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Quark-Gluon Plasma From Big Bang to Little Bang · 2015. 6. 12. · NTNU Seminar, 2015/06/04 陳勁豪 1 Quark-Gluon Plasma From Big Bang to Little Bang ... resistivity of the fluid

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  • 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

  • NTNU Seminar, 2015/06/04 陳勁豪 2


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

  • NTNU Seminar, 2015/06/04 陳勁豪 3

    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

  • NTNU Seminar, 2015/06/04 陳勁豪 4

    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

  • NTNU Seminar, 2015/06/04 陳勁豪 5

    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?

  • NTNU Seminar, 2015/06/04 陳勁豪 6

    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

  • NTNU Seminar, 2015/06/04 陳勁豪 7

    Phase transition of nuclear matter?

  • NTNU Seminar, 2015/06/04 陳勁豪 8

    How do we melt the nucleon?

    But how hot do we need?

  • NTNU Seminar, 2015/06/04 陳勁豪 9

    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?

  • NTNU Seminar, 2015/06/04 陳勁豪 10

    Creating the Mini-Bang

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

  • NTNU Seminar, 2015/06/04 陳勁豪 11

    The birth of J/ψ

  • NTNU Seminar, 2015/06/04 陳勁豪 12

    The birth of J/ψ

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

  • NTNU Seminar, 2015/06/04 陳勁豪 13

    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.

  • NTNU Seminar, 2015/06/04 陳勁豪 14

    Detectors at RHIC

    STARspecialty: large acceptancemeasurement of hadrons

    PHENIXspecialty: rare probes, leptons,

    and photons

  • NTNU Seminar, 2015/06/04 陳勁豪 15

    Events viewed by detectors

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

  • NTNU Seminar, 2015/06/04 陳勁豪 16

    Seen in many places!

  • NTNU Seminar, 2015/06/04 陳勁豪 17

    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

  • NTNU Seminar, 2015/06/04 陳勁豪 18

    Some properties of QGP will be discussed

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

  • NTNU Seminar, 2015/06/04 陳勁豪 19

    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

  • NTNU Seminar, 2015/06/04 陳勁豪 20

    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

  • NTNU Seminar, 2015/06/04 陳勁豪 21

    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






    of p



  • NTNU Seminar, 2015/06/04 陳勁豪 22

    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, vodd = 0

    ● If v2 = 0 → particle distributed homogeneously in φ direction

  • NTNU Seminar, 2015/06/04 陳勁豪 23

    v2 vs pT● Au+Au vs Cu+Cu

    – Size difference– Geometry difference (different

    eccentricity, ε)

    ● Non-zero v2● Central collisions

    (0-10%): smaller v2● Mid-central collisions (30-

    40%): larger v2

  • NTNU Seminar, 2015/06/04 陳勁豪 24

    Geometry dependence

    ● Different geometry of the interaction area leads to different v2

    ● Use the eccentricity to remove the geometrical contributions

    ● Central collision, ε2 ~ 0

    ● ε2 increases when moving to peripheral collisions

  • NTNU Seminar, 2015/06/04 陳勁豪 25

    v2 vs pT

    After normalized by ε2, Au+Au/Cu+Cu in different centralities follows a universal curve

  • NTNU Seminar, 2015/06/04 陳勁豪 26

    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”

  • NTNU Seminar, 2015/06/04 陳勁豪 27

    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)

  • NTNU Seminar, 2015/06/04 陳勁豪 28

    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!

  • NTNU Seminar, 2015/06/04 陳勁豪 29

    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

  • NTNU Seminar, 2015/06/04 陳勁豪 30

    vn vs theory

    • All theory predicts v2 well• v3 adds in additional discrimination power• Data favors Glauber + η/s = 1/4π

  • NTNU Seminar, 2015/06/04 陳勁豪 31

    How do quark interact with QGP?

    ● Use nuclear modification factor (RAA)

    ● RAA = / = /

    ● 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 * pp is our expected yield in AA

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

  • NTNU Seminar, 2015/06/04 陳勁豪 32

    Quark vs QGP

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

    R = 1 No modification

  • NTNU Seminar, 2015/06/04 陳勁豪 33

    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 (RAA ~1)

    ● Quarks interacts with QGP, but photons are not

    RAA=YieldAuAu〈N binary 〉AuAu×Yieldpp

  • NTNU Seminar, 2015/06/04 陳勁豪 34

    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

  • NTNU Seminar, 2015/06/04 陳勁豪 35

    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/pTtζ ~ -ln(zT)IAA = DAA/Dpp

    High zT Low zT

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

  • NTNU Seminar, 2015/06/04 陳勁豪 36

    Energy loss vs √sNN

  • NTNU Seminar, 2015/06/04 陳勁豪 37

    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.

  • NTNU Seminar, 2015/06/04 陳勁豪 38


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

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