859 research outputs found
NONLINEAR EFFECTS IN THE DYNAMICS OF SHAPE AND VOLUME OSCILLATIONS FOR A GAS BUBBLE IN AN EXTERNAL FLOW
No full textThis paper considers the dynamics of a gas bubble in response to either a pressure pulse or a pressure step at t = 0, both in the presence and absence of a mean flow. Our work utilizes small-deformation, domain perturbation analysis carried to second and higher order in the amplitude of deformation, epsilon. In the absence of a mean flow, our analysis of the small deformation problem for an initial impulsive perturbation of the bubble volume and shape is closely related to recently published work by Longuet-Higgins on the time-dependent oscillations of an initially deformed bubble in a quiescent fluid. However, in the presence of a mean flow which deforms the bubble, the bubble response to pressure changes is more complex. Specifically, the present analysis identifies a number of different mechanisms for resonant interaction between shape deformation modes and the volume or radial breathing mode of oscillation. This includes not only a fundamental change in the resonant interactions at O(epsilon2)- where resonant interaction is also found in the absence of mean flow - but resonant interactions also at the level of O(epsilon3/2) which are not present without the mean flow. On the other hand, the bubble dynamics in response to a step change in the pressure distribution in a quiescent fluid exhibits similar resonant interactions at O(epsilon2) to those obtained for a pressure pulse in the presence of mean flow because the bubble oscillates around a non-spherical steady-state shape owing to the non-uniform pressure distribution on the bubble surface in both the cases
Zc(3900): What has been really seen?
No full textAbstractThe Zc±(3900)/Zc±(3885) resonant structure has been experimentally observed in the Y(4260)→J/ψππ and Y(4260)→D¯⁎Dπ decays. This structure is intriguing since it is a prominent candidate of an exotic hadron. Yet, its nature is unclear so far. In this work, we simultaneously describe the D¯⁎D and J/ψπ invariant mass distributions in which the Zc peak is seen using amplitudes with exact unitarity. Two different scenarios are statistically acceptable, where the origin of the Zc state is different. They correspond to using energy dependent or independent D¯⁎D S-wave interaction. In the first one, the Zc peak is due to a resonance with a mass around the DD¯⁎ threshold. In the second one, the Zc peak is produced by a virtual state which must have a hadronic molecular nature. In both cases the two observations, Zc±(3900) and Zc±(3885), are shown to have the same common origin, and a D¯⁎D bound state solution is not allowed. Precise measurements of the line shapes around the DD¯⁎ threshold are called for in order to understand the nature of this state
Search for Zc(3900) ± → ωπ ±
No full textÇetin, Serkant Ali (Dogus Author)The decay Zc(3900)±→ωπ± is searched for using data samples collected with the BESIII detector operating at the BEPCII storage ring at center-of-mass energies s=4.23 and 4.26 GeV. No significant signal for the Zc(3900)± is found, and upper limits at the 90% confidence level on the Born cross section for the process e+e-→Zc(3900)±π →ωπ+π- are determined to be 0.26 and 0.18 pb at s=4.23 and 4.26 GeV, respectively
Search for Zc (3900)± →ωπ± SEARCH for Zc (3900)± →ωπ± M. ABLIKIM et al
No full textThe decay Zc(3900)-->omega pi+- is searched for using data samples collected with the BESIII detector operating at the BEPCII storage ring at center-of-mass energies sqrt(s)=4.23 and 4.26 GeV. No significant signal for the Zc(3900)± is found, and upper limits at the 90% confidence level on the Born cross section for the process e+e- -->Zc(3900)±pi-+ -->omega pi+pi- are determined to be 0.26 and 0.18 pb at sqrt(s)=4.23 and 4.26 GeV, respectively
Observation of Zc (3900)0 in e+e- →π0π0J/ψ
Get PDFÇetin, Serkant Ali (Dogus Author)Using a data sample collected with the BESIII detector operating at the BEPCII storage ring, we observe a new neutral state Zc(3900)0 with a significance of 10.4σ. The mass and width are measured to be 3894.8±2.3±3.2MeV/c2 and 29.6±8.2±8.2MeV, respectively, where the first error is statistical and the second systematic. The Born cross section for e+e-→π0π0J/ψ and the fraction of it attributable to π0Zc(3900)0→π0π0J/ψ in the range Ec.m.=4.19-4.42GeV are also determined. We interpret this state as the neutral partner of the four-quark candidate Zc(3900)±
Confirmation of a charged charmoniumlike state Zc (3885)∓ in e+e- →π± (D D ¯ ∗)∓ with double D tag
No full textÇetin, Serkant Ali (Dogus Author)We present a study of the process e+e-→π±(DD¯∗)∓ using data samples of 1092 pb-1 at s=4.23 GeV and 826 pb-1 at s=4.26 GeV collected with the BESIII detector at the BEPCII storage ring. With full reconstruction of the D meson pair and the bachelor π± in the final state, we confirm the existence of the charged structure Zc(3885)∓ in the (DD¯∗)∓ system in the two isospin processes e+e-→π+D0D∗- and e+e-→π+D-D∗0. By performing a simultaneous fit, the statistical significance of Zc(3885)∓ signal is determined to be greater than 10σ, and its pole mass and width are measured to be Mpole=(3881.7±1.6(stat)±1.6(syst)) MeV/c2 and Γpole=(26.6±2.0(stat)±2.1(syst)) MeV, respectively. The Born cross section times the (DD¯∗)∓ branching fraction (σ(e+e-→π±Zc(3885)∓)×Br(Zc(3885)∓→(DD¯∗)∓)) is measured to be (141.6±7.9(stat)±12.3(syst)) pb at s=4.23 GeV and (108.4±6.9(stat)±8.8(syst)) pb at s=4.26 GeV. The polar angular distribution of the π±-Zc(3885)∓ system is consistent with the expectation of a quantum number assignment of JP=1+ for Zc(3885)∓
Observation of a neutral charmoniumlike state Zc (4025)0 in e+e- → (D∗ D ¯ ∗)0π0
No full textÇetin, Serkant Ali (Dogus Author)We report a study of the process e+e-→(D∗D¯∗)0π0 using e+e- collision data samples with integrated luminosities of 1092 pb-1 at s=4.23 GeV and 826 pb-1 at s=4.26 GeV collected with the BESIII detector at the BEPCII storage ring. We observe a new neutral structure near the (D∗D¯∗)0 mass threshold in the π0 recoil mass spectrum, which we denote as Zc(4025)0. Assuming a Breit-Wigner line shape, its pole mass and pole width are determined to be (4025.5-4.7+2.0±3.1) MeV/c2 and (23.0±6.0±1.0) MeV, respectively. The Born cross sections of e+e-→Zc(4025)0π0→(D∗D¯∗)0π0 are measured to be (61.6±8.2±9.0) pb at s=4.23 GeV and (43.4±8.0±5.4) pb at s=4.26 GeV. The first uncertainties are statistical and the second are systematic
Observation of e+e−→π0π0hc and a Neutral Charmoniumlike Structure Zc(4020)0
No full textUsing data collected with the BESIII detector operating at the Beijing Electron Positron Collider at center-of-mass energies of sqrt(s)=4.23, 4.26, and 4.36 GeV, we observe e+e-→π0π0hc for the first time. The Born cross sections are measured and found to be about half of those of e+e-→π+π-hc within less than 2σ. In the π0hc mass spectrum, a structure at 4.02 GeV/c2 is found. It is most likely to be the neutral isospin partner of the Zc(4020)± observed in the process of e+e-→π+π-hc being found. A fit to the π0hc invariant mass spectrum, with the width of the Zc(4020)0 fixed to that of its charged isospin partner and possible interferences with non-Zc(4020)0 amplitudes neglected, gives a mass of (4023.9±2.2±3.8) MeV/c2 for the Zc(4020)0, where the first error is statistical and the second systematic
Time-resolved photoluminescence spectra of self-assembled InAs/GaAs quantum dots
No full textTwo types of InAs self-assembled Quantum dots (QDs) were prepared by Molecular beam epitaxy. Atomic force microscopy (AFM) measurements showed that, compared to QDs grown on GaAs substrate, QDs grown on InGaAs layer has a significantly enhanced density. The short spacing (several nanometer) among QDs stimulates strong coupling and leads to a large red-shift of the 1.3 mu m photoluminescence (PL) peak. We study systematically the dependence of PL lifetime on the QDs size, density and temperature (1). We found that, below 50 K, the PL lifetime is insensitive to temperature, which is interpreted from the localization effects. As T increases, the PL lifetime increases, which can be explained from the competition between the carrier redistribution and thermal emission at higher temperature. The increase of carriers in QDs migrated from barriers and wetting layer (WL), and the redistribution of carriers among QDs enhance the PL lifetime as T increases. The thermal emission and non-radiative recombination have effects to reduce the PL lifetime at higher T. As a result, the radiative recombination lifetime is determined by the wave function overlapping of electrons and holes in QDs, and QDs with different densities have different PL lifetime dependence on the QDs size. (c) 2005 Elsevier B.V. All rights reserved
Observation of Zc(39000)0 in e+e− → π0π0J/ψ
No full textUsing a data sample collected with the BESIII detector operating at the BEPCII storage ring, we observe a new neutral state Zc(39000)0 with a significance of 10.4σ. The mass and width are measured to be 3894.8 ± 2.3 ± 3.2 MeV=c2 and 29.6 ± 8.2 ± 8.2 MeV, respectively, where the first error is statistical and the second systematic. The Born cross section for e+e− → π0π0J=ψ and the fraction of it attributable to ψ0Zc(39000)0 → π0π0J=ψ in the range Ec.m. 4.19−4.42 GeV are also determined. We interpret this state as the neutral partner of the four-quark candidate Zc(3900)±
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