CLEO-c Measurements of Purely Leptonic Decays of Charmed Mesons & other Wonders

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CLEO-c Measurements of Purely Leptonic Decays of Charmed Mesons & other Wonders. Sheldon Stone, Syracuse University. In general for all pseudoscalars:. Calculate, or measure if V Qq is known. Leptonic Decays: D   + n. Introduction: Pseudoscalar decay constants - PowerPoint PPT Presentation

Text of CLEO-c Measurements of Purely Leptonic Decays of Charmed Mesons & other Wonders

  • CLEO-c Measurements of Purely Leptonic Decays of Charmed Mesons & other WondersSheldon Stone,Syracuse University

  • Leptonic Decays: D +n Introduction: Pseudoscalar decay constants c and q can annihilate, probability is to wave function overlap Example :


    (s)or cs

  • New Physics Possibilities Besides the obvious interest in comparing with Lattice & other calculations of fP there are NP possibilitiesAnother Gauge Boson could mediate decayOr leptoquarks (see Kronfelds talk)Ratio of leptonic decays could be modified e.g. in Standard Model

    If H couples to M2 no effect

    See Hewett [hep-ph/9505246] & Hou, PRD 48, 2342 (1993).

  • New Physics Possibilities II Leptonic decay rate is modified by HCan calculate in SUSY as function of mq/mc, In 2HDM predicted decay width is x by

    Since md is ~0, effect can be seen only in DSFrom AkeroydSee Akeryod [hep-ph/0308260]= meas rate/SM ratetan b/MH

  • Experimental methodsDD production at threshold: used by Mark III, and more recently by CLEO-c and BES-II.Unique event propertiesOnly DD not DDx producedLarge cross sections:s(DoDo) = 3.720.09 nb s(D+D-) = 2.820.09 nbs(DSDS*) = ~0.9 nbContinuum ~12 nb Ease of B measurements using "double tags BA = # of A/# of D'sWorld Ave

  • Technique for D+ m+nFully reconstruct a D-, and count total # of tagsSeek events with only one additional oppositely charged track and no additional photons > 250 MeV (to veto D+ p+po)Charged track must deposit only minimum ionization in calorimeter (< 300 MeV case 1)Compute MM2. If close to zero then almost certainly we have a m+n decay.

    We know ED+ =Ebeam, pD+ = - pD-

  • D- Candidates (in 281 pb-1)# of tags = 158,354496, includes charge-conjugate modes

  • The Missing Mass Squared To find signal events, we compute

    Monte Carlo Signal mn Monte Carlo Signal tn, tpn

  • Measurement of fD+Data: 50 events in the signal region in 281 pb-1Backgrounds

    B(D+ e+n)

  • Systematic Errors

    Source of Error %Finding the m+ track 0.7Minimum ionization of m+ in EM cal 1.0Particle identification of m+ 1.0MM2 width 1.0Extra showers in event > 250 MeV 0.5Background 0.6Number of single tag D+ 0.6Monte Carlo statistics 0.4Total 2.1

  • Upper limit on D+t+nBy using intermediate MM2 regionB(D+t+n) 300 MeV

  • Measurements of fDsTwo separate techniques. [Here expect in SM: G(DSt+n)/ G(DSm+n) = 9.72](1) Measure DS+m+n along with DSt+n, t p+n. This requires finding a DS- tag, a g from either DS*-g DS- or DS*+g m+n. Then find the muon or pion & apply kinematical constraints (mass & energy) to resolve this ambiguity & improve resolution (use 314 pb-1, results are published)(2) Find DS+t+n, t e+nn opposite a DS- tag (use 298 pb-1, results are final arXiv:0712.1175 )

  • Invariant massesDS studies done at Ecm=4170 MeVTo choose tag candidates:Fit distributions & determine sCut at 2.5 sDefine sidebands to measure backgrounds 5-7.5 sTotal # of Tags = 31,302 472 (stat)

  • Tag Sample using g First we define the tag sample by computing the MM*2 off of the g & DS tag

    Total of 11880399504 tags, after the selection on MM*2.

    All 8 ModesData

  • The MM2 To find the signal events, we compute

    Monte Carlo Signal mn Monte Carlo Signal tn, tpn

  • MM2 In DataClear DS+m+n signal for case (i)Most events 0.3GeV in CC92 events31 events25 eventsmKo2

  • Branching Ratio & Decay Constant DS+m+n92 signal events, 3.5 background, use SM to calculate tn yield near 0 MM2 based on known tn/mn ratioB(DS+m+n) = (0.5970.0670.039)%DS+t+n, t+ p+nSum case (i) 0.2 > MM2 > 0.05 GeV2 & case (ii) MM2 < 0.2 GeV2. Total of 56 signal and 8.6 bkgrndB(DS+t+n) = ( summing both cases above, find Beff(DS+m+n) = (0.6380.0590.033)%fDs=274 13 7 MeV, for |Vcs| =0.9737B(DS+e+n)< 1.3x10-4

  • B(DS+m+n) Systematic errors

  • Measuring DS+t+n, t+e+nnB(DS+t+n)B(t+e+nn)~1.3% is large compared with expected B(DS+Xe+n)~8%We will be searching for events opposite a tag with one electron and not much other energyOpt to use only a subset of the cleanest tags

  • Measuring DS+t+n, t+e+nnTechnique is to findevents with an e+ opposite DS- tags & no othertracks, with calorimeter energy < 400 MeVNo need to find g from DS* B(DS+t+n)=(6.170.710.36)%fDs=273 16 8 MeV

    400 MeV

  • & Weighted Average: fDs=274105 MeV, the systematic error is mostly uncorrelated between the measurementsUsing

    M. Artuso et al., Phys .Rev. Lett. 95 (2005) 251801fDs/fD+= (DS+m+n) =, SM=9.72, consistent with lepton universalityRadiative corrections i.e. DS+m+ng not included, estimated to be ~1% (see Burdman et al., PRD 51, 11 (1995)

  • Comparison with Other ExperimentsCLEO-c is most precise result to date for both fDs & fD+ preliminaryManchester EPS

  • Comparisons with TheoryWe are ~3s above Follana et al. Either:Calculation is wrongThere is new physics that interferes constructively with SMNote: No value of MH is allowed in 2HDM at 99.5% c..Comparing measured fDS/fD+ with Follana prediction we find mH>2.2 GeV tanbUsing Follana ratio find |Vcd/Vcs|=0.2170.019 (exp) 0.002(theory)

  • ProjectionsWe will almost triple the D+ sample, including some improvements in technique, error in fD+ should decrease to ~9 MeVWe doubled the DS sample, improved the technique, expect error in fDs to decrease to ~7 MeV

  • Discover of DS+pnUse same technique as for m+n, but plot MM from a detected protonNo backgroundFirst example of a charm meson decaying into baryons neutron mass

  • Semileptonic DecaysPrecise B(DoK-e+n) & B(Dop-e+n)

  • Form Factors: DoK-e+n

  • Dop-e+n

  • The End

  • Check: B(DS+K+ Ko)Do almost the same analysis but consider MM2 off of an identified K+Allow extra charged tracks and showers so not to veto Ko decays or interactions in EMSignal verifies expected MM2 resolutionFind (2.900.190.18)%, compared with result from double tags (

  • CLEO DS+ Results at 4170 MeVSince 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 314 pb-1 of dataMBCMBC from DS*Signal MCBeam Constrained Mass (GeV)

  • Measurement of DS+m+nIn this analysis we use DS*DS events where we detect the g from the DS* g DS decayWe see all the particles from e+e- DS*DS, g, DS (tag) + m+ except for the nWe use a kinematic fit to (a) improve the resolution & (b) remove ambiguitiesConstraints 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*) fixedLowest c2 solution in each event is keptNo c2 cut is applied

  • Combining Semileptonics & LeptonicsSemileptonic decay rate into Pseudoscalar:

    Note that the ratio below depends only on QCD:

  • Background SamplesTwo sources of backgroundA) Backgrounds under invariant mass peaks Use sidebands to estimateIn m+n signal region 3.5 background (92 total)bkgrnd MM2
  • Sum of DS+m+n + t+n, t p+n As we will see, there is very little background present in any sub-sample for MM2
  • Radiative CorrectionsNot just final state radiation which is already corrected for.Includes DD*gDgm+n. Based on calculations of Burdman et al.G(D(S)+gm+n)/ G(D(S)+m+n) ~ 1/40 1/100Burdman etal ~1%Using narrow MM2 region makes this much smallerOther authors in general agreement, see Hwang Eur. Phys. J. C46, 379 (2006), except Korchemsky, Pirjol & Yan PRD 61, 114510 (2000)