2012 Vol. 36, No. 2
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The T2K Collaboration has recently reported a remarkable indication of the ν→ν oscillation which is consistent with a relatively large value of θ13 in the three-flavor neutrino mixing scheme. We show that it is possible to account for such a result of θ13 by introducing a natural perturbation to the democratic neutrino mixing pattern, without or with CP violation. A testable correlation between θ13 and θ23 is predicted in this ansatz. We also discuss the Wolfenstein-like parametrization of neutrino mixing, and comment on other possibilities of generating sufficiently large θ13 at the electroweak scale.
Open-flavor strong decays are studied based on the interaction of a potential quark model. The decay process is related to the s-channel contribution of the same scalar confinement and one-gluon-exchange (OGE) interaction in the quark model. After we adopt the prescription of massive gluons in a time-like region from the lattice calculation, the approximation of four-fermion interaction is applied. The numerical calculation is performed to the meson decays in u, d and s light flavor sectors. The analysis of the D/S ratios of b1→ωπ and a1→ρπ shows that the scalar interaction should be dominant in the open-flavor decays.
We indicated in our previous work that for QED the role of the scalar potential which appears at the loop level is much smaller than that of the vector potential and is in fact negligible. But the situation is different for QCD, one reason is that the loop effects are more significant because αs is much larger than α, and second the non-perturbative QCD effects may induce a sizable scalar potential. In this work, we study phenomenologically the contribution of the scalar potential to the spectra of charmonia, bottomonia and bc(bc) families. Taking into account both vector and scalar potentials, by fitting the well measured charmonia and bottomonia spectra, we re-fix the relevant parameters and test them by calculating other states of not only the charmonia and bottomonia families, but also the bc family. We also consider the Lamb shift of the spectra.
The Halo and cluster structure at the ground state of unstable nuclei are among the most exciting phenomena of current nuclear physics. Probing these structures requires a careful selection of reaction tools. In the past twenty years, knockout reactions have been used intensively to investigate spectroscopically the structure of unstable nuclei. In this report we have illustrated the latest development of the knockout reaction tool and have emphasized the recoiled proton tagging method. A quantitative criteria is developed to evaluate the quasi-free feature of the knockout process. The newly discovered "towing mode" reaction tool is also outlined and its applicability at transit energies is discussed.
The fission cross section and fission probability of 197Au, induced by (1665 MeV) π-, have been studied using CR-39 track detectors. A 4π-geometry was used to count track statistics. A beam of negative pions of 1665 MeV was produced at AGS of Brookhaven National Laboratory, USA, and allowed to fall normally on the stack. Two detectors from the stack were scanned for fission fragment tracks after etching in 6N NaOH at 70℃. The statistics of fission fragment tracks in both detectors were obtained. It was found that there was a marked asymmetry of registered tracks with respect to the forward and backward hemispheres. This asymmetry could be partly accounted for on the basis of momentum transfer to the struck nucleus. On the basis of counting statistics fission cross section was measured, and fission probability was determined by dividing the fission cross section with the reaction cross section. The fission cross-section and fission probability were compared with the computed values using the cascade-exciton model code CEM95.
A new geometrical scaling method with a gluon saturation rapidity limit is proposed to study the gluon saturation feature of the central rapidity region of relativistic nuclear collisions. The net-baryon number is essentially transported by valence quarks that probe the saturation regime in the target by multiple scattering. We take advantage of the gluon saturation model with geometric scaling of the rapidity limit to investigate net baryon distributions, nuclear stopping power and gluon saturation features in the SPS and RHIC energy regions. Predictions for net-baryon rapidity distributions, mean rapidity loss and gluon saturation feature in central Pb+Pb collisions at the LHC are made in this paper.
The gas gain and energy resolution of single and double THGEM detectors (5 cm×5 cm effective area) with mini-rims (rim less than 10 μm) were studied. The maximum gain was found to reach 5×103 and 2×105 for single and double THGEMs respectively, while the energy resolution for 5.9 keV X-rays varied from 18% to 28% for both single and double THGEM detectors of different hole sizes and thicknesses. Different combinations were also investigated of noble gases (argon, neon) mixed with a quantity of other gases (isobutane, methane) at atmospheric pressure.
A high resolution solar soft X-ray spectrometer (SOX) payload onboard a satellite is developed. A silicon drift detector (SDD) is adopted as the detector of the SOX spectrometer. The spectrometer consists of the detectors and their readout electronics, a data acquisition unit and a payload data handling unit. A ground test system is also developed to test SOX. The test results show that the design goals of the spectrometer system have been achieved.
We propose and analyze a scheme to produce comb bunches, i.e. a bunch consisting of micro-bunch trains, with tunable subpicosecond spacing. In the scheme, the electron beam is first deflected by a deflecting cavity which introduces a longitudinal-dependent linear transverse kick to the particles. After passing through a drift space, the transverse beam size is linearly coupled to the longitudinal position of the particle inside the beam, and a mask is placed there to tailor the beam, then the mask distribution is imprinted on the beam's longitudinal distribution. A quadrupole magnet and another deflecting cavity are used in the beam line to compensate the transverse angle due to the first deflecting cavity. Analysis shows that the number, length, and spacing of the trains can be controlled through the parameters of the deflecting cavity and the mask. Such electron bunch trains can be applied to an infrared free electron laser, a plasma-wakefield accelerator and a supper-radiance THz source.
The RF performance of a 1.3 GHz 9-cell superconducting niobium cavity was evaluated at cryogenic temperatures following surface processing by using the standard ILC-style recipe. The cavity is a TESLA-style 9-cell superconducting niobium cavity, with complete end group components including a higher order mode coupler, built in China for practical applications. An accelerating gradient of 28.6 MV/m was achieved at an unloaded quality factor of 4×109. The morphological property of mechanical features on the RF surface of this cavity was characterized through optical inspection. Correlation between the observed mechanical features and the RF performance of the cavity is attempted.
In a Rapid Cycling Synchrotron (RCS), power loss due to an eddy current on the metal vacuum chamber would cause heating of the vacuum chamber. It is important to study the effect for estimating eddy current induced power loss and temperature growth. Analytical formulas for eddy current power loss for various types of vacuum chambers are derived for dipole and quadrupole repectively. By using the prototype of dipole of CSNS/RCS, an experiment was done to test the analytical formula. The derived formulas were applied to calculating the eddy current power loss on some special structures of an RCS vacuum chamber.
A 30 mA drift tube linac (DTL) accelerator has been designed using SUPERFISH code in the energy range of 3-55 MeV in the framework of the Turkish Accelerator Center (TAC) project. Optimization criteria in cavity design are effective shunt impedance (ZTT), transit-time factor and electrical breakdown limit. In geometrical optimization we have aimed to increase the energy gain in each RF gap of the DTL cells by maximizing the effective shunt impedance (ZTT) and the transit-time factor. Beam dynamics studies of the DTL accelerator have been performed using beam dynamics simulation codes of PATH and PARMILA. The results of both codes have been compared. In the beam dynamical studies, the rms values of beam emittance have been taken into account and a low emittance growth in both x and y directions has been attempted.
An RF power coupler is one of the key components in a superconducting (SC) linac. It provides RF power to the SC cavity and interconnects different temperature layers (1.8 K, 4.2 K, 70 K and 300 K). The TTF-Ⅲ coupler is one of the most promising candidates for the High Energy (HE) linac of Project X, but it cannot meet the average power requirements because of the relatively high temperature rise on the warm inner conductor, so some design modifications will be required. In this paper, we describe our simulation studies on the copper coating thickness on the warm inner conductor with RRR values of 10 and 100. Our purpose is to rebalance the dynamic and static loads, and finally lower the temperature rise along the warm inner conductor. In addition, to get stronger coupling, better power handling and less multipacting probability, one new cold part design was proposed using a 60 mm coaxial line; the corresponding multipacting simulation studies have also been investigated.
We report the results of a natural phenacite from 0 to 30.9 GPa using in situ angle-dispersive X-ray diffraction and a diamond anvil cell at the National Synchrotron Light Source, Brookhaven National Laboratory. Over this pressure range, no phase change or disproportionation has been observed. The isothermal equation of state was determined. The values of V0, K0, and K0′ refined with a third-order Birch-Murnaghan equation of state are V0=1116.1±1.2 Å3, K0=223±9 GPa, and K0′=5.5±0.8. Furthermore, we confirm that the linear compressibilities (β) along a and c directions of phenacite are elastically isotropic (βa=1.50×10-3 and βc=1.34×10-3 GPa-1). Consequently, it can be concluded that the compressibility of phenacite under high pressures has been accurately constrained.
Many modulation techniques have been widely applied to improve the quality of conventional spectra. Here a pressure-modulated EXAFS method is proposed to detect the small changes of local structure induced by the modulation of high pressure. In the experiment a dynamic diamond anvil cell was used to put a periodic load on the sample and lock-in amplifier to measure the modulated EXAFS signals. We have applied this technique to ZnSe and revealed a sensitivity to atomic displacement of 0.1 pm that is about ten times better than that of traditional EXAFS.
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