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Physics of the Charm Quark
Gene GolowichPhysics Department
Univ. of MassachusettsAmherst MA
ColloquiumWayne State Univ. September 22, 2005
Rough Outline
• Some Background Comments
• Some Standard Model
• Some New Physics
‘Coals to Newcastle’
• ExperimentCLEO: Bonvicini, Cinabro, Dubrovin
CDF: Harr, Karchin
• TheoryPetrov, Gabbiani, AlFiky
Discovery of Charm
Age: c-quark will turn 31 on 11/11
Birth: East Coast (BNL) West Coast (SLAC)
SLAC Method:
Narrow resonance at E = 3.1 GeV!
Thereafter called the `J/’
The Standard Model
NuTeV Anomaly?
Three Years of Tests
Spectrum of Quark Masses
Predict this Spectrum: Easy/Hard?
Quark Masses and Theory
• Predict quark masses? No viable models
exist
• What about String Theory? String ground state huge! `Landscape’ description. Many-universes scenario. Elementary constants random! Lucky us! We EXIST!!
• What about mc = 1.3 GeV? Difficult theoretically. Not heavy enough! Not light enough! Complications of QCD
QED vs QCD
QED
QCD
ρ E
JtE/B
baabcccAEgερE
)AB(Egε
Jt/EB
babaabc
aaa
V
Progress in Lattice QCD
Standard Model Physics
• D Meson Ground State
• The spectator c-quark: Bc Mesons
• D Decays: Leptonic, Semileptonic,
Nonleptonic
• Spectroscopy: Exotic states?
D Meson Ground State
Predict the States: Easy/Hard?
qC
D Meson Ground State
q = u D0
q = d D+
q = s Ds+
Easy! 3* of SU(3)
qC
Flavored Mesons
Each quark has its own ‘flavor’
Quark composites are ‘flavored’
s-quark: K’s =
c-quark: D’s =
b-quark: B’s =
The t-quark decays too quickly!
qs
qc
qb
Bc Mesons!
Leptonic Decay of D+
Decay Amplitude:
Decay Constant fD:
Non-perturbative efect.Requires Lattice QCD!
fD: Theory vs Experiment
Semileptonic Decays
Decay Amplitude:
D0 K e+ e
Form Factor Slopes
Nonleptonic Decays
Decay Amplitude:
A = a ei
Dalitz Studies
Phase Information
More Dalitz
Comparative Lifetimes
B: B- = b B0 = d
-/0 = 0.92
u b
Comparative Lifetimes
B: B- = b B0 = d
-/0 = 0.92
D: D0 = c D+ = c
-/0 = 2.55
du
u b
Comparative Lifetimes
B: B- = b B0 = d
-/0 = 0.92
D: D0 = D+ =
-/0 = 2.55
K: K- = K0 =
-/0 = 139.
u b
uc dc
sdus
Charm Production
e+e- collisions produce charm.
There are predictions for this.
Not all data are understood!
Heavy Meson Spectroscopy
X(3872) Sighting
Is X(3872) a Molecule?
AlFiky, Gabbiani, Petrov (2005) [plus others]
Interpret X(3872) as a bound state of hadrons ( )
Analogous to the Deuteron!
Similar molecular state predicted long ago.
Beware: other interpretations possible.
00 KK
00 DD
Y(3940)
2/d.o.f. = 15.6/8
stat. sig. = 8.1
above D*D threshold
not found in DD or
D*D final states
Is Y(3940) a ‘Hybrid’?
Hybrid Meson : Color-octet quark-antiquark couples to
color-octet gluon to yield color-singlet hadron
G
]q[C
D0 K- +
Where are CP Violations?
New Physics and Charm
• Methodology?
• Rare Decays of D Mesons
• Flavor Oscillations
• CP Violations (not discussed here)
Methodology
How to find ‘New Physics’?
Study systems where SM signals are small. Ideal
forcharm:
A] Rare Decays
B] Flavor Oscillations
D0 + - in the SM
Data and D0 + -
D0 0 e+ e-
Flavor Oscillations
Mixing
Mixing also in K0,Bd and Bs.
Each of these is different!
00 DD
Two Coupled Penduli
The ‘Spring’
New Physics and Mixing
The Normal Modes
Normal Modes
Effect of CP:
2/]D[DD 00
00 D|D|CP
D|D|CP
Mixing of Bd Mesons
Mixing of Bs Mesons
Mixing of K Mesons
Mixing of D0 Mesons
Recent Work on D0 Mixing
Theory:Effect of QCD incorporated
intoanalysis of D0 mixing by
Golowichand Petrov. Work continues.
Experiment;Especially interesting are
attemptsto measure D at the 1%
level.
Summary I
• The c-quark is a remarkably spry 31 year old!
• A very active social life: Spectroscopy Flavor oscillations Rare decays CP violation searches
• After studies at CDF, CLEO, Belle and BaBar will come the long awaited LHC.
Summary II
• Flavor mixing of D mesons will be a hot topic for both experimenters and theorists.
• Exotic charm states (hybrid and/or molecular) will continue to attract much attention.