Semileptonic Charm Decays

1
Semileptonic Charm Decays

• Will E. Johns
• (for the FOCUS Collaboration)
• Vanderbilt University,
• BEACH 2004, July 1

2
Subjects Covered
Published Results
Coming Soon
Works in Progress
3
Data from 96-97 run of FOCUS
-Vertex Resolution -Particle ID -Mass Resolution
Lots of Pubs
Over 1,000,000 Recod. Charm
Very Good
4
Semileptonic Charm Decays
More than just CKM measurement tools
"Simple" Equation
(D decay, No form factors, V decays to spin 0
particles)
Neutrino is left handed
Prefers W spin along muon,e
Prefer LZ0
Gets Complicated...
V products spinless
Scalar Resonance?
CP?
Form Factors
5
FOCUS saw discrepancies in the data
Focus K signal
Yield 31,254
DataMC
Phys.Lett.B53543-51, 2002 hep-ex/0203031
6
FOCUS added a term, things got better
Signal Events weighted by avg(cosqV)
No added term
L0 ansatz
7
FOCUS Semileptonic cuts description
Look for N bodies with a muon
Vertexing cuts
ss
sp
ISO1 CL DKs in prim
L/s
L
DCL CL of DK vertex
OOM No DKs in stuff
ISO2 No Xtra trks in DK
Particle ID cuts
TRKFITcl Muon P consistency
MuCL CL for Muon ID
Cuts on
P(m) for ms Cerenkov for ps and Ks (from
4-60 GeV/c)
MISID?MCS Radius, Decay Prob
(Ask me offline for all the detailed cut values!)
8
FOCUS Form Factors
Tried in fit, no sensitivity (E791?)
(common vary generated parameters in
Montecarlo by using agreement with reconstructed
distributions and data)
Technique
Pioneered by D.M. Schmidt for E691 Kev analysis
NIM A 328 (1993)
1st find S-wave with PDG r's, then fit for r's
S-wave term and rs essentially decouple
S-wave term Breaks symmetry
9
FOCUS Form Factors
Cuts similar to previous, some change to get
uniform acceptance, one extra
Cut on q2 lt 0.2 GeV2/c2
rs are flat, feeling mµ?
Goodness of fit issue
Very Clean Data

• Systematic Checks
• S-wave varied cuts
• 35 fits Sample Variance
• Form Factor (3 sources)
• Varied Cuts
• Split sample
• Vary MC input
• Charm Backgrounds

Results
Right sign Wrong sign
Phys.Lett.B54489-96, 2002 hep-ex/0207049
Charm Background
10
Form Factors Comparison
S-Wave effects apparent only with high statistics
Lattice Gauge!
Experiment
Models
11
A more detailed look at the Kp line shape
Take advantage of the very clean signal
Previous best K parameters Lass (1988) Kp
scattering
Spectra is complicated
Mass range limit in fit
More Blatt-Weisskopf radius info away from pole
FOCUS sees S-wave effects primarily Below K
12
FOCUS PRELIMINARY
Using LASS parameters for ER model of d

• Careful studies of resolution effects too

K Mass K Width BL-WK radius K events Scalar
Fraction
Mass and Width Dont change
Constant d
13
FOCUS PRELIMINARY
Systematics by varying cuts, background
contribution, shapes
14
FOCUS Form Factors
- Event by Event version of discrete transform
method
- No evidence for S - wave
- Backgrounds higher (cut on M(f))
Phys.Lett.B586183-190, 2004 hep-ex/0401001
15
Ds ? fmn form factor enigma
Ds ? fmn versus D ?Kln
Theoretically the Ds?fln form factor should be
within 10 of D ?Kln . The rV values were
consistent but r2 for Ds?fln was ? 2? higher than
D ?Kln .
16
Backgrounds Make a difference!
A peek at
Biggest Players Signal, 400 events (red
and dots) Combinatoric Background, 750 events
(pink hatch) Muon Misid, 300 events (faint black
histogram)
17
Search for Cabibbo Suppressed Ds semileptonic
decay
Note kaon and muon have same sign
In Fact
K p mass in Kp m events
K K- mass in KKm events
Whats this?
18
Preliminary results of the search
We compared the WS Kp spectrum to a MC that
incorporated all known charm decay and normalize
the MC to the D?Kmn yield observed in the data
With tight cuts, the MC matched the data away
from the K peak. We saw a 3.9s excess in K
yield in data over MC
In the loosely cut sample, the MC was a poor
match to the observed WS Kp spectrum. Large
non-charm contribution?
MKp (GeV/c2)
MKp (GeV/c2)
If this K excess were interpreted as Ds?Kmn ,
we would obtain...
preliminary
This BR is very consistent with (10 1.3)
predicted by R.J. Oakes et al. (1997)
(hep-ph/9708277)
19
FOCUS BR Measurements
Phys.Lett.B54025-32, 2002 hep-ex/0206013
events / 5 MeV/c2
events / 10 MeV/c2
Includes S-wave interference
20
BR Comparisons to Exp. Models
but,
BR relative to Kpp not so good
21
?
What about

• Could resolve lepton ID issues
• Topological trouble though
• gt need an extra particle for K
• Most Experiments measure 0.5 (E687 too!)
• (some use rates thoughcompare D ?D0)

But CLEO2 Reported
Using the
From the PDG
But using PDG values we also find
Isospin Violation?
22
Reconstruct both
FOCUS
In the FOCUS silicon
Drawback Only about 10 of Ksgtpp-
Decays occur in the FOCUS silicon
Find Background Dominated by DgtKsXmn
23
hep-ex/0406060 Submitted to PLB
FOCUS is worlds best
Measure
Correct for S-Wave
Use Focus Kmn and PDG Kpp, compare to D0
Isospin OK again
Long standing difference for D0 is in wrong
direction
?1.03?
24
Comparison to other Experiments and Theory
Focus measurements suggest little
missing Semileptonic rate
Other Exps
Models
PDG
Sum of PDG CA e modes
Focus ms as es
Hard to believe PDG for PS electron is correct
25
Preview of other FOCUS analysis
-Plot of pseudo D-D mass difference -Will repeat
Vector analysis (tough to see S-wave) -measure q2
shape and BR for pmn and Kmn (expect
dBR/BRlt10)
26
Conclusions

• Weve gotten a lot of physics out of the careful
  analysis of the Vector decays (S-wave,
  B(K,f), M(K), rs, W(K), CS(K)

• Resolved some outstanding enigmas (f
  ffs, V/PS Ratio, PDG rates)

• Raised some new ones (low q2 in K, proper S-wave
  description

• Looking at new things