23 Juin 2003 Yves Schutz 1 ALICE A Large Ion Collider Experiment

23 Juin 200323 Juin 2003 Yves SchutzYves Schutz 11

ALICEALICE

A Large Ion Collider A Large Ion Collider ExperimentExperiment


ALICEALICE

The club of those who smash atomic nuclei The club of those who smash atomic nuclei against each other…against each other…• Why ?Why ? Attempt to dissolve the vacuum and rewind the Attempt to dissolve the vacuum and rewind the

timetime• How ?How ? Heat and compress matter Heat and compress matter• Observe a phenomenon which: Observe a phenomenon which:

Lasts in a second as much as a lightening in the 15 billions Lasts in a second as much as a lightening in the 15 billions years elapsed since the birth of the universe, years elapsed since the birth of the universe,

Creates a temperature equal to 100,000 times the Creates a temperature equal to 100,000 times the temperature in the heart of the sun andtemperature in the heart of the sun and

Compresses matter to densities such as all matter Compresses matter to densities such as all matter contained in the Kheops pyramid would fill a volume of the contained in the Kheops pyramid would fill a volume of the size of a pinhead. size of a pinhead.

Recreate “color”


In the heart of matterIn the heart of matter

Matter is built up from “elementary” particles, the mass is Matter is built up from “elementary” particles, the mass is concentrated inside the atomic nucleus.concentrated inside the atomic nucleus.

Stable matter in the universe is made of 4 elementary Stable matter in the universe is made of 4 elementary particles.particles.

O(10-10 m) O(10-15 m) < O(10-19 m)

QUARKS LEPTONS

é

é


The Standart ModelThe Standart Model

• The theory which explains the bricks of the universe and the forces through which they interact:

12 elementayconstituents

4 interactions

graviton photon W, Z gluon


Open questionsOpen questions

How did particles acquire mass ? How did particles acquire mass ? mm,g,g=0, m=0, mtt = 340.000 m = 340.000 me e !!

Does there exist an universal force from Does there exist an universal force from which all other forces derive ?which all other forces derive ?

Why does there exist 3 families of particles ?Why does there exist 3 families of particles ? What happened to anti matter ?What happened to anti matter ? Why is the stable universe colorless ?Why is the stable universe colorless ? What is the structure of the vacuum ?What is the structure of the vacuum ? What was the form of primordial matter ?What was the form of primordial matter ? Where does the mass of composite particles Where does the mass of composite particles

come from ?come from ?


Quantum Chromodynamics : the theory Quantum Chromodynamics : the theory of the strong interactionof the strong interaction

A formal theory:A formal theory:• Quarks carry a charge called Quarks carry a charge called ccoolloorr; there are 3 colors ; there are 3 colors RR, , BB, , GG

• Quarks interact by exchanging a gluon (mQuarks interact by exchanging a gluon (mgg=0) which carries a =0) which carries a color charge and its anti-charge !color charge and its anti-charge !

• The strong interaction is strong at large distance and weak at The strong interaction is strong at large distance and weak at small distance !small distance !

• The vacuum is filled with virtual quarks and anti-quarks pairsThe vacuum is filled with virtual quarks and anti-quarks pairs

• Observables can be calculated only when the interaction is weak !Observables can be calculated only when the interaction is weak !

MFFDiL aa

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1


Quantum Chromodynamics : the theory Quantum Chromodynamics : the theory of the strong interactionof the strong interaction

Empirical adds on:Empirical adds on:

• Quarks (valence) are bound inside Quarks (valence) are bound inside hadrons (baryons and mesons) such as to hadrons (baryons and mesons) such as to form colorless objectsform colorless objects

• Interactions of valence quarks with the Interactions of valence quarks with the vacuum contribute to the mass of vacuum contribute to the mass of hadronshadrons

• It is not possible to isolate a color chargeIt is not possible to isolate a color charge

q q

F=kR1

q q

F=kR2

q q

F=kr2

qq

F=kr1


Big Bang …Big Bang …Until 10-6 secondsafter the birth of the Universe, matter is colored: quarks and gluons move freely.

As soon as the universe has cooled down to about 1012 K, matter becomes colorless: quarks and gluons are locked forever in particles out of which only protons and neutrons have survived.


Let’s go backwardsLet’s go backwards

Why ?Why ? • Observe the strong interaction in actionObserve the strong interaction in action

How do elementary particles interactHow do elementary particles interact How did the interaction give rise to the How did the interaction give rise to the

composite particles which constitute the composite particles which constitute the universeuniverse


Let’s go backwardsLet’s go backwards How ?How ?

• Heating the vacuum to create high energy densities over Heating the vacuum to create high energy densities over a mesoscopic volumea mesoscopic volume

• Collisions between heavy ions accelerated at the speed Collisions between heavy ions accelerated at the speed of light provide the necessary “calories” of light provide the necessary “calories”

Compression Chaleur Plasma de quarks et gluons


Laboratory

2. The energy of collision is materialized into quarks and gluons

1. Accelerated ions will collide head on

The mini Big BangThe mini Big Bang

3. Quarks and gluons interact via the strong interaction: matter equilibrates

v/c = 0,99999993Lorentz Contraction: 7 fm 0,003 fm

t~10-24 sT~5×1012 K

4. The system expands and cools down

5. Quarks and gluons condensate into hadrons

t~10-23 sT~1012 K


Mini Big Bang : the movieMini Big Bang : the movie


Accelerating nucleiAccelerating nuclei Nuclei (atomes stripped off Nuclei (atomes stripped off

electrons) are accelerated by electrons) are accelerated by an electric fieldan electric field

The trajectory of nuclei are The trajectory of nuclei are bent by dipolar magnetic bent by dipolar magnetic fieldsfields

The flux of nuclei are focalised The flux of nuclei are focalised by quadrupol magnetic fieldsby quadrupol magnetic fields


LHC: world championLHC: world champion• 27 km circumference• 40 m underground• Cryogeny at 1.9 K

×10

12 Accelerates p @ 7×10Accelerates p @ 7×101212 eV & ions @ 2,76×10 eV & ions @ 2,76×101212 eV (99.999993% c) eV (99.999993% c) A collision generates up to 0,2×10A collision generates up to 0,2×10-3-3 Joules, T=1,000×10 Joules, T=1,000×1099 K K ~10~1088 ions cross 10 ions cross 1088 ions 10 ions 1066 times every second times every second Only 8.000 collisions every second, out of which 1% produce Only 8.000 collisions every second, out of which 1% produce

”extraordinary” events ”extraordinary” events


Thermodynamics : water, a known Thermodynamics : water, a known casecase

• Phase diagram; Equation of state (PV/T = Cte)• Phases and Phase transitions• Ordre of the transition and critical point


Thermodynamics of matter Thermodynamics of matter

We are here

The Big Bang started here

Pb collisions at LHC will take us there

And we will study this trajectory


QCD tells us…QCD tells us…

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Tc 173 MeV, mq0, Nf=2,3 Order of the transition : cross over c 0.3-1.3 GeV/fm3


Observing the phenomenonObserving the phenomenon Imagine…Imagine…

• You lived in a frozen world where water existed only as ice• and ice comes in only quantized sizes ~ ice cubes• and theoretical friends tell you there should be a liquid phase• and your only way to heat the ice is by colliding two ice cubes• So you form a “bunch” containing a billion ice cubes• which you collide with another such bunch• 10 million times per second• which produces about 1000 IceCube-IceCube collisions per

second• which you observe from the vicinity of Mars

Change the length scale by a factor of ~1013

You’re doing physics at LHC !


ALICE : The answer to the ALICE : The answer to the challengechallenge


The todo programThe todo program About 16.000 particles cross the detectors in each collision ; the About 16.000 particles cross the detectors in each collision ; the

particle density reaches 90 particles per cmparticle density reaches 90 particles per cm22, near the interaction , near the interaction point !point !

Measure every particle individually: count them, localise their Measure every particle individually: count them, localise their trajectory, identify their nature, establish their 4-momentum ; trajectory, identify their nature, establish their 4-momentum ;

Localise the origin within a few Localise the origin within a few m ;m ;

Identify the interesting rare events in less than 100 Identify the interesting rare events in less than 100 s ;s ;

Store data 1,2 Go/s (2 CD/s) et 1 Po/an (a 4 Km high CD pile) ;Store data 1,2 Go/s (2 CD/s) et 1 Po/an (a 4 Km high CD pile) ;

Give access of data to 1,000 physicists spread in 80 institutes in Give access of data to 1,000 physicists spread in 80 institutes in 28 countries.28 countries.


Un champ magnétiqueUn champ magnétique

Identify the charge

Measure the momentum

Greater momentum

Smaller momentum


Sensitive materials in the way of Sensitive materials in the way of the particlesthe particles

t=0 t=t2t=t1 t=t3 t=t4


Internal trajectography (ITS): p, id

ALICE : Many cells everywhere …ALICE : Many cells everywhere … To localise, segmenting the system in hundreds of millions of To localise, segmenting the system in hundreds of millions of

sensitive cells ; sensitive cells ; Surround the interaction point with detector enveloppesSurround the interaction point with detector enveloppes

Time projection chambre (TPC) : p, pid

Transition radiation detector (TRD):

électrons


… … and a few specialized detectorsand a few specialized detectors

Muons spectrometre :• Passif absorber • B dipole• Trajectographe• Filter• Trigger

Photons


How does it workHow does it work Internal trajectographe : 6 layers of Si diodes with 2D localisation Internal trajectographe : 6 layers of Si diodes with 2D localisation

m

Si-pSi-n

-HV


3 technologies Si3 technologies Si

256 anodes, 294 m pitch


How does it workHow does it work The main trajectographe : 1 time projection chamberThe main trajectographe : 1 time projection chamber

-HVE E

Arrival time


TPC ALICETPC ALICE

Readout plane segmentation

18 trapezoidal sectors

each covering 20 degrees in azimuth

EE

510 cm

EE

88s

GAS VOLUME88 m3

DRIFT GAS90% Ne - 10%CO2

Pb P

E

E

5 m

5.6 m

1.6

400 V / cm

NE / CO2 88s

End plate

Central electrode

Drift volume

Co2 insulation


Identification of particlesIdentification of particles

Measure energy loss

Trajectography: charge and momentum

Measure time of flight

p pp p

K K -


Still smarterStill smarter Distinguish relativistic electrons and pionsDistinguish relativistic electrons and pions

• When a relativisticparticle crosses an inhomogenuous medium an X ray is emitted

• Select the medium such as only electrons create the transition radiation

• Detect both the charged particle and the X ray

• Multi-wire chamber filled with a heavy gas (Xe)


And to be completeAnd to be complete Dense like lead and transparent like crystal to stop Dense like lead and transparent like crystal to stop

photons photons • Photons materialise as a cascade of electrons and positons

• Electrons excite atomes of the crystal

• Atomes deexcitent by emetting an UV radiation

•UV radiations are detected at one end of the crystal by a photodiode


From volts to bytesFrom volts to bytes

The signal of each cell (~16 millions) is procesed by The signal of each cell (~16 millions) is procesed by highly miniaturised electronic systems ;highly miniaturised electronic systems ;

The electric signal is digitalised to be processed by The electric signal is digitalised to be processed by computers ;computers ;

The information is transported by optical fibers.The information is transported by optical fibers.


Design the detectorDesign the detector Simulations : Simulations :

• Generate physics events at the best of our theoretical knowledgeGenerate physics events at the best of our theoretical knowledge

• Construct a virtual detecteor and simulate its response based of Construct a virtual detecteor and simulate its response based of our knowledge on the interactions of particles with matterour knowledge on the interactions of particles with matter

Tools :Tools :

• Programming techniques : object orientedProgramming techniques : object oriented

• Huge computing and storage capacities : distributed computingHuge computing and storage capacities : distributed computing


3 million volumes


What we should be prepared toWhat we should be prepared to

60 << 62 One collision : Pb+Pb @ 5.5 TeV

dN/dy = 8,000


What we should be prepared toWhat we should be prepared to

One event : p+p @ 14 TeV

20 collisions overlay


To process the dataTo process the data

Yerevan

CERN

Saclay

Lyon

Dubna

Capetown, ZA

Birmingham

Cagliari

NIKHEF

GSI

Catania

BolognaTorino

PadovaIRB

Kolkata, India

OSU/OSCLBL/NERSC

Merida

Bari

Nantes

Distributing ressources :• CPU• Data storage

Are distributed around the world


Exemple of physics signal (1)Exemple of physics signal (1)1. Ordinary matter1. Ordinary matter

Transverse momentum

dN

/dp

Fragmentationfunction

dN

/d

Relative angle

-180 O 18O


Exemple of physics signal (1)Exemple of physics signal (1)2. Quark matter2. Quark matter

Transverse momentum

dN

/dp

Fonction de fragmentation

dN

/d

Relative angle

-18O O 18O


Exemple of physics signal (2)Exemple of physics signal (2)1. Ordinary matter1. Ordinary matter

Mass

dN

/dp

J/cc


Exemple of physics signal (2)Exemple of physics signal (2)2. Quark matter2. Quark matter

Mass

dN

/dp

J/cc


ALICE todayALICE today

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23 Juin 2003 Yves Schutz 1 ALICE A Large Ion Collider Experiment