Measurement of the angular distribution in anti-p p ---> psi(2S) ---> e+ e- Page: 5 of 10
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Fig. 1. Invariant mass distributions of pp .+ e+e- (X) candidates. The shaded area
represents events in the pp -+ 4(2S) - e+e-- sample.
the 5x5 grid or the electron had radiated a bremsstrahlung photon in the
material in front of the calorimeter.
To avoid possible contamination from 0(2S) -+ J/4 X events, we finally re-
quire that Me+e- > 3.4 GeV (see fig. 1).
The amount of material in front of the calorimeter and the size of the calorime-
ter counters both varied with angle. This means that the probability of bremsstrahlung
and the number of low energy satellite clusters distinct from the high energy
cluster could vary with angle.
A full Monte Carlo (MC) detector simulation based on GEANT [14] was per-
formed to evaluate the efficiency correction as a function of cos 0* (shown in
fig. 2).
With the cuts chosen, the efficiency is essentially independent of angle.
To ensure uniform efficiency we limit our acceptance to I cos 0* < 0.58, where
the efficiency ranges between 0.83 and 0.93. The bin by bin differences depend
mainly on the CCAL counters' geometry (including two dead channels) that
are accurately modelled in the MC.
The statistical error on the efficiency due to the size of the MC sample (330,000
events) is negligible given the size of our data sample.
The final sample has 2391 and 4457 events from the 1996-1997 and 2000 runs,5
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Ambrogiani, M.; Andreotti, M.; Argiro, S.; Bagnasco, S.; Baldini, W.; Bettoni, D. et al. Measurement of the angular distribution in anti-p p ---> psi(2S) ---> e+ e-, article, December 1, 2004; Batavia, Illinois. (https://digital.library.unt.edu/ark:/67531/metadc1406092/m1/5/: accessed July 16, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.