Heavy Quark

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Heavy Quark Leptons 2002
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Contents

• Why are we interested in charmed mesons
• leptonic decays ?
• semileptonic decays ?
• hadronic decays ?
• Whats new ?
• LEP (e e-) at Z ALEPH
• SLAC (e e-) B B pair production threshold
  BABAR
• CESR (e e-) at ?(4S) CLEO
• lt180gt GeV ? on fixed target FOCUS
• Whats next ?

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Why Charm Leptonic Decays
Cabibbo allowed Annihilation diagram
Easiest experimentally accessible heavy
meson decay Extract decay constant fDs
Standard Model predicts
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Why Charm Leptonic Decays
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Ds ? ??? from ALEPH
and Ds? ??
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Ds ? ??? from ALEPH Signal - Background
separation

• Get the maximum separation
• between signal and bkg by
• using Linear Discriminant Variables
• technique
• Find the best linear combination
• between a number of variables
• (mainly fitted PDs, angle between
• Pl and Phemi, btag neural net,
• Pt of lepton w.r.t. jet)
• and build
• Ub to separate signal from bb bkg
• Uc to separate signal from cc bkg

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Ds ? ??? from ALEPH 2D Fit for Ds???
Projecting the fit in each variable Contribution
from fitted signal
Muon channel
Uc
Same distributions after subtracting the fitted
bkg
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Ds ? ??? from ALEPH Main Systematics
Main source of uncertainty 21 on f(c?Ds)
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Ds ? ??? from ALEPH Results and comparisons
with other experiments
consistent Ds? ?? signals in e?? and ???
the worlds most accurate
Combined ?,e BR(Ds???) (5.790.771.84) fDs
(2731843) MeV
Combined fDs (2851940) MeV
Phys. Lett. B 528 (2002) 1-18
Lattice QCD ? fDs 240 30 - 25 MeV
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Why Charm Semileptonic Decays

• Semileptonic decays are easy
• to access experimentally
• Cabibbo allowed decays have
• large branching fractions

• Transition amplitudes proportional
• to the product of leptonic and
• hadronic currents
• Theoretical predictions of
• form factors for the hadronic
• current are not easy

• Precise experiment
• measurement needed to
• help theoretical progress

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D ? K0 l ? from CLEO
?m signal shape from MC (ISGW2)
Signal events
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D ? K0 l ? from CLEO
The 2 most precise measurements differ by about
3? Possible explanation ..different
modelling (ISGW2 vs WSB) investigated No
significant differences found ???!!

• Dominant systematic errors
• uncertainty on the ?m signal shape from MC
• (finite statistics)
• ?m background shape

D? K-?? used for normalization BR(D? K-??
)(9.0?0.6) (PDG)
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D ? (K-?) ? ? from FOCUS
Data collected in 96-97 _at_ Fermilab Fixed target
run lt180gt GeV ? on BeO
Well and old (20 years) established believing
the peak comes from K0 (892) only
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27178 right-sign events in the mass
window 0.8-1.0 GeV/c2
hep-ex/0203031 March 2002
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D ? (K-?) ? ? from FOCUS
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MC
MC
15 forward-backward asymmetry in cos?V below
the K0 pole
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D ? (K-?) ? ? from FOCUS
mo?
m0
mo-?
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Why Charm Hadronic Decays
Hadronic decays are rich of infos about QCD
Hadronic decays provide information on relative
strengths in decay diagrams (spectator, W
exchange, annihilation etc.)
Resonant analyses provide information on light
resonances. Not so easy in multi-body final
states
The charm sector is rich in hadronic decay modes
Deviation from naïve expectations leads to an
improved understanding of charm quark decay
dynamics and final state interaction
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Ds ? K0S K0S ?? from BaBar
?( ee- ? cc) 1.3 nb
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For 60 fb-1 this gives 80M charm pairs
150K tagged D
To compare with E791 ( 35.4K ) or FOCUS (120K)
Cutting on the P is very effective in reducing
the background
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Ds ? K0S K0S ?? from BaBar
Ds ? Ds ? tag
fj (1710)
K (892)
Studies have just begun Dalitz fits under way
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New hadronic decay modes
Many of these modes have never been observed
before
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Summary of new D meson modes and improved
Branching Ratios
First observations are shown in red
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Whats next ? Cleo-c Program
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Expectations from CLEO-c project fDq from
leptonic decays
fDq 2
? (Dq ? l ? ) ?
Vcq 2
MC
MC
l
?
Candidates /0.01 GeV2/c4
Candidates /0.01 GeV
KL??
Ds???
D???
M(?)2
M(?)2
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Expectations from CLEO-c project Semileptonic
decays
VCKM2
D0? ?l?
D0? ?-e?
f(q2)2
D0? Kl?
MC 1 fb-1
? BR(D? ? l ?) /?D ? Vcq 2
d? (D? ? l ?) / dq2 Vcq 2 f(q2)2
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Expectations from CLEO-c project Hadronic decays
Absolute Branching Ratios
Almost zero background in hadronic modes
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Conclusions
. Plenty of new interesting results still to
come
Many thanks to Steve Wasserbaech
David Williams Thomas Coan David
Cinabro Stefano Bianco for the help they
gave me in collecting the material used in this
talk.