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ALICE: Today and Tomorrow

4th-9th October 2010

David Evans

The University of Birmingham

With thanks to Paolo Giubellino, John Harris, & Rene Bellwied

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Physics Motivations

Study of QCD

In particular QCD phase transition from

hadronic matter to Quark-Gluon Plasma

Detector designed to cope with extreme

environment of Pb-Pb collisions

Excellent tracking, particle ID etc

Play-off: limited interaction rate

pp for baseline – also ALICE is an excellent

detector for studying global event properties

of pp collisions, cross-sections etc.

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Detector Overview

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Optimised for PbPb collisions:

•High granularity (dN/dy~8000)

•Minimised material

UK-built Central Trigger Processor (CTP)

Delivers L0, L1 and L2 triggers

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Why Heavy Ions @ LHC

?

4-101.5-4.0<1QGP (fm/c)

2x1047x103103Vf(fm3)

15-403.52.5(GeV/fm3)

3-8 x103650500dNch/dy

550020017s1/2(GeV)

Central collisions

hotter - bigger -longer lived

ALICE is the only experiment able to study almost all

observables (many on an event-by-event basis).

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Questions to be

Answered• Determine initial conditions – sets the stage for particle

production/dynamics

• Expect larger timescales, energy densities (T), etc w.r.t RHIC– Does the system still equilibrate quickly?

• Thermal model still applies? – Tfreeze-out ~ TC (lattice QCD)?

– Does it Flow?• Elliptic Flow change? →v2 still saturated? More or less v2? pT

dependence?

– Is QGP still strongly (or weakly) coupled?• Liquid? More like a gas? → No longer “nearly-perfect” fluid flow?

viscosity? → Impact on energy loss!!

• Understand parton energy loss

• Colour screening of medium?– Deconfinement? (compare LQCD), initial T, other effects →J/ψ &

states

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Elliptic FlowEccentricity:

x

y

X

Z

Y

It’s been predicted (Phys Lett B474 (2000) 27.) in the low

density limit, elliptic flow (v2) and the density of scattering

centres.

Ie. v2/ (1/S) dNch/d where S is the area of overlap.

v2/ should saturate at large particle densities (hydro-limit).

Ed3N

d3p

1

2

d2N

pTdp

Tdy

1 2 vncos n

rn 1

Angle of reaction planeFourier coefficient

V1 = directed flow. V2 = elliptic flow.

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Is the QGP an ideal

fluid ?L

H

C

Hydro limitRHIC data runs out

at predicted hydro

limit. Will data

trend continue or

does it flatten?

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Suppression of high pT

hadronsCentral collisions

Peripheral collisions

RAA( p

T)

d2N

AA/ dp

Td

TAAd2 NN

/ dpTd

Scale factor p+p referenceno. binary collisions

TAA

Nbinary inelastic

pp

Nuclear modification factor

Divide PT Spectra of AA

by pp (with scaling

factor)

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Use RAA to determine

the medium density

Need fully reconstructed, higher energy jets to

determine medium density and process of energy loss.

Hence need to go to higher energy collisions.

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New Measurements

from the LHC

• Large production cross-sections for large

mass particles, high pT and jets – hard probes.

• Some measured for first time - , Z0, jets

X 2000

Pion Production

Jets up to 200 GeV

Factor > 1000 in high PT

All observables in a single,

high precision detector –

ALICE

Many on event-by-event basis

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ALICE programme

• First 6 years+ of ion running: full exploitation of present ALICE detector (notnecessarily in this order)

– First pp run (now)

– 1 yr (106s) Pb-Pb at low Luminosity (initially ~1/20th design, i.e. L~5x1025 cm-2s-1)

– PbPb: 2010 pilot run, 2011 run at half energy, >2013 run at full energy

– 2-3 yrs Pb-Pb at nominal L~1027, target integrated L~1nb-1

– 1 yr p-A (initial state interaction effects)

– 1 yr low mass A-A (system size dependence)

– Continuous running with p-p (comparison data and some genuine pp physics:charm, baryon, high multiplicity, etc.)

• Following 5 years: programme and priorities will be set based on results from first 5years

Either lower energies or additional AA and pA combinations or increasedstatistics for PbPb.

In the past, HI Physics has been generous with surprises, so a detailed plan willhave to wait at least for the analysis of the first PbPb data.

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sNN ~ 2 c pproton (Z1 Z2 / A1 A2 )½

yNN = ½ log (Z1 A2 / A1 Z2 )

LHC’s two-in-one design requires fixed rigidity of beams:

pPb / ZPb = pproton

Ref: J.M. Jowett, Workshop on pA Collisions at LHC (2005)

Kinematics at LHC

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Detector Configuration 2010

ITS, TPC, TOF, HMPID, MUON, V0, T0, FMD, PMD, ZDC (100%)

TRD (7/18)

EMCAL (4/10)

PHOS (3/5)

HLT (60%)

full hadron and muon capabilities

partial electron and photon

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Size: 16 x 26 metres

Weight: 10,000 tonsCollaboration:

> 1000 members

> 100 institutes

> 30 countries

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Detector Performance

TPC only

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pp Physics Analysis • First proton-proton collisions at the LHC as observed with the ALICE detector:

measurement of the charged particle pseudorapidity density at sqrt(s) = 900 GeV

K Aamodt et al: EPJ C 65 (2010) 11, arXiv:0911.5430

• Charged-particle multiplicity measurement in proton-proton collisions at sqrt(s) = 0.9

and 2.36 TeV with ALICE at LHC

K Aamodt et al: EPJ C 68 (2010) 89, arXiv:1004.3034

• Charged-particle multiplicity measurement in proton-proton collisions at sqrt(s) = 7 TeV

with ALICE at LHC

K Aamodt et al: EPJC: Vol. 68 (2010) 345, arXiv:1004.3514,

• Midrapidity antiproton-to-proton ratio in pp collisions at sqrt(s) = 0.9 and 7 TeV

measured by the ALICE experiment

K Aamodt et al: PRL 105 (2010) 072002, arXiv:1006.5432

• Two-pion Bose-Einstein correlations in pp collisions at sqrt(s) = 900 GeV

K Aamodt et al: PRD: Vol. 82 (2010) 052001 , arXiv:1007.0516

• Transverse momentum spectra of charged particles in proton-proton collisions at sqrt(s) = 900 GeV

with ALICE at the LHC

K Aamodt et al: PL B: Vol. 693 (2010) 53 ,arXiv:1007.0719

– 2 papers in draft

• Identified charged hadron spectra and yields in pp at 0.9 TeV

• Strange particle production in pp at 0.9 TeV

– Other analyses well underway

• High multiplicity pp events, azimuthal correlations, event structure, 0 spectra, charm production,...

First LHC physics paper

First LHC high-energy

physics paper

See Jean-Pierre’s talk on Tuesday

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Pb schedule for 2010

• Expect 1/20 of nominal luminosity ∫Ldt = 5·1025 cm-2 s-1

• ~1st November 2010 – Ion setup and commissioning

• 9th November – Ion physics run begins

• 6th December – End of Ion running

• Expect to collect between 106 and 107 events depending on LHC performance (probably closer to 106 ).

• Should have ~ 107 events by end of 2011

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Expected first Heavy-ion

physics with ALICE

Pb-Pb (November 2010 – 4 weeks):

1/20 of nominal luminosity ∫Ldt = 5·1025 cm-2 s-1 x

106s

Alignment calibration available from pp

Global event properties (105 events):

Multiplicity, rapidity density

Elliptic flow

Source characteristic (106 events):

Particle spectra, resonances

Differential flow

interferometry

High pt and heavy flavours (107 events):

Jet quenching

Quarkonia production

Few days

Minimum

expected in

2010

By end of

2011

Unless we

get lucky

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Detector upgrades

• Ongoing

– Transition Radiation Detector (TRD) completion

– Electro-Magnetic Calorimeter (EMCal) completion

– Di-Jet Calorimeter (DCal)

• Future

– Very High Momentum Particle Identifier (VHMPID)

– 2nd Generation Vertex Detectors (Inner Tracker (ITS))

– Forward Calorimeter (FoCal)

– TPC, DAQ, Trigger rate increases and upgrades

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Ongoing ALICE Upgrades

• A programme to upgrade some elements of ALICE is already ongoing– the TRD has been approved much later than the other central

detectors • 7/18 installed

• complete by 2011

– a new EMCAL calorimeter has been added recently• US project, with French and Italian involvement.

• 4 out of 10 SM installed in 2009

• complete by 2011

– New Dijet electromagnetic calorimeter (Dcal) for di-jets & π0-

jets proposed/approved/funded by US-Japan-France-Italy-

China

• Complete by 2012 shutdown & installation period.

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DCAL: Di-Jet CalorimeterA 60% expansion of EMCal acceptance arranged to permit

back-to-back hadron-jet and jet-jet correlations

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Upgrades Beyond 2011

• PID for pT~ 5 –20 GeV/c (based on

results from RHIC)

– for PID particle & resonance

spectra/correlations, flow, recombination,…..

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VHMPID

Would be located on both sides of PHOS, below

space frame (10% of TPC acceptance)

– RICH-like detector in focusing geometry with

segmented spherical mirrors, gas radiator

(C4F10) and CsI-based photodetector (with

MWPC or Thick-GEM)

– Same HMPID FEE, based on Gassiplex chip

– Dedicated trigger logic based on TRD & new

detector

• Most of the design derived from HMPID know-

how, issues needing R&D:

– CsI-TGEM reliability over large area

– Pad cathode segmentation and structure

– Large area quartz windows segmentation and

fixation

– Spherical mirror structure and segmentation

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Upgrades Beyond 2011

• PID for pT~ 5 –20 GeV/c (based on

results from RHIC)

– for PID particle & resonance

spectra/correlations, flow, recombination,…..

• New detectors for forward physics

(low-x in pA& AA)

– Forward calorimeter for π0

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Forward Physics

Upgrade (FoCal)• Forward Experimental Study

– Strong effects expected at large η• gluon shadowing gluon saturation, CGC?

• At LHC like at RHIC– Small x region –forward at large η

• Present ALICE accessibility –µ-arm

• Add a Forward Calorimeter– Highly segmented (⊥, ||) EM-Cal

• 3.6 m from vertex 2.3 < η <4.0

– to measure• π0, 1 < pT< 50 GeV/c

• jets, 20 < ET< 100 GeV

• Extending forward coverage to – 4.5 < |η |< 6.5 region and beyond FoCal

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Upgrades Beyond 2011

• PID for pT~ 5 –20 GeV/c (based on results

from RHIC)

– for PID particle & resonance spectra/correlations,

flow, recombination,…..

• New detectors for forward physics (low-x in

pA& AA)

– Forward calorimeter for π0

• 2nd generation vertex detector (smaller beam-

pipe)

– for improved heavy quark physics

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ITS Upgrade– x2 impact parameter resolution (for pT< 1 GeV/c)

• Increases charm sensitivity x100

• Access to charmed baryons– Charm B/M big issue for reco!

• Allows study of exclusive B decays

• Allows total B x-section to pT~ 0

• Improves flavour tagging

– Techniques?• Thinnest / smallest beam pipe

– Reduce R = 2.9 cm to ~1.3 cm

– Reduce thickness from present 800 µm to 400 µm

• New pixel technology– thinner (≤ 200 µm + 150 µm)

– higher granularity (≤ 150 µm x 425 µm)

TPC

SSD

SDD

SPD

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ITS Upgrade Time-scale

R&D phase: 2010-2013/14

• Explore two Pixel technologies:

- Hybrid pixel detectors: “state of the art”- low cost bump-bonding- new sensor type (3D, edgeless planar)- further thinning (SPD: 200 m sensor + 150 m FEE)

- Monolithic pixel detectors: Mimosa and LePix

- larger detector areas at considerably lower cost

• Layout Studies and Technical Design report

Production and pre-commissioning: 2014-2016

Installation and commissioning: 2016 – ready for 2017 run

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Finally … A Possible LHC Mid-

term Heavy-Ion Programme

2010 (official) – sNN = 2.76 TeV Pb + Pb for physics (4 weeks)

2011 (anticipated) – sNN = 2.76 TeV Pb + Pb for physics (4 weeks)

2012 (official) – Shutdown for maintenance, installation & repairs

2013 – sNN = 5.5 TeV Pb + Pb for physics

2014 – sNN = 5.5 TeV Pb + Pb for physics

2015 – sNN = 5.5 TeV p + Pb & Pb + p, (lighter A + A, p + p) for physics

2016 – 12 month shutdown – IR detector upgrade, vertex detector

upgrades

2017 – sNN = 5.5 TeV lighter A + A, p + p for physics

2018 – sNN = 5.5 TeV high L Pb + Pb for hard probe physics

2019 – sNN = 5.5 TeV high L Pb + Pb for hard probe physics

2020 – 12 month shutdown

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Summary• 2010 running very successful

– All detector, online and offline systems working well

– Alignment and calibration under control

– About 600 million 7 TeV events collected

• Physics analysis well underway– 6 papers published

– others on the way

• Preparations for Pb collisions this November well underway– Can do a lot of exciting physics even with relativity low

stats.

– Higher stats expected in 2011 – jets, heavy flavour, etc.

• Exciting 10-year+ programme ahead with a number of upgrades already planned.

• ALICE has got off to a great start and we look forward to some new and interesting physics from the Pb data.