Upload
others
View
1
Download
0
Embed Size (px)
Citation preview
Study of Charmonium States in Vacuum and High Density Medium
Juan Alberto Garcia,
The University of Texas at El Paso
Advisor: Dr. Ralf Rapp
Cyclotron REU 2009
Overview
• Some words about Quarks • The Quark Gluon Plasma• The Charmonium System• The Schrödinger Equation• The Hydrogen Atom• Cornell Potential• Color Screening Potentials • Lattice QCD Potential
Quarks
• Nucleons and other hadrons are made up of quarks.Proton
Quarks
Gluons• Quarks interact with one another
via the Strong Force; described by Quantum Chromodynamics (QCD).
• The Force is mediated by Gluons.
• Each quark and gluon carry a color charge, which is conserved in Strong interactions.
• Quarks are confined to one another, by a phenomenon called “quark confinement”.
• This happens because the force between becomes
constant with distance.
• Quarks also undergo the Annihilation‐Creation process in which a quark‐antiquark pair is
either converted or created from or into a gluon.
The Quark Gluon Plasma
• QCD predicts a new phase of quark matter above
temperatures of about 170 MeV (2*1012
K), the Quark
Gluon Plasma (QGP).• In this state quarks are deconfined from the
hadrons that contain them and form a hot and dense plasma.
• The picture shows a Au‐Au collision at RHIC in which a QGP is believed to have been created, but
for this to happed a probe its needed!!
• Hadrons containing heavy quarks(charm and bottom) have been identified as possible probes
for the QGP.• This is believed because if the QGP is created,
charmonium should be suppressed which is one of the signals of formation of the QGP.
• Charmonium consists of a charm quark and an anticharm antiquark pair in a bound state.
• Since the charm has a large mass a non relativistic approach is valid for its study.
Charmonium
The Schrödinger Equation
• Describes the time
evolution of the physical
state of a quantum system.• In its time independent
form, it becomes an eigen
value equation.• If a central potential is used
then the PDE is separable
and can be set in the form
Ψ(r, θ, φ)=R(r)*Θ(θ)*Φ(φ), where R(r) is the equation
for the radial part of the
solution.
The Hydrogen Atom (Test)
• A proton and electron pair form a bound state
called Hydrogen‐1 (Hydrogen atom).
Proton
Electron
Not to scale.
• Schrödinger’s equation can be solved for the hydrogen system analytically.
• The electromagnetic potential is used in this
scenario to solve the Schrödinger radial equation.
Photon
‐
+
Methods• In order to solve
Schrödinger’s equation, for
the given potential; it was
rewritten in finite
difference form (FDF). • FDF consists in
approximating the
derivatives using finite
difference relations.• With these approximations,
one is able to evolve the
system from a given initial
condition.
• A solution to the problem must
satisfy boundary conditions
which are: R(0)=C and R(∞)=0.• The solution can not be obtained
by a simple evolution of our
initial condition because the
boundary conditions can only be
satisfied with a discrete number
of Energies.• The algorithm is based on the
Shooting method:
Shooting
R(0)=C
E4
E1
E2
E31.
Choose initial condition and initial energy.2.
Solve Equation for given energy3.
If condition for a solution is met then keep eigen energy and quit.4.
If the function has the different sign as the previous one, decrease the
energy the previous amount and decrease energy steps by a factor
of 2.5.
Increase energy by a small amount.6.
Go back to step 2.
Back to Hydogen• Hydrogen was solved
to test the numerical accuracy of our
program because it had an analytic
solution it can be compared to.
n=1, l=0
n=1, l=0 • As can be seen on the left solution
does diverge but only after large
distances where effects can be
neglected
Plots for n=1, l=0; n=2, l=0; n=2, l=1.
n=1, l=0
n=2, l=1n=2, l=0
The Cornell Potential• A potential to simulate non
relativistic quark interactions in
Vacuum
• Two terms: “coulomb”
which
accounts for one‐gluon exchange;
and linear which accounts for
quark confinement.
• As the quarks are separated, the system stops being
energetically favored and the quarks go to a lower state of
energy by forming bound states with lighter quarks. This is
referred as “String Breaking”.
• The potential does not contain
“String Breaking”.
• J/ψ
‐‐‐‐> 3.0969
• ψ’
‐‐‐‐> 3.659
• χc
‐‐‐‐> 3.4513
• n=3, l=2‐‐‐‐> 3.6985
α=.212σ=.422
GeV2
o A charm bare mass of
1.2351 GeV was used in
order to match the total
mass of the J/ψ
to 3.096 which is about its real mass.o The total mass is given by
2 times the bare mass plus
the Eigen Energy of the
State.
Vacuum Potential
fm
fm
fm
fm
Color Screening
• Interacting matter of sufficient temperature and pressure is
predicted to undergo a transition to a state of deconfined quarks and
gluons (the QGP). • We say deconfinement occurs
when color charge screening becomes strong enough that it
shields the quark binding potential with any other quark or anti quark.
Cornell potential with screening mass
r radiusμ(T) temperature dependent “Screening mass”σ
0.192 GeV2
α
0.471
• The Screening mass is defined as μ(T)=
1/rD
; where rD
is the color screening
length.• The screening
length is the distance at which
the color force becomes
suppresed
• From the graph we can see that as expected
the radius increases with the screening
mass, and data tells us that the system is
completely dissolved with a screening mass higher than about
600MeV. • This is expected
because μ(T) increases as the temperature
increases
fm
Lattice QCD Potential
• Computed by
numerical
simulations of QCD
at finite
temperatures• Vacuum limit
potential is used to
match bare mass.• Bare mass is set so
that J/ψ
mass matches 3.035 GeV
mass = 1.249 ‐‐‐‐> 3.0349E 1 = 0.5369 l= 0
r1
=.317 fm
Medium Potential
V(r, T)
• By comparing the energies with the screening threshold, we can calculate
the Kinetic and Binding Energies for Each state.
• As can be seen in the table both BE and KE decrease as T increases.
• All other states have been dissolved.
T (Tc) Mass (GeV) BE (GeV) KE (GeV)
1.2 3.3506 .2031 .4263
1.8 3.0999 .0576 .3009
2.4 3.0073 .0466 .2546
Acknowledgements
• Advisor: Dr Ralf Rapp• Dr. Riek Felix• Xingbo Zhao• Dr. Sherry Yennello
References
• R. Rapp and H. van Hees. 2008. Heavy Quark Diffusion as a probe for the Quark‐Gluon Plasma.
arXiv:0803.0901v2.• Stephen Gasiorowicz. 2003. “Quantum Physics”. • E. Eichten, K. Gottfried, T. Kinoshita, K. D. Lane, T.
M. Yan. 1980. Charmonium: Comparison with Experiment. Physical Review D.
• F. Karsch, M.T. Mehr, H. Sartz. 1988. Color Screening and deconfinement
for bound States of
Heavy quarks. Zeitschnft fur Physik C.