1. Experimental High Energy Nuclear Physics in Norway
Kalliopi Kanaki
University of Bergen

2. Norwegian activities in…
hardware/software contribution
physics analysis
ALICE upgrades
Side activities
Medical physics

3. Physics goals of ALICE
LHC accesses the QCD phase diagram at low μB, high T
What can we learn about the system produced in the collisions?
Does it have the same properties as the state produced at RHIC?
Is the QGP weakly or strongly (fluid) coupled?
Is there a sharp phase transition?
How do partons interact with the medium?

4. Di-hadron correlations & jet quenching
Hard parton scattering observed via leading (high momentum) particles
Strong azimuthal correlations at  =  expected
Result: complete absence of away-side jet
away-side partons are absorbed in the medium
strong energy loss
medium is opaque to fast partons

5. γ-hadron correlations
Fragmentation g
Jet
Prompt g p0
The point-like photon remains unmodified by the medium and provides the reference for the hard process
The prompt photon provides a measurement of the medium modification on the jet because they are balanced

6. Direct photons Sources of direct γ pQCD (“prompt”) photons Compton
Annihilation
Bremsstrahlung
Thermal photons  sensitive to initial temperature
Challenging to obtain, necessary for γ-jet studies
measure inclusive spectrum
subtract background from hadronic decays

7. Nuclear modification factor RAA
At RHIC the matter produced is opaque
High pT particles are suppressed
The medium is transparent to photons

8. Collective flow baryons mesons
Initial state spatial anisotropy of reaction zone causes
final state momentum anisotropy
asymmetric particle emission
Higher initial density results in larger pressure gradient
The system has very low viscosity/ideal hydrodynamical fluid
Flow is formed at the partonic level
baryons
mesons

9. ALICE setup TOF TRD HMPID ITS PMD Muon Arm PHOS TPC
Size: 16 x 26 meters
Weight: 10,000 tons
TOF
TRD
HMPID
ITS
PMD
Muon Arm
PHOS
Added since 1997:
V0/T0/ACORDE
TRD(’99)
EMCAL (’06)
ALICE setup
TPC

10. Technical contribution to ALICE
Time Projection Chamber (TPC)
radiation tolerant readout electronics
calibration and online processing
PHOton Spectrometer (PHOS)
readout electronics and trigger (L0 and L1)
High Level Trigger (HLT)
calibration framework – interfaces to other systems (ECS, DCS, DAQ, CTP)
online event reconstruction/display and analysis software
Commissioning of all the above
GRID computing – part of Nordic distributed Tier1 center

11. The ALICE TPC
main tracking device for momentum reconstruction |η|<0.9
drift length 2 x 2.5 m
PID for pt up to 100 GeV/c in combination with other detectors (e.g. TOF, HMPID)
momentum resolution ~1%
for pt < 2 GeV/c
tracking efficiency 90%
dE/dx resolution < 10%
readout channels
rate capabilities > 1 kHz for pp

13. Readout Control Unit (RCU)

14. calibrated data raw data TPC calibration momentum and dE/dx
gain
electron attachment
reconstruction
calibrated data
momentum and dE/dx
reconstructed tracks
alignment
raw data
electrostatic
distortions
RCU figure
E x B effects
t0, drift velocity

15. Drift velocity calibration (I)
Drift velocity = f(E-field, gas density (T, p), ...)
Monitoring tools:
Laser tracks
Electrons from the central electrode
Tracks from collisions
Traversing central electrode
Matching with ITS
Cosmics
External drift velocity monitor

16. Drift velocity calibration (II)

17. The ALICE PHOS spectrometer
PbO4W crystal calorimeter for photons, neutral mesons ( GeV/c)
Crystal size 2.2 × 2.2 cm2, 20 X0, APD readout, operated at –25° C
σ(E)/E ≈ 3%, σ(x,y) ≈ 4 mm, σ(t) ≈ 1 ns at 1 GeV
|η| < 0.12, Δφ = 100° at R = 460 cm
L0 trigger available at < 900 ns

18. Trigger hierarchy L1: select events according to centrality (ZDC, ...)
Collision
L0: Trigger detectors detect collision
(V0/T0, PHOS, SPD, TOF, dimuon trigger chambers)
L1: select events according to
centrality (ZDC, ...)
high-pt di-muons
high-pt di-electrons (TRD)
high-pt photons/π0 (PHOS)
jets (EMCAL, TRD)
L2: reject events due to
past/future protection
HLT rejects events containing
no J/psi, Y
no D0
no high-pt photon
no high-pt pi0
no jet, di-jet, γ-jet
1.2
6.5 88
t [μsec]

19. The PHOS L0 and L1 triggers
Array of crystals APD preamp trigger logic readout
DAQ
L0 trigger
tasks
shower finder
energy sum
implementation
FPGA
VHDL firmware
L0/L1 trigger

20. The ALICE High Level Trigger
dNch/dη = 2000 – 4000 for Pb+Pb
After L0, L1 and L2 rates can still be up to 25 GB/s
DAQ archiving rate: 1.25 GB/s → imperative need for HLT
Goals:
Data compression
Online reconstruction of all events
Handle rates of > 1 kHz for p+p and 200 Hz for central Pb+Pb
Physics triggers application for event characterization

21. HLT Processing Data Flow
DAQ
HLT
mass storage
raw data
copy sent to HLT
trigger decision
for every event

22. HLT cluster status 2010 Run Setup 123 front-end nodes 968 CPU cores
1.935 TB RAM
472 DDL
53 computing nodes
424 CPU cores
1.152 TB RAM
Pb+Pb upgrade
100 computing nodes
2.4 TB RAM
Full network infrastructure
Full service infrastructure
HLT decision sent to DAQ for every event

23. HLT activities in Norway
Analysis framework
Both online and offline (emulation) version
Analysis software
TPC cluster finder and calibration
ITS reconstruction
PHOS reconstruction and calibration
EMCAL and PHOS analysis integration
ESD production online
Trigger implementation and trigger menu for DAQ
Infrastructure maintainance and improvement
Reconstruction and trigger evaluation
Interfaces to other online systems

24. HLT online display

25. Physics contribution to ALICE
High pT π0 (calorimeters)
High pT π0 from conversions (TPC)
High pT charged particles and jet reconstruction
Total ET (calorimeters+TPC)
High pT direct γ (calorimeters)
γ-hadron and π0-hadron correlations (calorimeters+TPC)
Collective flow
Ultra-peripheral collisions
Online D0 reconstruction (ITS+TPC)
Online π0 reconstruction (TPC)

26. Invariant mass in PHOS in pp@7 TeV

27. π0 reconstruction from conversion γ
γ-ray picture of ALICE

28. Di-hadron correlations
December status for 900 GeV data

29. D0 in ALICE
Implementation of online D0 trigger in the HLT framework

30. Ultra-peripheral collisions
Photon induced interactions with photons produced
by the EM field of the protons/nuclei
Possible in pp and in Pb+Pb interactions
Ongoing work: simulation studies+trigger
conditions (software & hardware)
p+p → p+p+μ++μ-
purely QED part γ+γ → μ++μ-
photonuclear part γ+p → J/ψ+p → μ+μ-+p
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31. ALICE upgrade plans Timeslots for potential upgrades
2012: 1 year shutdown (minor upgrades)
2018 (?): 1 year shutdown (major upgrades,
e.g. beam line modifications)
Ongoing projects
completion of PHOS trigger
upgrade of TPC and PHOS readout
HLT “dynamic” upgrade
Potential new project: Forward calorimeters

32. Forward physics at LHC Measurements at small angle/large η
low-x parton distributions
Main physics topics
p(d)+A
gluon saturation
study of ”cold” nuclear matter
probing the initial condition
A+A
elliptic flow
jet quenching
long-range rapidity correlations
baryon transfer

33. RHIC vs. LHC

34. Proposal for a forward spectrometer
EM calorimeter for γ, π0, η, J/ψ at y=5
O(10) meters away from IP
large dynamic range
high occupancy to cope with A+A
two γ separation (π0 → 2γ kinematics)
highly segmented (also longitudinally) tracking calorimeter

35. Other activities (I) CBM@FAIR Fixed target experiment, Ebeam = 30 AGeV
Production of super-dense baryonic matter
Chiral symmetry restoration/in-medium properties of hadrons
Potential Norwegian contribution:
Monolithic Active Pixel Sensor readout (3D stacking)
Projectile Spectator Detector (forward calorimeter)
High Level Trigger
So far no Norwegian funding for FAIR

36. Other activities (II)
Generic R&D projects with potential medical physics applications
Highly segmented calorimeters
Characterization of pixel arrays of G-APD (Avalanche Photodiodes operated in Geiger mode)
Collaboration with the microelectronics
group at UiB and the PET-center of
Bergen University Hospital (HUS)
→ high resolution TOF PET-scanner
Radiation effects in microelectronics
SEU in SRAMs: neutron dosimetry
Collaboration with HUS,
and CERN (EN/STI)
→ hadron therapy purposes

37. Other activities (III)
Next generation pixel detectors
Sensor: Monolithic Active Pixel Sensor
3D integration
high spatial resolution, lower capacitance (and hence, lower noise), and enough logic per pixel cell to implement fast, intelligent readout
by thinning the wafers lower material budget is obtained
collaboration with the microelectronics group at UiB

38. Summary Norway has a strong presence in:
Hardware design/prototyping/construction
Software
Commissioning of hardware & software
Run coordination for detectors & the whole of ALICE
Time to harvest the fruit of physics for the next years
Ambitious ALICE upgrade program