ALICE @ LHC

Marek KowalskiInstitue of Nuclear Physics, Cracow

PbPb collisions at 1150 TeV = 0.18 mJ

TheThe designdesign LHC LHC performanceperformance

BeamsBeams ,,TeVTeV LLmaxmax, cm, cm--22 ss--11

protonsprotons 7.0+7.0 = 14.07.0+7.0 = 14.0 10103434

LightLight nucleinuclei 3.5+3.5 = 7.03.5+3.5 = 7.0 10103030 -- 10103131

LeadLead nucleinuclei 2.75+2.75 = 5.52.75+2.75 = 5.5 10102727

S

LHC will run 1 LHC will run 1 monthmonth per per yearyear withwith heavyheavy ionsions

StructureStructure andand intensityintensity ofof LHC LHC beamsbeamsprotonsprotons PbPb8282 ionsions

No. No. of bunches of bunches per ringper ring 28352835 608608

Distance between bunches Distance between bunches [[nsns]] 2525 125125

No. No. of particles of particles per per bunchbunch 10101111 6*106*1077

No. No. of particles of particles per ringper ring 3*103*101414 3*103*101010

Beam current Beam current [[mAmA]] 530530 55

Luminosity lifetime Luminosity lifetime [h][h] 1010 1010

WhatWhat do we do we expectexpect

Observation of the Observation of the phase transitionphase transition

ExperimentExperiment

NatureNature1010--66 s 10s 10--44 s 3 min s 3 min 15*1015*1099 yearsyears

ALICE ALICE physicsphysics

•• Alice Physics History Alice Physics History –– Physics MotivationPhysics Motivation(1(1stst period)period)

–– First Ideas (First Ideas (AachenAachen, 1990), 1990)–– Expression of Interest (Evian, 1992)Expression of Interest (Evian, 1992)–– Letter of Intent (1993) and its addendum (1995)Letter of Intent (1993) and its addendum (1995)–– Technical Proposal (1995) and its addenda (1996, 1999)Technical Proposal (1995) and its addenda (1996, 1999)–– Technical Design Reports (1998 Technical Design Reports (1998 –– 2004)2004)–– Physics Performance Report (2003 Physics Performance Report (2003 –– 2004)2004)

•• HeavyHeavy--ion collisions at LHCion collisions at LHC

–– ALICE initially conceived as ‘soft physics experiment’ALICE initially conceived as ‘soft physics experiment’–– Main challenge Main challenge –– tracking at high densitytracking at high density–– and PIDand PID

•• Physics Performance in Physics Performance in EoIEoI and and LoILoI

–– TrackingTracking–– Particle IdentificationParticle Identification–– Boson Boson InterferometryInterferometry–– Lepton pairs (Lepton pairs (ωω, , φφ, J/, J/ψψ))–– Prompt PhotonsPrompt Photons–– Global Event CharacteristicsGlobal Event Characteristics

TowardsTowards hardhard physicsphysics•• LHCC gave us strong encouragement to look how to study LHCC gave us strong encouragement to look how to study

DebyeDebye screening (screening (YY) with ALICE detector) with ALICE detector

–– Initially intentionally left to LHC pp experiments (CMS)Initially intentionally left to LHC pp experiments (CMS)–– HoweverHowever

•• High pt cutoff for High pt cutoff for muonsmuons in central regionin central region•• MuonMuon absorber far from absorber far from the the interaction interaction point point –– large large

backgroundbackground•• Not clear situation with Not clear situation with muonmuon tracking in front of tracking in front of the the

absorberabsorber–– impact on mass resolutionimpact on mass resolution

–– Led to proposal Led to proposal for for the the Forward Forward MuonMuon SpectrometerSpectrometer

•• Open charm detection (’95)Open charm detection (’95)–– existing silicon tracker existing silicon tracker –– not sufficientnot sufficient–– attempt to put additional layer in attempt to put additional layer in the the vacuum pipevacuum pipe

•• to be closerto be closer•• no materialno material,, butbut•• technically extremely complicatedtechnically extremely complicated

–– Lead to Lead to the the redesign of redesign of the the inner part of inner part of the the ITSITS•• two layers of pixel detectorstwo layers of pixel detectors•• as close as we can negotiate (38mm)as close as we can negotiate (38mm)•• vacuum tube vacuum tube –– as thin as we can negotiateas thin as we can negotiate

•• Electron detection Electron detection && trigger (’98)trigger (’98)

–– Electron identification based on Electron identification based on the the dEdE//dxdx from TPCfrom TPC–– dEdE//dxdx resolution worsenresolution worseneded as we sophisticated our simulationas we sophisticated our simulation–– No trigger possible No trigger possible –– maybe J/maybe J/ψψ but not but not ΥΥ–– Led to Led to the the proposal of proposal of the the Transition Radiation DetectorTransition Radiation Detector

•• Jet physics Jet physics ((boostedboosted byby the results fromthe results from RHICRHIC))

–– Large Electromagnetic Calorimeter ?Large Electromagnetic Calorimeter ?

HMPID

ITS

TPCTRD

MUON SPEC.PMD

TOFPHOS

FMD

ALICE ALICE detectordetector

ALICE AcceptanceALICE Acceptance

00

--11

11

--22

22

00 11 22 33

ηη

pptt

PHOSHMPID

TRD TOF

TPC

ITS

ALICE isALICE is optimisedoptimised totostudy lowstudy low--ptpt observablesobservablesstudy highstudy high--ptpt observablesobservablescross correlate themcross correlate them

2020 100100

Particle Identification in ALICEParticle Identification in ALICEALICE uses almost all ALICE uses almost all

known methodsknown methods

0 1 2 3 4 5 p (GeV/c)

π/K K/pe /π

TPC + ITSTPC + ITS((dEdE//dxdx))

π/Ke /πTOFTOF K/pπ/K

HMPID HMPID (RICH) K/p(RICH)

TRDTRD e/e/ππPHOSPHOS γ /π0

MUON SPECTROMETERMUON SPECTROMETER

1 10 1 10 100 100 GeVGeV/c/c

Fast Fast vertexingvertexingMain vertex in the Main vertex in the ITS ITS –– correlation of correlation of 2 2 innermost pixelinnermost pixellayerslayers ((without trackingwithout tracking))

σσxx = 15 = 15 µµmm

σσyy = 15 = 15 µµmm

σσzz = 5 = 5 µµmm

no Bno B--dependencedependence

TrackingTracking –– TPC+ITS+TRDTPC+ITS+TRD

TPC TPC standalonestandalone

∆p/p (%) TPC+ITS

TPC+ITS+TRD

∆∆p/p (%)p/p (%) <P<PTT>> PPTT > 5 > 5 GeVGeV/c/cB (T)B (T) 0.20.2 0.50.5 0.20.2 0.50.5TPCTPC 2.42.4 1.21.2 8.58.5 5.85.8TPC+ITSTPC+ITS 1.61.6 0.70.7 3.43.4 1.41.4

positionpositionresolutionresolution

massmassresolutionresolution

momentumomentumm

resolutionresolution

efficiencyefficiency

200200--300 300 µµmm

66--8 8 MeVMeV 1.51.5--1.8%1.8% 0.210.21--0.250.25

500 500 µµmm 33--4 4 MeVMeV 1.3%1.3% 0.150.15

0K

Λ

−+→ ππ0K −− Λ→Ξ π

ParticleParticle ID ID inin ALICE ALICE detectordetector

TPCTPC

ITSITS

HMPIDHMPID (RICH)(RICH)

Data Data taken at taken at STARSTAR

TOFTOF

ElectronElectron andand γγ//ππ00 separationseparation

Inclusive γ: Direct + π 0

Direct γ

With high With high PT PT triggertrigger

From From ππ00 decaysdecays ππ00 after background subtractionafter background subtraction

HadronicHadronic observablesobservables

CharmCharm andand beautybeauty

•• in inclusivein inclusive semileptonicsemileptonic decaysdecays•• via evia e--µµ coincidencecoincidence•• in in hadronichadronic decaysdecays

DD00 →→ ππKK and Dand D++ →→ ππππKK

crucial crucial problem problem –– impact parameterimpact parameterresolutionresolution

Charm from hadronic decaysCharm from hadronic decaysdNdN//dy dy S/B S/B

8000 2.8% 8000 2.8%

4000 11%4000 11%PbPb++PbPb p+pp+p

QuarkoniaQuarkoniaµµµµ channelchannel

ee channelee channel

ALICE ALICE withwith EMCALEMCAL

jet

γ

Collision axis

pppp physicsphysicsAll HI All HI observablesobservables have to be measured also inhave to be measured also inpppp collisions for comparison with heavycollisions for comparison with heavy--ion resultsion results

However, there are interesting questions regarding pp However, there are interesting questions regarding pp collisions themselvescollisions themselves

-- charged multiplicity distributioncharged multiplicity distribution-- correlations between mean pcorrelations between mean ptt and multiplicity or and multiplicity or

strangenessstrangeness-- study of diffractive events study of diffractive events -- with large rapidity gapswith large rapidity gaps-- jetjetss-- ……

ALICE ALICE adventagesadventages::•• lower Plower Ptt cutcut--offoff•• particle particle IDID

Global Global observablesobservables::Multiplicities, Multiplicities, ηη distributionsdistributions

Degrees of freedom as a function of T:Degrees of freedom as a function of T:hadronhadron ratios and spectra, ratios and spectra, dileptondilepton continuum, direct photonscontinuum, direct photons

Early state manifestation of collective effects:Early state manifestation of collective effects:elliptic flow elliptic flow

Energy loss of Energy loss of partonspartons in quark gluon plasma:in quark gluon plasma:jet quenching, high pt spectra, open charm and open beautyjet quenching, high pt spectra, open charm and open beauty

Study Study deconfinementdeconfinement::charmoniumcharmonium and and bottobottommiumium spectroscopyspectroscopy

Study Study chiralchiral symmetry restoration:symmetry restoration:neutral to charged ratios, resonance decaysneutral to charged ratios, resonance decays

Detect fluctuation phenomena Detect fluctuation phenomena -- critical behavior:critical behavior:eventevent--byby--event particle composition, spectraevent particle composition, spectra

Measure the geometry of the emitting source:Measure the geometry of the emitting source:HBT, impact parameter via zeroHBT, impact parameter via zero--degree energy flowdegree energy flow

Study pp collisions in the new energy domainStudy pp collisions in the new energy domainSearch for:Search for: CentauroCentauro events, events, strangeletsstrangelets

SummarySummary

ALICE is ALICE is optimisedoptimised for a comprehensive measurement for a comprehensive measurement of:of:•• low low PT PT observablesobservables

explore new low baryochemical regime of the explore new low baryochemical regime of the QCD QCD phasephase diagramdiagram

••hard probeshard probesparton propagation in dense and hot nuclear matterparton propagation in dense and hot nuclear matter