A First Look at Charm Physics from Selex (e781)

  I.  The experiment

      First data in 1996-97 run with 600 gev pi-, sigma-, and proton beams
      Online charm selection, using full vertex reconstruction
      Emphasis on fast, forward charm decays with particle id in RICH

  II. Analysis progress

      First charm peaks shown a year ago in the URA review
      Now making run through all data before starting first production pass

      ALL DATA SHOWN HERE ARE PRE-PRELIMINARY.  
        These data have significant cut losses in the current analysis.  

        There are indications from the current analysis that significant 
        improvements in reconstruction efficiency, and thus charm yields, 
        are possible.

  III.	State of the data - what's known?

      A) RICH performed as designed: >96% efficiency and
         pi/K separation (2 sigma) up to 180 [GeV/c]

      B) Vertex detector performed as designed: >98% efficiency
         average primary vertex Z resolution 250 microns at 600 GeV/c
      C) Mass resolution extremely good - D0 width ~10 MeV/c^2 for
         charm momenta above 200 GeV/c.
      D) Charm mass scale good to 1 MeV/c^2 for all states, set from
         kshort mass.

  IV. State of the data - what's not settled?

      A) Reconstruction efficiency is not known, so yields cannot
         yet be estimated.
      B) Acceptance corrections have not yet been applied.  [this
         affects chiefly data for x_f < 0.3.]
      C) Charm-strange baryon reconstructions are still under development.

  V. Preliminary physics indications for hadroproduction

      A) Data were taken with unselected, Sigma- and Proton beams
         triggered with a beam TRD.

         Beam type      Beam fraction            Live interactions
                        Sigma-/Proton  Pi-/Pi+      
         ---------      -------------  -------   -----------------
         negative       50%            50%          2.2B
         sigma-         93%             7%         20.0B
         proton                92%         8%       1.8B

      B) Charm baryon production for x_F > 0.1 is large, comparable
         to charm meson production. (refer to yellow plot)
      C) Pion D+/D- data for x_F > 0.3 agrees with trend in e791 and has
         more events in this kinematic region.

      D) The charm baryon particle/anti-particle production asymmetry 
         looks very different for pion, sigma beams.

Conclusions:	Selex(e781) sensitivity is good enough to make important 
                comparisons among pion, sigma, and proton data, to probe PQCD.

  VI. Preliminary physics indications from weak decay studies

      Major goal is lifetime studies of short-lived states.  We have
      a first look at the raw lifetime systematics in a d0 lifetime study.

      A) Uncorrected data fits to simple exponential over two decades,
         so we think that acceptance corrections will be small, even
         for very short lifetimes.
      B) Uncorrected fit lies close to the present world average, so that 
         corrections and systematic errors are not likely to be large.

Conclusions:	Selex(e781) lifetime resolution is as designed, even for 
                large x_F events.  Good results are anticipated.