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

Subjects Covered

Data from run of FOCUS Over 1,000,000 Reco’d. Charm -Vertex Resolution -Particle ID -Mass Resolution Very Good Lots of Pubs

Semileptonic Charm Decays (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 L Z =0 Form Factors Scalar Resonance? CP? More than just CKM measurement tools…

FOCUS saw discrepancies in the data Phys.Lett.B535:43-51, 2002 hep-ex/ Yield 31,254 Data MC Focus “ K* ” signal matches model -15% F-B asymmetry!

FOCUS added a term, things got better L=0 ansatz Signal Events weighted by avg(cos  V ): No added term

FOCUS Semileptonic cuts description Look for N bodies with a muon L/  – L pp s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 MISID  MCS Radius, Decay Prob (Ask me offline for all the detailed cut values!)

FOCUS Form Factors Tried in fit, no sensitivity (E791?) (common – vary generated parameters in Montecarlo by using agreement with reconstructed distributions and data) Pioneered by D.M. Schmidt for E691 K*ev analysis: NIM A 328 (1993) S-wave term Breaks symmetry S-wave term and r’s essentially decouple

FOCUS Form Factors Cuts similar to previous, some change to get uniform acceptance, one extra Cut on q 2 < 0.2 GeV 2 /c 2 r’s are flat, feeling m μ ? Goodness of fit issue Right sign – Wrong sign Charm Background Systematic Checks S-wave – varied cuts 35 fits – Sample Variance Form Factor (3 sources) 1)Varied Cuts 2)Split sample 3)Vary MC input Charm Backgrounds Phys.Lett.B544:89-96, 2002 hep-ex/ Very Clean Data

Form Factors Comparison S-Wave effects apparent only with high statistics Lattice Gauge! Experiment Models

A more detailed look at the K  line shape Take advantage of the very clean signal Previous best K* parameters Lass (1988) K  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*

Using LASS parameters for ER model of  Constant  FOCUS PRELIMINARY K* Mass K* Width BL-WK radius #K* events Scalar Fraction Mass and Width Don’t change -Careful studies of resolution effects too

FOCUS PRELIMINARY Systematics by varying cuts, background contribution, shapes

FOCUS Form Factors - Event by Event version of discrete transform method - No evidence for S - wave Phys.Lett.B586: , 2004 hep-ex/ Backgrounds higher (cut on M 

Ds   form factor enigma Theoretically the Ds  l form factor should be within 10% of D+  K*l The rV values were consistent but r2 for Ds  l was  2  higher than D+  K*l circa 1999 But the (2004) FOCUS measurement has consistent r2 values as well! D s   versus D+  K*l

Backgrounds Make a difference! 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 Cabibbo suppressed SL Decay Would be a discovery! A Cabibbo favored SL decay Easy to see and study Right Sign Wrong Sign M Kp (GeV/c 2 ) D s  K*  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 data MC After lots of cuts In the loosely cut sample, the MC was a poor match to the observed WS K  spectrum. 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 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 D s  K* , we would obtain... M Kp (GeV/c 2 ) This BR is very consistent with (10 ±1.3)% predicted by R.J. Oakes et al. (1997) (hep-ph/ )

FOCUS BR Measurements events / 5 MeV/c 2 Includes S-wave interference Phys.Lett.B540:25-32, 2002 hep-ex/ events / 10 MeV/c 2

BR Comparisons to Exp. & Models  BR relative to  are consistent  K*l  /  K  muonselectrons 0.62  0.02 BR relative to K  …not so good

What about ? -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 +  D 0 ) But CLEO2 Reported Using the From the PDG But using PDG values we also find: Isospin Violation?

FOCUS In the FOCUS silicon Reconstruct both Drawback: Only about 10% of K s >  +  - Decays occur in the FOCUS silicon Find Background Dominated by D>K s X 

FOCUS is world’s best Correct for S-Wave: hep-ex/ Submitted to PLB Measure: Use Focus K*  and PDG K  compare to D 0 : Isospin OK again ?=1.03=? Long standing “difference” for D 0 is in “wrong” direction

Other Exp’sModels Comparison to other Experiments and Theory Focus measurements suggest little “missing” Semileptonic rate PDG Sum of PDG CA e modes Focus  ’s as e’s Hard to believe PDG for PS electron is correct

Preview of other FOCUS analysis -Plot of pseudo D*-D mass difference -Will repeat Vector analysis (tough to see S-wave) -measure q 2 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 q 2 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