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Identified particle spectra and
jet interactions with the
medium
Paul Sorensen — Lawrence Berkeley National Lab
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Quark Matter 2005 - Budapest
Heavy Ion Goals and QCD
1) Create a system of
quasi-free quarks and
gluons:
•
Learn about the EOS
2) Study the deconfined-toconfined transition:
•
•
hadronization of the
matter
development of mass
3) Determine properties of
the matter:
•
•
•
•
Lattice QCD
Tc~170
for finite
MeVtemperature
energy density
gluon density
temperature T
coupling s(Q, T)
PDG
s(Q)s(Q,T/Tc)
Quark Matter — Budapest — August 2005
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Modifications to s
heavy quark-antiquark coupling at finite T from lattice QCD O.Kaczmarek, hep-lat/0503017
Chiral symmetry is
broken, but the
confining forces are
still modified:
Are these hadrons,
dressed quarks,
proto-hadrons,
resonances?
chiral symmetry breaking limit s,c=0.43 (hep-ph/0302011)
high Q2
Varying the
coupling behavior
allows us to study
confinement,
hadronization, and
these intermediate
objects.
low Q2
heating the vacuum modifies soft/long-wave-length processes (like
hadronization): At RHIC we’re trying to probe these modifications
Quark Matter — Budapest — August 2005
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probing the fireball
We can’t perform scattering experiments with the fireball so we
rely on internally created probes. This only tells us half the story.
k
k’
k’
?
?
?
But can we learn enough from the information we have: pT, , y?
For example, can we determine the dof from different pT regions?
intermediate
low pT
≈10 fm

 
 

≈1 fm
?
high pT
 
 
  
  
  

0 fm << 1 fm
Quark Matter — Budapest — August 2005
*
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***
* **
* *
≈0 fm
3
review
• First a large proton excess is observed.
nucl-ex/0412003
• These measurements could be interpreted several ways:
flow, scaling with N-binary (i.e. absence of jet quenching),
etc.
• Enhancement is noted to be related to the number of
constituent quarks rather mass
• also an upper pT limit is placed on the baryon excess.
• Finally elliptic flow is found to scale with the number of
quarks
• also the large baryon v2 excluded scenarios involving less
energy loss for protons.
PHENIX PRC69, 0304909 (2004)
STAR Phys. Rev. C 72 (2005) 014904
Matter — Budapest
— August 2005
Evidence gathered Quark
for modifications
to hadronization
at intermediate pT
4
Baryon to Meson
How might the B/M ratio be related to modifications to hadronization?
Phenix: PRL 91, 172301
h
d pp
Dh0/ c Factorization is not likely to hold for
d
 K   dxa dxb f a ( xa , Q ) f b ( xb , Q )
( ab  cd )
ˆ
dyd 2 pT
d
t
z c these collision at this pT:
abcd
fragmentation functions become
cross talk between the matter, the probes, and
hadronization invalidates factorization. We see
energy and system-size dependent
2
2
lots of evidence for this cross-talk
Quark Matter — Budapest — August 2005
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Outline
1. Azimuthal dependence of spectra
2. Centrality dependence of spectra
3. Jet interactions with the medium
Quark Matter — Budapest — August 2005
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Event anisotropies
Azimuthal momentum-space anisotropy: a self quenching
probe of early interactions
The initial spatial anisotropy evolves
out-of-plane
(via interactions and density gradients)
y
Au nucleus
in-plane
Au nucleus
into a momentum space anisotropy

d 3N
1
d 2 N  
E 3 
1  2v n cosn 
d p 2 pT dpT dy  n1

v 0 "radial flow", v1"directed flow"
v 2 "elliptic flow" (largest).
Non-central Collisions

sensitivity to the system geometry can arise
through secondary rescattering, soft-gluon
radiation, etc.
Quark Matter — Budapest — August 2005
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v2 vs. pT
Large values indicate strong sensitivity to the system geometry for
production at all measured pT
v2 at intermediate pT is grouped by quark number
Quark Matter — Budapest — August 2005
PRL 92 (2004) 052302; PRL 91 (2003) 182301
Intermediate pT
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Extended pT
Year 4 data gives RHIC higher statistics and greater coverage
for identified particle v2
Quark Matter — Budapest — August 2005
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Extended pT
Year 4 data gives RHIC higher statistics and greater coverage
for identified particle v2
Quark Matter — Budapest — August 2005
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Extended pT
PHENIX/STAR comparison shows consistency
Consistent with no particle type dependence at 7 GeV/c
But why not earlier?
PHENIX Preliminary
 Charged Hadrons
Quark Matter — Budapest — August 2005
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Quark-number scaling
PRL 92 (2004) 052302; PRL 91 (2003) 182301
Since hadronization is a soft
process, it should be modified by
changes to the shape of the
running coupling at low Q2.
In one simple hadronization model
quark v2 is approximately related to
hadron v2 through
v2q = v2h(pT/n)/n,
where n is the number of quarks in
the hadron
 implies v2 is developed before
hadronization
 model implies deconfinement
Quark Matter — Budapest — August 2005
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Run IV update
The observed scaling does
not appear to follow the
simple 3 vs. 2 constituent
quark number relationship
Is this related to a jet
component, a breakdown
of simple approximations,
or something new?
Numerical approximations
give a 1% relative error
STAR Preliminary (Talk by M.Oldenburg)
Imperfect v2/n was also
anticipated within models
incorporating more realistic
assumptions.
Quark Matter — Budapest — August 2005
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a closer look
Inclusion of gluons in
recombination was predicted to
lead to a larger meson v2/n
than baryon v2/n:
B.Müller, et al. nucl-th/0503003
g
STAR Preliminary

To 1st order: the constituents
look like massive valence
quarks with no sub-structure
g
Probing more deeply reveals
substructure in the form of
sea quarks or gluons
qq
Further daughter partons are
revealed as the scale Q2 is
increased
Including contributions from
sea quarks and gluons should
cause deviations from v2/n
Quark Matter — Budapest — August 2005
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comparison to predictions
Inclusion of gluons in
recombination was predicted to
lead to a larger meson v2/n
than baryon v2/n:
B.Müller, et al. nucl-th/0503003
Tantalizing indication for the fate of gluons and the nature of the constituents
Systematic errors on the data and calculations need to be carefully addressed
Quark Matter — Budapest — August 2005
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comparison to predictions
MPC + Coalescence/Jetset: jet fragmentation contribution + spatial correlations
also can spoil the scaling of v2/n: D. Molnar nucl-th/0406066
0
1
2
pT/n (GeV/c)
pT/n (GeV/c)
1. Original quark v2 is not recovered by v2/n. The trend is correct but
deviations are larger than what’s seen in the data
2. Calculations will also miss the Baryon to Meson ratio but the fragmentation
component appears to show up in correlation measurements
Quark Matter — Budapest — August 2005
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The multi-strange hadrons
Even the (ss), and (sss) have large v2 values and appear to
follow baryon vs. meson systematics
(in)dependence of v2 on hadronic x-sections or flavor/mass:
• can phi and Omega v2 be understood without prehadronic flow?
Quark Matter — Budapest — August 2005
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v2 at intermediate pT
Constituent quarks appear to be the relevant
degrees-of-freedom just prior to hadronization
With sufficient precision we can address questions
about the nature of the constituents and the
microscopic nature of the matter
The centrality dependence of spectra compliments
v2 measurements
more flow (pT>0)
v2 
RCP 
more quench (pT<0)
v2 
RCP 
Quark Matter — Budapest — August 2005
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the centrality dependence
v2 and RCP: complimentary measures to probe flow vs. energy loss. RCP is a better than RAA for
many studies because it’s not sensitive to the change in chemistry from p+p to Au+Au
Baryon production increases more quickly with collision overlap density
than meson production
more evidence of constituent quark number instead of mass
Quark Matter — Budapest — August 2005
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Update on  RCP
2.5
Ratio
2.0
1.5
RdAu
RAA(60~80/pp)
RAA(05/pp)
1.0
0.5
STAR Preliminary
STAR Preliminary
Talk by Xiangzhou Cai
0.0
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
PT (GeV/c2 )
PHENIX Preliminary: Talk by D. Pal
The  RCP is well below proton or lambda RCP. Consistent with NCQ
scaling expectations.
a discrepancy arises between PHENIX and STAR RAA (RAA ≠ RCP)
Quark Matter — Budapest — August 2005
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Non-photonic electron RAA
Are D’s just like other
mesons?
There inclusive yield scales
with Nbin but the RAA is
similar to meson RAA.
At intermediate pT, do we
see evidence for flow +
coalescence or do we only
see energy loss?
Comparing PHENIX and STAR electron RAA to
charged hadrons we note a similar and
surprisingly large suppression!
v2 distinguishes between
these scenarios.
Quark Matter — Budapest — August 2005
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electron v2: dE/dx or flow
See talk by F. Laue
• Collisional energy loss can give us charm RAA ~ 0.3 and v2 ~ 5%
• A push from below (flow) is likely needed to get a larger charm v2.
• D v2~5% can come from v2c=0 + coalescence or v2c=5% + no coal.
Quark Matter — Budapest — August 2005
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Lower energy
1. Features of the particle-type dependence are common to different energies.
But the underlying behavior changes between 17.2 and 200 GeV
2. At low energy RCP is larger but v2 is smaller. Reveals what’s happening to
the spectra: change in underlying spectrum, more energy loss (pT<0) and
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more flow (pT>0) Quark Matter — Budapest — August 2005
4-quark candidates
The centrality dependence of 4-quark-state candidates (a0(980) and f0(980) for
example) can be used to probe their quark content.
f0(980): 2-quark state
f0(980): 4-quark state
accessible through +minv cocktail analysis
Quark Matter — Budapest — August 2005
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Jet-like correlation structures
J. Adams et al, Phys. Rev. Lett. 91 (2003) 072304
1. Dihadron correlations at intermediate pT indicate the presence of
jet-like correlations
2. Can these measurements be reconciled with the apparent nonfragmentation nature suggested by other measurements?
3. Notice the enhanced near-side peak in AuAu: we’ll see more of
this.
Quark Matter — Budapest — August 2005
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identified trigger particles
PHENIX; arXiv:nucl-ex/0408007
PHENIX; arXiv:nucl-ex/0408007
• Baryons and mesons have similar probabilities to have an associated hadron
• But why do both of them have a higher probability to have an associated
hadron in Au+Au collisions than in p+p collisions?
• This may arise from interactions between soft matter and hard partons.
What indications do we have for this?
Quark Matter — Budapest — August 2005
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identified trigger particles
PHENIX; arXiv:nucl-ex/0408007
PHENIX; arXiv:nucl-ex/0408007
• Mesons have a greater probability to have an associated hadron (thanks Barbara)
• But why do both of them have a higher probability to have an associated
hadron in Au+Au collisions than in p+p collisions?
• This may arise from interactions between soft matter and hard partons.
What indications do we have for this?
Quark Matter — Budapest — August 2005
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mediums response to jets
Correlations from fluctuations
data-peak
The fluctuation bin-size dependences
are related to two-particle
correlations
Fluctuations are inverted to
autocorrelations
Subtract elliptic flow and the nearside jet-peak
Mediums response to an impinging
jet is revealed
pick gluons from
the vacuum
gluon density
dNg/dy ~ 1000
STAR Preliminary: see posters by Duncan Prindle
look for modifications to particle composition in the away-side/recoil region
Quark Matter — Budapest — August 2005
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Near- and away-side B/M
away-side: comoving
partons enhance the
probability for baryon
production
near-side
like p+p
The larger B/M ratio in the away side is also suggestive of recombination:
wherever the density of comoving constituents is larger (in-plane, central vs. peripheral,
and now in the wake of quenched jets), it becomes easier to produce baryons.
We already knew that it was partons losing energy in a dense medium,
this may help us determine if the matter is hadronic or not (dAu?).
Quark Matter — Budapest — August 2005
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Conclusions
Production is highly sensitive to the fireball geometry.
Either from:
- hadronization — a long-wave-length/soft process or
- soft pushes (i.e. flow)
- quenching in medium (soft gluon radiation)
Quark degrees of freedom are apparent from RCP, and v2:
the flavor dependence is apparently not from mass, quark vs.
gluon, or hadronic cross-section. Rather, particles are grouped by
constituent quark number.
Measurements of large collectivity developed for  and 
challenge any non-QGP or hadronic scenario
Significant modification to s at low and intermediate Q2
are demonstrated through modifications to hadronization
Quark Matter — Budapest — August 2005
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QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
1. It’s highly interacting
2. It doesn’t appear to
be hadronic
3. What do we call it?
chiral symmetry breaking limit s,c=0.43 (hep-ph/0302011)
Quark Matter — Budapest — August 2005
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the end
Thanks to the organizers and S. Blyth, J. Chen,
X. Dong, H. Huang, Y. Lu, H-G. Ritter, A.
Rose, M. Oldenburg, K. Schweda, and N. Xu
Quark Matter — Budapest — August 2005
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Jet remnants (thermalization)
What happens to a hard probe that traverses a colored medium?
Can we observe effects of dissipation or thermalization?
Trigger pT:
4–6 GeV/c
SOFTENING
BROADENING
STAR Preliminary: F. Wang,
J.Phys.G30:S1299-S1304,2004
Quark Matter — Budapest — August 2005
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Anti-baryon to baryon ratio
Also, notice that the pbar/p ratios don’t yet reach pQCD predictions
PHENIX PRC69, 0304909 (2004)
QuickTime™ and a
TIFF (Uncompressed) decompressor
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Quark Matter — Budapest — August 2005
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Baryon/anti-baryon ratios
Au Au Central
Some indication of gluon vs. quark jet dependence
Quark Matter — Budapest — August 2005
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year 4 ratios
Au+Au Central
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year 4 RCP
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