Transcript ppt

Recent Activities of
CLQCD
J.P. Ma
ITP, Academia Sinica, Beijing
Talk given at NTU, 0.1.06.2007
Outline
1. CLQCD
2. Selected Topics
Charmonium Spectrum
Pion-Pion Scattering Phase Shift
3. Future Interests
1. CLQCD
CLQCD: Chinese Lattice QCD Collaboration, exists since
July, 2006, roughly.
People:
Faculty Members:
Ying Chen
Institute of High Energy Physics, CAS
Chuan Liu
Peking University
Yubin Liu
Nankai University
Xiang-Qian Luo Sun Yat- Sen University
Jian-Ping Ma
Institute of Theoretical Physics, CAS
Jianbo Zhang
Zhejiang University
Graduate Students (not complete):
Ming Gong (PKU), Xin Li (PKU), Ji-Yuan Liu (PKU),
Xiang-Fei Meng (NKU), Gang Li (IHEP), Yuan-Jiang
Zhang (IHEP) , …………….etc.
• Machines:
Deepcomp 6800
Dawning 4000A
NKStars
Speed
4.2Tflop
(Linpack)
10.2 Tflops(peak)
8 Tflops (Linpack)
4.7 Tflops (peak)
3.2 Tflops (Linpack)
Node Numbers
197 Compu,
4 I/O, 1 Console
512 Compu.,
16 I/O, 4 Console
384 Compu.
12 I/O, 4 Console
Processors
4 CPU/node
(1.3GHzIntel
Itanium, 8/16GB)
4 CPU/node
(2.4 GHz AMD
Opereron, 8GB)
2 CPU/node
(IBM Xserver, 2GB)
Network
Globus, MPI-G;
Oracle 10G
Myrinet 2000
Myrinet
Hard Disk
80TB
20TB
54TB
At present, Roughly 0.6-1.0 million CPUhours are allocated
per year.
• Forthcoming Machines
Supercomputing Center of CAS (SCCAS)
A 100 ~ 200Tflops new computer is planned and
expected to be available in 2008.
Shanghai supercomputer Center (SSC)
A 100 Tflops new computer is expected to be
available in 2008.
Current Activities:
1. Software for unquenching simulation
2. Charmonium spectrum and charmed
hadrons
3. Scattering length and phase
4. ……………….
2. Selected Topics
Parts of results in the papers of CLQCD:
hep-lat/0701021 , hep-lat/0703015
Charmonium Spectrum
• Motivation
A series of heavy meson states of open-charm and
closed-charm have been observed recently(XYZ…)
•Y(4260) (likely a 1  hybrid charmonium?)
• X(3872) (most likely 1  ,
but refuses to fit
into the 2P state predictions of non-relativistic quark
models ).
Many model-dependent theoretical interpretation of the
newly observed meson states.
• Lattice Formalism
Anisotropic lattices: with finer lattice in time
direction. It is very helpful to measure large
energy of a system.
Tadpole improved Symanzik’s gauge action.
Tadpole improved Clover fermion action.

as (fm) L3  T
2.4
0.222(1)
83  40
1.78
200
2.6
0.176(1)
123  64
2.11
200
2.8
0.139(1)
163  80
2.22
200
Las
(fm) #config
• Lattice interpolation field operators
The operators are
constructed by quark
bilinears sandwiched with
Gamma matrices and color
fields.
When calculating the twopoint functions, the
disconnected diagrams
are neglected by assuming
the OZI suppression.
• Data analysis ---Sequential Empirical Bayes Method
(Y. Chen et al., hep-lat/0405001)
Bayes: constrained-curve fitting
prior
Empirical: priors are derived from part of data
**(‘prior’ means the prior information of parameters)
Sequential: states fitted one by one from low to high.
C (t )  Wi e
i
 mi t
0++
Three-mass-term fitting
prodecure in 0++ channel
meff
1
C (t )
 ln
a C (t  1)
Red points are data from
the simulation, the blue
curve is the plot of fit
model with fitted
parameters.
1++
Three-mass-term fitting
prodecure in 1++ channel
Red points are data from
the simulation, the blue
curve is the plot of fit
model with fitted
parameters.
1+Three-mass-term fitting
prodecure in 1+- channel
Red points are data from
the simulation, the blue
curve is the plot of fit
model with fitted
parameters.
• nS states and nP states
• 2P states and X(3872)
BGS represents the predictions of Swanson et al quark model. It is difficult to change quark model, as it
can reproduce precisely the masses of almost all the known charmonium states (Swanson, hepph/0601110).
For 2P states, earlier (quenched) lattice QCD predictions (CP-PACS and Chen) of their masses are
roughly 100 MeV larger than QM prediction. This may be attributed to their two-mass-term fitting
where the contamination of higher states to the first excited states cannot be neglected.
Our result for 2P(1++) is consistent with X(3872) in mass.
• Hyperfine splitting
M  M ( J / )  M (c )
• Continuum limit
extrapolation performed.
M  83(3) MeV
• The result is in agreement
with previous (quenched)
works
•
c cg
hybrids (with exotic quantum numbers)
M (1 )  4.18(3)GeV
M (0 )  4.67(17)GeV
•These results are in
agreement with
previous quenched
lattice QCD results.
M (0 )  5.88(15)GeV
• Non-exotic
•
c cg hybrids and conventional charmonium
Masses from the four-mass-term SEB fitting of hybrid-hybrid (HH) and mesonmeson (MM) correlation functions in 1– and 0-+ channels.
• It is understandable that the masses of the ground states are almost the same and
the masses of the first excited states are consistent with each other, because the
operators with the same quantum numbers can overlap to the same hadron states.
• The masses of the second excited state of HH are very different from those of MM
• Still work on them….
• A summary to the charmonium spectrum study
1.
With SEB, the masses of the first excited
states (even the second excited states in
some channel) can be reliably derived from
charmonium two-point functions.
2. The masses of 2S charmonium states agrees
well with experimental data.
3. The masses of 2P charmonium states obtained
in this work are 3.798( 70), 3.827(50), and
3.799(60) for 0++, 1++ and 1+- states,
respectively. Given 1++ for X(3872), 2P(1++) is
consistent with X(3872) in mass.
4. Masses of hybrid charmonia with exotic quantum
numbers can be derived more soundly, since there
are no admixtures of conventional charmonia.
Howver for hybrid charmonia with no-exotic
quantum numbers, it still a tough task to separate
them from conventional charmonia unambiguously in
the present lattice study.
5.
Specifically, we have not observed a clear hybrid
states with mass around 4260 MeV in the vector
channel.
6. We are still working on ……….
Pion-Pion Scattering Phase Shift
•Scattering is a powerful method to study
hadron structure. Many data exist in the low
energy range which can not be explained with
perturbative QCD and QCD!
•Scattering amplitudes are determined by
their scattering phase shifts (Quantum
Scattering Theory)
• Lattice QCD provides a way to study
How ? Finite Volume……
them.
In a cubic box:
A momentum is
quantized:
A two-pion system: one with
another
Define:
The energy of the system, can be
measured with lattice QCD
Luescher’s formula:
The phase shift:
If L is large enough, one can get the
scattering length:
Cubic box: degenerated momentum modes! Fewer
data points in a given q^2 range.
More data points can be obtained if one uses
asymmetrical box:
the degeneration can be lifted and
Still, tadpole improved Symanzik’s gauge action.
Tadpole improved Clover fermion action.
Anisotropic lattices
Chiral extrapolation, continuum limit…. Etc.
Isospin = 2, J=0 channel
Results for scattering length:
Previous results:
The phase shift: (“physical “ results)
3. Future Interests
Say “good bye” to QCD without dynamical fermions
Numerical study of lattice QCD with dynamical fermions.
How far we can go depends on our effort and the
computing resource available !!
Thank You!
谢谢