Was Einstein right or are there extra Was Einstein right or are there extra space-time dimensions?space-time dimensions?

Nigel Glover

Institute for Particle Physics PhenomenologyInstitute for Particle Physics Phenomenology

Durham UniversityDurham University

Standard Model of Particle PhysicsStandard Model of Particle Physics

19741974

1977197719761976

19951995

1949194919371937

Standard Model of Particle PhysicsStandard Model of Particle Physics

Gravity not here! Much too weak – 1040 times weaker than the strong forceOnly becomes strong at the Planck scale 1019 GeVString theory best candidate for quantum gravity

Higgs, H?

19831983

19831983

19791979

Extra Dimensions?Extra Dimensions?

• What are they?• Why are we asking the question?• Why haven’t we found them yet?• What are their consequences?• How are we going to find evidence for

them?

Where are the extra dimensions?Where are the extra dimensions?

From a distance, we see only the rope – one dimension

From close up, the ant sees two dimensions

So far, we only see three space dimensions because we haven’t been able to resolve them

Extra DimensionsExtra Dimensions

• One possibility is that we live in a subspace of the extra dimensions

• All particles and most forces might be confined to our world: photons (electromagnetism), electrons, protons, …

But gravity, the weakest of the four forces, might be able to propagate in the extra dimensions

x, y, z

w, v,…

gravity E&M

Extra dimensions could explain Extra dimensions could explain why gravity is so weak!why gravity is so weak!

Potential falls off asV ~ G3/r

Potential falls off asV ~ Gd/rd-2

Gravitational flux lines travel into the normal dimensions

andand into the extra dimensions for r < Lr < L: gravitational potential is increased in proportion

M

L

This changes the force of gravityThis changes the force of gravity

gravity

EM

Str

engt

h

r1/mstrong

…Gravity could become strong at small distances!

• Lots of mass/energy in a small volume black hole

Making Black Holes!Making Black Holes!

• If two particles pass close enough with enough energy, they will form a microscopic black hole

• For 3 spatial dimensions, gravity is too weak for this to happen. But with extra dimensions, gravity becomes stronger, micro black holes could be created in particle collisions!

Micro Black HolesMicro Black Holes

• Where could they be produced?

• How will we know if we’ve seen one?

S. Harris

Black HolesBlack Holes

• But quantum mechanically, black holes Hawking radiate; black holes emit light

• Classically, light and other particles do not escape; black holes are black.

Black Hole EvaporationBlack Hole Evaporation

• “Normal” black holes:Mass: MBH ~ Msun

Size: kilometerTemperature: 0.01 KLifetime: ~ forever

• Micro black holes:Mass: MBH ~ 1000 Mproton

Size: 10-18 mTemperature: 1016 KLifetime: 10-27 s

They explode!

Extra Dimensional MatterExtra Dimensional Matter

• A particle moving in an extra dimension of size L appears to us as a set of particles with masses

0, 1/L, 2/L, 3/L, 4/L, …

• Each known particle has a heavy partner at each mass level.

• We can search for these particles by looking for their decay into lighter particles

mas

s

1/L

2/L

3/L

4/L

0

…

World’s most powerful particle accelerator

Superconducting magnets

– 8.3T at 1.9K

2 beams of protons will collide 40 million times a second

In construction since 1998Due to start later this year

The Large Hadron Collider at CERNThe Large Hadron Collider at CERN

CMS

ATLASLHCb

ALICE

aside: LHC vs. circle line

LHC Circle line

Length 27km 22.5km

Depth 100m 15m

Diameter 3.8m 3.4m

LHC Beam Stored EnergyLHC Beam Stored Energy

Same as colliding 2 x 120 elephants...

120 elephants with 40 km/h 120 elephants with 40 km/h

eye of a needle:0.3 mm diameter

proton beams at interaction point are 10x smaller:0.03 mm diameter

The energy of a single 7 TeV proton is equivalent to a flying mosquito (1 µJ)

2808 bunches, 1.1 x 1011 protons/bunch @ 7 TeV350 MJ stored energy per proton beam

LHC Magnet InstallationLHC Magnet Installation

Quality Control

Storage on car-parks all over CERN

Interconnection welding

Lowering through an elliptical shaft

Transport withoptically guidedvehicle

Last connection made 7 November 2007

Cooldown Status Cooldown Status (as of 28(as of 28thth Apr 2008, 5pm) Apr 2008, 5pm)

sector 12: warmsector 23: 50-150 Ksector 34: 180-280 Ksector 45: warmsector 56: 1.9 Ksector 67: 30-90 Ksector 78: 1.9 Ksector 81: 1.9 K

http://lhc.web.cern.ch/lhc/

total cold mass: 40,000 tons10,000 tons of liquid nitrogen120 tons of superfluid Helium (1.9 K) for cooling

vacuum: 10-10 Torr = 3 million molecules per cm3

ATLASATLAS ((AA TToroidal oroidal LLHC HC AApparatupparatuSS))

Length = 55 mWidth = 32 mHeight = 35 m

Construction from Oct 2003 – Mar 2008

CMS CMS ((CCompact ompact MMuon uon SSpectrometer)pectrometer)

15 m

22 m

main assembly on surface, then lowering into cavern in 5 big parts by ~2500 t crane

~12,500 t

210 m2 silicon detectors

4 T

CMS Lowering of 2000 t Central Part CMS Lowering of 2000 t Central Part (Feb 2007)(Feb 2007)

Black Hole event at ATLAS simulated by CHARYBDIS

Are micro black holes dangerous?Are micro black holes dangerous?

• On 21 March, Luis Sancho, from Spain, and Hawaii resident Walter Wagner filed a lawsuit in Hawaii's US District Court against CERN and US contributors to the project demanding that they do not operate the LHC until they prove it is safe.

• The lawsuit's claims are "complete nonsense", said James Gillies, a spokesman for CERN. "The LHC will start up this year, and it will produce all sorts of exciting new physics and knowledge about the universe," he said, adding: "A year from now, the world will still be here."

SummarySummary

• Extra dimensions are well-motivated theoretically (string theory)– May lead to micro black hole production or other phenomena at the

LHC

– May shed light on longstanding puzzles on the weakness of gravity

• LHC startup approaching – later this summer

– “discoveries are guaranteed…at least the Higgs boson…likely observe new symmetries of nature, new particles and forces”

– Biggest leap in energy since discovery of jets/W/Z/SUSY/top at UA1/UA2 in 1983

STFC delivery plan

Are micro black holes dangerous?Are micro black holes dangerous?

Q What if the micro black holes produced at the LHC do not decay as rapidly as calculated, or might even not be prone to decay and, if unable to rapidly evaporate, they could start interacting, grow larger and potentially be disastrous to Earth itself?

A Collisions at these energies (and higher) have been happening in nature for billions of years apparently without hazardous effects, as ultra high energy cosmic rays impact Earth's atmosphere.

Q What if the micro black holes created at LHC have less than the Earth's escape velocity (of 11.2 km/s), and therefore would be captured by the Earth's gravitational field?

A If so, its very likely that cosmic rays would destroy dense objects like neutron stars/pulsars

The

Sun

TRIU

MFAT

LAS

CERN Accelerator ComplexCERN Accelerator Complex

start here

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PROTONS

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2

3

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LINAC2

BOOSTER

PS

SPS

LHC

50 MeV

1.4 GeV

26 GeV

450 GeV

7 TeV

I’ll try to keep it simple…but please askI’ll try to keep it simple…but please ask