Beyond the Higgs Boson

Beyond the Higgs Boson

The Higgs is just one of the questions

being studied at the LHC

John Ellis

King’s College London (& CERN)

Beyond the Higgs Boson

The Higgs is just one of the questions

being studied at the LHC

John Ellis

King’s College London (& CERN)

The ‘Standard Model’ of Particle Physics

Proposed byAbdus Salam, Glashow and Weinberg

Tested by experiments at CERN

Perfect agreement between theory and experiments

in all laboratories

The matter particles

The ‘Standard Model’

The fundamental interactions

Gravitation electromagnetism weak nuclear force strong nuclear force

= Cosmic DNA

Where does mass

come from?

Summary of the Standard Model

• Particles and SU(3) × SU(2) × U(1) quantum numbers:

• Lagrangian: gauge interactions

matter fermions

Yukawa interactions

Higgs potential

Now direct evidence

Status of the Standard Model

• Perfect agreement with all confirmed accelerator data

• Consistency with precision electroweak data (LEP et al) only if there is a ‘Higgs boson’

• Agreement seems to require a relatively light Higgs boson weighing < ~ 180 GeV

• Raises many unanswered questions:

mass? flavour? unification?

Combining the Information from Direct Searches and Indirect Data

m

= 125 ± 10 GeV

Open Questions beyond the Standard Model

• What is the origin of particle masses?

due to a Higgs boson?

• Why so many flavours of matter particles?

• What is the dark matter in the Universe?

• Unification of fundamental forces?

• Quantum theory of gravity?

LHC LHC

LHC

LHC

LHC

At what Energy is the New Physics?

A lot accessible to the LHC

Some accessible only via astrophysics & cosmology Dark matter

Origin of mass

Why do Things Weigh?

0

Where do the masses come from ?

Newton:

Weight proportional to Mass

Einstein:

Energy related to Mass

Neither explained origin of Mass

Are masses due to Higgs boson?

(the physicists’ Holy Grail)

Think of a Snowfield

Skier moves fast:

Like particle without mass

e.g., photon = particle of light Snowshoer sinks into snow, moves slower:

Like particle with mass e.g., electron

Hiker sinks deep, moves very slowly:

Particle with large mass The LHC will look for

the snowflake:

The Higgs Boson

Introduction

Standard Model Particles:

Years from Proposal to Discovery

The (NG)AEBHGHKMP Mechanism

The only one who mentioned a massive scalar boson

Nambu EB, GHK and Higgs

Spontaneous symmetry breaking: massless Nambu- Goldstone boson ‘eaten’ by gauge boson ‘eaten’ by gauge boson

Accompanied by massive particle

EB, GHK

A Phenomenological Profile of the Higgs Boson

• First attempt at systematic survey

A Simulated Higgs Event @ LHC

Astronomers tell us that most of the matter in the

universe is invisible

We will look for it with the LHC

Dark Matter in the Universe

Astronomers say that most of the matter in the Universe is invisible

Dark Matter

‘Supersymmetric’ particles ? We shall look for

them with the LHC

Dark Matter in the Universe

Classic Dark Matter Signature

Missing transverse energy

carried away by dark matter particles

General Interest in Antimatter Physics

Physicists cannot make enough for

Star Trek or Dan Brown!

How do Matter and Antimatter Differ?

Dirac predicted the existence of antimatter:

same mass

opposite internal properties:

electric charge, … Discovered in cosmic rays

Studied using accelerators

Matter and antimatter not quite equal and opposite: WHY?

Why does the Universe mainly contain matter, not antimatter?

Experiments at LHC and elsewhere looking for answers

How to Create the Matter in the Universe?

• Need a difference between matter and antimatter observed in the laboratory

• Need interactions able to creat matter present in unified theories

not yet seen by experiment

• Must break thermal equilibrium

Possible in the decays of heavy

particles

Sakharov

Will we be able to calculate using laboratory data?

300,000 years

3

minutes 1 micro-

second 1 pico- second

Formation of atoms Formation

of nuclei Formation

of protons

& neutrons Appearance

of mass?

Appearance of dark matter?

Appearance

of matter?

 … but he never succeeded

Unification via extra dimensions of space?

Unify all the

Fundamental Interactions:

Einstein’s Dream …

Would vanish instantly Eat up

the entire Earth?

Will LHC experiments create black holes?

The Large Hadron Collider (LHC)

Proton- Proton Collider 7 TeV + 7 TeV

1,000,000,000 collisions/second

•Origin of mass

•Nature of Dark Matter

•Primordial Plasma

•Matter vs Antimatter Also collisions of Lead ions

Vista General del LHC y sus Experimentos

27km in circumference

~ 100m deep

General View of LHC & its Experiments

ATLAS: Higgs and supersymmetry

CMS: Higgs and supersymmetry ALICE: Primordial cosmic plasma

LHCb: Matter-antimatter difference

Higgs Production at the LHC

A la

recherche du

Higgs

perdu …

Many production modes measurable if M

~ 125 GeV

• Couplings proportional to masses (?)

• Important couplings through loops:

– gluon + gluon → Higgs → γγ

Higgs Decay Branching Ratios

Many decay modes measurable if M

~ 125 GeV

Is the Higgs Boson finally being Revealed?

Mass Higgsteria

Interesting Events

July 4

2012

The discovery of a

new particle

Higgsdependence Day!

How the Higgs Signal has Grown

Unofficial Combination of Higgs Search Data from March 6th

Is this the Higgs Boson?

No Higgs here!

No Higgs

here!

Theoretical Constraints on Higgs Mass

• Large M

→ large self-coupling → blow up at low-energy scale Λ due to

renormalization

• Small: renormalization due to t quark drives quartic coupling < 0 at some scale Λ

→ vacuum unstable

• Vacuum could be stabilized by Supersymmetry

Degrassi, Di Vita, Elias-Miro, Giudice, Isodori & Strumia, arXiv:1205.6497 Instability @

10¹⁰ – 10¹³ GeV

Vacuum Instability in the Standard Model

• Very sensitive to m

as well as M

• Present vacuum probably metastable with lifetime >> age of the Universe

Degrassi, Di Vita, Elias-Miro, Giudice, Isodori & Strumia, arXiv:1205.6497

The Particle Higgsaw Puzzle

Is LHC finding the missing piece?

Is it the right shape?

Is it the right size?

Elementary Higgs or Composite?

• Higgs field:

<0|H|0> ≠ 0

• Quantum loop problems

• Fermion-antifermion condensate

• Just like QCD, BCS superconductivity

• Top-antitop condensate?

needed m

> 200 GeV New technicolour force?

-Heavy scalar resonance?

-Inconsistent with

precision electroweak data?

Cut-off Λ ~ 1 TeV with Supersymmetry?

e.g., cutoff Λ = 10 TeV

Higgs as a

Pseudo-Goldstone Boson

Loop cancellation mechanism

Supersymmetry Little Higgs

‘Little Higgs’ models

(breakdown of larger symmetry)

Couplings resemble Higgs of Standard Model

• No indication of any significant deviation from

the Standard Model predictions

Global Analysis of Higgs-like Models

• Rescale couplings: to bosons by a, to fermions by c

• Standard Model: a = c = 1

b bbar W W Z Z τ τ γ γ Global

No evidence for deviation from SM

It Walks and Quacks like a Higgs

• Do couplings scale ~ mass? With scale = v?

• Red line = SM, dashed line = best fit

JE & Tevong You, arXiv:1303.3879

Global

fit

[1] = JE & Tevong You, arXiv:1303.3879

Dixit Swedish Academy

Today we believe that “Beyond any reasonable doubt, it is a Higgs boson.” [1]

http://www.nobelprize.org/nobel_prizes/physics/laureates/2013/a dvanced-physicsprize2013.pdf

Without Higgs …

… there would be no atoms

– massless electrons would escape at the speed of light

… there would be no heavy nuclei

… weak interactions would not be weak

– Life would be impossible: everything would be radioactive

Its existence is a big deal!

What else is there?

Supersymmetry

• Successful prediction for Higgs mass

– Should be < 130 GeV in simple models

• Successful predictions for Higgs couplings

– Should be within few % of SM values

• Could explain the dark matter

• Naturalness, GUTs, string, … (???)

“Classic” missing-energy search

Searches ~ 5/fb @ 8 TeV Searches with 8 TeV Data

Multiple searches including b, leptons

p-value of simple models < 10%

2012 20/fb

Scan of CMSSM

Update of Buchmueller et al: arXiv:1207.3715

1 5 ^20/fb 2012

CMSSM

Favoured values of gluino mass significantly above pre-LHC, > 2 TeV

Update of Buchmueller, JE et al: arXiv:1207.3715

Gluino mass

Reach of LHC at High luminosity

1 5

χ

20/fb 2012

CMSSM

Favoured values of squark mass:

~ 2000 GeV or more

Update of Buchmueller, JE et al: arXiv:1207.3715

Squark mass

Reach of LHC at High luminosity

A Vision for the 21 ^st Century

350 GeV Circular e⁺e^- collider 100 TeV proton-proton collider

Conversation with Mrs Thatcher: 1982

What do you do?

Think of things for the experiments to look for, and hope they find

something different

Wouldn’t it be better if they

found what you predicted?

Then we would not

learn so much!