swedish teachers program 10/2012 1 alice a large ion collider experiment outline the quark-gluon...

Swedish teachers program 10/2012

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ALICEA Large Ion Collider

Experiment

Outline• The quark-gluon plasma :QGP;• The ALICE experiment and the particle

identification;• Data analysis and the scientific method.

G De Cataldo, INFN , Bari, It.

Thank you very much to Y. Schutz and D. Hatzifotiadou for their help

Countries in the ALICE collaboration


2G De Cataldo, INFN , Bari, It.

The ALICE collaboration




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The physics program of ALICE The club of physicists smashing head-on heavy

ions!…• Why ? Trying to de-confine quarks and gluons in a soup

(QGP) and stepping backward in the time up to one millionth of second after the Big Bang;

• How ? Heating and compressing nuclear matter (lead-lead nucleus collisions in LHC);

• Watching a phenomena that Lasts in one second as a light in the 15 billions of years

after the universe was born, Gets a temperature equal to 100.000 times the sun core

temperature and Squeeze the matter such that the pyramid of Cheops fits in

a needle’s head; The observer is on MARS while describing what is

happening on the Earth;G De Cataldo, INFN , Bari, It.


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Laboratory

2. The collision energy materialize in quarks and gluons.

1. The accelerated lead nucleus (ordinary matter) undergo head-on collisions.

The mini Big Bang :let’s re-do backward the path:

3. The de-confined quarks and gluons experience the Strong Interaction effects: this is the QGP! The soup then moves toward the equilibrium.

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

t~10-24 sT~5×1012 K

4. The plasma dilutes and cools down.

5. Quarks and gluons condensate to form hadrons, and between them the protons: the ordinary matter!

t~10-23 sT~1012 K


ALICE setup

ITS

TPC

TRD

TOFPHOS

HMPID

PMD

FMD

MUON SPEC.

But what does mean ‘to see’ in ALICE end how we do it??


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Tonneau central


Lead Collisions 2011


G De Cataldo, INFN , Bari, It. 7

Products of Pb-Pb collisions @ 2.76TeV for nucleon pairs (Nov. 2010)




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The scientific program About 5.000 particles cross the experiment on each collision;

Carry out the tracking procedure on each particle, identifying them one by one measuring their momenta, electric charge and finally the mass;

localize the track origin with about hundred mm precision;

Identify interesting and rare events in less than 100 ms ;

Archive data with a rate of 1,2 Mbytes/s (2 CD/s) which means 1 Pbytes/year (a CD stack of of 4 Km/y) ;

Give access to the data for the data analysis to about 1000 physicists spread out all over the world.


The kinetic energy of a proton accelerated from rest by 1V of difference of potential :

Ek = qV = (½ mpv2) (classic) q=1 (elementary charge; 1.6 x10-19 C) V=1 Volt E= 1 eV = 1.6x10-19 Joule

A mosquito is approaching you with a speed of 40 km / h. A collision will do nothing. A truck is approaching you with a speed of 40 km / h. A collision will be fatal! (move away!)This is because of the mass of the truck plays an important role. However, a stopped truck, does not scare you. So it is not only the mass, but also the speed, it is the momentum p that makes the difference!

The Kinetic Energie Ek

p = (pxi+pyj+pzk) = mv (classic)


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An oscillating Electric field in LHC (RF) accelerates the protons! Each proton beam @ 7 TeV has the same energy of a 400 t TGV launched at 150 Km / h! This energy is enough to 'melt 500 kg copper!


Physics complements for particle identification Momentum (p)



What does it means particle identification?

Identify a particle it means to measure: its momenta, electric charge and mass.

For what purpose the identification is useful for?

In order to study the QGP a good probe is to study the so called ‘strange particles’. For this we have to:1. First identify the daughter particles in the strange particle decay,

2. and form them look for the ‘strange’ parent particle! ’( see later the exercises).

Momentum measurement and electric charge identification


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p

qR=p/qB

p = momentum to be measuredR = curvature radiusB = magnetic field q = particle electric charge,

R


HMPID: particle identification by Cherenkov light



!!

TPC, TOF and ITS particle identification



Looking for “starnge” parent particle:the invariant mass for the particle identification


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Conservation laws: energy, momenta and electric charge. Then:E=E1+E2p=p1+p2Neutre=(+) + (-)

This makes me laughing!!!

After t10^-10 s

Summary:In order to identify the ‘parent’ particles then the electric charge, the momenta and finally the mass have to be measured on the particles daughter!

-

+

m1

p1

E1

m2

p2

E2

Daughter Particles after the decay

According to the relativity

E = m+pm= E- p

2 2 2

2 2 2

The invariant mas is then: m = m1+m2+2(E1*E2) -2(p1*p2)

2 2 2

mpE

Parent neutral particle before the decay

Inter.

Beam 2

Beam 1


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http://www.google.fr/imgres?imgurl=http://afrochild.files.wordpress.com/2011/01/einstein460x276.jpg&imgrefurl=http://afrochild.wordpress.com/2011/01/19/1192/&usg=__ksVyEggihw740DxrvZpt5SqlRNI=&h=276&w=460&sz=18&hl=fr&start=17&zoom=1&itbs=1&tbnid=4BSvV9XZFIyPFM:&tbnh=77&tbnw=128&prev=/images?q=albert+einstein&hl=fr&gbv=2&tbs=isch:1&ei=986FTf-DPMuSswaz-LWOAw

M

The distribution of the invariant mass


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m1

p1

E1

m2

p2

E2

m

For particles of the same type with random values of momenta, not related to the parent particle, then M=:

M = m1+m2+2(E1*E2)-2(p1p2)2 2 2


The decays to be studied in the excercise:


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Lambda

pion


V0 decay• A neutral particle (no tracks left) after its decay

produces suddenly two charged traces.• In a magnetic field particles of opposite electric

charge move in opposite directions.

® L pp+K0s ® pp

symmetric asymmetric

anti Λ→ π+p-




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For the data analysis: after the web, GRID is the CERN answer!

Yerevan

CERN

Saclay

Lyon

Dubna

Capetown, ZA

Birmingham

Cagliari

NIKHEF

GSI

Catania

BolognaTorino

PadovaIRB

Kolkata, India

OSU/OSCLBL/NERSC

Merida

Bari

Nantes

• The huge amount of data per event prevents the analysis to be carried out in ONLY ONE place even with hundred of computers! Then the idea was:

• Distribute the computation tasks all over the world! How?• CPU resources and data storage are spread out all over the world,

interconnected via INTERNET and in some a way synchronized. • Only with this virtual giant computer the data analysis can be carried out!

Great the physicists at CERN!


GRID!

Data analysis for the Physics : Geometry of a Pb-Pb collision

Azimuthal Asymmetry Y direction: longer particle trajectory then less particles that

get out; X direction: shorter particle trajectory then more particles that

get out; Studying this asymmetry we can study the nature of the

crossed de-confined matter.

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Reactionplane

In-planeOut

-of-

plan

e

Y

XFlow

Flo

w

Reactionplane

In-planeOut

-of-

plan

e

Y

XFlow

Flo

w

Reactionplane

In-planeOut

-of-

plan

e

Y

XFlow

Flo

w


Data analysis for the Physics : Geometry of a Pb-Pb collision

Peripheral Collision • Large distance between the nucleus

center(w.r.t nucleus size) , small number of participants then few charged particle produced (small multiplicity).

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Central Collision • small distance between the nucleus center,

high number of participants then many charged particle produced (large multiplicity).

And now some Physics

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As an example: the sum of the signal amplitude in the centrality detector, named V0, (the central the collision the higher the signal) is well represented by means of a simple physics model named Glauber (red line)

centralperiferal



Theories, models and Scientific Papers


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A theory is not true or false but good or bad depending on if it is predictive or not. We consider a theory as a good one until experiments will not provide different results from what predicted!

In the spirit of the scientific method (Galileo Galilei 1564-1642), that theory or physics models (less than a theory!) which doesn’t agree with the results is abandoned! Or modified! In the paper below this comparison is discussed.


Summary


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• LHC, smashing lead nucleus at an energy never reached before (5.5 ZTeV) can recreate a state of the matter, named Quark Gluon Plasma @10^12 ⁰C (QGP, a de-confined state of quarks and gluons) that should have existed few microseconds after the Big-Bang!

• The ALICE experiment has been designed for hunting evidences of the Quark Gluon Plasma state. It combines different techniques of detection that provide unique capabilities of particle identification among the four major experiments at LHC;

• Thanks to a very powerful computation network, GRID, ALICE can carry out the data analysis and compare the results with the model’s predictions;

• In the spirit of the experimental method (Galileo Galilei), some models are reinforced, others are abandoned or modified. This is the way humanity improves its knowledge on the fundamental laws of the nature!


swedish teachers program 10/2012 1 alice a large ion collider experiment outline the quark-gluon...

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