Search of a new State of Matter: Quark Gluon Plasma, �in Relativistic Heavy Ion Physics�(Fermi Scale)

Wen-Chen Chang 章文箴

Institute of Physics, Academia Sinica, Taiwan

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Baryon 重子

Meson 介子

Interactions

Evolvement of Interactions

物理的挑戰 李政道院士

我以為21世紀有四個大問題，這四個大問題是什麼？

• 第一個大問題：對稱的理論基礎，不對稱的實驗結果
• 三大作用的理論基礎都是對稱的，可是我們的實驗結果很多是不對稱的。也許各位會覺得這個問題可以很簡單地解決，把理論物理學家都趕走就完了。顯然這樣做不合理，也不解決物理問題。理論對稱，實驗不對稱，這是一大問題。
• 第二個大問題：夸克單獨看不見
• 12種基本粒子中，其中占一半的夸克是單獨看不見的，所有的夸克都是不能被單獨觀察到的，這是另一個大謎。
• 第三個大問題：暗物質
• 宇宙中90%以上的物質，不是我們知道的物質，而是不能發光也不吸收和反射光的暗物質。構造我們的物質和我們所知道的物質在宇宙中是少數。這是第三個大問題。
• 第四個大問題：類星體
• 現在至少巳知有一百多萬個類星體，每一個類星體的能量，約是太陽能量的10的15次方到16次方。大陽的能量來自核能，核能比燒煤得到的能量大幾萬倍到10萬倍左右。類星體的能量遠遠超過了太陽的能量。不是我們所知道的能量。這是第四個大問題。

http://forums.chinatimes.com.tw/tech/techforum/030105C2.htm

Quantum-Chromo-Dynamics:� Strong Interaction

Two observations: (T.D. Lee)

• Fundamental degree of freedoms, quarks and gluons, of QCD is not isolated.
• No isolated quarks and gluons are seen.
• Color confinement.
• Fundamental symmetry, (SU_L(3)xSU_R(3)), of QCD is broken for the ground state.
• Unequal mass for u, d and s quarks.
• Splitting spectra of pseudo-scalar/scalar and vector/axial-vector particles.

QCD and Color Confinement

Phase Transition of Water

H₂O molecules can move freely in gas state.

New State of Matter?

Is there a state of matter where

• quarks and gluons are moving freely?
• the broken chiral symmetry is (partially) restored?

Lattice QCD suggests of a QCD phase transition beyond a region of

high energy and/or

high baryon density.

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The question is that how do we realize it?

Create a MESS by �Heavy Ion Collisions! �(Nuclear Firework)

QCD Phase Diagram

Early Universe

RHIC,LHC

AGS,SPS

Neutron Star

Quark Gluon Plasma

Relativistic Heavy Ion Programs

GSI

SPS

AGS & RHIC

LHC

Relativistic Heavy Ion Collision

Temperature = 1,000,000,000,000 K for RHIC.

QGP Signatures

If QGP is formed:

• Strong gluon-gluon and gluon-quark interaction:

→ equilibrium achieved in a short time and an enhancement of strangeness and anti-baryon production.

• High temperature:

→ thermal radiation by direct photon.

• High density:

→ J/ψ screening, modification of vector mesons and jet quenching.

• Slow pressure build-up:

→ transverse expansion.

Relativistic Heavy Ion Physics

Pressure gradients lead

to collective motion

High-Pt

hadrons

Fragmentation

Heavy flavor quark endures;

Is there medium interaction?

Thermal production?

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Hard-scattered partons travel

through early medium; modification?

Difference in pressure gradients

can lead to anisotropic motion

Identical pair correlations reveal space-time geometry

Br?

Press Release by SPS of CERN

Evidence for a New State of Matter:

An Assessment of the Results from the CERN Lead Beam Programme

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Ulrich Heinz and Maurice Jacob (nucl-th/0002042) on 02/07/2000

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“A common assessment of the collected data leads us to conclude that we now have compelling evidence that a new state of matter has indeed been created, at energy densities which had never been reached over appreciable volumes in laboratory experiments before and which exceed by more than a factor 20 that of normal nuclear matter. The new state of matter found in heavy ion collisions at the SPS features many of the characteristics of the theoretically predicted quark-gluon plasma.”

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http://cern.web.cern.ch/CERN/Announcements/2000/NewStateMatter/

NA50 J/ψ Production

RHIC: Relativistic Heavy Ion Collider

• Brookhaven National Laboratory.
• Schedule:
• Commissioning: 06/99-07/99.
• Run1: May, 2000 - Sep. , 2000.
• Run2: June, 2001- Feb., 2002.
• Run3: Nov, 2002- May, 2003.
• Collisions: pp, pA, AA (Au+Au).
• Energy:
• 500 GeV for p-p (polarized)
• L ~2 x 10³² cm^-2 s^-1
• 200 GeV for Au-Au
• L ~2 x 10²⁶ cm^-2 s^-1
• Experiments:
• PHENIX
• STAR
• PHOBOS
• BRAHMS.

PHENIX at RHIC

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• 2 central �spectrometers

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• 2 forward �spectrometers

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• 3 global �detectors

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West

East

South

North

24

24-Jul-97

25

10-Jan-98

26

12-Jan-99

27

23-Dec-99

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PHENIX: electrons,muons, photons, hadrons

• 2 Arm central spectrometers + 2 muon endcaps
• -0.35< η <0.35 (e,γ, hadrons)
• 1.2<| η |<2.5 (muons-2nd year)
• Tracking : DC, PC, TEC
• Particle ID : RICH, TEC , EMCal, TOF
• Global Detectors (centrality)
• Zero Degree Calorimeters (ZDC)
• Beam-Beam Counter (BBC)

Central Magnet

Muon ID

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Muon Magnet

Central Arms

Beam

STAR: a large acceptance TPC

• Large acceptance TPC
• Solenoidal Field
• -1< η <1
• Vertex Detection - SVT
• Primarily Hadrons - year 1
• Multi-strange baryons
• EMCAL - 2nd year - photons/electrons

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STAR Central Event – year 1

PHOBOS

Electronics rack

magnet - with top half removed

silicon pad detectors

1% solid angle, near y=0, two arm multiparticle spectrometer

• P_t distributions
• very low P_t threshold
• π / K / p / φ ratios
• particle correlations (HBT)
• mass and width φ → K⁺ K^-

10,000 element 4π detector

• event by event - N, dN/dη, d²N/dηdφ
• unbiased global look at very large number of collisions (~10⁹)
• sensitive to large fluctuations in global variables

time of flight

Preliminary Results from RHIC

• Dependence of charged multiplicity on N_binary : evidence of hard collisions.
• Ratio of (p/π-) ≥1 at intermediate pt range.
• Independence of (p/p) ratio over centrality.
• Large elliptic flow close to hydrodynamic prediction and a saturation of elliptic flow at large pt regions.
• Jet quenching.

http://www.rhic.bnl.gov/qm2001/

http://alice-france.in2p3.fr/qm2002/

Hard Probe: Jet Quenching

• Deep-inelastic scattering of quarks in the initial hard collisions.
• Penetrate through hot and dense matter.
• IF the leading particle loses dE/dx by strong interaction (mostly gluon radiaton), a suppression of particles of high transverse momentum is expected.

Peripheral Events

• Good agreement with pQCD calculation including the effects of intrinsic k_T, Cronin, nuclear shadowing...
• Baseline is O.K.

Central Events

• pQCD over-estimates the cross-section
• for π⁰ at least a factor of 5.
• Shadowing and p_t-broadening effect seem insufficient.
• Calculation including constant energy loss
• consistent with π^{0 .}

dE/dx=0.25 GeV/fm

dE/dx = 0 (pQCD)

Evidence of Jet Quenching?-- A dense medium?

Research Team of RHIC Physics in Taiwan

• 實驗：
• PHOBOS:
• 中央大學物理系；林宗泰教授
• 中正大學物理系：湯兆崙教授
• PHENIX：
• 中央研究院：章文箴博士
• 介紹：物理雙月刊二十四卷六期，2002年十二月。

Summary

• Relativistic heavy ion physics is aimed to search for the existence of a de-confined state of quarks and gluons, Quark Gluon Plasma, where many fundamental questions are concerned.
• Preliminary RHIC results shows many new exciting phenomena, e.g. jet quenching.