RHIC II Upgrade
and Science Program
QCD Town Meeting
Rutgers, NJ
13-Jan-07
W.A. Zajc
Columbia University
Outline


A capsule history of the initial
discovery phase of RHIC operations
Compelling scientific questions
for RHIC II

The elements of RHIC II

The primacy of QCD
13-Jan-07
The Plan c. 2000

Use RHIC’s unprecedented capabilities

Large √s 
 Access
to reliable pQCD probes
 Clear separation of valence baryon number and glue


Polarized p+p collisions
Two small detectors, two large detectors
Complementary capabilities
 Small detectors envisioned to have 3-5 year lifetime
 Large detectors ~ facilities

 Major
capital investments
 Longer lifetimes
 Potential for upgrades in response to discoveries
13-Jan-07
Since Then…

Accelerator complex


Routine operation at 2-4 x design luminosity (Au+Au)
Extraordinary variety of operational modes
Species: Au+Au, d+Au, Cu+Cu, p+p
 Energies: 22 GeV (Au+Au, Cu+Cu, p), 56 GeV (Au+Au),
62 GeV (Au+Au,Cu+Cu, p+p)
, 130 GeV (Au+Au),
200 GeV (Au+Au, Cu+Cu, d+Au, p+p), 410 GeV (p), 500 GeV (p)


Experiments



Science



Worked
Collaborations worked
160 refereed publications, 89(!) PRL’s
Major discoveries
Future



13-Jan-07
Demonstrated ability to upgrade
Key science questions identified
Accelerator and experimental upgrade program
developed to perform that science
A Non-Surprise: RHIC Energy Reduces Scale Dependence


The high √s of RHIC


makes contact with rigorous pQCD calculations
minimizes “scale dependence”


Spin program
Providing calibrated probes in A+A
A huge advantage in
PHENIX p+p  p0 + X
-NLO pQCD
F. Aversa et al. Nucl. Phys. B327, 105 (1989)
-CTEQ5M pdf/PKK frag
-Scales m=pT/2, pT, 2pT
m=pT/2
m=2pT
13-Jan-07
RHIC Spin Successes
Absolute Polarimeter
(H jet)
RHIC pC Polarimeters
BRAHMS & PP2PP (p)
Lmax  2 1032 s 1cm 2
Achieved 60-65%
polarization during
RHIC Run-6 !
70% Polarizati on
50 
s  500 GeV
PHENIX (p)
STAR (p)
Siberian Snakes
Spin Rotators
Partial Siberian Snake
LINAC
BOOSTER
Pol. Proton Source
500 mA, 300 ms
2  1011 Pol. Protons / Bunch
e = 20 p mm mrad
AGS
200 MeV Polarimeter
AGS Internal Polarimeter
Rf Dipoles
RHIC accelerates heavy ions to 100 GeV/A
and polarized protons to 250 GeV
13-Jan-07
Our First Hard Look
“Standard” value of Dg
from pre-RHIC DIS data
Δg(x)  g (x) - g - (x)
Assuming Dg = 0
13-Jan-07

Discovery of
strong “elliptic” flow:

Elliptic flow in Au + Au collisions at
√sNN= 130 GeV,
STAR Collaboration, (K.H.
Ackermann et al.).
Phys.Rev.Lett.86:402-407,2001

307 citations
Discovery of
“jet quenching”

Suppression of hadrons with large
transverse momentum in central
Au+Au collisions at √sNN = 130 GeV,
PHENIX Collaboration (K. Adcox et
al.), Phys.Rev.Lett.88:022301,2002

357 citations
13-Jan-07
Suppresion Factor

Flow strength
RHIC’s Two Major Discoveries
To Summarize
The
hottest T ~ 200- 400 MeV
densest
ei ~ 30-60 eo
matter
(thermal yields)
ever studied in the laboratory
flows
large “elliptic” flow
as a (nearly) perfect fluid
with systematic patterns consistent with
quark degrees of freedom valence quark scaling
and a viscosity to entropy density ratio
lower (?) than any other known fluid
with a value near (?) a conjectured quantum
bound
13-Jan-07
h/s ~ (2-3)  /4p
See aS Run

The low viscosity is
“understood” as a result of



Short mfp’s
Large cross sections
Strong coupling
near the phase “transition”
(really cross-over)

Small h/s  sQGP


Strongly-coupled
Quark-Gluon “Plasma”
“Perfect liquid"
We need to understand as
when it is large!
“The strong coupling constant at low Q2”,
A. Deur, hep-ph/0509188
“Perturbative QCD theory (includes our knowledge of as )”,
Y. Dokshitzer, hep-ph/9812252
13-Jan-07
How Perfect is “Perfect” ?

All “realistic” hydrodynamic calculations for RHIC fluids to
date have assumed zero viscosity
 Viscosity h = 0  “perfect fluid”

But there is a (conjectured) quantum limit: “A Viscosity Bound
Conjecture”, P. Kovtun, D.T. Son, A.O. Starinets, hep-th/0405231
h


( Entropy Density ) 
s
4p
4p
Where do
“ordinary”
fluids sit wrt
this limit?

RHIC “fluid” might
be at ~2-3 on this
scale (!)
4p

13-Jan-07
T=1012 K
RHIC Future
The fundamental matter created at RHIC compels further investigation





How imperfect is its “perfection” ?
How does it respond to truly heavy probes? (charm, bottom)
Can even higher energy densities be achieved in U+U collisions?
Is there a critical point in the QCD phase diagram ?
All of this (and more) is addressed by RHIC II:


EBIS  Electron Beam Ion Source to extend ranges of species
Upgrades to STAR and PHENIX
Vertex detectors for precision heavy flavor tomography
 Increased coverage in forward regions
 Increased rate and triggering capabilities


x10 Luminosity increase by electron cooling
Efficient access to the rare probes that have proven so incisive
in the first generation discovery measurements at RHIC.
13-Jan-07
RHIC II Luminosity Enhancement via e-Cooling
Gold collisions (100 GeV/n x 100 GeV/n):
Ave. store luminosity [1026 cm-2 s-1]
Pol. Proton Collision (250 GeV x 250 GeV):
Ave. store luminosity [1032 cm-2 s-1]
13-Jan-07
no e-cooling
8
1.5
with e-cooling
70
5.0
Ongoing experiments and simulations in progress
Detector Upgrades
Ongoing effort with projects in different stages
PHENIX
STAR
forward meson spectrometer
DAQ & TPC electronics
Key:
full ToF barrel
Completed
heavy flavor tracker
ongoing
barrel silicon tracker
proposal submitted
forward tracker
proposal in preparation
13-Jan-07
hadron blind detector
muon Trigger
silicon vertex barrel (VTX)
forward silicon
forward EM calorimeter
Fundamental Questions for RHIC II

What are the phases of QCD Matter?

What is the wave-function of a heavy nucleus?

What is the wave-function of the proton?

13-Jan-07
What is the nature of non-equilibrium
processes in a fundamental theory?
Compelling Physics of RHIC II
Provide key measurements so far inaccessible at RHIC in three broad areas:

High T QCD (A+A, d+A, and p+p):





Spin structure of the nucleon:



Electromagnetic radiation (e+e pair continuum)
Heavy flavor (c- and b-production)
requires highest
Jet tomography (jet-jet and g-jet)
AA luminosity
Quarkonium ( J/, ’ , c and (1s),(2s),(3s) )
Quark spin structure Dq/q (W-production)
Gluon spin structure Dg/g (heavy flavor and g-jet correlations)
Low x phenomena

“Low x”  “forward measurements”
gluon saturation in nuclei
(particle production at forward rapidity)
All measurements require upgrades of detectors and/or RHIC luminosity
13-Jan-07
What is the
wave-function
of the proton?
13-Jan-07
Spin Goals for RHIC II

Use the increased luminosity
to achieve a precision in Dg comparable to
(at least) present knowledge
of DS :
ΔΣ    Δq(x)dx  0.1  0.3
q
1 3nf
 0.18
2 3nf  16


1
 DS  Lq  Dg  Lg
2
}
}
1
2
proton
0.32 
1 16
2 3nf  16
Asymptotic expectation
( X. Ji, J. Tang, P. Hoodbhoy,
Phys.Rev.Lett. 76, 740 (1996) )
Cleanest probe for Dg(x) :



Prompt-photon production ( g-jet, to determine parton kinematics )
Also the rarest, clearly benefits from increased luminosity
RHIC II samples of ~ 1 fb -1 allow


13-Jan-07
Systematic cross checks (e.g., same x measured at variety of Q2 )
Extension to small x regions (using forward upgrades)
Spin Goals for RHIC II (Cont’d)

Sea quark/antiquark polarization



Flavor decomposition likely to be
key to understanding
small value of DS .
Major tool: Parity-violating
single-spin asymmetry AL
from W ± decays.
Requires
~ 1 fb-1 data sets RHIC II luminosity
 Detector upgrades



Ultimate goal: charm-tagged W’s
Transverse spin measurements



13-Jan-07
To study transversity
To understand role of quark angular momentum
To extract Sivers functions over unparalled range of x and Q2 .
What is the
wave-function
of a heavy nucleus?
13-Jan-07
A Surprise: RHIC Multiplicities Are “Low”

PHOBOS Central Au+Au (200 GeV)

Low, that is, compared to
pre-data predictions of
“cascading partons”
Consistent with predictions
based on gluon saturation :
Kharzeev & Levin, Phys. Lett. B523 (2001) 79
Compilation by K. Eskola
Color Glass
600
From Eskola, QM 2000
13-Jan-07
1200
Rapidity Density
Data: PHOBOS,
Phys. Rev. Lett. 87, 102303 (2001)
Assertion

In these complicated events, we have
(a posteriori ) control over the event geometry:

Degree of overlap  Number of (nucleon) participants  NPart
“Central”

13-Jan-07
Orientation with respect to overlap
“Peripheral”
Saturation  Running of aS
dN/dh / .5Npart
23
2
QS
NCH
1
~
~
log(
) ~ log(NPart )
2
2
NPart αS (Q S )
Λ
NPart 
Fundamental Fields in Nuclei




Nucleus increases saturation momentum scale QS 2 ~ (A/x)1/3
Occupation numbers ~ 1 / aS(QS) > 1
This is the condition
for ~ classical fields:
That is:


Quasi-classical states of the gluon field
may be explored at low x in a nucleus
Exploration tools:
Near-term: d+A collisions (RHIC  RHIC II)
 Long-term: Electron-ion Collider


Goal:

13-Jan-07
To understand
the
wave-function
of a heavy
nucleus
Relevance to Heavy Ion Collisions

Lesson from RHIC:
A+A collisions
are very efficient
in translating
Initial gluon state



Strong shadowing?
Saturated gluons?
Color Glass
Condensate?
into
Final thermal state


It is difficult to
understand this
efficiency without
invoking some form of
dense gluonic initial
state
We need to measure
rather than invoke
13-Jan-07
What are the phases
of QCD Matter?
What is the nature
of non-equilibrium processes
in a fundamental theory?
13-Jan-07
Understanding the Medium

Energy loss in a fluid:
☑ Jets travel faster than the
speed of sound in the
medium.
☑ While depositing energy
via interactions with same
QCD “sonic boom” or
“Mach cone”
To be expected
in a dense fluid
which is strongly-coupled
13-Jan-07
Observation of Mach Cone?


Seen in di-hadron correlation functions in Df :
Modifications to di-jet hadron pair correlations in Au+Au collisions at
√sNN = 200 GeV, (S.S. Adler et al.), Phys.Rev.Lett.97:052301,2006
Df
Sensitive to
Df


13-Jan-07
Speed of
sound
Equation
of state
The Ultimate Calibrated Probe

Extend the di-hadron correlations to
(direct) photon-hadron correlations




Photons emerge directly, unaffected by the medium
A clean measure of initial (hard) Q2
Heavy ion analog to tagged photon beam
Current state of the art:
g-h
h-h
as
compared
to
A potentially beautiful technique, desperately in need
of RHIC II luminosities !
13-Jan-07
Heavy Flavor at RHIC II
Because the u, d, (s) current masses are small compared to T


Properties of the medium are
(at zero baryon number)
uniquely determined by T
But “introducing” heavy flavor
establishes a new scale:


Mc ~ 1.3 GeV
Mb ~ 5.0 GeV
with associated length scales


1 / Mc ~ 0.15 fm
1 / Mb ~ 0.04 fm
 Flavor tagged jets to measure
Mach cones, heavy quark energy loss
Flow strength

Bohr radii (onium):


J/Y ~ 0.29 fm
U ~ 0.13 fm
 “Onium” spectroscopy
RHIC
to measure plasma
screening lengths
 Measurements of such essential medium properties using rare probes
becomes possible via RHIC II luminosities and the detector upgrades
13-Jan-07
The Promise of Heavy Flavor

Present measurements
rely on detection of e’s, m’s
from semi-leptonic decay
of heavy flavor


Little or no ability to determine
relative contributions of
charm versus bottom
But recent results for
Energy loss: RAA(pT)
 Flow
: v2 (pT)


Strongly suggest
h
s
~ (2  3)

4p
“Energy Loss and Flow of Heavy Quarks in Au+Au Collisions
at √sNN = 200 GeV”, A. Adare et al., submitted to PRL,
nucl-ex/0611018

Similar estimates obtained from
Light quark flow
 PT fluctuations

13-Jan-07
“What do elliptic flow measurements tell us about the
matter created in the little bang at RHIC?”,
R. Lacey and A. Taranenko, nucl-ex/0610029
“Measuring Shear Viscosity Using Transverse
Momentum Correlations in Relativistic Nuclear
Collisions”, S. Gavin and M. Abdel-Aziz,
nucl-th/0606061
Water  RHIC  Water  RHIC

h/s

The search for QCD phase transition of course was
informed by analogy to ordinary matter
Results from RHIC are now “flowing” back to
ordinary matter
“On the Strongly-Interacting Low-Viscosity Matter
Created in Relativistic Nuclear Collisions”,
L.P. Csernai, J.I. Kapusta and L.D. McLerran,
Phys.Rev.Lett.97:152303,2006, nucl-th/0604032
13-Jan-07
Is There a QCD Critical Point?

Here the analogy with phase transitions
in ordinary matter breaks down:
Recall “ Properties of the medium are
(at zero baryon number)
uniquely determined by T ”
Pressure = P(T) can’t vary independently
(unlike water)
 But if baryon number is non-zero
 (intensive order parameter) baryon chemical potential mB :


To increase mB :

Lower collision energy
Raise atomic mass

Both part of RHIC II

13-Jan-07
EBIS Status

EBIS  Electron Beam Ion Source



Replaces tandems (thereby avoiding ~$9 M reliability investment)
Extends range of species (polarized 3He, noble elements, uranium )
Approved for construction
CD-1 obtained
 $19.4M cost

($4.5M NASA)

3.5 yr schedule
FY06-09
New Physics!
(Next slide)
13-Jan-07
U+U collisions

13-Jan-07
Static deformation provides a way to vary the ‘other’
order parameter (baryon chemical potential mB )
RHIC’s Energy Range Ideal For The Hunt


There is considerable
uncertainty in
the location of
the QCD critical point
RHIC  RHIC II
can make major
advances on
the “other” QCD front:
U+U beams
 Comprehensive
detectors
 Collider  superb control of systematics when changing √s
Major importance when varying √sNN from 5 to 200 GeV !

 RHIC II will be the ideal facility for systematically exploring
the major region of the QCD phase diagram.
13-Jan-07
Heavy Ions at the LHC



How could we not choose to investigate “QGP” at every
opportunity?
LHC offers unparalleled
increase in √s
Will this too create a
strongly-coupled fluid?

Active pursuit via


13-Jan-07
Dedicated experiment (ALICE)
Targeted studies (CMS, ATLAS)
RHIC II and LHC


Heavy ion collisions at the LHC could reveal entirely new phenomena.
With RHIC II and LHC together
we explore deconfined QCD matter
over an unprecedented range …
With RHIC II e-cooling,
log 1/x

the integrated luminosity per year
is 36x larger at RHIC
than LHC for heavy ions.

From yesterday (Urs Wiedemann):
from
“The properties of the hot and dense QCD matter produced at the LHC may differ
those produced at RHIC. We can state already now that testing QCD evolution
of properties of hot and dense QCD matter is of fundamental interest and is
experimentally testable in an interplay of RHIC and LHC… Knowledge about (rare
hard high-pT) probes at RHIC can be improved significantly with a luminosity
upgrade, which thus could enhance the interplay between RHIC and LHC
significantly (in particular if operational during the LHC discovery era).”

RHIC II will continue the demonstrated RHIC capabilities



13-Jan-07
Precision probes
Extended data runs
Wide variety of beams and energies.
From Urs Wiedemann (yesterday)

1. Results from the LHC heavy ion run will provide substantial
novel tests for the key dynamical ideas (hydrodynamic
behavior, hard parton propagation in matter, saturation)
developed in the context of the RHIC heavy ion program.

Consequence:


2. The properties of the hot and dense QCD matter produced at
the LHC may differ from those produced at RHIC. We can state
already now that testing QCD evolution of properties of hot and
dense QCD matter is of fundamental interest and is
experimentally testable in an interplay of RHIC and LHC.

Consequence:

13-Jan-07
Any theory initiative (even if it aims primarily at meeting the challenges
of the RHIC heavy ion program), must aim at an unbiased use of all
experimental constraints. The most successful theory efforts will work
towards a phenomenological framework testable in the entire energy
range spanning RHIC and LHC.
We should recognize this novel opportunity. Rare hard high-pt probes
provide the most versatile class of tools for characterizing properties of
matter. Knowledge about these probes at RHIC can be improved
significantly with a luminosity upgrade, which thus could enhance the
interplay between RHIC and LHC significantly (in particular if
operational during the LHC discovery era).
Long Term Timeline of Heavy Ion Facilities
2009
2006
2012
2015
QCD Laboratory at BNL
RHIC
Vertex tracking, large acceptance, rate capabilities
PHENIX & STAR upgrades
electron cooling “RHIC II”
electron injector/ring “e RHIC”
LHC
FAIR
Phase III: Heavy ion physics
13-Jan-07
RHIC and RHIC II in World Context
: 2009
: 2000RHIC II 
: 2012
13-Jan-07
New Dimensions

Expanding our theoretical tools





Perturbative QCD (pQCD) for understanding jet quenching
Lattice QCD (LQCD) for calculating static properties (s, e)
Hydrodynamics as zero-mean-free-path limit of strong coupling
AdS/CFT for calculating static and dynamic properties of
strongly-coupled gauge theories
Both sides of this equation

( Vis cosity )R H IC 
( Entropy Density )R H IC
4p
were calculated using black hole physics (in 5 dimensions)
MULTIPLICITY
Entropy  Black Hole Area
c
c
DISSIPATION
Viscosity  Graviton
Color Screening
13-Jan-07
Absorption
New Dimensions in RHIC Physics
“The stress tensor of a quark moving through N=4
thermal plasma”, J.J. Friess et al., hep-th/0607022

Our 4-d
world
String
theorist’s
5-d world
13-Jan-07
The stuff formerly
known as QGP
Jet modifications
from wake field
Heavy quark
moving
through
the
Energy loss medium
from string
drag
SGP


“Formerly known as quark-gluon plasma?”
You can still use that label if you like, but- PARADIGM SHIFT



RIHC does not produce asymptotically “free” quarks and gluons
Contrary to expectations (and announcements ! ), we did not find
evidence for “quarks (that) are liberated to roam freely”
The analogy to atomic plasmas is also strained:

Atomic plasmas:
Can vary density and temperature independently
 Photon momentum-energy density (usually) irrelevant
 Can be strongly-coupled or weakly coupled


“QGP”
One number (the temperature T ) determines all properties
 Intrinsically strongly-coupled fluid for any(?) accessible T


The matter created at RHIC could be called “S G P”


13-Jan-07
S G P  Sui Generis Plasma
Sui generis : “Being the only example of its kind; unique ”
The Primacy of QCD

While the (conjectured) bound
h 

s 4p
is a purely quantum mechanical result . . .
It was derived in and motivated by
the Anti-de Sitter space / Conformal Field Theory correspondence

Weak form:

“Four-dimensional N=4 supersymmetric SU(Nc) gauge theory is
equivalent to IIB string theory with AdS5 x S5 boundary conditions.”
( The Large N limit of superconformal field theories and supergravity,
J. Maldacena, Adv. Theor. Math. Phys. 2, 231, 1998 hep-th/9711200 )

Strong form:

“Hidden within every non-Abelian gauge theory, even within the weak
and strong nuclear interactions, is a theory of quantum gravity.”
( Gauge/gravity duality, G.T. Horowitz and J. Polchinski, gr-qc/0602037 )

Strongest form: Only with QCD can we explore experimentally these
fascinating connections over the full range of the coupling constant
to study QGP  Quantum Gauge Phluid
13-Jan-07
RHIC Scientific Future

Fundamental Strings(??)

Fundamental Particles
Understand the spin structure of the nucleon
 p+p  at RHIC, RHIC II, …. Polarized e-p collider


Fundamental Fields
Understand the wave-function of a heavy nucleus
 d+A at RHIC, RHIC II, …. Electron-ion collider


Fundamental Matter
Understand the phase diagram of QCD
 A+A at RHIC, RHIC-II,
LHC, FAIR

13-Jan-07