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Introduction: D   + n

D Leptonic Decays near Production Threshold Steven Blusk Syracuse University (on behalf of the CLEO Collaboration). Introduction: D   + n. or cs. (s). Partial width measurement probes the hadronic vertex Soft-gluon effects  Non-perturbative QCD

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Introduction: D   + n

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  1. D Leptonic Decays nearProduction ThresholdSteven BluskSyracuse University(on behalf of the CLEO Collaboration) CHARM 2007, Cornell University, Aug. 5-8, 2007

  2. Introduction: D +n or cs (s) • Partial width measurement probes the hadronic vertex • Soft-gluon effects  Non-perturbative QCD • Decay constant, fDdescribes the hadronic vertex, and is proportional to the wave-function overlap (Prob  cd(s)W annihilation) • General solution (SM) for partial width _ Calculate, or measure if VQq known CHARM 2007, Cornell University, Aug. 5-8, 2007

  3. Leptonic Decays in SM • Measurement provides critical test of theory to compute fB, fBs. • In a few years, we will have a precision measurement (~5o)of g(f3) by LHCb. • Expect s(g)~5owith 2 fb-1 • Could provide signsof NP if g measurementdoesn’t coincide withDm(s,d) band. • B t+n gives VubfB, buthard to measure directly. Constraints from Vub, Dmd, Dms & B t+n CHARM 2007, Cornell University, Aug. 5-8, 2007

  4. New Physics in D(s) leptonic decays • Interference between H± and W± suppresses Dsln, but NOT Dln Akeroyd, hep-ph/0308260 • Deviations from lepton universality possible if tanb large Hewett [hep-ph/9505246] & Hou, PRD 48, 2342 (1993). Deviations of this ratio from SM value of 9.72 would signal New Physics CHARM 2007, Cornell University, Aug. 5-8, 2007

  5. D and Ds Landscape near threshold • Produce DD at y(3770). • No additional particles • Coherent 1– state • Ideal for absolute BF measurements • Measurements from 281 pb-1(Phys. Rev. Lett. 95, 251801 (2005)) • Not reviewed in this talk • Ds Leptonic Decays • Dedicated scan to find optimal energyfor Ds physics (see talk by B. Lang) • At Ecm = 4170 MeV s(DsDs*)~0.9 nb • Additional photon, ~100 MeV to contend with. CHARM 2007, Cornell University, Aug. 5-8, 2007

  6. Reconstructed Ds “Tags” at 4170 MeV • Leptonic analyses requireone fully reconstructed Dsdecay (“tag”). • 8 tag modes • Signal region: • |Mrec-MDs| < 2.5 s • Sidebands: • 5.0<|Mrec-MDs| < 7.5 s • Total # of Tags = 31,302 ± 472 (stat) K*K* from KsK-p+p+ CHARM 2007, Cornell University, Aug. 5-8, 2007

  7. Measurements of fDs “Missing Energy” Analysis (195 pb-1) Preliminary “Missing Mass” Analyses (314 pb-1) Accepted to PRD arXiv:0704.0437v2 Ds(m,t)n from Ds Ds(m,t)n from Ds* g Dtag Dtag Ds Dtag e- Ds* e+ Ds e- e+ e- e+ Ds Ds Ds tenn n g m or tpn n m or tpn n g • Only one additional track, consistentwith electron hypothesis • Signal discriminant: Remaining energy in calorimeter after tag and electron are removed. • Only one additional track, K± rejection using PID • No additional g with E>300 MeV • Use (missing) mass recoiling against (Ds*+m) CHARM 2007, Cornell University, Aug. 5-8, 2007

  8. Anatomy of Missing Mass Analyses Ds(m,t)n from Ds Ds(m,t)n from Ds* g Dtag Dtag Ds* Ds e- e+ e- e+ Ds Ds m (or tpn) m (or tpn) n n g CHARM 2007, Cornell University, Aug. 5-8, 2007

  9. Ds(m,t)n from Ds* Ds(m,t)n from Ds g Dtag Dtag Ds* Ds* e- e- e+ e+ Ds Ds All 8 Modes All 8 Modes m (or tpn) m (or tpn) g n n Missing Mass Analyses – Ntag* • Take each Ds tag and photon candidate and compute the recoil mass against (Dstag+g). regardless of whether Ds+g forms Ds*, recoil mass peaks at M(Ds)2 • Ntag*= 18645±426(stat) tags, after 2.5s selection on MM*2. All 8 modes combined CHARM 2007, Cornell University, Aug. 5-8, 2007

  10. Missing Mass Analyses – Signal Side Ds(m,t)n from Ds* Ds(m,t)n from Ds g Dtag Dtag For each Ds* candidate, perform a kinematic fit,imposing the following constraints: Ds* Ds* e- e- e+ e+ • Two solutions for each Ds* candidate • g belongs with Ds tag • g belongs with Dsmn(try both) Ds Ds All 8 Modes All 8 Modes m (or tpn) m (or tpn) g n n CHARM 2007, Cornell University, Aug. 5-8, 2007

  11. Missing Mass Analyses – Signal Side Ds(m,t)n from Ds* Ds(m,t)n from Ds g Dtag Dtag For each Ds* candidate, perform a kinematic fit,imposing the following constraints: Ds* Ds* e- e- e+ e+ • Two possibilities for each Ds* candidate • g belongs with Ds tag • g belongs with Dsmn(try both) Ds Ds All 8 Modes All 8 Modes m (or tpn) m (or tpn) g n n Signal Dsmn Signal Dstn, t→pn Choose solution with lowest c2(but no cut), and compute: Signal MC CHARM 2007, Cornell University, Aug. 5-8, 2007

  12. MM2 from CLEO-c Data EtrkCC < 0.3 GeV in CC Return to 3 separate cases: • EtrkCC<300 MeV • “Dmn-like”: (e~99%)-0.05<MM2<0.05 GeV2 • “Dtn(tpn)-like”:(e~60%)0.05<MM2<0.20 GeV2 • EtrkCC>300 MeV • “Dtn(tpn)-like”:(e~40%)-0.05<MM2<0.20 GeV2 • Electron-like 92 events 31 events EtrkCC > 0.3 GeV in CC 25 events Electron Sample CHARM 2007, Cornell University, Aug. 5-8, 2007

  13. Backgrounds • Combinatoric background under peaks:Use Ds cand. mass sidebands • Dstn backgrounds from real DS decays Signal region Low SB region High SB region Negligible real Ds decay background to Dsmn Since B(Ds p+p0) <1.1x10-3 @ 90% CL CHARM 2007, Cornell University, Aug. 5-8, 2007

  14. Branching fractions B(DS+→m+n) • Ntag =18645±426±1081 • = efficiency for reconstructing m+/p+ = 80.1% • m = efficiency for ECC<300 MeV + |MM2|<50 MeV = 91.4% • t = efficiency for ECC<300 MeV(60%) + |MM2|<50 MeV(13%) = 13.2% Nmn = 92 – (3.5±1.4) = 88.5±9.7 B(DS+→m+n) = (0.597±0.067±0.039)% B(DS+→t+n) B(DS+→t+n) = (8.0±1.3±0.4)% CHARM 2007, Cornell University, Aug. 5-8, 2007

  15. Combined fDs Combine (i) and (ii). (still applies) • m = 91.4% • t = 45.2% Nmn = 148 – (10.7+2.9-2.3) Results Signalregion • Beff(DS+→m+n) = (0.638±0.059±0.033)% • fDs= 274 ± 13 ± 7 MeV • B(DS+→e+n) < 1.3x10-4 @90%CL CHARM 2007, Cornell University, Aug. 5-8, 2007

  16. Missing Energy AnalysisDS+→t+n, t+→e+nn • Use 195 pb-1 at Ecm=4170 MeV • Reconstruct Ds tag, use recoil from Ds to get N(DsDs*) • Require one extra electron candidate + no other tracks. • No need to find g from DS* • Main backgrounds from DS+→Xe+n ~ 8% • Discriminant is ECCextra: extra energy in CCleft over after showers associated to reconstructed particles are removed. • Signal region: ECCextra< 400 MeV • Background obtained by scaling MC • B(DS+→t+n)=(6.29±0.78±0.52)% • fDs= 278 ± 17 ± 12 MeV (Preliminary) Xe+n CHARM 2007, Cornell University, Aug. 5-8, 2007

  17. Weighted Average: fDs=275±10±5 MeV, the (systematic errors are mostly uncorrelated between the measurements) Previously CLEO-c measured M. Artuso et al., Phys .Rev. Lett. 95 (2005) 251801 Thus fDs/fD+=1.24±0.10±0.03 G(DS+→t+n)/G (DS+→m+n)= 11.5±2.0, SM=9.72, consistent with lepton universality Combined results D+→m+n 281 pb-1at y(3770) K0p+ m+n CHARM 2007, Cornell University, Aug. 5-8, 2007

  18. Comparisons with theoretical expectations • CLEO-c data consistent with most models, more precision needed • Using Lattice ratio find |Vcd/Vcs|=0.2166±0.020 (exp) ±0.0017(theory) CHARM 2007, Cornell University, Aug. 5-8, 2007

  19. 275±10±5 -2 -2 Comparison to previous measurements • CLEO-c is most precise result to date for both fDs & fD+ CHARM 2007, Cornell University, Aug. 5-8, 2007

  20. Summary • Decay constants from CLEO-c are most precise to date • Expect to reach a precision of ~4.0-4.5% onthese decay constants with full CLEO-c (through Apr 2008). CHARM 2007, Cornell University, Aug. 5-8, 2007

  21. Backups CHARM 2007, Cornell University, Aug. 5-8, 2007

  22. Missing Mass Distributions - MC Check of resolution, procedure using DsKsK- Remove extra track/shower/K± veto • MC resolution consistent w/ data • Find BF=(2.90±0.19±0.18)%, Result from double tags: (3.12±0.16±0.10)% • This background is wiped out by the PID requirement on the stiff m/p. CHARM 2007, Cornell University, Aug. 5-8, 2007

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