Physics Reach

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Physics Reach

• Christoph Blume
• University of Frankfurt/Main
• for the ALICE Collaboration

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Physics ReachOutline

• ALICE physics
• Strongly interacting matter
• Observables
• pp physics
• The ALICE experiment
• Running conditions for PbPb and pp running
• Acceptance
• Tracking performance
• Particle identification

• Low pt physics examples
• Heavy quarks
• Open charm
• Open beauty
• Quarkonia family
• Parton energy loss
• High pt particle spectra
• Jets via correlations

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ALICE Physics Phases of Strongly Interacting
Matter

• Exploring the phase diagram of strongly
  interacting matter
• LHC provides access to the high T, vanishing mB
  QGP phase

Lattice QCD, mB 0
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ALICE PhysicsProperties of QGP Phase _at_ LHC

• Initial conditions
• Hard processes
• Probe of early state of reaction
• Pertubative QCD
• Significant part of cross section

• High density parton distributions
• Bulk of partons at x ? 10-3
• Saturated gluon densities
• Classical QCD Qs ? A1/3/ xd
• Evolution of system will be dominated by partons
• Longer lifetime of QGP phase
• Collective effects will be strongly influenced by
  parton dynamics ? partonic flow

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ALICE PhysicsObservables
Jets
Open charm, beauty
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ALICE PhysicsObservables

• Soft Regime pt 02 GeV/c
  non-perturbative
• Particle yields ? chem. freeze-out
• HBT interferometry ? thermal freeze-out
• Flow ? expansion

• Semi-hard Regime pt 25/10 GeV/c
  
• Thermal photons ? temp. evolution
• Open charm, J/Y ? plasma screening
• pt-Spectra ? mini-jets

• Hard Regime pt gt 10 GeV/c
  perturbative
• Hard photons
• Open beauty, U
• Jets ? initial collisions

• ALICE will cover the transition from the soft
  (hadronic) to the hard (partonic) regime
• Correlations between soft and hard probes only
  possible within ALICE

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ALICE Physicspp Physics

• Benchmark for PbPb
• Multiplicities (strangeness)
• J/Y and U
• Parton energy loss (jets)
• Thermal photons
• High energy densities _at_ LHC
• e ? 1.2 GeV/fm3
• Comparable to NN _at_ SPS/RHIC
• Bulk of cross section at low pt
• Investigation in a new energy regime
• pA program
• Nuclear structure functions
• Benchmark for PbPb

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The ALICE Experiment
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The ALICE ExperimentRunning conditions for PbPb

• Large charged multiplicity
• Estimates quite uncertain
• Design for dNch/dymax 8000
• Luminosity Lmax 1?1027 cm-2s-1
• Event rate
• 8000 minimum bias coll./ s
• 109 events/year
• 1 collected
• Trigger for low cross section observables
• MUON, PIXEL, PHOS, TRD
• High-Level Trigger (HLT)

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The ALICE ExperimentEvent Display PbPb
HMPID
TOF
TRD
TPC
60? lt J lt 62?!
PHOS
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The ALICE Experimentpp Running Conditions

• Low luminosity Lmax 2-5 ? 1030 cm-2 s-1
• Event pile-up
• TPC drift 88 ms
• On average 25 events (for Lmax 2 ? 1030 cm-2
  s-1)
• Pile-up can be removed with High-Level Trigger
• Reduction in data volume ? factor 5
• Short run periods with ultra-low luminosity ?
  no pile-up Lmax ? 1029 cm-2 s-1

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The ALICE ExperimentAcceptance Central Barrel
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The ALICE ExperimentTracking Performance
TPC primary tracks
? 9

• Reconstruction efficiency
• dNch/dy 8000, B 0.4T
• 98 in TPC
• Acceptance at high pt 90

• Momentum resolution
• dNch/dy 8000, B 0.4T
• Combined tracking ITSTPCTRD
• 9 (pt 100 GeV/c)

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The ALICE ExperimentMain Vertex Determination

• For heavy-ion collisions
• Large track statistics
• Resolution in bending projection 1015 mm (beam
  spot 15 mm)
• Resolution in non-bending projection better
  than 10 mm
• For pp collisions
• Low track statistics
• Effect on charm measurement

pp
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The ALICE ExperimentParticle Identification
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The ALICE ExperimentPID Summary
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Low pt Physics ExamplesEvent-by-Event pp HBT

• Single event
• Raw correlation function
• Uncorrected for Coulomb
• R 8 fm, l 0.5
• Tracking with ITSTPC, B 0.2T

C(Qinv)
Qinv (GeV)
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Low pt Physics ExamplesResonances K

• Decay channel K? Kp-
• Invariant mass distribution for 550 events

Entries
M(Kp-) (GeV/c2)
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Heavy Quarks
Uncertainty of factor ? 4 in predictions for pp
_at_ LHC

• Heavy quarks probe dynamics of whole QGP phase
• Perturbative in intial collisions
• Thermal production in QGP
• Direct measurement of heavy flavour in pp and
  AA mandatory
• Quarkonia (J/Y and U states)
• Binding energy in the order of mean energy in QGP
• Sensitive to screening effects
• Aim correlation of heavy quark and quarkonia
  production as function of pt

• Quarkonia ? mm- MUON
• Quarkonia ? ee- TPCTRD
• D ? Kp, ITSTPCTOF
• Semileptonic decays of D B
  ITSTPCTRD and MUON
• DD (BB) via em coincidences TRDMUON

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Heavy QuarksOpen Charm via Hadronic Decays
cuts depend on D0 pt
D0 ? K-p ct 123.7 ? 0.8 mm BR (3.83 ? 0.09)
Affected by main vertex resolution in pp case
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Heavy QuarksOpen Charm via Hadronic Decays

• Input to simulation
• cc PYTHIA, tuned to NLO calculations, with
  CTEQ4L and nuclear shadowing EKS98
• Background HIJING
• Reconstruction effects included
• PID with TOF

PbPb
sminv 12 MeV (B 0.4T)
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Heavy QuarksOpen Charm via Hadronic Decays
PbPb
pt gt 1 GeV/c
Significance
dN/dpt
pp
pt gt 0 GeV/c !
Significance
Significance
dN/dpt
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Heavy QuarksOpen Beauty via Semileptonic Decays

• B ? e- X
• Electron ID in TPC TRD
• Cuts
• Impact parameter d0
• Electron pt

Entries (a.u.)
d0 (mm)
pt gt 2 GeV/c d0 gt 150 mm 5-10104 e with
S/(SB) 90
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Heavy QuarksJ/Y and U via Dielectrons
J/Y
Mass resolution for U 100 MeV (B 0.4T)
U
Acceptance down to pt 0!
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Heavy QuarksSecondary J/Y from B Meson Decays

• B ?J/Y ? ee- (BR ?1)
• Large contribution to observable J/Y signal
• Possibility to disentangle primary and secondary
  J/Ys

J/Y from B decays
Impactparameter
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Parton Energy Loss
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Parton Energy Loss

• Medium induced gluon radiation
• Depends on traversed distance ? L2
• Stronger in deconfined matter
• Effects
• Reduction of single inclusive high pt particles
• Parton specific (stronger for gluons than quarks)
• Flavour specific (stronger for light quarks)
• Measure identified hadrons (p, K, p, L, etc.)
  partons (charm, beauty) at high pt

• Suppression of mini-jets
• same-side / away-side correlations
• Change of fragmentation function for hard jets
  (pt gtgt 10 GeV/c)
• Transverse and longitudinal fragmentation
  function of jets
• Jet broadening ? reduction of jet energy, dijets,
  g-jet pairs
• pp and pA measurements crucial

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High pt RHIC Results

• RAA clearly different between mesons and baryons
• Importance of PID at high pt
• pp baseline measurement!

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High ptMinimum Bias PbPb and pp
Scaled to 107 PbPb min. bias events

• Estimates for the pt limit in one year ALICE
  running
• 107 PbPb events
• 109 pp events
• pp simulation PYTHIA 6.210 CTEQ5L (default
  tuning)

dN/dpt
2?103 tracks pt gt 50 GeV/c
High pt trigger (TRD, HLT) will extend pt range
to gt 100 GeV/c
pt (GeV/c)
N(? pt)

• 109 pp events
• 103 tracks with
• pt ? 40 GeV/c

104 rec. pp evts.
pt (GeV/c)
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High ptIdentified Particles L

• One year of ALICE running (107 events) ? Ls
  up to pt 12 GeV/c
• Can be improved using PID for L daughters

of rec. Ls vs pt
S/B ? 1 5.5 L/event
pt (GeV/c)
Entries
L Yield
Reconstructed pt spectrum
M(pp) (GeV/c2)
pt (GeV/c)
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High ptIdentified Particles gp0
with high-pt trigger
without high-pt trigger for 107 events
dN/dpt
dN/dpt
Inclusive g Direct p 0
Direct g
pt (GeV/c)
pt (GeV/c)

• Separation of g/p0 and p0 detection up to 100
  GeV/c
• Statistically for low pt (lt 30-40 GeV/c)
• E-by-E at higher pt (gt 30-40 GeV/c)

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Jets in PbPbCorrelations with Leading Particle
pt(seed) 5 GeV/c pt gt 3 GeV/c
1 lt R lt 2
1/R dN/dR
R lt 0.3
pt (GeV/c)
R

• Transformation d2N/dfdh ? 1/R dN/dR with R2
  Dh2 Df2
• 1000 HIJING events (default)

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Jets in PbPbTwo Particle Correlations

• Correlation increases with pt
• Effect of gluon radiation
• System size dependence
• pp

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Summary

• ALICE physics reach extends from
• Low pt gt 0.1 GeV/c
• Identified particles
• Correlations, HBT
• Event-by-event observables
• Flow
• to
• High pt 100 GeV/c
• Heavy quarks
• Quarkonia
• Photons
• Jets

• pp and pA physics
• Baseline for AA
• Important physics on its own
• Integral part of ALICE physics program
• Physics Performance Report
• Full simulations for all projected physics
  observables