CLEO-c Measurement of the Pseudoscalar Decay Constant f Ds & the Ratio f Ds / f D +

CLEO-c Measurement of the Pseudoscalar Decay Constant fDs & the Ratio fDs/ fD+ Sheldon Stone, Syracuse University

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) ICHEP Moscow, July 26 – Aug. 2, 2006

Goals in Leptonic Decays • Test theoretical calculations in strongly coupled theories in non-perturbative regime • 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) h r Constraints from Vub, Dmd, Dms & B t+n ICHEP Moscow, July 26 – Aug. 2, 2006

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: s(DoDo) = 3.720.09 nbs(D+D-) = 2.820.09 nb s(DSDS*) = ~0.9 nb Continuum ~14 nb • Ease of B measurements using "double tags“ • BA = # of A/# of D's World Ave ICHEP Moscow, July 26 – Aug. 2, 2006

CLEO DS+ Results at 4170 MeV • Since e+e-DS*DS, the DS from the DS* will be smeared in beam-constrained mass. • cut on MBC & plot invariant mass (equivalent to a p cut) • We use ~200 pb-1 of data Signal MC MBC MBC from DS* Beam Constrained Mass (GeV) ICHEP Moscow, July 26 – Aug. 2, 2006

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 = 19,185±325(stat) ICHEP Moscow, July 26 – Aug. 2, 2006

New 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 ICHEP Moscow, July 26 – Aug. 2, 2006

Measurement of DS+→m+n • In this analysis we use DS*DS events where we detect the g from the DS*→ g DS decay • We see all the particles from e+e- → DS*DS, g,DS (tag) + m+ except for the n • We use a kinematic fit 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 ICHEP Moscow, July 26 – Aug. 2, 2006

Tag Sample using g • First we define the tag sample by computing the MM*2 off of the g & DS tag • Total of 11880±399±504 tags, after the selection on MM*2. Data All 8 Modes ICHEP Moscow, July 26 – Aug. 2, 2006

The MM2 • To find the signal events, we compute Signal tn, t→pn Signal mn ICHEP Moscow, July 26 – Aug. 2, 2006

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 ICHEP Moscow, July 26 – Aug. 2, 2006

MM2 Results from 200 pb-1 • Clear DS+→m+n signal for case (i) • Will show that events <0.2 GeV2 are mostly DS→t+n, t→p+n in cases (i) & (ii) • No DS→e+n seen, case (iii) 64 events DATA 200/pb <0.3GeV in CC Case (i) 24 events DATA 200/pb >0.3GeV in CC Case (ii) 12 events Electron Sample ICHEP Moscow, July 26 – Aug. 2, 2006

Sum of DS+→m+n + t+n, t→p+n • Sum contains 100 m+n + t+n events for MM2 <0.2 GeV2 Sum of case (i) & case (ii) mn +tn signal line shape K0p+ 100 events ICHEP Moscow, July 26 – Aug. 2, 2006

Background Samples • Two sources of background • A) Backgrounds under invariant mass peaks – Use sidebands to estimate • Inm+n signal region 2 background (64 signal) • Total 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 • B(DS→p+po) < 1.1x10-3 & g energy cut yields <0.1 evts Signal region Low SB region High SB region Backgrounds from real DS+ ICHEP Moscow, July 26 – Aug. 2, 2006

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±0.03)% • 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 ICHEP Moscow, July 26 – Aug. 2, 2006

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 ICHEP Moscow, July 26 – Aug. 2, 2006

& • Weighted Average: fDs=280.1±11.6±6.0 MeV, the systematic error is mostly uncorrelated between the measurements • Previously CLEO-c measured M. Artuso et al., Phys .Rev. Lett. 95 (2005) 251801 • Thus fDs/fD+=1.26±0.11±0.03 • G(DS+→t+n)/G (DS+→m+n)= 9.9±1.7±0.7, SM=9.72, consistent with lepton universality D+→m+n m+n K0p+ ICHEP Moscow, July 26 – Aug. 2, 2006

Comparisons with Theory • We are consistent with most models, more precision needed • Using Lattice ratio find |Vcd/Vcs|= 0.22±0.03 ICHEP Moscow, July 26 – Aug. 2, 2006

Comparison with Previous Experiments • CLEO-c is most precise result to date for both fDs & fD+ 280.1±11.6±6.0 ? ? ICHEP Moscow, July 26 – Aug. 2, 2006

The End

CLEO-c Measurement of the Pseudoscalar Decay Constant f Ds & the Ratio f Ds / f D +