Jet Physics at RHIC Jiangyong Jia Every paper

Jet Physics at RHIC Jiangyong Jia Every paper can be found at: https: //www. phenix. bnl. gov/WWW/p/talk/papers. php n 2021/6/14 1

Quarks, gluons and Confinement No free quark. “coulomb” type of potential QCD is a “confining” gauge theory, leads to QCD bound states with an effective potential: QED “Coulomb” QCD “Confining” V(r) Hydrogen atom r 2021/6/14 Jiangyong Jia 2

Confining Potential: k r Energy used to separate quarks is converted to potential, which excites from the vacuum. r String with tension k ~ 1 Ge. V/fm faster slower hadrons Now image collide two high energy quarks leading particle q Jet : the collection of particles from the “same” quark/gluon 2021/6/14 q hadrons Jiangyong Jia leading particle 3

Plasma Hydrogen gas Heat to 13. 6 e. V or 120 K Full ionization Hot plasma of p, e, photon Strong EM field Normal Nuclear matter Heat to 170 Me. V or 2 x 1012 Full melting Quark Gluon Plasma Strong QCD field 2021/6/14 Jiangyong Jia 4

The Quark Gluon Plasma Energy density for “g” massless d. o. f, g = 3 for normal nuclear matter g = 37 for Quark Gluon Plasma (gluons, quarks, spin, color) “Lattice QCD” predicts a transition to a Quark Gluon Plasma. e/T 4 Transition values: T = 170 Me. V e = 0. 8 Ge. V/fm 3 hadrons quark/gluon Assumes thermal system. T/Tc 2021/6/14 Jiangyong Jia 5

One Head on Au + Au Collision at RHIC 1000’s of particles Au Au s. NN = 200 Ge. V (center-of-mass energy per nucleon-nucleon collision) 2021/6/14 Jiangyong Jia 6

Space-time Evolution of Collisions time g p+ p jet K p 0 e L J/Y Hadronization Ex p an si o n Freeze-out QGP Thermaliztion Hard Scattering Our interest space Au Au 2021/6/14 Jiangyong Jia 7

Goals of heavy-ion collisions n n Create QGP as transient state in heavy-ion collisions Verify existence of QGP Study properties of QGP Study QCD confinement and how hadrons get their masses 2021/6/14 Jiangyong Jia 8

Questions n Have we created a matter? Is there a well-defined n n Energy density Temperature Chemical potential Size z e T m R y n What is the collective behavior of the matter? n n n Expansion velocity Elliptic flow It’s viscosity x v v 2 h Have we created a quark gluon matter? n What is the dynamical properties of the matter? n n Opacity Debye (color) screening in quark gluon state 2021/6/14 Jiangyong Jia 9

Tools n Deduce from particles emitted by the matter hadrons , K, p frequent, produced “late” when particles stop to interact, temperature of late stage n electro-magnetic radiation g, e+e-, m+mrare, emitted “any time”; reach detector unperturbed by strong final state interaction p p K p J/ temperature of plasma stage p n cc q q p n g Using penetrating probes p p p p “hard” probes: Jets, J/psi very rare, created “early” before QGP formation, penetrate hot and dense matter. n 2021/6/14 Jiangyong Jia p p p e- 10 e+

Energy Density e = E/V Bjorken hydrodynamics: p. R 2 2 ct 0 Time to thermalize the system PHENIX: Central Au+Au yields For 0 = 0. 2 fm/c e. Bj = 23 Ge. V/fm 3 !!! For 0 = 1 fm/c e. Bj = 4. 6 Ge. V/fm 3 !!! Energy density far above transition value predicted by lattice PRL 87 052301 (2001) 2021/6/14 Phys. Rev. C 71, 034908 (2005) Jiangyong Jia 11

Temperature and Chemical Potential n Determined by statistical models: for example n Boltzmann distributions (temperature T , chemical potential m) : n One ratio determines m / T : PLB 518 (2001) 41 All hadrons reach chemical equilibrium at T> 170 Me. V m ~ 0, , Temperature is much higher at earlier plasma stage 2021/6/14 Jiangyong Jia 12

Hydrodynamics of an Expanding Source expanding source purely thermal source T light T, v heavy p. T More push for heavier particles + Collective velocity fields superimposed on thermal (~Boltzmann) distributions Large flow velocity: v~ 0. 5 -0. 6 c Heinz & Kolb hep-ph/0204061 PRL 88, 242301 (2002) , PRC 69, 024904 (2004) PRC 69, 034909 (2004) 2021/6/14 Jiangyong Jia 13

Hydrodynamics of Elliptic Flow Out of plane Less matter, easy to expand, large v More matter, difficult to expand, small v In plane azimuthal asymmetry Large v 2 : v 2 ~0. 15 => yield in plane and out of plane differ by 50%! v 2 Thermalization time 0=0. 6 fm/c and e=20 Ge. V/fm 3 And no viscosity *viscosity = resistance of liquid to shear forces (and hence to flow) perfect fluid 2021/6/14 p. T White. Jiapaper: Jiangyong NPA 757, (2005) 184 14

What we know about this matter? Energy density and temperature above threshold Near 0 chemical potential: Baryon number free Strong collective flow, requires: early themalization, high energy density and perfect fluid. Quark-Gluon (partonic) Matter 2021/6/14 Jiangyong Jia 15

Probing the QGP “matter box” “ideal” experiment Absorption or scattering pattern Calibrated source QGP N 1 N 2 But, the fleeting QGP can not be put in box. Need auto generated probe: Hard-scattered jets hadrons Leading particle • Generated early • Rate calculable hadrons 2021/6/14 Jiangyong Jia leading particle 16

Calculate Hard-scattering rate: perturbative QCD n Incoming quarks and gluons (a, b) parton distribution function: f Parton scattering: fa/A Afa/p fa/B Bfa/p. cross section momentum dist. of particles created by outgoing quark or gluon (i. e. in a jet) : known D(z) : fa/A A fb/B z) n calculable a/A D( n c a d b B J. Owens Rev. MP, 59 (1987) 465 2021/6/14 Jiangyong Jia 17

Calibrating Our Probes High Energy Probes are well described in Proton reactions by Perturbative QCD. In A+A collisions: Scales by number of nucleon-nucleon collisions: Ncoll 2021/6/14 Phys. Rev. Lett. 91, 241803 (2003) Produced pions Jiangyong Jia 18

What happens to the jets in Medium? we produce a high energy quark or gluon. Central collisions : If the plasma is dense enough we expect the quark or gluon to be swallowed up: “Jet quenching” Peripheral collisions: escape with no or small modifications Peripheral Collision Central Collision 2021/6/14 Jiangyong Jia 19

Transverse Momentum spectrum Au+Au 0 Spectra From PHENIX n Expected Observe only 20% of expected yield @ high p. T Energy density ~15 Gev/fm 3 100 x normal nuclear energy density!! Reminder: critical energy density ~ 1 Ge. V/fm 3 Calculations with no energy loss Calculations with energy loss RAA Observed/Expected Using p-p data as baseline 2021/6/14 Jiangyong Jia 20

RAA PHENIX: Au+Au Final Results from 2002 p (Ge. V/c) Unequivocal observation of strong suppression at high p in central Au+Au collisions. 2021/6/14 Jiangyong Jia 21

PHENIX: Au+Au High-p. T 0 Suppression from 2005 We are now measuring out to truly high p. T 2021/6/14 Jiangyong Jia 22

PHENIX: Au+Au High-p. T 0 Suppression n constancy for p. T > 4 Ge. V/c for all centralities! 2021/6/14 Jiangyong Jia 23

0 Suppression: d. E/dx Comparisons n n Measured RAA shows little/no variation with p. T up to 20 Ge. V/c Consistent with energy loss calculations n 2021/6/14 Suppressed hard production over “whole” p. T range? Jiangyong Jia 24

Jet tomography: path length dependence Out of plane • Energy loss depends on path length In plane RAA Dave’s QM proceedings https: //www. phenix. bnl. gov/WWW/p/draft/winter/QM 2005/Proceedings/ 30 -40 % PHENIX preliminary f 2021/6/14 Jiangyong Jia 25

Surface Emission Picture side view front view 2021/6/14 Jiangyong Jia 26

Surface Emission Picture side view The detected high p. T particles comes mainly from the surface region The away side jet is quenched by the medium front view 2021/6/14 The measured rate is ~ surface volume Jiangyong Jia 27

Jet quenching papers n Measurements: n n n Discovery paper: PRL. 88, 022301 (2002) Systematic studies: PRL. 91, 072301 (2003), PRC 69, 034910 (2004) Comparison with d. Au: Phys. Rev. Lett. 91, 072303 (2003) Non suppression of direct photons: Phys. Rev. Lett. 94, 232301 (2005) QM 05 proceedings. Theories n n BDMS : hep-ph/0106347. X. N. Wang, M. Gulassy, I. Vitev, nucl-th/0302077. U. A. Wiedemann: hep-ph/0402251, hep-ph/0406319. Related: CGC, hadronic energy loss, heavy flavor energy loss. 2021/6/14 Jiangyong Jia 28

Jets and Hard-scattering hadrons Correlate hadrons with leading particles Near side peak: same jet Away side peak: away side jet Leading particle jet 1 p+p Df jet 2 hadrons leading particle Df • Establish the method • Cold nuclear modification, j. T, k. T. x. E, Pout distributions nucl-ex/0510021 nucl-ex/0409024, ppg 029 2021/6/14 Jiangyong Jia p+p 29

Evolution of away-side jet shape low p. T Intermediate p. T nucl-ex/0507004 p. T, assoc 0. 2 Ge. V/c nucl-ex/0501016 Moderate high p. T 4 -6 x 2 -4 Ge. V/c p. T, assoc 2 Ge. V/c Phys. Rev. Lett. 90, (2003) Do we have a (qualitative) picture? 2021/6/14 Jiangyong Jia 30

Di-jet correlation at moderate high p. T Number of pairs 4 -6 x 2 -4 Ge. V/c p. T, assoc 2 Ge. V/c 0º 180º Ø In Au+Au collisions we see only one “jet” at a time ! Ø Jet quenching! 2021/6/14 Jiangyong Jia 31

What happens to the lost energy? Moderate high p. T → Away-side suppression Low p. T → Away-side enhancement p. T, assoc 4 -6 x 2 -4 Ge. V/c p. T, assoc 2 Ge. V/c 0. 2 Ge. V/c Lost energy recovered at low p. T How the medium responds to the jet? 2021/6/14 Jiangyong Jia 32

How the medium responds to the jets? Mach cone/shock wave? Jets travel faster than the speed of sound in the medium Create shock wave at: cos(q)=cs/c 0 -5% QCD “shock wave” PHENIX preliminary 2. 5 -4 x 1 -2 Ge. V/c Triggering jet Other possible mechanisms: Cherenkov radiation, bending jet, Gluon radiation… 2021/6/14 Jiangyong Jia 33

Di-jets at high p. T : PHENIX Near side jet yield is constant with centrality. Clear away side peak Suppression of away-side peak increases with centrality 2021/6/14 Jiangyong Jia 34

Di-jets at high p. T: STAR 8 < p. T(trig) < 15 Ge. V/c p. T(assoc)>6 Ge. V/c Clear emergence of jet structure at the away-side Away side width consistent with constant Away side yield is suppressed in central collisions But the amount of suppression is independent of p. T, assoc for p. T, assoc/p. T, trig > 0. 4 (i. e. large p. T, assoc) 2021/6/14 Small modifications require both jets emitted from surface, results in a. Jiangyong tangential emission pattern Jia 35

PHENIX: Cu+Cu high p. T Jet Correlations Di-jet signal persists even for the most head-on Cu+Cu collisions. May allow better determination of matter properties! 2021/6/14 Jiangyong Jia 36

Comparison Au + Au and Cu + Cu n n Npart and Ncoll between the two are close The comparison between the two could provide constrains on the collision geometry dependence of the modification 30 -40% Au+Au Npart = 114 0 -10% Cu+Cu Npart = 98 2021/6/14 Jiangyong Jia 37

Away jet One of the possible picture? Thermallized gluon radiation Shock wave or cherenkov? Punch through jets or tangential contribution? Trigger and associated p. T Low p. T 2021/6/14 Intermediate p. T Moderate high p. T Jiangyong Jia high p. T 38

The picture High p. T trigger hadron selects surface emission. Thus, away side partner has maximum path through the medium. 2021/6/14 Jiangyong Jia 39

The picture Jet correlations in proton-proton reactions. Strong back-toback peaks. 2021/6/14 Azimuthal Angular Correlations Jiangyong Jia 40

The picture Jet correlations in in Jet central Gold-Gold. proton-proton central Gold-Gold. reactions. Away side jet Away disappears Strong back-toreappears atfor lower p. T particles p. T ~ 2 Ge. V back peaks. 2021/6/14 Azimuthal Angular Correlations Jiangyong Jia 41

Jet energy is transported to the medium along certain directions The picture Some punch through jet might remains 2021/6/14 Azimuthal Angular Correlations Jiangyong Jia 42

“Double trigger bias” High p. T trigger hadron selects surface emission. Requiring second high p. T hadron bias second hadron to surface Because di-jets are back-to-back, both jets has to be tangential. the number of initial di-jets satisfying such condition is significantly reduced. But the away side jet shape can have a peak structure 2021/6/14 Jiangyong Jia 43

Much more n Direct photons yield not quenched n n Charm quarks also are quenched n n n Can only be established at the quark level. J/Psi is suppressed similar as in SPS! Large baryon excess for 2 < p. T < 5 Ge. V/c and quark number scaling of elliptic flow. n n And show rapid thermalization! Large charm quark elliptic flow signal n n Jet quenching is due to energy loss in final state Hadron formation by quark recombination. Many of these has been studied as function of collisions system and collision energies Au+Au @ 62 Ge. V, Cu+Cu @ 62, 200 Ge. V n With accurate baseline measurements in p+p and d+Au Full list: n https: //www. phenix. bnl. gov/WWW/p/talk/papers. php 2021/6/14 Jiangyong Jia 44

Summary n We have successfully created “matter” that exhibits bulk thermodynamic properties n n n Density and temperature exceeds the condition required for QGP formation. final state particle flavor compositions consistent with “freeze-out” from chemically equilibrated system Collective behavior well described by hydrodynamics n n Strongly interacting fluid with small viscosity: s. QGP Remarkable properties of the “matter” revealed with high p. T particle (i. e. jet) rate and di-jet correlation. n n Strong suppression of single particle rate : jet quenching @ RHIC Suppression consistent with energy-loss calculations. n n n Which requires ~ 100 x energy density of normal nuclei Di-jet correlation reveals complicated interaction between jet and medium in central Au+Au Away side jet quenched, it’s lost energy create low p. T particles, and also used to excite shock wave in the medium. 2021/6/14 Jiangyong Jia 45

It’s In The News 2021/6/14 46

What happens to photons in the Medium? Sometimes a high energy prompt photon is created in the collision. We expect it to pass through the plasma without pause. Produced in hard scattering processes But, no final-state effects, emitted from the whole region Jet 2021/6/14 Jiangyong Jia g 47

The production rate is known Well described in Proton reactions by NLO Perturbative QCD. 2021/6/14 Jiangyong Jia 48

PHENIX: Au+Au direct photon Results Scaling of photons shows excellent calibrated probe. Quarks and gluons into medium, except consistent Calculations of hard disappear scattering rates in A+A collisions OK with surface emission. High-p. T hadron suppression must be due to jet quenching Survival Probability (from quark and gluon jets) 2021/6/14 Jiangyong Jia 49

Collision Geometry Impact parameter b n n Spectators Impact parameter: b Number of participating nucleons: Npart Number of binary nucleon-nucleon collisions: Ncoll Small b ~ large Npart, Ncoll ~ more particles Express impact parameter b in terms of “centrality” n n n Participants Key quantities n n Spectators Total cross section 4 R 2. 0 -10% most central: [0, b], where b 2 / 4 R 2 =0. 1 Connection to yield or probability of physics process n n Soft process (large cross section) ~ Npart Hard process (small cross section) ~ Ncoll 2021/6/14 Jiangyong Jia 50

How to calibrate the rate of the probe n Consider a process where production rate for each nucleon collision is s. soft processes: s~1. Total production rate ~ 3 + 5~ Npart hard processes: s<<1. Total production rate ~ 3 x 5~ Ncoll n Particle production via hard processes should scale with Ncoll. n n n s can be measured in proton – proton process. The initial rate of the probe is: Ncoll x s. Any modification to this expectation reduce it to f x Ncoll x s Yield. AA/ Ncoll x yieldpp = f General strategy : pp, p. A and Au Au 2021/6/14 Jiangyong Jia 51

Centrality dependence of the jet shape D D PHENIX preliminary Away side: splitting Near side : broadening 2021/6/14 Jiangyong Jia 52

Near side width Trigger p. T = 2. 5 -4 x 2 -3 Ge. V/c p 0 -hadron-hadron Broadening is seen for pairs at intermediate p. T Energy loss effect? Or baryon/meson difference? 2021/6/14 Jiangyong Jia 53

D parameter D D Splitting Parameter D increasing with centrality Turn on in rather peripheral bins Similar trend for all systems and energies 2021/6/14 Jiangyong Jia 54

Evolution of away-side jet shape 2021/6/14 Jiangyong Jia 55

Evolution of away-side jet shape 2021/6/14 Jiangyong Jia 56

Put things together Higher p. T → Away-side suppression p. T(assoc) > 2 Ge. V/c Lower p. T → Away-side enhancement p. T(assoc) > 0. 15 Ge. V/c Pedestal&flow subtracted Surface emissions (again? ) 2021/6/14 Interaction of the jet with the flowing medium Jiangyong Jia 57

d+Au Control Experiment Nucleusnucleus collision n n Collisions of small with large nuclei were always foreseen as necessary to quantify cold nuclear matter effects. Recent theoretical work on the “Color Glass Condensate” model provides alternative explanation of data: n n Proton/deuteron nucleus collision Jets are not quenched, but are a priori made in fewer numbers. Small + Large distinguishes all initial and final state effects. 2021/6/14 Jiangyong Jia 58

No suppression seen in d+Au collisions The combined data from Runs 1 -3 at RHIC on p+p, Au+Au, and d+Au collisions establish that a new effect (a new state of matter? ) is produced in central Au-Au collisions Au + Au Experiment Final Data 2021/6/14 d + Au Control Experiment Preliminary Data Jiangyong Jia 59

Phase Diagrams Nuclear Matter 2021/6/14 Water Jiangyong Jia 60

Jet properties via two particle correlation p+p 1 d. N Ntrig d 1) Jet shape 2) Jet Yield 3) Underlying event 2021/6/14 Jiangyong Jia 61

Underlying event in Au. Au 1 d. N combinatorial background is large in Au+Au! flow+jet Ntrig d And is not constant! flow elliptic flow causes another correlation in them: jet l(1+2 v 2(p. Ttrig)v 2(p. Tassoc)cos(2 )) CF = J(Df) + l(1+2 v 2 tv 2 a cos 2 Df) 2021/6/14 Jiangyong Jia 62

The Correlation function 0 -5% C(Df) 2. 5 -4 x 3 -5 Ge. V/c 2. 5 -4 x 1 -2. 5 Ge. V/c PHENIX Preliminary Flat or slight dip at the away side! Small jet signal! (1/50) Shape can’t be pure di-jet broadening 2021/6/14 Jiangyong Jia 63

Now subtract the v 2 CF = J(Df) + l(1+2 v 2 tv 2 a cos 2 Df) n n n v 2 background is scaled to match the correlation function (ZYAM). l 2 v 2 tv 2 a ~ few %, thus the change in B only slightly affect subtracted away side jet shape. Sensitive to the v 2 systematic. 2021/6/14 Jiangyong Jia 64

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n n n Heavy-ion collisions, scaling behavior (Ncoll, Npart) Initial collisions, bulk dynamics, final state interaction. Goal Phase transition n The diagram Energy density (expected and measured) n Probes (Jets) spectra Correlations Reaction plane pp? n Atlas n n 2021/6/14 To do: Atlas, Phase transition, cross over or what? Speed of sound Chemical freeze out Jiangyong Jia 67

n Probing the Quark Gluon Plasma at RHIC with jets n A novel, hot, dense matter has been created in relativistic heavy ion collider at Brookhaven National Laboratory. It's energy density and n temperature are found to exceed the hadron to quark-gluon plamsa phase transition values predicted by lattice QCD calculations. Significant n progresses have been made in understanding the properties of the created matter in the past five years. I will show results from experiments at the Relativistic Heavy Ion Collider, fucusing on the remakable properties revealed by high transverse n momentum hadrons and back to back hadron pairs. n 2021/6/14 Jiangyong Jia 68