Measurement of the resonance parameters of the chi(1)(1**3P(1)) and chi(2)(1**3P(2)) states of charmonium formed in antiproton-proton annihilations Page: 3 of 12
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III. DATA ANALYSIS
The data presented here were collected by experiment E835, in three scans performed at the Xci in August 1997
(scan I), February 2000 (scan II), and July 2000 (scan III), and one scan performed at the xc2 in February 2000. The
center of mass energy, f&, width of the d& distribution, FWHMS, and integrated luminosity, Ldt, for each run are
given in Table I.
Our data analysis methods are described in detail in reference [4]. The offline selection of Xci and Xc2 events
compatible with reaction (1) is done in three steps; the first two are illustrated in Fig. 2 which shows, at each
step, the invariant mass distribution of the e+ e- candidates for on-resonance data and (shaded) for data taken
off-resonance, normalized to the integrated luminosity of the data taken in the resonance region. In the first step (Fig.
2a), all events with two electron (i.e. electron-positron) candidates within the Cerenkov fiducial region (15 < B < 60)
and an invariant mass (Mee) above 2600 MeV/c2 are selected. A clear enhancement is seen in the on-resonance data at
the mass of the J/ . In the next step, the electron candidates are identified by using an "electron weight" parameter,
which is a likelihood ratio for the electron hypothesis versus the background hypothesis. It uses the pulse heights
in the three hodoscopes (H1,H2',H2) and Cerenkov counter, and the transverse energy distribution of the CCAL
clusters, and distinguishes single electron tracks from background (predominantly e+e- pairs from photon conversions
in the 0.18 mm thick steel beam-pipe and ur0 - e+e--y decays). The resulting e+e- invariant mass distribution is
shown in Fig. 2b. The slight enhancement in the background level at the J/4 mass peak comes from the continuum
of pp - r J/b events.
2 2 800
700
0
i 600
500
c
a)
> 400
300
200
100 -
0
2600 2800 3000 3200 3400 3600 3800
Mee [MeV Oc2
. 400
a)
350
O
IC) 300
- 250
W 200
150
100
50
0
2600 2800 3000 3200 3400 3600 3800
M8 [MeV 6 ]
FIG. 2: Reconstructed e+e- invariant-mass distribution for events in the xci resonance region(clear), and for events off-
resonance(shaded): (a) all events with both electron candidates within the Cerenkov fiducial volume, (b) events remaining
after applying the electron-weight cut.
We select J/X events by applying a 1C kinematical fit to the reaction: pp - xcJ - J/ + anything -
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Andreotti, M.; Bagnasco, S.; Baldini, W.; Bettoni, D.; Borreani, G.; Buzzo, A. et al. Measurement of the resonance parameters of the chi(1)(1**3P(1)) and chi(2)(1**3P(2)) states of charmonium formed in antiproton-proton annihilations, article, March 1, 2005; Batavia, Illinois. (https://digital.library.unt.edu/ark:/67531/metadc1411637/m1/3/: accessed July 16, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.