Title: Starting the Energy Scan - First Results from 62.4 GeV Au Au Collisions
1Starting the Energy Scan - First Results from
62.4 GeV AuAu Collisions
- Introduction.
- High pT.
- Bulk matter observations.
- Collective motion.
- Summary
2The story so far.
- We have discovered a strongly interacting medium
with extremely high energy density which cannot
be described in terms of simple hadronic degrees
of freedom.
Phobos
3Nuclear modification factor at 200 GeV
Charged Hadrons
d2N/dpTd? (AuAu)
RAA
NColld2N/dpTd? (pp)
High pT suppression and loss of back-to-back
signal in AuAu but not in dAu showed that
effect due to Jet Quenching in final state NOT
initial state parton saturation (GCG).
BRAHMS
Can we turn this effect off?
Observed by all 4 experiments
4Need for an energy scan
- Provide constraints on jet quenching models.
- Study the excitation function of baryon
transport. - Constrain models for hadron production at
intermediate pT.
Why 62.4 GeV?
- Located (on log scale) mid-way between SPS and
-
RHIC top energies. - Many reference data from ISR.
5Ncoll definition
Participants
Npart/2 A
LA1/3
Ncoll of NN collisions A4/3
Collisions
At 62.4 GeV Ncoll very different to 200 GeV
6First immediate result
Paddle Counter Signal top 50 of cross-section
200 GeV
62.4 GeV
PHOBOS Preliminary
Significant decrease in maximal multiplicity
7Charged hadron spectra and yields
Expect 62.4 GeV fit into vs systematics
8Jet quenching predictions at 62.4 GeV
I. Vitev nucl-th/0404052
Adil Gyulassy nucl-th/0405036
RAA (p0) 0.5 - 0.3 at pT 4 GeV
9RAA charged particles
same results from all 4 experiments
BRAHMS Preliminary
Maximum significantly higher than at 200 GeV.
There is a suppression for most central data
Similar shape evolution with centrality
10Universal centrality evolution?
- But, varying the beam energy changes
- Initial state sNN, Ncoll/Npart
- System ?, mB, Nch,
- Partonic xT, dE/dx
- Energy-independent
- Weak function of Npart, pT
.
- Use central AA as denominator
- Scale with 1/ltNpartgt
- Allows comparison between different experiments
nucl-ex/0405003
11PID spectra
BRAHMS
Phenix preliminary p0
W-
X-
12RAA for p0 for central data
Predictions 0.3 - 0.5 at 4 GeV/c Again maximum gt
200 GeV
STAR Preliminary
Charged ISR reference used for p0
Still discrepancy between charged and p0 Large
baryon contribution up to at least 4 GeV/c
13Rcp of baryons and mesons
Stat. Errors Only
STAR preliminary
STAR Preliminary
(stat. errors only)
The RCP(baryon) gt RCP(meson) at intermediate pT.
Problem with limited statistics.
14Baryon/meson ratios
- Again, large proton contribution at intermediate
pT - Small difference as function of centrality (not
very peripheral 30-60)
STAR Preliminary
Less?p in central collisions at 62.4 GeV
Ratios factor 2-3 higher than in pp at pT 2-4
GeV
15Ratios at mid-rapidity
Clear systematic trend with collision energy
Minbias (0-80)
62.4 GeV
STAR Preliminary
Stat. Errors Only
STAR Preliminary
?L/L
?-/ ? 1.0170.002 K-/K 0.8350.006 ?p/p
0.4580.005
confirm varying y same effect as varying vs.
Ratios flat as function of pT
16Statistical model results
STAR preliminary AuAu at vsNN200GeV
and 62 GeV
TLQCD160-170MeV
TLQCD160-170MeV
Energy dependence but small Nch dependence
17(In)dependence of mid-rapidity yields
Preliminary
Preliminary
- T, µB, and V all vary with energy,
but in such a way as to ensure yields stay
constant
Preliminary
18Radial flow
Blastwave fit
Shape of the mT spectrum depends on mass
Tch
Radial flow!
p K p
STAR Preliminary
STAR Preliminary
STAR Preliminary
Same flow as at 200 GeV
19Kaon Slopes
Top 5 central collisions
20? interferometry
- HBT probes space-time evolution of system and
system size at freeze-out. - Studies at vs130, 200 GeV yielded similar HBT
radii to SPS energies (HBT puzzle). - Severe challenge to hydrodynamic calculations.
- At an intermediate energy, a larger expansion
time might point to a long-lived mixed phase.
Systematics of central 0-5
Fully consistent Coulomb treatment in kT
dependence
same results from PHOBOS
21HBT from SPS to RHIC
No sign of qualitatively different expansion
dynamics at 62 GeV.
- Continues to be a severe
- challenge
submitted to Phys. Rev. C Rapid Communications
Same results from STAR
22Charged particle correlations
pT
Substantial signals attributable to elliptic flow
(v2 ltcos(2f)gt)
v2 apparently saturates and is the same as at 200
GeV
Jets are going to be a challenge
23Longitudinal elliptic flow
hh-ybeam
Longitudinal scaling of v2
nucl-ex/0406021
24Identified Elliptic Flow
Although statistics not great again resembles 200
GeV
25Quark coalescence?
Coalescence at intermediate pT leads to
v2 /nquark
The scaling works as for 200 GeV AuAu
Seems to be slightly lower than 200 GeV for
pT/nquarklt1 GeV/c
pT /nquark GeV/c
26Summary
Many of the results indicate environment similar
at 62.4 GeV to 200 GeV but its not identical
- Initial energy density lower
- Evidence of jet quenching
- Cronin effect is stronger
- HBT radii at 6 fm
- Chemical freeze-out conditions similar to 200 GeV
(fn Nch) - Baryon chemical potential much higher
- Radial flow as strong as at 200 GeV (fn Nch)
- Elliptic flow as strong as at 200 GeV (fn
centrality) - Consistent with Nquark scaling
- Elliptic flow appears universal at forward
rapidities - Jet contribution much weaker than at 200 GeV
As yet un-answered questions Are the gluon
densities the same in both systems? Do they spend
the same amount of time in each stage? i.e. do
they reach the same freeze-out conditions in
the same manner?
27 28Why an energy scan?
Varying the geometry (A,b)
- jet quenching
- vary overall path length
- vary asymmetry
- Elliptic (and directed) flow
- Study A dependence at fixed eccentricity.
Npart
eccentricity
29pp references
/-25 uncertainty
p0 reference
charged reference
p0 reference