Top Banner
Randall-Sundrum KK Gluon & Energetic Tops at the LHC Joseph Virzi, LBL K. Agashe, A. Belyaev, T. Krupovnickas, G. Perez and JV / hep-ph/612015 Work in Progress with K.Agashe, T.Han, G.Perez
57

Randall-Sundrum KK Gluon & Energetic Tops at the LHC

Feb 07, 2016

Download

Documents

Bunny

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 - PowerPoint PPT Presentation
Welcome message from author
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
Page 1: Randall-Sundrum KK Gluon & Energetic Tops at the LHC

Randall-Sundrum KK Gluon & Energetic Tops at the LHC

Joseph Virzi, LBL

K. Agashe, A. Belyaev, T. Krupovnickas, G. Perez and JV / hep-ph/612015Work in Progress with K.Agashe, T.Han, G.Perez

Page 2: Randall-Sundrum KK Gluon & Energetic Tops at the LHC

May 2007 Joseph Virzi UC Berkeley 2

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

Page 3: Randall-Sundrum KK Gluon & Energetic Tops at the LHC

May 2007 Joseph Virzi UC Berkeley 3

Randall-Sundrum Modelwith SM fields propagating in the bulk

• solves the hierarchy problem for

ckrWM ke

22 2 2

& 0

ckrc

PL

ds e dx dx r d

k M

10ckr

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

4D metric

Page 4: Randall-Sundrum KK Gluon & Energetic Tops at the LHC

May 2007 Joseph Virzi UC Berkeley 4

• SM phenomenology constrains profiles in 5th dimension• Yukawa couplings are given by overlap with Higgs on

TeV brane

Warp Factor

ckr

Page 5: Randall-Sundrum KK Gluon & Energetic Tops at the LHC

May 2007 Joseph Virzi UC Berkeley 5

Particle Profiles

• Couplings to tops are enhanced and parity violating

• Dominant coupling to tR because of pheno’ constraints

LIGHT HEAVY

ckr

Page 6: Randall-Sundrum KK Gluon & Energetic Tops at the LHC

May 2007 Joseph Virzi UC Berkeley 6

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)

Page 7: Randall-Sundrum KK Gluon & Energetic Tops at the LHC

May 2007 Joseph Virzi UC Berkeley 7

RS1 KK Gluon

• 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

Branching Ratio of KKG vs MKKG

Page 8: Randall-Sundrum KK Gluon & Energetic Tops at the LHC

May 2007 Joseph Virzi UC Berkeley 8

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

+

Page 9: Randall-Sundrum KK Gluon & Energetic Tops at the LHC

May 2007 9

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)

σ vs Invariant Mass

Page 10: Randall-Sundrum KK Gluon & Energetic Tops at the LHC

May 2007 10

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

Page 11: Randall-Sundrum KK Gluon & Energetic Tops at the LHC

May 2007 Joseph Virzi UC Berkeley 11

L/R Polarization Asymmetry Introduction to PLR

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

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

θ

Page 12: Randall-Sundrum KK Gluon & Energetic Tops at the LHC

May 2007 Joseph Virzi UC Berkeley 12

• Dileptonic channel → 2 neutrinos– Difficulty resolving neutrino– 10% BR

• Fully hadronic decay– Background more difficult– 60% BR

semileptonic

hadronic

leptonic

• Semileptonic (ttbar→bbjjℓν) channel most promising for this analysis.– BR(ttbar →{μ,e}) = 30%

Production & Decaytt

Page 13: Randall-Sundrum KK Gluon & Energetic Tops at the LHC

May 2007 Joseph Virzi UC Berkeley 13

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

Page 14: Randall-Sundrum KK Gluon & Energetic Tops at the LHC

May 2007 Joseph Virzi UC Berkeley 14

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

Page 15: Randall-Sundrum KK Gluon & Energetic Tops at the LHC

May 2007 Joseph Virzi UC Berkeley 15

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

Page 16: Randall-Sundrum KK Gluon & Energetic Tops at the LHC

May 2007 Joseph Virzi UC Berkeley 16

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 eventsNumber of Jets

Nu

mb

er

of E

ven

ts

Page 17: Randall-Sundrum KK Gluon & Energetic Tops at the LHC

May 2007 Joseph Virzi UC Berkeley 17

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)

Page 18: Randall-Sundrum KK Gluon & Energetic Tops at the LHC

May 2007 Joseph Virzi UC Berkeley 18

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

Page 19: Randall-Sundrum KK Gluon & Energetic Tops at the LHC

May 2007 Joseph Virzi UC Berkeley 19

Invariant Mass Plots

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

• The conventional method is more appropriate for lower energies

• Shape of the background

Where’s the peak?

TopJet Method

Conventional Method

Page 20: Randall-Sundrum KK Gluon & Energetic Tops at the LHC

May 2007 Joseph Virzi UC Berkeley 20

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

Page 21: Randall-Sundrum KK Gluon & Energetic Tops at the LHC

May 2007 21

• Boost profile for com is central for large invariant mass

• Primary production is through qqbar

Motivates stiff PT cut

Kinematicstt

Page 22: Randall-Sundrum KK Gluon & Energetic Tops at the LHC

May 2007 Joseph Virzi UC Berkeley 22

JETS

Page 23: Randall-Sundrum KK Gluon & Energetic Tops at the LHC

May 2007 Joseph Virzi UC Berkeley 23

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

Page 24: Randall-Sundrum KK Gluon & Energetic Tops at the LHC

May 2007 Joseph Virzi UC Berkeley 24

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

Page 25: Randall-Sundrum KK Gluon & Energetic Tops at the LHC

May 2007 Joseph Virzi UC Berkeley 25

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

Page 26: Randall-Sundrum KK Gluon & Energetic Tops at the LHC

May 2007 Joseph Virzi UC Berkeley 26

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.

Taken from ATL-SOFT-2003-010

Jet Energy Scale for b & light jets

Page 27: Randall-Sundrum KK Gluon & Energetic Tops at the LHC

May 2007 Joseph Virzi UC Berkeley 27

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

Page 28: Randall-Sundrum KK Gluon & Energetic Tops at the LHC

May 2007 Joseph Virzi UC Berkeley 28

Background Analysis

Page 29: Randall-Sundrum KK Gluon & Energetic Tops at the LHC

May 2007 Joseph Virzi UC Berkeley 29

Efficiency of CutsOn Signal & Background

• RED survives all cuts

Signal (RS+SM)

W+JETSSINGLE TOP

Page 30: Randall-Sundrum KK Gluon & Energetic Tops at the LHC

May 2007 30

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

Page 31: Randall-Sundrum KK Gluon & Energetic Tops at the LHC

May 2007 Joseph Virzi UC Berkeley 31

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

Page 32: Randall-Sundrum KK Gluon & Energetic Tops at the LHC

May 2007 Joseph Virzi UC Berkeley 32

ConclusionsConclusions• 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

Page 33: Randall-Sundrum KK Gluon & Energetic Tops at the LHC

May 2007 Joseph Virzi UC Berkeley 33

Backup Slides

Page 34: Randall-Sundrum KK Gluon & Energetic Tops at the LHC

May 2007 Joseph Virzi UC Berkeley 34

Summary of CutsCUT VALUE

Leptonic Top Mass 174 GeV ± 50 GeV

Hadronic Top Mass 174 GeV ± 50 GeV

Hadronic W Mass 81 GeV ± 50 GeV

Missing ET > 30 GeV

Lepton Isolation ∆R > 0.4 or MBL>40 GeV

Lepton PT > 10 GeV

Lepton η < 2.5

Jet PT > 20 GeV

Jet η < 4.5

Leptonic Top PT > 600 GeV

Page 35: Randall-Sundrum KK Gluon & Energetic Tops at the LHC

May 2007 Joseph Virzi UC Berkeley 35

Jet PT Distributionsfrom signal sample

• B-jet spectrum is harder than for light jets

Page 36: Randall-Sundrum KK Gluon & Energetic Tops at the LHC

May 2007 36

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

Evolution of cuts for single top production

green is conventional mode

Page 37: Randall-Sundrum KK Gluon & Energetic Tops at the LHC

May 2007 37

PT of leptonic top after cuts

Page 38: Randall-Sundrum KK Gluon & Energetic Tops at the LHC

May 2007 38

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

Page 39: Randall-Sundrum KK Gluon & Energetic Tops at the LHC

May 2007 39

Efficiencies of Cuts

• Conventional Reconstruction Method

• TopJet Reconstruction Method– Stiff PT cut provides the coup-de-grace

(discuss later)– Has high signal efficiency

RED are events passing all cutsBoth plots are drawn to same scale

GREEN is conventional reconstruction

Page 40: Randall-Sundrum KK Gluon & Energetic Tops at the LHC

May 2007 Joseph Virzi UC Berkeley 40

Conventional Reconstruction

RS1 W+Jets Single Top

# of events 880000 650000 478700

# passing preselection 21314 50 36701

# passing lepton cuts 17640 40 31427

# pass leptonic top mass cuts

9483 19 20171

# pass leptonic top PT cut

48 0 137

Page 41: Randall-Sundrum KK Gluon & Energetic Tops at the LHC

May 2007 Joseph Virzi UC Berkeley 41

TopJet Cut Statistics

RS1 W+Jets Single Top

# of events 880000 650000 478700

# pass preselection 59081 147 116471

# pass lepton cuts 46348 120 89768

# pass leptonic top mass cuts

18862 22 68097

# pass leptonic top PT cut

2033 0 190

Page 42: Randall-Sundrum KK Gluon & Energetic Tops at the LHC

May 2007 Joseph Virzi UC Berkeley 42

Efficiencies of Reconstructionusing Different Modes

Leptonic topPT>600 GeV

Page 43: Randall-Sundrum KK Gluon & Energetic Tops at the LHC

May 2007 Joseph Virzi UC Berkeley 43

Efficiencies of Reconstructionusing Different Modes

Leptonic topPT>400 GeV

Page 44: Randall-Sundrum KK Gluon & Energetic Tops at the LHC

May 2007 Joseph Virzi UC Berkeley 44

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

Page 45: Randall-Sundrum KK Gluon & Energetic Tops at the LHC

May 2007 Joseph Virzi UC Berkeley 45

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

Page 46: Randall-Sundrum KK Gluon & Energetic Tops at the LHC

May 2007 Joseph Virzi UC Berkeley 46

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

Page 47: Randall-Sundrum KK Gluon & Energetic Tops at the LHC

May 2007 Joseph Virzi UC Berkeley 47

single tops-channel

PT(leptonic top)

Page 48: Randall-Sundrum KK Gluon & Energetic Tops at the LHC

May 2007 Joseph Virzi UC Berkeley 48

Page 49: Randall-Sundrum KK Gluon & Energetic Tops at the LHC

May 2007 Joseph Virzi UC Berkeley 49

Page 50: Randall-Sundrum KK Gluon & Energetic Tops at the LHC

May 2007 Joseph Virzi UC Berkeley 50

Single top t-channelTruth Level Analysis

Page 51: Randall-Sundrum KK Gluon & Energetic Tops at the LHC

May 2007 Joseph Virzi UC Berkeley 51

Single top t-channel

Page 52: Randall-Sundrum KK Gluon & Energetic Tops at the LHC

May 2007 Joseph Virzi UC Berkeley 52

Page 53: Randall-Sundrum KK Gluon & Energetic Tops at the LHC

May 2007 Joseph Virzi UC Berkeley 53

Page 54: Randall-Sundrum KK Gluon & Energetic Tops at the LHC

May 2007 Joseph Virzi UC Berkeley 54

Page 55: Randall-Sundrum KK Gluon & Energetic Tops at the LHC

May 2007 Joseph Virzi UC Berkeley 55

Page 56: Randall-Sundrum KK Gluon & Energetic Tops at the LHC

May 2007 Joseph Virzi UC Berkeley 56

• jlkajsdkθ

22 2 2sin2BL B L TM p p M

θ

Page 57: Randall-Sundrum KK Gluon & Energetic Tops at the LHC

May 2007 Joseph Virzi UC Berkeley 57

W+Jets Jet PT Distribution