2012 Vol. 36, No. 7
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Scenarios for the τ mass measurement at the upgraded Beijing Electron-Positron Collider (BEPC-Ⅱ) are studied. A nested minimization procedure is used to optimize the data taking plan. It is found that by using five energy points with the total integrated luminosity of 100 pb-1, the τ mass can be determined with a statistical error of 50 keV.
Since the birth of the quark model, the diquark, which is composed of two quarks, has been considered as a substantial structure of a color anti-triplet. This is not only a mathematical simplification for dealing with baryons, but also provides a physical picture where the diquark would behave as a whole object. It is natural to ask whether such a structure is sufficiently stable against external disturbance. The mass spectra of the ground states of the scalar and axial-vector diquarks, which are composed of two-light (L-L), one-light-one-heavy (H-L) and two-heavy (H-H) quarks, respectively, have been calculated in terms of the QCD sum rules. We suggest a criterion as the quantitative standard for the stability of the diquark. It is the gap between the masses of the diquark and √s0 where s0 is the threshold of the excited states and continuity, namely the larger the gap is, the more stable the diquark would be. In this work, we calculate the masses of the H-H type to complete the series of the spectra of the ground state diquarks. However, as the criterion being taken, we find that all the gaps for the various diquarks are within a small range. In particular, the gap for the diquark with two heavy quarks, which is believed to be a stable structure, is slightly smaller than that of the other two types of diquarks. Therefore we conclude that because of the large theoretical uncertainty, we cannot use the numerical results obtained with the QCD sum rules to assess the stability of diquarks, but need to invoke other theoretical framework.
In the framework of factorization, we study direct CP violation in the decays of B(s)→J/ψP(V) (P(V) refer to the pseudoscalar (vector) meson). The CP violation depends strongly on Cabibbo-Kobayashi- Maskawa (CKM) matrix elements and the effective parameter, Nc. The recent experimental data for the branching ratios of B(s)→J/ψP(V) are accurate enough and we can give a strong constraint on the range of Nc. We nd that the CP violating asymmetry is consistent with the available experiment values for the b→d transition, and a little smaller than the b→s transition. We also predict the CP violation of other decay channels for B(s)→J/ψP(V). We expect our results can give valuable guidance for experiments.
This paper studies the entanglement dynamics of the system S composed of two non-interactional qubits A and B. The third qubit C is its environment, E, which only interacts with the S qubit B by the Dzyaloshinskii-Moriya spin-orbit coupling. Considering the following states as the whole (S+E): the initially S-E correlated state and the separable one, the entanglement of S has no sudden death for the former case. This result sheds some light on the control of quantum entanglement, which will be helpful for quantum information processing.
A novel determinate joint remote preparation scheme of an arbitrary W-class quantum state is proposed to improve the probability of successful preparation. The presented scheme is realized through orthogonal projective measurement of the Hadamard transferred basis, which converts a global measurement to several local measurements. Thus orthogonal projective measurement of the Hadamard transferred basis enables quantum information to be transmitted from different sources simultaneously, which is a breakthrough for quantum network node processing. Finally, analysis shows the feasibility and validity of the proposed method, with a 100% probability of successful preparation.
We have recently shown that, as a compact star containing mixed-phase matter slows down, the compression can cause deconfinement phase transition, and thus enhance the chemical deviations and raise the chemical heating efficiency. In a previous study, only the direct Urca processes in nucleon and quark matter were considered. In this work, we extend the previous analysis to the case where the much slower modified Urca processes operate in nucleon matter. We find a fast promotion in the surface effective temperature of hybrid stars, and that the cooling process is dominated by both the nucleon and quark channels.
The luminosity for a WASA-at-COSY experiment involving the pd reaction at 2.14 GeV proton-beam energy is determined by the forward pd elastic scattering, which yields an average beam-on-target value of [5.2 ± 0.3(stat) ± 0.3syst] × 1030s-1cm-2. In addition, the forward pd elastic-scattering angular distribution is obtained with four-momentum transfer squared -t between 0.16 (GeV/c)2 and 0.78 (GeV/c)2 at this beam energy, which is compared with other experimental data and the pd double scattering model.
We report the density measurement through e-3He elastic scattering with a 1.23 GeV electron beam in Jefferson Lab experiment E06-010. The extracted 3He density is (9.26±0.06) amagats and the N2/3He ratio is (1.49±0.08)%. In addition, these results are consistent with the deduced target densities based on pressure broadening measurement.
The rapidity densities at mid-rapidity and the transverse momentum distributions for strange hadrons produced in pp collisions are analyzed using the modi ed PACIAE model by considering the effect of inelastic (re)scattering processes ss→gg and gg→ss in parton (re)scattering. The calculated results of the transverse momentum spectra of the strangeness fitting with data measured by STAR and ALICE Collabora- tions can be improved, especially at large transverse momentum levels. This demonstrates that the effect of inelastic (re)scattering processes of ss→gg and gg→ss is not negligible at RHIC and LHC energy levels.
The online Data Quality Monitoring (DQM) tool plays an important role in the data recording process of HEP experiments. The BESⅢ DQM collects data from the online data flow, reconstructs them with offline reconstruction software and automatically analyzes the reconstructed data with user-defined algorithms. The DQM software is a scalable distributed system. The monitored results are gathered and displayed in various formats, which provides the shifter with current run information that can be used to identify problems quickly. This paper gives an overview of the DQM system at BESⅢ.
Tyvek is widely used as the inner lining material of water Cherenkov detectors. Therefore, information about its optical properties plays an important role in the simulation and reconstruction of particles passing through water Cherenkov detectors. In this paper, a water tank experiment is performed to study the Tyvek reflectivity in water. The so-called UNIFIED model, which is an optical model of surface reflection in Geant4, is adopted to describe the Tyvek reflectivity. Two key optical parameters are obtained from a comparison between the measured data and a Monte Carlo simulation.
The performance of a MultiPixel Photon Counter (MPPC) from room to liquid nitrogen temperatures were studied. The gain, the noise rate and bias voltage of the MPPC as a function of temperature were obtained. The experimental results show that the MPPC can work at low temperatures. At nearly liquid nitrogen temperatures, the gain of the MPPC drops obviously to 35% and the bias voltage drops about 9 V compared with that at room temperature. The thermal noise rate from 106 Hz/mm at room temperature drops abruptly to 0 Hz/mm at -100 ℃. The optimized operation point can be acquired by the experiment.
Short copper standing wave (SW) structures operating at an X-band frequency have been recently designed and manufactured at the Laboratori Nazionali di Frascati of the Istituto Nazionale di Fisica Nucleare (INFN) using the vacuum brazing technique. High power tests of the structures have been performed at the SLAC National Accelerator Laboratory. In this manuscript we report the results of these tests and the activity in progress to enhance the high gradient performance of the next generation of structures, particularly the technological characterization of high performance coatings obtained via molybdenum sputtering.
On the basis of an energy-recovery linac, a terahertz source with a potential for kilowatts of average power is proposed in Shanghai, which will serve as an effective tool for material and biological sciences. In this paper, the physical design of two free electron laser (FEL) oscillators, in a frequency range of 2--10 THz and 0.5--2 THz respectively, are presented. By using three-dimensional, time-dependent numerical modeling of GENESIS in combination with a paraxial optical propagation code, the THz oscillator performance, the detuning effects, and the tolerance requirements on the electron beam, the undulator field and the cavity alignment are given.
We designed a 100 MeV/100 kW electron linear accelerator for NSC KIPT, which will be used to drive a neutron source on the basis of subcritical assembly. Beam dynamics studies have been conducted to reach the design requirements (E=100 MeV, P=100 kW, dE/E<1% for 99% particles). In this paper, we will present the progress of the design and the dynamic simulation results. For high intensity and long beam pulse linear accelerators, the BBU effect is one big issue; special care has been taken in the accelerating structure design. To satisfy the energy spread requirement at the linac exit, the particles with large energy difference from the synchronous particle should be eliminated at a low energy stage to ease the design of the collimation system and radiation shielding. A dispersion free chicane with 4 bending magnets is introduced downstream of the 1st accelerating section; the unwanted particles will be collimated there.
An oil dielectric helical pulse line to demonstrate the principles of a Pulse Line Ion Accelerator (PLIA) has been designed and fabricated. The simulation of the axial electric field of an accelerator with CST code has been completed and the simulation results show complete agreement with the theoretical calculations. To fully understand the real value of the electric field excited from the helical line in PLIA, an optical electric integrated electric field measurement system was adopted. The measurement result shows that the real magnitude of axial electric field is smaller than that calculated, probably due to the actual pitch of the resister column which is much less than that of helix.
For CSNS RCS tune measurement, tune value is measured by exciting the bunch with a strip-line kicker fed with white noise and using a FFT algorithm. This article simulates the strip-line kicker in RCS and the efficiency of the kicker is discussed in a Matlab environment. The parameters of the kicker with an arc electrode structure such as a VSWR, wake impedance, and thermal state are analyzed based on the advantages of this design.
In order to check the conceptual design of the subcritical blanket in a fusion-fission hybrid reactor, a depleted uranium/polyethylene simulation device with alternate shells has been established. The measurement of the 238U(n, 2n) reaction rate was carried out using an activation technique, by measuring the 208 keVγ rays emitted from 237U. The self-absorption of depleted uranium foils with different thicknesses was experimentally corrected. The distribution of the 238U(n, 2n) reaction rate at 90° to the incident D+ beam was obtained, with uncertainty between 5.3% and 6.0%. The experiment was analyzed using MCNP5 code with the ENDF/BVI library, and the calculated results are all about 5% higher than the measured results.
A dedicated breast CT system (DBCT) is a new method for breast cancer detection proposed in recent years. In this paper, the glandular dose in the DBCT is simulated using the Monte Carlo method. The phantom shape is half ellipsoid, and a series of phantoms with different sizes, shapes and compositions were constructed. In order to optimize the spectra, monoenergy X-ray beams of 5-80 keV were used in simulation. The dose distribution of a breast phantom was studied: a higher energy beam generated more uniform distribution, and the outer parts got more dose than the inner parts. For polyenergtic spectra, four spectra of Al filters with different thicknesses were simulated, and the polyenergtic glandular dose was calculated as a spectral weighted combination of the monoenergetic dose.
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