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1
ALICE: Today and Tomorrow
4th-9th October 2010
David EvansThe University of Birmingham
With thanks to Paolo Giubellino, John Harris, & Rene Bellwied
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Physics Motivations
Study of QCDIn particular QCD phase transition from
hadronic matter to Quark-Gluon PlasmaDetector designed to cope with extreme
environment of Pb-Pb collisionsExcellent 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)
LHCRHICSPSCentral 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
React
ion
plan
e
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).
Ed 3Nd 3p
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d 2NpTdpTdy
1 2vn cos n r n1
Angle of reaction planeFourier coefficient
V1 = directed flow. V2 = elliptic flow.
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Is the QGP an ideal fluid ?
LHC
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 (pT ) d 2N AA /dpTdTAAd
2 NN /dpTd
Scale factor p+p referenceno. binary collisions
TAA
Nbinary
inelasticpp
Nuclear modification factor
Divide PT Spectra of AA by pp (with scaling factor)
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Use RAA to determine the medium density
The medium is dense (30-50 x normal matter), but RAA provides limited sensitivity.
Eskola, Honkanen, Salgado, Wiedemann (2004)Eskola, Honkanen, Salgado, Wiedemann (2004)
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 2000X 2000
Pion Production
Jets up to 200 GeVFactor > 1000 in high PT
All observables in a single, high precision detector – ALICEMany on event-by-event basis
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ALICE programme
• First 6 years+ of ion running: full exploitation of present ALICE detector (not necessarily 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 5 years
Either lower energies or additional AA and pA combinations or increased statistics for PbPb.
In the past, HI Physics has been generous with surprises, so a detailed plan will have 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 metresWeight: 10,000 tons
Collaboration:> 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 2011Unless 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.
20
DCAL: Di-Jet Calorimeter A 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 + 150m 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.