2010 Vol. 34, No. 12
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Trigger efficiencies at BESⅢ were determined for both the J/ψ and ψ′ data taking of 2009. Both dedicated runs and physics datasets are used; efficiencies are presented for Bhabha-scattering events, generic hadronic decay events involving charged tracks, dimuon events and ψ′→π+π－J/ψ, J/ψ→l+l－ events. The efficiencies are found to lie well above 99% for all relevant physics cases, thus fulfilling the BESⅢ design specifications.
Based on the branching fractions of J/ψ(ψ(2S))→VP from different collaborations, pseudoscalar mixing is extensively discussed with a well established phenomenological model. The mixing angle is determined to be －14° by fitting to the new world average if only quark content is considered. After taking into account the gluonic content in η and η′ simultaneously, the investigation shows that η favors only consisting of light quarks, while the gluonic content of η′ is Zη′2=0.30±0.24.
Subject to neutrino experiments, the mixing matrix of ordinary neutrinos can still have small violation from unitarity. We introduce a quasi-unitary matrix to interpret this violation and propose a natural scheme to parameterize it. A quasi-unitary factor ΔQF is defined to be measured in neutrino oscillation experiments and the numerical results show that the improvement in experimental precision may help us figure out the secret of neutrino mixing.
Applying an effective Lagrangian method and an on-shell scheme, we analyze the electroweak corrections to the rare decay b→s+γ from some special two loop diagrams in which a closed heavy fermion loop is attached to the virtual charged gauge bosons or Higgs. At the decoupling limit where the virtual fermions in the inner loop are much heavier than the electroweak scale, we verify the final results satisfying the decoupling theorem explicitly when the interactions among Higgs and heavy fermions do not contain the nondecoupling couplings. Adopting the universal assumptions on the relevant couplings and mass spectrum of new physics, we find that the relative corrections from those two loop diagrams to the SM theoretical prediction on the branching ratio of B→Xsγ can reach 5% as the energy scale of new physics ΛNP=200 GeV.
The Low Energy X-ray Instrument (LE) of the Hard X-ray Modulation Telescope (HXMT) uses the Swept Charge Device (SCD) to detect the X-rays in 1—15 keV. The performance of SCD is vulnerable to temperature. We analyzed the thermal condition of LE at different satellite working attitudes with the Finite Element Method (FEM). It is shown that the angle between the sunlight and the normal line of the barrier should be less than 26°, to keep the SCD detectors working in the required temperature range, i.e. －40 ℃ to －80 ℃. We find that the performance of LE is very stable in this temperature range, with a typical energy resolution of 160 eV at 5.9 keV.
Employing phenomenological density-dependent critical temperatures of strong singlet-state proton pairing and of moderate triplet-state neutron pairing, we investigate the effects of rotochemical heating on the thermal evolution of superfluid neutron stars whose cores
consist of npe matter with the Akmal-Pandharipande-Ravenhall equation of state. Since the star is not quite in the weak interaction equilibrium state during spin-down, the departure from the chemical equilibrium leads to the rotochemical heating in a rotating NS which will increase the stellar's temperature. Our calculations show that the rotochemical heating delays the cooling of superfluid neutron stars considerably and makes the previous classification of NS cooling ambiguous. What's more, our model is currently consistent with all the observational data, and in particular some middle-aged and cold NSs (PRS J0205+6449 in 3C 58, PRS J1357-6429, RX J007.0+7303 in CTA 1, Vela) can be better explained when taking into account rotochemical heating.
The interacting boson model with isospin (IBM-3) is applied to study the band structure and electromagnetic transition properties of the low-lying states in the cross-conjugate nuclei 44Ti and 52Fe. The isospin excitation states with T=0, 1 and 2 are identified and compared with available data. The E2 and M1 matrix elements for the low-lying states have been investigated. According to this study, the 23+ state is the lowest mixed symmetry state in the cross-conjugate nuclei 44Ti and 52Fe. The excitation energy of the second 02+ and 22+ states with T=0 in the nucleus 52Fe are identified. The agreement between the model calculations and data is reasonably good.
By using the rigorous spectral representation of relativistic random phase approximation, the low-lying excitation of finite nuclei and its longitudinal response function for quasielastic
electron scattering are calculated in the σ-ω model of quantum hadrodynamics. It is shown that the reproduction of the correct order of the 1－ and 3－ excitation states of 16O is due to the contribution of the exchange vertex. There is no significant influence of the retardation effect on the low-lying excitation states. In contrast, the retardation effect plays an important role in the electron scattering process of nuclei. The theoretical longitudinal responses of 12C and 40Ca, including the contributions of the exchange vertex and the retardation effect, are suppressed and reproduce the experimental data better than the results excluding them.
The experimentally observed ten rotational bands in 179Re are analyzed with the particle-number conserving method for treating the cranked shell model with pairing interaction, in which the blocking effects are taken into account exactly. The experimental moments of inertia of these bands are reproduced quite well by our calculations with no free parameter and the deformation driving effects are discussed. The bandhead energies and the variation in the occupation probability of each cranked orbital are also analyzed.
The optical model analysis of the alpha particle elastic scattering on a carbon target was performed on the basis of the dispersion relation between the real and imaginary parts of
the calculated volume integrals. A nuclear dispersion anomaly in an α+12C system was observed and interpreted clearly.
The present paper describes the design and simulation results of a position-sensitive charged particle detector based on the Double Sided Silicon Strip Detector (DSSSD). Also, the characteristics of the DSSSD and its testing result were are discussed. With the application of the DSSSD, the position-sensitive charged particle detector can not only give particle flux and energy spectra information and identify different types of charged particles, but also measure the location and angle of incident particles. As the detector can make multi-parameter measurements of charged particles, it is widely used in space detection and exploration missions, such as charged particle detection related to earthquakes, space environment monitoring and solar activity inspection.
The Beijing Spectrometer Ⅲ (BESⅢ) is a general-purpose detector used for the study of τ-charm physics at the Beijing Electron-Positron Collider Ⅱ (BEPCⅡ). This paper presents our studies of the dE/dx measurement in the drift chamber of BESⅢ, which is important for the identification of charged particles. Corrections applied to the dE/dx measurement in data reconstruction are discussed. After our current dE/dx calibration, a resolution of about 6% has been obtained for minimum ionization particles, and a 3σ K/π separation is obtained for momenta up to 760 MeV/c. These results meet the design goals of the BESⅢ drift chamber.
The magnetic proton recoil (MPR) spectrometer is a novel diagnostic instrument with high performance for measurements of neutron spectra in inertial confinement fusion (ICF) experiments and high power fusion devices. A compact MPR-type spectrometer dedicated to the research of pulsed deuterium-tritium (DT) neutron spectroscopy of special experimental conditions is currently under design. Analyses of the main parameters and performance of the magnetic analysis system through 3-D particle transport calculations and MonteCarlo simulations and calibration of the system performance as a test using CR-39 solid track detector and α particle from 239Pu and 226Ra radioactive sources are presented in this paper. The results indicate that the magnetic analysis system will achieve a detection efficiency level of 10－5—10－4 at an energy resolution of 1.5%—2.1%, and fulfills the design goals of the spectrometer.
In order to overcome the difficulty brought by the circling charged tracks with transverse momentum less than 120 MeV in the BESⅢ Main Drift Chamber (MDC), a specialized method called TCurlFinder was developed. This tracking method focuses on the charged track reconstruction under 120 MeV and possesses a special mechanism to reject background noise hits. The performance of the package has been carefully checked and tuned by both Monte Carlo data and real data. The study shows that this tracking method could obviously enhance the reconstruction efficiency in the low transverse momentum region, providing physics analysis with more and reliable data.
A pick-up parallel-setting high order mode coupler (pps-HOM coupler) has been fabricated at Peking University. It has been tested on a coaxial transmission line and a 2-cell TESLA-shape copper cavity. The test result of the 2-cell TESLA cavity shows that the coupler can cut off the fundamental mode TM010 and absorb HOMs electively. As its RF properties are insensitive to the probe dip length, there is no need to adjust the probe repeatedly during practical operation.
The Heavy Ion Research Facility and Cooling Storage Ring (HIRFL-CSR) accelerator in Lanzhou offers a unique possibility for the generation of high density and short pulse heavy ion beams by non-adiabatic bunch compression longitudinally, which is implemented by a fast jump of the RF-voltage amplitude. For this purpose, an RF cavity with high electric field gradient loaded with Magnetic Alloy cores has been developed. The results show that the resonant frequency range of the single-gap RF cavity is from 1.13 MHz to 1.42 MHz, and a maximum RF voltage of 40 kV with a total length of 100 cm can be obtained, which can be used to compress heavy ion beams of 238U72+ with 250 MeV/u from the initial bunch length of 200 ns to 50 ns with the coaction of the two single-gap RF cavity mentioned above.
A penning plasma surface H－ ion source test stand for the CSNS has just been constructed at the IHEP. In order to achieve a safe and reliable system, nearly all devices of the ion source are designed to have the capability of both local and remote operation function. The control system consists of PLCs and EPICS real-time software tools separately serving device control and monitoring, PLC integration and OPI support. This paper summarizes the hardware and software implementation satisfying the requirements of the ion source control system.
The superconducting quadrupole magnets (SCQs) are powered by 16 power supplies in the interaction region of the BEPCⅡ. The control application of these power supplies must be interlocked with the quench protection system to protect the superconducting magnet and relevant devices. This paper describes the development procedures of this control application using EPICS and the operating result with the quench protection system on-site.
Positronium time of flight spectroscopy (Ps-TOF) is an effective technique for porous material research. It has advantages over other techniques for analyzing the porosity and pore tortuosity of materials. This paper describes a design for Ps-TOF apparatus based on the Beijing intense slow positron beam, supplying a new material characterization technique. In order to improve the time resolution and increase the count rate of the apparatus, the detector system is optimized. For 3 eV o-Ps, the time broadening is 7.66 ns and the count rate is 3 cps after correction.
The variation in environmental scattering background is a major source of systematic errors in X-ray inspection and measurement systems. As the energy of these photons consisting of environmental scattering background is much lower generally, the Cerenkov detectors having the detection threshold are likely insensitive to them and able to exclude their influence. A thickness measurement experiment is designed to verify the idea by employing a Cerenkov detector and an ionizing chamber for comparison. Furthermore, it is also found that the application of the Cerenkov detectors is helpful to exclude another systematic error from the variation of low energy components in the spectrum incident on the detector volume.
The permanent magnets of the discharge chamber in a multi-cusp proton source are studied and designed. The three electrode extraction system is adopted and simulated. A method to extract different amounts of current while keeping the beam emittance unchanged is proposed.
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