roman lietava, university of birmingham uk hep forum 1 alice experiment physics motivation detectors...

UK HEP Forum Roman Lietava, University of Birmingham

1

ALICE Experiment

• Physics motivation

• Detectors

• Observables and Physics Performance

• Summary

Roman LietavaRoman LietavaUniversity of BirminghamUniversity of Birmingham


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SOUTH AFRICA

UKPORTUGAL

JINR

GERMANY

SWEDEN

CZECH REP.

HUNGARYNORWAY

SLOVAKIA

POLANDNETHERLANDS

GREECEDENMARK

FINLAND

SWITZERLAND

RUSSIA CERN

FRANCE

MEXICOCROATIA

ROMANIA

CHINA

USAARMENIA

UKRAINE

INDIA

ITALY

S. KOREA937 members (63% from CERN MS)

77 Institutions, 29 Countries

ALICE Collaboration

ALICE UK:6 members

University of Birmingham


3

Collision Systems

Collision system

pp

PbPb

107

Run time

(s/year)

L0

(cm-2s-1)

√sNN

(TeV)

103114.0

106 10275.5

Other collision systems and energies: • pA, lighter ions (Sn, Kr, Ar, O) • pp @ 5.5 TeV

Year

April 2007

2007/2008


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Physics Motivation

The study of Quantum Chromodynamics:• A-A collisions: - physics of many particles interacting strongly, QCD phase transition• p-p and p-A collisions: - benchmark for AA collisions - specific aspects• Ultra peripheral AA collisions – physics• Cosmic ray physics


5

QCD Phase Diagram

Lattice QCDLattice QCD

Nonperturbative phenomena

hep-ph/020516

PLB478(2000)447


6

Space Time Evolution of the Collisions


7

ALICE Physics Goals

Deconfinement: charmonium and bottomonium spectroscopy

Chiral symmetry restoration: neutral to charged ratios, res. decays

Fluctuation phenomena - critical behaviour: event-by-event particle comp. and spectra

Geometry of the emitting source: HBT, impact parameter via zero-degree energy flow

pp collisions in a new energy domain

Degrees of freedom as a function of T hadron ratios and spectra, dilepton continuum, direct photons

Global observables: Multiplicities, distributions

Early state manifestation of collective effects: elliptic flow

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

Large acceptance Good tracking capabilities Selective triggering Excellent granularity

Wide momentum coverage P.I.D. of hadrons and leptons Good sec. vertex reconstr. Photon Detection

Use a variety of experimental techniques!


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Alice Detector

• Tracking (B=0.2-0.5 T): - Inner Tracking System (ITS) – pixels,drift,strips - Time Projection Chamber (TPC)

- Transition Radiation Detector (TRD) • PID: - TPC - TRD - Time Of Flight (TOF) - High Momentum PID (HMPID)• Muons: dimuon arm• Calorimetry: - PHOton Spectrometer (PHOS) - Electromagnetic Calorimeter

(EMCAL) - under discussion


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Bat 40

ALICEALICE

ATLAS

CMS

From R.J.Cashmore,IOP Bham


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ALICE Detector Acceptance

Muon arm: 2.4<<4 PMD 2.3<<3.5 FMD: -5.4<<-1.6, 1.6<<3


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PT Resolution


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ALICE PID

, K, p identified in large acceptance (2 * 1.8 units ) via a combination of dE/dx in Si and TPC and TOF from ~100 MeV to 2 (p/K) - 3.5 (K/p) GeV/cElectrons identified from 100 MeV/c to 100 GeV/c (with varying efficiency) combining Si+TPC+TOF with a dedicated TRD In small acceptance HMPID extends PID to ~5 GeV Photons measured with high resolution in PHOS, counting in PMD, and in EMC

/K

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

1 10 100 p(GeV/c)

TRD e / PHOS /

TPC+ITS

(dE/dx)

/K

/K

K/p

K/p

K/p

e /

e /

HMPID (RICH)

TOF


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ALICE Trigger (Birmingham)

Triggering on:

• collision centrality

• high pT muons

• high pT electrons

• jets

ALICE trigger features:• Global trigger selection• Past-Future protection• Different trigger rates for group of detectors• Dynamic suppression of common triggers

Rates and pile-up:• Pb-Pb collisions: 8 kHz interaction rate L=1027 cm-2 s-1 • 60 % pile-up probability

• p-p collisions: 200 kHz interaction rate L=3x1030 cm-2 s-1 • 100 % pile-up probability

• TPC drift time 90 s


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First ALICE trigger board (LTU)


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Observables

Medium characteristics

• Particle multiplicities• Particle spectra • Particle ratios• Flow• Particle correlation• Fluctuations

Hard probes

• Jets • Heavy quark and

quarkonium production• Direct photons and dileptons


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Multiplicity

(from K.Kajantie, K.Eskola)

dNch/d ~ 2500We can extrapolate from RHIC data:

What multiplicity do we expect?What multiplicity do we expect?

ALICE design: dN/dy=8000ALICE design: dN/dy=8000


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Transverse mass spectra

5% most central events

NA57 Pb-Pb at s=17GeV

rdrT

pI

T

mKmA

mym

N GRtt

TjTT

j

0 01

2sinhcosh

dd

d

)(tanh)( 1 rr

G

n

GS Rr

R

rr

)(

Transverse mass spectra

Freeze out temperatureTransverse flow

NA5NA577

FA - QM`04 Strangeness ReportRoman Lietava, University of Birmingham

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Hadron Ratios

Degree of chemical equlibrium: Constraint on timescales of flavour production mechanism


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Detection

• One year of ALICE running

(107 events) s up to pt = 12 GeV/c

• Topological signature, not reliant on identification of daughters

S/B 15.5 /event

S/B 15.5 /event

% of rec. s vs pt% of rec. s vs pt

Reconstructedpt spectrumReconstructedpt spectrum

M(p) (GeV/c2)

Ent

ries

%

pt (GeV/c)

pt (GeV/c)

Y

ield


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Hard Processes Modified by the Medium

• Jet quenching:– energy degradation of leading hadrons, pt dependence;

– modification of genuine jet observables;

– energy imbalance in dijet events

• Open charm/beauty production• c’onium & b’onium bound states production

Final state (medium) interaction versus initial state (Cronin,shadowing) interaction

p-p and p-A measurement are mandatory


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High pT Suppression

• High pt particles suppressed

in Au-Au relative to pp, d-Au.

RAB = d2N/dpTd

TABd2pp/dpTdSTAR results:

d-Au, Cronin effect

Au-Au, jet quenching

AA coll

pp collNumber of coll

J. Adams et al., Phys. Rev. Lett. 91, 072304 (2003).


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Di-jets

In central Au-Au events,although trigger jet is clearly visible, “away-side” jet is not visible, as predicted from strong absorption in a high colour charge density volume, e.g. that produced in a QGP

Mini-jets in Au+Au at RHIC (STAR)

Missing jet


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Jets Reconstruction in ALICE

• Jets are produced copiously.

• Jets are distinguishable from the HI underlying event.

pt (GeV)2 20 100 200

100/event 1/event 100K/year

100 GeV jet + HI event


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Heavy Quarks

• Initially produced quarks experience the full collision history:– Short time scale for production: 1/mQ

– Production suppressed at larger times: mQ»T– Long time scale for decay decay»QGP

• The large masses of c and b quarks make them qualitatively different probes ( massless partons)

Observables: • Total production rate• transverse momentum distribution• correlation between quark and antiquark


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Heavy Quarks D0 K-+ reconstruction in ALICE

Affected by main vertexresolution in p+p caseAffected by main vertexresolution in p+p case

D0 K-c= 123.7 0.8mBR: (3.83 0.09) %

D0 K-c= 123.7 0.8mBR: (3.83 0.09) %

cuts depend on D0 ptcuts depend on D0 pt


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Heavy Quarks D0 K-+ reconstruction in ALICE

PbPb: pT>1 GeV/cpp: pT>0 GeV/c


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Heavy QuarkoniaJ/ and via Dielectrons

Mass resolution for 100 MeV (B = 0.4T)Mass resolution for 100 MeV (B = 0.4T)

::

J/:J/:

Acceptance down to pt = 0 GeV/c !Acceptance down to pt = 0 GeV/c !


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Motivation for pp Study

• First insight in pp collisions in new energy domain (s 14 TeV), study of evolution of soft hadronic physics

• Contribution to knowledge of underlying minimum bias (background) pp events to complement other LHC physics programmes (Higgs search, Bphysics, etc.)

• Provide pp data as a reference for study of other collision systems (p-A, A-A)

• Low multiplicity data to commission and calibrate various components of ALICE


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ALICE Features for pp

Magnetic field (T) ALICE 0.2 0.5 ATLAS 2.0 CMS 4.0

Material thicknessX/X0 (%)

Minimal pion ()

momentum (MeV)Minimal kaon (K

)

momentum (MeV)ALICE 7 80 200ATLAS 30 130 305CMS 20 115 280

Excellent particle identification (TOF and HMPID)

pt cut-off

Magnetic field (but this could be lowered)

Material thickness (hard to change)

ATLAS and CMS have better -coverage


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Permanent closure of L3 door in RB26 (05/03/04)SummaryALICE experiment is getting ready:

- the detectors are being built

-the software is getting ready

... and so does the number of people involved

- the understanding of the physics potential grows …


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ALICE Setup

ITS

TPCTRD

TOFPHOS

HMPID

MUON SPEC.PMD

FMD


32

Low pt Physics ExamplesResonances: K*

• Decay channel K* K+-

• Invariant mass distribution for 550 events

En

trie

s

Au+Au minimum bias

pT 0.2 GeV/c

|y| 0.5Statistical error only

STAR Preliminary

STAR data shows clear K* on

background

Other resonances (f0... ) are being

extracted


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HBTEvent-by-Event ++ HBT

• Single event

• Raw correlation function

– Uncorrected for Coulomb

– R = 8 fm, = 0.5

– Tracking with ITS+TPC, B = 0.2T

Qinv (GeV)C

(Qin

v)

Resolution for B=0.2T

d6N

d3p1d3p2

C(p1,p2)=d3N d3N

d3p1 d3p2


34

Number of Participants

pA:

AA:

Participants Npart

SpectatorsNpart=+1


35


36

Charged Particle Multiplicity 130 GeV AuAu 200 GeV AuAu

25-35%cent

0-6%cent

45-55%cent

Ntot

= 4100 ±210 Ntot

= 4960 ±250

dN/d


37

EMCAL => trigger and -jet, + improve resolution on Ejet

2%

8%

jet

Collision axis

TPC

PHOS+EMCAL

Proposed EMCAL||<0.7 ~ 120o

-jet with PHOS+EMCAL + TPC


38

Elliptic flow

dN(pT,b,y,)=A(1 + 2v1(pT,b,y) cos() + 2v2(pT,b,y)cos(2 ) +…)

- the angle relative to reaction plane

STAR Preliminary

scaled with n(quarks)

•v1=0 at y=0 by symmetry

•v2 – information about the information about the equation of state


39

Why is elliptic flow interesting?

• Coordinate space configuration anisotropic (almond shape) however, initial momentum distribution isotropic (spherically symmetric)

• Only interactions among constituents generate a pressure gradient, which transforms the initial coordinate space anisotropy into a momentum space anisotropy (no analogy in pp)

• Multiple interactions lead to thermalization -> limiting behavior ideal hydrodynamic flow

y

x

py

px

coordinate space

Momentum space

12 , tan ( )cos 2( ) y

xrv

p

p

3 2

31

11 2 cos

2 n rnt t

d N d NE v n

d p p dp dy

Raimond Snellings


40

Elliptic flow as a function of centrality

STAR Nucl. Phys. A698 (2002) 193

Non-flow considerable for central and peripheral events


41

0 1 2 10 100

pt (GeV/c)

Bulk propertiesHard processes

Modified by the medium

ALICE

CMS&ATLAS

1+2 Experiments

PID

T=QCD Qs


42

High pt RHIC Results

• RAA clearly different between mesons and baryons

• Importance of PID at high pt

• p+p baseline measurement!

tdpppdtdpAAd

collNtpAAR

)()(1)(


43

Heavy QuarksOpen Charm via Hadronic Decays

Pb+Pb:Pb+Pb:

dN/dpt Significance

pt > 1 GeV/cpt > 1 GeV/c

p+p:p+p:

pt > 0 GeV/c !pt > 0 GeV/c !

dN/dpt SignificanceSignificance =

BSS /


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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

8437Significance

for107(109)evts

50 %11 %S/B

2000013000Signal

for107(109)evts

pp (14TeV)Pb-Pb (5.5TeV)System (s)

Pb+PbPb+Pb

minv = 12 MeV (B = 0.4T)minv = 12 MeV (B = 0.4T)

PbPb:pT>1 GeV;pp: pT>0


45

Parton Energy Loss

- Reduction of single inclusive high pt particles

• Parton specific (stronger for gluons than quarks)

• Flavour specific (stronger for light quarks)

• Measure identified hadrons (, K, p, , etc.) + partons (charm, beauty) at high pt

– Suppression of mini-jets• same-side / away-side

correlations

– Change of fragmentation function for hard jets (pt >> 10 GeV/c)

• Transverse and longitudinal fragmentation function of jets

• Jet broadening reduction of jet energy, dijets, -jet pairs- p+p and p+A measurements crucial


46

Parton Energy Loss


47


48


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Permanent closure of L3 door in RB26 (05/03/04)


50

c/b Quarkonia

• 1 month statistics of PbPb √sNN=5.5 TeV;

Even

ts/1

00 M

eV

103

J/Y

5 10 15

102

dN/d=8000

M+- (GeV)

Even

ts/2

5 M

eV

104

J/Y

2 3 4 9 10 11 0

105

104

dN/d=5000

|| < 2.4 2.5 < < 4

via dimuons


51

ALICE Pb-Pb central event

Nch(-0.5<<0.5)=8000


52

The LHC facility

• Running conditions:

• + other collision systems: pA, lighter ions (Sn, Kr,

Ar, O) & energies (pp @ 5.5 TeV).

Collision system

pp

PbPb

√sNN

(TeV)

L0

(cm-2s-1)

<L>/L0

(%)

Run time

(s/year)

geom

(b)

14.0 1034* 107 0.075.5 1027 70-50 106 * * 7.7

April 2007

End 2007Early 2008 *Lmax(ALICE) = 1031 ** Lint(ALICE) ~ 0.7 nb-1/year


53

Experimental Conditions @ LHC

• pp commissioning start April 2007

• wish list of the HI community for the LHC• Initial few years (1HI ‘year’ = 106 effective s, ~like at SPS)

– 2 - 3 years Pb-Pb L ~ 1027 cm-2s-1

– 1 year p - Pb ‘like’ (p, d or ) L ~ 1029 cm-2s-1

– 1 year light ions (e.g. Ar-Ar) L ~ few 1027 to 1029 cm-2s-1

plus, for ALICE (limited by pileup in TPC):

– reg. pp run at s = 14 TeV L ~ 1029 and < 3x1030 cm-2s-1

• Later: different options depending on Physics results

• Heavy Ion running part of LHC initial program, early pilot run expected by end of 2007

roman lietava, university of birmingham uk hep forum 1 alice experiment physics motivation detectors...

Documents

gevc slide

discussion slide

b physics

alice pbpb

collision systems p

pmd fmd slide

iop bham slide

qcd phase transition