Overview of the CLEO experiment

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Leptonic Charm Decays at CLEO

• Overview of the CLEO experiment
• D and DS leptonic decays to ?? and ??
• Measurements of absolute branching fractions
• Measurements of absolute decay constants
• Comparison with theory (LQCD)

Victor Pavlunin on behalf of the CLEO
collaboration DPF-2006
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The CLEO detector

• The CLEO detector was developed for B physics at
  the Y(4S). CLEO-III configuration
• B-field 1.5 T
• Gas (drift chamber) He and C3H8
• Tracking 93 of 4?, ?P/P?0.6 for a 1.0 GeV
  track
• Hadron particle ID RICH (80 of 4?) and dE/dx
• E/M crystal calorimeter 93 of 4p, ?E/E ? 2.0
  (4.0) for a 1.0 GeV (100 MeV) photon
• Muon prop. chambers at 3, 5 and 7 ?I .
• Transition from CLEO III to CLEO-c
• B-field 1.5 T ? 1.0 T
• Silicon vertex detector ? low mass stereo drift
  chamber
• Advantages of running at the ?(3770) for charm
  physics
• Pure DD, no additional particles
• ?DD at ?(3770) 6.4 nb ?(cc) at Y(4S) 1.3
  nb
• Low mulitplicity, high tagging efficiency (gt20)

6-layer all-stereo
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Why a Charm Factory?

• The main task of the CLEO-c open charm program
• Calibrate and Validate Lattice
  QCD
• Help heavy flavor physics constrain the CKM
  matrix now
• Precision tests of the Standard Model or
• Discovery of new physics beyond the SM
• in b or c quark decays
• Difficulty hadronic uncertainties complicate
  the
• interpretation of exp. results
  

Reduce theory error on B form factors and B decay
constants using tested LQCD
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Examples of LQCD tests and their impact

• Leptonic decays (D??? and Ds???)
• Semileptonic decays (D ? ?e?, D ? Ke? )
• Combination of leptonic and semileptonic decays

Lattice predicts fB/fD and fB/fBs with small
errors ? precise fD gives precise fB and Vtd
fD/fDs checks fB/fBs and allows precise
Vtd/Vts
The main topic of this talk
Test LCQD calculations of f(q2) in the D system
and apply them to the B system for Vub and
Vcb
The topic of the next CLEO talk
Test LQCD with no errors from CKM couplings
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CLEO-c Data Samples

• Results presented in this talk were obtained
  using the following data samples
• ?(3770) total luminosity 280 pb ?1
• ECM 4170 MeV total luminosity 200 pb?1
• CLEO scanned ECM 3.97 4.26 GeV
• Optimal energy for Ds physics
• ECM 4.170 GeV
• Dominant production mechanism
• Additional 120 pb-1 at ECM 4170 MeV already
  collected to be analyzed

DATA
Preliminary
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D(s) Leptonic Decays

• Standard Model predicts
• D decays
• Ds decays
• Use Vcd and Vcs to extract fD and fDs, and
  compare them to theory

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• D? ?? and D? ?? at the ?(3770)
• References

PRL 95, 25801 (2005) PRD 73, 112005 (2006)
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Tagging at the ?(3770)

• The ?(3770) is about 40 MeV above the DD pair
  threshold ( )
• Variables used in the tag reconstruction
• Leptonic decays are identified
• using missing mass squared

Tagging creates a beam of D mesons with known
momentum
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D?? Tags
Cut on ?E and fit MBC

DATA (280/pb) All 6 modes
Total number of tags 158.4 ? 0.5 (stat)??103
DATA (280/pb)
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D ? ?? and e?

• Full event reconstruction
• require a tag,
• require a muon cand. (ECCtrack lt 300 MeV),
• veto events with extra tracks and energy
• clusters gt 250 MeV.
• Results
• 50 D ? ?? candidates
• Estimated bckg 2.8 events
• The same analysis is repeated for D ? e?. No
  signal candidates are seen

DATA
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D ? ??

• Reconstruct D??? with ????
• B(???? ) 11 the same technique but two
  ?s complicate the analysis
• Consider two cases
• Case I ECCtrack lt 300 MeV (? and ?)
• Case II ECCtrack gt 300 MeV (mostly ?)
• No significant signal ??

DATA
DATA
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• DS??? and DS??? at ECM 4170 MeV
• References

CLEO CONF 06-17 hep-ex/0610026
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D?S Tags (1)
DATA (200/pb)

• Recall at ECM 4170 MeV
• DS decays to DS via emission of 150 MeV
  photon 95 of the time ? significant smearing
  of MBC
• Tag modes used in the analysis

Total number of tags from M(Ds) 19.2 ? 0.3
(stat)??103
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D?S Tags (2)

• To fully reconstruct the event, the photon must
  be detected. The missing mass squared can be used
  to obtain the number of tags

Total number of tags in the signal region of
MM2 11.9 ? 0.4 (stat) ? 0.5 (syst)??103
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DS ? ?? and ?(??)? (1)

• Full event reconstruction
• Require a tag and a ? from DS,
• Require one additional track,
• Veto events with ECC gt 300 MeV or extra
  tracks.
• Use MM2 to separate ??, ?(??)? and
  background
• Consider three cases
• Case I ECCtrack lt 300 MeV (accept
• 99 of muons and 60 of pions)
• Case II ECCtrack gt 300 MeV (accept
• 1 of muons and 40 of pions)
• Case III require an electron

Kinematical constraints are used to improve
resolution and remove multiple combinations
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DS ? ?? and ?(??)? (2)
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DS ? ?? and ?(??)? (3)

• DS? ?? (Case I, Reg.A)
• 64 signal candidates, 2.0 bkg events
• DS? ?? (Case I,Reg.BCase II)
• 36 signal candidates, 4.8 bkg events
• Use the SM B(??)/B(??) to average results
  above
• DS? e? (Case III)

Preliminary
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DS ? ?(e? ?)?

• Complimentary analysis
• DS ? ?? with ??e? ?.
• B(DS???)B(??e??)1.3 is large cf.
  B(DS?Xe?)8
• Analysis Technique
• Find e and DS?? tag (? from DS is not
  reconstructed, same tag modes)
• Veto events with extra tracks
• Extra energy in CC lt 400 MeV
• Results

Preliminary
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Comparison with theory

• Summary of CLEO-c results
• Unquenched LQCD PRL 95, 122002 (2005)

Weighted average syst. errors are mostly
uncorrelated
Preliminary
CLEO-c statistically limited
An example of theor. preditions
LQCD systematically limited
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Conclusions

• An important task of CLEO-c is to calibrate and
  validate LQCD.
• Charm leptonic decays provide particularly
  stringent tests.
• Current precision of CLEO-c and LQCD results is
  comparable. CLEO-c results are statistically
  limited LQCD results are limited by systematic
  uncertainties.
• Expect a three fold increase in the size of
  CLEO-c data sample and a complete suite of
  leptonic and semileptonic measurements in the
  next few years.
• On a longer time scale, BES III (China) should be
  able to improve CLEO-c results and further
  constrain the theory.

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• Additional Slides

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CESR and CLEO

• The CLEO experiment is located at the Cornell
  Electron Storage Ring (CESR), a symmetric ee-
  collider that operated in the region of the
  Upsilon resonances for over 20 years
• Max inst luminosity achieved 1.3?1033 cm-2s-1
• Total integrated luminosity at the Y(4S) 16
  fb-1
• Lots of important discoveries, e.g., Y(nS), b?s?,
  b?uW.
• In 2003, CLEO started running at the ?(3770),
  40 MeV above DD production threshold, and
  slightly higher energies for DS studies.
• Transition from CESR to CESR-c
• 12 wigglers are installed to increase synchrotron
  radiation/beam cooling
• Max luminosity achieved 7?1031 cm-2s-1

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Why a Charm Factory?

• The main task of the CLEO-c open charm program
• Calibrate and Validate Lattice
  QCD
• Help heavy flavor physics constrain the CKM
  matrix now
• Precision tests of the Standard Model or
• Discovery of new physics beyond the SM in b or c
  quark decays
• Difficulty hadronic uncertainties complicate
  interpretation of exp. results
• Help LHC search for and interpret new physics
  (future)

A realistic example using recent CKM status (new
Bs mixing results are not included)
Reduce theory error on B form factors and B decay
constants using tested LQCD
200 fb-1 at Babar/Belle
500 fb-1 at Babar/Belle
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Why now?

• C. Davies opened her talk in Lisbon at EPS-2005
  
• There has been a revolution in LQCD

LQCD demonstrated that it can reproduce a wide
range of mass differences and decay constants in
unquenched calculations. These were
postdictions.
NOW unquenched PRL 92, 022001 (2004)
BEFORE quenched
Testable predictions are now being made
for Decay constants fD and fB D and B
Semileptonic form factors
CLEO-c can test fD and D semileptonic form
factors
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Tagging at the ?(3770)

• The ?(3770) is about 40 MeV above the DD pair
  threshold ( )
• One of the two Ds is reconstructed in a hadronic
  tag mode (e.g., K? - ). Two key variables
• From the remaining tracks and showers the
  semileptonic decay is reconstructed (e.g., K?e?)
• U ? Emiss ? Pmiss is used to identify signal,
  where Emiss and Pmiss are the missing energy and
  momentum approximating the neutrino E and P.
  The signal peaks at zero in U.
• Full event reconstruction allows to measure any
  kinematic variable with no ambiguities and with
  high precision

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D?S Tags at 4170