Heavy-Ion Physics @ LHC

QM2004 Yves Schutz 1

Heavy-Ion Physics @ LHC

Program Detectors Observables

~1100 participants:

26 experimental contributions QM04 6 oral: P. Glaessel, V. Manzari, A. Vestbo, H. Takai, B. Wyslouch, S. Blyth. 20 posters: Spectra 23, HBT 1, High pT 17, 20, 21, Flavor 18, 19, 23, Instr. 1, 2, 7, 8, 10, 12, 14, 15, 16, 17, 22, 30.

1000 ALICE 60 CMS 25 ATLAS


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 0.07

5.5 1027 70-50 106 * * 7.7

April 2007

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


Novel aspects:

Probe initial partonic state in a novel Bjorken-x range (10-3-10-5): nuclear shadowing, high-density saturated

gluon distribution. Larger saturation scale

(QS=0.2A1/6√s= 2.7 GeV): particle production dominated by the staturation region.

Qualitatively new regime

J/ψ

ALICE PPR CERN/LHCC 2003-049

10-6 10-4 10-2 100

x

108

106

104

102

100

M2 (

GeV

2)

10 GeV


Novel aspects: Qualitatively new regime

Hard processes contribute significantly to the total AA cross-section (σhard/σtot = 98%): Bulk properties

dominated by hard processes;

Very hard probes are abundantly produced.

Weakly interacting probes become accessible (, Z0, W±).

LHC

RHIC

SPS

(h+

+h-)/20

17 GeV

200 GeV

5500 GeV=√s

LO p+p y=0


3 experiments

JURA

ALPES


hep-ph0104010

5

√s (GeV)10 102 103 102 103 104

1.0

5.0

10.0

15.0

Nch

/(0

.5N

part)

dN

ch/d|

<1

2

5

103

Which particle multiplicity to expect at LHC ?

ALICE optimized for dNch/dY = 4000, checked up to 8000 (reality factor 2).

CMS & ATLAS (checked up to 7000) will provide good performances over the expected range.

dNch/d ~ 1500

HI experiments

dNch/d ~ 2500


ALICE: the dedicated HI experiment

Solenoid magnet 0.5 T

Central tracking system:• ITS •TPC• TRD• TOF

MUON Spectrometer:• absorbers• tracking stations• trigger chambers• dipole

Specialized detectors:• HMPID• PHOS

Forward detectors:• PMD• FMD, T0, V0, ZDC

Cosmic rays trigger


Pb/Sci EMCal x = 1.4 x 2/3

TPC

TRD

TOF

PHOS

RICH

ITS

US EMCaL (under discussion)


ALICE: the dedicated HI experiment

Measure flavor content and phase-space distribution event-by-event: Most (2 * 1.8 units ) of the hadrons (dE/dx + ToF),

leptons (dE/dx, transition radiation, magnetic analysis) and photons (high resolution EM calorimetry);

Track and identify from very low (< 100 MeV/c; soft processes) up to very high pt (~100 GeV/c; hard

processes); Identify short lived particles (hyperons, D/B meson)

through secondary vertex detection; Jet identification;


ALICE PID performancesALICE PPR CERN/LHCC 2003-049


ALICE tracking efficiency

p/p < 1%

100%

pt (GeV/c)1 3 5

0

0.4

0.8

1.2


TPC only


ALICE track resolution at high pt

10 100pt (GeV/c)50

p/p

(%

)

10

30

50



ALICE construction status


ALICE TPC


ALICE Space Frame


ALICE Dipole coil


ALICE pixel40K channels200+150 m


CMS

• Central tracker• High resolution EM calorimeter• Hadronic calorimeter

Superconducting solenoid magnet 4T

• Muon spectrometer

• Very forward calorimeters• ZDC• CASTOR• TOTEM


ATLAS

Inner detector

Solenoid 2TEM calorimeter

H calorimeter

detectors


CMS & ATLAS Experiments designed for high pt physics in

pp collisions: Precise tracking systems in a large solenoid

magnetic field; Hermetic calorimeters (EM+Hadronic)

systems with fine grain segmentation; Large acceptance muon spectrometers; Accurate measurement of high energy

leptons, photons and hadronic jets. Provide adequate performances for selected

high pt (> 1 GeV/c) probes for HI physics.


0 1 2 10 100

pt (GeV/c)

Bulk propertiesHard processes

Modified by the medium

ALICE

CMS&ATLAS

3 Experiments

PID

T=QCD Qs


QGP probes: hard processes modified by the medium

Q » QCD, T, Qs , r ~ 1/Q

Jet quenching: Energy degradation of leading hadrons, pt

dependence; Modification of genuine jet observables; Mass dependence of energy loss (light and heavy

quarks). Dissolution of c’onium & b’onium bound

states.


Leading hadron quenching

Nuclear modification factor pattern very different at LHC: Final state interactions

(radiative & collisional energy loss) dominate over nuclear effects (shadowing+Cronin).

Measurement of suppression pattern of leading partons remains experimentally the most straightforward observable for jet-tomography analysis. 0 20 40 60 80 100

pt (GeV)

0.05

0.1

0.5

1

RAA

A+A √sNN = 200, 5500 GeV

Vitev&Gyulassy QM02


Jets reconstruction 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


Performance by ATLAS

50 150 250 3500

40

80

%

Efficiency

Fake jets

Et

Cone algorithm R=0.4Et > 30 GeV

50 150 250 350Et

0

20

10

Energy resolutionPbPb

pp

E/E (%)


50 150 250 3500

40

80

%

Et

0

20

10

E/E (%)

200 3000 1000

Performance by CMS

Cone algorithm R=0.5Et > 30 GeV

Energy resolution

Et


Jet quenching Excellent jet reconstruction…

but challenging to measure medium modification of its shape…

Et=100 GeV (reduced average jet energy fraction inside R): Radiated energy ~20% R=0.3 E/E=3% Et

UE ~ 100 GeV

RMedium induced redistribution of jet energy occurs inside cone.

C.A. Salgado, U.A. Wiedemann hep-ph/0310079

vacuum

medium

Et = 50 GeV

Et = 100 GeV

0.200

0.4 0.6 0.8 1

0.2

R=√(2+2)

0.4

0.6

0.810

0.20.4

0.6

0.8

1

(R

)


Exclusive jets: Redistribution of jet energy

Jet shape: distance R to leading particle; pT of particles for R < Rmax;

Multiplicity of particles for R < Rmax ;

Heating: kT = p sin((particle, jet axis)) ;

Forward backward correlation(particle, jet axis);

Fragmentation function: F(z)=1/NjdNch/dz z=pt/pjet.

Requires high quality tracking down to low pt .


Fragmentation functions

0 0.5 1z

10-4

10-2

1vacuummedium

0 0.5 1z

1/N

jetsdN

c/dz

10-1

10

103

reconstructed

input

pjet

z

kt

z=pt/pjetpjet


Exclusive jets: Tagging

Direct measurement of jet energy: , *, Z0

40500Z0 (μ+ μ-)-jet

50104*(μ+ μ-)- jet

50106-jet

pt

(GeV)

Statistics(evts/month)

Channel

50600

1006103


Exclusive jets: Tagging

Direct measure of jet energy: , *, Z0

Low (< 10%) background as compared to /0


Heavy flavor quenching observables

Inclusive: Suppression of dilepton invariant mass

spectrum (DDl+l-, BB l+l- , B D+ l+)l-

Suppression of lepton spectra Exclusive jet tagging:

High- pT lepton (B→Dl) & displaced vertex

Hadronic decay (ex. D0 K-+) & displaced vertex


D quenching (D0 K-+) Reduced

Ratio D/hadrons (or D/0) enhanced and sensitive to medium properties.

nucl-ex/0311004

tpp

tAA

collAA dpdN

dpdN

NR

/

/1


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


Looking forward For a timely completion of LHC and

experiments construction in April 2007; Accelerators and experiments are today in the

production phase. For an exciting decade of novel HI physics

in continuation of the SPS and complementary to RHIC; Detailed physics program, complementary

between 1+2 experiments, takes shape (see PPRs, Yellow reports…).

The 2004 challenge: demonstrate world-wide distributed Monte-Carlo production and data analysis.


Backup


The LHC facility


Time (h)

The LHC facility: average L

1

23

Experiments

* = 2 - 0.5 mIO = 108 ions/bunch

70%

55%

50%

Tuning time

0.2

0.4

0.6

0.8

1<L>/L0

0 5 10 15 200ALICE PPR CERN/LHCC 2003-049


Novel aspects:

SPS RHIC LHC

√sNN (GeV) 17 200

dNch/dy 500 850

0QGP (fm/c) 1 0.2

T/Tc 1.1 1.9

(GeV/fm3) 3 5

QGP (fm/c) ≤2 2-4

f (fm/c) ~10 20-30

Vf(fm3) few 103 few 104 few 105 bigger

5500 X 28

1500-8000 ?

0.1 faster

3.0-4.2 hotter

15-60 denser

≥10longer

30-40

Quantitatively new regime


Novel aspects: Qualitatively new regime

mu= md = ms

mu = md

mu = md ; ms mu,d

HQ suppressed exp(-mc,b,t/T)

Thermodynamics of the QGP phase Thermodynamics of massless 3-flavor QCD.

Parton dynamics (QGP/0>50-100) dominate the fireball expansion and the collective features of the hadronic final state.

s(T)=4/(18log(5T/Tc))


Scientific objectives of HI physics

Study the QCD phase transition and the physics of the QGP state: How to apply and extend the SM to a complex

and dynamically evolving system of finite size; Understand how collective phenomena and

macroscopic properties emerge from the microscopic laws of elementary particle physics;

Answer these questions in the sector of strong interaction by studying matter under conditions of extreme temperature and density.

RHIC + CBM

LHC


Heavy-ion running scenario Year 1

pp: detector commissioning & physics data PbPb physics pilot run: global event-properties, observables

with large cross-section Year 2 (in addition to pp @ 14 TeV, L< 5.1030 cm-2s-1 )

PbPb @ L~ 1027 cm-2s-1: rare observables Year 3

p(d, )Pb @ L~ 1029 cm-2s-1 : Nuclear modification of structure function

Year 4 (as year 2) : Lint = 0.5-0.7 nb-1/year Year 5

ArAr @ L~ 1027 -1029 cm-2s-1 : energy density dependencies Options for later

pp @ 5.5 TeV, pA (A scan to map A dependence), AA (A scan to map energy-density dependence), PbPb (energy-excitation function down towards RHIC), ….


Combined PID

Probability to be a pion

Probability to be a kaon

Probability to be a proton


Inclusive jets by ALICE

● Original spectrum● Measured spectrum E/E = 25%● Original spectrum for measured energy 90 < ET < 110 GeV

R=0.3

pt > 2 GeV


Exclusive jets: Tagged jets

pt (GeV)

RAA

PbPb + 40 GeV -jet

1

0 10 20 30 400

2

3

4

Tagging

0 10 20 30 40

No Tagging


Heavy quarks jets A. Dainese QM04

Initially produced Qs 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)

Radiative energy loss suppressed as compared to q, g: (1+0

2/2)-2; 0=mQ/EQ


D0 K-+ reconstruction in ALICE




ALICE TPC

EE

510 cm

EE

88s

Central electrode



D0 K-+ reconstruction in ALICEA. Dainese QM04

Invariant-mass analysis of fully-reconstructed topologies originating from displaced secondary vertices


Cone angle (°)0 20 40

0

0.1

0.2

C.A. Salgado, U.A. Wiedemann

E/E

Documents

Heavy-Ion Physics @ LHC