440 research outputs found
Parallel momentum distribution of the Si fragments from P
Distribution of the parallel momentum of Si fragments from the breakup
of 30.7 MeV/nucleon P has been measured on C targets. The distribution
has the FWHM with the value of 110.5 23.5 MeV/c which is consistent
quantitatively with Galuber model calculation assuming by a valence proton in
P. The density distribution is also predicted by Skyrme-Hartree-Fock
calculation. Results show that there might exist the proton-skin structure in
P.Comment: 4 pages, 4 figure
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
The effect of internal pressure on the tetragonal to monoclinic structural phase transition in ReOFeAs: the case of NdOFeAs
We report the temperature dependent x-ray powder diffraction of the
quaternary compound NdOFeAs (also called NdFeAsO) in the range between 300 K
and 95 K. We have detected the structural phase transition from the tetragonal
phase, with P4/nmm space group, to the orthorhombic or monoclinic phase, with
Cmma or P112/a1 (or P2/c) space group, over a broad temperature range from 150
K to 120 K, centered at T0 ~137 K. Therefore the temperature of this structural
phase transition is strongly reduced, by about ~30K, by increasing the internal
chemical pressure going from LaOFeAs to NdOFeAs. In contrast the
superconducting critical temperature increases from 27 K to 51 K going from
LaOFeAs to NdOFeAs doped samples. This result shows that the normal striped
orthorhombic Cmma phase competes with the superconducting tetragonal phase.
Therefore by controlling the internal chemical pressure in new materials it
should be possible to push toward zero the critical temperature T0 of the
structural phase transition, giving the striped phase, in order to get
superconductors with higher Tc.Comment: 9 pages, 3 figure
Measurements of the absolute branching fractions of decays
Based on 2.93~fb collision data taken at center-of-mass
energy of 3.773 GeV by the BESIII detector, we report the measurements of the
absolute branching fractions of , , , , , ,
, , and . The decays , , , , and are observed for the
first time. The branching fractions of the decays , , ,
and are measured with improved precision compared
to the world-average values.Comment: 11 pages, 5 figure
Measurement of the branching fraction of and search for a CP-violating asymmetry in η′→π+π−e+e− at BESIII
The rare decay η′→π+π-e+e- is studied using a sample of 1.3×109 J/ψ events collected with the BESIII detector at BEPCII in 2009 and 2012. The branching fraction is measured with improved precision to be (2.42±0.05stat±0.08syst)×10-3. Due to the inclusion of new data, this result supersedes the last BESIII result on this branching fraction. In addition, the CP-violating asymmetry in the angle between the decay planes of the π+π - pair and the e+e - pair is investigated. A measurable value would indicate physics beyond the standard model; the result is ACP=(2.9±3.7stat±1.1syst)%, which is consistent with the standard model expectation of no CP-violation. The precision is comparable to the asymmetry measurement in the KL0→π+π-e+e- decay where the observed (14±2)% effect is driven by a standard model mechanism
Amplitude analysis and branching fraction measurement of D+s → K+K− π +
We report an amplitude analysis and branching fraction measurement of D+-
s → K+K−π+- decay using a data sample of 3.19 fb−1 recorded with BESIII detector at a center-of-mass energy of 4.178 GeV. We perform a model-independent partial wave analysis in the low KþK− mass region to determine the K+K−S-wave line shape, followed by an amplitude analysis of our very pure high-statistics sample. With the detection efficiency based on the amplitude analysis results, the absolute branching fraction is measured to be B(D+
s → K+K−π+-) = (5.47 pm 0.08stat pm 0.13sys)
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
Observation of a structure in at from 2.05 to 3.08 GeV
The process has been studied for the
first time in detail using data sample collected with the BESIII detector at
the BEPCII collider at center of mass energies from 2.05 to 3.08 GeV. A
resonance with quantum numbers is observed with mass =
(2177.5 4.8 (stat) 19.5 (syst)) MeV/ and
width = (149.0 15.6 (stat) 8.9 (syst)) MeV with a
statistical significance larger than 10. The observed structure could
be identified with the , then the ratio of partial width between
the by BESIII and by BABAR is
( = 0.23 0.10 (stat) 0.18 (syst),
which is smaller than the prediction of the hybrid models by
several orders of magnitude
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