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Experimental High Energy Nuclear

Physics in Norway Kalliopi Kanaki

University of Bergen

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Norwegian activities in…

• ALICE@CERN• hardware/software contribution• physics analysis

• ALICE upgrades• Side activities

• CBM@FAIR• Medical physics

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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?

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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

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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

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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

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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

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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

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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)

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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

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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

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Readout Control Unit (RCU)

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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

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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

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Drift velocity calibration (II)

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• 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

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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

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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

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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

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HLT Processing Data Flow

DAQ HLT

mass storage

raw data copy sent to HLT

trigger decisionfor every event

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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

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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

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HLT online display

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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)

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Invariant mass in PHOS in pp@7 TeV

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π0 reconstruction from conversion γ

γ-ray picture of ALICE

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Di-hadron correlations

December status for 900 GeV data

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D0 in ALICE

Implementation of online D0 trigger in the HLT framework

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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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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

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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

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RHIC vs. LHC

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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

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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

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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

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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

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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