Transcript PHENIX at RHIC - New York Science Teacher

The PHENIX Experiment
at RHIC:
Can We Rewind the Clock to Catch a
Glimpse Near the Beginning of Time?
Thomas K Hemmick, Stony Brook University
for the PHENIX Collaboration
The Beginning of Time

Time began with the Big Bang:
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Since then the Universe has cooled
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All energy and matter of the universe was in a state
of intense heat and compression.
While cooling, the material of the universe
underwent several phase changes.
2.7 Kelvin is the temperature of most of the
universe today.
However, there exist a few “hot spots” where the
expanding matter has collapsed back in upon itself.
What do we know and what can we learn from
laboratory experiments about this past history?
T.K. Hemmick
Evolution of the Universe
Reheating
Matter
Too
hot for quarks
to bind!!!
QuarkGluon
Standard Model (N/P) Physics
 Collisions of “Large”
Plasma??
nuclei convert
beam
Too hot for nuclei to bind
energy to temperatures
above 200 MeV or
Nuclear/Particle (N/P) Physics
Hadron
1,500,000,000,000 K
Gas
~100,000 times higher
Nucleosynthesis builds nuclei up
to He than the
temperature
center of our sun.
Nuclear Force…Nuclear Physics

“Large” as compared
E/M
to mean-free path
of
Universe too hot for electrons
to bindparticles.
Plasma
produced
Stars convert gravitational
E-M…Atomic
(Plasma) Physics
energy
to temperature.

They “replay” and finish
nucleosynthesis
Today’s Cold
Universe
~15,000,000
K in the
center
of our
sun.
Gravity…Newtonian/General
Relativity
T.K. Hemmick
Solid
Liquid
Gas
Relativistic Heavy Ion Collider (RHIC)
Pioneering High Energy Nuclear Interaction eXperiment (PHENIX)
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2 counter-circulating rings, 3.8 km
circumference
Any nucleus on any other.
Top energies (each beam):
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Maximal Set of Observables
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Highly Selective Triggering
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100 GeV/nucleon Au-Au.
250 GeV polarized p-p.
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T.K. Hemmick
Photons, Electrons, Muons, IDhadrons
High Rate Capability.
Rare Processes.
Nature is in Charge
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RHIC provides the energy to reheat matter.
PHENIX observes the debris of the collision.
Creation of a primordial medium is out of our
hands:
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How and whether the collisions express the energy as
new phases of matter cannot be controlled by us.
The collisions are so fleeting (Dt ~10-22 sec) the signals
from a single such collision travel only several nuclear
diameters before the system breaks apart.
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Nature must create both the medium and its
diagnostic signatures.
 We set the stage and fill the audience,
Nature puts on the show.
T.K. Hemmick
The Medium and the Probe
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At RHIC energies different
p+p->p0 + X
mechanisms are
responsible for different
regions of particle
Thermallyshaped Soft
production.
Production
The rare process (Hard
“Well Calibrated”
Scattering or “Jets”) is the
Hard
probe of whether the soft
Scattering
production products form a
medium.
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Calibrated Probe
“The tail that wags the dog”
(M. Gyulassy)
T.K. Hemmick
hep-ex/0305013 S.S. Adler et al.
Fate of Hard Scattered
Partons
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Hard scatterings in
nucleon collisions
produce jets of particles.
 In the presence of a
color-deconfined
medium, the partons
strongly interact
(~GeV/fm) losing much
of their energy.
 “Jet Quenching”
schematic view of jet production
hadrons
leading
particle
q
q
hadrons
leading particle
Once quenched, the jets could not
re-appear since this would violate
the 2nd Law of Thermodynamics
T.K. Hemmick
Particle Spectra Evolution
“Central”
Nuclear
Physics
Particle
Physics
K. Adcox et al, Phys Lett B561 (2003) 82-92
T.K. Hemmick
“Peripheral”
Nuclear Modification Factor: RAA
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We define the nuclear
modification factor as:
Au+Au->p0+X
1 d 2 N A A
N evt dpT d
RAA ( pT ) 
 N binary  d 2 N  N
N N
 inel
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dpT d
RAA is what we get divided by
what we expect.
By definition, processes that
scale with the number of
underlying nucleon-nucleon
collisions (aka Nbinary) will
produce RAA=1.
RAA is well below 1 for both charged
hadrons and neutral pions.
The neutral pions fall below the charged
hadrons since they do not contain
contributions from protons and kaons.
T.K. Hemmick
nucl-ex/0304022 S.S. Adler et al.
d+Au Control Experiment
Proton/deuteron
nucleus
collision
Nucleusnucleus
collision
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Collisions of small with large nuclei were always foreseen
as necessary to quantify cold nuclear matter effects.
Recent theoretical work on the “Color Glass Condensate”
model provides alternative explanation of data:
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Jets are not quenched, but are a priori made in fewer numbers.
Color Glass Condensate hep-ph/0212316; Kharzeev, Levin, Nardi,
Gribov, Ryshkin, Mueller, Qiu, McLerran, Venugopalan, Balitsky,
Kovchegov, Kovner, Iancu
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Small + Large distinguishes all initial and final state effects.
T.K. Hemmick
d+Au Spectra
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Final spectra for charged hadrons and identified pions.
Data span 7 orders of magnitude.
T.K. Hemmick
RAA vs. RdA for Identified p0
d+Au
Initial State
Effects Only
Au+Au
Initial + Final
State Effects
d-Au results rule out CGC as the explanation for Jet
Suppression at Central Rapidity and high pT
T.K. Hemmick
Charged Hadron Results
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Striking difference of
d+Au and Au+Au results.
Charged Hadrons higher
than neutral pions.
Cronin Effect:
Multiple Collisions
broaden high PT
spectrum
T.K. Hemmick
Centrality Dependence
Au + Au Experiment
d + Au Control Experiment
“PHENIX
Preliminary”
results,
consistent
with PHOBOS
data in
submitted
paper
Final Data
Preliminary Data
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Dramatically different and opposite centrality
evolution of Au+Au experiment from d+Au control.
 Jet Suppression is clearly a final state effect.
T.K. Hemmick
1.01
C
1.1
The “Away-Side” Jet
1.00
0.9
0.99
1.3
2.0 < pT < 3.0 (GeV/c)
2.0 < pT < 3.0 (GeV/c)
1.03
1.2
1.02
C(D)
d+Au
1.1
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1.01
60-90%
0-10%
Min Bias
1.0
1.00
0.9
0.99
0
Lost Jet
“Far Side”
Au+Au
30
60
90
120
150
Ddeg.
Near
PHENIX Preliminary
Jets produced on the periphery of
the collision zone coming out
should survive.
However, their partner jet will
necessarily be pointed into the
collision zone and be absorbed.
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180
0
Far
30
60
Near
90
120
150
Ddeg.
180
Far
PHENIX Preliminary
Peripheral Au+Au similar to d+Au
“PHENIX Preliminary”
Central
Au+Au
shows
distinct
results,
consistent
with
reduction
farinside
correlation.
STARin
data
submitted
paperJet is missing in Au+Au
Away-side
T.K. Hemmick
C(D)
Escaping Jet
“Near Side”
1.0
What’s Next
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We must investigate other probes that look deeply into the
medium to characterize it.
Same paradigm, The Rare Processes Probe the Medium:
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Heavy Quark States
• Dissolution of J/Y & Y’, the bound states of charm-anticharm quarks
probes quark deconfinement.
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Electromagnetic Probes (no strong interaction)
• Lack of strong interaction allows them to penetrate the black medium
and see through the hadronic veil
• Direct Photons, e+e-, m+m-
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PHENIX plans to make these measurements in the next
Au+Au run.
T.K. Hemmick
Summary
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We have seen via Au+Au Jet Quenching and the d+Au
control experiment that a medium with strong final state
effects is formed in Au+Au collisions at RHIC.
 Our announcement today is that we indeed have the
opportunity to learn about the conditions of our universe
soon after the Big Bang.
 We have set the stage and Nature has granted us a show.
We will measure the properties of the medium and will
learn whether or not the quarks are confined.
 It would be presumptuous without having measured the
additional medium probes to now label the medium in
accordance with our preconceptions as being the QuarkGluon Plasma.
 Nature has been known to include surprise endings, the
observation and understanding of which represent the real
progress in science.
T.K. Hemmick
T.K. Hemmick