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ALICE Status

Orlando Villalobos Baillie

University of Birmingham

NuPECC Meeting Edinburgh 10th October 2014

ALICE Physics We collide lead ions (& p-p, p-Pb) to study QCD at extreme

energy densities over large volumes and long time-scales.

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Study the role of chiral symmetry in the generation of mass in hadrons (accounts for ~ 99% of mass of nuclear matter). Study the nature of quark confinement. Study the QCD phase transition from nuclear 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).

QCD Phase Diagram

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Early

Uni

vers

e

ALICE

colour

Only gauge theory phase transition accessible to experiment

Heavy Ion Collisions

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Colliders: AGS, SPS, RHIC, LHC

Create QGP by colliding ultra-relativistic heavy ions

SNN (GeV) = 5.4 19 200 2760 (5500)

Jets

Open charm, beauty

Probe properties of QGP by studying characteristics of all particles produced in collisions.Use p-p & p-Pb collisions as baseline.

ALICE Physics

• A lot of high-quality data to work with from the PbPb, pPb and pp runs

• The harvest of results continues– Over 60 journal publications so far– The impact of physics publications remains

extremely high - after the 4 Higgs discovery papers the next three highest cited LHC physics papers come from ALICE.

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Size: 16 x 26 metresWeight: 10,000 tonnesDetectors: 18

The ALICE Experiment

Collaboration:> 1300 Members> 120 Institutes > 35 countries

Birmingham-built Central Trigger ProcessorElectronic Brain of the detector.

Some Highlights of Run 1• We have measured many of the global features

– Phase transition temperature - Agrees with theory Tc ~ 164 MeV

– Energy density - Over 10x critical energy density, > 15 GeV/fm3 (> 3X RHIC)

– size & lifetime of system ~ 5000 fm3, ~ 10-11 fm/c – Highest temperature ever measured (from low pT photon

spectrum)– Very strong radial flow, b ≈ 0.66

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Thermal Models

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Fit to extended set of particle species using an equilibrium model (SHARE). 2/ndf ~ 2

One of the largest contributions to 2 comes from low yield of protons w.r.t. pions.

QGP is Perfect Liquid

• Elliptic Flow:• Collective effects

of data fit hydro-dynamical models

• Most ideal liquid ever created

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x

z

y

React

ion

Plane

Viscosity/Entropy density, h/S 0.2

AdS/CFT prediction limit: h/S > 1/4 p ≈ 0.08

Study angular dependence of emitted particles

Flow – Ideal Liquid

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V2 = elliptic flowCollective effects of data fit hydro-dynamical models Most ideal liquid ever created

Evidence for flow from D-mesons suggests collective effects from charm. More data needed (Run 2)

Jet Quenching

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Large suppression of jets seen in central collisions

192 GeV168 GeV

10-20% peripheral

DhDf

47 GeV

102 GeV

0-10% central

DhDf

High pT Suppression (RAA)

• High pT particles supressed by factor 7 in central Pb-Pb w.r.t. weighted p-p data

• No such suppression seen in p-Pb

• Direct photons, of course, not supressed in Pb-Pb.

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TDppcoll

TDAA

TDAA dpdN

dpdpR

/

/)(

< 1 : Medium effect= 1 : No medium effect

First measurement of RD

AA/Rp

AAProbe QGP with different quark flavours: u, d, s, c (b only after upgrade)Theoretical expectation: E

light quark

> Emassive quark

First indication of mass effects ?High pT Suppression of charm

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p and Pb at the LHC

• When b > (R1 + R2), hadronic interactions are very much suppressed, and photon processes become important.

• Photon flux Z2 • Photons are quasi-real; virtuality

limited by size of nuclei.

• from p Q2~ (250 MeV)2

• from Pb Q2 ~ (35 MeV)2

• Photon energy determined by boost of emitting particle.

• from p (4 TeV):• from Pb:

2 2( / )Q c R

max 1200 GeVE max 50 GeVE

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J/ photoproduction

• J/ photoproduction cross-section is proportional to square of gluon structure function (at LO)

• J/ sets a hard scale GeV2.

• At LHC energies, xBj~10-2-10-5 is accessible.

• J/ photoproduction in Pb-Pb UPC gives information on gluon shadowing in nuclei at low x.

*2

p/P

3 2p/Pb 2s5

em /b

d ( 0) 16

d 3,ee

J

Gt

Qt

xM

Q

2

A 2 Ag 2

p

( , )( , )

,

G x QR x Q

G x Q

Leading Order

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p-Pb Measurements• Our knowledge

of the photon emitter allows us to solve for (Wp) using the measured d/dy

• A power law fit ((W)~W) to ALICE data points gives =0.670.06.

p

d dp Pb p Pb /

d d

nJ k W

y k

HERA MeasurementsH1 =0.670.03ZEUS =0.690.02

ALICE Upgrade

17Opens a new and unique window of discovery with rare charm and beauty physics

ALICE Upgrade • Focus on rare probes, study their coupling with QGP medium and

their (medium-modified) hadronisation process– precision studies of charm and beauty at low-pT

– low mass lepton pairs and thermal photons– -jet and jet-jet with particle identification from low momentum up to 30 GeV.– exotic nuclear states

• low-transverse momentum observables (complementary to the general purpose detectors ATLAS and CMS)– Many features not triggerable => need to examine full statistics.– Target:

• Pb-Pb recorded luminosity ≥ 10 nb-1 8 x 1010 events• pp (@5.5 Tev) recorded luminosity ≥ 6 pb-1 1.4 x 1011 events• Gain a factor 100 over the statistics of the approved programme

• Operate ALICE at high rate while preserving its uniqueness, superb tracking and PID, and enhance its vertexing capability and tracking at low-pT 18

Summary of Upgrades

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Trigger electronics (CTP + LTUs)

Muon Forward Tracker (MFT)

Muon Arm Readout

Data Acquisition (DAQ)High Level Trigger (HLT)

MAPS Inner Tracking System (ITS)

UK ObjectivesTo build upon and significantly enhance the UK’s current prominence & leadership in ALICE.• Design, build & commission new trigger system for ALICE

Upgrade– Build upon the Birmingham’s existing leadership & prominence within

ALICE. (Responsible for the current trigger system. Represented on the ALICE Management, Technical, & Physics Boards)

• To make a major contribution to the Inner Tracking System (ITS) Upgrade.– The key sub-detector for the proposed enhanced physics programme

post Long Shutdown 2 (LS2).– Utilise the strong international reputation of Liverpool & Daresbury in

Si tracking systems.– Significantly strengthen the UK’s role in this important field and place

us in an ideal position to fully exploit ALICE physics post LS2. 20

An exciting long-term Research Programme at the LHC Related STFC Roadmap questions: • How did the universe begin and how is it evolving?

• What is the physics of the early universe?

• What are the fundamental constituents and fabric of the universe and how do they interact?

• What is the nature of nuclear and hadronic matter?

Studying the phase diagram of strongly interacting matter• New probes, properties of deconfined matter• Thermodynamics of the Standard Model?

A major opportunity for UK to play a leading role in:• Construction of ALICE Upgrade (Trigger and Inner Tracking System)

Summary