Semileptonic Charm Decays
Will E. Johns (for the FOCUS Collaboration)
Vanderbilt University,BEACH 2004, July 1
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Subjects Covered
Data from 96-97 run of FOCUS
Over 1,000,000Reco’d. Charm
-Vertex Resolution-Particle ID-Mass Resolution
VeryGood
Lots ofPubs
Semileptonic Charm Decays
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(D decay, No form factors, V decays to spin 0 particles)
Neutrino is left handed
Prefers W spin along muon,e
V products spinless
Prefer LZ=0
Form Factors
Scalar Resonance? CP?
More than just CKM measurement tools…
FOCUS saw discrepancies in the data
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Ki
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Phys.Lett.B535:43-51, 2002hep-ex/0203031
0*KD
Yield 31,254
DataMC
Focus “K*” signal
matches model
-15% F-B asymmetry!
FOCUS added a term, things got better
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Ki
V
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V
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L=0 ansatz
Signal Events weightedby avg(cosV):
No added term
FOCUS Semileptonic cuts description ),( KDLook for N bodies with a muon
L/ – Lp
s ISO1 – CL DK’s in prim
DCL – CL of DK vertex
MuCL – CL for Muon ID Cuts on P( for ’s
Cerenkov for ’s and K’s (from ~ 4-60 GeV/c)
Vertexing cuts:
ISO2 – No Xtra trks in DK OOM – No DK’s in stuff
Particle ID cuts: TRKFITcl – Muon P consistency
MISIDMCS Radius, Decay Prob
(Ask me offline for all the detailed cut values!)
FOCUS Form Factors
and ,parameters waveS and)0(
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tKD
DKD
Tried in fit,no sensitivity (E791?)
(common – vary generated parameters in Montecarloby using agreement with reconstructed distributions and data)
Pioneered by D.M. Schmidt for E691 K*ev analysis: NIM A 328 (1993)
0*
KD
2max
2V /in 3 and in 3 ,cosin 5 ,cosin bins 5 qq
Kmin 4 and in 3 ,cosin 3 ,cosin bins 3 V
S-wave termBreaks symmetry
S-wave term andr’s essentially decouple
FOCUS Form Factors 0*
KDCuts similar to previous, some change to get uniform acceptance, one extra
Cut on q2 < 0.2 GeV2/c2
r’s are flat, feeling mμ? Goodness of fit issue
Right sign – Wrong sign
Charm Background
Systematic ChecksS-wave – varied cuts35 fits – Sample VarianceForm Factor (3 sources)1) Varied Cuts2) Split sample
3) Vary MC input Charm Backgrounds
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Phys.Lett.B544:89-96, 2002hep-ex/0207049
Very Clean Data
0*
KDForm Factors Comparison
S-Wave effects apparent only with high statistics
Lattice Gauge!
Experiment Models
A more detailed look at the K line shapeTake advantage of the very clean signal
Previous best K* parametersLass (1988) K scattering
Spectra is complicated
Mass range limit in fitMore Blatt-Weisskopf radius info away from pole
FOCUS sees S-wave effects primarily Below K*
Using LASS parametersfor ER model of
Constant
FOCUS PRELIMINARY
K* MassK* WidthBL-WK radius#K* eventsScalar Fraction
Mass and WidthDon’t change
-Careful studies of resolution effects too
FOCUS PRELIMINARY200051.0
00022.0*
200015.000016.0*
/00081.004751.0
/00030.089463.0
cGeV
cGeVM
K
K
Systematics by varying cuts,
background contribution, shapes
FOCUS Form Factors SD
- Event by Event version of discrete transform method
)()(
284.0202.0713.02
0148.0250.0549.1
sysstat
r
rV
- No evidence for S - wave
Phys.Lett.B586:183-190, 2004hep-ex/0401001
- Backgrounds higher (cut on M
Ds form factor enigma
Theoretically the Dslform factor should be within 10% of D+ K*l The rV values were consistent but r2 for Dslwas 2 higher than D+ K*l
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RV
But the (2004) FOCUS measurement has consistent r2 values as well!
Ds versus D+ K*l
Backgrounds Make a difference! 0D
Biggest Players:Signal, ~400 events (red and dots)Combinatoric Background,~750 events (pink hatch)Muon Misid, ~300 events(faint black histogram)
A peek at:
Search for Cabibbo Suppressed Ds semileptonic decay
c
ss
d
W
u u
K
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Cabibbo suppressed SL Decay
*K
sD
Would be a discovery!
A Cabibbo favored SL decay
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sc
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W
csV
u u
K
K sD
Easy to see and study
Right SignWrong Sign
MK (GeV/c2)
DsK*decay is a small WS background component in our previous D+K*work
Note kaon and muon have same sign
K+ K- mass in KK events K mass in K events
What’s this?
Preliminary results of the search
dataMC
After lots of cuts
In the loosely cut sample, the MC was a poor match to the observed WS Kspectrum. Large non-charm contribution?
With tight cuts, the MC matched the data away from the K* peak. We saw a excess in K* yield in data over MC
*
12.9 3.3 ??? %s
s
D K
D
We compared the WS K spectrum to a MC that incorporated all known charm decay and normalize the MC to the D+K*yield observed in the data
If this K* excess were interpreted as DsK*, we would obtain...
MK (GeV/c2) MK (GeV/c2)
This BR is very consistent with (10 ±1.3)% predicted by R.J. Oakes et al. (1997) (hep-ph/9708277)
FOCUS BR Measurements
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Phys.Lett.B540:25-32, 2002hep-ex/0206013
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BR Comparisons to Exp. & Models
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BR relative to are consistent
K
*l /K
E691
E653
Focus
Argus
Omega
Cleo 1
Cleo 2
Cleo 2
E687
0.3
0.4
0.5
0.6
0.7
0.8
0.9
muons electrons
0.620.02
BR relative to K …not so good
What about
0
0*
KD
KD?
-Could resolve lepton ID issues- Topological trouble though > need an extra particle for K*-Most Experiments measure ~0.5 (E687 too!) (some use rates though…compare D+ D0)
10
0*
KD
KDBut CLEO2 Reported )( 0 KDBUsing the
From the PDG
nsDD eKeK /)7.925()()( 00
But using PDG values we also find: Isospin Violation?
0
0*
KD
KDFOCUS
In the FOCUS silicon
)(&)( 0*0 KKKS
Reconstruct both
Drawback: Only about 10% of Ks>+-
Decays occur in the FOCUS silicon
Find Background Dominated by D>KsX
FOCUS is world’s best
0
0*
KD
KD
034.0045.0625.00
KD
KD
nsDD KK /)1111()()( 00
Correct for S-Wave:
hep-ex/0406060Submitted to PLB
030.0043.0594.00
0*
KD
KD
Measure:
Use Focus K* and PDG Kcompare to D0: Isospin OK again
11.072.00
0
KD
eKD?=1.03=? 07.012.1
0
0
KD
eKDLong standing “difference” for D0 is in “wrong” direction
Other Exp’s Models
Comparison to other Experiments and Theory
Focus measurementssuggest little “missing”Semileptonic rate
%9.12.17)( anythingeDPDG
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Sum of PDG CA e modes
Focus ’s as e’s
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KKD
Hard to believe PDG forPS electron is correct
Preview of other FOCUS analysis
)( 00SKD 0D KD0
-Plot of pseudo D*-D mass difference-Will repeat Vector analysis (tough to see S-wave)-measure q2 shape and BR for and K (expect BR/BR<10%)
Conclusions:
• Resolved some outstanding enigmas ( ff’s, V/PS Ratio, PDG rates)
• Raised some new ones (low q2 in K*, proper S-wave description
• We’ve gotten a lot of physics out of the careful analysis of the Vector decays (S-wave, B(K*,f), M(K*), r’s, W(K*), CS(K*)…
• Looking at new things