{anti p} and {anti {Lambda}} production in Si+Au collisions at the AGS Page: 2 of 9
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2 Y. D. Wu
104
103 <- 15%
040 60 80 100 120 140 160 180 200
Figure 1: The charged particle multiplicity distributions for the E859 minimum bias (INT) trigger and
central (TMA) trigger (shadow area).
chambers and, more importantly, a new second level on-line PID trigger, E859 had the
capability to study the production of rare particles such as p, A, A and 4. For the data
presented here, the second level trigger was set to select only those events in which at least
one p candidate track passed through the spectrometer. Such an on-line trigger selection
substantially enriched the number of p's in the event samples. As a result, E859 collected
about 10 times more p's than that E802 collected. The improved data samples not only
produced a better p measurement but also made it possible to measure the m1 spectrum of
the A, a first in any BNL-AGS heavy ion experiment.
The data were collected during the 1991 and 1992 runs at the BNL-AGS, the beam was
28Si at 14.6 A-GeV/c and the targets were Au with thickness of 1% and 2% of an interaction
length. The p data were taken primarily at the 50, 140, and 24* spectrometer settings, but
only at the 14* setting were enough data collected for A analysis because of the limited
acceptance of the larger angle settings and the limited statistics of the 50 setting. In this
presentation only central events taken at the 140 spectrometer angle setting (covering the
polar angle range from 14* to 28*) were analyzed. Central events were selected with a
Target Multiplicity Array (TMA) on-line hardware trigger and off-line software cuts. The
qualifying events corresponded to the top 15% of the charged particle multiplicity distribution
as measured by the TMA (Fig. 1). The p data covered the rapidity range from 0.9 to 1.5,
and the A data covered the rapidity range from 1.15 to 1.75 (Fig. 2).
3. Data Analysis and Preliminary Results
To reduce the systematic error contributed from background subtraction, small m1 bins
(0.025 GeV/c2) and y bins (0.1 unit) were used in the p data analysis. The number of p's
in each m1-y bin was obtained by fitting the 6(TOF) distribution (Fig. 3), which was the
difference between the measured time of flight (TOF) of a track and the expected value
of TOF assuming that the particle was a p. The reason for fitting the S(TOF) distribution
instead of fitting the mass distribution was that the S(TOF) is a constant hardware parameter
that does not depend on the particle's momentum so that a single gaussian function can be
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Wu, Yuedong & Collaboration, E802 /E859. {anti p} and {anti {Lambda}} production in Si+Au collisions at the AGS, article, December 31, 1996; Upton, New York. (https://digital.library.unt.edu/ark:/67531/metadc677164/m1/2/: accessed April 19, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.