First Charm Physics Results from Selex(e781) Feb 27, 1998
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
Selex(E781) Apparatus in the Fermilab Proton-Center beamline
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,
PRELIMINARY Reconstructed charm states
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]
Selex RICH on a page slide
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
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
--------- ------------- ------- -----------------
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.
PRELIMINARY x_F>0.3 Lc and D+ particles and anti-particles produced by
600 GeV/c sigma- and pi- beams
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.
PRELIMINARY D0 proper decay length distribution
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.
Peter S. Cooper
Last modified: Fri Mar 13 15:02:50 CST 1998