Heavy-Ion Collisions -
examining the Quark Gluon Plasma
Physics in Collisions Kobe - Japan
Helen Caines - Yale University
September 2nd 2009
Outline:Studying sQGP via jetsUsing sQGP to observe local strong
parity violation effectsOutlook
RHIC BRAHMSPHOBOSPHENIX
STAR
AGS
TANDEMS
Physics in Collisions - 30th August - 2nd September 2009Helen Caines 2
1 km
v = 0.99995⋅c
RHIC - Relativistic Heavy Ion Collider
counter-rotating beams of ions from p to Au @ √sNN=5-500 GeV
PHENIX and STAR - multi purpose experiments still running
RHIC BRAHMSPHOBOSPHENIX
STAR
AGS
TANDEMS
Physics in Collisions - 30th August - 2nd September 2009Helen Caines 2
1 km
v = 0.99995⋅c
RHIC - Relativistic Heavy Ion Collider
counter-rotating beams of ions from p to Au @ √sNN=5-500 GeV
PHENIX and STAR - multi purpose experiments still running
Physics in Collisions - 30th August - 2nd September 2009Helen Caines
“A first-order QCD phase transition that occurred in the early universe would lead to a surprisingly rich cosmological scenario.” Ed Witten, Phys. Rev. D (1984)
Creating a Quark Gluon Plasma
3
Physics in Collisions - 30th August - 2nd September 2009Helen Caines
“A first-order QCD phase transition that occurred in the early universe would lead to a surprisingly rich cosmological scenario.” Ed Witten, Phys. Rev. D (1984)
Creating a Quark Gluon Plasma
Apparently it did not !Thus we suspect a smooth cross over or
a weak first order transition
NASA/WMAP
3
• Energy density in the collision region is way above that where hadrons can exist
• The initial temperature in the collision region is way above that where hadrons can exist
• The medium has quark and gluon degrees of freedom in initial stages
• A sQGP: flows like an almost “perfect” liquid interacts strongly with partons passing through it
Physics in Collisions - 30th August - 2nd September 2009Helen Caines
At RHIC we create a new state of matter
4
We have created a new state of matter at RHIC - the sQGP
Physics in Collisions - 30th August - 2nd September 2009Helen Caines 5
q
q
hadronsleadingparticle
leading particle
Schematic view of jet production
hadrons
Early production in parton-parton scatterings with large Q2
Must pass through the medium to escape
Direct interaction with partonic phases of the reaction
Studying sQGP properties
Physics in Collisions - 30th August - 2nd September 2009Helen Caines 5
q
q
hadronsleadingparticle
jet production in quark matter
• interaction of partons with medium → attenuation/absorption of jets
• compare Au-Au to p-p
Early production in parton-parton scatterings with large Q2
Must pass through the medium to escape
Direct interaction with partonic phases of the reaction
Studying sQGP properties
Use jets to probes sQGP
Physics in Collisions - 30th August - 2nd September 2009Helen Caines
High pT particles - proxy for jetp-p → dijet
• Trigger: highest pT track
• Δφ distribution:6
Physics in Collisions - 30th August - 2nd September 2009Helen Caines
trigger Phys Rev Lett 90, 082302
min. bias p-p collisions
High pT particles - proxy for jetp-p → dijet
6
Physics in Collisions - 30th August - 2nd September 2009Helen Caines
central Au-Au collisions
High pT particles - proxy for jetp-p → dijet
?
6
Δφ ≈ 0: central Au-Au similar to p-pΔφ ≈ π: strong suppression of back-to-back
correlations in central Au-Au
Physics in Collisions - 30th August - 2nd September 2009Helen Caines
Gluon radiation: Multiple final-state gluons radiate off from produced hard parton - induced by the traversed dense colored medium Medium
EHard
Production
!=xE
!=(1-x)E
"!
"qT~µ
Interpretation
7
Physics in Collisions - 30th August - 2nd September 2009Helen Caines
• Mean parton energy loss ∝ medium properties:• ΔEloss ~ ρgluon (gluon density)
• ΔEloss ~ ΔL2 (medium length) ⇒ ~ ΔL with expansion
• Characterization of medium• transport coefficient
• is 〈pT2〉 transferred from the medium to a hard gluon per unit path length
Gluon radiation: Multiple final-state gluons radiate off from produced hard parton - induced by the traversed dense colored medium Medium
EHard
Production
!=xE
!=(1-x)E
"!
"qT~µ
0. 1 1 10 100
0. 01
0. 1
1. 0
10. 0
R. Baier, Nucl. Phys. A715, 209c
QGP
Hadronic Matter
cold nuclear matter
q (
GeV
2/fm
)
! (GeV/fm3)
sQGP
Interpretation
7
~5-10 GeV/fm
ξ=ln(EJet/phadron)
pThadron~2 GeV
Jet quenching
“hump-backplateau”
Physics in Collisions - 30th August - 2nd September 2009Helen Caines
Towards a complete study of jet-quenchingDi-hadrons indirect measurements of jet quenching !
Needed to develop techniques to allow full jet reconstruction:
• MLLA: good description of vacuum fragmentation (basis of PYTHIA)
• Introduce medium effects at parton splitting Borghini and Wiedemann, hep-ph/0506218
“full” partonic energy recovered FF highly modified
Physics in Collisions - 30th August - 2nd September 2009Helen Caines
Can you “see” jets a RHIC?
9
!"#$%&$'&&$(&)'$")$*+,!-$
!"#$%&'()*+*,-'.%
#/0#/%1(,2'-
)%
!" #"
34%!(5*)%!-)/'%
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!"#$%&'()*+*,-'.%
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)%
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34%!(5*)%!-)/'%
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+*,-'.%
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Yue Shi Lai QM2009 Joern Putschke HP2008
Clearly visible above background in both experiments
Physics in Collisions - 30th August - 2nd September 2009Helen Caines
Jet reconstruction - algorithms
• Rcone=√(Δφ2+Δη2)
• all particles used.• Splitting/Merging destroys cone shape.
Fastjet package - [Cacciari, Soyez, arXiv:0704.0292]
Seedless Cone - SISCone:
10
Physics in Collisions - 30th August - 2nd September 2009Helen Caines
Jet reconstruction - algorithms
• Rcone=√(Δφ2+Δη2)
• all particles used.• Splitting/Merging destroys cone shape.
Fastjet package - [Cacciari, Soyez, arXiv:0704.0292]
[Cacciari, Salam, Soyez, arXiv:0802.1189]
Seedless Cone - SISCone:
Recombination kT /Anti-kT: • starts from low (high) pT.
• merges weighted by 1/pT (pT) i.e. high (low) pT is dis-favored.
10
Physics in Collisions - 30th August - 2nd September 2009Helen Caines
Jet reconstruction - algorithms
• Rcone=√(Δφ2+Δη2)
• all particles used.• Splitting/Merging destroys cone shape.
Fastjet package - [Cacciari, Soyez, arXiv:0704.0292]
[Cacciari, Salam, Soyez, arXiv:0802.1189]
Seedless Cone - SISCone:
Recombination kT /Anti-kT: • starts from low (high) pT.
• merges weighted by 1/pT (pT) i.e. high (low) pT is dis-favored.
10
Gaussian Filter:• cone like but no infrared/collinear issues.• focusses on core
Run-5�!�spectrum
)c (GeV/T
p0 10 20 30 40 50 60 70
)!2 )c
) (m
b (G
eV/
y d Tpd Tp
/(!2
d!1 )
"(2 !1410
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!1210
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!910
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!310
!210 PHENIX Preliminaryc = 200 GeV/s p + pRun!5
= 0.3!Gaussian filter,
uncertaintyT
pwidth not a
=0.3!PHENIX, =0.3! = 2.5, KPYTHIA,
= 0.3 (Vogelsang) RNLO SCA, =0.4 (PRL 97, 252001) RSTAR HT,
NLO calculation for larger��range and using filter is needed
(Yue Shi Lai, for the PHENIX Collaboration) APS DPF Meeting 2009, Heavy Ions III 8 / 35
Physics in Collisions - 30th August - 2nd September 2009Helen Caines 11
STAR : PRL 97 (2006) 252001PHENIX: Y.Lai QM2009
Jets at RHIC – a calibrated probe?
• Jet cross-section in p-p is well described by NLO pQCD calculations over 7 orders of magnitude.• Excellent description when included in world data
T. Kluge, K.Rabbertz, M.Wobish
Run-5�!�spectrum
)c (GeV/T
p0 10 20 30 40 50 60 70
)!2 )c
) (m
b (G
eV/
y d Tpd Tp
/(!2
d!1 )
"(2 !1410
!1310
!1210
!1110
!1010
!910
!810
!710
!610
!510
!410
!310
!210 PHENIX Preliminaryc = 200 GeV/s p + pRun!5
= 0.3!Gaussian filter,
uncertaintyT
pwidth not a
=0.3!PHENIX, =0.3! = 2.5, KPYTHIA,
= 0.3 (Vogelsang) RNLO SCA, =0.4 (PRL 97, 252001) RSTAR HT,
NLO calculation for larger��range and using filter is needed
(Yue Shi Lai, for the PHENIX Collaboration) APS DPF Meeting 2009, Heavy Ions III 8 / 35
Physics in Collisions - 30th August - 2nd September 2009Helen Caines 11
STAR : PRL 97 (2006) 252001PHENIX: Y.Lai QM2009
• Minimum bias particle production in p-p also well modeled.
Jets at RHIC – a calibrated probe?
STAR : PLB 637 (2006) 161S. Albino et al, NPB 725 (2005) 181
• Jet cross-section in p-p is well described by NLO pQCD calculations over 7 orders of magnitude.• Excellent description when included in world data
T. Kluge, K.Rabbertz, M.Wobish
Run-5�!�spectrum
)c (GeV/T
p0 10 20 30 40 50 60 70
)!2 )c
) (m
b (G
eV/
y d Tpd Tp
/(!2
d!1 )
"(2 !1410
!1310
!1210
!1110
!1010
!910
!810
!710
!610
!510
!410
!310
!210 PHENIX Preliminaryc = 200 GeV/s p + pRun!5
= 0.3!Gaussian filter,
uncertaintyT
pwidth not a
=0.3!PHENIX, =0.3! = 2.5, KPYTHIA,
= 0.3 (Vogelsang) RNLO SCA, =0.4 (PRL 97, 252001) RSTAR HT,
NLO calculation for larger��range and using filter is needed
(Yue Shi Lai, for the PHENIX Collaboration) APS DPF Meeting 2009, Heavy Ions III 8 / 35
Physics in Collisions - 30th August - 2nd September 2009Helen Caines 11
STAR : PRL 97 (2006) 252001PHENIX: Y.Lai QM2009
• Minimum bias particle production in p-p also well modeled.
Jets at RHIC – a calibrated probe?
STAR : PLB 637 (2006) 161S. Albino et al, NPB 725 (2005) 181
• Jet cross-section in p-p is well described by NLO pQCD calculations over 7 orders of magnitude.• Excellent description when included in world data
What about fragmentation?
T. Kluge, K.Rabbertz, M.Wobish
)TPart
/pTjet
(=ln(p!0 1 2 3 4 5
!d
N/d
jet
1/N
0.2
0.4
0.6
0.8
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1.2
1.4
1.6
1.8
2
2.2SISCone
TK
TAnti-K
Pythia 6.4
p-p data
)TPart
/pTjet
(=ln(p!0 1 2 3 4 5
!d
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jet
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0.2
0.4
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p-p data
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(=ln(p!0 1 2 3 4 5
!d
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jet
1/N
0.5
1
1.5
2
2.5 SISCone
TK
TAnti-K
Pythia 6.4
p-p data
Physics in Collisions - 30th August - 2nd September 2009Helen Caines
Charged hadrons fragmentation Fns
20<pTreco<30 GeV/c 30<pTreco<40 GeV/c
R=0.4
R=0.7
Reasonable agreement between PYTHIA and data 12
Preliminary
PreliminaryPreliminary
Preliminary|ηjet|<1-RpTtrack>0.2 GeV/c
Data not corrected to particle level.
“PYTHIA” = PYTHIA+GEANT
Physics in Collisions - 30th August - 2nd September 2009Helen Caines
The underlying event in p-p collisions
13
STAR Preliminary
p t p
er g
rid c
ell [
GeV
]
~ 21 GeV
η ϕ
p-p JP triggerSTAR preliminary
Leading jet
• RHIC data support smaller UE activity from MPI at LHC than standard “ATLAS” tunes predict. PYTHIA “tune-A” closer to data
Physics in Collisions - 30th August - 2nd September 2009Helen Caines
The underlying event in p-p collisions
13
STAR Preliminary
p t p
er g
rid c
ell [
GeV
]
~ 21 GeV
η ϕ
p-p JP triggerSTAR preliminary
Leading jet
STAR Preliminary
Insensitive to initial/final state radiationSensitive to initial/final state radiation
Very little initial/final state radiation at large angles at RHIC energies
• RHIC data support smaller UE activity from MPI at LHC than standard “ATLAS” tunes predict. PYTHIA “tune-A” closer to data
Before looking at scattering effects in Au-Au we want to again investigate what happens in d-Au (where we expect no QGP).
Already showed that the away-side di-hadron correlation is not suppressed.
Physics in Collisions - 30th August - 2nd September 2009Helen Caines
Cold nuclear matter effects on kT
14
• Intrinsic kT - scattering of parton in matter before fragmentation
• Results in non back-to-back jets even in Δϕ
• kT,raw = pT1*sin(Δϕ)
Trigger Jet
Recoil Jet
Before looking at scattering effects in Au-Au we want to again investigate what happens in d-Au (where we expect no QGP).
Already showed that the away-side di-hadron correlation is not suppressed.
Physics in Collisions - 30th August - 2nd September 2009Helen Caines
Cold nuclear matter effects on kT
14
• Intrinsic kT - scattering of parton in matter before fragmentation
• Results in non back-to-back jets even in Δϕ
• kT,raw = pT1*sin(Δϕ)
No significant CNM effects seen
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Physics in Collisions - 30th August - 2nd September 2009Helen Caines
Full-jet reconstruction in HI collisions
15
p t p
er g
rid c
ell [
GeV
]
~ 21 GeV
η ϕ
p+p JP trigger
STAR preliminary
Underlying event background a significant challenge - magnitude and fluctuations
Tools have been developed (i.e. FastJet package) and methods (unfolding) to correct via data driven approach
Need to avoid (as far as possible) reliance on theory
Physics in Collisions - 30th August - 2nd September 2009Helen Caines
Full-jet reconstruction in HI collisions
15
p t p
er g
rid c
ell [
GeV
]
~ 21 GeV
η ϕ
p+p JP trigger
STAR preliminary
ϕη
p t p
er g
rid c
ell [
GeV
]
STAR preliminary
~ 21 GeV
Underlying event background a significant challenge - magnitude and fluctuations
Tools have been developed (i.e. FastJet package) and methods (unfolding) to correct via data driven approach
Need to avoid (as far as possible) reliance on theory
Multiplicity
ρ (G
eV/area)
Physics in Collisions - 30th August - 2nd September 2009Helen Caines
Background - central Au-Au collisionsEvent-by-event basis: pT (Jet Measured) ~ pT (Jet) + ρ A ± σ √A
ρ - background energy per unit areaA - jet area
Ebg~ 45 GeV for RC=0.4 (S/B ~0.5 for 20 GeV jet)
Multiplicity
ρ (G
eV/area)
Rc
Back
grou
nd fl
uctu
atio
ns [G
ev]
Physics in Collisions - 30th August - 2nd September 2009Helen Caines
Background - central Au-Au collisionsEvent-by-event basis: pT (Jet Measured) ~ pT (Jet) + ρ A ± σ √A
ρ - background energy per unit areaA - jet area
Ebg~ 45 GeV for RC=0.4 (S/B ~0.5 for 20 GeV jet)
Substantial region-to-regionbackground fluctuations
σ - comparable magnitude from FastJet and naïve random cones
Both reduced significantly by increasing pTcut
Physics in Collisions - 30th August - 2nd September 2009Helen Caines
What’s expected from Au-Au jet spectrum
17
p and E MUST be conserved even with quenched jets• Study nuclear modification factor (RAA) of jets
Average number of p-p collisionin A-A collision
• If jet reconstruction complete and unbiased RAA==1
Physics in Collisions - 30th August - 2nd September 2009Helen Caines
What’s expected from Au-Au jet spectrum
17
1
Cross‐sec)onra)oAu‐Au/p‐p
p‐p
Au‐Au
Energyshi6?
Absorp)on?
p and E MUST be conserved even with quenched jets• Study nuclear modification factor (RAA) of jets
Average number of p-p collisionin A-A collision
• If jet reconstruction complete and unbiased RAA==1
• If some jets absorbed and/or not all energy recovered RAA<1
Run-5 Cu! Cu spectra with fake rejection
)c (GeV/pprec!T
p0 5 10 15 20 25 30 35 40 45 50
)2 )cdy
) ((G
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Tpd Tp/(
N d
!1 evt
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!(2
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!810
!710
!610
!510
!410
Cu + Cu0!20%20!40%40!60%60!80%
ABT " p + p0!20%20!40%40!60%60!80%
PHENIX Preliminaryc = 200 GeV/NNsRun!5 Cu + Cu
= 0.3#Gaussian filter,
compared to p + puncorrected background!unfolded Cu + Cu
(Yue Shi Lai, for the PHENIX Collaboration) APS DPF Meeting 2009, Heavy Ions III 19 / 35
Physics in Collisions - 30th August - 2nd September 2009Helen Caines
Inclusive jet x-section in Au-Au and Cu-Cu
18
Au-Au collisions 0-10%
lines=unfolding uncertainties
STAR Preliminary
Extends reach of jet quenching studies to pT > 40 GeV
Y. Lai QM2009M.Ploskon QM2009
Inclusive jet spectrum measured in A-A collisions for first time
Run-5 Cu! Cu RAA
)c (GeV/pprec!T
p0 5 10 15 20 25 30 35
AAR
00.20.40.60.8
11.21.41.61.8
2PHENIX Preliminary
60!80%40!60%20!40%0!20%
= 200 GeVNNsRun!5 Cu + Cu = 0.3!Gaussian filter,
(Yue Shi Lai, for the PHENIX Collaboration) APS DPF Meeting 2009, Heavy Ions III 20 / 35
Physics in Collisions - 30th August - 2nd September 2009Helen Caines
Jet RAA in Cu-Cu using Gaussian Filter
19
• Reconstructed jets highly suppressed in central collisionsGaussian Filter: designed to find vacuum like fragmentation
Y. Lai QM2009
Run-5 Cu! Cu RAA compared to !0
)c (GeV/pprec!T
p0 5 10 15 20 25 30 35
AAR
00.20.40.60.8
11.21.41.61.8
2PHENIX Preliminary
0!20% = 0.7 (PRL 101, 162301)!z" 0!10%, 0#
= 200 GeVNNsRun!5 Cu + Cu = 0.3$Gaussian filter,
(Yue Shi Lai, for the PHENIX Collaboration) APS DPF Meeting 2009, Heavy Ions III 23 / 35
Run-5 Cu! Cu RAA
)c (GeV/pprec!T
p0 5 10 15 20 25 30 35
AAR
00.20.40.60.8
11.21.41.61.8
2PHENIX Preliminary
60!80%40!60%20!40%0!20%
= 200 GeVNNsRun!5 Cu + Cu = 0.3!Gaussian filter,
(Yue Shi Lai, for the PHENIX Collaboration) APS DPF Meeting 2009, Heavy Ions III 20 / 35
Physics in Collisions - 30th August - 2nd September 2009Helen Caines
Jet RAA in Cu-Cu using Gaussian Filter
19
• Reconstructed jets highly suppressed in central collisions
• Jets as suppressed as single particles
Gaussian Filter: designed to find vacuum like fragmentationY. Lai QM2009
Run-5 Cu! Cu RAA compared to !0
)c (GeV/pprec!T
p0 5 10 15 20 25 30 35
AAR
00.20.40.60.8
11.21.41.61.8
2PHENIX Preliminary
0!20% = 0.7 (PRL 101, 162301)!z" 0!10%, 0#
= 200 GeVNNsRun!5 Cu + Cu = 0.3$Gaussian filter,
(Yue Shi Lai, for the PHENIX Collaboration) APS DPF Meeting 2009, Heavy Ions III 23 / 35
Run-5 Cu! Cu RAA
)c (GeV/pprec!T
p0 5 10 15 20 25 30 35
AAR
00.20.40.60.8
11.21.41.61.8
2PHENIX Preliminary
60!80%40!60%20!40%0!20%
= 200 GeVNNsRun!5 Cu + Cu = 0.3!Gaussian filter,
(Yue Shi Lai, for the PHENIX Collaboration) APS DPF Meeting 2009, Heavy Ions III 20 / 35
Physics in Collisions - 30th August - 2nd September 2009Helen Caines
Jet RAA in Cu-Cu using Gaussian Filter
19
• Reconstructed jets highly suppressed in central collisions
• Jets as suppressed as single particles Energy shift or jet not reconstructed?
Gaussian Filter: designed to find vacuum like fragmentationY. Lai QM2009
(GeV/c)Jet
Tp
15 20 25 30 35 40 45 50
Yie
ld R
ati
o:
R=
0.2
/R=
0.4
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
STAR Preliminary
=200 GeV/cNN
sAu+Au and p+p at
Au+Au: 10% most central Au+Au kt
Au+Au anti-kt
p+p kt
p+p anti-kt
Physics in Collisions - 30th August - 2nd September 2009Helen Caines
Look at the jet energy profile
20
p-p: “Focussing” of jet fragmentation with increasing jet energy
Au-Au:“Broadening” of jet fragmentation with increasing jet energy
De-focussing of energy profile when jet passes through sQGP
R=0.2
R=0.4
M. Ploskon QM2009
0.2<pt,assoc<1.0 GeV 1.0<pt,assoc<2.5 GeV
pt,assoc>2.5 GeV
Open symbols p+p
STAR Preliminary0-20% Au+Au
STAR Preliminary0-20% Au+Au
STAR Preliminary0-20% Au+Au
J.Putschke RHIC/AGS 2009
Physics in Collisions - 30th August - 2nd September 2009Helen Caines
Jet-hadron correlations Au-Au vs. p-p
21
High Tower Trigger (HT): tower 0.05x0.05 (ηxϕ) with Et> 5.4 GeV
Δϕ=ϕJet − ϕAssoc.
ϕJet = jet-axis found by Anti-kT, R=0.4, pt,cut>2 GeV and pt,rec(jet)>20 GeV
Δϕ1
Recoiljet
Triggerjet
Δϕ2Open symbols p+p
Open symbols p+p
0.2<pt,assoc<1.0 GeV 1.0<pt,assoc<2.5 GeV
pt,assoc>2.5 GeV
Open symbols p+p
STAR Preliminary0-20% Au+Au
STAR Preliminary0-20% Au+Au
STAR Preliminary0-20% Au+Au
J.Putschke RHIC/AGS 2009
Physics in Collisions - 30th August - 2nd September 2009Helen Caines
Jet-hadron correlations Au-Au vs. p-p
21
High Tower Trigger (HT): tower 0.05x0.05 (ηxϕ) with Et> 5.4 GeV
Δϕ=ϕJet − ϕAssoc.
ϕJet = jet-axis found by Anti-kT, R=0.4, pt,cut>2 GeV and pt,rec(jet)>20 GeV
• Broadening of recoil-side
• Softening of recoil-side
First direct measurement of Modified Fragmentation due to presence of sQGP
Open symbols p+p
Open symbols p+p
Physics in Collisions - 30th August - 2nd September 2009Helen Caines
Summary of Jet Studies
22
• p-p jet reference measurements are well understood - we have a calibrated probe
• The UE at RHIC is small and suggests MPI at LHC will be smaller than initially predicted
• Cold nuclear matter effects on jets are small (d-Au compared to p-p)
• The large background under jets in A-A can be accounted for
• Jets reconstructed in A-A assuming vacuum frag. show same suppression as for single hadrons (Gaussian filter studies)
• Strong evidence of broadening and softening of the jet energy profile (R=0.2/R=0.4, jet-hadron)
Results can be explained as due to significant partonic energy loss in the sQGP before fragmentation
Physics in Collisions - 30th August - 2nd September 2009Helen Caines
Local Strong Parity Violation
23
NCS = -2 -1 0 1 2
instantonsphaleron
Energy of gluon field
• Topological charge density illustration of QCD vacuum structure of gluon-field configurations in 4-D (movie available) from lattice-based simulations Box volume = 2.4 X 2.4 X 3.6 fm3.Animation/Picture by Derek Leinweber
In QCD, chiral symmetry breaking is fundamental and due to nontrivial topological solutions; among the best evidence for this physics would be event-by-event local strong parity violation
Instantons and sphalerons are localized (in space and time) solutions describing transitions between different vacua via tunneling or go-over-barrier
Physics in Collisions - 30th August - 2nd September 2009Helen Caines
Local Strong Parity Violation
23
NCS = -2 -1 0 1 2
instantonsphaleron
Energy of gluon field
• Topological charge density illustration of QCD vacuum structure of gluon-field configurations in 4-D (movie available) from lattice-based simulations Box volume = 2.4 X 2.4 X 3.6 fm3.Animation/Picture by Derek Leinweber
In QCD, chiral symmetry breaking is fundamental and due to nontrivial topological solutions; among the best evidence for this physics would be event-by-event local strong parity violation
Instantons and sphalerons are localized (in space and time) solutions describing transitions between different vacua via tunneling or go-over-barrier
All non-Abelian gauge theories admit such non-trivial vacuum fluctuations – e.g., B- and CP-violating sphalerons frozen in at EW phase transition are (one) speculated origin of Baryon Asymmetry of the Universe!
24Physics in Collisions - 30th August - 2nd September 2009Helen Caines
LSPV and sQGP
Attempt to see this effect at RHIC in non-central collisions:
L or B Heavy-Ion collision: deconfined partons over large volume + chiral symmetry restoration
Usually this effect is confined within a nucleon and averages to zero over space and time
24Physics in Collisions - 30th August - 2nd September 2009Helen Caines
large orbital angular momentum perp. to RP + large localized B fields + deconfined phase ⇒ strong P violating domains with diff. no. of left & right handed quarks
Kharzeev et al. PRL 81 (1998) 512, and PRD 61 (2000) 111901
LSPV and sQGP
Attempt to see this effect at RHIC in non-central collisions:
L or B Heavy-Ion collision: deconfined partons over large volume + chiral symmetry restoration
Usually this effect is confined within a nucleon and averages to zero over space and time
24Physics in Collisions - 30th August - 2nd September 2009Helen Caines
⇒ Preferential emission of like sign particles in the direction of the angular momentum i.e. opposite sides of the reaction plane
(Voloshin PRC 70 (2004) 057901)
large orbital angular momentum perp. to RP + large localized B fields + deconfined phase ⇒ strong P violating domains with diff. no. of left & right handed quarks
Kharzeev et al. PRL 81 (1998) 512, and PRD 61 (2000) 111901
LSPV and sQGP
Attempt to see this effect at RHIC in non-central collisions:
L or B Heavy-Ion collision: deconfined partons over large volume + chiral symmetry restoration
Usually this effect is confined within a nucleon and averages to zero over space and time
dN±d!
! 1 + 2a±sin(!"!RP ) + ..
!cos(!! + !" " 2!RP )# $
Physics in Collisions - 30th August - 2nd September 2009Helen Caines
LSPV - making the measurement
25
the asymmetry
instead measure
Averages to zero due to random domains
Doesn’t average to zero
(v1,!, v1," ! a!a")
STAR Preliminary
Opposite side
Same side
S. Voloshin, QM09
dN±d!
! 1 + 2a±sin(!"!RP ) + ..
!cos(!! + !" " 2!RP )# $
Physics in Collisions - 30th August - 2nd September 2009Helen Caines
LSPV - making the measurement
25
the asymmetry
instead measure
Averages to zero due to random domains
Doesn’t average to zero
• Measurement follows expected trends
• Excellent statistical significance for Au-Au and Cu-Cu at top RHIC energies
(v1,!, v1," ! a!a")
STAR Preliminary
Opposite side
Same side
S. Voloshin, QM09
• P-even so may contain other effects: several investigated (resonances, jets) none result in observed magnitude and centrality dependence of signal
dN±d!
! 1 + 2a±sin(!"!RP ) + ..
!cos(!! + !" " 2!RP )# $
Physics in Collisions - 30th August - 2nd September 2009Helen Caines
LSPV - making the measurement
25
the asymmetry
instead measure
Averages to zero due to random domains
Doesn’t average to zero
• Measurement follows expected trends
• Excellent statistical significance for Au-Au and Cu-Cu at top RHIC energies
(v1,!, v1," ! a!a")
STAR Preliminary
Opposite side
Same side
S. Voloshin, QM09
• P-even so may contain other effects: several investigated (resonances, jets) none result in observed magnitude and centrality dependence of signal
dN±d!
! 1 + 2a±sin(!"!RP ) + ..
!cos(!! + !" " 2!RP )# $
Physics in Collisions - 30th August - 2nd September 2009Helen Caines
LSPV - making the measurement
25
B-field+deconfinement+chiral restoration→ strong threshold effect
the asymmetry
instead measure
Averages to zero due to random domains
Doesn’t average to zero
• Measurement follows expected trends
• Excellent statistical significance for Au-Au and Cu-Cu at top RHIC energies
(v1,!, v1," ! a!a")
Physics in Collisions - 30th August - 2nd September 2009Helen Caines
What’s next - RHIC: Beam Energy Scan
26
At RHIC we transition to a new state of matter - the sQGP
Lattice QCD predicts:• High T & Low µB
Cross-over• High µB & Low T -
1st order transition• Mid µB & Mid T - Critical Point
Physics in Collisions - 30th August - 2nd September 2009Helen Caines
What’s next - RHIC: Beam Energy Scan
26
Scan from √s=5-40 GeV starts 2010
At RHIC we transition to a new state of matter - the sQGP
Lattice QCD predicts:• High T & Low µB
Cross-over• High µB & Low T -
1st order transition• Mid µB & Mid T - Critical Point
(BES also at FAIR and SPS)
Location of CP not known - experimental search needed
Physics in Collisions - 30th August - 2nd September 2009Helen Caines
What’s next - RHIC: Beam Energy Scan
26
Evidence of a critical point and/or 1st order phase transition?
Does LSPV signal persist?
What √s does sQGP “turn off”?
Scan from √s=5-40 GeV starts 2010
At RHIC we transition to a new state of matter - the sQGP
Lattice QCD predicts:• High T & Low µB
Cross-over• High µB & Low T -
1st order transition• Mid µB & Mid T - Critical Point
(BES also at FAIR and SPS)
Location of CP not known - experimental search needed
Physics in Collisions - 30th August - 2nd September 2009Helen Caines 27
What’s next - LHC: The new energy frontierLHC starting in couple of months. Pb-Pb collisions in 2010Over an order of magnitude higher energy than at RHIC
ALICE, ATLAS, CMSAll have heavy-ion programs
sQGP: hotter, bigger, longer lived more detailed measurements
Jet and heavy flavour frontiers to be fully explored
LQCD, Z. Fodor, Lattice 2007
RHIC LHC Ideal Gas
Does matter at LHC still behave as near “perfect” liquid?
Physics in Collisions - 30th August - 2nd September 2009Helen Caines
Summary
28
• RHIC and LHC have exciting new programs that start during 2010.
• Many results still to be fully understood and predictions left to test. Key questions being asked:
• How do partons interact with the sQGP and what are the mechanisms of their energy loss? • What are the properties of the medium produced and how do they change at different energies?• What/where are the landmarks on the QCD phase diagram?
• Evidence of local strong parity violation - fundamental prediction of QCD
• continue to test with BES
If you understand everything, you must be misinformed - Japanese Proverb
Physics in Collisions - 30th August - 2nd September 2009Helen Caines 29
Geometry of a heavy-ion collision
Number of participants (Npart): number of incoming nucleons (participants) in the overlap regionNumber of binary collisions (Nbin): number of equivalent inelastic nucleon-nucleon collisions
Reaction plane
x
z
y
Non-central collision
“peripheral” collision (b ~ bmax)“central” collision (b ~ 0)
Nbin ≥ Npart
Physics in Collisions - 30th August - 2nd September 2009Helen Caines 30
Effect of hard scattering cut-off scaling
From Rick Field
Increasing ε creates smaller energy dependence for UE
➝ 35% more RHIC➝ 26% less LHC
ε = 0.16 (DWT) ➝ 0.25 (DW)
Measurable effect at RHIC
RHIC 200 GeV
LHC 14
TeV
Physics in Collisions - 30th August - 2nd September 2009Helen Caines
“Fake-Jet” contribution
31
STAR Preliminary
Trigger jet pT > 10 GeV
pTcut,particle = 0.1 GeV
STAR Preliminary
Au+Au HT 0-20%
“Fake” jets: signal in excess of background model from random association of uncorrelated soft particles (i.e. not due to hard scattering)
• Inclusive jet spectrum:Spectrum of “jets” after randomizing HI event in ϕ and removing leading jet particle
• Di-Jet / Fragmentation function:Background di-jet rate = “Fake” + Additional Hard Scattering
Estimated using “jet” spectrum at 90 deg.
Physics in Collisions - 30th August - 2nd September 2009Helen Caines
Spectrum Unfolding
32
Corrections for smearing of jet pt due to HI bkg. nonuniformities:
1) raw spectrum
2) removal of “fake”-correlations
3) unfolding (bayesian) of HI bkg. fluctuations
4) correction for pT resolutionSTAR Preliminary
Physics in Collisions - 30th August - 2nd September 2009Helen Caines
Recoil jet RAA in Au-Au
33
Recoiljet
Triggerjet
• Select unmodified trigger jet - comes from surface• Maximizes path-length for the back-to-back jets
Physics in Collisions - 30th August - 2nd September 2009Helen Caines
Recoil jet RAA in Au-Au
33
Jets no longer found due to extreme modification?
Recoiljet
Triggerjet
• Select unmodified trigger jet - comes from surface• Maximizes path-length for the back-to-back jets
(recoil) [GeV/c]t,rec
p10 15 20 25 30 35 40
AuAu
(0-2
0%)/p
p
0
0.2
0.4
0.6
0.8
1
1.2
1.4 >10 GeV/ctrigt
AntiKt R=0.4, p
1 GeV± bkgσBackground uncertainty
Trigger jet energy uncertainity
STAR PreliminaryAu+Au (0-20%) 200 GeVp+p 200 GeV
E.Bruna QM2009
yield now also strongly suppressed for R=0.4