Exploring QCD in the
Charmonium System
Matthew Shepherd
Indiana University
September 27, 2010
T(r)opical QCD -- Cairns, Australia
M. R. Shepherd
Topical QCD Workshop, Cairns
2 September 27, 2010
Outline
• Key charmonium experiments: BES III and CLEO-c
• Recent results: a sampler of various measurements
• the charmonium spectrum and radiative transitions
• radiative and electromagnetic decays of charmonium
• light meson spectroscopy in charm and charmonium
decays
• Summary
M. R. Shepherd
Topical QCD Workshop, Cairns
3 September 27, 2010
The Charmonium System
3900
• 1--
The states are easily populated in 3
D1
e+e- collisions -- well known and
I
3 DD Threshold
“clean” initial states S1
3700 1
c S0
• All expected cc states below DD 1
hc P1 2
threshold have been experimentally
3500
verified 1
0
• Provides an opportunity to explore
3300
the qq bound state in heavy quark
regime 3
S1
• Decays of cc into light hadrons 3100 1
c S0
proceed via “glue-rich” OZI
suppressed channels
2900
0 + 1+ 0, 1, 2++
I
I
I
I
1
M. R. Shepherd
Topical QCD Workshop, Cairns
4 September 27, 2010
Charmonium Experiments
Solenoid Coil
Barrel
•
Calorimeter
CLEO-c Ring Imaging Cherenkov
Detector
Drift
•
Chamber
Cornell Electron Storage Ring (Ithaca, SC Quadrupole
Inner Drift Chamber /
Beampipe
NY) Pylon
• e+e- collisions at ψ’, ψ(3770), and
Ecm = 4160 MeV
Endcap
SC Calorimeter
Quadrupoles
• decommissioned in 2008 -- analysis still
Rare Earth
Quadrupole Iron
Polepiece
ongoing Magnet
Iron
Barrel Muon
Chambers
• BES III
• Institute for High Energy Physics (Beijing)
• successor to BES II
• world’s largest sample of ψ’ and J/ψ
decays (and still growing)
• vibrant current and future program
M. R. Shepherd
Topical QCD Workshop, Cairns
5 September 27, 2010
Spectrum and Transitions
3900
• Mass of the hc: P-wave hyperfine 3
D1
splitting
I
3 DD Threshold
S1
•
3700 1
Multipole amplitudes in photon c S0
transitions through the χc states 1
hc P1 2
3500
1
0
•
3300
Measurements test
•
3
cc quark model calculations S1
3100 1
• lattice QCD predictions c S0
2900
0 + 1+ 0, 1, 2++
I
I
I
I
1
M. R. Shepherd
Topical QCD Workshop, Cairns
6 September 27, 2010
The P-wave singlet state: hc
• Last state below open charm 3900
3
threshold to be identified D1
I
3 DD Threshold
S1 π0
• E835 (2005): 3σ
3700 1
c S0
CLEO (2005): 5σ 1
hc P1 2
3500
• Its mass gives P-wave hyperfine 1
splitting which is naively γ 0
predicted to be zero 3300
• Production in isospin violating 3
S1
decay 3100 1
c S0
• Predicted to have large radiative
branching fraction to the ηc 2900
0 + 1+ 0, 1, 2++
I
I
I
I
1
M. R. Shepherd
Topical QCD Workshop, Cairns
7 September 27, 2010
hc Properties
• New high-stats study from BES III
BESIII: PRL 104, 132002 (2010)
• Reconstruct specific hc→γηc decays (a) or
inclusively by just finding hc→γηc photon
(b)
• Recent precision results form BES:
• M(hc) = 3525.40 ± 0.13 ± 0.18 MeV
• Γ(hc) 7.2 σ
X(2370) 2371 ± 6 108 ± 15 > 6.7 σ
M. R. Shepherd
Topical QCD Workshop, Cairns
20 September 27, 2010
J/ψ→ωηππ
BES III Preliminary
• Related channel: expect 1+ (f1), 0- (η),
or 2- (η2) states
• Clear signals for known
f1(1285) and η(1405)
• Additional state observed around
1870 GeV/c2
• JP not known
• Is X(1870) the same as X(1835)?
Results of a Breit-Wigner fit (statistical errors only):
State Mass (MeV/c2) Γ (MeV/c2)
f1(1285) 1285 ± 1 21 ± 3
η(1405) 1400 ± 3 57 ± 8
X(1870) 1873 ± 11 82 ± 19
Initial results show great promise -- expect improvements with more statistics and more
sophisticated analyses.
M. R. Shepherd
Topical QCD Workshop, Cairns
21 September 27, 2010
D+→K-π+π+
...from e+e-→ψ(3770)→DD
• Perform a fit to the Dalitz plot, including
contributions from κ, K*(892),
K0*(1430), K2*(1430), and K*(1680)
CLEO Collaboration
• Asymmetry in K*(892) peak is a Phys. Rev. D 78, 052001 (2008)
indicates interference with a scalar Kπ
component
• Additional I=2 π+π+ S wave is needed
to achieve an adequate fit to the data
• Isobar model description not sufficient
for high precision analysis
• likely to be case for many future
analyses
• is there a more model independent
approach?
M. R. Shepherd
Topical QCD Workshop, Cairns
22 September 27, 2010
D+→K-π+π+
• Fit for amplitude and phase in bins of Kπ or ππ mass (quasi-model-independent PWA)
[E791: PRD 73, 32004]
• Kπ S wave does not look like a Breit-Wigner resonance
• I=2 ππ S wave consistent with ππ scattering data CLEO Collaboration
Phys. Rev. D 78, 052001 (2008)
Example: K-π+ D wave K-π+ S wave I= 2 π+π+ S wave
M. R. Shepherd
Topical QCD Workshop, Cairns
23 September 27, 2010
Summary and Discussion
• Many opportunities for studying QCD using charmonium
• very high statistics and low backgrounds make almost any measurement possible
• have an idea for measurement? let us know!
• Some results seem to confirm expectations: e.g. radiative transitions between
states, multipole amplitudes, and cc hyperfine splittings
• Some results are surprising: e.g. apparent suppression of ψ’→γη, enhancement of
χc1→γ(ρ,ϕ,ω)
• Analysis of light hadron spectrum in multi-body charmonium decays shows
extraordinary potential for exciting results
• need close collaboration with theory to develop analysis techniques:
phenomenological systematic errors are likely to dominate
• clean charmonium environment can serve as a test bed for analysis techniques
that can be extended to current and future dedicated light hadron experiments
M. R. Shepherd
Topical QCD Workshop, Cairns
24 September 27, 2010