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.