119115603
Charmed Scalar Meson Production in $B$ Decays
The study on the charmed scalar meson spectroscopy has become a hot topic both experimentally and theoretically. The $B_{(s)}$ decays provide an ideal place to study their property. We employ the $B$-meson light-cone sum rules to compute the $\bar B_s^0\to D_s^{*+}(2317)$ and $B^-\to D_0^{*0}(2400)$ transition form factors at large recoil, assuming $D_s^{*+}(2317)$ and $D_0^{*0}(2400)$ being scalar quark-anti-quark states. The results are extrapolated to the whole momentum region with the help of HQET. Considering large uncertainties, our results can be consistent with the previous studies, while the power corrections should be large. We also estimate the semi-leptonic decays $\bar B_s^0\to D_s^{*+}(2317)l \bar{\nu}_l$ and $B^-\to D_0^{*0}(2400)l \bar{\nu}_l$. The branching fraction of the semi-leptonic $\bar B_s^0\to D_s^{*+}(2317)l \bar{\nu}_l$ decay is around $6\times 10^{-3} $ for light leptons and $0.8\times 10^{-3} $ for tau final state. The predicted branching ration of $B^-\to D_0^{*0}(2400)l \bar{\nu}_l$ is slightly larger than $\bar B_s^0\to D_s^{*+}(2317)l \bar{\nu}_l$, and we hope the future data in LHCb can test these results.
12644662
Observation of thundercloud-related gamma rays and neutrons in Tibet
During the 2010 rainy season in Yangbajing (4300 m above sea level) in Tibet, China, a long-duration count enhancement associated with thunderclouds was detected by a solar-neutron telescope and neutron monitors installed at the Yangbajing Comic Ray Observatory. The event, lasting for similar to 40 min, was observed on July 22, 2010. The solar-neutron telescope detected significant gamma-ray signals with energies >40 MeV in the event. Such a prolonged high-energy event has never been observed in association with thunderclouds, clearly suggesting that electron acceleration lasts for 40 min in thunderclouds. In addition, Monte Carlo simulations showed that >10 MeV gamma rays largely contribute to the neutron monitor signals, while >1 keV neutrons produced via a photonuclear reaction contribute relatively less to the signals. This result suggests that enhancements of neutron monitors during thunderstorms are not necessarily clear evidence for neutron production, as previously thought.
118614193
Reexamination of reaction rates for a key stellar reaction of $^{14}$O($\alpha$,p)$^{17}$F
The reaction rates of the key stellar reaction of O(α,p)F have been reexamined. The previous conclusion, the 6.15-MeV state (Jπ=1−) dominating this reaction rate, has been overthrown by a careful reanalysis of the previous experimental data [J. Gómez del Campo et al., Phys. Rev. Lett. 86, 43 (2001)]. According to the present R-matrix analysis, the previous 1− assignment for the 6.15MeV state is definitely wrong. Most probably, the 6.286-MeV state is the 1− state and the 6.15-MeV state is a 3− one, and hence the resonance at Ex=6.286 MeV (J π=1−) dominates the reaction rates in the temperature region of astrophysical interests. The newly calculated reaction rates for the O(α,p)F reaction are quite different from the previous ones, for instance, it’s only about 1/6 of the previous value around 0.4 GK, while it’s about 2.4 times larger than the previous value around 2 GK. The astrophysical implications have been discussed based on the present conclusions.
119226741
Spectroscopic factors for low-lying $^{16}$N levels and the astrophysical $^{15}$N $(n,\gamma)^{16}$N reaction rate
Fluorine is a key element for nucleosynthetic studies since it is extremely sensitive to the physical conditions within stars. The astrophysical site to produce fluorine is suggested to be asymptotic giant branch (AGB) stars. In these stars the 15N(n, g)16N reaction could affect the abundance of fluorine by competing with 15N(a, g)19F. The 15N(n, g)16N reaction rate depends directly on the neutron spectroscopic factors of the low-lying states in 16N. The angular distributions of the 15N(7Li, 6Li)16N reaction populating the ground state and the first three excited states in 16N are measured using a Q3D magnetic spectrograph and are used to derive the spectroscopic factors of these states based on distorted wave Born approximation (DWBA) analysis. The spectroscopic factors of these four states are extracted to be 0.96+-0.09, 0.69+-0.09, 0.84+-0.08 and 0.65+-0.08, respectively. Based on the new spectroscopic factors we derive the 15N(n,g)16N reaction rate. The accuracy and precision of the spectroscopic factors are enhanced due to the first application of high-precision magnetic spectrograph for resolving the closely-spaced 16N levels which can not be achieved in most recent measurement. The present result demonstrates that two levels corresponding to neutron transfers to the 2s1/2 orbit in 16N are not so good single-particle levels although 15N is a closed neutron-shell nucleus. This finding is contrary to the shell model expectation. The present work also provides an independent examination to shed some light on the existing discrepancies in the spectroscopic factors and the 15N(n, g)16N rate.
110035692
DESIGN OF LOW IMPEDANCE ELECTROSTATIC SEPARATORS FOR BEPC II
The multi bunch train collision is adopted in BEPC II. There are 4 horizontal electrostatic separators in the main ring to generate close-orbit displacement as "pretzels" which allow the electrons and positrons to be stored in the same vacuum chamber simultaneously without unwanted destructive collisions. In the separator the beam current (576mA) and the gap voltage (220 kV) are both very high. So there are five key problems that must be handled well: To reduce the beam impedance and loss factor; To absorb the high order modes (HOMs); To reduce the leakage of RF EM field; To extract the heats due to the HOMs losses and the SR power; To reduce the spark rate. Their analysis and the solutions are presented in this paper.
118454051
Investigation of excited states in $^{18}$Ne via resonant elastic scattering of $^{17}$F+p and its astrophysical implication in the stellar reaction of $^{14}$O($\alpha$,$p$)$^{17}$F
Properties of proton resonances in $^{18}$Ne have been investigated efficiently by utilizing a technique of proton resonant elastic scattering with a $^{17}$F radioactive ion (RI) beam and a thick proton target. A 4.22~MeV/nucleon $^{17}$F RI beam was produced via a projectile-fragmentation reaction, and subsequently separated by a Radioactive Ion Beam Line in Lanzhou ({\tt RIBLL}). Energy spectra of the recoiled protons were measured by two sets of $\Delta$E-E silicon telescope at center-of-mass scattering angles of $\theta_{c.m.}$$\approx$175${^\circ}$$\pm$5${^\circ}$, $\theta_{c.m.}$$\approx$152${^\circ}$$\pm$8${^\circ}$, respectively. Several proton resonances in $^{18}$Ne were observed, and their resonant parameters have been determined by an $R$-matrix analysis of the differential cross sections in combination with the previous results. The resonant parameters are related to the reaction-rate calculation of the stellar $^{14}$O($\alpha$,$p$)$^{17}$F reaction, which was thought to be the breakout reaction from the hot CNO cycles into the $rp$-process in x-ray bursters. Here, $J^\pi$=(3$^-$, 2$^-$) are tentatively assigned to the 6.15-MeV state which was thought the key 1$^-$ state previously. In addition, a doublet structure at 7.05 MeV are tentatively identified, and its contribution to the resonant reaction rate of $^{14}$O($\alpha$,$p$)$^{17}$F could be enhanced by at least factors of about 4$\sim$6 in comparison with the previous estimation involving only a singlet. The present calculated resonant rates are much larger than those previous values, and it may imply that this breakout reaction could play a crucial role under x-ray bursters conditions.
110270067
PRELIMINARY DESIGN OF FAST KICKER SYSTEM FOR BEPC II
With in BEPC II injection system there are two sets injection lines in storage ring each consisting of a pair of kicker magnets and one Lambertson magnet for e + and e injection respectively. The incoming beam is injected horizontally inside the storage ring. The linac provides the short pulsed bunch train of 3 micro bunches. There are six e + and six e -- bunch trains countermove in a same ring. The single bunch train injection is chosen. The duration of bunch train is 16ns. The kick of field is 130 Gauss-meter. The type of lumped ferrite inductance magnet with ceramic vacuum chamber is chosen. Per magnet consists of four modules each of 30 cm long, The field strength of magnet is 108 gauss. Excitation current is 631 A .The pulse field of magnet is a trapezoidal wave with duration less than 110ns, rise / fall time of K1 and fall / rise time of K2 is 33ns / 50ns respectively. The lumped LC network with impedance of 30ohm and voltage of 38kV is chosen as a pulser. The stray inductance of lead is controlled to be small enough by an air-insulated coaxial construction. Field rise time is reduced by the compensating capacitance and the fall time is reduced by second switch and saturable reactor. A ZVS PWM type of high voltage power supply is chosen as the charger for PFN. The details are described in this paper.