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Tom Barber

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Tom Barber – PowerPoint PPT presentation

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Title: Tom Barber


1
  • Tom Barber

2
The Large Hadron Collider
  • Located at CERN
  • Franco-Swiss border
  • 27km diameter ring
  • 100m underground
  • Accelerates protons to nearly the speed of light
  • Two counter rotating beams.

27km
3
The Large Hadron Collider
  • Using superconducting magnets.
  • 300 degrees below zero.
  • 800 million collisions per second
  • Energy in the beam as much as a 400 tonne train
    at 150 km/h.
  • Only 14 TeV of energy in each collision.

4
High Energy Physics?
  • Units of electron volts (eV)
  • LHC produces 7 TeV protons
  • But how much is 1 TeV?
  • 1 TeV 1012 eV 1000000000000 eV
  • 1 eV 10-19 J 0.0000000000000000001 J
  • 1 TeV 10-7 J 0.0000001

5
Not so High Energy
  • Kinetic Energy
  • K.E. ½ m v2
  • Something small a mosquito
  • How heavy?
  • m 0.001 kg
  • How fast?
  • v 0.01 m/s
  • Kinetic Energy
  • KE 0.001 x 0.01 x 0.01 J
  • 0.0000001 J 10-7 J
  • 1 TeV !!

6
Large Mosquito Collider!
7 TeV
7 TeV
  • So why high-energy physics

7
Which contains more water?
Clouds?
OR
Water Droplet?
8
  • Clouds contain more water molecules in total.
  • Try standing outside in the rain!
  • The drop contains more molecules in a fixed
    volume.
  • The water drop has a higher

density
9
High Energy Density
  • The droplet contains water in a small volume.
  • The LHC squeezes the energy into a space
  • a million million times smaller
  • than a mosquito.
  • The same energy density as during the Big Bang!
  • Looking back to the start of the universe!

10
The ATLAS Experiment
  • Protons collide at 4 points on LHC.
  • ATLAS at point 1
  • Records the aftermath of collisions.

11
Who is ATLAS?
12
  • 2000 physicists
  • 166 universities
  • 37 countries
  • Multi-national collaboration

13
The ATLAS Detector
  • The detector is made of many parts
  • What do they all do?

14
Building a Particle Detector
  • Time
  • Position
  • Charge
  • Momentum
  • Energy
  • How do we do it

15
Measuring Position
  • Particle Motion
  • Track particle position using silicon layers.
  • Charged particles in silicon cause electric
    current.
  • Current measured by electronics.
  • Tracks reconstructed by computer programs.

electric current
charged particle
silicon layer
16
ATLAS Tracker
420,000 Xenon Straws
6 Million Silicon Strips
135 Million Pixels
17
SemiConductor Tracker
  • 4 barrel layers
  • 9 endcap wheels
  • 6 million silicon strips
  • Need to configure and read-out each module.
  • I work on the Data AcQuisition (DAQ) software.

18
Momentum
  • What is momentum?
  • p m x v
  • Charged particles on the move
  • Force on charged particle in a magnetic field
  • F B x e x v
  • Force at right angles
  • ? circular arcs
  • With a centripetal force
  • F m v2 / r
  • Put them together

19
Making Tracks
  • Measure radius of tracks to measure momentum
  • p B x e x r
  • We need a magnet
  • a really big magnet.

20
ATLAS Magnets
  • Solenoid
  • 5.3m long
  • 2.4m bore
  • 5.7 tons
  • 2 T Field

21
Toroid Magnets
Endcap
Barrel
22
Energy
  • Measured by calorimeters

23
What about muons?
  • Muons are heavy.
  • They through most of ATLAS.
  • Need their own outer detector.

24
Summary
  • Now we can measure
  • Position
  • Momentum
  • Energy
  • Muons
  • Lets put it all together

25
An ATLAS Event
26
Needle in a Haystack
  • Signals converted to data for computers.
  • Protons collide
  • 40,000,000 times a second
  • Enough data to fill 100,000 CDs per second!
  • But
  • only one in 5,000,000 is interesting.
  • How do we decide which to keep?

27
Event Selection 1
  • Use computers to recognise interesting patterns.
  • What do you think of this event?
  • Accept
  • Or
  • Reject?

Reject!
28
Event Selection 2
  • Use computers to recognise interesting patterns.
  • What do you think of this event?
  • Accept
  • Or
  • Reject?

electron
Accept!
Z boson production
29
Event Selection 3
  • Use computers to recognise interesting patterns.
  • What do you think of this event?
  • Accept
  • Or
  • Reject?

Reject!
30
Event Selection 4
  • Use computers to recognise interesting patterns.
  • What do you think of this event?
  • Accept
  • Or
  • Reject?

muon
electron
electron
Accept!
Higgs boson production
31
Event Selection 5
  • Use computers to recognise interesting patterns.
  • What do you think of this event?
  • Accept
  • Or
  • Reject?

Reject!
32
Event Selection 6
  • Use computers to recognise interesting patterns.
  • What do you think of this event?
  • Accept
  • Or
  • Reject?

muon
energy
Accept!
Supersymmetric event
33
Event Selection 7
  • Use computers to recognise interesting patterns.
  • What do you think of this event?
  • Accept
  • Or
  • Reject?

Reject!
34
Event Selection 7
  • Use computers to recognise interesting patterns.
  • What do you think of this event?
  • Accept
  • Or
  • Reject?

Missing energy
Accept!
More supersymmetry
35
Event Selection 8
  • Use computers to recognise interesting patterns.
  • What do you think of this event?
  • Accept
  • Or
  • Reject?

Accept!
Lots of energy
Black Hole??
36
Trigger and Computing
  • Now try it 40,000,000 times a second!
  • Need a trigger system to filter events.
  • 1 Petabyte of data each year
  • 4 tonnes of DVDs!
  • Need to use the grid
  • Data from LHC machines is copied to sites around
    the world.
  • Physicists send their analysis code to run on the
    data
  • here are some examples of what we do

37
Testing the Standard Model
Allowed in SM
  • I work on testing one aspect of the Standard
    Model
  • Triple Gauge Couplings forbidden!
  • Should improve limits by ten times.

Forbidden in SM
38
and beyond?
  • Our current theories work well, but
  • there are lots of problems, e.g.
  • Where does mass come from?
  • Why are particle masses so different?
  • Why do we have different forces?
  • How does gravity fit in?
  • Are there extra dimensions?
  • Is there a Theory of Everything?
  • How do Swiss buses run on time?
  • Still lots to understand

39
The Higgs Boson
  • Why do we have mass?
  • Peter Higgs proposed a new scalar field.
  • Wine bottle potential naturally explains mass.
  • Predicts existence of a new particle
  • The Higgs Boson
  • How does it work?

40
Imagine a party of physicists
41
a celebrity comes onto the scene
42
he wants a drink,
but everyone wants to talk to him.
43
Now there is a rumour of free wine
44
the rumour spreads through the room.
45
The Higgs so Far
  • Direct search at LEP
  • Mass gt 114 GeV
  • Possible candidate at 115 GeV!
  • Other experiments indirectly give upper limits
  • W mass, t mass
  • Current limit
  • Mass lt 186 GeV

46
Finding the Higgs in ATLAS
  • H ? ZZ ? 2e2mu
  • Higgs decays into characteristic signature.
  • Could ATLAS be the first to see this particle?

47
Could ATLAS find it?
  • Significance is a statistical measure of signal
    quality.
  • SNsignal/vNbackground
  • If significance gt 5, we claim discovery!
  • ATLAS has good chance over large mass range.

48
SUSY
  • Why do we have different forces?
  • Why are particle masses so different?
  • Supersymmetry to the rescue
  • Each particle has a supersymmetric partner
  • Could explain Dark Matter?

49
Black Holes
  • Could produce microscopic Black Holes
  • Decay via
  • Hawking Radiation
  • into very complex events.
  • Finding them will be a challenge!

50
Will the LHC destroy the world?
  • Could a black hole/strangelet from the LHC eat
    the world?
  • No!
  • Particles from space have been bombarding the
    earth for billions of years.
  • Cosmic Rays are far more energetic than LHC
    collisions.
  • These have not harmed the earth since it formed.
  • Dont be scared of the LHC!

51
A Golden Age?
  • ATLAS is nearly finished!
  • The LHC is due to start next year.
  • It will run for 15 years.
  • Could change our view of the universe.
  • You will be able to see the data!
  • A very exciting time
  • will you be part of it?

52
Some Links
  • This Talk
  • http//www.hep.phy.cam.ac.uk/barber/talks.html
  • ATLAS page (videos, webcam, photos)
  • http//atlas.ch
  • CERN Webpage
  • http//public.web.cern.ch/public/
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