tracey prattdurham exotics workshop exotic searches at cdf in run ii motivation for exotic searches...

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


“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 ?


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


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


“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


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


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


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


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


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'


Little Higgs Z`


Technicolor

T, T

l-

l+q

q

Use Z` limit


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


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


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


Dilepton: ee + 126pb-1

results being updated with 200

pb-1


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


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


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


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.


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


Run II diphoton search

?Plan to set limits on new physics models:

RS, ADD, generic search…


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 !


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


“Model-Based” Signature Searches

• excited electrons

• leptoquarks

•Perform search for a particular favourite Model

•Search for a particular signature/s predicted by the model


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, .


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


ee limitsContact Interaction

Gauge Mediated


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


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)


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


Leptoquarks

Competition between world’s accelerators:

•HERA, LEP and Tevatron

•At Tevatron: independent of coupling λ

e e


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!


THE END!

tracey prattdurham exotics workshop exotic searches at cdf in run ii motivation for exotic searches...

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