The Coming Revolutions in Particle Physicslutece.fnal.gov/Talks/HeidelbergRevolutions.pdf · 2015....

The Coming Revolutions in Particle Physics

Universität Heidelberg· 20 July 2007

Chris QuiggFermi National Accelerator Laboratory

1

A Decade of Discovery Past

! Electroweak theory ! law of nature

! Higgs-boson influence observed in the vacuum

! Neutrino flavor oscillations: !µ ! !! , !e ! !µ/!!

! Understanding QCD

! Discovery of top quark

! Direct CP violation in K ! "" decay

! B-meson decays violate CP

! Flat universe dominated by dark matter & energy

! Detection of !! interactions

! Quarks & leptons structureless at TeV scale

2

A Decade of Discovery Past

! Electroweak theory ! law of nature [Z, e+e−, p̄p, !N , (g " 2)µ, . . . ]

! Higgs-boson influence observed in the vacuum [EW experiments]

! Neutrino flavor oscillations: !µ ! !τ , !e ! !µ/!τ [!", !atm]

! Understanding QCD [heavy flavor, Z0, p̄p, !N , ep, lattice]

! Discovery of top quark [p̄p]

! Direct CP violation in K ! "" decay [fixed-target]

! B-meson decays violate CP [e+e− ! BB̄]

! Flat universe dominated by dark matter & energy [SN Ia, CMB, LSS]

! Detection of !τ interactions [fixed-target]

! Quarks & leptons structureless at TeV scale [mainly colliders]

3

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Our Picture of Matter (the revolution just past)

Pointlike (r ≤ 10−18 m) quarks and leptons

Interactions: SU(3)c ⊗ SU(2)L ⊗ U(1)Y gauge symmetries

4

Our Picture of Matter (the revolution just past)

Pointlike (r ≤ 10−18 m) quarks and leptons

Interactions: SU(3)c ⊗ SU(2)L ⊗ U(1)Y gauge symmetries

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5

The World’s Most Powerful Microscopesnanonanophysics

Fermilab’s Tevatron Collider & Detectors

900-GeV protons: c− 586 km/h980-GeV protons: c− 495 km/h

Improvement: 91 km/h!

Protons, antiprotons pass my window 45 000 times / second

. . . working toward 20 × increase in luminosity⇒ 107 collisions / second

CERN’s Large Hadron Collider, 7-TeV protons: c− 10 km/h

achieved

7

CDF dijet event (√

s = 1.96 TeV): ET = 1.364 TeV qq̄ → jet + jet

The World’s Most Powerful Microscopesnanonanophysics

9

Gauge symmetry (group-theory structure) tested in

e+e− → W+W−

(a) (b)

(c)(d)

e+e–

e– e–

e–

e+ e+

e+

W–

W+

W+

W+ W+

W–

W–

W–

!

"

Z

H

10


e+e− → W+W−

0

10

20

30

160 180 200

!s (GeV)

"W

W (

pb

)

YFSWW/RacoonWW

no ZWW vertex (Gentle)

only #e exchange (Gentle)

LEPPRELIMINARY

17/02/2005

11


e+e− → W+W−

(a) (b)

(c)(d)

e+e–

e– e–

e–

e+ e+

e+

W–

W+

W+

W+ W+

W–

W–

W–

!

"

Z

H

Massive weak bosons:

Higgs boson

Meissner effect

12

The Importance of the 1-TeV Scale

EW theory does not predict Higgs-boson massThought experiment: conditional upper bound

W+L W−

L , Z0LZ0

L,HH,HZ0L satisfy s-wave unitarity,

provided MH !(8!"

2/3GF

)1/2= 1 TeV

• If bound is respected, perturbation theory is everywhere reliable

• If not, weak interactions among W±, Z, H become strong on 1-TeV scale

New phenomena are to be found around 1 TeV13

Precision Measurements Test the Theory …

LEP EWWG

Measurement Fit |Omeas!Ofit|/"meas

0 1 2 3

0 1 2 3

#$had(mZ)#$(5) 0.02758 ± 0.00035 0.02768mZ [GeV]mZ [GeV] 91.1875 ± 0.0021 91.1875%Z [GeV]%Z [GeV] 2.4952 ± 0.0023 2.4957"had [nb]"0 41.540 ± 0.037 41.477RlRl 20.767 ± 0.025 20.744AfbA0,l 0.01714 ± 0.00095 0.01645Al(P&)Al(P&) 0.1465 ± 0.0032 0.1481RbRb 0.21629 ± 0.00066 0.21586RcRc 0.1721 ± 0.0030 0.1722AfbA0,b 0.0992 ± 0.0016 0.1038AfbA0,c 0.0707 ± 0.0035 0.0742AbAb 0.923 ± 0.020 0.935AcAc 0.670 ± 0.027 0.668Al(SLD)Al(SLD) 0.1513 ± 0.0021 0.1481sin2'effsin2'lept(Qfb) 0.2324 ± 0.0012 0.2314mW [GeV]mW [GeV] 80.398 ± 0.025 80.374%W [GeV]%W [GeV] 2.140 ± 0.060 2.091mt [GeV]mt [GeV] 170.9 ± 1.8 171.3

14

… and determine unknown parameters

LEP 2494.6 ± 2.7 MeV

mH

= 60 – 1000 GeV

s = 0.123 ± 0.006

mZ

= 91 186 ± 2 MeV

100

150

200

250

2480 2490 2500

Z [MeV]m

t [G

eV

/c ]

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MW

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GeV"

Mass of the W Boson (preliminary)

Mt = 171.4#2.1 GeV

linearly added to

0.02758#0.00035

!"(5)

!"had=

Experiment MW

!GeV"

ALEPH 80.440 # 0.051

DELPHI 80.336 # 0.067

L3 80.270 # 0.055

OPAL 80.416 # 0.053

#2 / dof = 49 / 41

LEP 80.376 # 0.033

10

102

103

80.2 80.4 80.6

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61-7

… and determine unknown parameters

16

Revolution:

Understanding the Everyday

! Why are there atoms?! Why chemistry?! Why stable structures?

17

Imagine a world without a Higgs mechanism

18

If electroweak symmetry were not hidden …

•Massless quarks and leptons•QCD confines quarks into color-singlet hadrons•Nucleon mass little changed•QCD breaks EW symmetry, gives tiny W, Z masses;weak-isospin force doesn’t confine

•p outweighs n: rapid β-decay ⇒ lightest nucleus is n … no hydrogen atom

•Some light elements from BBN, but ∞ Bohr radius

•No atoms means no chemistry, no stable composite structures like liquids, solids, …

… character of the physical worldwould be profoundly changed

19

Searching for the mechanism of electroweak symmetry breaking, we seek to understand

why the world is the way it is.

This is one of the deepest questions humans have ever pursued, and

it is coming within the reach of particle physics.

20

The agent of electroweak symmetry breaking represents a novel fundamental interaction at an energy of a few hundred GeV …

We do not know the nature of the new force.

21

The agent of electroweak symmetry breaking represents a novel fundamental interaction at an energy of a few hundred GeV …

We do not know the nature of the new force.

22

What is the nature of the mysterious new force that hides electroweak symmetry?

✴A force of a new character, based on interactions of an elementary scalar

✴A new gauge force, perhaps acting on undiscovered constituents

✴A residual force that emerges from strong dynamics among electroweak gauge bosons

✴An echo of extra spacetime dimensions

Which path has Nature taken?

23

✴ Is it there? How many?

✴ Verify quantum numbers (spin, parity, …)

✴ Does H generate mass for gauge bosons and for fermions?

✴ How does H interact with itself?

Essential step toward understanding the new force that shapes our world:Find the Higgs boson and explore its properties.

Finding the Higgs boson starts a new adventure!

24

Tevatron

25

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27

CMS

28

CMS

29

29

CMS

30

31

ATLAS

31

ATLAS

32

ATLAS

33

What the LHC is not really for …1. Find the Higgs boson,the Holy Grail of particle physics,the source of all mass in the Universe.

2. Celebrate.

3. Then particle physics will be over.

We are not ticking off items on a shopping list …

We are exploring a vast new terrain… and reaching the Fermi scale

35

Revolution:

The Meaning of Identity

Varieties of matter

! What sets masses and mixings of quarks and leptons?

! What is CP violation trying to tell us?

! Neutrino oscillations give us another take, might hold akey to the matter excess in the Universe.

All fermion masses and mixings mean new physics

! Will new kinds of matter help us to see the pattern?

What makes a top quark a top quark,an electron an electron, a neutrino a neutrino?

39

Flavor physics may be where we see, or diagnose,

the break in the SM.

Parameters of the Standard Model

3 coupling parameters αs,αem, sin2 θW

2 parameters of the Higgs potential1 vacuum phase (QCD)6 quark masses3 quark mixing angles1 CP-violating phase3 charged-lepton masses3 neutrino masses3 leptonic mixing angles1 leptonic CP-violating phase (+ Majorana . . . )

26+ arbitrary parameters

40

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datacosine with A=1.28

CDF Run II Preliminary -1L = 1.0 fb

Bs - B̄s Oscillations: sb̄↔ s̄b

f = 17.77± 0.10± 0.07 ps−1

41

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Quark family patterns: generations

Veltman: Higgs boson knows something we don’t know!44

Neutrino family patterns (an example)

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45

Neutrino Masses

46

New Physics on the Fermi ScaleMore?

If dark matter interacts weakly …

… its likely mass is 0.1 to 1 TeV: Fermi scale

COSMOS

48

Many extensions to EW theoryentail dark matter candidates

✴Predicts that Higgs field condenses, breaking EW symmetry, if top is heavy

✴Predicts a light Higgs mass✴Predicts cosmological cold dark matter✴In a unified theory, explains the values of

standard-model coupling constants

Supersymmetry is highly developed, has several important consequences:

50

Revolution:

The Unity of Quarks & Leptons

! What do quarks and leptons have in common?

! Why are atoms so remarkably neutral?

! Which quarks go with which leptons?

! Quark-lepton extended family " proton decay:SUSY estimates of proton lifetime ∼ 5× 1034 y

! Unified theories " coupling constant unification

! Rational fermion mass pattern at high energy?(Masses run, too)

51

SU(3)c

SU(2)L

U(1)Y

log10

(E

1 GeV

)

1/α

60

40

20

0 5 10 15

52

ParticlePhysicsrejoin

sGravity r

ejoins

53

Natural to neglect gravity in particle physics

GNewton small ⇐⇒MPlanck =!

!c

GNewton

" 12

≈ 1.22× 1019 GeV large

Estimate B(K → πG) ∼(

MK

MPlanck

)2

∼ 10−38

But gravity is not always negligible …

Higgs field contributes uniform vacuum energy density

!H ≡ M2Hv2

8≥ 108 GeV4 ≈ 1024 g cm!3

Observed vacuum energy density !vac ! 10−46 GeV4

Mismatch by 54 orders of magnitude

54

Evidence that vacuum energy is present …

recasts old problem, gives us properties to measure

A chronic dull headache for thirty years …

Why is empty space so nearly massless?

55

How to separate EW, higher scales?

Does MH < 1 TeV make sense?The peril of quantum corrections – hierarchy problem

-2-2

-1.5

-1

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0

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input

5 TeV

56

How to separate EW, higher scales?

Traditional: change electroweak theory to understandwhy MH, electroweak scale ≪ MPlanck

To resolve hierarchy problem: extend standard modelon the 1-TeV scale …

SU(3)c ⊗ SU(2)L ⊗ U(1)Y

composite Higgs boson

technicolor / topcolor

supersymmetry

…

Ask instead why gravity is so weak,why MPlanck ≫ electroweak scale

57

Revolution:

A New Conception of Spacetime

! Could there be more space dimensionsthan we have perceived?! What is their size? Their shape?! How do they influence the world?! How can we map them?

string theory needs 9 or 10

58

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Suppose at scale R … gravity propagates in 4+n dimensions

Gauss law: GN ~ M*–n–2 R–n M* : gravity’s true scale

1/r 2

1/r 2+n

MPlanck would be a mirage!59

Range !G (meters)

Lamoreaux

Irvine

Eöt-Wash

Boulder

10–6 10–5 10–4 10–3 10–2

108

104

100

10–4

Rel

ativ

e S

tren

gth "

G

Stanford

V (r) = !∫

dr1

∫dr2

GNewtonρ(r1)ρ(r2)r12

[1 + εG exp(!r12/λG)]

Gravity follows Newtonian force law down to ≲ 1 mm

60

V (r) = !∫

dr1

∫dr2

GNewtonρ(r1)ρ(r2)r12

[1 + εG exp(!r12/λG)]

Gravity follows Newtonian force law down to ≲ 1 mm

Range !G (meters)

Lamoreaux

Irvine

Eöt-Wash

Boulder

10–6 10–5 10–4 10–3 10–2

108

104

100

10–4

Rel

ativ

e S

tren

gth "

G

1 0.110E (meV)

Stanford

61

Might extra dimensions explainthe range of fermion masses?

eR!

!q uRdR

!e

fermions ride separate tracks in 5th dimensionsmall offsets in x5 ⇒ exponential mass ratios

62

Other extradimensional delights …(provided gravity is intrinsically strong)

✴ Graviton emission (Emissing signatures) or graviton exchange (angular distributions)

✴ Resonances spaced at TeV intervals

✴ If extra dimensions are 1/TeV-scale, tiny black holes: collider hedgehogs, spectacular cosmic-ray showers

Reminders that we haven’t seen (or imagined) everything yet

63

A Decade of Discovery Ahead

! Higgs search and study; EWSB / 1-TeV scale

! CP violation (B); Rare decays (K, D, . . . )

! Neutrino oscillations

! Top as a tool

! New phases of matter; hadronic physics

! Exploration!Extra dimensions / new dynamics / SUSY / new forces & constituents

! Proton decay

! Composition of the universe

64

A Decade of Discovery Ahead

! Higgs search and study; EWSB / 1-TeV scale [p±p colliders; e+e− LC]

! CP violation (B); Rare decays (K, D, . . . ) [e+e−, p±p, fixed-target]

! Neutrino oscillations [ν", νatm, reactors, ν beams]

! Top as a tool [p±p colliders; e+e− LC]

! New phases of matter; hadronic physics [heavy ions, ep, fixed-target]

! Exploration! [colliders, precision measurements, tabletop, . . . ]Extra dimensions / new dynamics / SUSY / new forces & constituents

! Proton decay [underground]

! Composition of the universe [SN Ia, CMB, LSS, underground, colliders]

65

✴ Experiments at the energy frontier

✴ High-sensitivity experiments

✴ Fundamental physics with “found beams”

✴ Astrophysical / cosmological observations

✴ Diversity and scale diversity!

Need to prepare many revolutions …

The most ambitious accelerators drive our scienceRefine e,p· Exotic technologies· Exotic particles

66

Connections …

67

In a decade or two, we can hope to . . .

Understand electroweak symmetry breaking

Observe the Higgs boson

Measure neutrino masses and mixings

Establish Majorana neutrinos (!!0!)

Thoroughly explore CP violation in B decays

Exploit rare decays (K, D, . . . )

Observe neutron EDM, pursue electron EDM

Use top as a tool

Observe new phases of matter

Understand hadron structure quantitatively

Uncover the full implications of QCD

Observe proton decay

Understand the baryon excess

Catalogue matter and energy of the universe

Measure dark energy equation of state

Search for new macroscopic forces

Determine GUT symmetry

Detect neutrinos from the universe

Learn how to quantize gravity

Learn why empty space is nearly weightless

Test the inflation hypothesis

Understand discrete symmetry violation

Resolve the hierarchy problem

Discover new gauge forces

Directly detect dark-matter particles

Explore extra spatial dimensions

Understand the origin of large-scale structure

Observe gravitational radiation

Solve the strong CP problem

Learn whether supersymmetry is TeV-scale

Seek TeV-scale dynamical symmetry breaking

Search for new strong dynamics

Explain the highest-energy cosmic rays

Formulate the problem of identity

68





Establish Majorana neutrinos (ββ0ν)




Use top as a tool



























. . . learn the right questions to ask . . .

69





Establish Majorana neutrinos (ββ0ν)




Use top as a tool



























. . . learn the right questions to ask . . .

. . . and rewrite the textbooks!

70

Reserve slides on the new accelerators

71

Toward a New World of Accelerators

•Refine standard electron and proton technologies: LHC, ILC, VLHC, …

•Develop exotic accelerator technologiesCLIC, laser / plasma acceleration

•Exotic particles: γγ, μ storage ring, μμ, β-beams, …

72

Muon Accelerators

Possible path to a few-TeV l+l– colliderto study electroweak symmetry breaking, explore

µ: elementary lepton, so energy efficientsynchrotron radiation not crippling

small collider would reach 1-TeV scale?? modest size ↔ modest cost ??

But muons decay – must move fast!Fierce detector, machine environment

73

The Ultimate Neutrino Source?

Muon storage ring with a millimole of muons per year

Beam from µ− contains νµ, ν̄e, but no ν̄µ, νe, ν! , or ν̄! .

oscillation studies, scattering on thin targets

74

Beyond the LHC: a Very Large Hadron Collider

LHC Discoveries could point to much higher energies

✴ Heavy Higgs boson

✴ New strong dynamics

✴ New gauge bosons

✴ Hints of large extra dimensions

VLHC is the one multi-TeV machine we know we can build

Pointlike cross sections ! 1/E2cm "

L! = 1032 - 33 cm−2 s−1 (Ecm/40 TeV)2

For Ecm = 100 TeV, target L! # 1034 cm−2 s−1

75

e+e– Linear Collider

A lovely idea! (40 years in the making)

✴ Multi-TeV to match LHC reach: CLIC✴ Detailed studies of Higgs, top, light SUSY: 500 GeV

✴ Additional Higgs, sleptons, EW gauginos: 1 TeV

✴ Ultraprecision: 109 Z bosons

Advantages: point particle, little backgroundChallenges: reaching high energy, high luminosity

76

International Linear Collider Goals

Ecm ≈ 1 TeV, first operation at 500 GeVLuminosity : 1/2 ab–1 per year≳ 80% electron polarization

Science opportunities:Past decade sharpened case for exploring 1-TeV scale

TeV LC is an ideal complement to LHC, a Higgs lab

Higgs lifetime, JPC, for MH ≲ 200 GeV

Higgs contributions to W, Z, b, c, τ masses, MH ≲ 2 MW

Probe Higgs-boson self interactions

77

The Coming Revolutions in Particle Physicslutece.fnal.gov/Talks/HeidelbergRevolutions.pdf · 2015....

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