Probing QuarkGluon Plasma in HeavyIon Collisions Nihar Ranjan

Probing Quark-Gluon Plasma in Heavy-Ion Collisions Nihar Ranjan Sahoo Texas A&M University, Texas, USA SDU, Nihar Sahoo, 20 th Aug, 2018 1

Matter at High Temperature and/or Density Temperature > ~1012 K (~175 Me. V) and/or Density > ~1018 kg/m 3 (~1 Ge. V) Atom Quark Gluon Plasma(QGP) Hadrons (Proton, neutron, pion, etc) [Quantum Chromodynamics (QCD)] What is the landscape of different phase of matter? SDU, Nihar Sahoo, 20 th Aug, 2018 2

Landscape of Different Phase of Matter QED interaction: Water to vapor transition QCD Phase diagram QCD Critical Point: Experimental attempt to find the location (My Thesis work) PRL 12, 032302(2014); PRL 113, 092301(2014) [200+ citations] What is our theoretical understanding on this phase? SDU, Nihar Sahoo, 20 th Aug, 2018 3

Equation of State: Fine temp. lattice QCD S. Borsanyi et al. , JHEP 1011, 077 (2010) Energy Density Finite temperature Lattice QCD at μB=0 Significant deviation from Steffan-Boltzmann limit “Strongly interacting plasma” Cross-over (No sharp transition) Temperature How can we create this state of matter in the laboratory? SDU, Nihar Sahoo, 20 th Aug, 2018 4

Gold Ions Heavy Ions SDU, Nihar Sahoo, 20 th Aug, 2018 Courtesy: Paul 5 Sorensen

Hot QCD in the laboratory Au+Au √s. NN=200 Ge. V LHC @ CERN RHIC @ BNL PHENIX Pb+Pb √s. NN=2. 76 Te. V STAR ALICE CMS ATLAS SDU, Nihar Sahoo, 20 th Aug, 2018 6

RHIC, USA PHENIX (Decommissioned) STAR SDU, Nihar Sahoo, 20 th Aug, 2018 7

How can we study the properties of this new form of matter (QGP) ? We need a probe for it. (QCD Jet) Quark Gluon Plasma(QGP) SDU, Nihar Sahoo, 20 th Aug, 2018 8

Jets from QCD Jet: Energy flow Inclusive differential jet cross-section PRL 97 (2006) 252001 (STAR) Jet cross-section can be calculated by p. QCD. Remarkable achievement understanding QCD (Theory and Experiment ). SDU, Nihar Sahoo, 20 th Aug, 2018 9

Jet tomography for QGP • Good Tomography probe (p. T > Q >> ΛQCD ) • Produced on very short time scale (τ ~ 0. 1 fm/c) • Involved in very high momentum transfer ( Δx ~ 1/Δp : Q >> 20 Ge. V, x << 0. 01 fm) Jet interacts with the medium and losses energy. [Both collisional and radiative energy loss] SDU, Nihar Sahoo, 20 th Aug, 2018 10

Particles from hot and dense QCD medium • In central Au+Au collisions: • Strong suppression of inclusive hadron production • Direct photon, W, and Z bosons not suppressed • Difficult to estimate precisely the true energy loss of a parton from these measurements SDU, Nihar Sahoo, 20 th Aug, 2018 11

Jet energy loss in QCD medium Direct photon production Jet Experimental challenges in HIC • Direct photon detection and • Recoil jet detection • Jet Different energy loss models (Initial gluon density, expanding plasma) GLV approach : Gyulassy, Leva, Vitev PRL. 85, 5535 (2000) BDMPS approach: (transport coefficient) Baier, Dokshitzer, Mueller, Peigne, Schiff Nucl. Phys. B 484 265 (1997) SDU, Nihar Sahoo, 20 th Aug, 2018 ©Nihar Sahoo 12

Experimental technique: π0/ϒdir discrimination Barrel Electromagnetic Calorimeter (BEMC) STAR HL Online Trigger (L 2 Gamma) BEMC module Shower Maximum Detector(BSMD) Shower shape profile π0 sample Photon sample Smaller TSP ϒ π0 SDU, Nihar Sahoo, 20 th Aug, 2018 ϒ Larger TSP ϒ 13

Jet background in Heavy-Ion collisions pp collisions at 200 Ge. V Au. Au collisions at 200 Ge. V Difficult to study jets in heavy Ion collisions because of large uncorrelated soft background. SDU, Nihar Sahoo, 20 th Aug, 2018 14

Jet-like correlation function STAR: PLB 760 (2016) 689 Event display of Au+Au collision • Large combinatory background in Au+Au in comparison with p+p collision (non high-Q 2) • Need to subtract the bulk contributions in heavy-ion collisions SDU, Nihar Sahoo, 20 th Aug, 2018 15

Away side jet energy loss STAR: PLB 760 (2016) 689 Nuclear Modification factor Jet-like correlation measurements =p. Tassoc/p. Ttrig Transverse momentum fraction Jet energy loss Large suppression due to QGP medium (~70% suppression at high p. T) • Strong signature of energy loss in the QGP medium SDU, Nihar Sahoo, 20 th Aug, 2018 16

Direct-photon+Jet in STAR experiment Direct photon+jet in HIC Au+Au collisions Off-axis cone π–π/2 π– 3π/4 π – π/4 Recoil jet Trigger π0/γ π +3π/4 π +π/2 π + π/4 Off-axis cone • Charged and full jet reconstruction of direct photonπ0 tagged jet Color factor and path length dependence effect • Study of underlying activity in heavy-ion collisions • Ongoing work in the STAR experiment SDU, Nihar Sahoo, 20 th Aug, 2018 17

Semi-inclusive hadron trigger recoil jet (h+jet) Per high-p. T trigger recoil jets Recoil jet(s) search area • High p. T trigger: 9 < p. Ttrig < 30 Ge. V/c • Jet reconstruction: • Constituent charged hadrons: 0. 2<p. Ttrack<30 Ge. V/c • Algorithm: anti-k. T Trigger particle • Recoil jet centroid acceptance: [π-π/4, π+π/4] SDU, Nihar Sahoo, 20 th Aug, 2018 18

Event display on η-φ plane -η Tracks and trigger tower in η-φ plane +η φ Au+Au 200 Ge. V, central collisions Before applying anti-k. T Tracks η Trigger Apply anti-k. T algorithm… φ [rad] SDU, Nihar Sahoo, 20 th Aug, 2018 19

Event display on η-φ plane • Large number of uncorrelated jets in recoil region • Signal+Bg. in the recoil jet search area. After anti-k. T algorithm Au+Au 200 Ge. V, central collisions anti-k. T, R=0. 3 Recoil jet search area η Trigger φ [rad] SDU, Nihar Sahoo, 20 th Aug, 2018 20

h+jet in STAR experiment Recoil jet(s) search area PRC 96, 024905 (2017) S+B B Trigger particle Distribution matches with mixed event background. SDU, Nihar Sahoo, 20 th Aug, 2018 21

h+Jet yield suppression STAR: PRC 96, 024905 (2017) Per trigger yield Jet R= 0. 2 Trigger hadron Recoil Jet R=0. 2 Peripheral collision Ratio Central collision Large suppression due to QGP medium (80% suppression at high p. T) Transverse momentum of the recoil jet in Ge. V/c SDU, Nihar Sahoo, 20 th Aug, 2018 22

h+Jet yield suppression STAR: PRC 96, 024905 (2017) Per trigger yield Jet R= 0. 5 Trigger hadron R=0. 2 Peripheral collision R= 0. 5 Quantitative estimation RHIC(STAR) 200 Ge. V: ~3 Ge. V/c LHC (ALICE) 2. 76 Te. V: ~8 Ge. V/c ALICE: JHEP 09(2015)170 Central collision Ratio Recoil Jet Negligible suppression at Jet Radius = 0. 5 Transverse momentum of the recoil jet in Ge. V/c • • Energy transported out of the cone: Jet-quenching effect Parton energy loss SDU, Nihar Sahoo, 20 th Aug, 2018 23

Di-Jet in p+p collisions pp 200 Ge. V Leading jet Sub-leading jet Di-jet Selection: Jet p. TLead>20 Ge. V/c , Jet p. TSub. Lead>10 Ge. V/c, |Δφ – π| < 0. 4 To measure degree of di-jet imbalance SDU, Nihar Sahoo, 20 th Aug, 2018 24

Di-Jet imbalance in Au+Au collisions STAR: Phys. Rev. Lett. 119 (2017) 62301 • Central Au. Au collisions significantly imbalanced than pp for constituent p. T > 2 Ge. V/c • Balance is restored for R=0. 4 when including jet constituents p. T < 0. 2 Ge. V/c Indication of energy loss of di-jet interacting with the medium and lost energy reappears as soft particles SDU, Nihar Sahoo, 20 th Aug, 2018 25

Still open questions in “jet quenching” • Parton energy loss in QCD medium (How? ) • • A quantitative estimation of parton energy loss Redistribution of lost energy within the medium RHIC vs. LHC (temperature dependence of the medium ) Energy loss of Quark vs. Gluon (Color factor, CF) • Gluon contribution dominates at LHC energy • Jet shape modification in hot/dense QCD medium • Jet modification in the cold QCD matter and gluon saturation regime SDU, Nihar Sahoo, 20 th Aug, 2018 26

Forward upgrade in STAR experiment Physics cases forward upgrade: • Transverse polarization effect in proton and Spin physics • Ridge in p+p, p+A and A+A • Hot and dese nuclear matter effect Detector upgrade: • Forward Tracking System • Forward Calorimeter System Shandong University plays an important role in this program. SDU, Nihar Sahoo, 20 th Aug, 2018 27

A team work Thank you! SDU, Nihar Sahoo, 20 th Aug, 2018 28

Backup SDU, Nihar Sahoo, 20 th Aug, 2018 29

Recoil and uncorrelated background jet A hadron trigger: Recoil jet + uncorrelated background jet PRC 96, 024905 (2017) -η φ +η One event display Trigger hadron Each colored cluster: possible jet Anti-k. T jet algorithm: SDU, Nihar Sahoo, 20 th Aug, 2018 30

Beyond Heavy-Ion Collisions [2025+] nonlinear regime (gluon density) ar. Xiv: 1708. 01527 v 1 • gluons radiate and recombine at the same rate electron proton x = Q 2/p. q x is the momentum fraction of the proton carried by a parton. A SDU, Nihar Sahoo, 20 th Aug, 2018 31

Correlated and uncorrelated jet background Off-axis cone π– 3π/4 STAR Preliminary π–π/2 π – π/4 Recoil jet Trigger π0/γ π +3π/4 π +π/2 π + π/4 • Off-Axis cone method • Correlated background (Unexplored topic) • What is the source of this correlated background? SDU, Nihar Sahoo, 20 th Aug, 2018 32

x is the momentum fraction of the proton carried by a parton. x = Q 2/p. q SDU, Nihar Sahoo, 20 th Aug, 2018 33

Heavy-Ion Collision Centrality Peripheral Collision Central Collision Gold Ion Impact parameter b = 0 b ≠ 0 • Large energy deposited • Comparably less energy deposit (high energy density) • High enough energy density for the creation of Quark-Gluon Plasma SDU, Nihar Sahoo, 20 th Aug, 2018 34

Equation of State: Fine temp. lattice QCD S. Borsanyi et al. , JHEP 1011, 077 (2010) Energy Density Finite temperature Lattice QCD at μB=0 Significant deviation from Steffan-Boltzmann limit “Strongly interacting plasma” Cross-over (No sharp transition) Temperature How can we create this state of matter in the laboratory? SDU, Nihar Sahoo, 20 th Aug, 2018 35

Di-Jet imbalance R=0. 4 R=0. 2 SDU, Nihar Sahoo, 20 th Aug, 2018 36

SDU, Nihar Sahoo, 20 th Aug, 2018 37

Experimental technique: π0/ϒdir discrimination STAR HL Online Trigger (L 2 Gamma) π0 sample Photon sample Smaller TSP ϒ BEMC π0 ϒ Larger TSP ϒ Shower Maximum Detector(BSMD) BEMC module Transverse Shower Profile Ecluster: Cluster energy, ei: BSMD strip energy, ri: distance of the strip from the center of the cluster SDU, Nihar Sahoo, 20 th Aug, 2018 38 /23

Our strategy in STAR experiment In Experiment Event display of Au. Au collisions ϒdir Charged tracks Triggered tower Recoil jet peak Au. Au 200 Ge. V Δφ Calorimeter towers in STAR experiment SDU, Nihar Sahoo, 20 th Aug, 2018 39

Hot and dense QCD matter effect In central Au+Au collisions: • Strong suppression of inclusive hadron production • Direct photon, W, and Z bosons not suppressed Signature of hot and dense of QCD matter SDU, Nihar Sahoo, 20 th Aug, 2018 40

Underlying event activity in HIC Underlying event activity in p+p collisions Au+Au collisions Off-axis cone π– 3π/4 π–π/2 π – π/4 proton Recoil jet Trigger π0/γ π +3π/4 Off-axis cone π + π/4 π +π/2 Off-axis jet contribution • • Correlated background of a jet Estimated from the same event Same background energy density Underlying event activity in HIC? SDU, Nihar Sahoo, 20 th Aug, 2018 41

Hints of QCD Critical Point ? Theory and Experiment Susceptibilities -> Cumulants Q= net-charge, net-baryon, net-strangeness [200+ citations] • Proposed Future BES-II program (2019 -2020) • Future CBM experiment (2025+) STAR Experiment (My Thesis work) Phys. Rev. Lett. 112, 032302(2014) Phys. Rev. Lett. 113, 092301(2014) Nuclear Physics A 956 (2016) 75 -82 How conserved charges are correlated as a function of beam energy? SDU, Nihar Sahoo, 20 th Aug, 2018 42 /22

Correlation between different conserved charges Working with a Ph. D student: A. Chatterjee, VECC. Kolkata (Will be submitted to the journal soon) Correlation measure • Off-diagonal cumulants Signature of Quark-gluon plasma state STAR Preliminary • Constraining Freeze-out Temperature and chemical potential • Lattice and HRG: Tfo: 135 -151 Me. V, (μB)fo: 326 -23 Me. V [7. 7 to 200 Ge. V] [My Thesis work] Phys. Rev. Lett. 112, 032302(2014) Phys. Rev. Lett. 113, 092301(2014) Beam energy [Ge. V] SDU, Nihar Sahoo, 20 th Aug, 2018 43 /22

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