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

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Presentation on theme: "23 Juin 2003 Yves Schutz 1 ALICE A Large Ion Collider Experiment."— Presentation transcript:

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

2 23 Juin 2003 Yves Schutz 2 ALICE ALICE The club of those who smash atomic nuclei against each other… The club of those who smash atomic nuclei against each other… Why ? Attempt to dissolve the vacuum and rewind the timeWhy ? Attempt to dissolve the vacuum and rewind the time How ? Heat and compress matterHow ? 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 years elapsed since the birth of the universe, Lasts in a second as much as a lightening in the 15 billions years elapsed since the birth of the universe, Creates a temperature equal to 100,000 times the temperature in the heart of the sun and Creates a temperature equal to 100,000 times the temperature in the heart of the sun and Compresses matter to densities such as all matter contained in the Kheops pyramid would fill a volume of the size of a pinhead. Compresses matter to densities such as all matter contained in the Kheops pyramid would fill a volume of the size of a pinhead. Recreate “color”

3 23 Juin 2003 Yves Schutz 3 In the heart of matter Matter is built up from “elementary” particles, the mass is concentrated inside the atomic nucleus. Matter is built up from “elementary” particles, the mass is concentrated inside the atomic nucleus. Stable matter in the universe is made of 4 elementary particles. Stable matter in the universe is made of 4 elementary particles. O( m)O( m)< O( m) QUARKS LEPTONS é é

4 23 Juin 2003 Yves Schutz 4 The Standart Model The theory which explains the bricks of the universe and the forces through which they interact: 12 elementay constituents 4 interactions gravitonphotonW, Zgluon

5 23 Juin 2003 Yves Schutz 5 Open questions How did particles acquire mass ? m ,g =0, m t = m e ! How did particles acquire mass ? m ,g =0, m t = m e ! Does there exist an universal force from which all other forces derive ? Does there exist an universal force from 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 come from ? Where does the mass of composite particles come from ?

6 23 Juin 2003 Yves Schutz 6 Quantum Chromodynamics : the theory of the strong interaction A formal theory: A formal theory: Quarks carry a charge called color; there are 3 colors R, B, GQuarks carry a charge called color; there are 3 colors R, B, G Quarks interact by exchanging a gluon (m g =0) which carries a color charge and its anti-charge !Quarks interact by exchanging a gluon (m g =0) which carries a color charge and its anti-charge ! The strong interaction is strong at large distance and weak at small distance !The strong interaction is strong at large distance and weak at 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 !

7 23 Juin 2003 Yves Schutz 7 Quantum Chromodynamics : the theory of the strong interaction Empirical adds on: Empirical adds on: Quarks (valence) are bound inside hadrons (baryons and mesons) such as to form colorless objectsQuarks (valence) are bound inside hadrons (baryons and mesons) such as to form colorless objects Interactions of valence quarks with the vacuum contribute to the mass of hadronsInteractions of valence quarks with the vacuum contribute to the mass of hadrons It is not possible to isolate a color chargeIt is not possible to isolate a color charge q q F=kR 1 q q F=kR 2 q q F=kr 2 q q F=kr 1

8 23 Juin 2003 Yves Schutz 8 Big Bang … Until seconds after the birth of the Universe, matter is colored: quarks and gluons move freely. As soon as the universe has cooled down to about K, matter becomes colorless: quarks and gluons are locked forever in particles out of which only protons and neutrons have survived.

9 23 Juin 2003 Yves Schutz 9 Let’s go backwards Why ? Why ? Observe the strong interaction in actionObserve the strong interaction in action How do elementary particles interact How do elementary particles interact How did the interaction give rise to the composite particles which constitute the universe How did the interaction give rise to the composite particles which constitute the universe

10 23 Juin 2003 Yves Schutz 10 Let’s go backwards How ? How ? Heating the vacuum to create high energy densities over a mesoscopic volumeHeating the vacuum to create high energy densities over a mesoscopic volume Collisions between heavy ions accelerated at the speed of light provide the necessary “calories”Collisions between heavy ions accelerated at the speed of light provide the necessary “calories” CompressionChaleur Plasma de quarks et gluons

11 23 Juin 2003 Yves Schutz 11 Laboratory 2. The energy of collision is materialized into quarks and gluons 1. Accelerated ions will collide head on The mini Big Bang 3. Quarks and gluons interact via the strong interaction: matter equilibrates v/c = 0, Lorentz Contraction  : 7 fm  0,003 fm t~ s T~5×10 12 K 4. The system expands and cools down 5. Quarks and gluons condensate into hadrons t~ s T~10 12 K

12 23 Juin 2003 Yves Schutz 12 Mini Big Bang : the movie

13 23 Juin 2003 Yves Schutz 13 Accelerating nuclei Nuclei (atomes stripped off electrons) are accelerated by an electric field Nuclei (atomes stripped off electrons) are accelerated by an electric field The trajectory of nuclei are bent by dipolar magnetic fields The trajectory of nuclei are bent by dipolar magnetic fields The flux of nuclei are focalised by quadrupol magnetic fields The flux of nuclei are focalised by quadrupol magnetic fields

14 23 Juin 2003 Yves Schutz 14 LHC: world champion LHC: world champion 27 km circumference 40 m underground Cryogeny at 1.9 K ×10 12 Accelerates 7×10 12 eV & 2,76×10 12 eV ( % c) Accelerates 7×10 12 eV & 2,76×10 12 eV ( % c) A collision generates up to 0,2×10 -3 Joules, T=1,000×10 9 K A collision generates up to 0,2×10 -3 Joules, T=1,000×10 9 K ~10 8 ions cross 10 8 ions 10 6 times every second ~10 8 ions cross 10 8 ions 10 6 times every second Only collisions every second, out of which 1% produce ”extraordinary” events Only collisions every second, out of which 1% produce ”extraordinary” events

15 23 Juin 2003 Yves Schutz 15 Thermodynamics : water, a known case Phase diagram; Equation of state (PV/T = Cte) Phases and Phase transitions Ordre of the transition and critical point

16 23 Juin 2003 Yves Schutz 16 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

17 23 Juin 2003 Yves Schutz 17 QCD tells us…  T c  173 MeV, m q  0, N f =2,3  Order of the transition : cross over   c  GeV/fm 3

18 23 Juin 2003 Yves Schutz 18 Observing 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 ~10 13 You’re doing physics at LHC !

19 23 Juin 2003 Yves Schutz 19 ALICE : The answer to the challenge

20 23 Juin 2003 Yves Schutz 20 The todo program About particles cross the detectors in each collision ; the particle density reaches 90 particles per cm 2, near the interaction point ! About particles cross the detectors in each collision ; the particle density reaches 90 particles per cm 2, near the interaction point ! Measure every particle individually: count them, localise their trajectory, identify their nature, establish their 4-momentum ; Measure every particle individually: count them, localise their trajectory, identify their nature, establish their 4-momentum ; Localise the origin within a few m ; Localise the origin within a few m ; Identify the interesting rare events in less than 100 s ; Identify the interesting rare events in less than 100 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 28 countries. Give access of data to 1,000 physicists spread in 80 institutes in 28 countries.

21 23 Juin 2003 Yves Schutz 21 Un champ magnétique Identify the charge Measure the momentum Greater momentum Smaller momentum

22 23 Juin 2003 Yves Schutz 22 Sensitive materials in the way of the particles t=0t=t 2 t=t 1 t=t 3 t=t 4

23 23 Juin 2003 Yves Schutz 23 Internal trajectography (ITS): p, id ALICE : Many cells everywhere … To localise, segmenting the system in hundreds of millions of sensitive cells ; To localise, segmenting the system in hundreds of millions of sensitive cells ; Surround the interaction point with detector enveloppes Surround the interaction point with detector enveloppes Time projection chambre (TPC) : p, pid Transition radiation detector (TRD): électrons

24 23 Juin 2003 Yves Schutz 24 … and a few specialized detectors Muons spectrometre : Passif absorber B dipole Trajectographe Filter Trigger Photons

25 23 Juin 2003 Yves Schutz 25 How 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-p Si-n -HV      

26 23 Juin 2003 Yves Schutz 26 3 technologies Si 256 anodes, 294  m pitch

27 23 Juin 2003 Yves Schutz 27 How does it work The main trajectographe : 1 time projection chamber The main trajectographe : 1 time projection chamber -HV EE                Arrival time 

28 23 Juin 2003 Yves Schutz 28 TPC ALICE Readout plane segmentation 18 trapezoidal sectors each covering 20 degrees in azimuth E E 510 cm E E 88  s GAS VOLUME 88 m 3 DRIFT GAS 90% Ne - 10%CO 2 PbP E E 5 m 5.6 m V / cm NE / CO 2 88  s End plate Central electrode Drift volume Co 2 insulation

29 23 Juin 2003 Yves Schutz 29 Identification of particles Measure energy loss Trajectography: charge and momentum Measure time of flight p K K -  

30 23 Juin 2003 Yves Schutz 30 Still smarter Distinguish relativistic electrons and pions Distinguish relativistic electrons and pions When a relativisticparticle 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)

31 23 Juin 2003 Yves Schutz 31 And to be complete Dense like lead and transparent like crystal to stop photons Dense like lead and transparent like crystal to stop 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

32 23 Juin 2003 Yves Schutz 32 From volts to bytes The signal of each cell (~16 millions) is procesed by highly miniaturised electronic systems ; The signal of each cell (~16 millions) is procesed by highly miniaturised electronic systems ; The electric signal is digitalised to be processed by computers ; The electric signal is digitalised to be processed by computers ; The information is transported by optical fibers. The information is transported by optical fibers.

33 23 Juin 2003 Yves Schutz 33 Design 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 our knowledge on the interactions of particles with matterConstruct a virtual detecteor and simulate its response based of our 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

34 23 Juin 2003 Yves Schutz 34 3 million volumes

35 23 Juin 2003 Yves Schutz 35 What we should be prepared to 60  <  < 62  One collision : 5.5 TeV dN/dy = 8,000

36 23 Juin 2003 Yves Schutz 36 What we should be prepared to One event : 14 TeV 20 collisions overlay

37 23 Juin 2003 Yves Schutz 37 To process the data Yerevan CERN Saclay Lyon Dubna Capetown, ZA Birmingham Cagliari NIKHEF GSI Catania Bologna Torino Padova IRB Kolkata, India OSU/OSC LBL/NERSC Merida Bari Nantes Distributing ressources : CPU Data storage Are distributed around the world

38 23 Juin 2003 Yves Schutz 38 Exemple of physics signal (1) 1. Ordinary matter Transverse momentum dN/dp Fragmentation function dN/d  Relative angle -180O18O

39 23 Juin 2003 Yves Schutz 39 Exemple of physics signal (1) 2. Quark matter Transverse momentum dN/dp Fonction de fragmentation dN/d  Relative angle -18OO18O

40 23 Juin 2003 Yves Schutz 40 Exemple of physics signal (2) 1. Ordinary matter Mass dN/dp  J/cc

41 23 Juin 2003 Yves Schutz 41 Exemple of physics signal (2) 2. Quark matter Mass dN/dp  J/cc

42 23 Juin 2003 Yves Schutz 42 ALICE today


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