checks on Z + jets for the = 1.0
= 0.5
Checks on the MET distribution for = 0
e
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Simona Rolli - Tufts UniversityConclusionsMany exciting results are currently produced at the Tevatron!So far a fraction of 1.2 fb-1 delivered has been analyzed (Run IIa).
Many of the results interplay nicely :from testing the SM processes to searches for Exoticasame signature, different physics
A long shutdown is underway: detectors upgrades are almost finished and the luminosity integrated will increase by a factor 3-6 (Run IIb).A bump can be around the corner before the LHC turns on….