results from experiments at rhic international school for high-energy nuclear collisions 31 oct –...
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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