Kinetic Analysis of the Thermal Processing of Silica and Organosilica

The incorporation of an organic group into sol–gel-derived silica causes significant changes in the structure and properties of these materials. Therefore, the thermal treatment of organosilica materials may require a different approach. In the present paper, kinetic parameters (activation energy, pre-exponential constant, and reaction models) have been determined from mass loss data for the dehydration, dehydroxylation, and decomposition reactions that take place upon heating silica and organosilica. Parameters were obtained by employing model-free isoconversional methods to data obtained under multiple heating rates as well as by multivariate analysis of the kinetics using a multistep reaction model with distributed activation energy. For silica, it can be concluded that the reaction atmosphere (i.e., inert or thermo-oxidative) has no influence on the reaction rate of the dehydration and dehydroxylation reactions that are responsible for the densification of the material. Under inert atmosphere, full dehydration can be reached without affecting the organic moiety. Achieving complete dehydroxylation of the organosilica is practically impossible as decomposition does manifest itself under commonly employed calcination temperatures. This indicates that prudence is required in designing a heat treatment program for these hybrid materials. To aid in optimizing the thermal treatment, a predictive model was developed, which can be used to forecast the extent of dehydration, dehydroxylation, and decomposition reactions under a multitude of temperature program

Measurement of Proton Electromagnetic Form Factors in e(+) e(-) -> p(p)over-bar in the Energy Region 2.00-3.08 GeV

The process of e+e-→pp̄ is studied at 22 center-of-mass energy points (s) from 2.00 to 3.08 GeV, exploiting 688.5 pb-1 of data collected with the BESIII detector operating at the BEPCII collider. The Born cross section (σpp̄) of e+e-→pp̄ 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 (|GE/GM|) and the value of the effective (|Geff|), electric (|GE|), and magnetic (|GM|) form factors are measured by studying the helicity angle of the proton at 16 center-of-mass energy points. |GE/GM| and |GM| are determined with high accuracy, providing uncertainties comparable to data in the spacelike region, and |GE| is measured for the first time. We reach unprecedented accuracy, and precision results in the timelike region provide information to improve our understanding of the proton inner structure and to test theoretical models which depend on nonperturbative quantum chromodynamics

Measurement of the branching fraction of the doubly Cabibbo-suppressed decay D0 →k+π-π0 and search for D0 →k+π-π0π0

Using 2.93 fb-1 of e+e- collision data collected at a center-of-mass energy of 3.773 GeV with the BESIII detector, we present a measurement of the branching fraction of the doubly Cabibbo-suppressed (DCS) decay D0→K+π-π0 and a search for the DCS decay D0→K+π-π0π0. The branching fraction of D0→K+π-π0 is determined to be [3.13-0.56+0.60(stat)±0.15(syst)]×10-4. No signal is observed for D0→K+π-π0π0, and an upper limit of 3.6×10-4 is set on the branching fraction at the 90% CL. We combine these results with the world-average branching fractions of their counterpart Cabibbo-favored decays to determine the ratios of the DCS over the Cabibbo-favored branching fractions, B(D0→K+π-π0)/B(D0→K-π+π0)=(0.22±0.04)% and B(D0→K+π-π0π0)/B(D0→K-π+π0π0)<br/

Observation of a New X (3872) Production Process e+e- →ωX (3872)

Using 4.7 fb-1 of e+e- collision data at center-of-mass energies from 4.661 to 4.951 GeV collected by the BESIII detector at the BEPCII collider, we observe the X(3872) production process e+e-→ωX(3872) for the first time. The significance is 7.8σ, including both the statistical and systematic uncertainties. The e+e-→ωX(3872) Born cross section and the corresponding upper limit at 90% confidence level at each energy point are reported. The line shape of the cross section indicates that the ωX(3872) signals may be from the decays of some nontrivial structures

Observation of ψ (3770) →ηJ/ψ

Using a data sample collected with the BESIII detector operating at the BEPCII storage ring, the Born cross section of the process e+e-→ηJ/ψ at a center-of-mass energy s=3.773 GeV is measured to be (8.88±0.87±0.42) pb. We fit the cross section line shape before correcting for the initial state radiation from s=3.773 to 4.600 GeV to obtain the branching fraction B(ψ(3770)→ηJ/ψ). We obtain B(ψ(3770)→ηJ/ψ)=(11.3±5.9±1.1)×10-4 when the ψ(3770) decay amplitude is added coherently to the other contributions, and (8.7±1.0±0.8)×10-4 when it is added incoherently. Here the quoted uncertainties are statistical and systematic, respectively. In both cases, the statistical significance of ψ(3770) resonance is above 7σ. This is the first time the decay ψ(3770)→ηJ/ψ is observed with a statistical significance greater than 5σ

Measurement of the CP -even fraction of D0 →k+K-π+π-

A determination of the CP-even fraction F+ in the decay D0→K+K-π+π- is presented. Using 2.93 fb-1 of e+e-→ψ(3770)→DD¯ data collected by the BESIII detector, one charm meson is reconstructed in the signal mode and the other in a CP eigenstate or the decay D→KS,L0π+π-. Analysis of the relative rates of these double-tagged events yields the result F+=0.730±0.037±0.021, where the first uncertainty is statistical and the second is systematic. This is the first model-independent measurement of F+ in D0→K+K-π+π- decays

Helicity amplitude analysis of χcJ → ϕϕ

Using (447.9 ± 2.3) million ψ(3686) events collected with the BESIII detector, the decays of χcJ → ϕϕ (J = 0, 1, 2) have been studied via the decay ψ(3686) → γχcJ. The branching fractions of the decays χcJ → ϕϕ (J = 0, 1, 2) are determined to be (8.59 ± 0.27 ± 0.20) × 10−4, (4.26 ± 0.13 ± 0.15) × 10−4, and (12.67 ± 0.28 ± 0.33) × 10−4, respectively, which are the most precise measurements to date. From a helicity amplitude analysis of the process ψ(3686) → γχcJ , χcJ → ϕϕ, ϕ → K + K −, the polarization parameters of the χcJ → ϕϕ decays are determined for the first time. [Figure not available: see fulltext.]