Two Cultures in High Energy

Nuclear Physics

Tom Trainor

November, 2014

Agenda

• Early data on flows – the QGP/flow culture

• Jets and fragmentation – the HEP culture

• RHIC evidence leading to claim of perfect liquid

• p-p collisions as A-A reference

• Au-Au spectra and angular correlations

• Confront conventional (QGP) RHIC analysis

• Examine LHC results in a HEP context

• Bayesian inference – a guide for the future

2

A Tale of Two Cultures

3

QCD

large l

QCD

small l

HEP

narrative

QGP/flow

narrative

ISR/SppS/FNAL

HEP data

HERA/LEP

BEV/AGS

data

RHIC/LHC

data

Compton scattering,

fragmentation, jets

LGT

QFT/CGC

e.g. F Gelis

nucleon matter

flow reality

“parton” matter

flow reality?

1980s, 90s

2000-present

1980s-present

1980s-present

Flows at the Bevalac, AGS and SPSdirected, radial and elliptic flows, early days

4

A A

directed flow “v1” radial flow bt elliptic flow v2

≈1984 ≈1992

x

zdeviation from MB

interpreted as flow

≈1998

NA35

NA49

Pb-Pb

Phys Rev Lett 80, 4136 (1998); nucl-ex/9711001Phys Lett B 157, 146 (1985)

all azimuth structure

interpreted as flows

memory of b?

‹px›

CM

Jets in p-p at the ISR and SppSFirst low-energy jet reconstruction –

MB jet spectra down to 3 GeV partons

5

simple expression predicts jet spectra

for all p-p collision energies above 10 GeV

3 GeV 3 GeVearly eighties

Phys Rev D 89, 094011 (2014); arXiv:1403.3685

2014

6

phadron

Parton Fragmentation in e+- e-

e-

e+

g, Z0

LEP

PETRA

q

q color

dipole

how are parton fragments (jet hadrons) distributed on momentum?

s = Q2

LEP, PETRA fragmentation data: 1988-2000

color dipole radiation:

ln(phadron)

LEPPETRA

e-e

ln(pparton)

s, Q2

?

an “equilibration” process

when plotted on ln(pz) → yz (as from ALEPH)

internal structure of jets

7

ln(p) rapidity y

Fragment Distributions on Momentum

xp = ln(1/xp)

fragmentation functions on logarithmic variables

alternative:

fragmentation functions

on rapidity y

ln ( ) /y E p m

s

conventional:

fragment momentum

relative to

parton momentum

D(x

p,s

)D

(y,y

ma

x)

D(l

n(p

),s)

D(x

p,s

)

xp = phadron/pparton fragmentation function

D(x,s) D(y, ymax)

LEPPETRA

non-pQCD

physics!

scaling violations

FFs self-similar on y

DGLAP DGLAP

8

Accurate Analysis of Fragmentation

1 1

max( , ) ( ; , ) (1 ) / ( , )p qg u y u p q u u B p qb - - -

max max max( , ) 2 ( ) ( , )D y y n y g u y

fragmentation functions well described by simple model function

g(u

,ym

ax)

beta distribution on normalized rapidity u

accurately models fragmentation functions

( ) ( )( , )

( )

p qB p q

p q

min

max min

y yu

y y

-

-

(normalized)

ymin

( ; , )u p qb

normalized rapidity

redundant

a form of

equilibration

via least action

p-pp-p - FNALe-e - LEP

D(y

,ym

ax)

dijet multiplicity

Phys Rev D 74, 034012 (2006); hep-ph/0606249

2006

9

The STAR Detector at RHIC

Brookhaven National Laboratory - BNL

Long Island

10

Single RHIC Au-Au Central Collision

4 m

4 m

1500 charged particles

UW graphic

Early RHIC Results – Flows

11

first RHIC paper - STAR

v2(b)

v2(pt)

all hadrons

all hadrons

ideal hydro

isentropic expansion?

p-p

radial flow

Au-Au

𝜼/𝒔?

bt(b)

viscous?

“mass ordering”

elliptic flow

elliptic flow

peripheral central

Phys Rev Lett 92, 112301 (2004); nucl-ex/0310004

Phys Rev Lett 86, 402 (2001); nucl-ex/0009011Phys Rev C 72, 014904 (2005); nucl-ex/0409033

spectra

azimuth correlations

hydro2003

2000

2004

Early RHIC Results – Jet Quenching

12

HIJING

CGC

major

problem:2004

minijets

quench

“too slow growth”

RAA Phys Rev C 73, 064907 (2006); nucl-ex/0411003

away-side jet

disappears

Phys Rev Lett 91, 072304 (2003); nucl-ex/0306024Phys Rev C 70, 021902 (2004); nucl-ex/0405027

pt cuts?

3 GeV

partons!

problem

2004

2003

The Perfect-Liquid Pronouncement

Elliptic flow: “The smallness of dissipative corrections

[required for hydro descriptions of v2 data]...is in itself a

remarkable and unexpected discovery. […] ...the QGP at RHIC

is almost a perfect liquid. […] Elliptic flow measurements

confirm...local thermal equilibrium...” early in the collisions.

Jet quenching: “The observed jet quenching in Au-Au

[collisions] is due to parton energy loss. […] Theoretical

analysis of jet quenching...strengthens the case for multiple

strong interactions of the quark and gluon constituents of the

matter made at RHIC.”

The CGC: “...the surprising very weak centrality and beam

energy dependence [“too slow growth”] observed [in the data,

compared to HIJING] is most satisfactorily explained and

predicted by the CGC....” The comparison (interpreted to rule

out minijets and the TCM in favor of the CGC) “...is one of the

strongest lines of empirical evidence...” for the CGC .

13

A tale of two theorists – 2004

Miklos Gyulassy (Columbia) and Larry McLerran (BNL)

Nu

clP

hys

A 7

50

, 3

0 (

20

05

); n

ucl

-th

/04

05

01

3

PL

sQGP

CGC IC

Confronting Perfect-Liquid Claims

• Understand minimum-bias dijets in isolation

• Understand p-p (N-N) collisions in isolation

• Construct a reference for transparent A-A collisions

• Determine what is truly novel about A-A collisions

14

Int J Mod Phys E 23, 1430011 (2014); arXiv:1303.4774

RHIC review:

what should a responsible scientist do?

Minimum-bias p-p Spectra

15

A-A reference is p-p collisions

quantum transition!

dijets nh ns2

- no eikonal approximation

nch = ns + nh

nh ≈ 0.005 ns2

solid curve is pQCD

prediction from FFs

and MB jet spectrum

subtract S0

NSD

0ln ( ) /t t ty m p m

two-component model

soft + hard (jets) = TCM

Phys Rev C 80, 044901 (2009); arXiv:0901.3387Phys Rev D 74, 032006 (2006); nucl-ex/0606028

Phys Rev D 87, 054005 (2013); arXiv:1210.5217

PYTHIA

2004

2008

16

Minimum-bias p-p Correlations

subtract soft reference

minijet

fragments

Dr

/√r

ref

same side

1D 2Dp-p

200 GeV

nch=1

nch=11

pt yt

0.15 61pt (GeV/c)

proton fragments

away side hadron pt ~ 0.6 GeV/c

yt1

yt2 yt2

Dr/√rref

nch

parton fragments

0ln ( ) /t t ty m p m

minimum-bias: no trigger condition

soft hard

spectrum TCM

correlation TCM

J Phys Conf Ser 27, 98 (2005); hep-ph/0506172 2005

Au-Au Spectra vs Centrality

17

subtract S0

subtract S0

spectrum hard components

solid curve is pQCD prediction from

(modified) FFs and MB dijet spectrum

centrality evolution of

jet contributions to hadron spectra

pion hard components full proton spectra

pions

protons

mp

spectrum TCM

IJMPE 17, 1499 (2008), 0710.4504

Phys Rev C 80, 044901 (2009); arXiv:0901.3387

20072009

GLS

Au-Au Correlations vs Centrality

18

85-95% 55-65%

20-30% 0-5%

fraction of total cross section 200 GeV

centralities

Phys Rev C 86, 064902 (2012); arXiv:1109.4380

peripheral

central

2008

Sample Fit – 62 GeV Au-Au

45-55%

data fit residuals SS 2D peak

NJ quadrupole AS dipole 1D on eta 2D exponential

dijets

dijets

v2

Phys Rev C 86, 064902 (2012); arXiv:1109.4380

soft

2008

Sharp Transition in Jet Structure

20

SS 2D peak amplitude AS dipole SS 2D peak width

Glauber Model: n = 2Nbin / Npart

sharp transition ST ≈ 50% central @ n = 3

ST

dijets dijets

2004

Phys Rev C 86, 064902 (2012); arXiv:1109.4380

2008

Conflict between Narratives

• Dense or opaque flowing QCD medium

• Strong jet quenching, most jets thermalized

• Viscous hydro describes low-viscosity medium

• At least 50% of Au-Au collisions are transparent

• Almost all jets survive, but quantitative modification

• Jet phenomena described quantitatively by pQCD

• Hydro fails to describe claimed “flow” phenomena

21

QGP/flow narrative:

HEP narrative:

Int J Mod Phys E 23, 1430011 (2014); arXiv:1303.4774

RHIC review:

given the same data

Resolving “Too Slow Growth”

22

Pb-Pb

HAA

ST n = 3, 50%

p-p

CGC

STHIJING

one basis (CGC) for

“perfect liquid” claim

dijet frequency

per A-A collision

predicted hard

component HAA

HIJING is based on

PYTHIA: incorrect30% of hadrons in central Au-Au

collisions are included in resolved dijets

CGC falsified by peripheral data

p-p

Phys Rev C 83, 034903 (2011); arXiv:1008.4759

HIJING

PHOBOS?

50% of s

CGC ~ ln(8n)

Radial Flow vs Jets

23blast-wave BW fits accommodate hard component – jets

soft

hard

larger T

smaller bt

smaller T

larger bt

slope break

is jet effect

J Phys G 37, 085004 (2010); arXiv:0906.1229

fit fit

19 GeV

200 GeV

17 GeV

sum sum

BW

20.5pt =

24

Elliptic Flow – Standard Narrative

xz

y

pyy

x

2 21

22 2cos2 , tan ( )

y

x

py xv

y x p - -

Reaction plane: z-x plane

hydro evolution

v2 data “hot and dense matter with partonic collectivity”

I D

Au

Auspectators

participantsparticipants

hadron density

hydro

mass scaling

2006

Nonjet (NJ) Azimuth Quadrupole

25

derived from model fits to 2D angular correlations

conventional methods

simple formula predicts all centralities and energies

2D method

jet bias:

nonflow

p-p v2

predicted

by pQCD!

(color dipole)

premise:

all azimuth

structure

is flows –

no jets

Eur Phys J C 62, 175 (2009); arXiv:0907.2686

𝐀𝐐 = ρ𝟎𝐯𝟐𝟐 no jet

contribution

2007

26

Underestimating Jet Yieldssimulation STAR data

background estimated

by ZYAM and v2

1) v2 over-estimated,

2) offset is over-

estimated by “ZYAM”

true jet yields

Au-Au 0-12% (solid)

p-p (open), both 200 GeV

with correct

background

Au-Au jet yield

six times larger

than p-p:

near-transparent

A-A system

ZYAM underestimates jet yields up to 10×

true backgroundZYAM background

ZYAM jet yields

ZYAM: zero yield at minimum

claim jet quenching, parton thermalization

J Phys G 37, 085004 (2010); arXiv:0906.1229

ZYAM corrected

0-5%

27

NJ Quadrupole Energy Systematics

A new QCD phenomenon at RHIC?

saturation?

2

2 [2]{2 }

ref

v Dn

r

r

D

squeezeout

per-pair

Bevalac

AGSSPS

RHIC

small-x glue

quadrupole

star preliminary

nucleon hydro

AGS

Bevalac

SPS

RHIC

per-particle

hydro extrapolation is misleadingAQ{2D}

LHC

AQ

arXiv:1302.0300 tbp J Phys G

LHC?

𝐀𝐐 = ρ𝟎𝐯𝟐𝟐

2007

NJ Quadrupole vs A-A Transparency

28

dijet structure scales exactly

with the number of binary

N-N collisions Nbin – as

expected for A-A transparency

“elliptic flow” based on re-

scattering in a dense medium

increases to 60% of its maximum

ST ST

in either case the energy dependence is consistent with QCD

?

but no rescattering

arXiv:1302.0300 tbp J Phys G

SS jet

peak

amplitude

“elliptic

flow”

29

NJ Quadrupole Source Boostnonjet quadrupole distributions for identified hadrons

centrality average

add deuterons

hydro is falsified by PID v2 data!

RR

200 GeV Au-Au

source boost Lambdas only

0-10%

minimum-bias data

replot v2 data as v2 / pt on yt

new information is quadrupole source boost distribution

trend predicted

dash-dot curve

add most-central data

viscous hydro

“mass scaling”

hydro

Phys Rev C 78, 064908 (2008); arXiv:0803.4002

NJ Quadrupole Spectrum

30

unidentified hadrons

30

Phys Rev C 78, 064908 (2008); arXiv:0803.4002

quadrupole boost is

centrality independent –

no coupling to A-A dense medium

universal spectrum

FF spectrum

centrality dependence

fixed boost

𝐐(𝐲t) ∝ ρ𝟎(𝐲t, 𝐛) 𝐯𝟐(𝐲𝐭, 𝐛)/pt

statistical

model!

quadrupole source

2010

31

ALICE “Higher Harmonics”

NJ quadrupole

jet structure

2 2 2 2

2 2 2 2v {2} v {EP} = v {SS}+ v {2D}

2 2

m mv {2} = v {SS} m > 2 ST

points from ALICE

curves from UW

controlled by pt spectrum

SS 2D jet peak

jet bias

J Phys G 40, 055104 (2013);

arXiv:1109.2540

7 citations

200 GeV Au-Au

Phys Rev Lett 107, 032301 (2011);

arXiv:1105.3865

250 citationsno h cut

sextupole

octupole

quadrupole

BEC +

electrons

32

Sextupole Relation to SS 2D Peak

true SS baseline

ST ST

SS 2D jet peak

3 parametersSS peak amplitude SS peak h width

50-60%

50-60%

BEC

SS peak

jets

note sharp transition ST

std

fit

triangular flow from jets

prediction:

1D projection

Phys Rev C 88, 014904 (2013); arXiv:1301.2187Phys Rev C 86, 064905 (2012); arXiv:1206.5428

2008

STAR data

STAR data2013

2012

140 parameters

LHC Spectra and Yields

33

prediction

ns scale up soft by 1.8

nh scale up hard by 1.82

2.76 TeV is not

a simple multiple

(2.1) of 200 GeV

dijets play a

major role

fluctuations depend on

detector acceptance,

change endpoint

structure

little shape change from 0.2 to 2.76 TeV

PHENIX

STAR

Phys Rev Lett 106, 032301 (2011); arXiv:1012.1657

arXiv:1402.4071 tbp Phys Rev C

p-p

data

eikonal

ALICE ensemble ‹pt› vs RHIC

34

equivalent

dijet production

ALICE: All MCs are falsified

Phys Lett B 727, 371 (2013); arXiv:1307.1094

PYTHIA

Two-component Model for ‹pt›

35

simple TCM

describes

all ‹pt› data

hard components

jet spectrum width

result consistent

with hard component

from dijets

TCM also

describes

p-Pb, Pb-Pb

curves are TCM

Phys Rev C 90, 024909 (2014); arXiv:1403.6494.

ALICE event-wise ‹pt› Fluctuations

36

soft

fluctuation systematics, agreement with MB dijet expectations

Eur Phys J C 74, 3077 (2014); arXiv:1407.5530 TCM description – dijets

dijets

2014

2006

2006

J Phys G 32, L37 (2006); nucl-ex/0509030

C “covariance”

2014

A ≈ 0.4

like nh /ns

Interaction of Two Cultures

37

QCD

large l

QCD

small l

HEP

narrative

QGP/flow

narrative

ISR/SppS/FNAL

HEP data

HERA/LEP

BEV/AGS

data

RHIC/LHC

data

Compton scattering,

fragmentation, jets

LGT

QFT/CGC

e.g. F. Gelis

nucleon matter

reality

“parton” matter

reality?

1980s, 90s

2000-present

1980s-present

reality datamodel1model2

induction

predictionmeasurement

Bayesian inference – scientific method – models compete

model3

1980s-present?

Summary

• The QGP/flow culture has captured various HEP jet

manifestations from spectra and correlations and

reinterpreted them as flows carried by a dense

“partonic” medium → “perfect liquid”

• Differential measurements and optimized plotting

formats reveal the jet character of various claimed

flow phenomena – reaffirming the HEP narrative

• True novelties of high energy nuclear collisions are

(a) a nonjet (and nonflow!) quadrupole and (b) dijet

modifications in A-A and p-p, new aspects of QCD

38

Abstract

Since the mid eighties a community originating within the Bevalac program

at the LBNL has sought to achieve formation of a color-deconfined quark-

gluon plasma in heavy ion (A-A) collisions using successively higher

collision energies at the AGS, SPS, RHIC and now the LHC, emphasizing a

flowing dense "partonic" medium as the principal phenomenon. During the

same period the high energy physics (HEP) community studying

elementary collisions (e-e, e-p, p-p) has developed the modern theory of

QCD, emphasizing dijet production (fragmentation of scattered partons to

observable hadrons) as the principal (calculable) phenomenon. Initially it

was assumed that the QGP phenomenon in more-central A-A collisions

might be distinguished from the HEP dijet phenomenon in elementary

collisions. However, strong overlaps in phenomenology have revealed

significant conflicts between QGP and HEP "cultures," especially at RHIC

and LHC energies. In this talk I review some of the history and present an

assortment of experimental evidence and interpretations from the two

cultures with suggested conflict resolution.

39