Mini Big Bangs with ALICE at the LHC

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Mini Big Bangs with ALICE at the LHC

• Dr David Evans
• The University of Birmingham

Goldsmiths Summer School Brunel University 24th
July 2008
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Somewhere in Switzerland
Situated on the Swiss-French border, near Geneva
Is the Worlds largest physics laboratory
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CERN
Deep underground, they are building the Worlds
largest machine
The Large Hadron Collider (LHC)
Which will accelerate sub-atomic particles to
0.999999991 the speed of light .
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Large Hadron Collider
. and collide them together in four
cathedral-sized caverns around the 27 km ring.
Creating sub-atomic explosions, and conditions
that existed less than a billionth of a second
after the Big Bang.
In four massive particle detectors
Up to 600 million times per second
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• Four Main Detectors
• ALICE, ATLAS, CMS LHCb

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Four Main Detectors
ATLAS CMS designed to look for and study new
heavy particles (Higgs, SUSY etc) and rare
processes. Record pp collisions at high rate.
LHCb designed to study beauty (particles which
contain b-quarks) look for asymmetries between
matter and anti-matter.
ALICE designed to study the collisions of lead
nuclei as well as protons. High precision
measurements but at a lower rate. Designed to
study the Strong force in detail.
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A QUICK RECAPThe Forces
Force Range Mediator Rel.
Strength Gravitational long
graviton (massless) ?? 1 Electromagnetic long
photon (massless) 1035 Weak
short W, Z bosons (heavy)
1033 Strong short gluons (massless)
1038
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The Standard Model

c
t
u
quarks
s
b
d

?
?
e
leptons
??
?e
??
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The Weak Force

c
t
u
quarks
s
b
d

?
?
e
leptons
??
?e
??
W
W-
Z0
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The Electromagnetic Force

c
t
u
quarks
s
b
d

?
?
e
leptons
??
?e
??
?
Photon
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The Strong Force

c
t
u
quarks
s
b
d

?
?
e
leptons
??
?e
??
g
gluon
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Back to the Strong Force

• Electromagnetic Force
• 1 electric charge ( its opposite charge)
• Mediated by photons (Of course, photons do not
  have electric charge themselves)

Vem -? / r
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The Strong Force
Free quarks are not observed experimentally Potent
ial between quarks
V - (4?s / 3r) kr
Linear term ? need infinite energy to have a free
object with colour.
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Quark Mass

• Quarks have a much higher effective mass when
  confined in particles.
• Only account for 2 of proton mass
• Rest due to QCD effects - We dont really
  understand how this works.
• So, 98 of your mass actually comes from the
  strong force.
• So it wasnt all those cream cakes after all!

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The Quark-Gluon Plasma
At extreme temperatures and/or densities hadronic
matter melts into a plasma of free quarks and
gluons.
This new state of matter would have existed up to
about 10 millionths of a second after the Big
Bang, and could be created in the core of
collapsing neutron stars.
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Phases of Strongly Interacting Matter
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How to Make a QGP

• Need very high energy densities
• Create sub-atomic volumes of hot, dense matter
  similar to conditions 10-6s after Big Bang
• Fireball must live long enough for phase
  transition to take place
• Collide lead ions (lead nuclei) at highest
  energies

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The Fireball

• Temperature of our fireball 1013K i.e. gt
  1,000,000 times the temp of centre of Sun.
• Density Great Pyramids crushed to the size of a
  pin-head similar to neutron star densities (but
  much hotter!)

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Early Universe
Recreate conditions similar to those some 10-6
seconds after the Big Bang
Learn about the evolution of the very early
Universe
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What Happens ?

• Energy is converted into many quarks, anti-quarks
  and gluons.
• QGP lasts for about 10-22 seconds
• Then thousands of particles are produced

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Observables
Jets
Open charm, beauty
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The ALICE Detector
52 feet (16 metres) high, 85 feet (26 metres)
long, and weighs about 10,000 tons
TOF PID
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Inner Tracking System (ITS)
SSD
SDD
SPD
Lout97.6 cm
Rout43.6 cm

• 6 Layers, three technologies (keep occupancy
  constant 2 for max mult)
• Silicon Pixels (0.2 m2, 9.8 Mchannels)
• Silicon Drift (1.3 m2, 133 kchannels)
• Double-sided Strip Strip (4.9 m2, 2.6 Mchannels)

Material Budget lt 1 X0 per layer !
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TPC

• largest ever
• 88 m3, 570 k channels

drift gas 90 Ne - 10CO2
Central Electrode
25 µm aluminized Mylar on Al frame
Field Cage Inner Vessel
3 m diameter
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TPC Field Cage
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TPC
As well as detecting charged particles, the TPC
can also deduce their mass by measuring their
rate of energy loss.
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Precision Measurements
ALICE was designed to be able to reconstruct and
measure up to 20,000 particles produced in a
single lead-lead collision. Its design means
that ALICE has excellent resolution and particle
identification. This makes ALICE ideal for
studying event characteristics in proton-proton
collisions and the production of lighter
particles.
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Whats Our Contribution?Birmingham Trigger

• Bham group responsible for the ALICE trigger
  (electronic brain).
• Receives up to 60 inputs from various detectors
  sensors (every 25ns).
• Has to make first complex decision within 100ns.

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ALICE - 2007
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The ALICE Detector
ALICE in December photo by Simon Hadley,
Birmingham Post
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Event Display PbPb
HMPID
TOF
TRD
TPC
60? lt J lt 62?!
PHOS
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Data Computing Challenges

• Write data to tape 1.2 Gbytes/sec (2 CDs/sec)
• Equivalent to writing the Encyclopaedia
  Britannica every two seconds
• 2 Pbytes / year (3.3 million CDs worth thats
  a stack of CDs 3 miles high - gt12 miles high for
  all LHC experiments)
• Computing requirements 50,000 PCs (3 GHz)

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Summary

• Particle physics has discovered much about how
  the Universe works
• Still many outstanding questions
• The Worlds largest machine (LHC) will add to
  this knowledge
• Huge challenges ahead
• But LHC will find new exciting physics
• We will learn more about the very early Universe
• ALICE will play an important role in this.
• Thank you for listening.

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Particle Physics Spin-offs
Education
Research
Medical Imaging
For every 10 spent on NHS, only 1p is spent on
particle physics. No, PET scanners, no MRS scans,
no cancer killing particle beams etc. without
particle physics
Computing
Technology