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Tracey Pratt Durham Exotics Workshop
Exotic Searches at CDFin Run II
Motivation for Exotic Searches
Introduction to the Tevatron and CDF
“Signature-Based” Model Searches
- dielectron, dimuon, dijet, diphoton
“Model-Based” Signature Searches
- leptoquarks, excited e
Conclusions and Outlook
Tracey PrattUniversity of Liverpool
April 2004
Tracey Pratt Durham Exotics Workshop
“Exotic” Physics : Why ?The SM describes experimental measurement very well,
but raises crucial questions
Hierarchy problem MEW << MPl ?
SupersymmetrySupersymmetry
Extra-dimensionsExtra-dimensions
technicolor (H→ qTqT), topcolortechnicolor (H→ qTqT), topcolor
Questions which the SM (or SM + SUSY) does not answer :• “Replication” of three families ?• Particle masses & their hierarchy ?
Compositeness ? Superstrings ?Extra-dimensions ?
The Standard Model of electroweak and strong interactions continues to describe experimental measurement very well. In the Standard Model, electroweak symmetry breaking is responsible for giving rise to massive particles. The broken symmetry arises from a Higgs scalar filed and as yet unobserved Higgs boson. An alternative explanation for the broken symmetry is through a dynamical interaction known as technicolor, where the Higgs boson is replace by states of two techniquarks, called technipions, bounds by the technicolor force. A recent walking technicolor model predicts color singlet technirho production in high energy PbarP collisions throught a s-channel qbarq annihilation. This technirho can decay to technipions and to bosons , with a relatively high production cross section.
In the SM, EW symmetry breaking is responsible for giving rise to massive particles. The broken symmetry arises from a Higgs scalar field.
Where/what is the Higgs boson ?Is it a fundamental scalar field?
Or is the symmetry broken through a dynamical interaction ?
Tracey Pratt Durham Exotics Workshop
CDF
Run I (1992-1996)s 1.8 TeV, 110/pb
Run II (2001-2009)s 1.96 TeV, Ldelivered ~400/pbPhysics Analyses use ~ 200/pb taken between 03/02 and 09/03
Tevatron pp collider Highest energy collider operating in the world!
D0
Expect 2 /fb by 2006 and 4.4-8.6 /fb by 2009 sensitivity to New Physics improved by>5 compared to Run 1
CDF
pp
Tracey Pratt Durham Exotics Workshop
CDF at the Tevatron
Muon System
COT
Plug Calorimeter
Time-of-Flight
Central Calorimeters
Solenoid
Silicon Tracker
New for Run 2• Tracking System
• Silicon Vertex detector (SVX II)• Intermediate silicon layers (ISL)• Central Outer tracker (COT)
• Scintillating tile forward calorimeter• Intermediate muon detectors• Time-Of-Flight system• Front-end electronics (132 ns)• Trigger System (pipelined)• DAQ system
Retained from Run 1• Solenoidal magnet (1.4 Tesla)• Central Calorimeters• Central Muon Detectors
Tracey Pratt Durham Exotics Workshop
“Signature-Based” Exotic Searches
Why?initial signature motivated by some modelapply same search results to several models
How?• search for a particular signature• understand backgrounds • provide cross section limits: try to be as
generic/model-independent as possible - study acceptance as a function of spin• interpret in context of specific models applicable to future models!
Signatures? ee jj + ET
Tracey Pratt Durham Exotics Workshop
Di-electron Production @ High MassSearch selection2 opposite sign leptons: ee
2 central e (CC) 1 central and 1 forward e (CP)
NEW: 2 forward e’s (PP)
Plug Calorimeter
Central Calorimeters
Good agreement with SM prediction
Tracey Pratt Durham Exotics Workshop
Model IndependenceSpin-dependent efficiency times acceptance
To obtain cross-section limits: need efficiency times acceptance of detecting a particle decaying into a
electron-positron pair as function of the mass. Angular distribution of decay particles depends on the spin of the particle.
spin-0 spin-1 spin-2
Tracey Pratt Durham Exotics Workshop
Model Independent σxBR limits: spin-0, spin-1 and spin-2 particles
1sigma error and 2 sigma error on the expected limit
spin-0 spin-1
spin-2
• Observed limit consistent with expectation
• Applicable to any new possible future theory
Tracey Pratt Durham Exotics Workshop
Interpretation of results: Specific Models
• Observed limit consistent with SM expectation• Therefore set limits on new physics
– Z' bosons – Little Higgs Z'– Technicolor– Randall-Sundrum graviton – Large Extra Dimensions
Tracey Pratt Durham Exotics Workshop
Z' bosons
Z' occurs naturally in extensions of SM towards GUT scale, e.g. “E6” models– M(Z')>570 GeV for E6 models
(depends on exact model:
couplings to quarks and leptons)– M(Z')>750 GeV for SM coupling
(D0 M(Z')>719 GeV, 122 pb-1)
Z'
Tracey Pratt Durham Exotics Workshop
Little Higgs Z`
Tracey Pratt Durham Exotics Workshop
Technicolor
T, T
l-
l+q
q
Use Z` limit
Tracey Pratt Durham Exotics Workshop
Randall-Sundrum graviton
Extra Dimensional Model
- 1 highly curved extra dimension
- gravity localised in the ED
Planck TeV brane
for k/M_Pl=0.05 masses less than 500 GeV are ruled out at 95% C.L..
500 GeVDilepton channel
400 600 800 1000
Tevatron 700 GeV KK graviton
K/MPl10-2
10-4
10–6
10-8
d/dM (pb/GeV)
GeV
g
g
l+
l-
l+ l+
l- l-
q
q
/Z
KKn
KKn
q
q
10.70.50.30.20.1
Tracey Pratt Durham Exotics Workshop
Large Extra DimensionsSet a limit on the effective Planck scale in ADD type models
Parameterise the cross section in terms of = / s4
= SM + INT + 2 KK
Tracey Pratt Durham Exotics Workshop
Searches for New Physics in High Mass Dimuon Channel
Search selection
2 isolated PT>20 GeV/c, ||<1
Cosmic ray rejection cuts
Good agreement with SM prediction
being updated with 200 pb-1
Tracey Pratt Durham Exotics Workshop
Dilepton: ee + 126pb-1
results being updated with 200
pb-1
Tracey Pratt Durham Exotics Workshop
Run II dijet search at CDF
Inclusive Jet samples2 highest ET jets selected
Highest mass event 1364 GeV/c2
ET=666 GeV (corr)
583 GeV (raw)
=0.31 (detector)=0.43 (correct z)
ET=633 GeV (corr)
546 GeV (raw)
=-0.30 (detector)=-0.19 (correct z)
z vertex = - 25 cm
z
Tracey Pratt Durham Exotics Workshop
Dijet Limits 75pb-1
•Fit the mass spectrum with a simple background parameterization and •Search for bumps comparable with our mass resolution.
No significant evidence for a new particle
Tracey Pratt Durham Exotics Workshop
Dijet Limits 75pb-1
200 and 980 GeV
200 and 570 GeV and 580 and 760 GeV
260 and 480 GeV
290 and 420 GeV
300 and 420 GeV
CDF Run I
95
% C
L
Tracey Pratt Durham Exotics Workshop
Dijets Limits 75pb-1
In Run 2 exclude Randall-Sundrum Gravitons with coupling k/Mpl=0.3 between 220 and 840 GeV.
The Randall-Sundrum model did not exist in Run 1.
Tracey Pratt Durham Exotics Workshop
Run II diphoton search
Results
Highest mass event is: 168 GeV/c2
Above 150 GeV/c2: Observed 2 events
Expected 3.3 events
Search selection
Isolated with ET > 13 GeV, || < 0.9
No 3D tracks pointing to em cluster
No excess observed at high invariant mass
Main backgrounds
fakes from -jet and jet-jet,
where jet fragments into a hard 0
Tracey Pratt Durham Exotics Workshop
Run II diphoton search
?Plan to set limits on new physics models:
RS, ADD, generic search…
Tracey Pratt Durham Exotics Workshop
Et
Search Selection - One with ET > 47 GeV and ||<1 - Missing ET > 42 GeV - No jets with ET > 10 GeV - No tracks with pT > 5 GeV
ResultsExpected background: 19.8 2.3 Observed: 18
W e (““) 7.9 1.8
Z0+ 5.1 0.5
Cosmic Ray Muons 4.6 1.1
1.2 0.4
W 1.0 0.3
Main backgrounds
91 pb-1
95 % C.L. of 10.1 events →AL = 110 fb-1
2.0 times expected Z signal
3.1 times expected Zgamma signal found in Run I !
Tracey Pratt Durham Exotics Workshop
Run I Limits (87pb-1)n=4 MD > 0.55 TeV
n=6 MD > 0.58 TeV
n=8 MD > 0.60 TeV
qq GKK
Intrepret in terms of models predicting
qq → X
1) Large Extra Dimensions
2) LSP
+ ET
Tracey Pratt Durham Exotics Workshop
“Model-Based” Signature Searches
• excited electrons
• leptoquarks
•Perform search for a particular favourite Model
•Search for a particular signature/s predicted by the model
Tracey Pratt Durham Exotics Workshop
Excited/exotic e Signature
pp→ee*→ee
Interpretation of limitExcited electrons are expected in
many compositeness models. • Model 1: based on excited fermions
coupling to quarks and leptons via contact interaction, described by an effective four-fermion Lagrangian (Baur, U. Phys Rev D 42, 3).
• Model 2: excited electrons produced via gauge mediated interaction
(Baur, U. Phys Rev D 42, 3).
The cross section depends the e* mass and the compositeness scale, .
Tracey Pratt Durham Exotics Workshop
Excited/exotic e Signature
pp→ee*→eeThere is very little background
A benefit of searching for eegamma production is the absense of significant background. The primary sources of background are Zgamma, Z+jet (where a jet fakes a photon), WZ (where an electron is misidentified as a photon, W+jets (where one jet fakes a photon and one jet fakes electrons), multijet background (where one jet fakes a photon and two jets fake electrons), and diphoton+jet (where a jet fakes an electron). We use U. Baur's ZGAMMA program to predict the Zgamma contribution and PYTHIA for WZ and diphoton+jet. We have calculated and applied the fake rates needed for the processes involving jets. This link has the integrated background number of events prediction as a function of the three body masss. Additionally, we plot two distributions: the number of M(e+gamma) entries and the number of events as a function of M(e+e+gamma).
344 GeV
e, 96 GeV, 73 GeV
e, 165 GeV
3 candidate events
Tracey Pratt Durham Exotics Workshop
ee limitsContact Interaction
Gauge Mediated
Tracey Pratt Durham Exotics Workshop
Lepton + Quark Resonances:Leptoquarks
LQs appear in many extensions of SM (compositeness, technicolor…)Additional symmetry/transition between leptons and quarks → Leptoquarks•have both lepton and baryon number •fractional em. charge: +-1/3, +-4/3,etc.•Branching Ratio unknown, convention:
β=1 means 100% BR(LQ→l±q)β=0 means 100% BR(LQ→q)
Productionqq → LQ LQ qg → LQ LQ
Experimental SignatureHigh pt isolated leptons (and/or ET) + jets e,
u,d
•Connect lepton & quark sectors
DecayLQ LQ → l+l-qq, l+/-qq, qq
gg → LQ LQ
Generation refers to the lepton/quark generation
Tracey Pratt Durham Exotics Workshop
Leptoquarks: 1st generation
Signature: ejj Result: M(LQ)>166 GeV for β=0.5 (72 pb-1)
Signature: jj (New in Run II)
2 jets and ET>60 GeVResult: 124 events observed
118.3±14.5 events expectedexclude LQ masses with
78<M<117 GeV β=0
Signature: eejj Result: M(LQ)>230 GeV for β=1 (72 pb-1)
Tracey Pratt Durham Exotics Workshop
Leptoquarks: 2nd generation• Signature
– 2 high Pt muons– 2 high Et jets– Main background from /Z→μμ
accompanied by jets due to radiation
• Suppress Z→μμ background
Expect 3±1 events, observe 2
Exclude LQ’s M(LQ)<240 GeV
Tracey Pratt Durham Exotics Workshop
Leptoquarks
Competition between world’s accelerators:
•HERA, LEP and Tevatron
•At Tevatron: independent of coupling λ
e e
Tracey Pratt Durham Exotics Workshop
Conclusion and Outlook
• Many Searches for New Physics have started
– Now have twice the Run I luminosity – Signature- and Model-based searches being
performed– Covering a broad range of possible signals – Many not in talk: monopoles, WIMPS, bb+…– No signals yet but constraining theoretical models
Many New Exciting Results coming soon!
Tracey Pratt Durham Exotics Workshop
THE END!