Transcript Physics295-winter01.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
07-Mar-01
Daniel Cebra - Physics 295 Seminar
Meet the Group
• FACULTY:
• Jim Draper (emeritus)
• Paul Brady
• Daniel Cebra
• Ramona Vogt
• Daniel Ferenc
• GRAD STUDENTS:
• Mike Anderson (2001)
• Jenn Klay (2001)
• Ian Johnson (2002)
• Agusta Loftsdottir
• Clay Bratton
• UNDERGRADS:
• STAFF:
• Stephenie Ritchey
• Juan Romero
• Mark Allen
• Tom Gutierrez
• Allen Thoe
Come visit us on the fifth floor - WEST end • Stephen Baumgarten
07-Mar-01
Daniel Cebra - Physics 295 Seminar
Recent Graduates
• 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
07-Mar-01
Daniel Cebra - Physics 295 Seminar
What Do We Do?
07-Mar-01
Daniel Cebra - Physics 295 Seminar
Cosmic Gamma Ray Astronomy
Ferenc, Bratton, Loftsdottir
07-Mar-01
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.
07-Mar-01
Daniel Cebra - Physics 295 Seminar
Basics
Hadrons =
Made of
quarks
Baryon = 3 q
meson = q q
p = uud
n = udd
p+ = ud
K+ = us
07-Mar-01
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.
07-Mar-01
Daniel Cebra - Physics 295 Seminar
Temperature
Nuclear Matter Phase Diagram
Baryon Density
07-Mar-01
Daniel Cebra - Physics 295 Seminar
How to make a Quark-Gluon Plasma
• Quantum Chromodynamics (QCD) predicts that heavy
nuclei collided at ultra relatavistic energies will
undergo a phase transition from ordinary hadronic
matter to a quark-gluon plasma (QGP).
07-Mar-01
Daniel Cebra - Physics 295 Seminar
07-Mar-01
Daniel Cebra - Physics 295 Seminar
History of the Rel. Heavy-ion Program
• 76-92 Bevalac, Au
@ 0.1 - 1.0 AGeV
• 86-98 AGS, Au @
2-10 AGeV
• 86-00? SPS, Pb @
40-160 AGeV
• 91 RHIC approved
• 00 Colliding beams
at RHIC, 130Gev
07-Mar-01
Daniel Cebra - Physics 295 Seminar
Status of the AGS/SPS Results
• AGS exps
track the Hot
Hadron gas
region
• Feb ‘00 Press release
on the
observation
of QGM at
SPS
07-Mar-01
Daniel Cebra - Physics 295 Seminar
The Start of RHIC - Summer 00
07-Mar-01
Daniel Cebra - Physics 295 Seminar
Brief History of the RHIC Project
•
•
•
•
•
•
•
•
•
•
•
07-Mar-01
Daniel Cebra - Physics 295 Seminar
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
1
07-Mar-01
Daniel Cebra - Physics 295 Seminar
The STAR Experiment - Plans
07-Mar-01
Daniel Cebra - Physics 295 Seminar
STAR - Under Construction
07-Mar-01
Daniel Cebra - Physics 295 Seminar
07-Mar-01
Daniel Cebra - Physics 295 Seminar
The Detector Now...
07-Mar-01
Daniel Cebra - Physics 295 Seminar
07-Mar-01
Daniel Cebra - Physics 295 Seminar
07-Mar-01
Daniel Cebra - Physics 295 Seminar
The FIRST
Event!
07-Mar-01
Daniel Cebra - Physics 295 Seminar
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
07-Mar-01
Daniel Cebra - Physics 295 Seminar
STAR - peripheral event - side
• Determines
the z
location of
the vertex
• emission
angles of the
tracks.
• Demonstrate
true 3D
tracking
07-Mar-01
Daniel Cebra - Physics 295 Seminar
STAR Event - Front View
Central events
have much
higher
multiplicity of
tracks. Up to
2000 charged
particles in the
TPC’s
accpectance
07-Mar-01
Daniel Cebra - Physics 295 Seminar
STAR Event -- Side View
07-Mar-01
Daniel Cebra - Physics 295 Seminar
STAR Calibration and Analysis
p
K
p
e
07-Mar-01
Daniel Cebra - Physics 295 Seminar
• 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
07-Mar-01
Daniel Cebra - Physics 295 Seminar
How we “see” Strangeness
• See Strange Hadrons
V0
kink
–
–
–
–
kaon (u or d and s)
lambda (uds)
Omega (sss)
etc...
• Distinguishing Decay
Topologies
vertex
07-Mar-01
– V0
– kink
Daniel Cebra - Physics 295 Seminar
07-Mar-01
Daniel Cebra - Physics 295 Seminar
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
07-Mar-01
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
07-Mar-01
Daniel Cebra - Physics 295 Seminar
ds/dN vs N
Comparison to
cascade models
demonstrates to
collective behavior
of nuclear systems
Used to determine
centrality of
collisions
07-Mar-01
Daniel Cebra - Physics 295 Seminar
%s 0-3
15-20
35-40
Data
07-Mar-01
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
07-Mar-01
Daniel Cebra - Physics 295 Seminar
Source
Radii
PHENIX
• The expected
expansion of the
outward radius is
not seen.
• Transition may be
at lower energy or
more subtle.
07-Mar-01
Daniel Cebra - Physics 295 Seminar
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…
07-Mar-01
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.
07-Mar-01
Daniel Cebra - Physics 295 Seminar
Hydrodynamic Flow - Results
midrapidity : |h| < 1.0
V2
Hydrodynamic model
Preliminary
RQMD
SPS
AGS
Centrality
07-Mar-01
Daniel Cebra - Physics 295 Seminar
Conclusions
• Summer ‘00 Heavy-ion running was
successful - physics results already. But the
QGP question is not yet resolved.
• RHIC should run heavy-ions for 6 months
in ‘01 (also 1 month of proton running).
• Detectors Continue to improve (5-10 years).
• Future: eRHIC
• Future: LHC
07-Mar-01
Daniel Cebra - Physics 295 Seminar
Compact Muon Solenoid
07-Mar-01
Daniel Cebra - Physics 295 Seminar
Advertisements...
07-Mar-01
Daniel Cebra - Physics 295 Seminar
APS - join Now
•
•
•
•
All active physicists should join APS
Students memberships a very reasonable
Go to meetings, give talks!
California Section - next meeting will likely
be in Davis
07-Mar-01
Daniel Cebra - Physics 295 Seminar
Intramural Sports!
• Basketball
• Soccer
•Softball
• Other sports?
07-Mar-01
Daniel Cebra - Physics 295 Seminar