CLEO-c Measurements of Purely Leptonic Decays of Charmed Mesons

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

• Sheldon Stone,
• Syracuse University

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Leptonic Decays D ? ? n

• Introduction Pseudoscalar decay constants
• c and q can annihilate, probability is ? to
  wave function overlap
• Example

_

or cs
(s)
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New Physics Possibilities

• Besides the obvious interest
  in comparing with Lattice
  other calculations
  of fP there are
  NP possibilities
• Another Gauge Boson could mediate decay
• Or 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).
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New Physics Possibilities II

• Leptonic decay rate is modified by H
• Can 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 DS

meas rate/SM rate
From Akeroyd
See Akeryod hep-ph/0308260
tan b/MH
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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 nb s(DD-)
  2.82?0.09 nb
• s(DSDS) 0.9 nb
• Continuum 12 nb
• Ease of B measurements using "double tags
• BA of A/ of D's

World Ave
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Technique for D ? mn

• Fully reconstruct a D-, and count total of tags
• Seek events with only one additional oppositely
  charged track and no additional photons gt 250 MeV
  (to veto D ? ppo)
• Charged track must deposit only minimum
  ionization in calorimeter (lt 300 MeV case 1)
• Compute MM2. If close to zero then almost
  certainly we have a mn decay.
• We know ED Ebeam, pD - pD-

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D- Candidates (in 281 pb-1)

• of tags 158,354496, includes
  charge-conjugate modes

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The Missing Mass Squared

• To find signal events, we compute

Monte Carlo Signal mn
Monte Carlo Signal tn, t?pn
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Measurement of fD
Backgrounds

• B(D ? en) lt2.4x10-5
• _at_ 90 c.l.

Data 50 events in the signal region in 281 pb-1
Mode Events
pp0 1.400.180.22
K0p 0.330.190.02
tn (t?pn) 1.080.150.16
Other D, Do lt0.4, lt0.4 _at_ 90 c.l.
Continuum lt1.2 _at_ 90 c.l.
Total
Vcd.2238
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Systematic Errors
Source of Error
Finding the m track 0.7
Minimum ionization of m in EM cal 1.0
Particle identification of m 1.0
MM2 width 1.0
Extra showers in event gt 250 MeV 0.5
Background 0.6
Number of single tag D 0.6
Monte Carlo statistics 0.4
Total 2.1
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Upper limit on D?tn
Ecal lt 300 MeV

• By using intermediate MM2 region
• B(D?tn)lt2.1x10-3
• where 2.65 is SM expectation
• both at 90 c.l

Ecal gt 300 MeV
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Measurements of fDs

• Two separate techniques. Here expect in SM
  G(DS?tn)/ G(DS?mn) 9.72
• (1) Measure DS?mn along with DS?tn, t
  ?pn. This requires finding a DS- tag, a g from
  either DS-?g DS- or DS?g mn. 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?tn, t ?enn opposite a DS- tag (use
  298 pb-1, results are final arXiv0712.1175 )

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Invariant masses

• DS studies done at Ecm4170 MeV
• To choose tag candidates
• Fit distributions determine s
• Cut at 2.5 s
• Define sidebands to measure backgrounds 5-7.5 s
• Total of Tags
• 31,302 472 (stat)

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Tag Sample using g

• First we define the tag sample by computing the
  MM2 off of the g DS tag
• Total of
• 11880399504 tags, after the selection on
  MM2.

Data
All 8 Modes
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The MM2

• To find the signal events, we compute

Monte Carlo Signal tn, t?pn
Monte Carlo Signal mn
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MM2 In Data
mKo2
92 events

• Clear DS?mn signal for case (i)
• Most events lt0.2 GeV2 are DS?tn, t ?pn in cases
  (i) (ii)
• No DS?en seen, case (iii)

lt 0.3GeV in CC
31 events
gt 0.3GeV in CC
25 events
Electron Sample
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Branching Ratio Decay Constant

• DS?mn
• 92 signal events, 3.5 background, use SM to
  calculate tn yield near 0 MM2 based on known
  tn/mn ratio
• B(DS?mn) (0.5970.0670.039)
• DS?tn, t ?pn
• Sum case (i) 0.2 gt MM2 gt 0.05 GeV2 case (ii)
  MM2 lt 0.2 GeV2. Total of 56 signal and 8.6 bkgrnd
• B(DS?tn) (8.01.30.4)
• By summing both cases above, find
• Beff(DS?mn) (0.6380.0590.033)
• fDs274 13 7 MeV, for Vcs 0.9737
• B(DS?en)lt 1.3x10-4

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B(DS?mn) Systematic errors
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Measuring DS?tn, t?enn

• B(DS?tn)?B(t?enn)1.3 is large compared
  with expected B(DS?Xen)8
• We will be searching for events opposite a tag
  with one electron and not much other energy
• Opt to use only a subset of the cleanest tags

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Measuring DS?tn, t?enn

• Technique is to find
• events with an e opposite
• DS- tags no other
• tracks, with ? calorimeter
• energy lt 400 MeV
• No need to find g from DS
• B(DS?tn)
• (6.170.710.36)
• fDs273 16 8 MeV

400 MeV
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• Weighted Average fDs274105 MeV, the
  systematic error is mostly uncorrelated between
  the measurements
• Using
• M. Artuso et al., Phys .Rev. Lett. 95
  (2005) 251801
• fDs/fD1.230.100.03
• G(DS?tn)/G (DS?mn) 11.01.40.6,
  SM9.72, consistent with lepton universality
• Radiative corrections i.e. DS?mng not included,
  estimated to be 1 (see Burdman et al., PRD 51,
  11 (1995)

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Comparison with Other Experiments
preliminary Manchester EPS

• CLEO-c is most precise result to date for both
  fDs fD

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Comparisons with Theory

• We are 3s above Follana et al. Either
• Calculation is wrong
• There is new physics that interferes
  constructively with SM
• Note No value of MH is allowed in 2HDM at 99.5
  c.?.
• Comparing measured fDS/fD with Follana
  prediction we find mHgt2.2 GeV tanb
• Using Follana ratio find Vcd/Vcs0.2170.019
  (exp) 0.002(theory)

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Projections

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

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Discover of DS?pn

• Use same technique as for mn, but plot MM from a
  detected proton
• No background
• First example of a charm meson decaying into
  baryons

neutron mass
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Semileptonic Decays

• Precise B(Do?K-en) B(Do?p-en)

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Form Factors Do?K-en
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Do?p-en
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The End
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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 EM
• Signal verifies expected MM2 resolution
• Find (2.900.190.18), compared with result from
  double tags (3.000.190.10)

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CLEO DS Results at 4170 MeV

• Since ee-?DSDS, 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 data

Signal MC
MBC
MBC from DS
Beam Constrained Mass (GeV)
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Measurement of DS?mn

• In this analysis we use DSDS events where we
  detect the g from the DS? g DS decay
• We see all the particles from ee- ? DSDS, 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,
  DmM(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

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Combining Semileptonics Leptonics

• Semileptonic decay rate into Pseudoscalar
• Note that the ratio below depends only on QCD

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Background Samples

• Two sources of background
• A) Backgrounds under invariant mass peaks Use
  sidebands to estimate
• In mn signal region 3.5 background (92 total)
• bkgrnd MM2lt0.20 GeV2 9.02.3
• B) Backgrounds from real DS decays, e.g. ppopo,
  or DS? tn, t ?ppon.... lt 0.2 GeV2, none in mn
  signal region
• B(DS ?ppo) lt 1.1x10-3
• g energy cut yields lt0.2 evts

Signal region
High SB region
Low SB region
Backgrounds from real DS
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Sum of DS?mn tn, t ?pn

• As we will see, there is very little background
  present in any sub-sample for MM2 lt0.2 GeV2

Sum of case (i) case (ii)
mn tn signal line shape
K0p
148 events
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Radiative Corrections

• Not just final state radiation which is already
  corrected for.
• Includes D?D?gD?gmn. Based on calculations of
  Burdman et al.
• G(D(S)?gmn)/ G(D(S)?mn) 1/40 1/100
• Burdman etal 1
• Using narrow MM2 region makes this much smaller
• Other authors in general agreement, see Hwang
  Eur. Phys. J. C46, 379 (2006), except Korchemsky,
  Pirjol Yan PRD 61, 114510 (2000)