2014 Vol. 38, No. 7
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The CMS and ATLAS experiments at the LHC have announced the discovery of a Higgs boson with mass at approximately 125 GeV/c2 in the search for the Standard Model Higgs boson via, notably, the γγ and ZZ to four leptons final states. Considering the recent results of the Higgs boson searches from the LHC, we study the lightest scalar Higgs boson h1 in the Next-to-Minimal Supersymmetric Standard Model by restricting the next-to-lightest scalar Higgs boson h2 to be the observed to the 125 GeV/c2 state. We perform a scan over the relevant NMSSM parameter space that is favoured by low fine-tuning considerations. Moreover, we also take the experimental constraints from direct searches, B-physics observables, relic density, and anomalous magnetic moment of the muon measurements, as well as the theoretical considerations, into account in our specific scan. We find that the signal rate in the two-photon final state for the NMSSM Higgs boson h1 with the mass range from about 80 GeV/c2 to about 122 GeV/c2 can be enhanced by a factor of up to 3.5 when the Higgs boson h2 is required to be compatible with the excess from latest LHC results. This motivates the extension of the search at the LHC for the Higgs boson h1 in the diphoton final state down to masses of 80 GeV/c2, particularly with the upcoming proton-proton collision data to be taken at center-of-mass energies of 13-14 TeV.
By employing the perturbative QCD (pQCD) factorization approach, we calculate the new physics contributions to the four B→Kη(') decays in the Standard Model (SM) with a fourth generation of fermions (SM4), induced by the loop diagrams involving t' quark. Within the considered parameter space of the SM4 we find that: (a) the next-to-leading order (NLO) pQCD predictions for the branching ratios and CP-violating asymmetries in both the SM and SM4 generally agree with the data within one standard deviation; (b) for Br( B→Kη), the inclusion of the fourth generation contributions can improve the agreement between the theoretical predictions and the data effectively; (c) however, for Br( B→Kη') the decrease due to t' loops is disfavored by the data; and, (d) the new physics corrections to the CP-violating asymmetries of the considered decays are only about 10%.
Multiplicity fluctuation of the target evaporated fragments emitted in 290 MeV/u 12C-AgBr, 400 MeV/u 12C-AgBr, 400 MeV/u 20Ne-AgBr and 500 MeV/u 56Fe-AgBr interactions is investigated using the scaled factorial moment method in two-dimensional normal phase space and cumulative variable space, respectively. It is found that in normal phase space the scaled factorial moment (ln<Fq>) increases linearly with the increase of the divided number of phase space (lnM) for lower q-value and increases linearly with the increase of lnM, and then becomes saturated or decreased for a higher q-value. In cumulative variable space ln<Fq> decreases linearly with increase of lnM. This indicates that no evidence of non-statistical multiplicity fluctuation is observed in our data sets. So, any fluctuation indicated in the results of normal variable space analysis is totally caused by the non-uniformity of the single-particle density distribution.
The spallation-neutron yield was studied experimentally by bombarding a thick lead target with 400 MeV/u carbon beam. The data were obtained with the activation analysis method using foils of Au, Mn, Al, Fe and In. The yields of produced isotopes were deduced by analyzing the measured γ spectra of the irradiated foils. According to the isotopes yields, the spatial and energy distributions of the neutron field were discussed. The experimental results were compared with Monte Carlo simulations performed by the GEANT4+FLUKA code.
When a Λ hyperon is embedded in a nucleus it can form a hypernucleus. The lifetime and its mass dependence of stable hypernuclei provide information about the ΛN interaction in the nuclear medium. This work will introduce the Jefferson Lab experiment (E02-017), which aims to study the lifetime of the heavy hypernuclei using a specially developed fission fragment detection technique: a multi-wire proportional chamber operating under low gas pressure (LPMWPC). The trajectory of the detected fragment is reconstructed and used to find the fission point on the target foil, the position resolution is less than 1 mm, which meets the original design, the separation of target materials and events mixture percentage in different regions are verified by Monte Carlo simulation.
High spin states of the odd-A 87Sr were populated by the fusion-evaporation reaction 82Se(9Be, 4n) 87Sr at a beam energy of 46 MeV. Excited levels of 87Sr have been extended up to an excitation energy of 7.4 MeV at spin 31/2295;. The coupling of a g9/2 neutron hole to the yrast states of the 88Sr core can account for the low-lying states in 87Sr. The structure of the higher spin states is discussed by analogy with those of the neighboring odd-A N=49 isotones and possible configurations are proposed.
High-spin yrast structures of even-even superheavy nuclei 254-258Rf are investigated by means of total-Routhian-surface approach in three-dimensional (β2, γ, β4) space. The behavior in the moments of inertia of 256Rf is well reproduced by our calculations, which is attributed to the j15/2 neutron rotation-alignment. The competition between the rotationally aligned i13/2 proton and j15/2 neutron may occur to a large extent in 256Rf. High-spin predictions are also made for its neighboring isotopes 254,258Rf, showing that the alignment of the j15/2 neutron pair is more favored than that of the i13/2 proton pair.
By introducing the Dzyaloshinsky-Moriya (DM) interaction, the Loschmidt Echo (LE) of a quantum system consisting of a central spin and its surrounding environment characterized by an XY spin chain was investigated analytically and numerically. At the critical points of the magnetic field, the LE presents an obvious decay. The decay amplitude can be tuned by the DM interaction. In some specific intervals the DM interaction can remarkably delay the decay of the LE. On the other hand, the DM interaction can change the effects of the anisotropy parameter on the LE.
The effects of pairing correlation in Yb isotopes are investigated by covariant density functional theory with pairing correlations and blocking effects treated exactly by a shell model like approach (SLAP). Experimental one- and two-neutron separation energies are reproduced quite well. The traditional BCS calculations always give larger pairing energies than those given by SLAP calculations, particularly for the nuclei near the proton and neutron drip lines. This may be caused because many of the single particle orbits above the Fermi surface are involved in the BCS calculations, but many of them are excluded in the SLAP calculations.
A phenomenological Lagrangian approach is employed to study the electromagnetic properties of deuteron. The deuteron is regarded as a loosely bound state of a proton and a neutron. The deuteron electromagnetic form factors are expressed in light-front representation in the transverse plane. The transverse charge density of the deuteron is discussed.
In the framework of the isospin-dependent quantum molecular dynamics transport model (QMD), the effects of symmetry potential on the collision number and the neutron-proton bremsstrahlung photon in the reactions of 40Ca+40Ca, 124Sn+124Sn, 40Ca+64Zn, 40Ca+124Sn at different incident beam energies are studied. It is found that the collision number shows moderate sensitivity to the stiffness of the symmetry potential and the number of hard photons calculated with stiff symmetry potential is obviously smaller than that with soft symmetry potential. Thus, the neutron-proton bremsstrahlung photons produced in heavy-ion collisions may be a useful probe for the high-density behavior of the nuclear symmetry potential.
A physical model for Geant4-based simulation of the galactic cosmic ray (GCR) particles' interaction with the lunar surface matter has been developed to investigate the production rates of cosmogenic nuclei. In this model the GCRs, mainly very high energy protons and α particles, bombard the surface of the Moon and produce many secondary particles, such as protons and neutrons. The energies of protons and neutrons at different depths are recorded and saved as ROOT files, and the analytical expressions for the differential proton and neutron fluxes are obtained through the best-fit procedure using ROOT software. To test the validity of this model, we calculate the production rates of the long-lived nuclei 10Be and 26Al in the Apollo 15 long drill core by combining the above differential fluxes and the newly evaluated spallation reaction cross sections. Our numerical results show that the theoretical production rates agree quite well with the measured data, which means that this model works well. Therefore, it can be expected that this model can be used to investigate the cosmogenic nuclei in future lunar samples returned by the Chinese lunar exploration program and can be extended to study other objects, such as meteorites and the Earth's atmosphere.
We propose a hyperbolic function form of the Cardassian component in the Cardassian model. Using the repartition of this Cardassian component, we can obtain a non-zero gravitational interaction between the time derivative of Ricci scalar curvature and the baryon/lepton number current in the radiation-dominated universe. Furthermore, the other term that acts like a non-zero cosmological constant would give an accelerated expansion of current universe and the features of this model do not violate our desired requirements.
A new digital logarithmic airborne gamma ray spectrometer is designed in this study. The spectrometer adopts a high-speed and high-accuracy logarithmic amplifier (LOG114) to amplify the pulse signal logarithmically and to improve the utilization of the ADC dynamic range because the low-energy pulse signal has a larger gain than the high-energy pulse signal. After energy calibration, the spectrometer can clearly distinguish photopeaks at 239, 352, 583 and 609 keV in the low-energy spectral sections. The photopeak energy resolution of 137Cs improves to 6.75% from the original 7.8%. Furthermore, the energy resolution of three photopeaks, namely, K, U, and Th, is maintained, and the overall stability of the energy spectrum is increased through potassium peak spectrum stabilization. Thus, it is possible to effectively measure energy from 20 keV to 10 MeV.
Simulations from Laboratory Sourceless Object Counting System (LabSOCS) software were used to determine self-attenuation correction factor, which is defined as the efficiency ratio of the sample with the absorbing medium to that of the sample without absorbing medium. The semi-empirical self-attenuation correction formula F(μ) used to correct self-attenuation of a sample was applied. A comparison of the two methods reveals that formula of sample with φ 75 mm× 25 mm and φ75 mm× 10 mm can be, respectively, used in the self-attenuation correction for μ in the ranges of 0 to 0.5 cm-1 and 0.5 cm-1 to 2.0 cm-1, indicating that the semi-empirical formula will not be used when μ has exceeded the interval. The semi-empirical formula value is consistent with the experimental value, within 7.9% accuracy. Therefore, this method is correct and effective. Both of our two methods can accurately produce a relative self-attenuation correction factor when the composition of the sample is known. The self-attenuation correction of a sample with unknown composition can only be carried out using a semi-empirical formula method.
The China Dark Matter Experiment (CDEX) Collaboration will carry out a direct search for weakly interacting massive particles with germanium detectors. Liquid argon will be utilized as an anti-Compton and cooling material for the germanium detectors. A low-background and large-area photomultiplier tube (PMT) immersed in liquid argon will be used to read out the light signal from the argon. In this paper we have carried out a careful evaluation on the performance of the PMT operating at both room and cryogenic temperatures. Based on the single photoelectron response model, the absolute gain and resolution of the PMT were measured. This has laid a foundation for PMT selection, calibration and signal analysis in the forthcoming CDEX experiments.
The cascade-exciton model has been used to observe the dependence of pion induced fission cross sections on the mass of the target. The analysis has been performed at energies 80 MeV, 100 MeV and 150 MeV for both the positive and negative pions. It has been shown that a single value of the ratio af/an can satisfactorily reproduce the experimental findings when compared with the available experimental data in the literature. The general trend of the fission cross sections with mass (fissility parameter) is seen to be low and slowly changing for the lighter nuclei, and it will steeply rise for the heavy nuclei.
KONUS beam dynamics design of uranium DTL with LORASR code is presented. The 238U34+ beam, whose current is 5.0 emA, is accelerated from injection energy of 0.35 MeV/u to output energy of 1.30 MeV/u by IH-DTL operated at 81.25 MHz in HIAF project at IMP of CAS. It achieves a transmission efficiency of 94.95% with a cavity length of 267.8 cm. The optimization aims are the reduction of emittance growth, beam loss and project costs. Because of the requirements of CW mode operation, the designed average acceleration gradient is about 2.48 MV/m. The maximum axial field is 10.2 MV/m,meanwhile the Kilpatrick breakdown field is 10.56 MV/m at 81.25 MHz.
China's first quasi-periodic undulator (QPU) has been developed for the Hefei Light Source (HLS). It uses a magnetic configuration with varied thicknesses of NdFeB blocks, which is based on the QPU of European Synchrotron Radiation Facility (ESRF). The depression of 3rd harmonic radiation is significantly improved over the ESRF QPU, as deduced from the measured magnetic fields. A method of configuring shims of different geometries and sizes, based on a symmetric principle to correct multi-pole field integrals, is demonstrated.
China Spallation Neutron Source (CSNS) is a high intensity proton accelerator-based facility. Its accelerator complex includes two main parts: an H- linac and a rapid cycling synchrotron (RCS). The RCS accumulates an 80 MeV proton beam and accelerates it to 1.6 GeV, with a repetition rate of 25 Hz. The AC dipole of the CSNS/RCS is operated at a 25 Hz sinusoidal alternating current which causes severe vibration. The vibration will influence the long-term safety and reliable operation of the magnet. The CSNS/RCS AC dipole-girder system takes vibration isolator to decrease the vibratory force and the vibration amplitude of the dipole. For the long-term safety and reliable operation of the dipole, it is very important to study the dynamic characteristics of the dipole-girder system. This paper takes the dipole-girder as a specific model system. A method for studying the dynamic characteristics of the system is put forward by combining theoretical calculation with experimental testing. The modal parameters with and without vibration isolator of the dipole-girder system are obtained through ANSYS simulation and testing. Then, the dynamic response of the system is calculated with modal analysis and vibration testing data. With the simulation and testing method, the dynamic characteristics of the AC dipole-girder are studied.
The beam position monitor (BPM) system is of most importance in a light source. The capability of the BPM depends on the resolution of the system. The traditional standard deviation on the raw data method merely gives the upper limit of the resolution. Principal component analysis (PCA) had been introduced in the accelerator physics and it could be used to get rid of the actual signals. Beam related information was extracted before the evaluation of the BPM performance. A series of studies had been made in the Shanghai Synchrotron Radiation Facility (SSRF) and PCA was proved to be an effective and robust method in the performance evaluations of our BPM system.
The stabilities of the beam and machine have almost the highest priority in a modern light source. Although a lot of machine parameters could be used to represent the beam quality, there is no single parameter that could indicate the global information for the machine operators and accelerator physicists. For the last few years, a new parameter has been studied as a beam quality flag in the Shanghai Synchrotron Radiation Facility (SSRF). Calculations, simulations and detailed analysis of the real-time data from the storage ring have been made and the interesting results have confirmed its feasibility.
XAL is a high level accelerator application framework that was originally developed by the Spallation Neutron Source (SNS), Oak Ridge National Laboratory. It has an advanced design concept and has been adopted by many international accelerator laboratories. Adopting XAL for ADS is a key subject in the long term. This paper will present the modifications to the original XAL applications for ADS. The work includes a proper relational database schema modification in order to better suit the requirements of ADS configuration data, redesigning and re-implementing db2xal application, and modifying the virtual accelerator application. In addition, the new device types and new device attributes for ADS online modeling purpose are also described here.
To investigate the feasibility of using a form cutter to machine the Radial Matcher Section (RMS) of the Radio Frequency Quadrupole (RFQ) for the Accelerator Driven System (ADS) project at Institute of Modern Physics, Chinese Academy of Sciences (IMP, CAS), the influence of RMS end shape on the RFQ cavity frequency is studied. The results indicate that using a form cutter to machine the RMS of an RFQ will indeed influence the cavity frequency. The RMS end shape will give more influence to a shorter RFQ cavity. For the 4.2 m ADS RFQ, the influence is negligible, which means that a form cutter can be used to machine the RMS.
Twelve very low Beta superconducting single spoke cavities, whose Beta is only 0.12 (Spoke012) when operating at 325 MHz, are adopted in Injector I for China-ADS linac. This type of spoke cavity is believed to be one of the key challenges for its very low geometric Beta. So far, in collaboration with Peking University and Harbin Institute of Technology, IHEP has successfully designed, fabricated, and tested the Spoke012 prototype cavity. This paper presents the details of the design, fabrication and test results for Spoke012 prototype cavity.
In this paper we discuss the theory of undulator radiation in an electromagnet undulator. We discuss the spectral properties of undulator radiation when electrons are injected off the undulator axis. This paper highlights the distinctive features of the radiation spectrum from electromagnet undulators, as compared to PPM undulators.
We present the design and optimization of a prompt γ-ray neutron activation analysis (PGNAA) thermal neutron output setup based on Monte Carlo simulations using MCNP5 computer code. In these simulations, the moderator materials, reflective materials, and structure of the PGNAA 252Cf neutrons of thermal neutron output setup are optimized. The simulation results reveal that the thin layer paraffin and the thick layer of heavy water moderating effect work best for the 252Cf neutron spectrum. Our new design shows a significantly improved performance of the thermal neutron flux and flux rate, that are increased by 3.02 times and 3.27 times, respectively, compared with the conventional neutron source design.
The small angle neutron scattering (SANS) instrument is presently being constructed at Chinese Spallation Neutron Source (CSNS) in China, and the biological shielding design is needed to prevent the instrument from causing excessive dose rates in accessible locations. In this paper, the study of shielding design for SANS that relies on Monte Carlo simulation is introduced. Beam line shielding calculations are performed considering both scenarios of closed versus open T0 chopper. The basic design scheme of the beam stop is discussed. The size of the T0 chopper rotor is also estimated.
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