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Leptonic & Semi-Leptonic Charm Decays

Leptonic & Semi-Leptonic Charm Decays. Sheldon Stone, Syracuse University. Need f Bs /f B from theory. Measure f D + /f Ds. h. r. What We Hope to Learn. Purely Leptonic Charm Decays D → l + n Check QCD calculations including Lattice (LQCD) Look for New Physics

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Leptonic & Semi-Leptonic Charm Decays

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  1. Leptonic & Semi-Leptonic Charm Decays Sheldon Stone, Syracuse University CKM 2006 Workshop, Nagoya, Japan, Dec. 12-16, 2006

  2. Need fBs/fB from theory. Measure fD+/fDs h r What We Hope to Learn • Purely Leptonic Charm Decays D→l+n • Check QCD calculations including Lattice (LQCD) • Look for New Physics • Semileptonic decay rates & form-factors • QCD checks • Use QCD to extract Vcq (See talk of M. Artuso) • Use dG/dq2 in conjunction with B decay rates to extract Vub. • Use Dpln to get form-factor for Bpln, at same v•v point using HQET (& rln) • Use Brln, BK*l+l-, along with Drln & DK*ln at the appropriate q2 • Due to lack of time, many interesting results are omitted S. Stone (Syracuse) CKM 2006 Workshop, Dec. 12-16, 2006

  3. Experimental methods • DD production at threshold: used by Mark III, and more recently by CLEO-c and BES-II. • Unique event properties • Only DD not DDx produced • Large cross sections at y(3770): s(DoDo) = 3.720.09 nbs(D+D-) = 2.820.09 nb • Ease of B measurements using "double tags:“ BA = # of A/# of D's • At y(3770) CLEO-c uses beam constrained mass • At 4170 MeV, invariant mass with energy cut World Ave • At Y(4S) s(charm) ~ 1 nb  s(DS) ~ 0.15 nb S. Stone (Syracuse) CKM 2006 Workshop, Dec. 12-16, 2006

  4. In general for all pseudoscalars: Calculate, or measure if VQq is known Leptonic Decays: D(s)+n Introduction: Pseudoscalar decay constants c and q can annihilate, probability is  to wave function overlap Example : _ or cs (s) S. Stone (Syracuse) CKM 2006 Workshop, Dec. 12-16, 2006

  5. New Physics Possibilities • Another Gauge Boson could mediate decay • Ratio of leptonic decays could be modified (e.g.) See Hewett [hep-ph/9505246] & Hou, PRD 48, 2342 (1993). S. Stone (Syracuse) CKM 2006 Workshop, Dec. 12-16, 2006

  6. r From Akeroyd New Physics Possibilities II • Leptonic decay rate is modified by H+ • Can calculate in MSSM. Is  mq/mc, so negligible for D+ but not for DS (mS/mc) • Leptonic decay for DS gets modified by factor of • or where R=tanb/mH See Akeryod [hep-ph/0308260] S. Stone (Syracuse) CKM 2006 Workshop, Dec. 12-16, 2006

  7. Old CLEO Measurements of fDs • Detected g & m from DS*→ g DS → m+n decay • Used missing energy & momentum in half of the event, to estimate n 4-vector. Event half determined using thrust axis • Correct n 4-vector to get right DS mass value • Measured real m background by doing same analysis on DS*→ g DS → e+n • Used D*o→ g, Do → K-(p+) to measure efficiencies, etc… • Used 4.8 fb-1 at or near Y(4S)(M. Chadha et al. Phys. Rev. D58, 32002 (1998)) S. Stone (Syracuse) CKM 2006 Workshop, Dec. 12-16, 2006

  8. New BABAR Measurements of fDs • Similar analysis to CLEO [1) detect g & m, 3) correct P4n, 4) use gen for backgrounds, 5) use D*o → g K-(p+)], but much improved because they use only events: e+e-→“D” x DS*-, where the “D” is a fully reconstructed Do, D+ or D*+(B. Aubert et al [hep-ex/0607094]) • This gives much better S/B and also missing energy resolution • Use 230 fb-1 S. Stone (Syracuse) CKM 2006 Workshop, Dec. 12-16, 2006

  9. New CLEO-c Measurement of DS+→m+n • In this analysis CLEO uses DS*DS events where they detect the g from the DS*→ g DS decay • They see all the particles from e+e- → DS*DS, g,DS (tag) + m+ except for the n • A kinematic fit is used to (a) improve the resolution & (b) remove ambiguities • Constraints include: total p & E, tag DS mass, Dm=M(gDS)-M(DS) [or Dm= M(gmn)-M(mn)] = 143.6 MeV, E of DS (or DS*) fixed • Lowest c2 solution in each event is kept • No c2 cut is applied S. Stone (Syracuse) CKM 2006 Workshop, Dec. 12-16, 2006

  10. Invariant masses hp+ K-K+p+ KsK+ hp+ f r+ hr+ p-p+p+ K*K* from KsK-p+p+ Inv Mass (GeV) Total # of Tags = 19185±325(stat) S. Stone (Syracuse) CKM 2006 Workshop, Dec. 12-16, 2006

  11. Tag Sample using g • First define the tag sample by computing the MM*2 off of a g & DS tag • Total of 11880±399±504 tags, after the selection on MM*2 Data All 8 Modes S. Stone (Syracuse) CKM 2006 Workshop, Dec. 12-16, 2006

  12. The MM2 (From Simulation) • To find the signal events, compute Signal tn, t→pn Signal mn S. Stone (Syracuse) CKM 2006 Workshop, Dec. 12-16, 2006

  13. MM2 Results from 200 pb-1 • Clear DS+→m+n signal for case (i) • Events <0.2 GeV2 are mostly DS→t+n, t→p+n in cases (i) & (ii) • No DS→e+n seen, case (iii) • 6 DS→t+n, t→p+n in case (i) m+n peak 64 events DATA 200/pb <0.3GeV in CC Case (i) accepts 99% of m+, 60% p+ & K+ 24 events accepts 1% of m+, 40% p+ & K+ DATA 200/pb >0.3GeV in CC Case (ii) 12 events Electron Sample S. Stone (Syracuse) CKM 2006 Workshop, Dec. 12-16, 2006

  14. Sum of DS+→m+n + t+n, t→p+n • Two sources of background • A) Backgrounds under invariant mass peaks – Use sidebands to estimate • Inm+n signal region 2 background (64 signal) • Sideband bkgrnd 5.5±1.9 • B) Backgrounds from real DS decays, e.g. p+popo, or DS→ t+n, t→p+pon.... < 0.2 GeV2, none in mn signal region. Total of 1.3 additional events. • B(DS→p+po) < 1.1x10-3 & g energy cut yields <0.1 evts • Total background < 0.2 GeV2 is 6.8 events, out of the 100 Sum of case (i) & case (ii) mn +tn signal line shape K0p+ 100 events S. Stone (Syracuse) CKM 2006 Workshop, Dec. 12-16, 2006

  15. Branching Ratio & Decay Constant • DS+→m+n • 64signal events, 2 background, use SM to calculate tn yield near 0 MM2 based on known tn/mn ratio • B(DS+→m+n) = (0.657±0.090±0.028)% • DS+→t+n, t+ →p+n • Sum case (i) 0.2 > MM2 > 0.05 GeV2 & case (ii) MM2 < 0.2 GeV2. Total of 36 signal and 4.8 bkgrnd • B(DS+→t+n) = (7.1±1.4±0.3)% • By summing both cases above, find Beff(DS+→m+n) = (0.664±0.076±0.028)% • fDs=282 ± 16 ± 7 MeV • B(DS+→e+n)< 3.1x10-4 Preliminary S. Stone (Syracuse) CKM 2006 Workshop, Dec. 12-16, 2006

  16. Measuring DS+→t+n, t+→e+nn • B(DS+→t+n)B(t+→e+nn)~1.3%is “large” compared with expected B(DS+→Xe+n)~8% • Technique is to find • events with an e+ opposite • DS- tags & no other tracks, • with  calorimeter energy < 400 MeV • No need to find g from DS* • B(DS+→t+n) • =(6.29±0.78±0.52)% • fDs=278 ± 17 ± 12 MeV 400 MeV Xe+n Preliminary S. Stone (Syracuse) CKM 2006 Workshop, Dec. 12-16, 2006

  17. D+→m+n m+n K0p+ & • Weighted Average: fDs=280.1±11.6±6.0 MeV, the systematic error is mostly uncorrelated between the measurements (More data is on the way) • Previously CLEO-c measured M. Artuso et al., Phys .Rev. Lett. 95 (2005) 251801 • Thus fDs/fD+=1.26±0.11±0.03 Preliminary S. Stone (Syracuse) CKM 2006 Workshop, Dec. 12-16, 2006

  18. Comparisons with Theory • We are consistent with most models, more precision needed • Using Lattice ratio find |Vcd/Vcs|= 0.22±0.03 1993 S. Stone (Syracuse) CKM 2006 Workshop, Dec. 12-16, 2006

  19. Comparison with Previous Experiments • Difficult to average without a clear measurement of B(DS→fp+). In any case CLEO-c result dominates 280.1±11.6±6.0 ? -2 ? -2 3.6±0.9 248 ± 15 ± 6 ± 31 S. Stone (Syracuse) CKM 2006 Workshop, Dec. 12-16, 2006

  20. Limits on New Physics • Lepton Universality • G(DS+→t+n)/G(DS+→m+n) = 9.9±1.7±0.7 SM = 9.72 • G(D+→t+n)/G(D+→m+n) < 4.77 (90% cl) SM = 2.65 • Limits on charged Higgs • According to Akeryod • Unquenched Lattice: fDs=249±3±16 MeV • Our result:280.1±11.6±6.0 MeV • Take ms/mc=0.076 (PDG) • Then the ratio of our result/SM gives >1, NP<1 S. Stone (Syracuse) CKM 2006 Workshop, Dec. 12-16, 2006

  21. Limits on Charged Higgs Mass • Can set limits in the tanb - mH± plane • Competitive with CDF • But depends on Lattice Model. Don’t take seriously yet Summary of the 95% CL exclusions obtained by LEP & CDF. The full lines indicate the SM expectation (no H±signal) and the horizontal hatching represents the ±1sbands about the SM expectation. S. Stone (Syracuse) CKM 2006 Workshop, Dec. 12-16, 2006

  22. Exclusive Semileptonic Decays VQiQf • Best way to determine magnitudes of CKM elements, in principle is to use semileptonic decays. Decay rate |VQiQf|2 • Kinematics: • Matrix element in terms of form-factors (for DPseudoscalar l+n • For l = e, f-(q2)0: S. Stone (Syracuse) CKM 2006 Workshop, Dec. 12-16, 2006

  23. Hill & Becher, Phys. Lett. B 633, 61 (2006) Form-Factor Parameterizations • In general • Modified Pole • Series Expansion S. Stone (Syracuse) CKM 2006 Workshop, Dec. 12-16, 2006

  24. 69928 679684 291055 29520 U = Emiss– |Pmiss| (GeV) CLEO-c Exclusive Decays (281 pb-1) • Both Tagged results & untagged using n reconstruction • n reconstruction has larger statistics but larger systematic errors Samples overlap, so choose only one result 14397132 134749 584688 45029 Beam Constrained mass using Emiss & Pmiss to find n S. Stone (Syracuse) CKM 2006 Workshop, Dec. 12-16, 2006

  25. Exclusive Branching Ratio Summary Do → K- e+ ν • Theory needs to catch up Do → π- e+ ν (2006) (2006) preliminary preliminary preliminary preliminary S. Stone (Syracuse) CKM 2006 Workshop, Dec. 12-16, 2006

  26. Belle . . Belle CLEO-c Form-Factors Compared to Lattice Assume Vcs = 0.9745 Lattice predictions* DKen f+(0)=0.73±0.03±0.07 • a=0.50±0.04±0.07 Dpen f+(0)=0.64±0.03±0.06 • a=0.44±0.04±0.07 *C. Aubin et al., PRL 94 011601 (2005) LQCD DATA FIT (tagged) CLEO-c Assume Vcd = 0.2238 CLEO-c LQCD DATA FIT (tagged) S. Stone (Syracuse) CKM 2006 Workshop, Dec. 12-16, 2006

  27. Unquenched LQCDQuenched LQCDSimple pole model Belle & FOCUS Kℓn ~2.5k signal events DoKℓn Belle pℓn LQCD: Aubin et al., PRL94, 011601(2005) 232 signal events Other Form-Factor Measurements BELLE: PRL 97, 061804 (2006) [hep-ex/0604049] • CLEO-c & Belle somewhat disagree with LQCD, Belle c2 28/18 (K) & 9.8/5 (p) (hep-ex/0607077) q2 (GeV2) S. Stone (Syracuse) CKM 2006 Workshop, Dec. 12-16, 2006

  28. Pseudoscalar Form Factors D→K e+n D→ p e+n S. Stone (Syracuse) CKM 2006 Workshop, Dec. 12-16, 2006

  29. Drn Form Factors (CLEO-c) • Can be used to detemine Vub along with Brn, DK*n & BK*+- (See Grinstein & Pirjol [hep-ph/0404250]) D+ro-n cos  Rv = 1.40  0.25  0.03, R2 = 0.57  0.18  0.06 B(D0 -e+)= (1.560.160.09)10-3 B(D+ 0e+)= (2.320.200.12)10-3 q2 Dor+-n cos e  Preliminary Line is projection for fitted RV, R2 S. Stone (Syracuse) CKM 2006 Workshop, Dec. 12-16, 2006 U = Emiss– |Pmiss| (GeV)

  30. CLEO-c Discovery of Do→Kpp e+n • B(Do→K1(1270)e+n)*B(K1(1270) →K-p+p-) = consistent with ISGW2 prediction Preliminary S. Stone (Syracuse) CKM 2006 Workshop, Dec. 12-16, 2006

  31. Conclusions • not preliminary • fDs=280.1±11.6±6.0 MeVpreliminary • fDs/fD+=1.26±0.11±0.03 preliminary • No violation of Lepton Universality observed • Accurate semi-leptonic form-factors confronting LQCD & perhaps indicating deviations • Much much more to do S. Stone (Syracuse) CKM 2006 Workshop, Dec. 12-16, 2006

  32. The End CKM 2006 Workshop, Nagoya, Japan, Dec. 12-16, 2006

  33. Untagged: Form-Factor Results Simp. Pole Mod. Pole S. Stone (Syracuse) CKM 2006 Workshop, Dec. 12-16, 2006

  34. D  p/Ken: Which Form Factor Parameterization? CLEO preliminary All these models describe the data pretty well (except when forcing pole mass to nominal value in pole model). S. Stone (Syracuse) CKM 2006 Workshop, Dec. 12-16, 2006

  35. Compare with Limits from Belle tn Belle: assumes fB and |Vub | are known, take the ratio to the SM BF. Excluded by CLEO-c 95% CL rB=1.130.51 But taking no theoretical error is abhorrent S. Stone (Syracuse) CKM 2006 Workshop, Dec. 12-16, 2006

  36. h r Goals in Leptonic Decays • fB & fBs/fB needed to improve constraints from Dmd & DmS/Dmd. Hard to measure directly (i.e. B t+n measures VubfB ),but we can determine fD+& fDs using Dl+n and use them to test theoretical models (i.e. Lattice QCD) Constraints from Vub, Dmd, Dms & B t+n S. Stone (Syracuse) CKM 2006 Workshop, Dec. 12-16, 2006

  37. New CLEO-c Measurements of fDs • Two separate techniques • (1) Measure DS+→m+n along with DS→t+n, t→p+n. This requires finding a DS- tag, a g from either Ds*-→g Ds- or Ds*+→g m+n. Then finding the muon or pion using kinematical constraints • (2) Find DS+→t+n, t→e+nn opposite a Ds- tag S. Stone (Syracuse) CKM 2006 Workshop, Dec. 12-16, 2006

  38. Comparisons with Theory • We are consistent with most models, more precision needed CLEO-c +2.8 -3.4 280.1±11.6±6.0 222.6±16.7 1.26±0.11±0.03 S. Stone (Syracuse) CKM 2006 Workshop, Dec. 12-16, 2006

  39. CLEO-c Untagged DK(or p) e n S. Stone (Syracuse) CKM 2006 Workshop, Dec. 12-16, 2006

  40. Define Three Classes • Class (i), single track deposits < 300 MeV in calorimeter (consistent with m) & no other g > 300 MeV. (accepts 99% of muons and 60% of kaons & pions) • Class (ii), single track deposits > 300 MeV in calorimeter & no other g > 300 MeV (accepts 1% of muons and 40% of kaons & pions) • Class (iii) single track consistent with electron & no other g > 300 MeV S. Stone (Syracuse) CKM 2006 Workshop, Dec. 12-16, 2006

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