Status & recent Results from the

ALICE Collaboration

David Evans

The University of Birmingham, UK

HEP-MAD 11

Madagascar August 2011

Outline of Talk

• Introduction

• The ALICE Experiment

• Status of Experiment

• Selection of results from ALICE– Particle spectra & ratios

– Flow

– Jet and high pT

suppression (RAA

)

– charm

• Future outlook

• Summary

Aims of ALICE

� Study strongly interacting matter at extreme energy

densities over large volumes and long time-scales (study of

QCD at its natural scale, ΛQCD ~ 200 MeV).

� Study the QCD phase transition from hadronic matter to a

deconfined state of quarks and gluons - The Quark-Gluon

Plasma.

�Study the physics of the Quark-Gluon Plasma (QCD under

extreme conditions).

4

Phases of Strongly Interacting Matter

Lattice QCD, µB = 0

Both statistical and lattice QCD predict that

hadronic matter will undergo a phase

transition, in to a deconfined state of

quarks and gluons – a quark-gluon plasma,

at a temperature of,

T ~ 170 MeV and energy density,

ε ~ 1 GeV/fm3.

ALICE will far exceed these

temperatures & densities at the

LHC.

5

Heavy Ion Collisions

pre-equilibration ⇒ QGP ⇒

hadronisation ⇒ freeze out

Colliders: AGS, SPS, RHIC, LHC

Create QGP by colliding ultra-relativistic heavy ions

√SNN (GeV) = 5.4 19 200 2360 (5200)

6

Observables

Jets

Open charm, beauty

7 7

Detector:

Size: 16 x 26 metres

Weight: 10,000 tons

Collaboration:

> 1000 Members

> 100 Institutes

> 30 countries

ALICE Detector

Technologies:18

Tracking: 7

PID: 6

Calo. : 5

Trigger, Nch

:11

ICPAQGP Goa 2010 J. Schukraft

8

Detector Status

PLC 20J. Schukraft8

Complete since 2008:

ITS, TPC, TOF, HMPID,

FMD, T0, V0, ZDC,

Muon arm, Acorde

PMD , DAQ

Partial installation (2010):

4/10 EMCAL* (approved 2009)

7/18 TRD* (approved 2002)

3/5 PHOS (funding)

~ 60% HLT (High Level Trigger)

2011

10/10 EMCAL

10/18 TRD

TRD to be completed end 2012

*upgrade to the original setup

ITS

TPC

TRD

TOF

EMCAL

PHOS

HMPID

L3 Magnet

Data Samples

Beam Energy # of Events

pp 900 GeV 300 k MB 2009, analysis finished

pp 900 GeV ~ 8 M MB 2010, partially analyzed

pp 2.36 TeV ~ 40 k MB 2009, only ITS, dNch/dη

pp 7 TeV ~ 800 M MB~ 120 M muons~ 20 M high Nch

2010

PbPb 2.76 TeV/N ~ 30 M MB 2010

pp 2.76 TeV ~ 70 M MB~ 20 nb-1 (rare triggers)

2011, analysis started

30 h only

Charged Particle Multiplicity

dNch

/dηηηη versus √√√√sdNch

/dηηηη (Pb-Pb) Theory

dNch

/dηηηη = 1584 ±±±± 4 (stat.) ±±±± 76 (syst.)

Larger than most model predictions

Rises with √s faster than pp

Fits power law: Pb-Pb ~ s0.15

Bjorken formula estimates energy density, εεεε > 15 GeV/fm3 (3 x RHIC)

11

Bose–Einstein correlations

(HBT)

• medium size: 2x larger than at RHIC– volume ~ 300 fm3

• medium life time: 40% longer than at RHIC– ττττ ~ 10-11 fm/c

ALICE, Phys. Lett. B 696 (2011) 328.

QM enhancement of identical Bosons at small

momentum difference

enhancement of e.g. like-sign pions at low

momentum difference qinv=|p1-p2|,

12

• dE/dx:

5% resolution

• Time-of flight,

resolution:

86 ps (Pb-Pb)

160 ps (p-p)

• TPC dE/dx: separate p from K up to 1.1 GeV

• Time of flight: separate K from πup to ~ 2.2 GeV

Particle ID

Identified Particle spectra

QM2011 J. Schukraft 13

Very significant changes in slope compared to RHIC

Most dramatically for protons

Very strong radial flow, ββββ ≈ 0.66even larger than predicted by most recent hydro

Blast Wave Fit

RHIC

Hydro Prediction

RHIC

RHIC

Pb-Pb: K/π

STAR (including feed down)

PHENIX, Brahms (feed down corrected)

p/π

Particle Ratios

14

- pp: Thermus thermal fit rather poor

(wasn't this better for pp at lower energies ??)

- K/ππππ grows slightly from pp value

- p/ππππ ≈ like pp

Pb: p/ππππ off by factor > 1.5

from predictions !but very compatible with RHIC !! ?

pp: 900 GeV & 7 TeV

Range of Thermal model prediction

Before we can conclude anything

we need more particle species..

'Baryon anomaly': ΛΛΛΛ/K0

15

Baryon/Meson ratio still strongly enhanced

x 3 compared to pp at 3 GeV

- Enhancement slightly larger than at RHIC 200 GeV

- Maximum shift very little in pT

compared to RHIC

despite large change in underlying spectra !

Ratio at Maximum

RHIC

Λ/K0

x 3

16

Does QGP Flow?

Ed 3Nd 3p

= 12π

d2NpTdpTdy

1+ 2vn cosn φ − Ψr( )[ ]n=1

∞∑

Angle of reaction planeFourier coefficient

φ

pT

Equal energy density contours

P

v2

v2 = cos2φ

V1 = directed flow. V2 = elliptic flow.

Study angular dependence of emitted particles

17

Elliptic Flow

� v2 shape is identical to

RHIC

� v 2 ~30% larger than

RHIC: larger <pT>

� π,K reproduced by

hydro calculation

� p ok for semi-

peripheral but is a

remaining challenge for

central collisions

ALICE, Phys. Rev. Lett. 105 (2010) 252302.

Hydro-calcs.: Shen, Heinz, Huovinen and Song, arXiv:1105.3226.

� Precision measurement of η/s:� current RHIC limit: η/S < (2-5) x 1/4π� η/S < 1/4π => conjectured AdS/CFT limit is wrong� η/S > 1/4π => measure σ� η/S ≈ 1/4π => quantum corrections

which are O(10-30%) in AdS/CFT!� 20% in v2 ~ 1/4π =>π =>π =>π => need few % precision

�Precision: How ? � fix initial conditions (geometrical shape is model dependent, eg Glauber, CGC)� quantify flow fluctuations σ (influence measured v2, depending on method)� measure non-flow correlations δδδδ (eg jets)� improve theory precision (3D hydro, 'hadronic afterburner', ...)� .........

18

Azimuthal Flow:

What next ?

ση mkT2=

22

22

}4{

}2{

nnn

nnn

vv

vv

σδσ

−≅

++≅

19

Higher Harmonics: v3,

v4, v5, ...

� fluctuations in the initial distribution

� non zero v3

� particle correlation is described by first five harmonics

Chiral Magnetic Effect

('strong parity violation')( )RPΨ−+ 2cos βα ϕϕ

B+-

Same charge correlations positiveOpposite charge correlations negativeRHIC ≈ LHCsomewhat unexpected

should decrease with Nchmay decrease with √s

RHIC : (++), (+-) different sign and magnitudeLHC: (++),(+-) same sign, similar magnitude?

( )βα ϕϕ −cos

+ -

B

?

RHIC

RHIC

Local Parity Violation in strong magnetic Field ?

21

Charged Jets in Pb-Pb

Large suppression of jets seen in central collisions

192 GeV168 GeV

10-20% peripheral

∆η∆η∆η∆η∆φ∆φ∆φ∆φ bin size: 0.1x0.147 GeV

102 GeV

0-10% central

∆η∆η∆η∆η∆φ∆φ∆φ∆φ

Back-to-back high-energy jets seen in peripheral collisions

Another way to study this effect is to look at high pTsuppression.

22

Nuclear Modification Factor

• particle interaction with

medium

• stronger suppression at LHC

• ~factor 7 at 7 GeV/c

TDppcoll

TDAA

TDAA dpdN

dpdpR

/

/)(

σσ

×><=

quark-gluon plasma

Divide pT

spectra in Pb-Pb by p-p

(with suitable normalisation factor)

RAA

vs centrality

• Suppression

increases with

centrality.

• Minimum remains

around 6-7 GeV

RAA

for different particles

Peripheral collisions

Central collisions

25

Charm Cross-Section in pp

26

RAA

Open Charm:

Nuclear Modification Factor

• mass ordering predicted: ∆E(π) > ∆E(D) > ∆E(B)

• charm RAA

is approaching πat p

T> 6 GeV/c

• Possible indication of smaller charm suppression at low p

T but overall

comparable with πs.

TDppcoll

TDAA

TDAA dpdN

dpdpR

/

/)(

σσ

×><=

27

RAA

Heavy Quarks to Leptons:

Nuclear Modification Factor

• semi-leptonic decays:

• b, c → e+X

• b, c → µ+X

• heavy quark suppressed

by factor ~ 3

• B feed-down

uncorrected

28

J/ψψψψ in Pb-Pb

•J/ψ→e+ e-

•J/ψ→µ+µ-

29

RAA

J/ψψψψ:

Nuclear Modification Factor

TDppcoll

TDAA

TDAA dpdN

dpdpR

/

/)(

σσ

×><=

• J/ψ suppressed by factor ~ 2

• inclusive J/ψ: ~10% B feed-down

• cold nuclear effect not

measured: need pPb collisions

• small centrality dependence

• a test of statistical hardonization

will need data in mid rapidity:

PbPb runs in this year

Inclusive J/ψψψψ RAA = 0.49 ±±±± 0.03 (stat.)

±±±± 0.08 (syst.)

Rather small suppression and less than at RHIC

30

LHC: Tentative Schedule

2010: long run with pp collisions at 7 TeV

08-Nov-2010: 1st Pb+Pb collisions at 2.76 TeV

2011: short run with pp at 2.76 TeV

long run with pp at 7 TeV

2nd Pb+Pb collisions at 2.76 TeV – 10x stats ?

2012: long run with pp at 7 TeV

2012/2013: Pb+Pb; or p+Pb control measurement

2013/14: Machine shutdown

2014 - : pp and Pb+Pb at full energy

Summary

� Charged particle multiplicity ~ factor 2 larger than RHIC

� energy density ~ 3 x RHIC

� 2 x volume, 40% longer lived than RHIC

� baryon anomaly still exists at LHC (similar to RHIC)

� stronger radial flow at LHC (β ~ 0.66)

� elliptic flow: v2

increases from RHIC to LHC

� same centrality and pT

dependence

� High PT

suppression (RAA): suppression stronger at LHC

� suppression decreases at pT

> 5-6 GeV

� no strong flavour dependence

� J/ψ has smaller suppression

�We are at the very beginning of a 10 year programme and have just

scratched the surface (with ~1% of required data).

� lots of work and exciting physics to look forward to.

� Thank you for listening