Ralf Averbeck Department of Physics & Astronomy Seminar at Department of Chemistry Stony Brook University, October 17, 2005 Big Bang Chemistry Exploring

Ralf Averbeck Department of Physics & Astronomy

Seminar atDepartment of Chemistry

Stony Brook University, October 17, 2005

Big Bang ChemistryExploring the Properties of Primordial Matter

at RHIC

Ralf Averbeck,2Stony Brook University, 10/17/2005

Outline Introduction Nuclear collisions at RHIC Establishing the “final” state Looking “inside” with penetrating probes

Direct photons Jets Heavy quarks Electromagnetic radiation

Summary Outlook


“Chemistry” at many scales what is Chemistry?

Merriam-Webster dictionary:“a science that deals with the composition, structure, and properties of substances and with the transformations that they undergo“

substances? “biological” structures complex “compounds” molecules atoms nuclei & electrons protons & neutrons quarks & gluons

today’s topic transformation of

nuclear matter into quark-gluon matter

study of the properties of quark-gluon matter

biolo

gy

physics


Nuclear matter as QCD laboratory nuclear matter is made from nucleons:

3 (light) constituent quarks, carrying color charge quarks interact via gluon exchange gluons carry color charge (“colored photons”)!

puzzles: isolated quarks are NEVER observed (“confinement“) quark masses account for ~1% of the nucleon mass

properties of the theory of strong interaction: QCD (Quantum Chromo Dynamics)

QCD vacuum is not empty


The QCD phase transition

learn about fundamental properties of matter by observing the QCD phase transition investigating the properties of quark-gluon matter

but how? look back at the first successful attempt of a QCD

phase transition

nuclear matter quark-gluon matter

phase transition

change of the relevant degrees

of freedom confinement dynamically

generated mass

asymptotic freedom constituent mass


A short history of the universe~ 10 s after Big Bang

Hadron Synthesisquarks & gluons → hadrons

~ 100 s after Big Bang

Nucleon Synthesisprotons & neutrons → nuclei

Temperature increases

Degrees of freedom are liberated


The tools of the trade how to excite matter to T ~ 1012 K (~200 MeV)?

heating by “brute force”

dump maximum energy into minimum volume

Relativistic Heavy Ion Collider: RHIC @ BNL

STARSTAR

4 experiments study collisions

(polarized) p+p A+A A+B

with maximum energy in CMS

500 GeV (p+p) 200 GeV (A+A)

per N-N pair!


The PHENIX experiment3 detectors for event characterization

collision vertex? centrality: peripheral or central? orientation of the reaction plane?

2 forward spectrometers muons pseudo rapidity

1.2 < || < 2.4 momentum p 2 GeV/c

2 central spectrometers hadrons electrons photons pseudo rapidity 0.35 momentum p 0.2 GeV/c


The experimental challengeSTAR ONE central

Au+Au collision at max. energy

production of MANY secondary particles

PHENIX


Critical energy densitynuclear matter: p,n quark-gluon matter: q, g

temperature and/or density

distance between nucleons:

2 r0 ~ 2.3 fm

nucleon radius: rn ~ 0.8 fm

more sophisticated QCD calculations on a discrete space-time lattice phase transition for

– critial temperature TC ≈ 170 MeV (1012 K)– critical energy density C ≈ 1 GeV/fm3

30

33

030

/15.0

/16.04

3

34

fmGeV

fmrR

A

3

330

/44.0

/47.04

3

fmGeV

fmr

c

n

naive estimate of critical energy density c: nuclear ground state critical: nucleons overlap


Energy density reached at RHIC

more sophisticated: Bjorken model relate with measured transverse energy ET

nuclear radiusR ~ 6.5 fm

dz dy

2R

formation time ~ 0.3- 1 fm/c

dy

dE

RdzR

dE

V

E TTBJ

22

1

BJ ~ 5 – 15 GeV/fm3

very naive estimate of assume ALL energy dumped in volume of Au nucleus = (197 x 200 GeV)/(4/3 R3

Au) ~ 34 GeV/fm3

lattice QCD relate with T BJ = 5 – 15 GeV/fm3 → Ti = 250 – 350 MeV

,T sufficient for QCD phase transition at RHIC


Anatomy of a Au+Au collisiontime

hard parton scattering

AuAu

hadronization

freeze-out

formation and thermalization of quark-gluonmatter?

Space

Time

expansion

Jet cc e pK


electromagnetic radiation: , e+e,

rare, no strong interaction → probe all time scales– thermal radiation (black

body) → initial temperature– in-medium properties of

vector mesons → chiral symmetry restoration

hadrons: , K, p, … abundant, final state

–yields, spectra → energy density, thermalization

–correlations, fluctuations, azimuthal asymmetries → collective behavior

Different probes tell different stories

cc

J

qq

ee

“hard” probes: jets, heavy quarks, direct

rare, produced initially (before quark-gluon matter is present!)–probe hot and dense matter

investigate evolution of a system that “lives” for ~10-22 s (~100 fm/c) in a volume ~10-42 m3 (~1000 fm3) with energy ~6 x 10-6 J (~40 TeV)

p

p


one particle ratio (e.g. p/p) determines B/T

a second ratio (e.g. /p) then determines T predict all other hadron abundances and ratios

do the huge yields of various hadron species in the final state reflect a THERMAL distribution?

abundances in hadrochemical equilibrium

Final state hadrochemistry

1

1

2 /3

3

22

Tmp

hhBh

e

pdVgN

lesantipartic and

,.......,,,,,,,,,, DdpKKh

spin isospindegeneracy

temperature atchemical freezeout

baryochemicalpotential

momentum spectra indicate kinetic equilibrium


Phase diagram of “nuclear” matter final state at RHIC: hadronic black body in kinetic

and chemical equilibrium very close to phase

boundary between hadronic and quark-gluon matter

B → 0 means B/B → 1 (early universe)

T = 177 MeV provides lower limit for initial temperature

necessary condition for phase transition are met at RHIC!


g

g

medium

A view behind the curtain “tomography” with scattering experiments

Rutherford: → atom discovery of the nucleus SLAC: electron → proton discovery of quarks

calibration of hard probes theoretically

– perturbative QCD (pQCD) experimentally

– measurement in p+p– in-situ control: photons

“tomography“ at RHIC problem: short life time probe has to be “auto

generated” early in the collision

hard parton (quark, gluon) scattering

scattered parton probes medium, fragments into hadrons

– high pT jets– heavy quark probes


Direct photons at √sNN = 200 GeV photons from quark-gluon Compton scattering

p-p

Au-Au

direct photons are a calibrated probe

Nbinary:number of binary collisions determined event-by-eventfrom collision geometry

no strong final state interaction


0 in p-p

peripheralN

binary = 12.3 4.0

centralN

binary = 975 94

Au-Au Au-Au

Hadrons 0 at √sNN = 200 GeV pQCD is (again) in reasonable agreement with p+p data

binary collision scaling works for 0 in peripheral Au+Au strong suppression at high pT in central collisions:

energy loss of hard scattered parton in medium?


Or is the production suppressed? saturation of parton density in nucleus at high

energy? (not here: direct photon data!) control experiment: d+Au at √sNN = 200 GeV

nuclear modification factor: ppinYieldN

AuAuinYieldR

binaryAA

High p T hadrons

are suppressed in

the hot medium

at RHIC!


charm: mc ~ 1.3 GeV; bottom: mb ~ 4.5 GeV

produced as quark-antiquark pair

hard process (mq >> QCD)– pQCD applicable at low pT!

most pairs separate and form “open heavy flavor”:

charm: D mesons; bottom: B mesons thermalization, energy loss mechanism

bound states (quarkonia) can be formed as well: charm: J; bottom: hadronic ↔ quark-gluon matter

Heavy quarks: the other hard probe

D mesons

, ’,


ideal (but difficult, in particular in Au+Au) full reconstruction of decays, e.g.

How to measure open heavy flavor?

alternative (but indirect) semileptonic decays contribute to lepton spectra

D0 K+ -

Meson D± (D0)

Mass 1.87 (1.87) GeV

BR D0 --> K (3.85 ± 0.10) %

BR D --> e +X 17.2 (6.7) %

BR D --> +X 17.2 (6.6) %


e± from heavy flavor many sources contribute

to the e± spectrum background subtraction

calculation of e± cocktail from all known (measured) sources

direct measurement of the dominant background

– Dalitz decay of – conversion of photons in

material– converter technique

excess beyond background semileptonic decays of heavy flavor

p+p @ 200 GeVPHENIX: hep-ex/0508034


electrons from heavy flavor decays at mid rapidity PYTHIA: LO pQCD FONLL: Fixed Order Next-to-

Leading Log pQCD (M. Cacciari, P. Nason, R. Vogt hep-ph/0502203)

Reference: pQCD comparison

pT < 1.5 GeV/c: pQCD works

pT > 1.5 GeV/c: pQCD “softer“ than data

fragmentation hard? bottom enhanced? higher order contributions? heavy quarks from

fragmentation of light quark or gluon jets?

crucial: rapidity dependence (PHENIX data at = -1.65)

PHENIX: hep-ex/0508034


PHENIX PRELIMINARY

1/T

ABE

dN/d

p3 [m

b G

eV-2]

Cold nuclear matter effects e± spectrum from

heavy flavor decays in d+Au at 200 GeV data divided by

nuclear overlap integral TAB (binary collision scaling assumption)

scaled d+Au data are consistent with fit to p+p reference

agreement holds for various d+Au centrality classes

.inelpp

binaryAB

NT

NO indicatio

n for

significant m

edium

effects in

cold

nuclear matte

r!


PHENIX: PRL 94, 082301 (2005)Hot matter: charm yield in Au+Au

spectra of e± from heavy flavor decays for different centralities (from converter analysis)

pT > 1.5 GeV/c: not enough statistics to address modification of spectral shape

total yield for pT > 0.8 GeV/c

total yield in Au+Au follows binary collision scaling (as expected for hard probe)!


Nuclear modification of e± spectra cocktail analysis of full statistics data sample (Run-2) strong modification of heavy flavor e± spectra

is evident at high pT!

PHENIX: nucl-ex/0510???

pp

AA

AAAA

dpd

T

dpNd

R

3

3

3

3

PHENIX: nucl-ex/0510???


Centrality dependence of e± RAA preliminary analysis of Run-4 data sample (~109 events!)

clear indication for stronger high pT suppression in more central collisions

collision centrality and “opaqueness” of the medium are related


Theory vs. data energy loss via induced gluon radiation in vacuum: gluon emission suppressed in “dead cone“

( < m/E) (Dokshitzer, Kharzeev: PLB 519(2001)199

in medium: “dead cone“ filled by medium induced radiation (Armesto et al.: PRD 69(2003)114003)

(3) q = 14 GeV2/fm

(2) q = 4 GeV2/fm

(1) q = 0 GeV2/fm

(4) dNg / dy = 1000

data favor models with large parton densities and strong coupling

major uncertainty: contribution from bottom decays at high pT

curves (1-3) are for charm decays only (Armesto et al.: PRD 71 (2005) 054027)

curve 4 includes bottom decays (M. Djordjevic et al., PRL 94 (2005) 112301)


Towards higher pT bottom decays should dominate the e± spectrum above

pT ~ 5 GeV/c bottom energy loss < charm energy loss RAA should rise again preliminary STAR e± data

consistent within errors for pT < 5 GeV/c

pT reaches 10 GeV/c

RAA stays small!!!! large bottom energy loss? reduced bottom production? other e± sources? experimental problems?


elliptic flowspatial anisotropy in initial stage

momentum anisotropy in final stage

elliptic flow strengthhydrodynamic calculations

measured v2 of hadrons requires thermalized matter at < 1 fm/c with > 5 GeV/fm3

Does charm thermalize? RAA << 1 → strong interaction of charm quarks with medium large charm mass implies long thermalization time scale unless medium is super dense quark-gluon matter does charm participate in collective motion?!

2 Rcos 2v

pY

pX

Y

X

ZReaction plane: Z-X plane

High pressure

Low pressureasymmetric pressure gradients (early, self quenching)

3 3

R30T T

2 cosnn

d N d NE v nd p p d dp dy


Heavy quark elliptic flowPHENIX: significant v2

rising to pT~2 GeV/c, but drops for pT>2 GeV/c (bottom contribution)

STAR: significant, almost constant v2 above pT~2 GeV/c

v2 of e± from heavy flavor from PHENIX & STAR are not consistent

parton thermalization?most likely, but what

happens to heavy quarks at high pT???

V. Greco et al.PLB 595(2004)202

theory curves from recombination model (V. Greco et al., PLB 595(2004)202)

non-flowing c quark coalesces with flowing light quark to form a D meson

c quark fully participates in partonic flow


~ 1% of cc forms bound state: J/ (m~3.1 GeV) “easy” to detect: J/→ l+l-, l=e, (BR~6%) color screening in quark-gluon medium

J/suppression (Matsui und Satz, PLB176(1986)416)

Bound cc states: J/

Perturbative Vacuum

cc

Color Screening

cc central Pb+Pb collisions at SPS (√sNN ~ 17 GeV) J/suppression beyond “normal” nuclear

absorption (NA50: PLB477(2000)28)

perspectives at RHIC large charm yield additional J/ enhancement via

cc coalescence? key quark-gluon matter probe!

crucial first steps reference measurement in p+p cold nuclear matter effects in d+Au


J/ at RHIC

factor ~3 suppression relative to binary scaled p+p in central collisions

data show same trends for

Cu+Cu Au+Au e+e- (|y|<0.35) +- (1.2<|y|<2.2) 200 GeV 62 GeV


Theory comparison: cold matter

cold nuclear matter model (R. Vogt: nucl-th/0507027)

in agreement with d+Au data shows trend to under predict suppression in central Au+Au

collisions

J/→ +- J/→ e+e-


Theory comparison: hot matter

models consistent with SPS data

fail to describe RHIC data too much suppression

models with regeneration mechanism

reasonable agreement

tests (still inconclusive) pT and y dependence


dileptons (e+e-) probe the full time

evolution of the collisions

unaffected by strong final state interaction

the “ultimate” tool to look “inside”

measure the full dilepton continuum

main difficulty combinatorial

background, e.g. via →e+e- and 0→e+e-

More fun with dileptonsThermal radiation Chiral symmetry restoration

continuum enhancement modification of vector mesons

thermal production or energy loss

suppression (enhancement)


e+e- pairs in Au+Au at 200 GeV (~0.8x109 events) foreground: form all e+e- pairs within one event combinatorial background: from “event mixing”

(combine e+ from one event with e- from other event) signal = foreground - background

Dielectron continuum at RHIC

systematic error dominated by uncertainty in background normalization: 0.25% !!


e+e- data agree within uncertainties with

cocktail from hadronic sources

charm from PYTHIA (LO pQCD without medium effects)

hint for enhancement below region

charm?? energy loss angular correlation?

systematics need to be reduced!

Comparison with expectation


Summary a new phase of matter is produced in Au+Au

collisions at RHIC it is hot it is dense it has degrees of freedom that are not color-neutral it is strongly coupled

effective tools to probe the sQGP are at hand penetrating probes autogenerated probes from hard scattering

– high pT jets– heavy quarks

electromagnetic probes– dilepton continuum– thermal radiation

sQGP


RHIC

The future is bright: RHIC baseline

detailed system size and energy dependence of now established probes

– threshold for sQGP formation?– mechanism of hadronization?

characterization of sQGP properties

PHENIX upgrades and RHIC-II (2006 - 2010) HBD (“Hadron Blind Detector“) → Dalitz & conversion

background rejection for single e± and e+e- pairs SVT (“Silicon Vertex Tracker” → Sekundärvertex (c,b) RHIC-II (40 x design luminosity) → (bb) spectroscopy


And elsewhere

highest temperature / lowest baryon density LHC @ CERN

moderate temperature / highest baryon density FAIR @ GSI

continue exploration of strongly interacting matter under extreme conditions at next frontiers


thermal radiation with T>>TC would prove beyond any doubt the presence of a quark-gluon black body

competition with photon emission from hadron gas initial pQCD processes (direct )

Approaching the “Holy Grail”

Turbide, Rapp, Gale: PRC69(2004)014903 promising window

1 < pT < 3 GeV/c

“real” photons signal/background currently

too small for significant measurement

“virtual” photons ANY source of real photons

emits also virtual photons: 0→ and Dalitz decay: 0→→e+e-


virtual photon spectrum at low mass is known EXACTLY (from QED): Dalitz pair mass spectrum

Dalitz pairs and virtual photons

32

222

2

2

2

2

112

14

13

21)

M

m()m(F

m)

m

m(

m

m

dm

dN

Nee

eeeeee

e

ee

e

ee

ee

phase-space facto

r

→1 fo

r high p T

el.magn fo

rm fa

ctor

→1 fo

r small m

ee

shape analysis of low mass e+e- spectrum

no thermal radiation → shape must agree with expectation from 0 and Dalitz decays

excess → direct *

then calculate *

direct/ *inclusive


significant direct virtual photon signal observed

trend towards stronger signal in more central events

translate into “real” photon spectrum direct=incl.(*

dir./ *incl.)

with incl. being the measured inclusive “real” photon spectrum

*direct/ *

inclusive


data are consistent with expectation from

direct photons from hard scattering (pQCD·TAB) (Gordon, Vogelsang: PRD48(1993)3136)

thermal radiation from quark-gluon matter (d’Enterria, Perresounko: nucl-th/0503054)

– hydrodynamical model– T0 = 590 MeV– t0 = 0.15 fm/c

thermal radiation? reference data from p+p and

d+Au are needed first!

Direct (thermal?) photon yield


The PHENIX Collaboration


How rare is charm at RHIC?

production cross section at RHIC: cc ≈ 1 mb in p+p

assume binary collision scaling (hard probe)central Au+Au collision: ≥ 20 cc (if NO medium effects)!


1/T A

B1/

T AB

1/T A

B1/

T AB

1/T

ABE

dN/d

p3 [m

b G

eV-2]

1/T

ABE

dN/d

p3 [m

b G

eV-2]

1/T

ABE

dN/d

p3 [m

b G

eV-2]

1/T

ABE

dN/d

p3 [m

b G

eV-2]

Centrality (in)dependence in d+Au

Documents

Ralf Averbeck Department of Physics & Astronomy Seminar at Department of Chemistry Stony Brook University, October 17, 2005 Big Bang Chemistry Exploring