Perspectives in High-Energy Physics · Perspectives in High-Energy Physics Chris Quigg Theoretical...

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Perspectives in High-Energy Physics Chris Quigg Theoretical Physics Department Fermi National Accelerator Laboratory [email protected] Neutrino Puzzles The World’s Most Powerful Microscope What Can We Learn from the Top Quark? How Many Dimensions to Spacetime? 1999 ICFA Instrumentation School C. Quigg, “Perspectives in High-Energy Physics” 1

Transcript of Perspectives in High-Energy Physics · Perspectives in High-Energy Physics Chris Quigg Theoretical...

Page 1: Perspectives in High-Energy Physics · Perspectives in High-Energy Physics Chris Quigg Theoretical Physics Department Fermi National Accelerator Laboratory quigg@fnal.gov Neutrino

Perspectives in High-Energy Physics

Chris Quigg

Theoretical Physics DepartmentFermi National Accelerator Laboratory

[email protected]

• Neutrino Puzzles

• The World’s Most Powerful Microscope

• What Can We Learn from the Top Quark?

• How Many Dimensions to Spacetime?

1999 ICFA Instrumentation School C. Quigg, “Perspectives in High-Energy Physics” 1

Page 2: Perspectives in High-Energy Physics · Perspectives in High-Energy Physics Chris Quigg Theoretical Physics Department Fermi National Accelerator Laboratory quigg@fnal.gov Neutrino

νNeutrinos . . .

• are tiny subatomic particles

• carry no electric charge

• have (almost) no mass; move (nearly) at the speed of light

• hardly interact at all

1999 ICFA Instrumentation School C. Quigg, “Perspectives in High-Energy Physics” 2

Page 3: Perspectives in High-Energy Physics · Perspectives in High-Energy Physics Chris Quigg Theoretical Physics Department Fermi National Accelerator Laboratory quigg@fnal.gov Neutrino

νNeutrinos are among the most abundant particles in the Universe

• Inside your body are more than 10 million (107) neutrinos left over from

the Big Bang.

• Each second, some 1014 neutrinos made in the Sun pass through your

body.

• Each second, about a thousand neutrinos made in Earth’s atmosphere by

cosmic rays pass through your body.

• Other neutrinos reach us from natural (radioactive decays of elements

inside the Earth) and artificial (nuclear reactors) sources.

1999 ICFA Instrumentation School C. Quigg, “Perspectives in High-Energy Physics” 3

Page 4: Perspectives in High-Energy Physics · Perspectives in High-Energy Physics Chris Quigg Theoretical Physics Department Fermi National Accelerator Laboratory quigg@fnal.gov Neutrino

Our awareness of neutrinos

Started with a puzzle in 1913 . . .

That led to an idea in 1930 . . .

That was confirmed by an experiment in 1956.

Today, neutrinos have become

An important tool for particle physics and astrophysics . . .

Fascinating objects of study that may yield

important new clues about the basic laws of nature.

1999 ICFA Instrumentation School C. Quigg, “Perspectives in High-Energy Physics” 4

Page 5: Perspectives in High-Energy Physics · Perspectives in High-Energy Physics Chris Quigg Theoretical Physics Department Fermi National Accelerator Laboratory quigg@fnal.gov Neutrino

The Puzzle

Natural (and Artificial) Radioactivity includes Beta (β) Decay,

AZ→ A(Z + 1) + β− ,

where β− is the old-fashioned name for an electron.

Examples are tritium β decay,

3H1 →3He2 + β− ,

neutron β decay,

n→ p+ β− ,

and β decay of Rhodium–106,

106Rh45 →106Pd46 + β− .

1999 ICFA Instrumentation School C. Quigg, “Perspectives in High-Energy Physics” 5

Page 6: Perspectives in High-Energy Physics · Perspectives in High-Energy Physics Chris Quigg Theoretical Physics Department Fermi National Accelerator Laboratory quigg@fnal.gov Neutrino

For such two-body decays, the Principle of Conservation of Energy

& Momentum says that

the β particle should have a definite energy.

In 1913, James Chadwick (later to discover the neutron) observed

that the electron energy has a continuous spectrum.

Beta Decay

Rhodium → Palladium + β98.652029 98.648488 0.51099907 MeV/c2

Beta particle energy [MeV]

Num

ber

of e

vent

s

Expected

Observed

1999 ICFA Instrumentation School C. Quigg, “Perspectives in High-Energy Physics” 6

Page 7: Perspectives in High-Energy Physics · Perspectives in High-Energy Physics Chris Quigg Theoretical Physics Department Fermi National Accelerator Laboratory quigg@fnal.gov Neutrino

Is energy not conserved?

For the simpler case of neutron β decay, sometimes this happens:

n

proton

electron

A system initially at rest spontaneously moves off to the right!

1999 ICFA Instrumentation School C. Quigg, “Perspectives in High-Energy Physics” 7

Page 8: Perspectives in High-Energy Physics · Perspectives in High-Energy Physics Chris Quigg Theoretical Physics Department Fermi National Accelerator Laboratory quigg@fnal.gov Neutrino

Wolfgang Pauli’s Proposal (1930)

The missing energy / momentum is carried away by a light neutral

particle that goes undetected:

n

proton

electronelectron's antineutrino

The (anti)neutrino!

n→ p+ β− + ν

1999 ICFA Instrumentation School C. Quigg, “Perspectives in High-Energy Physics” 8

Page 9: Perspectives in High-Energy Physics · Perspectives in High-Energy Physics Chris Quigg Theoretical Physics Department Fermi National Accelerator Laboratory quigg@fnal.gov Neutrino

Experimental Confirmation . . .

In 1953, Clyde Cowan and Fred Reines used the intense beam of

antineutrinos from a fission reactor

AZ→ A(Z + 1) + β− + ν ,

and a heavy target (10.7 ft3 of liquid scintillator) containing about

1028 protons to detect the reaction

ν + p→ e+ + n .

The observation was confirmed and extended by their team in 1956.

1999 ICFA Instrumentation School C. Quigg, “Perspectives in High-Energy Physics” 9

Page 10: Perspectives in High-Energy Physics · Perspectives in High-Energy Physics Chris Quigg Theoretical Physics Department Fermi National Accelerator Laboratory quigg@fnal.gov Neutrino

3 Families of Leptons

(Greek λεπτ oς = thin)

νe

e−

L

νµ

µ−

L

ντ

τ−

L

Like the electron (+ muon + tau), the neutrinos have spin = 1/2.

The muon’s neutrino is produced when the nuclear force particle,

the pion, decays . . .

πmuonmuon's neutrino

1999 ICFA Instrumentation School C. Quigg, “Perspectives in High-Energy Physics” 10

Page 11: Perspectives in High-Energy Physics · Perspectives in High-Energy Physics Chris Quigg Theoretical Physics Department Fermi National Accelerator Laboratory quigg@fnal.gov Neutrino

Neutrinos Traverse Vast Amounts of Material

Solar diameter

Lunar diameter

Earth diameter

Interaction Length of a 100-GeV ν = 25 million km H2O ≈ 230 Earth diameters.

In Fermilab’s neutrino beam, only 1 ν in 1011 will interact in your body.

1999 ICFA Instrumentation School C. Quigg, “Perspectives in High-Energy Physics” 11

Page 12: Perspectives in High-Energy Physics · Perspectives in High-Energy Physics Chris Quigg Theoretical Physics Department Fermi National Accelerator Laboratory quigg@fnal.gov Neutrino

Consequences of the Great Interaction Length

• Missing-energy signature for neutrinos

• Difficulty of detecting neutrino interactions

• Possibility of preparing filtered neutrino beams

1999 ICFA Instrumentation School C. Quigg, “Perspectives in High-Energy Physics” 12

Page 13: Perspectives in High-Energy Physics · Perspectives in High-Energy Physics Chris Quigg Theoretical Physics Department Fermi National Accelerator Laboratory quigg@fnal.gov Neutrino

How to Make a Neutrino Beam

p+ Target→ many π, K

π → µνµ, K → µνµ

Filter beam

Proton Beam

TargetDecay Space

Shield

Neutrino Beam

1999 ICFA Instrumentation School C. Quigg, “Perspectives in High-Energy Physics” 13

Page 14: Perspectives in High-Energy Physics · Perspectives in High-Energy Physics Chris Quigg Theoretical Physics Department Fermi National Accelerator Laboratory quigg@fnal.gov Neutrino

(Fermilab beam lines)

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Page 15: Perspectives in High-Energy Physics · Perspectives in High-Energy Physics Chris Quigg Theoretical Physics Department Fermi National Accelerator Laboratory quigg@fnal.gov Neutrino

Neutrinos Probe the Interior of the Proton

• Fermilab Tevatron delivers 1010 neutrinos in 5 pings over 2.5

seconds each minute, spread over the 100 ft2 face of the NuTeV

Detector.

• Detector is 690 T of iron, scintillator, and drift chambers.

Events studied from “fiducial volume” of 390 T.

• The 1010 neutrinos produce about 10 – 20 events.

Experiments like this give us our best look at the interior of the

proton, and reveal its quark structure in exquisite detail.

1999 ICFA Instrumentation School C. Quigg, “Perspectives in High-Energy Physics” 15

Page 16: Perspectives in High-Energy Physics · Perspectives in High-Energy Physics Chris Quigg Theoretical Physics Department Fermi National Accelerator Laboratory quigg@fnal.gov Neutrino

(NuTeV Detector and Collaboration)

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Page 17: Perspectives in High-Energy Physics · Perspectives in High-Energy Physics Chris Quigg Theoretical Physics Department Fermi National Accelerator Laboratory quigg@fnal.gov Neutrino

Neutrinos Are Very Light

No one has ever weighed a neutrino.

Neutrino Mass

νe < 0.000 015 MeV/c2

νµ < 0.17 MeV/c2

ντ < 18.2 MeV/c2

electron mass is 0.51099907 MeV/c2

1999 ICFA Instrumentation School C. Quigg, “Perspectives in High-Energy Physics” 17

Page 18: Perspectives in High-Energy Physics · Perspectives in High-Energy Physics Chris Quigg Theoretical Physics Department Fermi National Accelerator Laboratory quigg@fnal.gov Neutrino

If neutrinos are exactly massless,

neutrino physics is simple . . .

• No pattern of masses to explain

• No neutrino decays

• No mixing among lepton generations

• No neutrino oscillations

The only question is Why?

1999 ICFA Instrumentation School C. Quigg, “Perspectives in High-Energy Physics” 18

Page 19: Perspectives in High-Energy Physics · Perspectives in High-Energy Physics Chris Quigg Theoretical Physics Department Fermi National Accelerator Laboratory quigg@fnal.gov Neutrino

In the Quantum World, Particles are Waves

If . . .

• Neutrinos ν1, ν2, . . . have different masses m1,m2, . . .

• Each neutrino flavor is a mixture of different masses(νe

νµ

)=

(cos θ sin θ

− sin θ cos θ

)(ν1

ν2

). . . then a beam born as pure νµ may evolve a νe component with time.

Probability that a neutrino born as νµ remain a νµ at distance L is

Pνµ(L) = 1− sin2 2θ sin2

(1.27

∆m2

1 eV2 ·L

1 km·

1 GeV

E

)

1999 ICFA Instrumentation School C. Quigg, “Perspectives in High-Energy Physics” 19

Page 20: Perspectives in High-Energy Physics · Perspectives in High-Energy Physics Chris Quigg Theoretical Physics Department Fermi National Accelerator Laboratory quigg@fnal.gov Neutrino

Neutrino Oscillation as an Interference Phenomenon

Two sound waves (two tuning forks with almost the same pitch)

+

Sound swells and fades periodically . . .

. . . because the two waves are different,

reflecting the physical difference between the two tuning forks.

1999 ICFA Instrumentation School C. Quigg, “Perspectives in High-Energy Physics” 20

Page 21: Perspectives in High-Energy Physics · Perspectives in High-Energy Physics Chris Quigg Theoretical Physics Department Fermi National Accelerator Laboratory quigg@fnal.gov Neutrino

Pνe = sin2 2θ sin2(1.27∆m2L/E)

Depends on two experimental parameters:

• L, distance from ν source to detector [km]

• E, the neutrino energy [GeV]

. . . and two fundamental neutrino parameters:

• ∆m2 = m21 −m

22 [eV2]

• sin2 2θ, the neutrino mixing parameter

Distance from ν source, L

ν beam with energy E

Pro

babi

lity

0

1

P(νµ)

P(νe)sin2 2θ

∆L = πE/(1.27∆m2)

1999 ICFA Instrumentation School C. Quigg, “Perspectives in High-Energy Physics” 21

Page 22: Perspectives in High-Energy Physics · Perspectives in High-Energy Physics Chris Quigg Theoretical Physics Department Fermi National Accelerator Laboratory quigg@fnal.gov Neutrino

Detecting Neutrinos from the Sun

The nuclear burning that powers the Sun produces neutrinos as

well as light and heat. Overall, . . .

4p→ 4He + 2e+ + 2νe + 25 MeV

Borexino

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Page 23: Perspectives in High-Energy Physics · Perspectives in High-Energy Physics Chris Quigg Theoretical Physics Department Fermi National Accelerator Laboratory quigg@fnal.gov Neutrino

Reactions That Power the Sun

ppI ppII ppIII

7Li + p 2

4He

8B

8Be

*

7Be + e

– 7Li +

7Be + p

99.89% 0.11%

3He +

4He

7Be +

3He +

3He

4He + 2p

86% 14%

2H + p

3He +

99.75% 0.25%

p + p2H + e

++ p + p + e

– 2H +

8B + γ

+ e +–

Small high-energy contribution from 3He + p→ 4He + e+ + νe

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Page 24: Perspectives in High-Energy Physics · Perspectives in High-Energy Physics Chris Quigg Theoretical Physics Department Fermi National Accelerator Laboratory quigg@fnal.gov Neutrino

Detecting Neutrinos from the Sun

Neutrinos interact feebly =⇒ very massive target / detector.

SuperKamiokande Detector in Japan

• 50 000 tonnes of pure water

• 11 000 photomultiplier tubes to view Cherenkov light

• 1 km under a mountain, under 3 kmwe

• Detects neutrino interactions νe + n→ p+ e− in real time

• Determines the neutrino direction from the electron direction

• But is only sensitive to the highest-energy solar neutrinos

1999 ICFA Instrumentation School C. Quigg, “Perspectives in High-Energy Physics” 24

Page 25: Perspectives in High-Energy Physics · Perspectives in High-Energy Physics Chris Quigg Theoretical Physics Department Fermi National Accelerator Laboratory quigg@fnal.gov Neutrino

(SuperK Detector)

1999 ICFA Instrumentation School C. Quigg, “Perspectives in High-Energy Physics” 25

Page 26: Perspectives in High-Energy Physics · Perspectives in High-Energy Physics Chris Quigg Theoretical Physics Department Fermi National Accelerator Laboratory quigg@fnal.gov Neutrino

Brightest Object in the Neutrino Sky: the Sun

Proof that nuclear fusion powers the Sun.

1999 ICFA Instrumentation School C. Quigg, “Perspectives in High-Energy Physics” 26

Page 27: Perspectives in High-Energy Physics · Perspectives in High-Energy Physics Chris Quigg Theoretical Physics Department Fermi National Accelerator Laboratory quigg@fnal.gov Neutrino

Cosmic Rays Produce Neutrinos in the Atmosphere

Accelerator

Target

Opaque matter

p

p

p

Detector

Earth

p

ν

ν

µ

µ

γ

ν

ν

Sun

1999 ICFA Instrumentation School C. Quigg, “Perspectives in High-Energy Physics” 27

Page 28: Perspectives in High-Energy Physics · Perspectives in High-Energy Physics Chris Quigg Theoretical Physics Department Fermi National Accelerator Laboratory quigg@fnal.gov Neutrino

SuperK’s Zenith-Angle Dependence

Downward ν travel about 15 km; upward ν travel up to 13 000 km

10-1

1 10 102

-1

-0.5

0

0.5

1

10-1

1 10

-1

-0.5

0

0.5

1

e-like

µ-like

FC PC

(Up

– D

own)

/(U

p +

Dow

n)

Momentum (GeV/c)

Upward νµ, which travel the longest path, are fewer than expected.

Oscillations?

1999 ICFA Instrumentation School C. Quigg, “Perspectives in High-Energy Physics” 28

Page 29: Perspectives in High-Energy Physics · Perspectives in High-Energy Physics Chris Quigg Theoretical Physics Department Fermi National Accelerator Laboratory quigg@fnal.gov Neutrino

(MINOS Schematic)

1999 ICFA Instrumentation School C. Quigg, “Perspectives in High-Energy Physics” 29

Page 30: Perspectives in High-Energy Physics · Perspectives in High-Energy Physics Chris Quigg Theoretical Physics Department Fermi National Accelerator Laboratory quigg@fnal.gov Neutrino

The Ultimate Neutrino Source?

Muon storage ring with a millimole of muons per year.

µ− → e− + νµ + νe OR µ+ → e+ + νµ + νe

16 GeVSynchrotron

Target

DecayChannel

CoolingChannel

10 GeV Linac

400 MeV Linac

MuonStorageRing

νe + νµ

µ+

H-

Racetrack 70 meters long holds 20-GeV muons. Point anywhere! 15 Hz cycle.

µ charge, momentum, polarization determine ν composition, spectrum.

Beam from µ+ contains νµ and νe, but no νµ, νe, ντ , or ντ .

1999 ICFA Instrumentation School C. Quigg, “Perspectives in High-Energy Physics” 30

Page 31: Perspectives in High-Energy Physics · Perspectives in High-Energy Physics Chris Quigg Theoretical Physics Department Fermi National Accelerator Laboratory quigg@fnal.gov Neutrino

µ+ → e+νµνe

d2Nνµ

dxdΩ=x2

2π[(3 − 2x)− (1− 2x) cos θ] , cos θ = pν · sµ

µ+ → e+νµνe

d2NνedxdΩ

=3x2

π[(1− x)− (1 − x) cos θ]

0.5

1.0

–1.0

–0.5

0

0 1.00.2 0.4 0.6 0.8

x = 2Eν/mµ

z=co

0.5

1.0

–1.0

–0.5

0

z=co

0 1.00.2 0.4 0.6 0.8

x = 2Eν/mµ

1999 ICFA Instrumentation School C. Quigg, “Perspectives in High-Energy Physics” 31

Page 32: Perspectives in High-Energy Physics · Perspectives in High-Energy Physics Chris Quigg Theoretical Physics Department Fermi National Accelerator Laboratory quigg@fnal.gov Neutrino

The Ultimate International Collaboration?

Gran Sasso

Kamiok

ande

Kolar Gold FieldsS

outh

Pol

e Alice S

prings

F

Katmandu

Istanbu

l

1999 ICFA Instrumentation School C. Quigg, “Perspectives in High-Energy Physics” 32

Page 33: Perspectives in High-Energy Physics · Perspectives in High-Energy Physics Chris Quigg Theoretical Physics Department Fermi National Accelerator Laboratory quigg@fnal.gov Neutrino

COSMIC GALL

John Updike

Neutrinos, they are very small.

They have no charge and have no mass

And do not interact at all.

The Earth is just a silly ball

To them, through which they simply pass,

Like dustmaids down a drafty hall

Or photons through a sheet of glass.

They snub the most exquisite gas,

Ignore the most substantial wall,

Cold-shoulder steel and sounding brass,

Insult the stallion in his stall,

And, scorning barriers of class,

Infiltrate you and me! Like tall

And painless guillotines, they fall

Down through our heads into the grass.

At night, they enter at Nepal

And pierce the lover and his lass

From underneath the bed—you call

It wonderful; I call it crass.

1999 ICFA Instrumentation School C. Quigg, “Perspectives in High-Energy Physics” 33

Page 34: Perspectives in High-Energy Physics · Perspectives in High-Energy Physics Chris Quigg Theoretical Physics Department Fermi National Accelerator Laboratory quigg@fnal.gov Neutrino

Choosing Path Length and Matter Encountered

0

2

4

6

8

10

12

14

0

2

4

6

8

10

12

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6

Pat

h Le

ngth

[103

km]

Profile [10

9 gm/cm

2]

Dip Angle [rad]

Alice Springs

Kolar Gold Fields

South Pole

Gran Sasso

Kamiokande

Katmandu

Istanbul

1999 ICFA Instrumentation School C. Quigg, “Perspectives in High-Energy Physics” 34

Page 35: Perspectives in High-Energy Physics · Perspectives in High-Energy Physics Chris Quigg Theoretical Physics Department Fermi National Accelerator Laboratory quigg@fnal.gov Neutrino

The Detector Challenge

To distinguish oscillations among νe, νµ, ντ , and a possible fourth,

“sterile,” neutrino νs that does not experience weak interactions,

require

• A target / detector of several kilotonnes that can

• Distinguish electrons, muons, and taus, and

• Measure their charges.

Note: τ lifetime is 0.3 picosecond.

1999 ICFA Instrumentation School C. Quigg, “Perspectives in High-Energy Physics” 35

Page 36: Perspectives in High-Energy Physics · Perspectives in High-Energy Physics Chris Quigg Theoretical Physics Department Fermi National Accelerator Laboratory quigg@fnal.gov Neutrino

The World’s Most Powerful Microscope

Fermilab’s Tevatron Collider and Its Detectors

900-GeV protons: c− 586 km/h

1-TeV protons: c− 475 km/h

Improvement: 111 km/h!

Protons pass my window 45 000 times per second

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

1999 ICFA Instrumentation School C. Quigg, “Perspectives in High-Energy Physics” 36

Page 37: Perspectives in High-Energy Physics · Perspectives in High-Energy Physics Chris Quigg Theoretical Physics Department Fermi National Accelerator Laboratory quigg@fnal.gov Neutrino

(Tevatron + Main Injector)

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Page 38: Perspectives in High-Energy Physics · Perspectives in High-Energy Physics Chris Quigg Theoretical Physics Department Fermi National Accelerator Laboratory quigg@fnal.gov Neutrino

Physics Today: CDF

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Page 39: Perspectives in High-Energy Physics · Perspectives in High-Energy Physics Chris Quigg Theoretical Physics Department Fermi National Accelerator Laboratory quigg@fnal.gov Neutrino

Physics Today: DØ

1999 ICFA Instrumentation School C. Quigg, “Perspectives in High-Energy Physics” 39

Page 40: Perspectives in High-Energy Physics · Perspectives in High-Energy Physics Chris Quigg Theoretical Physics Department Fermi National Accelerator Laboratory quigg@fnal.gov Neutrino

DØ Wins the Lottery!

(Postcard plot of∑ET = 950 GeV event)

(LEGO plot)

10−18 m ≈ 109 × size of an atom

Do the quarks and leptons have structure?

1999 ICFA Instrumentation School C. Quigg, “Perspectives in High-Energy Physics” 40

Page 41: Perspectives in High-Energy Physics · Perspectives in High-Energy Physics Chris Quigg Theoretical Physics Department Fermi National Accelerator Laboratory quigg@fnal.gov Neutrino

What Can We Learn from the Top Quark?

• Top is an apparently elementary fermion with mass

≈ 175 GeV/c2 (≈ gold atom) and charge +2/3.

• For now, can only be produced in the Tevatron at Fermilab:

900-GeV p 900-GeV p–

up to 106 collisions per second (next year, 107);

1 collision in 1010 produces a top-antitop pair

• Top’s lifetime is ≈ 0.4× 10−24 second, yet it affects the

everyday world

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Page 42: Perspectives in High-Energy Physics · Perspectives in High-Energy Physics Chris Quigg Theoretical Physics Department Fermi National Accelerator Laboratory quigg@fnal.gov Neutrino

Full Professor’s View of Top Production

b

tW

q

+ W –

q—

—b

–t

1999 ICFA Instrumentation School C. Quigg, “Perspectives in High-Energy Physics” 42

Page 43: Perspectives in High-Energy Physics · Perspectives in High-Energy Physics Chris Quigg Theoretical Physics Department Fermi National Accelerator Laboratory quigg@fnal.gov Neutrino

The Remarkable Top Quark

Observed at the Tevatron in 900 GeV⊕ 900 GeV collisions

pp → t t+ · · ·|||→ W−b

|→ W+b

b identified by displaced vertices (τb ≈ 1.5 ps) or “soft” lepton tags b→ c`ν

Al l jets44%

τ +X21%

e + j e t s15%

eµ2.5%

µµ1.2%

e e1.2%

µ + j e t s15%

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Page 44: Perspectives in High-Energy Physics · Perspectives in High-Energy Physics Chris Quigg Theoretical Physics Department Fermi National Accelerator Laboratory quigg@fnal.gov Neutrino

(Detector’s View of Top Production)

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Page 45: Perspectives in High-Energy Physics · Perspectives in High-Energy Physics Chris Quigg Theoretical Physics Department Fermi National Accelerator Laboratory quigg@fnal.gov Neutrino

CDF: displaced vertices for b and b

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Page 46: Perspectives in High-Energy Physics · Perspectives in High-Energy Physics Chris Quigg Theoretical Physics Department Fermi National Accelerator Laboratory quigg@fnal.gov Neutrino

DØ: soft lepton tag for b

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1999 ICFA Instrumentation School C. Quigg, “Perspectives in High-Energy Physics” 46

Page 47: Perspectives in High-Energy Physics · Perspectives in High-Energy Physics Chris Quigg Theoretical Physics Department Fermi National Accelerator Laboratory quigg@fnal.gov Neutrino

The Detector Challenge

To select top-quark events with high efficiency, and to measure

them effectively, require

• The ability to decide quickly which few of the 107 events per

second (108 per second at the LHC) are interesting;

• Excellent b tagging, resolving secondary vertices within a few

tenths of a millimeter of the collision point in a hostile

high-radiation environment;

• Efficient lepton identification and measurement of both

electron and muon momenta, even for leptons in jets;

• Calorimetry that provides good jet-jet invariant mass

resolution and a reliable measurement of missing transverse

energy; a hermetic detector.

1999 ICFA Instrumentation School C. Quigg, “Perspectives in High-Energy Physics” 47

Page 48: Perspectives in High-Energy Physics · Perspectives in High-Energy Physics Chris Quigg Theoretical Physics Department Fermi National Accelerator Laboratory quigg@fnal.gov Neutrino

Spectrum of Quark Masses

0.001

0.01

0.1

1

10

100

Run

ning

Mas

s [G

eV/c

2 ]

u

d

s

c

b

t

1999 ICFA Instrumentation School C. Quigg, “Perspectives in High-Energy Physics” 48

Page 49: Perspectives in High-Energy Physics · Perspectives in High-Energy Physics Chris Quigg Theoretical Physics Department Fermi National Accelerator Laboratory quigg@fnal.gov Neutrino

Three Families of Quarks and Leptons

Quarks Leptons

I u (1963) νe (1956)

d (1963) e (1897)

II c (1974) νµ (1962)

s (1963) µ (1947)

III t (1995) ντ

b (1977) τ (1975)

The Problem of Identity:

What makes a top quark a top quark and an electron an electron?

1999 ICFA Instrumentation School C. Quigg, “Perspectives in High-Energy Physics” 49

Page 50: Perspectives in High-Energy Physics · Perspectives in High-Energy Physics Chris Quigg Theoretical Physics Department Fermi National Accelerator Laboratory quigg@fnal.gov Neutrino

Top Matters!

mt influences the low-energy value of αs.

21/6π

23/6π

25/6π

27/6π

2mt

2mt’

2mc

2mb

“log(E)”MU

1/α U

“1/α

s”

Smaller mt ←→ smaller αs.

1999 ICFA Instrumentation School C. Quigg, “Perspectives in High-Energy Physics” 50

Page 51: Perspectives in High-Energy Physics · Perspectives in High-Energy Physics Chris Quigg Theoretical Physics Department Fermi National Accelerator Laboratory quigg@fnal.gov Neutrino

How does ΛQCD depend upon mt?

Calculate αs(2mt) evolving up from low energies and down from the unification

scale, and match:

1/αU +21

6πln(2mt/MU ) = 1/αs(2mc)−

25

6πln(mc/mb)−

23

6πln(mb/mt).

Identifying

1/αs(2mc) ≡27

6πln(2mc/ΛQCD) ,

we find that

ΛQCD = e−6π/27αU(

MU

1 GeV/c2

)21/27 (2mt · 2mb · 2mc

(1 GeV/c2)3

)2/27

GeV .

We have learned from (lattice) QCD that Mproton ≈ CΛQCD

Mproton

1 GeV/c2∝

(mt

1 GeV/c2

)2/27

1999 ICFA Instrumentation School C. Quigg, “Perspectives in High-Energy Physics” 51

Page 52: Perspectives in High-Energy Physics · Perspectives in High-Energy Physics Chris Quigg Theoretical Physics Department Fermi National Accelerator Laboratory quigg@fnal.gov Neutrino

What is the dimensionality of spacetime?

Ordinary experience tells us that spacetime has 3 + 1 dimensions.

Could our perceptions be limited?

Victorian fable published in 1880 by a British schoolmaster, Edwin Abbott

Abbott (1839 – 1926), and still widely available.

1999 ICFA Instrumentation School C. Quigg, “Perspectives in High-Energy Physics” 52

Page 53: Perspectives in High-Energy Physics · Perspectives in High-Energy Physics Chris Quigg Theoretical Physics Department Fermi National Accelerator Laboratory quigg@fnal.gov Neutrino

Search for “Large” Extra Dimensions

§ String theory requires 10-ish spacetime dimensions.

Assumed natural to take

Runobserved '1

MPlanck=

1

1.22× 1019 GeV/c2= 1.6× 10−35 m

What goes on there does affect the observable world:

Excitations of Calabi–Yau manifolds determine fermion spectrum.

(Fermion mass problem lives in curled-up dimensions)

§ New wrinkle

• SU(3)c ⊗ SU(2)L ⊗ U(1)Y gauge fields (+ necessary

extensions) live on branes, cannot propagate in bulk.

• Gravity lives in the bulk (extra dimensions).

1999 ICFA Instrumentation School C. Quigg, “Perspectives in High-Energy Physics” 53

Page 54: Perspectives in High-Energy Physics · Perspectives in High-Energy Physics Chris Quigg Theoretical Physics Department Fermi National Accelerator Laboratory quigg@fnal.gov Neutrino

Sta

ndar

d M

odel

Hid

den

Sec

tor

Gravity

If gravity lives in 4 + n dimensions (n with radius R), Gauss’s law ;

GN ∼ M−2Planck

∼ M−n−2s R−n

Could extra dimensions be quasimacroscopic?

If Ms ∼ 1 TeV, then R∼< 1 mm for n ≥ 2.

Remarkably, might have escaped detection . . .

1999 ICFA Instrumentation School C. Quigg, “Perspectives in High-Energy Physics” 54

Page 55: Perspectives in High-Energy Physics · Perspectives in High-Energy Physics Chris Quigg Theoretical Physics Department Fermi National Accelerator Laboratory quigg@fnal.gov Neutrino

How large is large?

Radius of the n “large” extra dimensions

n = 1 n = 2 n = 3 n = 6

Ms = 1 TeV/c2 1013 m 10−3 m 10−8 m 10−14 m

Ms = 10 TeV/c2 1010 m 10−5 m 10−10 m 10−15 m

Ms = 100 TeV/c2 107 m 10−7 m 10−12 m 10−16 m

• One large extra dimension seems excluded, since gravity within the solar

system obeys Newton’s force law in three (not four) spatial dimensions.

• Two large extra dimensions are allowed by current knowledge of gravity on

short distances, but will be challenged soon.

• Extra dimensions seen by standard-model particles cannot be larger than

about 1 TeV−1 ≈ 10−19 m, or we would already have seen them at LEP2,

HERA, and the Tevatron.

• Future collider experiments can examine two or more large extra

dimensions with a low string scale.

1999 ICFA Instrumentation School C. Quigg, “Perspectives in High-Energy Physics” 55

Page 56: Perspectives in High-Energy Physics · Perspectives in High-Energy Physics Chris Quigg Theoretical Physics Department Fermi National Accelerator Laboratory quigg@fnal.gov Neutrino

Short-distance Deviations from Newton’s Law?

V (r) = −

∫dr1

∫dr2

Gρ(r1)ρ(r2)

r12[1 + α exp(−r12)/λ)]

10

10

10

10

10–6

10–5

10 –4 10–3 10–2

8

4

0

–4

Range λ [meters]

Excluded

Long, Chan, Price (proposed)

Lamoreaux

Mitrofanov, et al.

Irvine

Rel

ativ

e S

tren

gth

α

New experiments look for deviations from Casimir and Van der Waals forces.

J. C. Long, H. W. Chan, and J. C. Price, Nucl. Phys. B539, 23 (1999).

1999 ICFA Instrumentation School C. Quigg, “Perspectives in High-Energy Physics” 56

Page 57: Perspectives in High-Energy Physics · Perspectives in High-Energy Physics Chris Quigg Theoretical Physics Department Fermi National Accelerator Laboratory quigg@fnal.gov Neutrino

Graviton Excitation of Compact Dimensions

Any particle can radiate a graviton into extra dimensions.

An extradimensional graviton is only gravitationally coupled.

=⇒ won’t interact with detector.

Gravitons go off into extra dimensions and are lost.

Their signature is missing energy, /ET .

These processes, individually tiny, may be observable

because the number of excitable modes is very large.

Examine real and virtual effects of provatons*:

Graviton excitation of towers of extradimensional (“Ka luza–Klein”) modes

* provatons < πρoβατo (sheep, as in a flock)

G. Giudice, R. Rattazzi, and J. Wells, “Quantum Gravity and Extra Dimensions at High-Energy Colliders,”Nucl. Phys. B544, 3 (1999) (hep-ph/9811291).

1999 ICFA Instrumentation School C. Quigg, “Perspectives in High-Energy Physics” 57

Page 58: Perspectives in High-Energy Physics · Perspectives in High-Energy Physics Chris Quigg Theoretical Physics Department Fermi National Accelerator Laboratory quigg@fnal.gov Neutrino

Looking for provatons . . .

New signatures, like

pp → jet + /ET (parton + graviton)

`+`− + /ET (`+`− + graviton)

Informative metaphor of collider as ultramicroscope

Are extra dimensions large enough to see?

1999 ICFA Instrumentation School C. Quigg, “Perspectives in High-Energy Physics” 58

Page 59: Perspectives in High-Energy Physics · Perspectives in High-Energy Physics Chris Quigg Theoretical Physics Department Fermi National Accelerator Laboratory quigg@fnal.gov Neutrino

The Detector Challenge

To establish a jet + /ET signature at a hadron collider, require

• A hermetic detector with well-controlled /ET tails to establish

and quantify the missing-energy signature;

• Highly efficient rejection of cosmic-ray and accidental triggers;

• Ability to reject triggers originating from jet mismeasurments;

• Control over physics backgrounds, including Z0 + jets and

W± + jets.

If a missing-energy signal is found, it will be a challenge to

distinguish an extradimensional signal from the classic

R-parity–conserving signature for supersymmetry.

We should be so lucky!

1999 ICFA Instrumentation School C. Quigg, “Perspectives in High-Energy Physics” 59

Page 60: Perspectives in High-Energy Physics · Perspectives in High-Energy Physics Chris Quigg Theoretical Physics Department Fermi National Accelerator Laboratory quigg@fnal.gov Neutrino

Projected Sensitivities

Experimental sensitivity to graviton emission depends on collider energy,

luminosity, and species, and the number of large extra dimensions.

Theorist’s analysis:

n = 2 n = 4 n = 6

LEP2 4.7 × 10−4 m 1.9 × 10−11 m 6.9 × 10−14 m

Tevatron Run 1 1.1 × 10−3 m 2.4 × 10−11 m 5.8 × 10−14 m

Tevatron Run 2 3.9 × 10−4 m 1.4 × 10−11 m 4.0 × 10−14 m

Large Hadron Collider 3.4 × 10−5 m 1.9 × 10−12 m 6.1 × 10−15 m

1-TeV polarized LC 1.2 × 10−5 m 1.2 × 10−12 m 6.5 × 10−15 m

Mirabelli, Perelstein, Peskin, Phys. Rev. Lett. 82, 2236 (1999) (hep-ph/9811337).

1999 ICFA Instrumentation School C. Quigg, “Perspectives in High-Energy Physics” 60

Page 61: Perspectives in High-Energy Physics · Perspectives in High-Energy Physics Chris Quigg Theoretical Physics Department Fermi National Accelerator Laboratory quigg@fnal.gov Neutrino

An Extra Dimension Bibliography

1. Marcus Chown, “Five and Counting . . . ,” New Scientist 160, No. 2157 (24 October 1998),

http://www.newscientist.com/ns/981024/fifth.html

2. I. Antoniadis, “A Possible New Dimension at a Few TeV,” Phys. Lett. B246, 377 (1990).

3. J. D. Lykken, “Weak Scale Superstrings,” Phys. Rev. D54, 3693 (1996) (hep-th/9603133).

4. Nima Arkani-Hamed, Savas Dimopoulos, Gia Dvali, “The Hierarchy Problem and New

Dimensions at a Millimeter,” Phys. Lett. B429, 263 (1998) (hep-ph/9803315).

5. Ignatios Antoniadis, Nima Arkani-Hamed, Savas Dimopoulos, Gia Dvali, “New Dimensions

at a Millimeter to a Fermi and Superstrings at a TeV,” Phys. Lett. B436, 257 (1998)

(hep-ph/9804398).

6. I. Antoniadis, K. Benakli, M. Quiros, “Production of Kaluza–Klein States at Future

Colliders,” Phys. Lett. B331, 313 (1994) (hep-ph/9403290).

7. Eugene A. Mirabelli, Maxim Perelstein, Michael E. Peskin, “Collider Signatures of New

Large Space Dimensions,” Phys. Rev. Lett. 82, 2236 (1999) (hep-ph/9811337).

8. Keith R. Dienes, Emilian Dudas, Tony Gherghetta, “Extra Space-Time Dimensions and

Unification,” Phys. Lett. B436, 55 (1998) (hep-ph/9803466).

9. JoAnne L. Hewett, “Indirect Collider Signals for Extra Dimensions,” Phys. Rev. Lett. 82, 4765

(1999) (hep-ph/9811356).

1999 ICFA Instrumentation School C. Quigg, “Perspectives in High-Energy Physics” 61

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The Outlook for Extra Dimensions

• We are only beginning to explore the possible implications of

almost-accessible extra dimensions.

• Hard to distinguish a KK signal from other new physics.

• What might we observe above the threshold for exciting extra

dimensions?

• Although the basic concepts have a sound basis in string

theory, the scenarios put forward so far have more to do with

storytelling than with theoretical rigor.

• Our inability to disprove at once the preposterous idea of large

extra dimensions is a measure of the potential for experimental

surprises. An indication of Nature’s capacity to amaze us!

1999 ICFA Instrumentation School C. Quigg, “Perspectives in High-Energy Physics” 62

Page 63: Perspectives in High-Energy Physics · Perspectives in High-Energy Physics Chris Quigg Theoretical Physics Department Fermi National Accelerator Laboratory quigg@fnal.gov Neutrino

Final Thoughts

To a great degree, the progress of particle physics has followed from progress in

accelerator science and instrumentation. There is no substitute for experiment, and

experiment requires inventions (both hardware and software) and continuous

innovation in analysis.

“Yesterday’s sensation is today’s calibration and tomorrow’s background.”

In the middle of a revolution in our conception of Nature, when we deal withfundamental questions about our world, including

• What are the symmetries of Nature, and how are they hidden from us?

• Are the quarks and leptons composite?

• Are there new forms of matter, like the superpartners suggested by supersymmetry?

• Are there more fundamental forces?

• What makes an electron an electron and a top quark a top quark?

• What is the dimensionality of spacetime?

we cannot advance without new instruments that extend our senses and allow us to

create—and understand—new experience far beyond the realm of everyday human

experience. Good luck!

1999 ICFA Instrumentation School C. Quigg, “Perspectives in High-Energy Physics” 63