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CMS Sensitivity to Dijet Resonances

Robert M. Harris (Fermilab)

Kazim Gumus and Nural Akchurin (Texas Tech)

Selda Esen (Brown)

DPF Meeting

November 1, 2006

Robert Harris, Fermilab 2

Introduction

This study performed at the LHC Physics Center at Fermilab (LPC) A center of CMS software and analysis expertise in the U.S. Where students and postdocs learn CMS analysis from Tevatron experts.

Publicly available as CMS Note 2006 / 070 http://cms.cern.ch/iCMS/jsp/openfile.jsp?type=NOTE&year=2006&files=NOTE2006_070.pdf Ph.D thesis of Kazim Gumus at Texas Tech University.

Uses a jet trigger proposed in CMS Note 2006 / 069 http://cms.cern.ch/iCMS/jsp/openfile.jsp?type=NOTE&year=2006&files=NOTE2006_069.pdf Part of the Ph.D thesis of Selda Esen now at Brown.

She talked earlier today on “CMS sensitivity to contact interactions using dijets”.

Analysis Estimate 5 discovery and 95% CL exclusion sensitivity for dijet resonances. √s=14 TeV and ∫Luminosity of 100 pb-1 (2008?), 1 fb-1 (2009?), 10 fb-1 (2011?). Uses a full simulation of signal and background in the CMS detector.

Robert Harris, Fermilab 3

Motivation

Theoretical Motivation Dijet resonances are in many models that address important questions: Why Flavor ? Technicolor or Topcolor Octet Technirho or Coloron Why Generations ? Compositeness Excited Quarks Why So Many Forces ? Grand Unified Theory W’ & Z’ Can we include Gravity ? Superstrings E6 Diquarks Why is Gravity Weak ? Extra Dimensions Randall-Sundrum Gravitions

Experimental Motivation LHC is a parton-parton resonance factory in a previously unexplored region. We search for generic narrow dijet resonances, not specific models.

Nature may surprise us with unexpected new particles. It wouldn’t be the first time …

Dijet Resonances S-channel parton-parton resonances. Observe two high pT jets: Dijets. Dijet mass forms narrow resonance peak.

X

q, q, g

q, q, g

q, q, g

q, q, g

Robert Harris, Fermilab 4

Dijet Analysis Jets are reconstructed using a

cone algorithm Energy inside a circle of radius R

centered on jet axis is summed:

Dijet is two highest pT jets. Require each jet to have | | < 1

Reduces t-channel QCD background.

Dijet mass

Jet E and p are corrected for Calorimeter non-linear response Pile-up of extra soft proton-proton

collisions on top of our dijet event Correction varies from 33% at pT= 75

GeV to 7% at pT =2.8 TeV.

Jet 2

Jet 1

BARREL ENDCAPENDCAP

221

221 )()( ppEEm

5.022 R

Robert Harris, Fermilab 5

Narrow Resonance Shape in CMS

Model narrow resonance line shape at CMS with Z’ Simulation. All resonances with a width less than our resolution look like this in CMS.

Corrected dijet mass peaks around generated value Gaussian core with resolution Long tail to low mass comes mainly from QCD radiation.

Data here is in bins equal to the measured mass resolution above.

m / 1.3 0.045 /m

Robert Harris, Fermilab 6

Signal and Background

QCD cross section falls smoothly as a function of dijet mass. Resonances produce mass bumps we can see if xsec is big enough.

Robert Harris, Fermilab 7

Signal / QCD Many resonances give

obvious signals above the QCD error bars

Resonances produced via color force Excited Quark (shown) Axigluon Coloron Color Octet T

Resonances produced from valence quarks of each proton E6 Diquark (shown)

Others may be at the edge of our sensitivity.

Robert Harris, Fermilab 8

Statistical Sensitivity to Dijet Resonances

Sensitivity estimates Statistical likelihoods

done for both discovery and exclusion

5 Discovery We see a resonance

with 5 significance Likelihood found from a

sample that has a large signal.

95% CL Exclusion We don’t see anything

but QCD at 95% CL. Likelihood found from a

sample with QCD only.

Plots show resonances at 5 and 95% CL Compared to statistical

error bars from QCD.

5 TeV

2 TeV0.7 TeV

2 TeV0.7 TeV

Robert Harris, Fermilab 9

Systematic Uncertainties

We include all these systematic uncertainties in our sensitivity estimates.

Uncertainty on QCD Background Dominated by jet energy uncertainty

(±5%) which produces rate uncertainty. Background will be measured.

Trigger prescale edge effect Jet energy uncertainty has large effect at

mass values just above where trigger prescale changes.

Resolution Effect on Resonance Shape Bounded by difference between particle

level jets and calorimeter level jets.

Radiation effect on Resonance Shape Long tail to low mass which comes mainly

from final state radiation.

Luminosity

Robert Harris, Fermilab 10

Sensitivity to Resonance Cross Section

Cross Section for Discovery or Exclusion Shown here for 1 fb-1

Also for 100 pb-1, 10 fb-1

Compared to cross section for 8 models

CMS expects to have sufficient sensitivity to Discover with 5

significance any model above solid black curve

Exclude with 95% CL any model above the dashed black curve.

Can discover resonances produced via color force, or from valence quarks.

Robert Harris, Fermilab 11

Sensitivity To Resonance Models

CMS can discover the strongly produced models up to many TeV.

Discoveries with only 100 pb-1 !

Mass (TeV)

E6 Diquark

Excited Quark

Axigluonor Coloron

Color OctetTechnirho

CMS100 pb-1

CMS1 fb-1

CMS10 fb-1

5 Sensitivity to Dijet Resonances

0 1 2 3 4 5

E6 Diquark

Excited Quark

Axigluonor Coloron

Color OctetTechnirho

W ’

R S Graviton

Z ’

Published Exclusion (Dijets)

CMS100 pb-1

CMS1 fb-1

CMS10 fb-1

Mass (TeV)

95% CL Sensitivity to Dijet Resonances

0 1 2 3 4 5 6

Robert Harris, Fermilab 12

Conclusions

CMS will perform a generic search for narrow dijet resonances We’ve presented sensitivity estimates for 100 pb-1, 1 fb-1 and 10 fb-1 CMS capability to discover (5) or exclude (95% CL) resonances.

We can discover some models up to many TeV. Axigluon, Coloron, Excited Quark, Color Octet Technirho or E6 Diquark Produced via the color force or from the valence quarks of each proton.

Sensitivity to any new narrow resonance can be determined. Compare the model’s cross section for ||<1 to results in our CMS Note. Theorists can compare their latest ideas with CMS sensitivity estimates.

We look forward to the discovery of new physics at the LHC.