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

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

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

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

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

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

Hua Pei, Iowa State University on SQM2007 for PHENIX What’s the “New” Tool? Df p+p, PHENIX PRD, 74 072202 (06). Give definitions here. All of them. 2/23/2019 Hua Pei, Iowa State University on SQM2007 for PHENIX

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

How are jets modified then? PHENIX nucl-ex/0611019 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

How shall we quantify this modified jet? PHENIX nucl-ex/0611019 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

How do we quantify the change of medium itself, then? Au+Au / p+p s = 200 GeV arXiv:0705.3238 [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

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:0705.3238 [nucl-ex] 2/23/2019 Hua Pei, Iowa State University on SQM2007 for PHENIX

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:0705.3238 [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

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:0705.3238 [nucl-ex] 2/23/2019 Hua Pei, Iowa State University on SQM2007 for PHENIX

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

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

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

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/9605213 ~10 years ago p0 g g g hot dense medium 2/23/2019 Hua Pei, Iowa State University on SQM2007 for PHENIX

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

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

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

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

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, 034909 (2004) 2/23/2019 Hua Pei, Iowa State University on SQM2007 for PHENIX

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

Hua Pei, Iowa State University on SQM2007 for PHENIX PHENIX nucl-ex/0611019 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

Hua Pei, Iowa State University on SQM2007 for PHENIX arXiv:0705.3238 [nucl-ex] 2/23/2019 Hua Pei, Iowa State University on SQM2007 for PHENIX

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 Bielcikova @ Winter Workshop 2007. 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

Centrality dependence of near-side yield Jet + Ridge Jet Ridge Jet Copied from Jana Bielcikova @ 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

pTtrigger dependence of jet and ridge yields Jet + Ridge Jet Ridge Copied from Jana Bielcikova @ 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

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 Bielcikova @ 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

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:0705.3238 [nucl-ex] 2/23/2019 Hua Pei, Iowa State University on SQM2007 for PHENIX

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

√s=200 GeV, p+p => x NLO QCD agrees well with data D. d’Enterria nucl-ex/0611012 2/23/2019 Hua Pei, Iowa State University on SQM2007 for PHENIX