1. Medium effect on jet correlations in Au+Au and Cu+Cu collisions at sqrt(sNN) = 200GeV at RHIC-PHENIX
Hua Pei
Iowa State University
For the collaboration of PHENIX
2/23/2019
Hua Pei, Iowa State University on SQM2007 for PHENIX

2. Hua Pei, Iowa State University on SQM2007 for PHENIX
Outline
Physics Scheme
How parton-jet has been changed by the hot medium created at RHIC?
How this medium will make its own response to this jet?
In the Order of Slides
Detector
Analysis Method
Histograms of Jet Shape and Yield, comparing AA to p+p
2/23/2019
Hua Pei, Iowa State University on SQM2007 for PHENIX

3. Hua Pei, Iowa State University on SQM2007 for PHENIX
What are we looking at?
leading particle suppressed c d
hadrons a b
AA(AuAu or CuCu)
hadrons a b c d
p+p
leading particle (trigger)
vs.
Parton Distribution Functions
Hard-scattering cross-section
Fragmentation Function
Initial yields and pT distributions can be predicted from p+p measurements + pQCD + collision geometry + cold (initial) nuclear effects
Critical to perform measurements in reference p+p and p(d)+A systems
In AA collision, observed deviations from reference measurements can be attributed to the medium,
2/23/2019
Hua Pei, Iowa State University on SQM2007 for PHENIX

4. What experiment do we use?
EMCAL --- measure energy deposit of electrons and gammas
DC --- obtain momentum of charged particles
PC --- measure hit position of charged particles 
,0
Tracking and Matching (DC, PC)
charged hadrons  Ks 0 h+ h-
EMCAL (PbSc + PbGl)
,0,Ks
PID -- TOF and EMCal
2/23/2019
Hua Pei, Iowa State University on SQM2007 for PHENIX

5. What do we know from single particle measurement?
See more details on Monday’s talk from Arkadij Taranenko
Strong suppression (RAA ~ 0.2) is seen even at high pT
Constant for pT>4GeV/c for all centralities
2/23/2019
Hua Pei, Iowa State University on SQM2007 for PHENIX

6. Why we are not satisfied yet?
Remember at the beginning we asked two questions:
How parton-jet has been changed by the hot medium created at RHIC?
How this medium will make its own response to this jet?
Single spectrum is the convolution of these two effects. How do we identify them from each other?
2/23/2019
Hua Pei, Iowa State University on SQM2007 for PHENIX

7. Hua Pei, Iowa State University on SQM2007 for PHENIX
What’s the “New” Tool? Df
p+p, PHENIX
PRD, (06).
Give definitions here. All of them.
2/23/2019
Hua Pei, Iowa State University on SQM2007 for PHENIX

8. What does the jet look like now?
vs.
Observation of particles produced
~1 radian away from back-to-back!
Correlation survives high-multiplicity environment of A+A
But in more than one way …
2/23/2019
Hua Pei, Iowa State University on SQM2007 for PHENIX

9. How are jets modified then?
PHENIX nucl-ex/
We see in AA collisions the far-side peak not at Df = p as they used to be at p+p. Need to quantify this change
2/23/2019
Hua Pei, Iowa State University on SQM2007 for PHENIX

10. How shall we quantify this modified jet?
PHENIX nucl-ex/
Fit away-side peak with double Gaussian, each centered at
Df = p ± D
D scales with collision energy and system size!
Emission consistent with strong medium response to energy deposited by the traversing medium
2/23/2019
Hua Pei, Iowa State University on SQM2007 for PHENIX

11. How do we quantify the change of medium itself, then?
Au+Au / p+p s = 200 GeV
arXiv: [nucl-ex]
Establish the punch-through jet component (“Head Region”)
and the medium-induced component (“Shoulder Region”)
HR+SR (|Df-p|<=p/2) and HR (|Df-p|<=p/6).
Per-trigger yield vs. Df
In next slide we show various trigger and partner (pAT  pBT),
arranged by increasing pair momentum (pAT + pBT)
2/23/2019
Hua Pei, Iowa State University on SQM2007 for PHENIX

12. How is the medium changed itself?
Au+Au & p+p s = 200 GeV
Evolves from flat  concave  convex
Do the side peaks merge to form the reappearance of “header” peak? Or do the header/side peaks represent two different physics mechanisms?
arXiv: [nucl-ex]
2/23/2019
Hua Pei, Iowa State University on SQM2007 for PHENIX

13. How do we quantify this side-peak?
Analogous to RAA, but describes jet yield modification
HR exhibits early onset of suppression, relative to p+p
H+S (entire away side) exhibits overall enhancement
arXiv: [nucl-ex]
HR is suppressed due to jet quenching,
SR is enhanced, reflecting the response of medium to deposited energy.
2/23/2019
Hua Pei, Iowa State University on SQM2007 for PHENIX

14. Hua Pei, Iowa State University on SQM2007 for PHENIX
What PHENIX see further: Truncated mean-pT for 1<pTB< 5, vs. Npart
Near side: flat with Npart (>100), increase with pTA.
Far side: shows a very different centrality and pTA dependence of the <pT> between HR and SR.
HR smooth decrease with Npart up to 200, behaviors consistently with jet quenching
SR however, shows an universal partner spectra shape, reflecting the property of response of medium to lost energy.
Move to backup
arXiv: [nucl-ex]
2/23/2019
Hua Pei, Iowa State University on SQM2007 for PHENIX

15. How PID helps our jet analysis (1) ?
Trigger high-pT p0
Near side
We also observe jets broader in Near-side Cu+Cu than p+p, showing the medium effects at near-side as well.
2/23/2019
Hua Pei, Iowa State University on SQM2007 for PHENIX

16. How associated PID helps our jet analysis?
PHENIX Preliminary
Associated Charged
Baryon/Meson
Away side
Jet-pair distributions for associated mesons (squares) and baryons (circles) for 1 < pTassoc < 1.3 GeV/c (top) and 1.6 < pTassoc < 2.0 (bottom).
Results are for a hadron trigger (2.5 < pT < 4.0 GeV/c) and centrality selections of 0-20% and 20-40%.
2/23/2019
Hua Pei, Iowa State University on SQM2007 for PHENIX

17. How associated PID helps our jet analysis (con) ?
Associated Charged
Baryon/Meson
Near/Away side
There is a clear increase in the slope (for mesons, Fig. 3b) going from peripheral to central, showing that medium affects particle ratio on both near and away sides. The slope *parameter* aka 'temperature‘ also shows similar trend as inclusive p/p ratio going from central to peripheral.
2/23/2019
Hua Pei, Iowa State University on SQM2007 for PHENIX

18. How PID can do more on jet analysis?
PHENIX Preliminary
g trigger jets
Normal dijet (po-h):
Trigger bias: Ep < Ejet,
Possible surface bias
Direct g tagged jet:
No fragmentation: Eg ~ Ejet
No strong interaction, sensitive
to the whole medium
But!
Trigger g is a mixture of direct and hadron-decay photon. Need more effort to subtract decay part.
Proposed in hep-ph/
~10 years ago p0 g g g
hot dense medium
2/23/2019
Hua Pei, Iowa State University on SQM2007 for PHENIX

19. Summary and Conclusion
PHENIX physics program has steady progressed beyond “discovery” stage, addressing next level of questions mapping out properties of the plasma :
How are jets affected by passage through the medium created in RHIC collisions?
How does the medium respond to the impact of a high-pT probe?
Answers include:
splitting D universal with different systems => interaction of jet and medium
head-region decreases => suppression of jet
shoulder region increases with lower pt, => consistence with medium response
jets modified near and far side, including baryon-rich at central collision
What shown here only scratch the surface of the methods for studying the medium in PHENIX!
2/23/2019
Hua Pei, Iowa State University on SQM2007 for PHENIX

20. Hua Pei, Iowa State University on SQM2007 for PHENIX
Backup Slides
2/23/2019
Hua Pei, Iowa State University on SQM2007 for PHENIX

21. What We had Expected Expectation from Theorists.
QCD “Phase Diagram”
F. Karsch, Prog. Theor. Phys. Suppl. 153, 106 (2004)
Seeking the Quark Gluon Plasma (QGP)
Existed early in the universe
Expected to be created in RHIC collisions
Lattice QCD predicts a transition to the QGP
T ~ 170 MeV
e ~ 1.0 GeV/fm3
For QGP, strong interaction plays critical role
Deconfinement of quarks and gluons
Need properties and dynamics of this strongly interacting system
Expectation from Theorists.
2/23/2019
Hua Pei, Iowa State University on SQM2007 for PHENIX

22. Hua Pei, Iowa State University on SQM2007 for PHENIX
What particle do we use?
Backup Slides.
RHIC Run4 Au+Au data
Sampled 241 mb-1
1972 x 241 mb-1 ~ 1 pb-1 p+p equivalent
1.5 B events recorded
RHIC Run5 Cu+Cu data
Sampled 3 nb-1
632 x 3 nb-1 ~ 1 pb-1 p+p equivalent
2.2 B events sampled
59 M minimum bias events
1.9 M high-pT triggered
2/23/2019
Hua Pei, Iowa State University on SQM2007 for PHENIX

23. Hua Pei, Iowa State University on SQM2007 for PHENIX
What particle do we use?
Backup Slides.
And we have a good spectrum of identified particles at PHENIX
(Phys. Rev. C 69, (2004)
2/23/2019
Hua Pei, Iowa State University on SQM2007 for PHENIX

24. Where this CF tool has led us?
Azimuthal correlation functions show ~ complete absence of “away-side” jet
pT,trig: 4-6 or 3-4
pT,assoc: 2 - pT,trig
Pedestal&flow subtracted
Backup Slides.
Further evidence for surface emission only (?)
That is, “partner” in hard scatter is absorbed in the dense medium
Question: where has the energy gone?
(Partial) Answer: need to widen “search” in pT
Make sure to find out the pt ranges – this is the difference from the results that will follow.
Intro explanation of technique/consequences: the awayside jet disappears, but the energy has to go somewhere… but where????
2/23/2019
Hua Pei, Iowa State University on SQM2007 for PHENIX

25. Hua Pei, Iowa State University on SQM2007 for PHENIX
PHENIX nucl-ex/
The measured correlation C(Df) (squares) and the (di)jet correlation J(Df) (circles with boxes for point-to-point systematic errors) in central Au+Au collisions at sqrt(NN) = 200 GeV/c.
The full line shows the background term and the dotted line shows a C(Df) fit with Jet + Flow background.
The left axis shows the measured correlation amplitude and the right axis shows the (di)jet correlation amplitude.
2/23/2019
Hua Pei, Iowa State University on SQM2007 for PHENIX

26. Hua Pei, Iowa State University on SQM2007 for PHENIX
arXiv: [nucl-ex]
2/23/2019
Hua Pei, Iowa State University on SQM2007 for PHENIX

27. Hua Pei, Iowa State University on SQM2007 for PHENIX
What’s your knowledge about “Ridge” effect at RHIC?
relative ridge yield := ridge yield / Jet()
pt,assoc. > 2 GeV
3<pt,trigger<4 GeV
Au+Au 0-10%
STAR preliminary
Copied from Jana Winter Workshop Move to Backup Slides.
STAR preliminary
“jet” slope
ridge slope
inclusive slope
As STAR observed, the “ridge” is much softer than “jet” in high-pT trigger region (5-10GeV).
Do PHENIX also see that?
2/23/2019
Hua Pei, Iowa State University on SQM2007 for PHENIX

28. Centrality dependence of near-side yield
Jet + Ridge
Jet
Ridge
Jet
Copied from Jana Winter Workshop 2007
-> “ridge” yield increases with centrality
ridge of K0S < ridge of Λ
steep increase of near-side yield with centrality in Au+Au
ratio of yields in central Au+Au/d+Au ~ 4-5
-> “jet” yield is independent of centrality and agrees with d+Au
(effects of merged tracks under study)
2/23/2019
Hua Pei, Iowa State University on SQM2007 for PHENIX

29. pTtrigger dependence of jet and ridge yields
Jet + Ridge
Jet
Ridge
Copied from Jana Winter Workshop 2007
near-side associated yield is ridge dominated at intermediate pT
jet yield:
- increases steeply with pTtrigger
- smaller for Λ-triggers than for K0S-triggers ?
- baryon jet is wider than meson jet
- effects of merged tracks under study
jet/ridge ratio increases with pTtrigger
2/23/2019
Hua Pei, Iowa State University on SQM2007 for PHENIX

30. pT-distribution of associated particles
STAR preliminary
“jet” slope
ridge slope
inclusive slope
J. Putschke (STAR), QM’06
h-h correlations
pTassociated>2GeV/c
Copied from Jana Winter Workshop 2007
Ridge spectra similar
to particles from the bulk
Jet spectra are harder
(T increases steeply with pTtrig)
Trigger particle
T(ridge) MeV
T (jet) MeV
h+/-
438 ± 4 (stat.)
478 ± 8
K0S
406 ± 20 (stat.)
530 ± 61 Λ
416 ± 11 (stat.)
445 ± 49
2/23/2019
Hua Pei, Iowa State University on SQM2007 for PHENIX

31. What PHENIX see: Truncated mean-pT for 1<pTB< 5, vs. Npart
Intermediate pT: shows a very different centrality and pTA dependence of the <pT> between HR and SR.
HR behavior consistent with jet quenching
SR however, shows an universal partner spectra shape, reflecting the property of response of medium to lost energy.
Nearside: flat with Npart (>100), increase with pTA.
S region: flat with Npart (>100) and pTA.
H region: smooth decrease with Npart up to 200.
Move to backup
arXiv: [nucl-ex]
2/23/2019
Hua Pei, Iowa State University on SQM2007 for PHENIX

32. PID dependent Jet-correlation
PHENIX Preliminary
Jet-pair distributions for associated mesons (red) and baryons (blue) for 1.3 < pTassoc < 1.6 GeV/c and hadron trigger (2.5 < pT < 4.0 GeV/c) and centrality selections of 20-40% (top) and 70-90% (bottom).
2/23/2019
Hua Pei, Iowa State University on SQM2007 for PHENIX

33. √s=200 GeV, p+p => x NLO QCD agrees well with data
D. d’Enterria
nucl-ex/
2/23/2019
Hua Pei, Iowa State University on SQM2007 for PHENIX