RESULTS FROM EXPERIMENTS AT RHIC

International School for High-Energy Nuclear Collisions 31 Oct – 5 Nov, 2011

MotivationExperimentMajor observations ConclusionNear future

Bedangadas Mohanty, VECC, Kolkata

Outline:

Observations in Nature 2

Quarks are confinedinside hadrons

Such a big difference is not seen in molecules, atoms and nuclei

Chiral Symmetry brokenConsequence : valence quarks acquire dynamical masses - Constituent Quark

Mass ~ 350 MeVReview of particle physics (PDG), Phys. Lett. B 592 (2004)

Can we have deconfined matter ?Can we restore the symmetry ?

QCD – theory of strong interactions 3

Some key ingredients

Gauge Group - SU(3)

QCD potential

Strong coupling constant

Very successful

CP-PACS : PRL 84 (2000) 238

VQCD = - 4/3 / r + r

QCD Lagrangian

confinement

Symmetry breaking

Jet-production

Hadron massSTAR : PRL 97 (2006) 252001

Confinement and Symmetry 4

Asymptotic freedom: Quarks and Gluons weakly interacting (i) when close together(ii) when interact at large

momentumSuggest look at high density or high temperature state

The Nobel Prize in Physics 2008: "for the discovery of the mechanism of spontaneous broken symmetry in subatomic physics", "for the discovery of the origin of the broken symmetry which predicts the existence of at least three families of quarks in nature".Chiral Symmetry:(i) QCD vacuum (qqbar pairs) ordered in

flavor space (directionality), Symmetry broken

(ii) High T, Entropy wins over Order, disordered. All directions equivalent; Symmetry exists

QCD at high temperature 5

e/T4 gparton ~ 47.5

~ g (2/30)

g ~ 3

TC≈1708 MeV, eC≈1 GeV/fm3 gluon spin, color quark spin, color, flavor

Lattice QCD predicts a transition to Quark Gluon Plasma at high temperature

F. Karsch, Prog. Theor. Phys. Suppl. 153, 106 (2004)

Motivation – QCD phase transitions 6

Confined State Deconfined State

Chiral Symmetry Broken Chiral Symmetry Restored

How to study theseQCD transitions ?

Heavy Ion Collisions – QCD Transitions 7

J. D. Bjorken Physical Review D 27 (1983) 140

Colliding two nuclei we expect to create the QCD transitions

-- De-confinement-- Chiral Symmetry Restoration

in laboratory

p+p like collisions A+A collisions

Universe:QCD Phase Transition: T ~ 200 MeVElectroweak Phase Transition: T ~ 150 GeVGUT phase Transition: T ~ 1016 GeV

Heavy-ion Collisions - QCD Phase Diagram

Physical systems undergo phase transitions when external parameters such as the temperature (T) or a chemical potential (μ) are tuned.

Conserved Quantities: Baryon Number ~ Electric Charge ~ Q ~ small Strangeness ~ S ~ small

Signals for phase transition/phase boundary Search for Critical Point Tests of QCD

8

Major Goals:

Experiment 9

Collider Detector Measurements Data Collected

Bevalac-LBL and SIS-GSI fixed target max. 2.2 GeV

AGS-BNL fixed targetmax. 4.8 GeV

SPS-CERN fixed targetmax. 17.3 GeV

TEVATRON-FNAL (fixed target p-A)max. 38.7 GeV

RHIC-BNL collidermax. 200.0 GeV

LHC-CERN collidermax. 5500.0 GeV

1992Au-Au

1994Pb-Pb

2000Au-Au

E864/941, E802/859/866/917, E814/877,E858/878, E810/891, E896, E910 …

NA35/49, NA44, NA38/50/51, NA45,NA52, NA57, WA80/98, WA97, …

BRAHMS, PHENIX, PHOBOS, STAR

ALICE, ATLAS, CMS2010Pb-Pb

Ionization energy ~ eV, keVFission ~ 200 MeVHeavy Ion Collisions ~ GeV, TeV

RHIC – Basic structure 10

1) Cesium Sputter Ion Source• Au-1

2) Tandem van de Graaff• Au+32

• E = 1 MeV/A3) Heavy Ion Transfer Line4) Booster Synchrotron

• Au+77

• E = 1 GeV/A5) Alternating Gradient

Synchrotron• E = 10 GeV/A

6) AGS-to-RHIC• Au+79

7) RHIC Ring• E = 100 GeV/A

RHIC – Advantage over fixed target 11

Hadron Mass

Transv

ers

e M

om

entu

m

Beam Energy

Rapidity

200 GeV

62.4 GeV

39 GeV

9.2 GeV

Fixed

Target

Collider experiment : Uniform acceptance Variation of particle

density with beam energy slower

G. Roland

Apart from higher center of mass energy at RHIC and LHC

PHENIX Detector 12

Axial Field GeometryHigh Rate Capability

Selected solid angles for detection of leptons, photons, and hadronsSeveral detectors types in harmony

Pioneering High-Energy Nuclear Interactions eXperiment

NIM A499:469,2003

HBD

Mu

on

tra

ckin

g

Mu

on

tra

ckin

g

MP

C,

BB

C

MP

C,

BB

C

0

f

cove

rage

2

p

EM

CE

MC

trac

king

trac

king

RXNP RXNPVTX

-3 -2 -1 0 1 2 3 rapidity

STAR Detector 13

MRPC ToF Barrel

BBC

PMD

FPD

FMS

EMC BarrelEMC End Cap

DAQ1000FGT COMPLETE

Ongoing

MTD

R&DHFT

TPC

FHC

HLT

pp2pp’ pp2pp’

trigger computingFTPC

Solenoidal Tracker At RHIC NIM A499:624,2003

upVPD

MagnetTOF BEMC

BBC

EEMCTPC

© Maria & Alex Schmah

The Solenoid Tracker At RHIC (STAR)

Full particle identification at ~ 2 unit in midrapidity

RHIC – Basic Measurements 15

Spatial Position, Multiplicity, Momentum and Energy

N

No. of events

No. of events

RHIC – Particle Identification 16

Time of flight:

< > = L / = L (1 + m2/ p2) 1/2

Plot < > vs. 1/p

Ionization energy loss:

- < dE/dx > ~ A / 2 = A (1 + m2/ p2)

Plot - < dE/dx > vs. p

Momentum p = mm = [ p (1 -

5 charged particles: e, , , K, p

RHIC – Particle Identification 17

V0 decay vertices

Ks p + + p -

L p + p -

L p + p +

X- L + p -

X+ L + p +

W L + K -

Au+Au40% to 80%

0.2 pT 0.9 GeV/c

0

f0

K0S

K*0

“Kinks”:

K +

Electron ID viap/E in EMC

Resonances in invariant mass spectra

D0

Rest are constructed: Invariant Mass + Decay Topology

“Had I foreseen that, I would have gone into botany” - Fermi

0, K0s, , K*, D0

…..

ΚS

Λ

Ξ

Ω

M2 = E2 - p2

RHIC – Data Collected 18

19.6 GeV 62.4 GeV 130 GeV 200 GeV

Cu+Cu

d+Au

Au+Au

centralityIn addition:p+p: 400, 200, 62.4 GeVAu+Au : 39, 27,11.5, 9.2, 7.7 GeVCu+Cu : 22 GeV

Polarized p+p : 200 and 500 GeV

PHOBOSPhys.Rev.Lett.93:082301,2004Phys.Rev.Lett.87:102303,2001Phys.Rev.C74:021901,2006

In near future: U+U Au+Cu

Energy – Particle Production 19

p : 3108 p : 428K+ : 1628K- : 1093+ : 5888- : 6117

: 6004n : 3729n : 513K0 : 1628K0 : 1093

Energy (in GeV)

sum: 33.4 TeVproduced: 24.8TeV

Total energy available ~ Ebeam * Npart Total energy into particle prod.

Assume distributions for unmeasured hadrons and kinematics range

BRAHMS

Major portion of beam energy goes in particle production

BRAHMS:Phys.Rev.Lett.94:162301,2005.

Partonic phase signals 20

Direct Photons and initial temperature Jet Quenching and medium density Strangeness Enhancement and role of f-meson production Collectivity and transport properties Quarkonia production and Deby screening effect Higher moments of net-proton distribution and Transition temperature

Initial Temperature 21

Compton Annihilation Bremsstrahlung

q

g*

g q

e+

e-

Temperature of the system :Slope of transverse momentum distribution of photons

Faithfully caries the information of the temperature as they do not undergo strong interaction, have large mean free path, decouples from the medium as soon as they are produced

Initial Temperature 22

Direct photons :p+p 200 GeV described by NLO pQCD. Au+Au 200 GeV excess relative to p+p

Excess : Exponential Shape ~ Thermal source

Initial Temperature :

Tinitial > TC (Lattice)~ 3.5 - 7 X 1012 o Kelvin

PHENIX : Phys.Rev.Lett 104:132301,2010

Perspective on Temperature 23

~3 K

~300 K

~1012 K ~ 120 MeV

Cosmic Microwave Background

Room Temperature ~ 1/40 eV

~109 K Neutron Star Thermonuclear Explosion

~6000 K

~106 K

Solar Surface

Solar Interior

~10-6 K

Trapped Ions

~10-10 K Rhodium metal spin cooling (2000)

(Low-T World Record!)

Nucleus-Nucleus collisions

Jet Quenching – First time observed at RHIC 24

back-to-back jets disappear

leading particle suppressed

p+p Au + AuNuclear Modification Factor:

p+p A+A

Jet Quenching – p+p baseline 25

STAR : PLB 637 (2006) 161

High pT particle production wellexplained by NLO pQCD

calculations

Parton Distribution Functionsdominantly from deep-inelastic

Scattering experiments

Parton-Parton Cross-Section (pQCD)

Parton Fragmentation Functionsdetermined from e+e- annihilations

PHENIX:

Phys.Rev.Lett.91:241803,2003.

Suppression of high pT hadron production 26

High pT hadron production suppressed

Production of photons which do not participate in stronginteractions is not suppressedNo suppression in d+Au

collisions

Interpretation : Energy loss of partons in a dense medium, initial > C (Lattice)

Medium Density 27

dNg/dy ~ 1400Ti ~ 365 MeVEnergy Densityi = 12 GeV/fm3

Hwa-Kajante Model

Bjorken Energy Density PRD 27, 140 (1983)

or

Bj ~ 5 GeV/fm3

Cold Nuclear Matterecold ≈ u / 4/3pr0

3 ≈ 0.138 GeV/fm3

initial > C (Lattice)

Jet Quenching – yet to be understood 28

Quantitative: Amount of Energy Loss

Mechanism: Radiative vs. Collisional

Color factor: Difference in quark and gluon energy loss

Flavour: Heavy quark vs. Light Quark

Technical: Surface Bias / Full Jet Reconstruction

Jet-Medium interactions: Conical Emission, Ridge …

Jet

Prompt gEg

Eq

~ 9/4 Color factor: 4/3 for quarks3 for gluons

2 L<q>

CE saD ^

Partonic Phase – Strangeness Enhancement 29

Simple pictureZero Net-baryons, B = 0

TQGP > TC ~ ms = 150 MeV

Production Rate

Strangeness Enhancement – Long time issue 30

QGP scenario :

Strangeness enhancement relative to p+p collisionsStronger effect for multi-strange hadronsPhys. Rep. 88 (1982) 331

Phys. Rev. Lett. 48 (1982) 1066Phys. Rep. 142 (1986) 167

P. Koch, B. Muller,J. Rafelski et al..

Twenty year old issue:How to resolve the two scenarios

Non-QGP scenario :

Canonical Effect in p+p collisions : Quantum Numbers exactly conservedSuppression in p+p

causes :-Strangeness ordering-Beam energy dependence

J. Cleymans, A. Muronga, K. Redlich, A. Tounsi, et al.

Phys. Lett. B. 388 (1996) 401Phys. Rev. C 58 (1997) 2747Phys. Rev. C 57 (1998) 3319Phys. Lett. B. 486 (2000) 61Eur. Phys. J. C 24 (2002) 589

Strangeness Enhancement - RHIC 31

Strange particle production enhanced

meson :

Net-strangeness zero

No Canonical Suppression

Larger enhancement for higher beam energy

Evidence of partonic matter formationSTAR: Phys.Lett.B673:183-191,2009.

Collectivity 32

Pressure gradient

Spatial Anisotropy

Momentum Anisotropy

INPUT

OUTPUT

Interaction amongproduced particles

dN

/df

0 2p

dN

/df

f0 2p

2v2

x

y

Free streamingv2=0c2

s=dP/de

Initial spatial anisotropy

Collectivity - Partonic 33

Low pT: Heavier hadrons lower flow ( ~ hydrodynamic pattern)High pT: Grouped along baryon-meson lines ( ~ Hadronization by partonic recombination)All pT: Similar for hadrons with strange and light quark (~ developed at partonic stage)

Collectivity – Hadronic Interactions 34

meson v2 falls off the trend from other hadrons at 11.5 GeV

Different v2 for particle and anti-particle.

Small meson v2 indicates collectivity contribution from partonic interactions decreases with decrease in beam energy

Transport properties of QCD matter 35

Estimates of shear viscosity to entropy ratio at RHIC Some typical ways to get the estimate

Roy A. Lacey et al., - Phys. Rev. Lett. 98 (2007) 092301; . H-J. Drescher - Phys. Rev. C 76 (2007) 024905; . A Adare et al - Phys. Rev. Lett. 98 (2007) 172301

Strongly coupled system with smallest shear viscosityto entropy ratio estimated so far

Plasma and Screening 36

QED Plasma is a thermalized state of charge particles with overall charge neutrality, where the average K.E per particle is larger than the inter-particle P.E

The scale over which mobile charge carriers screen out fields in plasmas.A Debye sphere is a volume whose radius is the Debye length, in which there is a sphere of influence, and outside of which charges are screened.

QCD plasma : Color neutral

D ~ 1/gT ; g = color charge

How can we see this screening effect in QCD Plasma ?

Quarkonium and Screening 37

The J/y’s may melt in hot medium and the charm and anti-charm become unbound, and may combine with light quarks to emerge as “open charm” mesons.

T=0 T=200

aeff 0.52 0.20

0.41 fm 1.07 fm

∞ 0.59 fm

From Introduction to High-Energy Heavy-Ion Collisions, C.Y. Wong 1994

Matsui & Satz : Phys. Lett. B178 (1986) 416In the QGP the screening radius could become smaller than the J/Y radius, effectively screening the quarks from each other!J/y production will be suppressed if QGP is formed

ccbar - meson, produced earlier due to heavy mass ~ 3.1 GeV

An observable related to heavyquark potential !

Quarkonium suppression at RHIC 38

J/ is suppressedPHENIX PRL STAR QM2011

Fluctuations and test of QCD

Higher order correlations a test of thermodynamics of bulk strongly interacting matter

Short distance Non-perturbative regime

Long-distanceperturbative regime

39

Science 322 (2008) 1224

Science 332 (2011) 1525

Hadronic phase 40

Chemical Freeze-out Kinetic Freeze-out

Tests of Thermal/hadron resonance gas models

Hadronic Phase – Chemical Freeze-out 41

Inelastic collisions ceasesChemical composition or Particle ratios get fixedParticle Abundances: Grand Canonical Ensemble

Assumptions/Conditions:Thermal and Chemical Equilibrium (Constant T and n)System of non-interacting hadrons and resonancesConservation of baryon number, strangeness, isospin

Particle ratio:

Hadronic Phase – Chemical Freeze-out 42

Tch = 163 ± 4 MeVB = 24 ± 4 MeV

- In central collisions, the system is thermalized at RHIC- Short-lived resonances show deviations. There is life after chemical freeze-out. RHIC white papers - 2005, Nucl. Phys. A757, STAR: p102; PHENIX: p184.

RHIC now covers the mB range between20 – 400 MeV

L. Kumar, STAR QM2011

Success of thermal model

Fluctuations and Hadron Resonance Gas Model

Higher order correlations a test of hadron resonance gas model

arXiv: 1107.4267, And L. Chen

Success of Thermal model

STAR: NPA 757, 102 (2005)

43

Hadronic Phase – Kinetic Freeze-out 44

Elastic collisions ceasesMomentum distribution of particles get fixed

random

boosted

Extract thermal temperature Tfo and velocity parameter TSource is assumed to be:

– Locally thermal equilibrated

– Boosted in radial direction

Hadronic Phase – Kinetic Freeze-out 45

more

cen

tral

colli

sion

s

Light hadrons move with higher velocity compared to heavier strange hadrons

Multi-strange hadron Spectra ~ exponential

STAR: 2005, Nucl. Phys. A757, STAR: p102

Discovery at RHIC: Anti-matter nuclei 46

All fundamental particles have anti-matter partner

2011

4He

Anti Matter at STAR in RHIC 47

“Observation of the Antimatter Helium-4 Nucleus” by STAR Collaboration

Nature, 473, 353(2011).

“Observation of an Antimatter Hypernucleus” by STAR Collaboration

Science, 328, 58(2010).

Anti-Matter - History 48

“Surely something is wanting in our conception of the universe. We know positive and negative electricity, north and south magnetism, and why not some extra terrestrial matter related to terrestrial matter as the source is to sink …….Worlds may have been formed of this stuff, with elements and compounds possessing identical properties with our own, undistinguishable … until they are brought into each other’s vicinity.” (Matter-Anti-matter asymmetry)

“If there is negative electricity, why not negative gold, as yellow and as valuable as our own, with same boiling point and identical spectra lines; different only in so far that if brought down to us it would rise up into space with an acceleration of 981.” (CPT)

“Whether such thoughts are ridiculed as inspirations of madness or allowed to be serious possibilities of a future science … Astronomy, the oldest and yet most juvenile sciences, may still have some surprises in store.…. But I must stop - … we must return to sober science, and dreams must go to sleep till next year. Do dreams ever come true ?”

Nature 58, 367 (18 August 1898) Potential Matter.- A Holiday Dream - by Arthur Schuster

Discovery of anti-helium-4 49

Ionization energy loss: - < dE/dx > ~ A / 2 = A (1 + m2/ p2) Time of flight: < > = L / = L (1 + m2/ p2) 1/2

Measurement Production rate in nuclear collisions

Point of reference for possible future observations in cosmic radiationImplications to Cosmology:

Heavier anti-nuclei in space existence of anti-matter in universe

Discovery of anti-hypertriton 50

Nuclei with hyperon - hypernucleus

Understanding density of Neutron StarUnderstanding the nuclear force: L travel deep

Inside nucleus – no Pauli blocking

Near Future 51

Establish the QCD Phase diagram

Dileptons to probe collectivity in partonic phase

Heavy quark meson/baryon production

S. Gupta, QM2011

Experiment Program - BES

Varying beam energy varies Temperature and Baryon Chemical Potential

TPCTOF

Typical Experiment - STAR

52

Proton identification Uniform Acceptance

Nature 448:302-309,2007

STAR – Study structure of QCD phase diagram 53

Moments relates to Susceptibility (c) :

Study Bulk properties of QCD matter

Kurtosis x Variance ~ 4)/ [c T2]Skewness x Sigma ~ [3) T]/ [c T2]

< (N)2> ~ 2 < (N)3> ~ 4.5

< (N)4> - 3 < (N)2>2 ~ 7

Moments relates to Correlation length (): Study phase transition and Critical Point

Shape of distribution ~ higher ordercorrelations

Typical net-proton distributions

Product of moments cancel volume effectSTAR: Physical Review Letters 105 (2010) 022302

STAR – Study structure of QCD phase diagram 54

Deviation from Poissionian expectations for third moments

Important to have precise results in the energy range of 15 – 30 GeV

Critical Point: Enhanced fluctuations Non-monotonic variations as a function of beam energy

STAR QM2011

RHIC – Summary 55

Contribution to our understanding of bulk QCD matter

Discovery of anti-matter nuclei (anti-hypertriton and anti-alpha) Implications span the fields of nuclear physics and cosmology

Currently the best available machine to study and establish the QCD phase diagram. RHIC covers a baryon chemical potential range of 20 – 400 MeV.

Systematically established several properties of the QCD matterLike initial temperature (direct photons), medium density (jet quenching)Screening effect in plasma (J/Y suppression), small viscosity to entropy ratio(elliptic flow), Coalescence as a mechanism of particle production (elliptic flow)

Carried out further tests of QCD in both perturbative (p+p collisions) and non-perturbative (A+A) domains (baryon susceptibilities in Lattice QCD — Data)

Established the formation of matter where the degrees of freedom are partonic. JetQuenching and strangenessEnhancement as signatures of QGP

Remarkable success of thermal model calculations put to further tests from higher order correlation measurements