Transcript Physics295-winter02.ppt

The UCD
Nuclear Physics
Group
Daniel Cebra
Goal of this talk - to introduce the nuclear physics group
and explain what we do and why it is interesting
PS… Check out our web page at http://nuclear.ucdavis.edu
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Daniel Cebra - Physics 295 Seminar
Meet the Group
• FACULTY:
• Jim Draper (emeritus)
• Paul Brady (emeritus)
• Daniel Cebra
• Ramona Vogt
• Daniel Ferenc
• STAFF:
• Juan Romero
• Tom Gutierrez
• GRAD STUDENTS:
• Mike Anderson (2002)
• Ian Johnson (2002)
• Steve Oliver (2004)
• Roppon Picha (2005)
• UNDERGRADS:
• Mark Allen
• Trieu Mai
• Daniel Clayton
• Stephen Baumgarten
Come visit us on the fifth floor - WEST end
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Daniel Cebra - Physics 295 Seminar
Recent Graduates
• Jenn Klay (2001) Postdoc LBNL
• Mike Heffner (2000) Postdoc LLNL
• Tom Gutierrez (2000) Postdoc UCD
• Bill Caskey (1999) Z-World, Davis CA
• Lynn Wood (1998) Z-World, Davis CA
• Jerry Chance (1997) Postdoc LBNL
• Doug Mayo (1997) Staff Scientist LANL
• Jason Dunn (1997) Professor - Idaho Christian
• Isaac Huang (1997) FunMail.com
• Jack Osbourn (1995) Professor - Sac State
• Jessica Kintner (1995) Professor - St. Mary’s
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Daniel Cebra - Physics 295 Seminar
What Do We Do?
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Daniel Cebra - Physics 295 Seminar
Abstract of Research Goals
The study of collisions between relativistic nuclei will ultimately
allow the determination of the properties of nuclear matter over a
wide range of temperatures and densities. Without the possibility
of direct studies of nuclear matter in bulk (as in neutron stars,
supernovae, or the Big Bang), one resorts to the challenging
studies of finite and transient systems as provided by nucleusnucleus collisions. Our experiments search for signatures of the
Quark Gluon Plasma (QGP), a phase of matter which dominated
the early stages of the Big Bang.
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Basics
Hadrons =
Made of
quarks
Baryon = 3 q
meson = q q
p = uud
n = udd
p+ = ud
K+ = us
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Daniel Cebra - Physics 295 Seminar
Goals of Relativistic Heavy Ions
• To study the
properties of
nuclear matter.
• Specifically to
study the Quarkgluon plasma
• Allows a better
understanding of
the earliest phase
of the universe.
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Temperature
Nuclear Matter Phase Diagram
Baryon Density
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The Start of RHIC - Summer 00
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Brief History of the RHIC Project
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1947 BNL founded
1952 Cosmotron
1960 AGS
1970 Tandem
1979 ISABELLE
1983 CBA canceled
1983 RHIC
proposed
1991 RHIC
approved
1992 STAR
approved
1999 First Beams
2000 First collisions
2001 Full Energy
1
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The STAR Experiment - Plans
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STAR - Under Construction
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The Detector Now...
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The FIRST
Event!
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STAR - peripheral event - Front
• Tracks emerge
from common
vertex point
• Grazing collisions
produce few tracks
• Magnetic field
bends trajectories
into helices allows measure of
momentum
• Particle ID through
gas dE/dx
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STAR - peripheral event - side
• Determines
the z
location of
the vertex
• emission
angles of the
tracks.
• Demonstrate
true 3D
tracking
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STAR Event - Front View
Central events
have much
higher
multiplicity of
tracks. Up to
2000 charged
particles in the
TPC’s
accpectance
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STAR Event -- Side View
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STAR Calibration and Analysis
p
K
p
e
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• Spatial
resolution 700 m
• Tracking - better
then 90%
efficiency
• dE/dx resolution
= 8%
• momentum
resolution better
than 1%
Spectra
• Temperatures are
measured in the
range expected for a
QGP transition
• Suggestive result,
but further analysis
is needed
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Daniel Cebra - Physics 295 Seminar
How we “see” Strangeness
• See Strange Hadrons
V0
kink
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–
kaon (u or d and s)
lambda (uds)
Omega (sss)
etc...
• Distinguishing Decay
Topologies
vertex
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– V0
– kink
Daniel Cebra - Physics 295 Seminar
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Centrality: Participants vs. Spectators
The collision geometry (i.e. the impact parameter) determines
the number of nucleons that participate in the collision
“Spectators”
Zero-degree
Calorimeter
Only ZDCs measure Npart
“Participants”
“Spectators”
Many things scale with Npart:
• Transverse Energy
• Particle Multiplicity
• Particle Spectra
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Produced Particles
Daniel Cebra - Physics 295 Seminar
N part  A  N spec
ZeroDegreeCalo as centrality device
• Only shared detector
– Rates: luminosity via
well-known reference
process
– Timing: substantial
background rejection
– Pulse height: measures
centrality
• Directly confirms
monotonic relationship
between participants
with multiplicity
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ds/dN vs N
Comparison to
cascade models
demonstrates to
collective behavior
of nuclear systems
Used to determine
centrality of
collisions
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%s 0-3
15-20
35-40
Data
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h
Mean Npart
354
216
102
HIJING
(dNch/dh)/(½Npart)
dNch/dh
Data
(dNch/dh)/(½Npart)
dNch/dh
Shapes of dNch/dh for different Npart
Daniel Cebra - Physics 295 Seminar
HIJING
h
dN/dh
Higher
multiplicity than
comparable p+p
collisions indicates
collective nature.
STAR
PHENIX
BRAHMS
Impressive
agreement
between the exps
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Source
Radii
PHENIX
• The expected
expansion of the
outward radius is
not seen.
• Transition may be
at lower energy or
more subtle.
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Hydrodynamic Flow - Defined
• Radial flow
• Elliptic flow
– Not seen in angular
distributions
– Use HBT, spectra
(T = To + m<b2>
– Early time push,
hydrodynamic
evolution
– Strongest at y=0
• Directed flow
– Forward rapidities
– Not measured yet
PHOBOS/STAR
– Interesting
predictions for phase
transition…
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y  x 
 2
y  x 2 
2
Daniel Cebra - Physics 295 Seminar
2
v2  cos2
  atan
py
px
Hydrodynamic Flow - Results
The RQMD
cascade can
not account
for the
observed flow.
Collective
behavior is
demonstrated.
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Hydrodynamic Flow - Results
midrapidity : |h| < 1.0
V2
Hydrodynamic model
Preliminary
RQMD
SPS
AGS
Centrality
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Conclusions
• ‘00 and ‘01 Heavy-ion running was
successful - physics results already. But the
QGP question is not yet resolved.
• ‘02 polarized proton+proton running.
• Detectors Continue to improve (5-10 years).
• Future: eRHIC
• Future: LHC
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Compact Muon Solenoid
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APS - join Now
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All active physicists should join APS
Students memberships a very reasonable
Go to meetings, give talks!
California Section - next meeting will be in
Davis
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Daniel Cebra - Physics 295 Seminar
Intramural Sports!
• Basketball
• Soccer
• Softball
• Other sports?
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Daniel Cebra - Physics 295 Seminar