Randall sundrum kk gluon energetic tops at the lhc
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Randall-Sundrum KK Gluon & Energetic Tops at the LHC. K. Agashe, A. Belyaev, T. Krupovnickas, G. Perez and JV / hep-ph/612015 Work in Progress with K.Agashe, T.Han, G.Perez. Joseph Virzi, LBL. Outline. Brief Introduction to Randall-Sundrum (RS) Model

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Randall-Sundrum KK Gluon & Energetic Tops at the LHC

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Randall sundrum kk gluon energetic tops at the lhc

Randall-Sundrum KK Gluon & Energetic Tops at the LHC

K. Agashe, A. Belyaev, T. Krupovnickas, G. Perez and JV / hep-ph/612015

Work in Progress with K.Agashe, T.Han, G.Perez

Joseph Virzi, LBL


Outline

Outline

  • Brief Introduction to Randall-Sundrum (RS) Model

  • Focus on detection of KKG using top quark pair production

  • Top reconstruction @ high PT

    • discuss associated challenges

    • propose approaches to address these challenges

  • Polarization asymmetry measurement

  • Background Analysis & Discussion

  • Conclusions

Joseph Virzi UC Berkeley


Randall sundrum model with sm fields propagating in the bulk

Randall-Sundrum Modelwith SM fields propagating in the bulk

solves the hierarchy problem for

  • motivation for model is hierarchy problem – vast difference between the weak and Planck scales

4D metric

Joseph Virzi UC Berkeley


Randall sundrum kk gluon energetic tops at the lhc

Warp Factor

  • SM phenomenology constrains profiles in 5th dimension

  • Yukawa couplings are given by overlap with Higgs on TeV brane

Joseph Virzi UC Berkeley


Particle profiles

Particle Profiles

LIGHT

HEAVY

  • Couplings to tops are enhanced and parity violating

  • Dominant coupling to tR because of pheno’ constraints

Joseph Virzi UC Berkeley


Analysis

Analysis

  • The formalism of the RS1 model leads to KK excitations

  • We consider here the first excitation of the gluon, G(1)

    • Experimental constraints favor masses of G(1) > 2TeV

    • Case study: 3 TeV KK gluon

    • Will use 100 fb-1 of data (3 years at high luminosity @ LHC)

Joseph Virzi UC Berkeley


Rs1 kk gluon

RS1 KK Gluon

Branching Ratio of KKG vs MKKG

  • Prefers decay into heavier quarks, especially to tops.

    • BR > 0.95

  • Heavy quark couplings to G(1) are enhanced relative to the SM.

    • For tR ~5

    • For tL & bL ~1.

  • Light quarks & bR couplings are suppressed by factor ~5.

  • SM gluon couplings vanish due to orthogonality conditions

Joseph Virzi UC Berkeley


Feynman diagrams

Feynman Diagrams

  • Relevant Tree Level Diagrams for our discussion

  • The gg→KKG vertex does not exist because of orthogonality arguments

  • Primary production mechanism for top quark pairs

+

Joseph Virzi UC Berkeley


Signatures of kk gluon

Signatures of KK Gluon

  • The RS1 KK Gluon provides a resonance structure

    • Width ~0.2 MKKG ( 600 GeV )

  • total cross section 850 pb

  • ΔσRS = O(100 fb)

σvs Invariant Mass


Signatures of kk gluon cont d

Signatures of KK Gluon (cont’d)

  • The excess production will have more tR than tL

  • Strategy

    • G(1) contribution to PLR is large & opposite sign than SM

    • Correlate large L/R polarization asymmetry to the mass peak

L/R Polarization vs Invariant Mass

RS prediction

SM prediction


L r polarization asymmetry introduction to p lr

L/R Polarization Asymmetry Introduction to PLR

  • Look at the direction of the lepton in the top quark rest frame

θ

N+ & N- are the number of events where the lepton is forward (cos(θ) > 0.0) and where the lepton is backward, respectively in the top rest frame

Joseph Virzi UC Berkeley


Randall sundrum kk gluon energetic tops at the lhc

  • Dileptonic channel → 2 neutrinos

    • Difficulty resolving neutrino

    • 10% BR

  • Fully hadronic decay

    • Background more difficult

    • 60% BR

  • Semileptonic (ttbar→bbjjℓν) channel most promising for this analysis.

    • BR(ttbar →{μ,e}) = 30%

Joseph Virzi UC Berkeley


Monte carlo simulation strategy

Monte Carlo Simulation Strategy

  • Used a customized version of the Sherpa MC

    • Full spin correlations in top decays

  • 100 fb-1 of signal ( SM/RS ) with MKKG = 3 TeV

    • Invariant Mass > 1 TeV

    • σ(M>1TeV) x 0.3 semileptonic BR = 8.8 pb

  • 100 fb-1 of W+jets sample

    • Invariant Mass > 1 TeV & PT > 300 GeV

    • σ (M>1TeV) = 6.5 pb

  • 100 fb-1 of single top production sample

    • Invariant Mass > 1 TeV & PT > 50 GeV

    • σ (M>1TeV)= 5 pb

Joseph Virzi UC Berkeley


Signal reconstruction overview

Signal Reconstruction Overview

  • Conventional methods of top reconstruction at the LHC involve reconstruction of whole top decay chain

    • beats down background

    • Requires ≥4 jets, of which ≥2 are b-jets

  • The approach breaks down at energies ~ TeV

    • Jets collimate. We will discuss later

  • We overhauled the methods to address deficiencies

Joseph Virzi UC Berkeley


Conventional signal reconstruction

Conventional Signal Reconstruction

  • Reconstruction of top pairs

    • ≥4 jets, 2 are b-tagged

    • Isolated lepton - ΔR

    • Missing energy → neutrino

    • Top mass (174 GeV ) is an input

    • 1 b-jet + W reconstructs leptonic top

    • 2 light jets reconstruct hadronic side W

    • Other b-jet + W reconstructs hadronic top

Joseph Virzi UC Berkeley


Problem with conventional method

Problem with Conventional Method

  • As the invariant mass of the ttbar event ↑ the jet multiplicity ↓

  • Conventional approach works well here

  • Reconstruction efficiency is adversely affected @ high invariant mass

    • Very few 4 jet events

Number of Events

Number of Jets

Joseph Virzi UC Berkeley


Topjet reconstruction

TopJet Reconstruction

  • Hadronic side – giving up

    • Use the events where the decay products of the top are observed as a single jet

    • Impose a top-jet hypothesis on the hadronic side jet

    • remove b-tagging constraint on hadronic side

    • Stiff ( >600 GeV ) PT cut on the leptonic side top decimates background

  • Modify leptonic top reconstruction

    • Lepton isolation difficult (next)

Joseph Virzi UC Berkeley


Removing b decay leptons m bl

Removing B Decay Leptons - MBL

  • MBL – the invariant mass between b-jet and lepton

    • B decay leptons have MBL ~ 5 GeV

    • Signal leptons have MBL ~ 50 GeV

  • 20% of b-jets contain leptons

  • descriminate against B decay leptons

  • Keep leptons from t → bW →bℓν

Joseph Virzi UC Berkeley


Invariant mass plots

Invariant Mass Plots

TopJet Method

  • TopJet approach is vastly more statistically significant over the mass window

  • The conventional method is more appropriate for lower energies

  • Shape of the background

Conventional Method

Where’s the peak?

Joseph Virzi UC Berkeley


Efficiency plot

Efficiency Plot

Huge increase in reconstruction efficiency

The efficiency & mass curves are shaped by the physics

The mass curve is not shaped by the efficiency curve

Reconstruction Efficiency vs Invariant Mass

Joseph Virzi UC Berkeley


Randall sundrum kk gluon energetic tops at the lhc

  • Boost profile for com is central for large invariant mass

  • Primary production is through qqbar

Motivates stiff PT cut


Randall sundrum kk gluon energetic tops at the lhc

JETS

Joseph Virzi UC Berkeley


Jet p t over mass peak

Jet PT over mass peak

  • Distributions are normalized to unit area

  • <PT> of b-jets = 555 GeV

  • 50% of b-jets have PT > 300 GeV

Joseph Virzi UC Berkeley


B tagging @ high p t

B-tagging @ high PT

  • Important Issue but still relatively uncertain

    • Best estimates at low energies place ε = b-tag efficiency = 60%

  • Best estimates are approximately 20% at upper end of the PT spectrum

    • March, Ros, Salvachua ATL-PHYS-PUB-2006-002

  • Remain conservative & use 20% throughout

  • Conventional reconstruction methods depend on 2 b-tags. Quadratic dependence on ε

  • New approach described here only requires 1 b-tag. Linear dependence on ε

Joseph Virzi UC Berkeley


Light jet rejection

Light Jet Rejection

  • Ensuring that we do not label jets from lighter partons as b-jets

    • especially important for W+jets background

  • Current estimates

    • March, Ros & Salvachua ATL-PHYS-PUB-2006-002

    • Rc = 30. Ru = 130

  • This analysis is performed with a uniform rejection ratio Rq=30

Joseph Virzi UC Berkeley


L r polarization asymmetry

L/R Polarization Asymmetry

Challenges

  • Jet Energy Corrections

    • Jet Energy ≠ Parton Energy

    • Vital to reconstructing quark cm frame for PLR

    • Adds uncertainty to reconstruction of cms kinematics.

Jet Energy Scale for b & light jets

Taken from ATL-SOFT-2003-010

Joseph Virzi UC Berkeley


L r polarization asymmetry cont d lepton p t distribution

L/R Polarization Asymmetry Cont’dLepton PT Distribution

The L/R polarization asymmetry will manifest itself in the lepton <PT> (A.T.Holloway)

Lepton PT vs Invariant Mass

Joseph Virzi UC Berkeley


Background analysis

Background Analysis

Joseph Virzi UC Berkeley


Efficiency of cuts on signal background

Efficiency of CutsOn Signal & Background

RED survives all cuts

Signal (RS+SM)

W+JETS

SINGLE TOP

Joseph Virzi UC Berkeley


Results of top jet approach

Results of Top Jet Approach

  • The peak becomes much more statistically significant

  • We correlate the mass peak to the PLR

  • Additionally, we can observe the <PT> of the lepton


Lhc reach

LHC Reach

  • Our reconstruction efficiency remains relatively flat to 4 TeV

  • Current estimates place the reach of the LHC for our signal to 4 TeV

Joseph Virzi UC Berkeley


Conclusions

Conclusions

  • With new reconstruction technique, the signature(s) of the RS KK gluon becomes much more statistically significant

    • Combination of Topjet and Conventional techniques spans low to high MTT

    • The efficiency of reconstruction increases by O(5)

    • And turns out to stay relatively flat for increasing invariant mass ~4TeV

  • The W+jets and single top background is small

  • 100 fb-1 of data is a long time.

    • Depending on the mass of the KK gluon, efficiencies and fake rates, maybe we can get by with less data

    • Need to leave some wiggle room ( PDF & other uncertainties )

  • Preliminary analysis using more realistic reconstruction techniques shows consistency with the results herein

Joseph Virzi UC Berkeley


Backup slides

Backup Slides

Joseph Virzi UC Berkeley


Summary of cuts

Summary of Cuts

Joseph Virzi UC Berkeley


Jet p t distributions from signal sample

Jet PT Distributionsfrom signal sample

  • B-jet spectrum is harder than for light jets

Joseph Virzi UC Berkeley


Single top background

Single TopBackground

  • Sample used is single top production

    • Representing 100 fb-1

    • MCMS > 1 TeV

    • PT > 50 GeV

    • 5 pb cross section

    • PT cut yields high background rejection

    • 97% light jet rejection

    • t-channel production is dominant

green is conventional mode

Evolution of cuts for single top production


Randall sundrum kk gluon energetic tops at the lhc

PT of leptonic top after cuts


W jets background

W+JETS background

  • Sample is W+jets

    • representing 100 fb-1

    • MCMS > 1.5 TeV

    • PT > 300 GeV

    • cross section 6.5 pb

    • Light jet rejection → 97%

Evolution of cuts for W+jets background


Efficiencies of cuts

Efficiencies of Cuts

Conventional Reconstruction Method

  • TopJet Reconstruction Method

    • Stiff PT cut provides the coup-de-grace (discuss later)

    • Has high signal efficiency

GREEN is conventional reconstruction

RED are events passing all cuts

Both plots are drawn to same scale


Conventional reconstruction

Conventional Reconstruction

Joseph Virzi UC Berkeley


Topjet cut statistics

TopJet Cut Statistics

Joseph Virzi UC Berkeley


Efficiencies of reconstruction using different modes

Efficiencies of Reconstructionusing Different Modes

Leptonic top

PT>600 GeV

Joseph Virzi UC Berkeley


Efficiencies of reconstruction using different modes1

Efficiencies of Reconstructionusing Different Modes

Leptonic top

PT>400 GeV

Joseph Virzi UC Berkeley


W jets background1

W+JETS background

  • I focus here on background most likely to do damage

    • Invariant mass > 1.5 TeV

    • PT > 300 GeV

    • Cross section 6.5 pb

  • The background plot looks at all combinations of 2, 3 and 4 jets which pass the indicated cuts on the leptonic side.

    • Superset of actual background

    • No b-tagging / light jet rejection assumptions

Evolution of cuts for W+jets background

Joseph Virzi UC Berkeley


Single top background1

Single TopBackground

  • Sample used is single top production

    • MCMS > 1.5 TeV.

    • PT > 100 GeV

    • 5 pb cross section

  • The background plot looks at all combinations of 2, 3 and 4 jets which pass the indicated cuts on the leptonic side.

    • Superset of actual background

    • No b-tagging / light jet rejection assumptions

Evolution of cuts for single top production

Joseph Virzi UC Berkeley


Spectrum of hadronic side reconstruction modes

Spectrum of Hadronic SideReconstruction Modes

  • 2 light jet + 1 b jet events

    • b → semileptonic top

    • 2 light jets summed

  • 1 light jet + 2 b jet events

    • b → semileptonic top

    • hadronic top = b + j

  • 3 light jets + 1 b jet events

    • b → semileptonic top

    • hadronic top = j + j + j

  • 5+ jet events

  • In all cases, the jets on the hadronic side are summed to the top

  • Reconstruction modes are separated for different jet multiplicities

    • The final reconstruction depends weakly on jet reconstruction algorithm

    • Allows for weighing contribution from each mode

Joseph Virzi UC Berkeley


Single top s channel

single tops-channel

PT(leptonic top)

Joseph Virzi UC Berkeley


Randall sundrum kk gluon energetic tops at the lhc

Joseph Virzi UC Berkeley


Randall sundrum kk gluon energetic tops at the lhc

Joseph Virzi UC Berkeley


Single top t channel truth level analysis

Single top t-channelTruth Level Analysis

Joseph Virzi UC Berkeley


Single top t channel

Single top t-channel

Joseph Virzi UC Berkeley


Randall sundrum kk gluon energetic tops at the lhc

Joseph Virzi UC Berkeley


Randall sundrum kk gluon energetic tops at the lhc

Joseph Virzi UC Berkeley


Randall sundrum kk gluon energetic tops at the lhc

Joseph Virzi UC Berkeley


Randall sundrum kk gluon energetic tops at the lhc

Joseph Virzi UC Berkeley


Randall sundrum kk gluon energetic tops at the lhc

  • jlkajsdkθ

θ

Joseph Virzi UC Berkeley


W jets jet pt distribution

W+Jets Jet PT Distribution

Joseph Virzi UC Berkeley


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