Recent Results on Jet Quenching from STAR

2019 RHIG & AGS Annual User’s Meeting – High Pt/Jets Parallel Workshop June 4, 2019 Saehanseul Oh for the STAR Collaboration (Yale University - BNL) 1 Introduction

STAR, Phys. Rev. Lett. 91 (2003) 072304

• Early experimental evidence of “jet quenching” from STAR

Saehanseul Oh – Jet quenching @STAR 2 Introduction

STAR, Phys. Rev. Lett. 91 (2003) 072304

• Early experimental evidence of “jet quenching” from STAR

• Jets from heavy-ion collisions are suppressed and broadened compared to those from pp collisions

Saehanseul Oh – Jet quenching @STAR 3 Introduction

STAR, Phys. Rev. Lett. 91 (2003) 072304

• Early experimental evidence of “jet quenching” from STAR

• Jets from heavy-ion collisions are suppressed and broadened compared to those from pp collisions

Recent results on jet quenching from STAR ü Di-jet imbalance ü Semi-inclusive jet (triggered-jet) Various measurements can be connected to different aspects ü Event-plane dependent measurements of jet properties ü Jet flavor dependent measurements ü Jet angular scale dependent measurements

Saehanseul Oh – Jet quenching @STAR 4 Introduction

Key questions for more differential jet-quenching measurements

vs. vs.

Different jet vertex/direction in the medium Out-of-plane In-plane

Dependence on where the jet is produced inside of the medium?

vs. vs.

quark-jet gluon-jet Narrow jet Wide jet

Saehanseul Oh – Jet quenching @STAR 5 Introduction

Key questions for more differential jet-quenching measurements

vs. vs.

Different jet vertex/direction in the medium Out-of-plane In-plane

Path-length dependence in non-central AA collisions?

vs. vs.

quark-jet gluon-jet Narrow jet Wide jet

Saehanseul Oh – Jet quenching @STAR 6 Introduction

Key questions for more differential jet-quenching measurements

vs. vs.

Different jet vertex/direction in the medium Out-of-plane In-plane

vs. vs.

quark-jet gluon-jet Narrow jet Wide jet

Jet flavor dependence?

Saehanseul Oh – Jet quenching @STAR 7 Introduction

Key questions for more differential jet-quenching measurements

vs. vs.

Different jet vertex/direction in the medium Out-of-plane In-plane

vs. vs.

quark-jet gluon-jet Narrow jet Wide jet

Jet angular scale dependence?

Saehanseul Oh – Jet quenching @STAR 8 Introduction

Key questions for more differential jet-quenching measurements

vs. vs.

• STAR’s efforts to answer these questions will be addressed Different jet vertex/direction in the mediumin this presentation Out-of-plane In-plane • Some observables are connected to more than one of these questions

vs. vs.

quark-jet gluon-jet Narrow jet Wide jet

Saehanseul Oh – Jet quenching @STAR 9 The Solenoidal Tracker At RHIC (STAR)

BEMC ü Barrel Electromagnetic Calorimeter ü � < 1.0, 0 < � < 2� ü Trigger

TPC ü Time Projection Chamber ü � < 1.0, 0 < � < 2� ü Tracking, momentum, ��/��

Saehanseul Oh – Jet quenching @STAR 10 The Solenoidal Tracker At RHIC (STAR)

BEMC ü Barrel Electromagnetic Calorimeter ü � < 1.0, 0 < � < 2� ü Trigger

Neutral constituents

TPC ü Time Projection Chamber Full Jet ü � < 1.0, 0 < � < 2� Charged constituents ü Tracking, momentum, ��/�� Charged Jet

Saehanseul Oh – Jet quenching @STAR 11 Di-jet Imbalance

vs.

Different jet vertex/direction in the medium

Dependence on where the jet is produced inside of the medium?

Saehanseul Oh – Jet quenching @STAR 12 Di-jet Imbalance

• � = • Hard-core jet vs. Matched jet

STAR, Phys. Rev. Lett. 119 (2017) 062301

R=0.4 R=0.2 • For � = 0.4 hard-core jet, more di-jet momentum imbalance compared to �+� • Balance recovered when soft constituents are included (matched-jet) • For � = 0.2, balance no longer recovered in matched-jet ü Softening of jet constituents and Broadening of the jet structure

Saehanseul Oh – Jet quenching @STAR 13 Di-jet Imbalance

• � = • Hard-core jet vs. Matched jet

STAR, Phys. Rev. Lett. 119 (2017) 062301

• Cut Cut Constituent pT = 0.2 GeV/c • Constituent pT = 2 GeV/c • Geometrically matched to the • Reduce BG and combinatorial jets hard-core jet

Saehanseul Oh – Jet quenching @STAR 14 Di-jet Imbalance

• � = • Hard-core jet vs. Matched jet

STAR, Phys. Rev. Lett. 119 (2017) 062301

R=0.4 R=0.2 • For � = 0.4 hard-core jet, more di-jet momentum imbalance compared to �� • Balance recovered when soft constituents are included (matched-jet) • For � = 0.2, balance no longer recovered in matched-jet ü Softening of jet constituents and Broadening of the jet structure

Saehanseul Oh – Jet quenching @STAR 15 Di-jet Imbalance

• Varying the jet definition (�, constituent pT cut, …) effectively controls the path length and vertex of jets in the medium (Jet Geometry Engineering) 3.0 cut (GeV/c) T p 1.0 core constituent -

Hard 0.2 0.3 0.4 �

Saehanseul Oh – Jet quenching @STAR 16 Di-jet Imbalance

Saehanseul Oh – Jet quenching @STAR 17 Di-jet Imbalance

With Kolmogorov-Smirnov two-sample test

Imbalanced Semi-balanced balanced

Saehanseul Oh – Jet quenching @STAR 18 Di-jet Imbalance

Hard 0.2 0.3 0.4 �

• Matched jet with various hard-core constituent pT cut and � ü Imbalance at small � ü Balance ONLY restored with increased � (~0.35) when soft particles are included

Saehanseul Oh – Jet quenching @STAR 19 Di-jet Imbalance

Hard 0.2 0.3 0.4 �

• Matched jet with various hard-core constituent pT cut and � ü Imbalance at smallvs. � Jet Geometry Engineering Works! ü Balance ONLY restored with increased � (~0.35) when soft particles are included

Saehanseul Oh – Jet quenching @STAR 20 Jet Geometry Engineering at RHIC

• At RHIC energies, we can better utilize the jet vertex bias via different jet definitions for more differential measurements

200 GeV 2.76 TeV

Jet direction

T. Renk, Phys. Rev. C 88 (2013) 054902 Jet reconstruction with constituent

hadrons pT > 2.0 GeV/c

Saehanseul Oh – Jet quenching @STAR 21 Di-jet Imbalance

• More differential measurements with the help of increase in statistics with recent RHIC runs

• Centrality dependence of � – More balanced in peripheral Au+Au collisions

Saehanseul Oh – Jet quenching @STAR 22 Semi-inclusive Spectra

vs. vs.

Different jet vertex/direction in the medium quark-jet gluon-jet

Jet vertex dependence? Jet flavor dependence?

Saehanseul Oh – Jet quenching @STAR 23 h-Triggered Recoil Jets

STAR, Phys. Rev. C 96 (2017) 24905 60-80% 0-10%

Charged Jet ICP R=0.2 vs. R=0.5

• Fully corrected ℎ±-triggered charged recoil jet

ü Strong suppression via ICP ü Medium-induced broadening ⇦ Comparison between � = 0.2 and � = 0.5

Saehanseul Oh – Jet quenching @STAR 24 g-Triggered Recoil Jets

0 • �dir+jet and p +jet ü Path length ü Color factor (toward q-jet) ü Parton energy

• Similar level of suppression observed

Charged Jet

Saehanseul Oh – Jet quenching @STAR 25 Event-plane Dependent Measurements

vs.

Out-of-plane In-plane

Path-length dependence in non-central AA collisions?

Saehanseul Oh – Jet quenching @STAR 26 Event-plane Dependent Jet-hadron Correlations

• Previous jet-hadron correlations by STAR (Phys. Rev. Lett. 112 (2014) 122301)

ü Suppression of high-pT associated particle yield is balanced by low pT associated particle enhancement

• More differential measurement using the trigger jet angle with respect to the event plane ü In-plane, mid-plane, and out-of-plane

In-plane Mid-plane Out-of-plane All combined angles

φ assoc 1.0

2.0 GeV STAR Preliminary 0.6 0.6 T T 0.6 0.6 |∆η| < 0.6 Anti-k T full jets, R=0.4 Correlated unc. lead const. φ φ ch+ne φ p >4.0 GeV ∆

∆ p = 15-20 GeV/c ∆ T T unc, jet Background unc. -B)/d -B)/d 0.4 -B)/d 0.4 -B)/d 0.4 0.4 unc unc unc unc )d(N )d(N 0.2 0.2 0.2 )d(N 0.2 trig trig trig )d(N trig (1/N (1/N (1/N 0 0 0 0 (1/N −0.2 −0.2 −0.2 −0.2 −1 0 1 2 3 4 −1 0 1 2 3 4 −1 0 1 2 3 4 −1 0 1 2 3 4 ∆φ ∆φ ∆φ ∆φ

Saehanseul Oh – Jet quenching @STAR 27 Event-plane Dependent Jet-hadron Correlations

Au-Au s = 200 GeV, 20-50% Au-Au s = 200 GeV, 20-50% Near-side yield NN Away-side yield NN 1 Anti-k full jets, R=0.4 1 Anti-k full jets, R=0.4 ) T ) T ch+ne ch+ne -1 -1

) p = 15-20 GeV/c ) p = 15-20 GeV/c T unc, jet T unc, jet c c pchc, E clus>2.0 GeV pchc, E clus>2.0 GeV T T T T plead const.>4.0 GeV plead const.>4.0 GeV T T In-plane In-plane ((GeV/ ((GeV/

T Mid-plane T Mid-plane −1 p Out-of-plane p 10 Out-of-plane

/d Background unc. /d Background unc. unc 10−1 Scale uncertainty 6% unc Scale uncertainty 6%

)dN STAR Preliminary )dN STAR Preliminary trig trig |∆η|<0.6 |∆η|<0.6 −2 NS yield range: -π/3 < ∆φ < π/3 10 AS yield range: 2π/3 < ∆φ < 4π/3 (1/N (1/N points displaced for visibility points displaced for visibility 1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 10 passoc (GeV/c) passoc (GeV/c) T T

Au-Au sNN = 200 GeV, 20-50% Au-Au sNN = 200 GeV, 20-50% Near-side width Anti-k T full jets, R=0.4 Away-side width Anti-k T full jets, R=0.4 pch+ne = 15-20 GeV/c pch+ne = 15-20 GeV/c 0.3 T unc, jet T unc, jet pchc, E clus>2.0 GeV pchc, it{E}clus>2.0 GeV T T 1 T T plead const.>4.0 GeV plead const.>4.0 GeV T T In-plane In-plane 0.2 Mid-plane Mid-plane Out-of-plane Out-of-plane Background unc. Background unc. Scale uncertainty 6% 0.5 Scale uncertainty 6% STAR Preliminary STAR Preliminary Near-side width 0.1 Away-side width

|∆η|<0.6 |∆η|<0.6 NS width range: -1π/3<∆φ<π/3 AS width range: 2π/3<∆φ<4π/3 points displaced for visibility points displaced for visibility 0 0 1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 10 passoc (GeV/c) passoc (GeV/c) T T

Saehanseul Oh – Jet quenching @STAR 28 Event-plane Dependent Jet-hadron Correlations

Au-Au s = 200 GeV, 20-50% Au-Au s = 200 GeV, 20-50% Near-side yield NN Away-side yield NN 1 Anti-k full jets, R=0.4 1 Anti-k full jets, R=0.4 ) T ) T ch+ne ch+ne -1 -1

) p = 15-20 GeV/c ) p = 15-20 GeV/c T unc, jet T unc, jet c c pchc, E clus>2.0 GeV pchc, E clus>2.0 GeV No significant event plane dependence is observed within uncertaintiesT T T T plead const.>4.0 GeV plead const.>4.0 GeV T T In-plane In-plane ((GeV/ ((GeV/

T Mid-plane T Mid-plane −1 p Consistent with LHC resultsOut-of-plane p 10 Out-of-plane /d Background unc. /d Background unc. unc 10−1 Scale uncertainty 6% unc Scale uncertainty 6%

Saehanseul Oh – Jet quenching @STAR 29 Event-plane Dependent Di-hadron Correlations – Recoil Width

• After selecting events with high recoil momentum within 0.5 < � < 1.0, two-particle correlation functions in close-region and far-region

• Under the assumption that the flow contribution is equal in two regions, the difference between close-region and far-region correlation functions provides information on away-side width of jet-like correlations without the flow contribution

20-60% Au+Au, � = 200 GeV, 3 < � < 10 GeV/�, 1 < � <2 GeV/�

Saehanseul Oh – Jet quenching @STAR 30 Event-plane Dependent Di-hadron Correlations – Recoil Width

• After selecting events with high recoil momentum within 0.5 < � < 1.0, two-particle correlation functions in close-region and far-region

� = 200 3 < � < 10 � 1 < � < � 20-60% Au+Au, GeV, GeV/ , 2 GeV/ close - far

Saehanseul Oh – Jet quenching @STAR 31 Event-plane Dependent Di-hadron Correlations – Recoil Width

in-plane out-of-plane

• Depending on the trigger particle angle with respect to the event plane (= �), the difference of two-particle correlation functions shows different away-side widths (= �) after correcting for the EP resolution • Larger width for out-of-plane triggers – Hint of jet-medium interactions

Saehanseul Oh – Jet quenching @STAR 32 Event-plane Dependent Di-hadron Correlations with ESE

• Previous event-plane (EP) dependent di-hadron correlations ü Implication of path-length dependence of energy loss in the medium (shorter path-length for in-plane trigger and longer path-length for out-of-plane trigger) in-plane out-of-plane φ =0o-15o 15o-30o 30o-45o 45o-60o 60o-75o 75o-90o

φ s

∆ 0.3 (t) (a) Au+Au 200 GeV, 20-60%, 3

) dN/d 0.1 trig 0

(1/N -0.1 024 024 024 024 024 024 ∆φ = φ - φ [rad] t STAR, Phys. Rev. C 89 (2014) 041901 � : Trigger angle w.r.t. Ψ

• Event shape engineering (ESE) can further control the initial geometry with the fixed average energy

density – Measurements in small-q2 and large-q2 events separately

Saehanseul Oh – Jet quenching @STAR 33 Event-plane Dependent Di-hadron Correlations with ESE

• Polar representation of two-particle angular correlations

• Near-side – Higher peak in large-q2 events with in-plane trigger • Away-side ü Larger associated particle yields toward in-plane direction

ü Higher peak in large-q2 events with in-plane trigger ➭Consistent with path-length dependent picture?

Saehanseul Oh – Jet quenching @STAR 34 Event-plane Dependent Jet Shape

• Jet shapes represent the average distribution of jet energy as a function of distance from the jet axis

• In 20-50% centrality Au+Au collisions, jet shapes of

Anti-kT jets with 20 < pT < 40 GeV/c from different trigger jet angle with respect to the event plane ü In-plane, mid-plane, and out-of-plane

Saehanseul Oh – Jet quenching @STAR 35 Event-plane Dependent Jet Shape

• Hint of event plane ordering at low pT? • Correction for the event-plane resolution effects not applied

Saehanseul Oh – Jet quenching @STAR 36 Jet Flavor Dependent Measurements

vs.

quark-jet gluon-jet

Jet flavor dependence?

Saehanseul Oh – Jet quenching @STAR 37 D0-hadron Correlations

• Heavy Flavor Tracker (HFT) provides significantly better identification of heavy- flavor particles SSD

IST • � -hadron two-particle angular STAR HFT correlations with � → �±�∓ channel PXL

± Au+Au, � = 200 GeV, � � = 2−10 GeV/�, ℎ � > 0.15 GeV/�

0.1 STAR Preliminary

0.02 STAR Preliminary 0.04 STAR Preliminary +h 0 +h +h 0 0 D

D D 0.05 0.01 0.02 ME) ME) ME)

0 α

α α 0 0 /( /( /( +h 0

+h −0.01 +h 0 0 D D D −0.02 C −0.05 C −0.02 C

4 4 4 3 3 3 2 1.5 2 1.5 2 1.5 1 0.5 1 1 0.5 1 1 0.5 1 ∆ 0 0 ∆ 0 0 ∆ 0 φ − −0.5 φ − −0.5 φ 0 −0.5 −1 −1.5 1 −1 −1.5 1 −1 −1.5 −1 ∆η ∆η ∆η 0-20% 20-50% 50-80%

Saehanseul Oh – Jet quenching @STAR 38 D0-hadron Correlations

Near-side width Near-side yield

φ 2

∆ di-Hadron, Mean Trigger p = 5.7 GeV/c [3] di-Hadron, Mean Trigger p = 5.7 GeV/c [3] T T di-Hadron, Mean Trigger p = 2.56 GeV/c [3] T 1.8 0 0 NS, Pythia D -Hadron, Mean D p = 3 GeV/c di-Hadron, Mean Trigger p = 2.56 GeV/c [3] T σ T D0-Hadron AuAu 200 GeV, Mean D0 p = 3 GeV/c 1.6 T Pythia D0-Hadron, Mean D0 p = 3 GeV/c T STAR Preliminary 1.4 0 0 D -Hadron AuAu 200 GeV, Mean D p = 3 GeV/c T 10 1.2 STAR Preliminary

1 NS Associated Yield

0.8

0.6 1

0.4

0.2

0 pythia 50-80% 20-50% 0-20% pythia 50-80% 20-50% 0-20% Centrality (%) Centrality (%)

• Similar width and yield results to light-flavor correlations – Indication of similar behavior of correlations between light-flavor and charm-quarks

Saehanseul Oh – Jet quenching @STAR 39 Heavy-flavor Jet Tagging in pp

1 1

0.8 0.8

TC,1st TC,1st TC,2nd TC,2nd 0.6 TC,3rd 0.6 TC,3rd JP JP SV,1nd SV,1nd SV,2nd SV,2nd 0.4 0.4 PYTHIA:p+p s = 200 GeV PYTHIA:p+p s = 200 GeV misid. probability misid. probability Anti-kT Algo., R = 0.4 Anti-kT Algo., R = 0.4 0.2 6.0 < pJet < 60.0 GeV/c 0.2 6.0 < pJet < 60.0 GeV/c T T pTrack > 0.2 GeV/c pTrack > 0.2 GeV/c T T |ηJet| < 0.6 |ηJet| < 0.6 0 0 0 0.2 0.4 0.6 0.8 1 0 0.2 0.4 0.6 0.8 1 c-jet efficiency b-jet efficiency

• Heavy-flavor jet tagging performance in �� with low-level tagging algorithms • Possibility of future heavy-flavor tagged jet analysis in STAR with HFT

Saehanseul Oh – Jet quenching @STAR 40 Jet Angular Scale Dependent Measurements + Jet Substructure

vs.

Narrow jet Wide jet

Jet angular scale dependence?

Saehanseul Oh – Jet quenching @STAR 41 Jet Substructure in pp

• Experimental observables related to quantities in jet evolution o With SoftDrop algorithm Phys. Rev. D 91, 111501 (2015)

ü Momentum scale, zg Rg

ü Angular scale, Rg o Invariant jet mass, M

• Measurements of these observables in pp set a vacuum baseline

Saehanseul Oh – Jet quenching @STAR 42 Jet Substructure in pp - zg

• 1/z behavior recovered for jet pT > 20 GeV/c

• zg in pp described by leading order MC generators

Saehanseul Oh – Jet quenching @STAR 43 Jet Substructure in pp - Rg

• Momentum dependent narrowing of jet angular structure

• Rg overall shape in pp described by leading order MC generators

Saehanseul Oh – Jet quenching @STAR 44 Jet Substructure in pp - M

0.5 0.5 0.5 pp 200 GeV run12 JP2 0.45 0.45 0.45 STAR Preliminary anti-kT, R = 0.4 0.4 Ch+Ne jets, |η| < 0.6 0.4 0.4 25 < p < 30 GeV/c 30 < p < 40 GeV/c 20 < p < 25 GeV/c 1/N dN/dM 1/N dN/dM T T T 1/N dN/dM 0.35 0.35 0.35

0.3 0.3 Herwig7 0.3 Pythia6 Pythia8 Unfolded data 0.25 0.25 0.25

0.2 0.2 0.2

0.15 0.15 0.15

0.1 0.1 0.1

0.05 0.05 0.05

0 0 0 0 1 2 3 4 5 6 7 8 9 100 1 2 3 4 5 6 7 8 9 100 1 2 3 4 5 6 7 8 9 10 M [GeV/c2] M [GeV/c2] M [GeV/c2]

• Jet mass increases with increasing jet pT • PYTHIA-8 generally over-predicts jet mass and HERWIG-7 under- predicts jet mass

Opportunity to further tune MC generators at RHIC kinematics

Saehanseul Oh – Jet quenching @STAR 45 Jet Angular Scale Dependent AJ

• Interaction of the jet with medium could depend on the jet’s angular scale Majumder, A and Putschke, J Phys Rev C 93 054909 Mehtar Tani, Y and Tywoniuk, K arXiv:1707.07361

• Clustering all constituents into smaller radius jets (� = 0.1) → leading and

subleading subjets Jet classification based on qSJ • qSJ = DR(LeadingSJ axis, SubleadingSJ axis) • More robust to the heavy ion background

than SoftDrop Rg

Saehanseul Oh – Jet quenching @STAR 46 Jet Angular Scale Dependent AJ

• Interaction of the jet with medium could depend on the jet’s angular scale Majumder, A and Putschke, J Phys Rev C 93 054909 Mehtar Tani, Y and Tywoniuk, K arXiv:1707.07361

• Clustering all constituents into smaller radius jets (� = 0.1) → leading and subleading subjets

• qSJ = DR(LeadingSJ axis, SubleadingSJ axis) • More robust to the heavy ion background vs.

than SoftDrop Rg Wide jet Saehanseul Oh – Jet quenching @STAR Narrow jet Jet Angular Scale Dependent AJ

qSJ = DR(LeadingSJ axis, SubleadingSJ axis)

• � measurements for hard- core and matched jets with

different qSJ selections

• No significant difference

between different qSJ selections

� �

Saehanseul Oh – Jet quenching @STAR 48 Summary

• Various jet measurements are on-going in STAR

vs. vs. vs. vs.

• Di-jet imbalance for hard-core di-jets ü Balance recovered with soft particles within R = 0.4 ü More differential measurements (Centrality, jet reconstruction parameter) • Event-plane dependent measurements ü Indication of jet-medium interaction + path-length dependence ü On-going efforts for comprehensive understanding • Semi-inclusive measurements (h+jet, g+jet) and �-hadron measurements ü Model comparisons needed

• Jet angular scale dependent � - No significant dependence

Saehanseul Oh – Jet quenching @STAR 49 Backup

Saehanseul Oh – Jet quenching @STAR 50 Jet Geometry Egineering at RHIC

• Steeply falling pT spectrum at RHIC – good correlation between jet and parton energies

Leading trigger Di-jet imbalance 2+1 correlations ü Jet+hadron correlation ü h+jet spectra

• Surface bias from trigger selection, particuarly at RHIC energies, enables to use jet

definition (�, constituent pT cut, …) to select jet production vertex and di-jet origentation

Saehanseul Oh – Jet quenching @STAR 51 Event-plane Dependent Di-hadron Correlations – Recoil Width

• Event selection with high recoil momentum within 0.5 < � < 1.0

Saehanseul Oh – Jet quenching @STAR 52 D0-hadron Correlations

• Two-particle correlation functions are fitted with a model with 8 parameters

Saehanseul Oh – Jet quenching @STAR 53 SoftDrop Rg vs. qSJ

SoftDrop Rg qSJ

• SoftDrop Rg is more sensitive to background fluctuations

Saehanseul Oh – Jet quenching @STAR 54 Jet Angular Scale Dependence

Saehanseul Oh – Jet quenching @STAR 55