Sub-hadronic degrees of freedom in ultrarelativistic nuclear collisions at RHIC and beyond

Sub-hadronic degrees of freedom in ultrarelativistic nuclear collisions at RHIC and beyond Lawrence Berkeley National Laboratory Berkeley, US 1

Introduction: Heavy Ion Physics Today t = 5 10 17 sec T=1 mev Nucleus-nucleus collisions may probe the physics of this quark-hadron transition initial conditions 197 Au 197 Au formation Quark-hadron transition Hadrons form - protons & neutrons t = 10-6 sec T=1 GeV s NN =200 GeV MATTER? hadrons form The Planck epoch UrQMD Group Frankfurt observations 2

Introduction cont. initial conditions formation Goal: (study the bulk!) Identify and study the properties of the matter with partonic degrees of freedom. MATTER? Tools: (to study the matter) hard probes (high pt) jets, heavy flavors, ) hadrons form observations Probing Characterizing - direct photons, leptons - spectra, v1, v2 - jets and heavy flavor - partonic collectivity - fluctuations 3

Fundamental goal of high p T studies a q hadrons hadrons hadrons? d c q Jet Established theoretical framework leading connects particle partonic energy loss to fundamental properties of the medium gluon density, system size b To understand partonic interactions within a dense colored medium E BDMS 2 Debye glue Baier, Dokshitzer, Mueller, Schiff qˆ = µ λ = C α s 4 R α S ql ˆ ρ 2 glue 2E 3 EGLV = CRα S dττρ glue 2 µ L v~ Gyulassy, Levai, Vitev jet ( τ, r() τ ) Log 4

PHOBOS BRAHMS PHENIX STAR

PRL! 6

from the first three years of RHIC: All 4 experiments consistent! Jet quenching Partonic collectivity - nearly ideal fluid flow established most probably at a stage proceeding hadron formation progress in determining of EOS Number of constituent quark scaling At LHC: more measurements in this direction probing deeper gluon sea understanding medium properties 7

Characteristics of the collision The bulk 8

Anisotropy parameter v 2 Coordinate space anisotropy y momentum space anisotropy p y x p x ε = y 2 x 2 y 2 + x 2 v 2 = cos2ϕ, ϕ = tan 1 ( p y p x ) Initial/final conditions, EoS, degrees of freedom 9

Elliptic Flow v 2 at low pt Does pressure convert spatial anisotropy to momentum anisotropy according to the equations of ideal hydrodynamics? PRL 92 (2004) 052302; PRL 91 (2003) 182301 Mass ordering for soft particles indicative of a common velocity. Calculations are sensitive to the equation-of-state. Consistent with the formation of locally equilibrated matter. 10

Elliptic Flow v 2 intermidate p t At higher p T the mass ordering breaks: with v 2 larger for baryons than mesons PRL 92 (2004) 052302; PRL 91 (2003) 182301 Hydro calculations breakdown at higher p T (as expected). How is v 2 established at p T above 2 GeV/c? Why is baryon v 2 so large? 11

Multi-strange Baryon v 2 STAR Preliminary; PRL 91 (2003) 182301 Multi-strange hadrons, φ, Ξ and Ω, are expected to have smaller hadronic x-sections. Ξ and Ω v 2 values are large: apparently independent of hadronic x-section. Consistent with the creation of v 2 before hadron formation. 12

Constituent-quark scaling PRL 92 (2004) 052302; PRL 91 (2003) 182301 At intermediate p T v 2 depends on particle type For p T /n > 0.6 GeV/c, v 2 scales with the no. of constituent quarks n, as predicted for hadron formation by quark recombination Pions deviate: may be due to resonance decays X. Dong, et.al., nucl-th/0403030 13

Characteristics of the collision The bulk Partonic Collectivity! (thermalization?) 14

V 2 of open charm : Thermalization Heavy charm quark probes number of interactions with and degree of thermalization of light quark. charm quark will probe the properties of the bulk matter, but v 2 of D is NOT the bulk matter property STAR:PRL92, 052302(04); PHENIX:PRL91, 18230(03) Will v 2 of D mesons also be on this curve?? D e+x S.Batsouli et al., Phys.Lett.B577:26-32,2003 pqcd electron spectrum hydro Bad news: Unfortunately, the e ± spectrum is a poor indicator of the charm quark dynamics. Good news: But e ± v 2 may be a good indicator of charm dynamics. Future of Nuclear Collisions at High Energy, Kielce, Poland, October X.Dong 15 2004 et al., Phys.Lett.B597(2004)328 p t

Non-photonic electron v2 Greco, Ko, Rapp, Phys. Lett. B595, 202(04) STAR: 0-80% (F.Laue SQM04) statistical error only corrected for e± from π decay PHENIX: Minimum bias M. Kaneta et al, J.Phys. G30, S1217(04) 16

The tools High p t 17

Energy loss loss in in Au+Au A+A collisions Collisions leading particle suppressed p+p Au + Au back-to-back jets disappear Nuclear Modification Factor: R AA 2 1 d N ( pt ) = 2 T d σ NN AA AA / dp / dp T T dη dη 18

Jet Quenching Hadron suppression at intermediate p T, caused by energy loss of energetic objects - Jet quenching! 19

Nuclear modification R AB 2 AB d N / ( pt ) = 2 NN T d σ AB dpt dη / dp dη T T AB = <N binary >/σ inel p+p (Nuclear Geometry) Phys. Rev. Lett. 91, 072304 (2003) d+au ~20% more particles at intermediate p T Central Au+Au factor 5 suppression of expected yield! 20

Au+Au p+p dijet High p T Azimuthal Correlations Trigger: track with p T >4 GeV/c φ distribution: 2 GeV/c<p T <p T trigger Normalize to number of triggers PRL 90, 082302 (2003) Back-to-back jets seen in the event display How about in d+au and exhibit measurable Au+Au? correlation Trigger 21

The definitive proof of jet quenching After the initial hard-scattering, the produced jet interacts strongly with the dense medium in central Au+Au collisions Phys. Rev. Lett. 91, 072304 (2003) 22

The tools High p t Jet quenching! 23

from the first three years of RHIC: All 4 experiments consistent! Jet quenching Partonic collectivity - nearly ideal fluid flow established most probably at a stage proceeding hadron formation progress in determining of EOS Number of constituent quark scaling At LHC: more measurements in this direction probing deeper gluon sea understanding medium properties 24

Large Hadron Collider 2007/8 27 km around Systems: pp (14 TeV), pa (8 TeV), AA (5.5 TeV) 25

at LHC LHC will accelerate and collide heavy ions at energies far exceeding the range of existing accelerators - energy jump by a factor of 28! This is expected to result in: A hotter and longer lived partonic phase Increased cross sections and availability of new hard probes New properties of initial state, saturation at mid-rapidity K.Kajantie, Nucl.Phys. A715 (2003) 432c: Qualitatively, in minimum-bias Pb+Pb (or Au-Au) collisions, SPS is 98% soft and 2% hard, RHIC is 50% soft and 50% hard and LHC is 2% soft and 98% hard each LHC HI min bias collision produces hadron of high p t in the process involving perturbative scale Q >> LQCD 26

New at LHC: dominance of hard processes Initial hard processes contribute significantly to the total AA crosssection (σ hard /σ tot = 98%): Bulk properties dominated by hard processes; Very hard probes are abundantly produced. SPS LO p+p y=0 (h + +h - )/2 s = π 0 RHIC LHC 5500 GeV 200 GeV 17 GeV 27

Access to new region of x: Probe initial partonic state in a novel Bjorken-x range (10-3 - 10-5 ): nuclear shadowing, high-density saturated gluon distribution. Larger saturation scale (Q S =0.2A 1/6 s= 2.7 GeV): evolution (non-linear?) of a saturated gluon distribution, which generates the bulk properties of the collision, measured at mid-rapidity. M 2 (GeV 2 ) 10 8 10 6 10 4 10 GeV 10 2 J/ψ 10 0 10-6 10-4 10-2 10 0 x ALICE PPR CERN/LHCC 2003-049 28

Energy Density in Lattice QCD with 2 and 3 light quarks and with 2 light and 1 heavy (strange) quark at µ B =0 F.Karsh et al., Phys.Lett.B 478, 447 (2000) LHC plasma ~ QCD plasma: 1. µ B ~ = 0 at mid-rapidity at LHC y=8.6! (RHIC = 5.3, SPS=2.9) 2. ε/t 4 continue to rise for T>T c (2+1 flavor) (significant non-perturbative effects in lattice formalism up to T~ 2x T c ) µ B ~ 0 and T~ 3-4 T c (close to ideal conditions) makes comparison to theory reliable! 29

Measurements: Jets in Pb+Pb events at LHC 100 and 200 GeV jets in central PbPb event At higher p t, jets are identifiable as distinct objects above the Pb+Pb background Is there a measurable jet energy loss? 30

There is no jet energy loss!!! Excellent jet reconstruction but challenging to measure medium modification of its shape E t =100 GeV (reduced average jet energy fraction inside R): Radiated energy ~20% R=0.3 E/E=3% R Medium induced redistribution of jet energy occurs inside cone. ΣE q cone = ΣEnq cone ρ(r) 0.2 0 0 0.2 vacuum 1 0.8 0.6 0.4 0.2 0 1 0.8 0.6 0.4 medium E t = 50 GeV E t = 100 GeV 0.4 0.6 0.8 1 R= ( η 2 + φ 2 ) C.A. Salgado, U.A. Wiedemann hep-ph/0310079 Calorimetry alone can not be used to study jet quenching Tracking essential! 31

1+2 experiments JURA ALPES 32

1+2 Experiments T=Λ QCD Q s 0 1 2 10 100 Bulk properties p t (GeV/c) Hard processes modified by the medium ALICE PID CMS&ATLAS 33

EMCal proposed by ALICE-USA Collaboration HCal + EMCal TPC + EMCal and TPC (+ITS+TRD) tracking! RICH Pb/Sci EMCal η x φ = 1.4 x 2π/3 EMCal rail TPC ITS EMCal EMCal rail rails TRD TOF PHOS 34

from RHIC to LHC analysis From leading particle jet analysis at RHIC to full jet reconstruction at LHC Measurements of modifications to fragmentation function S. Blyth, MSc.Th. UCT (2004) undelying event must avoid case where fluctuations in background are of the same order as signal 35

Jet directions: 50GeV 50GeV reconstructed jet energy loss Excellent accuracy! Jet fragmentation function: Salgado, Wiedemann, hep-ph/0310079, PRD 68 (2003) 014008 100GeV Quenched 100 GeV = 80 + 20 GeV 36

at RHIC : Summary jet energy loss QCD at work evidence of partonic collectivity and deconfinement ( v 2 of D: thermalization? ) first time ever, reproduced partonic matter in the laboratory since big bang at LHC : deeper into gluon sea clean comparison with QCD (hydro limit exceeded?) probes the properties of deconfined QCD matter via hard probes and their quenching (fragmentation modification measurable) 37