581 research outputs found
Search for the decay
We search for radiative decays into a weakly interacting neutral
particle, namely an invisible particle, using the produced through the
process in a data sample of
decays collected by the BESIII detector
at BEPCII. No significant signal is observed. Using a modified frequentist
method, upper limits on the branching fractions are set under different
assumptions of invisible particle masses up to 1.2 . The upper limit corresponding to an invisible particle with zero mass
is 7.0 at the 90\% confidence level
Observation of in
Using a sample of events recorded with
the BESIII detector at the symmetric electron positron collider BEPCII, we
report the observation of the decay of the charmonium state
into a pair of mesons in the process
. The branching fraction is measured for the first
time to be , where the first uncertainty is
statistical, the second systematic and the third is from the uncertainty of
. The mass and width of the are
determined as MeV/ and
MeV.Comment: 13 pages, 6 figure
Measurement of proton electromagnetic form factors in in the energy region 2.00-3.08 GeV
The process of is studied at 22 center-of-mass
energy points () from 2.00 to 3.08 GeV, exploiting 688.5~pb of
data collected with the BESIII detector operating at the BEPCII collider. The
Born cross section~() of is
measured with the energy-scan technique and it is found to be consistent with
previously published data, but with much improved accuracy. In addition, the
electromagnetic form-factor ratio () and the value of the
effective (), electric () and magnetic () form
factors are measured by studying the helicity angle of the proton at 16
center-of-mass energy points. and are determined with
high accuracy, providing uncertainties comparable to data in the space-like
region, and is measured for the first time. We reach unprecedented
accuracy, and precision results in the time-like region provide information to
improve our understanding of the proton inner structure and to test theoretical
models which depend on non-perturbative Quantum Chromodynamics
Precise Measurements of Branching Fractions for Meson Decays to Two Pseudoscalar Mesons
We measure the branching fractions for seven two-body decays to
pseudo-scalar mesons, by analyzing data collected at
GeV with the BESIII detector at the BEPCII collider. The branching fractions
are determined to be ,
,
,
,
,
,
,
where the first uncertainties are statistical, the second are systematic, and
the third are from external input branching fraction of the normalization mode
. Precision of our measurements is significantly improved
compared with that of the current world average values
First observations of hadrons
Based on events collected with
the BESIII detector, five hadronic decays are searched for via process
. Three of them, ,
, and are observed for the first
time, with statistical significances of 7.4, , and
9.1, and branching fractions of ,
, and ,
respectively, where the first uncertainties are statistical and the second
systematic. No significant signal is observed for the other two decay modes,
and the corresponding upper limits of the branching fractions are determined to
be and at 90% confidence level.Comment: 17 pages, 16 figure
Measurements of Weak Decay Asymmetries of , , , and
Using production from a 567 pb
data sample collected by BESIII at 4.6 GeV, a full angular analysis is carried
out simultaneously on the four decay modes of , , , and . For the first time, the
transverse polarization is studied in unpolarized
collisions, where a non-zero effect is observed with a statistical significance
of 2.1. The decay asymmetry parameters of the weak
hadronic decays into , , and
are measured to be ,
,
, and
, respectively. In comparison with
previous results, the measurements for the and
modes are consistent but with improved precision, while the parameters for the
and modes are measured for the first time
Track-based alignment for the BESIII CGEM detector in the cosmic-ray test
The Beijing Electron Spectrometer III (BESIII) is a multipurpose detector
operating on the Beijing Electron Positron Collider II (BEPCII). After more
than ten year's operation, the efficiency of the inner layers of the Main Drift
Chamber (MDC) decreased significantly. To solve this issue, the BESIII
collaboration is planning to replace the inner part of the MDC with three
layers of Cylindrical triple-Gas Electron Multipliers (CGEM).
The new features of the CGEM detector will improve the spatial resolution to
130 m. To meet this goal, a careful calibration of the detector is
necessary to fully exploit the potential of the CGEM detector. In all the
calibrations, the detector alignment plays an important role to improve the
detector precision. The track-based alignment for the CGEM detector with the
Millepede algorithm is implemented to reduce the uncertainties of the hit
position measurement. Using the cosmic-ray data taken in 2020 with the two
layers setup, the displacement of the outer layer with respect to the inner
layer is determined by a simultaneous fit applied to more than 160000 tracks. A
good alignment precision has been achieved that guarantees the design request
could be satisfied in the future. A further alignment will be performed using
the combined information of tracks from cosmic-ray and collisions after the
CGEM is installed into the BESIII detector
Measurement of the J/ photoproduction cross section over the full near-threshold kinematic region
We report the total and differential cross sections for
photoproduction with the large acceptance GlueX spectrometer for photon beam
energies from the threshold at 8.2~GeV up to 11.44~GeV and over the full
kinematic range of momentum transfer squared, . Such coverage facilitates
the extrapolation of the differential cross sections to the forward ()
point beyond the physical region. The forward cross section is used by many
theoretical models and plays an important role in understanding
photoproduction and its relation to the proton interaction. These
measurements of photoproduction near threshold are also crucial inputs
to theoretical models that are used to study important aspects of the gluon
structure of the proton, such as the gluon Generalized Parton Distribution
(GPD) of the proton, the mass radius of the proton, and the trace anomaly
contribution to the proton mass. We observe possible structures in the total
cross section energy dependence and find evidence for contributions beyond
gluon exchange in the differential cross section close to threshold, both of
which are consistent with contributions from open-charm intermediate states.Comment: 15 pages 18 figure
Amplitude analysis of
Utilizing the data set corresponding to an integrated luminosity of
fb collected by the BESIII detector at a center-of-mass energy of 4.178
GeV, we perform an amplitude analysis of the decay.
The sample contains 13,797 candidates with a signal purity of 80%. The
amplitude and phase of the contributing wave are measured
based on a quasi-model-independent approach, along with the amplitudes and
phases of the and waves parametrized by Breit-Wigner
models. The fit fractions of different intermediate decay channels are also
reported.Comment: 14 pages, 6 figure
Search for New Hadronic Decays of and Observation of
Ten hadronic final states of the decays are investigated via the
process , using a data sample of events collected with the BESIII detector. The
decay channel is observed for
the first time with a significance of . The corresponding branching
fraction is determined to be (the
first uncertainty is statistical and the second systematical). Evidence for the
decays and is found with a significance of and , respectively. The corresponding branching fractions
(and upper limits) are obtained to be and
. Upper limits on the branching fractions for the final
states , ,
, ,
, , and
are determined at a confidence level of 90\%.Comment: 10 pages, 2 figure
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