Epiphany - 3.1.-6.1.2002 H.R. Schmidt - GSI

Status and Prospects of the CERN-LHC Experiment ALICE

Status and Prospects of the CERN-LHC Experiment ALICE

• Physics Issues– Experimental Conditions

– Signals & Observables

• The ALICE Experiment– Layout

– Subdetectors

The LHCThe LHC

• 4 approved experiments: Atlas, CMS, LHCb, ALICE

• 2006: start commissioning pp• 2007: start Pb+Pb• √sNN = 5.5 TeV

Ecm (Pb+Pb) = 1148 TeV

≈ 0.2 mJ ≈ 1 g * (0.5 m/s)2

Cosmic Rays - The Knee

Cosmic Rays - The Knee

LHC reaches energies beyond the “knee” - at drastically higher rates =>

verification of particle multiplicities from primary cosmic rays

≈ 1 km

quark-hadron

transition}

Heavy-Ions at LHC Energies Probe Low-x Region

Heavy-Ions at LHC Energies Probe Low-x Region

x ~ 2p0/√s

pt ~ p0 ~ 2 GeV

(at mid-rapidity)

Hera-Structure Fct:

=> large increase of initial gluon density at LHC

Hera

High Energy Heavy-Ion Collisions are Dominated by Hard Parton-Parton

Collisions

High Energy Heavy-Ion Collisions are Dominated by Hard Parton-Parton

Collisions

• gluons/proton at p0=2 GeV: SPS (4), RHIC (10), LHC (30)

• large cross section for gluon-gluon scattering partonic cascade with rapid equilibration at high

temperatures (< 0.1 fm/c and T≈1 GeV) up to 5500 minijets (pt > 2 GeV/c)

Fireball Evolution of Pb+Pb Collisions at the LHC

Fireball Evolution of Pb+Pb Collisions at the LHC

high energy densities: ≈ 1000 GeV/fm3

=1 fm/c ≈ 40 GeV/fm3

long life times: QGP >10 fm/c

freeze ≈ 70 fm/c

large volumes: dNch/dy ≈ 8000

Vfreeze(y=1) =105 fm3

Comparison SPS-RHIC-LHCComparison SPS-RHIC-LHC

SPS RHIC LHC

Ecm [GeV] 17 200 5500

dch/dy 500 700 3000 - 8000

j [Gev/fm3]0=1fm/c ≈2.5 ≈3.5 15 - 40

Vfreeze [fm3] ≈103 ≈9103 ≈3.7104 - 1.0 105

QGP [fm/c] <1 ≈1 ≈4.5-12

Pb+Pb, central collision (b<0.5 fm

significant increase in relevant parameters ( V,factor 10 from SPS to LHC

QGP probesQGP probes

HBTHBT

momentumdistributions

momentumdistributions

particleratios

particleratios

light mesondecays

light mesondecays

strangeletsstrangelets

collective flowcollective flow

fluctuation,correlations

fluctuation,correlations

thermalradiation

thermalradiation

jetsjets

heavy mesondecays

heavy mesondecays

hadronphase

hadronphase

phasetransition

phasetransition

QGPphase

QGPphase

Multiplicities for 208Pb+208Pb collisions at LHC

Multiplicities for 208Pb+208Pb collisions at LHC

• predictions for dNch/dy vary from 3000 to 8000

• this reflects uncertainties in the (pQCD dominated) physics

– gluon shadowing

– initial/final state parton saturation

– jet-quenching

HIJING with jet-quenching

HIJING w/o jet-quenching

Pb+Pb at √s =5.5 ATeV

Particle RatiosParticle Ratios• observables in ALICE

, π, , p, d, t, K, , D, B, J/’s,

• particle composition thermodynamic parameters (Tfreeze, b) of hadronic phase

• strangeness content of fireball via strange/non-strange ratios QGP/phase transition– quality of strangeness measurement:

0

20

40K0

s1 event 10events

0.4 0.5 0.6ππ (Mass GeV)

1.1 1.2πp (Mass GeV)

10

30

Events/5MeV

0

100

1.3 1.4

- 103events

1.6 1.7 1.8

- 10 4events

25

50

75

π (Mass GeV) K (Mass GeV)

Fluctuations & Event-by-Event PhysicsFluctuations & Event-by-Event Physics

low multiplicity events:

• interesting excursions from “normal” physics masked by statistical fluctuations

high multiplicity events:

• LHC Pb+Pb ideal to search for non-statistical, event-by-event fluctuations– precision 1/√N– EbE investigations can be extended to:.

• pt spectra (π, K, p) temperature, flow• HBT size, lifetime• N/Nch isospin fluctuations (“DCC”)• search for (critical) phenomena at phase

boundaries (K/π, +/-, …)

speciesdN/dy

(ALICE)

π- ≈ π+ ≈ π0 2500

K+≈K-≈ K0s 385

500

p ≈ p 250

≈ 126

Passage of Hard Probes through Matter Passage of Hard Probes through Matter

hadronicmatter

QGPmatter

hard probes:jets, J/..

dE/dx (energy loss) of parton significantly enhanced for passage through hot gluonic matter (“jet quenching”)

resonance melting via color screening in hot gluonic matter (“J/ suppression”)

Quarkonia Suppression MeasurementQuarkonia Suppression Measurement• two, complementary measurement

of J/ and suppression in ALICE:

– forward (-arm: 2.5 < < 4)

– J/ , ’

• ers (x 3)

• proven technology (NA38/50/60)

– mid-rapidity (ITS+TPC +TRD)

– J/ , ’ e+e-

• baryon-free region

• J/ from B-decays can be tagged

1.0

0.5

light ions heavy ions

1 2 3 4 5 10 20 30 50 100

0.5

3(GeV/fm)

S,'

J /comovers

J /deconf.

Υ'comovers

Υ'deconf.

Υcomovers Υdeconf.

1.0

1) Sequential quarkonia suppression below Tc - in-medium modification of open charm/beauty thresholds (Digal, Petreczky, Satz)

2) Stat. hadronization of cc results in J/ enhancement at LHC (J. Stachel, P. Braun-Munzinger)

gg cc J/

bb

BottoniumBottonium

• quality of data:– expected spectrum of the -

family after 106 s (1 ALICE year) running time as measured in the -arm

– no suppression taken into account

– m ≈ 100 MeV aimed at (to resolve different states)

0

100

200

300

8 9 10 11 12m (GeV)

'

''

Mid-Rapidity Open Charm/Bottom Mid-Rapidity Open Charm/Bottom

• D-mesons (cq), B-mesons (bq)– liftime: cD= 0.032 cm, cB=0.039 cm

– semi-leptonic decays: B, D e + anything

– tagging via high pt electron (TRD) + displaced vertices (ITS)

Mid-Rapidity J/ Mid-Rapidity J/

• direct production: gg cc J/ e+e-

• from B decay: B J/ e+e-

General Design ConsiderationsGeneral Design Considerations

• only one dedicated HI-experiment at LHC:

• no single/dedicated probe/messenger of QGP correlated measurement of many observables versatile /general purpose experiment to study hot and dense matter

SPS

NA49 (hadrons)

CERES (di-electrons)

WA98 (photons)

NA57 (hyperons)

NA60 (muons)

RHIC

STAR (hadrons)

Phenix (photons, leptons)

Phobos (dN/d)

Brahms (p, π, K spectra)

LHC

ALICE (everything)

Alice SetupAlice SetupTPCTPC

TOFTOF

TRDTRD

ITSITS

PHOSPHOS

RICHRICH

µ-ARMµ-ARM

L3-MagnetL3-Magnet

PMDPMD

ALICE @ Point2: Ready to move in!ALICE @ Point2: Ready to move in!

ALICE TPC LayoutALICE TPC Layout

5 m

Pad PlanePad Plane

pad size: 47.5 mm2

≈ 570 000 pads (36 sectors)

TPC occupancy pad-time spaceTPC occupancy pad-time space

• stability of chamber operation at high gain and load ? (√)• occupancy (pad-time) @ inner chambers up to 50% (!)

cluster finding & tracking very involved– NA49 experience: no track reconstruction at > 20% occupancy !

ALICE-simulation

Track Reconstruction at dNch/dy=8300 + BGNDTrack Reconstruction at dNch/dy=8300 + BGND

outer radius: ≈ 10% occupancy

inner radius: 40-50% occupancy

ALICE Tracking-group improves since 1993 reconstruction algorithms(„follow-your-nose“-tracking, Kalman-filter, ...)

STAR

Track Reconstruction & Momentum Resolution

Track Reconstruction & Momentum Resolution

Status (2001):• 88% of all (recognizable) tracks

are recognized correctly ()• fake tracks

Momentum Resolution (TPC only ) :

•<pt/pt> ≈ 2.4%5 GeV/c:

• pt/pt ≈ 14% ()

for high pt physics complementary information necessary (ITS, TRD)

•pt/pt ≈ 5%

Transition Radiation DetectorTransition Radiation Detector

• 6 layers of TRD’s 540 chambers, 1.16 106 channels

TRD module

Transition Radiation DetectorTransition Radiation Detector

• e/π discrimination employing transition radiation (ETR())

• π rejection factor > 100

Transition Radiation Detector - TriggerTransition Radiation Detector - Trigger

• trigger capability - latency < 6 µs ( high pt electrons, jets) – very challenging real-time

front-end data processing

– select events which occur with probability 10-5

– enriches e.g. sample by factor 12 (194 ’s 2878 ’s per 106 s)

ConclusionConclusion

• heavy ions at LHC offer a large physics potential– goes beyond QGP search (pQCD)

– significant step beyond RHIC

• ALICE is a versatile detector– employing proven detector technology (TPC, µ-arm, silicon detectors))

– big advances in technology (TDR, front-end processing, TOF)

TPC Production @ GSI & HDTPC Production @ GSI & HD

TPC working principle - 3D-imagingTPC working principle - 3D-imaging