Charmonium and Charmonium-Like States with BaBar Page: 2 of 4
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The BABAR experiment - which is described in detail elsewhere [1, 2] - has recently obtained
several important results in charmonium and charmonium-like physics. Below the DD threshold,
the expected charmonium states are well established and their properties, when measured, are in
good agreement with predictions. Nevertheless, in the last years, a plethora of unexpected states
has been observed above the DD threshold. This non-regular charmonium genealogy started with
the observation of the X(3872) resonance , and the interpretation of these states is still unclear.
In the studies of the charmonium(-like) spectrum, the complete data sample collected at the
PEP-II asymmetric energy e+e- collider has been used. This sample consists of integrated lumi-
nosities of 425.6 fb recorded at an energy in the e+e- center-of-mass (CM) frame equal to the
T(4S) mass, 28.0 fb at the T(3S), and 13.6 fb at the T(2S). Samples collected at CM energy
30-40 MeV below each T peak, which correspond to ~10% of the total luminosity are used as well.
Here we present two recent results obtained by BABAR. The first concerns the evidence for the
decay X(3872) -> J/yio reported in the study of the B ,+ _* J/1Iw+w-oKo,+ processes , while
the second involves the study of the charmonium resonances produced in two-photon interactions,
resulting in the K K wT and K+K-+- final states .
2. Evidence for the decay X(3872) -- J/iyw
The X(3872) state has been primarily observed in decays to J/iy'+ - . Evidence for
X(3872) -> J/ypydecay has established positive C-parity for the resonance . Moreover, analyses
of the w+- mass distribution and of the angular distribution have restricted the available JP values
for X(3872) to 1+ or 2- .
Here we analyze the decays BO,+ _ J/1p+w-oKo,+, selecting the mass window for the
three-pion (3w) system in the o region as 0.740 < m,1 < 0.795 GeV/c2. The same processes
have already been analyzed in , but selecting 0.770 < m,1 < 0.795 GeV/c2, with the aim of
confirming the Y(3490) -> J/yio decays. Apart from the enlarged o mass window for the 3w
system, the same selection criteria as in  are applied. )
We look at the J/ypo mass distribution on data collected at the T(4S) energy, corresponding e
to ~ 467 x 106 BB pairs, for both charged and neutral B decays. The mass spectra are shown in
Fig. 1 (a, c), with a zoom in the low-mass region in (b). The fit components are the X(3872)
resonance, the Y(3940) resonance, and a non-peaking background contribution. We find evi-
dence for the X(3872) decaying to J/yio with a 4.0- significance, when considering both sta-
tistical and systematic uncertainties. The mass of this resonance is measured to be: mx(3872) =
3873.0 1 (stat.) 1.3(syst.) MeV/c2. We also measure mass and width of the Y(3940) resonance:
my(394O) = 3919.1+34(stat.) t 2.0(syst.) MeV/c2 and -y(394o) = 31(g Statt.) 5(syst.) MeV.
In Fig. 1 (d, e, f) the mass distribution for the 3w system is shown for charged decays, neutral
decays, and combining them, respectively. Monte Carlo (MC) simulated events with either S- or
P-wave distributions are superimposed on the distribution obtained when combining charged and
neutral B decays. The analysis favors the P-wave description, so that among the JP values still
allowed for the X(3872) meson, 2- is preferred. For this assignment, the X(3872) mass falls
within the broad range available to the 1c2 (1D) charmonium state.
Charmonium and charmonium-like states with BABAR
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Guido, Elisa. Charmonium and Charmonium-Like States with BaBar, article, March 14, 2014; United States. (digital.library.unt.edu/ark:/67531/metadc864635/m1/2/: accessed November 13, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.