118 research outputs found
Study of and
The decays and have been
investigated with a sample of 225.2 million events collected with the
BESIII detector at the BEPCII collider. The branching fractions are
determined to be and . Distributions of the angle
between the proton or anti-neutron and the beam direction are well
described by the form , and we find
for and
for . Our branching-fraction
results suggest a large phase angle between the strong and electromagnetic
amplitudes describing the decay.Comment: 16 pages, 13 figures, the 2nd version, submitted to PR
Precision measurement of the branching fractions of J/psi -> pi+pi-pi0 and psi' -> pi+pi-pi0
We study the decays of the J/psi and psi' mesons to pi+pi-pi0 using data
samples at both resonances collected with the BES III detector in 2009. We
measure the corresponding branching fractions with unprecedented precision and
provide mass spectra and Dalitz plots. The branching fraction for J/psi ->
pi+pi-pi0 is determined to be (2.137 +- 0.004 (stat.) +0.058-0.056 (syst.)
+0.027-0.026 (norm.))*10-2, and the branching fraction for psi' -> pi+pi-pi0 is
measured as (2.14 +- 0.03 (stat.) +0.08-0.07 (syst.) +0.09-0.08 (norm.))*10-4.
The J/psi decay is found to be dominated by an intermediate rho(770) state,
whereas the psi' decay is dominated by di-pion masses around 2.2 GeV/c2,
leading to strikingly different Dalitz distributions.Comment: 15 pages, 2 figure
First Observation of the Decays chi_{cJ} -> pi^0 pi^0 pi^0 pi^0
We present a study of the P-wave spin -triplet charmonium chi_{cJ} decays
(J=0,1,2) into pi^0 pi^0 pi^0 pi^0. The analysis is based on 106 million
\psiprime decays recorded with the BESIII detector at the BEPCII electron
positron collider. The decay into the pi^0 pi^0 pi^0 pi^0 hadronic final state
is observed for the first time. We measure the branching fractions B(chi_{c0}
-> pi^0 pi^0 pi^0 pi^0)=(3.34 +- 0.06 +- 0.44)*10^{-3}, B(chi_{c1} -> pi^0 pi^0
pi^0 pi^0)=(0.57 +- 0.03 +- 0.08)*10^{-3}, and B(chi_{c2} -> pi^0 pi^0 pi^0
pi^0)=(1.21 +- 0.05 +- 0.16)*10^{-3}, where the uncertainties are statistical
and systematical, respectively.Comment: 7 pages, 3 figure
First observation of the M1 transition
Using a sample of 106 million \psi(3686) events collected with the BESIII
detector at the BEPCII storage ring, we have made the first measurement of the
M1 transition between the radially excited charmonium S-wave spin-triplet and
the radially excited S-wave spin-singlet states: \psi(3686)\to\gamma\eta_c(2S).
Analyses of the processes \psi(2S)\to \gamma\eta_c(2S) with \eta_c(2S)\to
\K_S^0 K\pi and K^+K^-\pi^0 gave an \eta_c(2S) signal with a statistical
significance of greater than 10 standard deviations under a wide range of
assumptions about the signal and background properties. The data are used to
obtain measurements of the \eta_c(2S) mass (M(\eta_c(2S))=3637.6\pm
2.9_\mathrm{stat}\pm 1.6_\mathrm{sys} MeV/c^2), width
(\Gamma(\eta_c(2S))=16.9\pm 6.4_\mathrm{stat}\pm 4.8_\mathrm{sys} MeV), and the
product branching fraction (\BR(\psi(3686)\to \gamma\eta_c(2S))\times
\BR(\eta_c(2S)\to K\bar K\pi) = (1.30\pm 0.20_\mathrm{stat}\pm
0.30_\mathrm{sys})\times 10^{-5}). Combining our result with a BaBar
measurement of \BR(\eta_c(2S)\to K\bar K \pi), we find the branching fraction
of the M1 transition to be \BR(\psi(3686)\to\gamma\eta_c(2S)) = (6.8\pm
1.1_\mathrm{stat}\pm 4.5_\mathrm{sys})\times 10^{-4}.Comment: 7 pages, 1 figure, 1 tabl
Two-photon widths of the states and helicity analysis for \chi_{c2}\ar\gamma\gamma}
Based on a data sample of 106 M events collected with the
BESIII detector, the decays \psi^{\prime}\ar\gamma\chi_{c0, 2},\chi_{c0,
2}\ar\gamma\gamma are studied to determine the two-photon widths of the
states. The two-photon decay branching fractions are determined
to be {\cal B}(\chi_{c0}\ar\gamma\gamma) = (2.24\pm 0.19\pm 0.12\pm
0.08)\times 10^{-4} and {\cal B}(\chi_{c2}\ar\gamma\gamma) = (3.21\pm 0.18\pm
0.17\pm 0.13)\times 10^{-4}. From these, the two-photon widths are determined
to be keV,
keV, and
, where the uncertainties
are statistical, systematic, and those from the PDG {\cal
B}(\psi^{\prime}\ar\gamma\chi_{c0,2}) and errors,
respectively. The ratio of the two-photon widths for helicity and
helicity components in the decay \chi_{c2}\ar\gamma\gamma is
measured for the first time to be .Comment: 10 pages, 4 figure
Feasibility studies of time-like proton electromagnetic form factors at PANDA at FAIR
Simulation results for future measurements of electromagnetic proton form
factors at \PANDA (FAIR) within the PandaRoot software framework are reported.
The statistical precision with which the proton form factors can be determined
is estimated. The signal channel is studied on the basis
of two different but consistent procedures. The suppression of the main
background channel, , is studied.
Furthermore, the background versus signal efficiency, statistical and
systematical uncertainties on the extracted proton form factors are evaluated
using two different procedures. The results are consistent with those of a
previous simulation study using an older, simplified framework. However, a
slightly better precision is achieved in the PandaRoot study in a large range
of momentum transfer, assuming the nominal beam conditions and detector
performance
Confirmation of the X(1835) and observation of the resonances X(2120) and X(2370) in J/psi->gamma pi^+pi^-eta'
With a sample of (225.2\pm2.8)*10^{6} J/psi events registered in the BESIII
detector, J/psi->gamma pi^+ pi^- eta' is studied using two eta' decay modes:
eta'->pi^+ pi^- eta and eta' -> gamma rho^0. The X(1835), which was previously
observed by BESII, is confirmed with a statistical significance that is larger
than 20\sigma. In addition, in the pi^+pi^-eta' invariant mass spectrum, the
X(2120) and the X(2370), are observed with statistical significances larger
than 7.2\sigma and 6.4\sigma, respectively. For the X(1835), the angular
distribution of the radiative photon is consistent with expectations for a
pseudoscalar
Observation of chi_{cJ} Decays to \Lambda \Lambda bar\pi^{+}\pi^{-}
Decays of the chi_{cJ} states (J=0,\ 1,\ 2) to \Lambda \Lambda bar\ pi^{+}
\pi^{-}, including processes with intermediate \Sigma(1385), are studied
through the E1 transition psi'-->\gamma chi_{cJ} using 106 million psi' events
collected with the BESIII detector at BEPCII. This is the first observation of
chi_{cJ} decays to the final state \Lambda\Lambda bar \pi^{+}\pi^{-}. The
branching ratio of the intermediate process chi_{cJ}-->\Sigma(1385)^{+/-}
\bar{\Sigma}(1385)^{-/+} is also measured for the first time, and the results
agree with the theoretical predictions based on the color-octet effect
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