Production and decay of the Lambda c charmed baryon from Fermilab E791 Page: 1 of 4
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Fermilab FERMILAB-Conf-01/350-E E791 Dec. 2001
Production and Decay of the A, Charmed
Baryon from Fermilab E791.
B. Meadows 1
University of Cincinnati, Cincinnati, OH, 45221, USA
Abstract. Results are presented for the 500 GeV/c pion production asymmetry and polarization of
the Ac (Ac) charmed baryon from Fermilab experiment E791. An analysis of the decay to the pK7c
final state is described. Resonant sub-channel fractions and phases are given and possible resonant
effects in the low mass pK system discussed. Significant decay to Ac -+ A++K- establishes for the
first time the importance of a W exchange mechanism in charmed baryon decay.
Measurements of asymmetry Ap = (dap - dG) / (dap + dG ) in the yield of par-
ticle P and anti particle P can provide information on the production mechanisms in-
volved. Dependences of A on xF and pT can distinguish different production models.
Several experiments [1, and refs 1-9 therein] have shown that production of charmed
mesons is characterized by leading particle effects and that asymmetries can be large.
Leading particle behaviour has also been observed in production of strange hyperons in
E791  - even in a very central region.
Branching fractions for baryon decays provide information on the relative importance
of lowest order decay mechanisms - W exchange or spectator processes. In Ac -+ pKn
decay, 2 W exchange can contribute to pK* , A*7c, E*c or pKac channels, but for the
A++K- mode it is the only low order process possible. Evidence for this decay requires
a large sample of pKn decays and proper analysis of interference effects in the system.
Reported here are the first published  measurements of both xF and pT dependence
of A for charmed baryon production. We also present  the first full analysis of charmed
baryon decay, measuring Ac branching fractions, relative phases and polarization.
This study is based on a sample of 2 x 1010 events produced from the interaction of
500 GeV/c -- incident on thin foils, one Pt and four C. Pt target data (unequal numbers
of n and p) were not used in the asymmetry study. The detector and data reconstruction
are described in . Cuts on geometric and kinematic quantities were made to identify
Ac -+ pK--T+ decays. The decay vertex had to be well separated (> 5() from both
production vertex and nearest target material. The yield, shown in Fig. 1(a)-(d), was
1,025+45 Ac -+pK-+ and 794 + 42 A,_ M-pK7+--. Events were divided into 5 regions
of xF and 5 of pT in the overall ranges: -0.1 < xF < 0.6 and pT < 8 (GeV/c)2 chosen
to have clear A, signals in each. Fits similar to those shown in the figure were made to
each sample to determine the number N(Ac) and N(Ac) of signal events in each range.
1 Representing the E791 Collaboration
2 Note that charged conjugate states are implied unless stated otherwise.
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Meadows, Brian. Production and decay of the Lambda c charmed baryon from Fermilab E791, article, December 11, 2001; Batavia, Illinois. (digital.library.unt.edu/ark:/67531/metadc723403/m1/1/: accessed November 14, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.