quark-gluon plasma from big bang to little bang · 2015. 6. 12. · ntnu seminar, 2015/06/04...

NTNU Seminar, 2015/06/04 陳勁豪 1

Quark-Gluon Plasma From Big Bang to Little Bang

John Chin-Hao Chen 陳勁豪

LeCosPA, NTU

NTNU Seminar, 2015/06/04


Outline

● What is quark gluon plasma (QGP)?● Some properties of QGP● From little bang to tiny bang


Everything Starts with an Atom…

● Everything is made of atoms● Atoms are made of protons

and neutrons (nucleons)● The protons and neutrons are

made of quarks.

• Quarks are the most fundamental blocks of the matter


Quarks are confined

● Quarks are confined in protons and neutrons

● The further quarks apart, the stronger the force; the closer the quarks, the weaker the interaction

● What will happen if we increase the energy “high enough”?

PDG 2014


Energy density frontier

● The universe starts from a big bang● As time goes by, big fireball starts to cool off● What is the very beginning of the universe

looks like?


How do we melt the ice?

● We heat up the ice● It will melt at critical temperature (0 Celsius)● A phase transition from ice to water


Phase transition of nuclear matter?


How do we melt the nucleon?

But how hot do we need?


Where in the universe can we achieve this extreme condition?

● In nature: T~1012 K: 10-6 second after the big bang● How about man-made conditions?


Creating the Mini-Bang

● Collides p+p, Au+Au and other species (Cu+Cu, Cu+Au, U+U) at various energies (√s

NN = 7.7-200 GeV)!!

● Maximum energy: Au+Au at √sNN

= 200 GeV per nucleon pair

● Each Au nucleus has 197 nucleons, so the energy carried by each Au is 100 GeV * 197 = 19.7 TeV


The birth of J/ψ


The birth of J/ψ

● Found by Sam Ting at AGS● p+Be collision!


What happens in heavy ion collisions

● The beams travel at 99.995% the speed of light.● The two ions look flat as a pancake due to Relativity. (γ~106 at full

energy collision @ RHIC).● The two ions collide and smash through each other for 10-23 s● The collision “melts” protons and neutrons, and liberates the quark

and gluons.● Thousands of particles are created and fly out from the collision area;

plasma cools off.


Detectors at RHIC

STARspecialty: large acceptancemeasurement of hadrons

PHENIXspecialty: rare probes, leptons,

and photons


Events viewed by detectors

~1500 charged particles are created in one Au+Au collisions!


Seen in many places!


A even hotter matter at LHC

● The Large Hadron/Heavy Ion Collider● Three experiments: ATLAS, CMS, ALICE (dedicated HI

experiment)● Collides Pb+Pb @ √sNN = 2.76 TeV, p+Pb at 5.02 TeV, and p+p

at √s = 2.76 TeV for reference (LHC run1)● For LHC run2, Pb+Pb will collide at √sNN = 5.5 TeV


Some properties of QGP will be discussed

● How hot is QGP?● How do quarks move in the QGP?● How do quarks interact with QGP?


Some useful terminology

Central collision:

the two nuclei collide “head on”. Most energetic collisions, with highest multiplicity. Roughly 300-350 participating nucleons.

Peripheral collision:

the two nuclei touch by edge, with fewer multiplicity. Roughly ~10 participating nucleons

p+p collision: no QGP (at least at RHIC energy)

Au: 197 nucleons


How do we know the temperature?

● When things are heated, they glow (emit photons)

● By measuring the emitted photon spectrum, we can measure the temperature of the object


How do we measure the temperature of QGP?

● We measured the photons emitted from pp and AuAu collisions

● We see enhancement in of photon yield in AuAu– Similar to black body radiation

from QGP!!– T ~ 220 MeV – Tc ~175 MeV

– Or 4 trillion degrees Celsius– Or 250000 times hotter than

the center of the Sun

enhancement

pp

AuAu

Nu

mb

er o

f p

ho

ton

s


How do the particles move?● Collision area has “almond”

shape due to overlap geometry of the nuclei.

● Almond shape leads to un-uniform momentum distribution.

● Pressure gradient pushes the “almond” harder in the short direction.

● For a symmetric colliding area, v

odd = 0

● If v2 = 0 → particle distributed

homogeneously in φ direction


v2 vs p

T

● Au+Au vs Cu+Cu– Size difference– Geometry difference (different

eccentricity, ε)

● Non-zero v2

● Central collisions (0-10%): smaller v

2

● Mid-central collisions (30-40%): larger v

2


Geometry dependence

● Different geometry of the interaction area leads to different v

2

● Use the eccentricity to remove the geometrical contributions

● Central collision, ε2 ~ 0

● ε2 increases when moving to

peripheral collisions


v2 vs p

T

After normalized by ε2,

Au+Au/Cu+Cu in different centralities follows a universal curve


What is viscosity

● Viscosity is the resistivity of the fluid

● Low viscosity: milk● High viscosity: honey● Low viscosity means

the energy can transfer through the fluid very fast

● no viscosity = “ideal fluid”


v2 and Viscosity

● String theory predicts there is a universal minimum on ratio of viscosity over entropy for strongly coupled system (η/s = 1/4π ∼0.08)

● QGP: tiny viscosity per particle (η/s ~0.08 in hydrodynamics)

Phys. Rev. Lett 99, 172301 (2007)


Measuring the shape fluctuations● The nucleus is not perfect in

shape● Nucleon distribution is not

smooth● Azimuthal symmetry of the

colliding area no longer available

● vodd is possible, due to shape fluctuations

● Measuring vodd, effectively means

measuring the fluctuations of the initial geometry

● More constraints to theory predictions!


Fluctuations in Cosmic Microwave Background

● Microwave background shows the tiny temperature fluctuations

● Multi-pole expansion shows the structure of the fluctuation distribution

Measurement of CMB from Planck Satellite


vn vs theory

• All theory predicts v2 well

• v3 adds in additional discrimination power

• Data favors Glauber + η/s = 1/4π


How do quark interact with QGP?

● Use nuclear modification factor (RAA

)

● RAA

= <meas. yield in AA> / <expected yield in AA>= <spectra in AA> / <N

coll><spectra in pp>

● Measure the spectra of the particle in pp as base line● Assume the particle production scales with number of

binary (Ncoll

) scaling in AA collisions, then <Ncoll

> * pp is our expected yield in AA

● Measure the particle spectra in AA● Difference between and ?


Quark vs QGP

The more the medium, the more the suppression (the less particles you found)

R = 1 No modification


How do single particles teach us?● RAA : nuclear modification

factor

– RAA

= 1 → no modification in AuAu

– RAA

< 1 → suppression in AuAu

● π0 and η are suppressed

(RAA

~0.2)

● Photons are unmodified (R

AA ~1)

● Quarks interacts with QGP, but photons are not

RAA=YieldAuAu

⟨N binary ⟩AuAu×Yieldpp


RAA @ LHC

● Similar suppression trend till 20 GeV/c● RAA increases with pT when pT > 20 GeV/c● No suppression in photon, Z (also in W)

Eur. Phys. J. C (2012) 72:1945


γ-jet (γ-hadron correlation)

• Quark-gluon Compton scattering• Use direct photon to tag jet energy to

study the energy loss

• IAA

< 1 when ζ < 1 (zT > 0.4)

•Modification of fragmentation function in AuAu compared to p+p•Jet energy is lost in AA collisions!

• IAA

>= 1 at ζ >1 (zT < 0.4)

•The lost jet energy recovered at low pT?

zT = pTa/pTt

ζ ~ -ln(zT)

IAA

= DAA

/Dpp

High zT Low zT

Phys. Rev. Lett. 111, 032301 (2013)


Energy loss vs √sNN


First observation of anti-Helium 4

Nature 473, 353(19 May 2011)

● Energy density similar to that of the Universe microseconds after the Big Bang; ● in both cases, matter and antimatter are formed with comparable abundance.

However, the relatively short-lived expansion in nuclear collisions allows antimatter to decouple quickly from matter, and avoid annihilation.


Summary

● Energy density frontier● QGP is hot: 250000 times hotter than the Sun● Particles move collectively● Energetic quarks lose energy in QGP

quark-gluon plasma from big bang to little bang · 2015. 6. 12. · ntnu seminar, 2015/06/04...

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