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1
Experimental High Energy Nuclear
Physics in Norway Kalliopi Kanaki
University of Bergen
2
Norwegian activities in…
• ALICE@CERN• hardware/software contribution• physics analysis
• ALICE upgrades• Side activities
• CBM@FAIR• 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 Jet
Prompt
0
• 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
dy/dpNd
dy/dpNd
N
1)(pR
Tpp2
TAA2
CcollCTAA
8
Collective flow
baryonsbaryons
mesonsmesons
• 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
9
ALICE setup
HMPID
Muon Arm
TRD
PHOS
PMDITS
TOF
TPC
Size: 16 x 26 meters
Weight: 10,000 tons
Added since 1997:-V0/T0/ACORDE- TRD(’99)- EMCAL (’06)
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)• calibration and online processing
• 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%• 557 568 readout channels• rate capabilities > 1 kHz for pp
12
13
Readout Control Unit (RCU)
14
TPC calibration
gain
reco
nst
ruct
ion
alignment
t0, drift velocity
electrostatic distortions
E x B effects
electron attachment
raw
data
calib
rate
d
data
reco
nst
ruct
ed t
rack
sm
om
entu
m a
nd d
E/d
x
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
• PbO4W crystal calorimeter for photons, neutral mesons (1 - 100GeV/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
The ALICE PHOS spectrometer
18
Trigger hierarchy
0 1.2 6.5 88 t [μsec]
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
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 decisionfor every event
22
HLT cluster status2010 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
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)
cm 2cm 20m) 50(L
00038.00038.0
74274(GeV/c)
101(GeV/c)
min2
tot
T
p
p
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, biophysics@GSI 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 10-15 years• Ambitious ALICE upgrade program