Lisa Randall, Harvard University Entering LHC Era Entering LHC Era - - PowerPoint PPT Presentation

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Lisa Randall, Harvard University Entering LHC Era Entering LHC Era - - PowerPoint PPT Presentation

Aug 25, 2022 109 likes •560 views

Lisa Randall, Harvard University Entering LHC Era Entering LHC Era Many challenges as LHC approaches Many challenges as LHC approaches Critical questions: Critical questions: Are we optimizing existing searches? Are we

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Lisa Randall, Harvard University

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Entering LHC Era Entering LHC Era

  • Many challenges as LHC approaches

Many challenges as LHC approaches

  • Critical questions:

Critical questions:

  • Are we optimizing existing searches?

Are we optimizing existing searches?

  • Are we doing all the searches possible?

Are we doing all the searches possible?

  • Models

Models

  • Lower

Lower-

  • Scale:

Scale: Supersymmetry Supersymmetry, Little Higgs , Little Higgs

  • Higher

Higher-

  • Scale: Strongly Interacting theories, Extra

Scale: Strongly Interacting theories, Extra dimensions dimensions

  • Focus today on extra dimensions

Focus today on extra dimensions

  • Bonus: Way to learn about quantum gravity

Bonus: Way to learn about quantum gravity and strongly interacting physics and strongly interacting physics

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Use Extra D to address Hierarchy Use Extra D to address Hierarchy Problem Problem

Need “fine-tuning” to get very different masses Key issue in particle physics today

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RS1 RS1 “ “Multiverse Multiverse” ” Warped Warped Spacetime Spacetime

  • Two branes
  • Gravity will be concentrated on

Gravitybrane

  • But we live on a second brane:
  • The Weakbrane/TeV Brane
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  • Small probability for

Small probability for graviton to be near graviton to be near the the Weakbrane Weakbrane

  • If we live anywhere

If we live anywhere but the but the Gravitybrane Gravitybrane, , gravity will seem gravity will seem weak weak

  • Natural consequence

Natural consequence

  • f warped geometry
  • f warped geometry

Natural for gravity to be weak! Natural for gravity to be weak!

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How to test? How to test?

  • Search for new particles!

Search for new particles!

  • Kaluza

Kaluza-

  • Klein (KK)

Klein (KK) particles particles

  • Carry momentum in extra dimensions

Carry momentum in extra dimensions

  • Looks like mass in 4 dimensions

Looks like mass in 4 dimensions

  • Connection to mass and

Connection to mass and weakness of weakness of gravity relative to other known forces gravity relative to other known forces tells tells us us

  • LHC will have the right energy to search

LHC will have the right energy to search for consequences of this theory for consequences of this theory

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Experimental Signal: Can search for Experimental Signal: Can search for extra dimensions! extra dimensions!

  • Kaluza

Kaluza-

  • Klein particles

Klein particles

  • TeV

TeV, 2 , 2 TeV TeV, 3 TEV , 3 TEV (rough) spectrum (rough) spectrum

  • With much stronger than

With much stronger than gravitational interaction gravitational interaction strength! strength!

  • Definite mass spectrum

Definite mass spectrum and and “ “spin spin” ”-

  • 2

2

  • Truly different than other

Truly different than other strongly interacting strongly interacting theories theories

  • Light spin

Light spin-

  • 2 but gap

2 but gap

  • No other strongly

No other strongly interacting states as light interacting states as light

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Reach for Graviton KK Modes Reach for Graviton KK Modes

Davoudiasl, Hewett, Rizzo

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graviton graviton has has spin 2 spin 2

M=1.5 TeV

100fb-1 Angular distributions

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  • RS1 gives clean

RS1 gives clean TeV TeV-

  • KK

KK-

  • graviton signal

graviton signal

  • One of first things LHC could find

One of first things LHC could find

  • Spin

Spin-

  • 2 and gap in spectrum definite indication of

2 and gap in spectrum definite indication of warped extra warped extra-

  • dimensional geometry

dimensional geometry

  • Could also exist lots of strongly interacting

Could also exist lots of strongly interacting TeV TeV-

  • scale physics to complement this measurement

scale physics to complement this measurement

  • But not the only implementation of RS1

But not the only implementation of RS1 mechanism mechanism

  • What does this imply about search

What does this imply about search strategies? strategies?

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Other warped Other warped models models addressing the addressing the hierarchy? hierarchy?

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Variations on RS1: Infinite extra Variations on RS1: Infinite extra dimension dimension

weakbrane Infinite dimenison

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Missing Energy Signal Missing Energy Signal

  • Looks like 6 large dimensions

Looks like 6 large dimensions

  • In this case KK mode decays to lighter KK

In this case KK mode decays to lighter KK modes modes

  • KK energy goes to missing energy

KK energy goes to missing energy

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  • Variations of RS1:

Variations of RS1: matter in bulk or on matter in bulk or on brane brane?? ??

  • Two key features that make bulk matter

Two key features that make bulk matter possible possible

  • Size of fifth dimension extremely small (only

Size of fifth dimension extremely small (only about 30 times fundamental scale about 30 times fundamental scale— — exponential hierarchy) exponential hierarchy)

Means coupling won Means coupling won’ ’t be too diluted/weak t be too diluted/weak

  • You only need Higgs on the

You only need Higgs on the Weakbrane Weakbrane to to address the hierarchy address the hierarchy

  • Problem only for the Higgs scalar: gauge boson

Problem only for the Higgs scalar: gauge boson and and fermion fermion masses are protected masses are protected

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Merits of bulk fermions and gauge Merits of bulk fermions and gauge fields fields

  • Because

Because 5D

5D cut

cut-

  • off is Planck scale
  • ff is Planck scale
  • Allows for unification!

Allows for unification!

  • Allows for interesting model

Allows for interesting model-

  • building:

building:

  • Fermion

Fermion masses from masses from wavefunction wavefunction overlap

  • verlap

with Higgs field (on with Higgs field (on Weakbrane Weakbrane) )

  • We

We’ ’ll see that bulk scenarios have ll see that bulk scenarios have distinctive signatures distinctive signatures

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Precise signatures depend on Precise signatures depend on fermion fermion wavefunction wavefunction profiles profiles

  • Might expect nontrivial profiles

Might expect nontrivial profiles

  • Masses depend on overlap with Higgs

Masses depend on overlap with Higgs

  • Expect light fermions localized near

Expect light fermions localized near Planck/Gravity Planck/Gravity brane brane

  • Top near

Top near Weakbrane Weakbrane since it since it’ ’s heavy s heavy

tR uL ,dL

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Important Differences from Important Differences from Brane Brane-

  • Localized Matter

Localized Matter

  • Richer Spectrum

Richer Spectrum

  • KK modes of

KK modes of

  • Weak bosons

Weak bosons

  • Gluons

Gluons

  • Fermions

Fermions

  • As well as gravitons

As well as gravitons

  • But

But… …lower Production Cross Section for Graviton lower Production Cross Section for Graviton

  • Plus decays primarily into tops

Plus decays primarily into tops

  • Changes search strategies dramatically

Changes search strategies dramatically

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Gluon, Gluon KK Gluon, Gluon KK WFs WFs

Planck brane TeV brane Gluon wavefunction Gluon KK wavefunciton Kk graviton

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Lower Production Cross Section Lower Production Cross Section for the Graviton for the Graviton

  • Light quarks are localized away from

Light quarks are localized away from Higgs Higgs

  • Hence away from

Hence away from TeV TeV brane brane

  • No

No Drell Drell-

  • Yan

Yan production from quarks production from quarks

  • Gluons are spread throughout the bulk

Gluons are spread throughout the bulk

  • Coupling to graviton volume

Coupling to graviton volume-

  • suppressed

suppressed

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KK Graviton Production KK Graviton Production

w/Liam Fitzpatrick,Jared Kaplan, Liantao Wang

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Final State? Dominant Decay to Final State? Dominant Decay to right right-

  • handed tops

handed tops

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Determining top jets: delta R: Determining top jets: delta R: Angle between decay products Angle between decay products

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More Promising With More Promising With Other Bulk Modes? Other Bulk Modes?

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Gluon KK Mode! Gluon KK Mode!

  • Gluon KK mode coupling to light quarks is

Gluon KK mode coupling to light quarks is much bigger than graviton much bigger than graviton

  • Gluon KK mode wave function peaked at

Gluon KK mode wave function peaked at TeV TeV brane brane

  • But relatively flat in bulk

But relatively flat in bulk

  • Also expect gluon KK mode lighter by

Also expect gluon KK mode lighter by factor 1.5 factor 1.5

  • Finally no 1/M

Finally no 1/M

  • Much larger reach for gluon KK mode

Much larger reach for gluon KK mode

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Gluon wave function

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Gluon Gluon fermion fermion interaction interaction

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Dominates over top jet background Dominates over top jet background

w/Ben Lillie, Liantao Wang

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However, signal doesn However, signal doesn’ ’t dominate t dominate

  • ver jet background
  • ver jet background
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Top mass determination: Top mass determination: dR dR? ?

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Clearly Clearly… …

  • Efficient top jet identification required,

Efficient top jet identification required, especially for heavier KK gluons especially for heavier KK gluons

  • Could be:

Could be:

  • Top jet mass measurement

Top jet mass measurement

  • Detailed substructure of jets

Detailed substructure of jets

  • Critical to do energetic top ID!

Critical to do energetic top ID!

  • Had been neglected but essential to any

Had been neglected but essential to any study of electroweak sector study of electroweak sector

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Summary So Far Summary So Far

  • Weak scale physics should be testable at LHC

Weak scale physics should be testable at LHC

  • Including RS1, whatever the implementation

Including RS1, whatever the implementation

  • Best signature: spin

Best signature: spin-

  • 2 resonance and mass gap

2 resonance and mass gap

  • In bulk, gluon KK mode will be important

In bulk, gluon KK mode will be important

  • Decays into tops critical

Decays into tops critical

  • Challenge is to maximize energy reach

Challenge is to maximize energy reach

  • But hope for pinning this down

But hope for pinning this down

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SLIDE 34

Other Signals? Other Signals?

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Indications of Low Scale Gravity? Indications of Low Scale Gravity?

  • Small higher

Small higher-

  • dimensional black holes?

dimensional black holes?

  • Since geometric cross section

Since geometric cross section

M~TeV=>~100 pb cross section Not suppressed by gauge couplings or phase space factors

Original claims: Original claims: Prolific Production! Prolific Production!

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Signature Signature

  • Claim was

Claim was multiparticle multiparticle final state final state

  • Spherically distributed: particles in all

Spherically distributed: particles in all directions directions

  • Characteristic of Hawking radiation

Characteristic of Hawking radiation

Spectacular fireball final states! Spectacular fireball final states!

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More realistically: More realistically:

  • LHC unlikely to make classical black holes

LHC unlikely to make classical black holes states that decay with high multiplicity via states that decay with high multiplicity via Hawking radiation Hawking radiation

  • Theshold

Theshold above M above M

  • Not all energy trapped behind horizon :

Not all energy trapped behind horizon : inelasticity inelasticity

  • PDFs

PDFs fall rapidly so cross section rapidly fall rapidly so cross section rapidly declines declines

w/Patrick Meade

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Constraints: Min value of M Constraints: Min value of M

BH BH

ADD RS xmin xmin

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2 2-

  • > 2! will be changed

> 2! will be changed

All is not lost All is not lost

  • Potentially much more prolifically produced 2

Potentially much more prolifically produced 2 body final states body final states

  • Uncalculable

Uncalculable, but distinctive experimental , but distinctive experimental signatures that will distinguish among modes signatures that will distinguish among modes

  • Might teach us about

Might teach us about quantum quantum gravity gravity

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What to study? What to study?

  • 2 Quantities

2 Quantities

  • Differential Cross Section

Differential Cross Section

  • R : tells us about angular distribution

R : tells us about angular distribution

  • Key point is quantum gravity events much

Key point is quantum gravity events much harder scattering than Standard Model QCD harder scattering than Standard Model QCD

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Example: Dijet Example: Dijet “ “Black Holes Black Holes” ”

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Stringy Results Stringy Results

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Summary Summary

  • Black holes not as

Black holes not as “ “spectacular spectacular” ” as as advertised advertised BUT BUT

  • Lots of information about quantum gravity

Lots of information about quantum gravity buried in 2 buried in 2-

  • > 2!

> 2!

  • Hadron

Hadron AND Lepton cross sections! AND Lepton cross sections!

  • Initial increase in rate for more central

Initial increase in rate for more central processes always occurs processes always occurs

  • “

“Black hole Black hole” ”, string resonances, different , string resonances, different forms for string, Z forms for string, Z’ ’ all distinctive all distinctive

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Testing for Warped Geometry Testing for Warped Geometry

  • Resonance and Compositeness Signals of

Resonance and Compositeness Signals of Interest Interest

  • Could be KK modes

Could be KK modes

  • Could be

Could be “ “compositeness effects compositeness effects” ”

  • Could be other models

Could be other models… …

  • Need to be prepared

Need to be prepared

  • Means thinking about high energy signals

Means thinking about high energy signals

  • Top quark ID, optimizing compositeness,

Top quark ID, optimizing compositeness, etc. etc.