Overview of the CLEO experiment D and D S leptonic decays to  and  :

1. 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

2. The CLEO detector An event taken at the Y(4S) • 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 4π, 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) forcharm physics: • Pure DD, no additional particles • [DD at (3770)] = 6.4 nb [(cc) at Y(4S) ~1.3 nb] • Low mulitplicity, high tagging efficiency (>20%) 6-layer all-stereo

3. 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: • Help LHC search for and interpret new physics if new physics is strongly coupled in the future Reduce theory error on B form factors and B decay constants using tested LQCD

4. Examples of LQCD tests and their impact |VCKM|2 |fD|2 Known to  1% from the CKM unitarity LQCD Experiment l D n |VCKM|2 l D n |f(q2)|2 p ( K ) Bd Bd • 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/fBsand 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

5. 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

6. 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

7. D+  and D+  at the (3770) References: PRL 95, 25801 (2005) PRD 73, 112005 (2006)

8. 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 abeam of D mesonswith known momentum

9. 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)

10. D+  +ande+ • Full event reconstruction: • require a tag, • require a muon cand. (ECCtrack< 300 MeV), • veto events with extra tracks and energy clusters > 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

11. D+  + Case I: ECCtrack< 300 MeV Sign. Candidates: 12 Est. Background: 6.1 Broad MM2 Case II: ECCtrack> 300 MeV Sign. Candidates: 8 Est. Background: 5.0 • Reconstruct D++ with ++ [B(++ ) ~11%]; the same technique but two ’s complicate the analysis: • Consider two cases: • Case I: ECCtrack < 300 MeV ( and ) • Case II: ECCtrack > 300 MeV (mostly ) • No significant signal  DATA DATA

12. DS and DS at ECM = 4170 MeV References: CLEO CONF 06-17 hep-ex/0610026

13. DS Tags (1) Yields from M(Ds) 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

14. DS Tags (2) DATA All 8 Modes • 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 MM*2: [11.9  0.4 (stat)  0.5 (syst)]103

15. DS +and+(+) (1) Signal region 64 events ECCtrack < 300MeV Case I: region A Mostly DS + 24 events region B DATA Mostly DS + Case II ECCtrack > 300MeV 12 events DATA Electron Sample Case III • Full event reconstruction: • Require a tag and a  from DS*, • Require one additional track, • Veto events with ECC > 300 MeV or extra tracks. • Use MM2 to separate +, +(+) and background: • Consider three cases: • Case I: ECCtrack < 300 MeV (accept 99% of muons and 60% of pions) • Case II: ECCtrack > 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]

16. DS +and+(+) (2) MC MC + + MM2 MM2 Note the scale limits: 0.20 and 0.80 GeV2 Sum of Case I and Case II DATA mn +tn signal line shape K0p+ 100 events Consistency Check

17. DS +and+(+) (3) Signal region 64 events ECCtrack < 300MeV Case I: region A Mostly DS + 24 events region B DATA Mostly DS + Case II ECCtrack > 300MeV 12 events DATA Electron Sample Case III • DS + (Case I, Reg.A) 64 signal candidates, 2.0 bkg events: • DS + (Case I,Reg.B+Case II) 36 signal candidates, 4.8 bkg events: • Use the SM B(+)/B(+) to average results above: • DS e+ (Case III): No signal candidates: Preliminary

18. DS +(e+ ) 400 MeV Xe+n • 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 < 400 MeV • Results: Preliminary

19. 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

20. 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.

21. Additional Slides

22. CESR and CLEO ~16 fb-1 at the Y(4S) Over 20 years operated at the Y(4S) Data taking started in the fall of 2003 Note: Log Scale • The CLEO experiment is located at the Cornell Electron Storage Ring (CESR), a symmetric e+e-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

23. 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

24. 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 predictionsare 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

25. Tagging at the (3770) (3770)D0D0 D0K+-, D0K-e+  K- K+  - e+ • The (3770) is about 40 MeV above the DD pair threshold ( ) • One of the two D’s 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

26. DS Tags at 4170 MC: DS  