ALICE
The ALICE Experiment
H. Qvigstad
Physics I
Why Collide?
QGP
Flow
Photons
Other Signals
ALICE
Henrik Qvigstad
henrik.qvigstad@fys.uio.no
University of Oslo
ITS
TPC
PHOS
30 March 2012
Physics II
Flow
Me & ALICE
UiO
H. Qvigstad (UiO)
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1 Physics Part I: Motivation
ALICE
H. Qvigstad
Why We Collide?
Quark Gluon Plasma
Flow
Photons As an Probe
Other Signals
Physics I
Why Collide?
QGP
Flow
Photons
Other Signals
ALICE
ITS
TPC
PHOS
2 ALICE
ITS
TPC
PHOS
3 Physics Part II: The Results
Physics II
Flow
Me & ALICE
UiO
Elliptic Flow
And more...
4 My Work and ALICE Activity In the Oslo
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The Large Hadron Collider
ALICE
H. Qvigstad
Physics I
Why Collide?
QGP
Flow
Photons
Other Signals
ALICE
ITS
TPC
PHOS
Physics II
Flow
Me & ALICE
UiO
Beam of (Design):
√
• p-p at 7 TeV, s = 14 TeV, and
√
• Pb-Pb at 2.76 TeV, s = 5.5 TeV
H. Qvigstad (UiO)
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Why We Collide
particles and nuclei
ALICE
H. Qvigstad
For Particles, collisions inform:
• structure,
Physics I
Why Collide?
QGP
Flow
Photons
Other Signals
• fundamental interactions, and
• resonances (particles.)
For Nuclei, collisions inform:
ALICE
ITS
TPC
PHOS
• structure,
• collective effects,
Physics II
Flow
Me & ALICE
UiO
• nuclear phase diagram.
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Why We Collide
Particles
Collisions provide information about structure.
ALICE
• The classic Rutherford Scattering:
H. Qvigstad
Physics I
Why Collide?
QGP
Flow
Photons
Other Signals
ALICE
ITS
TPC
PHOS
Physics II
Flow
Me & ALICE
UiO
with GeigerMarsden (Gold foil) experiment disproved the plum
pudding model in favor of nuclear model.
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Why We Collide
Particles
Collisions provide information about fundamental interaction
ALICE
H. Qvigstad
• Electron-positron annihilation produce “3-Jet Topology”
events:
Physics I
Why Collide?
QGP
Flow
Photons
Other Signals
ALICE
ITS
TPC
PHOS
Physics II
Flow
Me & ALICE
UiO
interpreted within the standard model to be product of qq̄
creation and radiation of gluons through QCD Bremsstrahlung.
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Why We Collide
Composite Particles
Protons
ALICE
• can be accelerated at a smaller accelerator radius
H. Qvigstad
Physics I
Why Collide?
QGP
Flow
Photons
Other Signals
, and collisions of
• provide a large range of discovery.
ALICE
ITS
TPC
PHOS
Physics II
Flow
Me & ALICE
UiO
A proton-proton collision at LHC typically consists of ∼ 10
hard interactions (collisions).
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Why We Collide
Nuclei
Nuclear collisions
ALICE
• provide an insight into the collective behavior of high
H. Qvigstad
density, high energy density, Nuclear Matter.
Physics I
Why Collide?
QGP
Flow
Photons
Other Signals
ALICE
ITS
TPC
PHOS
Physics II
Flow
Me & ALICE
UiO
H. Qvigstad (UiO)
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2012-03-30
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Why We Collide
Nuclei, QGP
The beginning of the universe was also quite dense and hot.
ALICE
H. Qvigstad
Physics I
Why Collide?
QGP
Flow
Photons
Other Signals
ALICE
ITS
TPC
PHOS
Physics II
Flow
Me & ALICE
UiO
H. Qvigstad (UiO)
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Quark Gluon Plasma
The evolution of the nuclear matter in an nuclear - nuclear
collisions
ALICE
H. Qvigstad
Physics I
Why Collide?
QGP
Flow
Photons
Other Signals
, produces a state of matter not seen since t ' 10−6 after The
Big Bang.
ALICE
ITS
TPC
PHOS
Physics II
Flow
Me & ALICE
UiO
H. Qvigstad (UiO)
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Quark Gluon Plasma
What is QGP really?
Imagine an Nuclear Phase Diagram,
ALICE
H. Qvigstad
Physics I
Why Collide?
QGP
Flow
Photons
Other Signals
ALICE
ITS
TPC
PHOS
Physics II
Flow
Me & ALICE
UiO
with an transition/crossover to an de-confided state of quarks
and gluons.
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Flow
Non-central Nuclear-Nuclear collisions exhibit flow:
ALICE
H. Qvigstad
Physics I
Why Collide?
QGP
Flow
Photons
Other Signals
ALICE
ITS
TPC
PHOS
Physics II
In “low” energy collisions, this is considered the product of:
Flow
Me & ALICE
UiO
• Bounce-Off, the collective “deflection” of the “spectating”
region of the collision, and
• Squeeze-Out, pressure gradiants act out of plane for the
“participating” region of the collision.
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ALICE
2012-03-30
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Flow
At “high” energy, flow is an product of the anisotropi of an
non-central collision.
ALICE
H. Qvigstad
Physics I
Why Collide?
QGP
Flow
Photons
Other Signals
ALICE
ITS
TPC
PHOS
Flow can be mathematically described as
Physics II
Flow
Me & ALICE
UiO
H. Qvigstad (UiO)
1
dN
∝
[1 + Σ∞
n=1 2vn cos n(φ − Ψn )]
dφ
2π
∝ 1 + 2v1 cos φ + 2v2 cos 2φ + . . .
ALICE
(1)
(2)
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Flow
Flow is an product of all the stages of the collision
ALICE
H. Qvigstad
Physics I
Why Collide?
QGP
Flow
Photons
Other Signals
ALICE
ITS
TPC
PHOS
Physics II
Flow
Me & ALICE
UiO
• Understanding all the phases of the collision and the their
contribution to the final state is an massive undertaking.
• Flow components are essential to understanding the
collision in terms of Hydrodynamic Models.
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Flow
The Equation Of Stadte (EOS), the
relationship between Temperature,
Pressure, and Volume, is informed by
the two first flow components.
ALICE
H. Qvigstad
Physics I
• Direct Flow, v1 ,
• Elliptic Flow, v2 .
Why Collide?
QGP
Flow
Photons
Other Signals
ALICE
ITS
TPC
PHOS
The higher order flow components,
• v3 , v4 ...
Physics II
Flow
Me & ALICE
UiO
contain information about Viscosity.
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Photons
ALICE
H. Qvigstad
Physics I
Why Collide?
QGP
Flow
Photons
Other Signals
Photons are not affected by the nuclear medium of the
collision, and are thus excellent candidates as an direct probe of
the interaction in the medium.
Sources of Photons:
• Direct Photons
• Prompt Photons, photons from initial hard scattering;
• Fragmentation Photons, photons that are part of the
fragmentation of an quark into a jet;
ALICE
ITS
TPC
PHOS
• Thermal Photons;
• Bremsstrahlung of high momentum quarks in the medium.
Physics II
Flow
Me & ALICE
UiO
• Decay Photons,
• decay of mesons, π 0 , η, ω, ...
• pair production, bremsstrahlung,
• ...
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Photon-Jet
Hard scatterings of patrons give rise to photon-jet, gq → γq,
ALICE
H. Qvigstad
Physics I
Why Collide?
QGP
Flow
Photons
Other Signals
ALICE
ITS
TPC
PHOS
Physics II
Flow
Me & ALICE
UiO
• The photon escapes the medium un–perturbed.
• The quark looses energy through Nuclear Bremsstrahlung
as it traverses the medium.
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RAA
ALICE
H. Qvigstad
Physics I
Why Collide?
QGP
Flow
Photons
Other Signals
ALICE
ITS
TPC
PHOS
Physics II
Flow
Me & ALICE
UiO
H. Qvigstad (UiO)
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RAA
ALICE
H. Qvigstad
Physics I
Why Collide?
QGP
Flow
Photons
Other Signals
ALICE
ITS
TPC
PHOS
Physics II
Flow
Me & ALICE
UiO
H. Qvigstad (UiO)
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ALICE
H. Qvigstad
Physics I
Why Collide?
QGP
Flow
Photons
Other Signals
ALICE
ITS
TPC
PHOS
Physics II
Figure: quark scaling at the PHENIX, RHIC
Flow
Me & ALICE
UiO
H. Qvigstad (UiO)
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ALICE
(A Large Ion Collider Experiment)
ALICE
H. Qvigstad
Physics I
Why Collide?
QGP
Flow
Photons
Other Signals
ALICE
ITS
TPC
PHOS
Physics II
Flow
Me & ALICE
UiO
Figure: ALICE Detektor Eksperimentet
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ALICE
(A Large Ion Collider Experiment)
ALICE
H. Qvigstad
Only a small selection of particles have a lifetime large enough
to reach the detectors:
• Charged Particles, e.g. e −/+ , µ−/+ ,π −/+ , p/p̄, and K −/+ ;
Physics I
Why Collide?
QGP
Flow
Photons
Other Signals
ALICE
• Photons (γ);
• Neutrons (n/n̄); and
• Neutrinos: νe , νµ , ντ , ν̄e , ν̄µ , and ν̄τ .
ITS
TPC
PHOS
Physics II
Flow
Me & ALICE
UiO
Charged Particles are measured by the tracking detectors
(ITS/TPC/TRD) Photons/Hadrons are measured by
calorimeters (PHOS/EMCAL). Together with special purpose
detectors (HMPID/TOF/ACORDE/TRD) particle
identification is achieved for a large range.
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ALICE Tracking
The tracks of an heavy Ion Collisions:
ALICE
H. Qvigstad
Physics I
Why Collide?
QGP
Flow
Photons
Other Signals
ALICE
ITS
TPC
PHOS
Physics II
Flow
Me & ALICE
UiO
. The measurement and reconstruction of tracks is one of the
main challenges in HIC.
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ALICE Tracking
ITS
The Inner Tracking System (ITS) of ALICE consists of 6
Layers:
ALICE
H. Qvigstad
• 2 Layers of Silicon Pixel Detectors (SPD),
• 2 Layers of Silicon Drift Detectors (SDD), and
Physics I
Why Collide?
QGP
Flow
Photons
Other Signals
• 2 Layers of Silicon Strip Detectors (SSD).
ALICE
ITS
TPC
PHOS
Physics II
Flow
Me & ALICE
UiO
H. Qvigstad (UiO)
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ALICE Tracking
ITS
The Inner Tracking System (ITS):
ALICE
H. Qvigstad
Physics I
Why Collide?
QGP
Flow
Photons
Other Signals
ALICE
ITS
TPC
PHOS
Physics II
Flow
Me & ALICE
UiO
• is used for vertex determination, and in conjunction with
the TPC for track parameterisation.
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ALICE Tracking
TPC
The Time Projection Chamber (TPC)
ALICE
H. Qvigstad
Physics I
Why Collide?
QGP
Flow
Photons
Other Signals
ALICE
ITS
TPC
PHOS
• . Charged particles Ionize the contained Ne-CO 2 gas. The
Physics II
Flow
Me & ALICE
UiO
ions travel toward the central electrode, and the electrons
travel towards the end planes, where they are measured.
• Position on the plane combined with the drift time, gives
position in 3D-space.
• dE /dx is measured through ionization charge.
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PID and tracking
ALICE
H. Qvigstad
Physics I
Why Collide?
QGP
Flow
Photons
Other Signals
The momentum of an particle traversing the TPC can be
measured by finding the radios of its track:
pT
R=
qB
Identification can be achieved when this momentum is
combined with energy loss:
(3)
ALICE
ITS
TPC
PHOS
Physics II
Flow
Me & ALICE
UiO
Figure: Stopping power for positive muons in copper ( dE
dx )
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ALICE Tracking
PID
ALICE
H. Qvigstad
Physics I
Why Collide?
QGP
Flow
Photons
Other Signals
ALICE
ITS
TPC
PHOS
Physics II
Flow
Me & ALICE
UiO
Figure: TPC
H. Qvigstad (UiO)
dE
dx
momentum performance.
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ALICE Calorimeters
The Photon Spectrometer (PHOS), is
• high energy resolution,
ALICE
H. Qvigstad
• high granularity (position),
Physics I
• small acceptance,
Why Collide?
QGP
Flow
Photons
Other Signals
electromagnetic calorimeter.
ALICE
ITS
TPC
PHOS
The ALICE ElectroMagnetic
Calorimeter (EMCAL)
Physics II
Flow
Me & ALICE
UiO
• is of lower resolution,
• but has higher acceptance.
H. Qvigstad (UiO)
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PHOS
The ALICE PHOton Spectrometer
ALICE
H. Qvigstad
Physics I
CARD A
Why Collide?
QGP
Flow
Photons
Other Signals
CASE
BODY
CARD B
Figure: A PHOS Module
ALICE
ITS
TPC
PHOS
• At design, PHOS consists of 5
modules, each containing 64 × 56
cells positioned in a array.
Physics II
Flow
Me & ALICE
UiO
• Each cell consists of a PbWO2
scintillation crystal and a
Avalanche Photo–Diode (APD).
Figure: A diagram and
image of the assembly of a
single PHOS cell.
H. Qvigstad (UiO)
• The crystals are 18 cm long, or
ALICE
20 radiation lengths 2012-03-30
(X ).
30 / 42
PHOS
The ALICE PHOton Spectrometer
ALICE
H. Qvigstad
Physics I
Why Collide?
QGP
Flow
Photons
Other Signals
ALICE
Figure: Illustration of an Electron Magnetic
Shower. X0 is an ”Radiation Length”.
ITS
TPC
PHOS
Physics II
• A high energy photon (or electron)
Flow
Me & ALICE
UiO
Figure: Close–up of
the front of a crystal
array.
entering PHOS deposits its energy in
the form of a electromagnetic shower.
• The cell APDs measure this energy in
the form of scintillation light.
H. Qvigstad (UiO)
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PHOS
Electronics
ALICE
Array of crystals
+ APD
+ preamp +
trigger logic
+
readout
H. Qvigstad
Physics I
Why Collide?
QGP
Flow
Photons
Other Signals
DAQ
energy
TOF
L0/L1 trigger
ALICE
• tasks
ITS
TPC
PHOS
• shower finder
• energy sum
Physics II
Flow
• implementation
Me & ALICE
UiO
L0/L1 trigger
• FPGA
11
• VHDL firmware
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PHOS
3
Physics I
Why Collide?
QGP
Flow
Photons
Other Signals
×10
-
� 0 → γγγγ → e+e e+e
pt > 0.4 GeV/c
14
-
ALICE Performance
pp @ 7TeV
Data: 9.572e+07 MinBias events
12
10
8
6
4
2
ALICE
0
ITS
TPC
PHOS
Physics II
Flow
Me & ALICE
UiO
0.1
0.2
0.3
0.4
0.5
0.6
0.7
arXiv: 1103.2217
H. Qvigstad
Counts/ 2.0e+00 MeV/c 2
ALICE
IP
π0
+
π
γ
γ
0.8
0.9
1
Mγ γ (GeV/c2 )
Figure: Invariant mass distribution of all photon pairs with
pT > 0.4 GeV/c
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Physics Part II: The Results
Elliptic Flow
ALICE
H. Qvigstad
Physics I
Why Collide?
QGP
Flow
Photons
Other Signals
ALICE
ITS
TPC
PHOS
Physics II
Flow
Me & ALICE
UiO
Remember, flow that happens in-plane*, Elliptic Flow, has a
positive v2 ,
dN
= 2v2 cos 2φ.
dφ
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Elliptic Flow
0.08
0.06
ALICE
0.04
H. Qvigstad
0.02
v2
Physics I
PRL 105,
Why Collide?
QGP
Flow
Photons
Other Signals
ALICE
ITS
TPC
PHOS
ALICE
STAR
0
PHOBOS
PHENIX
-0.02
NA49
CERES
-0.04
E877
EOS
-0.06
E895
FOPI
-0.08
Physics II
1
Flow
10
102
3
10
104
sNN (GeV)
Me & ALICE
UiO
Figure: Integrated elliptic flow at 2.76 TeV in Pb-Pb 20%-30%
centrality class compared with results from lower energies taken at
similar centralities.
H. Qvigstad (UiO)
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v2
Elliptic Flow
0.3
v2{SP, |∆η|>0.4, AA-pp}
ALICE
5-10%
ALICE Preliminary
Pb-Pb at sNN =2.76 TeV
H. Qvigstad
0.2
10-20%
20-30%
30-40%
Physics I
Why Collide?
QGP
Flow
Photons
Other Signals
40-50%
0.1
ALICE
ITS
TPC
PHOS
0
Physics II
0
Flow
2
4
6
8
10
12
14
16
18
20
p (GeV/c)
Me & ALICE
UiO
T
Figure: Integrated elliptic flow at 2.76 TeV in Pb-Pb
H. Qvigstad (UiO)
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Elliptic Flow
ALICE
H. Qvigstad
Physics I
Why Collide?
QGP
Flow
Photons
Other Signals
ALICE
ITS
TPC
PHOS
Physics II
Flow
Me & ALICE
UiO
Figure: Preliminary elliptic flow of Identified particles in ALICE. Take
note of mass splitting.
H. Qvigstad (UiO)
ALICE
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Flow, Higher harmonics
ALICE
H. Qvigstad
Higher harmonics of flow has gotten allot of attention as of
late:
Physics I
Why Collide?
QGP
Flow
Photons
Other Signals
ALICE
ITS
TPC
PHOS
Physics II
Flow
Me & ALICE
UiO
H. Qvigstad (UiO)
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Flow
v2 {2, | | > 1}
v3 {2, | | > 1}
v4 {2, | | > 1}
v3 {4}
v3/ RP
100 v 23/ 2
Why Collide?
QGP
Flow
Photons
Other Signals
vn
H. Qvigstad
Physics I
PRL 107, 032301 (2011)
ALICE
0.05
ALICE
ITS
TPC
PHOS
arXiv: 1105.3865
0.1
Physics II
Flow
0
Me & ALICE
UiO
10
20
30
40
50
centrality percentile
60
70
80
Figure: measurement of higher harmonics of flow at ALICE. The Low
contribution of higher order flow components indicates high viscosity.
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RAA
ALICE
H. Qvigstad
Physics I
Why Collide?
QGP
Flow
Photons
Other Signals
ALICE
ITS
TPC
PHOS
Physics II
Flow
Me & ALICE
UiO
Figure: pion RAA in central (0-20) and peripheral (60-80)
H. Qvigstad (UiO)
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My Work
• I started studying for a bachelor at UiB Fall 2004
• continued with a master in Nuclear Physics with the
ALICE
Bergen Nuclear/ALICE group Fall 2007, where I
H. Qvigstad
• did testing of electronics for PHOS, and
• wrote a thesis based on a study of the π 0 based calibration
Physics I
Why Collide?
QGP
Flow
Photons
Other Signals
algorithm of PHOS.
• I started as an PhD Student at UiO Spring 2010, where I
am involved
• with the analysis of data from the Trigger System of
ALICE
ITS
TPC
PHOS
PHOS,
• contribute to the maintenance/development of PHOS and
Physics II
its control system,
Flow
Me & ALICE
UiO
• am studying the possibility of an production cross section
measurement of the η 0 meson,
• and am currently functioning as the Run Coordination
Representative for PHOS, which entails 100% presence at
CERN for the period.
H. Qvigstad (UiO)
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Fin
ALICE
H. Qvigstad
Contacts for the ALICE group in Oslo:
Physics I
Why Collide?
QGP
Flow
Photons
Other Signals
ALICE
ITS
TPC
PHOS
• Trine S. Tveter (group leader): trine@lynx.uio.no
• Matthias Richter (postdoc): matthias.richter@fys.uio.no
• Henrik Qvigstad (Phd): henrik.qvigstad@fys.uio.no
ALICE Norway is also present in Bergen (UiB, HiB).
Also, take note of the opportunity to come to CERN as an
summer students.
Physics II
Flow
Me & ALICE
UiO
H. Qvigstad (UiO)
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