Geometry-driven physics at RHIC A work in progress

1
Geometry-driven physics at RHICA work in progress

• Mike Lisa
• The Ohio State University

2
Similar but somehow different
3
Geometry-driven physics at RHICA work in progress

• Mike Lisa
• The Ohio State University

• Reminder what are we doing, and why?
• Soft / firm / hard
• What could we see?
• What do we see?
• Whats next?
• Summary

4
1 km
v 0.99995?c
5
Why heavy ion collisions?
Much simpler systems (pp) under study
why on earth study AA?
R.H.I.C. physics partonic condensed matter
physics even more fundamental than electronic
C.M. physics

• Bulk systems
• rich new phenomena of fundamental importance
• access physics domains not accessible in small
  systems
• (connection between simple and bulk systems
  nontrivial theoretically intractable)

6
The real issue

• What happens when nuclei collide?
• important for experiment design
• (also, its fun to study in detail!)
• otherwise, who cares?

• The real issue is
• Can we use them to make a new type of matter in
  the lab?

7
11 Physics Questions for the New Century

1. What is dark matter?
2. What is dark energy?
3. How were the heavy elements from iron to uranium
   made?
4. Do neutrinos have mass?
5. Where do ultra-energy particles come from?
6. Is a new theory of light and matter needed to
   explain what happens at very high energies and
   temperatures?
7. Are there new states of matter at ultrahigh
   temperatures and densities?
8. Are protons unstable?
9. What is gravity?
10. Are there additional dimensions?
11. How did the Universe begin?

1. What is dark matter?
2. What is dark energy?
3. How were the heavy elements from iron to uranium
   made?
4. Do neutrinos have mass?
5. Where do ultra-energy particles come from?
6. Is a new theory of light and matter needed to
   explain what happens at very high energies and
   temperatures?
7. Are there new states of matter at ultrahigh
   temperatures and densities?
8. Are protons unstable?
9. What is gravity?
10. Are there additional dimensions?
11. How did the Universe begin?

The February 2002 issue of Discover magazine
based its cover story on the recent 105-page
public draft of the National Research Council
Committee on Physics of the Universe report,
Connecting Quarks with the Cosmos
RHIC-I obsession
propaganda reminiscent of lower ?s HI program
8
The real issue

• What happens when nuclei collide?
• important for experiment design
• (also, its fun!)
• otherwise, who cares?
• Can we use them to make a new type of matter in
  the lab?
• important for accelerator design
• important for propaganda
• in itself who cares?

• The real issue is
• What are the properties of this new state of
  matter? (T, P, ?, ?)

9
The real issue

• What happens when nuclei collide?
• important for experiment design
• (also, its fun!)
• otherwise, who cares?
• Can we use them to make a new type of matter in
  the lab?
• important for accelerator design
• important for propaganda
• in itself who cares?
• What are the properties of this new state of
  matter? (T, P, ?, ?)
• important for analysis design
• in itself who cares?

• The real issue is
• to use the QGP to understand hadronization /
  mass generation

10
The real issue

• What happens when nuclei collide?
• important for experiment design
• (also, its fun!)
• otherwise, who cares?
• Can we use them to make a new type of matter in
  the lab?
• important for accelerator design
• important for propaganda
• in itself who cares?
• What are the properties of this new state of
  matter? (T, P, ?, ?)
• important for analysis design
• in itself who cares?

We are now around here
Original motivation a focus of RHIC-II

• The real issue is
• QGP as calibrated tool to understand
  hadronization / mass generation

must go beyond partonic condensed matter
11
Discovery and Properties The Ideal Experiment
The first exploration of subatomic structure was
undertaken by Rutherford at Manchester in 1909
using Au atoms as targets and a particles as
probes.
NO
QGP
But we can get close
12
Fast Partons (Quarks Gluons) Traversing Matter

• Jets
• high-pT parton produced in a hard (high-Q)
  scattering process
• Calculable in QCD (at high-pT)
• partons fragment into many correlated white
  hadrons
• emitted in a cone
• created early in the collision

hadrons
quark
quark
hadrons
leading particle (highest-p particle)
13
Fate of jets in heavy ion collisions?
idea pp collisions _at_ same ?sNN 200 GeV as
reference
p
p
? what happens in AuAu to jets which pass
through medium?
?
AuAu
14
Impact parameter Reaction plane (esp impt for
AA)
Reaction plane (b) x (beam) anisotropic
participant zone
b
b gt 0
15
The Ubiquitous RAA
Mike Lisa remember all the jubulant press
conferences last summer (Wow, was it really only
last summer? I feel like Ive seen this data for
100 years)
5x fewer high pT particles than expected in AuAu

• Common wisdom
• d-Au null result ? final state effect
• so obvious that initialdAu AuAu?
• look at other hard probes from same initial
  processes, but withno final state effects

16
Hard non-mesonic (direct) photons
non-photonic (charming) electrons

• Created in earliest, hardest parton scatterings
  conserved thereafter
• binary scaling v
• (probably some Cronin inside errors)
• probe-once-created and creation itself in AA are
  calibrated (better than d-Au)

PHENIX QM04
NB pT-integrated
PHENIX 2004
17
The Ubiquitous RAA
5x fewer high pT particles than expected in AuAu

• Common wisdom
• d-Au null effect ? final state effect
• so obvious that initialdAu AuAu?
• look at other hard probes from same initial
  processes, but withno final state effects

• Common wisdom II
• final state effect is energy loss
  incolor-charge-dense(not necc. deconfined)
  medium
• ? 15 GeV/fm3 _at_ ? 0.2 fm
• consistent w/ ?BJ and hydro

18
If we are looking at energy loss
why quantify downward shift of spectrum (as in
RAA)?
It seems more natural to quantify leftward
shift. Tannenbaum/Mioduzewski

• NB ignores
• Cronin (see jets(?) coming up)
• mods in FF (logical to look at shift of partons
  not their fragments)

PHENIX PRL 2003
19
then lets look at energy loss
Empirical energy loss Tannenbaum/Mioduzewski
20
Initial pathlength dependence seems to work
PHENIX prelim AuAu vsNN200 GeV

• Gyulassy, Vitev, Wang
• 1D expansion, simple geometric scaling
• Well reproduced by experimental data.

21
Vary pathlength another way
qualitatively OK, now see about consistency
PHENIX prelim AuAu vsNN200 GeV
PHENIX B. Cole, HardProbes 04
22
No universal loss versus density path?
PHENIX preliminary
Overlap integral
1D expansion
pT gt 3 GeV/c
?part(x,y) vs centrality
50-60
10-20
23
Beyond leading particles
STAR pp event
find this
in this
24
Jets via azimuthal correlations
STAR pp event

• trigger highest pT track, pTgt4 GeV/c
• Df distribution for 2ltpTltpTtrigger
• normalize to number of triggers

PRL 90, 082302
25
Jets via azimuthal correlations
Try the same in Au-Au (large combinatorics)
26
Azimuthal distributions in AuAu
pedestal and flow subtracted
PRL 90, 082302

• Central collisions
• strong suppression
• of away-side jet

• Peripheral collisions
• very similar to pp

27
Further geometric detail
Suppression depends on pathlength thru
medium This analysis cannot be initial state
effect
28
Soft sector ashes of the QGP

• Ultimately, jet quenching will only measure
  overall color field density
• jets are probes of the system
• jets are not of the system

• medium (?) itself decays into low momentum
  particles (soft sector)
• QGP is non-perturbative, low-Q phenomenon (need
  exptl info)
• dynamics - difficult but crucial here

99.5

• Is it a big system/medium?
• bulk, collective behaviour
• How does it evolve in spacetime?
• dynamic response to pressure, EoS

29
How do semi-central collisions evolve?
1) Superposition of independent pp
momenta pointed at random relative to reaction
plane
30
How do semi-central collisions evolve?
1) Superposition of independent pp
high density / pressure at center
momenta pointed at random relative to reaction
plane
2) Evolution as a bulk system
Pressure gradients (larger in-plane) push bulk
out ? flow
zero pressure in surrounding vacuum
more, faster particles seen in-plane
31
v2 --gt bulk system
N
2) Evolution as a bulk system
Pressure gradients (larger in-plane) push bulk
out ? flow
v2(pT,m) consistent with anisotropic velocity
field (i.e. property of bulk)
more, faster particles seen in-plane
32
Elliptic flow collectivity sensitivity to
early system

• Elliptic flow
• Bulk collective motion
• x anisotropy?p anisotropy
• sensitive to early pressure
• evidence for
• early thermalization
• QGP in early stage

(H. Sorge, PRL 78 2309 82 2048.)
? ? 10 GeV/fm3
Hydrodynamic calculation of system evolution
33
A more direct handle?

• elliptic flow (v2) ? evidence towards QGP at RHIC
• oblique connection to crucial issue of
  dynamics/spacetime geometry
• theoretical dynamical evolution hope of peering
  through the mist

Two particle intensity interferometry a more
direct handle on spacetime
34
probing source geometry through interferometry
p1
r1
x1
p source r(x)
1 m
r2
x2
p2
experimentally measuring this enhanced
probability quite challenging
5 fm
35
Correlation functions for different colliding
systems
STAR preliminary
C2(Qinv)
Qinv (GeV/c)
Still amazing to me Interferometry probes the
smallest scales ever measured !
36
More detailed geometry
Relative momentum between pions is a vector ?
can extract 3D shape information
Rlong along beam direction
Rout along line of sight
Rside ? line of sight
37
Why do the radii fallwith increasing momentum ??
38

• Decreasing R(pT)
• usually attributed to collective flow
• flow integral to our understanding of R.H.I.C.
  taken for granted
• femtoscopy the only way to confirm x-p
  correlations impt check

Kolb Heinz, QGP3 nucl-th/0305084
39

• Decreasing R(pT)
• usually attributed to collective flow
• flow integral to our understanding of R.H.I.C.
  taken for granted
• femtoscopy the only way to confirm x-p
  correlations impt check

• Non-flow possibilities
• cooling, thermally (not collectively) expanding
  source
• combo of x-t and t-p correlations

early times small, hot source
late times large, cool source
40

• Decreasing R(pT)
• usually attributed to collective flow
• flow integral to our understanding of R.H.I.C.
  taken for granted
• femtoscopy the only way to confirm x-p
  correlations impt check

• Non-flow possibilities
• cooling, thermally (not collectively) expanding
  source
• combo of x-t and t-p correlations

1500 fm/c (!)
MAL et al, PRC49 2788 (1994)
41

• Decreasing R(pT)
• usually attributed to collective flow
• flow integral to our understanding of R.H.I.C.
  taken for granted
• femtoscopy the only way to confirm x-p
  correlations impt check

• Non-flow possibilities
• cooling, thermally (not collectively) expanding
  source
• combo of x-t and t-p correlations
• hot core surrounded by cool shell
• important ingredient of Buda-Lund hydro
  picturee.g. Csörgo LörstadPRC54 1390 (1996)

42
Each scenario generates x-p correlations

• Decreasing R(pT)
• usually attributed to collective flow
• flow integral to our understanding of R.H.I.C.
  taken for granted
• femtoscopy the only way to confirm x-p
  correlations impt check

but
?x2?-p correlation yes ?x?-p correlation yes

• Non-flow possibilities
• cooling, thermally (not collectively) expanding
  source
• combo of x-t and t-p correlations
• hot core surrounded by cool shell
• important ingredient of Buda-Lund hydro
  picturee.g. Csörgo LörstadPRC54 1390 (1996)

?x2?-p correlation yes ?x?-p correlation no
t
?x2?-p correlation yes ?x?-p correlation no
43

• flow-dominated models can reproduce soft-sector
  x-space observables
• imply short timescales
• however, are we on the right track? flow
• puzzles? ? check your assumptions!
• look for flows special signature ?x?-p
  correlation
• In flow pictures, low-pT particles emitted closer
  to sources center (along out)
• non-identical particle correlations(FSI at low
  ?v) probe
• ?(x1-x2)2? (as does HBT)
• ?x1-x2?

?
K
p
click for more details on non-id correlations
Csanád, Csörgo, Lörstad nucl-th/0311102 and
nucl-th/0310040
F. Retiere MAL, nucl-th/0312024
44

• extracted shift in emission point ?x1-x2?
  consistent w/ flow-dominated blastwave

• In flow pictures, low-pT particles emitted closer
  to sources center (along out)
• non-identical particle correlations(FSI at low
  ?v) probe
• ?(x1-x2)2? (as does HBT)
• ?x1-x2?

45
More information
Relative momentum between pions is a vector ?
can extract 3D shape information
Rlong along beam direction
Rout along line of sight
Rside ? line of sight
Rout
Rside
46
Source shape

• observe the source from all angles relative to
  the reaction plane
• expect oscillations in radii for non-round
  sources

reaction plane
47
Measured final source shape
STAR, PRL93 012301 (2004)
Expected evolution
?
48
Disintegration timescale
Relative momentum between pions is a vector ?
can extract 3D shape information
Rlong along beam direction
Rout along line of sight
? increases with emission timescale
Rside ? line of sight
Rout
Rside
49
Disintegration timescale - expectation
3D 1-fluid Hydrodynamics
Rischke Gyulassy, NPA 608, 479 (1996)
with transition
with transition
?
?

• Long-standing favorite signature of QGP
• increase in ?, ROUT/RSIDE due to deconfinement ?
  confinement transition
• expected to turn on as QGP energy threshold is
  reached

50
Disintegration timescale - observation

• no threshold effect seen
• RO/RS 1

RHIC
51
Disintegration timescale - observation

• no threshold effect seen
• RO/RS 1
• toy model calculations suggest very short
  timescales

F. Retiere MAL, PRC 70 (2004)
52
Disintegration timescale - observation

• no threshold effect seen
• RO/RS 1
• toy model calculations suggest very short
  timescales
• rapid, explosive evolution
• too explosive for real modelswhich explain all
  other data

N(?)
53
anything new in-between?

• Probes of the system (hard)
• interesting results
• important open questions
• System itself (soft)
• interesting/important results
• important open questions

If we bridge the gap (firm)?
?
54
Connecting the sectors
soft-firm connection v2

• hydro breaks down above 2 GeV/c (expected)
• mass systematic ?meson/baryon systematic?
• definitely not hydro!

55
Connecting the sectors
soft-firm connection v2

• hydro breaks down above 2 GeV/c (expected)
• mass systematic ?meson/baryon systematic?
• definitely not hydro!

hard-firm connection RAA
PID-differential ?meson/baryon systematic!
BUT!
56
Non-hydro / non-?E origin of firm v2?
meson/baryon (i.e. constituent quark number)
systematics suggest coalescence
(recombination) of already-flowing (!!) partons
()
well, constituent quarks
57
Most models anomalous B/M described
Many model variants Lin, Molnar, Pratt, Fries,
Bass, Mueller, Ko, Das, Levai, Hwa, Greco,
Voloshin, Nonaka But, data themselves (IMHO)
clearly indicate exciting, collective partonic
behaviour Hope for a hadronization testbed?
Clearly modified high pT hadronization (fragmentat
ion?) in AA
58
Wrap up
59
What data can tell us / what (we think) it has
told us /open issues

• Hard Sector
• incoherence of initial state
• calibration of number of initial hard scatterings
  (binary), which themselves have calibrated
  spectrum charm, gamma, d-Au
• early system color charge density (not
  deconfinement!)
• if gluonic bremstrahlung dNg/d? 1000 ???BJ
• BUT energy loss mechanism unclear (consistent
  scaling?)
• relevant upcoming data
• charm quench (early results limited) / dead cone
  effect
• ?-tagged jets
• q/g jet selection
• higher stats correlated quenching signal versus
  length

60
What data can tell us / what (we think) it has
told us /open issues

• Soft sector
• threshold behaviour
• no evidence evolution, not revolution too bad
  but not a killer
• degree to which it is system - real collectivity
• solid evidence from several observations - very
  important perfect fluid?
• global/thermodynamic properties T, ?, P, ?
• consistent with deconfinement - but! may be P.S.
  dominance
• dynamics - system response evolution and
  timescales
• 2x expansion, collective shape evolution
• timescales- correct dynamic signatures, wrong
  (x,t) evolution??

61
What data can tell us / what (we think) it has
told us /open issues

• Firm Sector
• transition bulk to probe (hadnt really been
  considered)
• clearly something new instead!
• ?is there a transition? does all fit smoothly?
• first calibration of QGP p.s. structure
• hope for well-defined ordered (x-p correlated)
  system of partons
• can we get beyond simple models? entropy issues?
  connection between constituent quarks and
  partons?

My feeling solution of open issues in hard
soft sectors will be well worth it, if we can
exploit apparent promise of firm. Launchpad of
next generation program understanding
hadronization