2016 Vol. 40, No. 11
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A cluster-transfer experiment of 9Be(9Be,14C→α+10Be)α at an incident energy of 45 MeV was carried out in order to investigate the molecular structure in high-lying resonant states in 14C. This reaction is of extremely large Q-value, making it an excellent case to select the reaction mechanism and the final states in outgoing nuclei. The high-lying resonances in 14C are reconstructed for three sets of well discriminated final states in 10Be. The results confirm the previous decay measurements with clearly improved decay-channel selections and also show a new state at 23.5(1) MeV. The resonant states at 22.4(3) and 24.0(3) MeV decay primarily into the typical molecular states at about 6 MeV in 10Be, indicating a well developed cluster structure in these high-lying states in 14C. Further measurements of more states of this kind are suggested.
By analyzing 2.93 fb-1 data collected at the center-of-mass energy √K0e+ve to be B(D+→K0e+ve)=(8.59±0.14±0.21)% using K0→KS0→π0π0, where the first uncertainty is statistical and the second systematic. Our result is consistent with previous measurements within uncertainties.. =3.773 GeV with the BESIII detector, we measure the absolute branching fraction of the semileptonic decay D+→
To measure the R value in an energy scan experiment with e+e- collisions, precise calculation of initial state radiation is required in the event generators. We present an event generator for this consideration, which incorporates initial state radiation effects up to second order accuracy. The radiative correction factor is calculated using the totally hadronic Born cross section. The measured exclusive processes are generated according to their cross sections, while the unknown processes are generated using the LUND Area Law model, and its parameters are tuned with data collected at √D threshold. =3.65 GeV. The optimized values are validated with data in the range √ =2.2324-3.671 GeV. These optimized parameters are universally valid for event generation below the D
For a resonance decaying to τ+τ-, it is difficult to reconstruct its mass accurately because of the presence of neutrinos in the decay products of the τ leptons. If the resonance is heavy enough, we show that its mass can be well determined by the momentum component of the τ decay products perpendicular to the velocity of the τ lepton, p⊥, and the mass of the visible/invisible decay products, mvis/inv, for τ decaying to hadrons/leptons. By sampling all kinematically allowed values of p⊥ and mvis/inv according to their joint probability distributions determined by the MC simulations, the mass of the mother resonance is assumed to lie at the position with the maximal probability. Since p⊥ and mvis/inv are invariant under the boost in the τ lepton direction, the joint probability distributions are independent upon the τ's origin. Thus this technique is able to determine the mass of an unknown resonance with no efficiency loss. It is tested using MC simulations of the physics processes m pp→Z/h(125)/h(750)+X→ ττ+X at 13 TeV. The ratio of the full width at half maximum and the peak value of the reconstructed mass distribution is found to be 20%-40% using the information of missing transverse energy.
We propose a new picture of black holes through a special holographic screen. This holographic screen contains all the degrees of freedom of a black hole. We find that this holographic screen is similar to the ordinary thermodynamic surface system. Meanwhile, through the "white-wall box" and the formula of sound velocity, we find some similarities between gravitons and photons. We further assume that such a holographic screen is a kind of Bose-Einstein condensate of gravitons. Through this assumption and those similarities, we finally get the area law of static black holes.
On several levels of theoretical physics, especially particle physics and early universe cosmology, de Sitter space-time has become an attractive possibility. The principle of local gauge invariance governs all known fundamental interactions of elementary particles, from electromagnetism and weak interactions to strong interactions and gravity. This paper presents a procedure for defining the gauge-covariant derivative and gauge invariant Lagrangian density in de Sitter ambient space-time formalism. The gauge invariant field equation is then explicitly calculated in detail for a massless spin-(3/2) gauge field.
Recently, a novel idea  has been proposed to relax the electroweak hierarchy problem through the cosmological inflation and the axion periotic potential. Here, we further assume that only the attractive inflation is needed to explain the light mass of the Higgs boson, where we do not need a specified periodic potential of the axion field. Attractive inflation during the early universe drives the Higgs boson mass from the large value in the early universe to the small value at present, where the Higgs mass is an evolving parameter of the Universe. Thus, the small Higgs mass can technically originate from the cosmological evolution rather than dynamical symmetry or anthropics. Further, we study the possible collider signals or constraints at a future lepton collier and the possible constraints from the muon anomalous magnetic moment. A concrete attractive relaxion model is also discussed, which is consistent with the data of Planck 2015.
Considering the constraints from collider experiments and dark matter detection, we investigate the SUSY effects in the Higgs production channels e+e-→Zh at an e+e- collider with a center-of-mass energy above 240 GeV and γγ→h→bb at a photon collider with a center-of-mass energy above 125 GeV. In the parameter space allowed by current experiments, we find that the SUSY corrections to e+e-→Zh can reach a few percent and the production rate of γγ→h→bb can be enhanced by a factor of 1.2 over the SM prediction. We also calculate the exotic Higgs production e+e-→Zh1 in the next-to-minimal supersymmetric model (NMSSM) (h is the SM-like Higgs, h1 is the CP-even Higgs bosons which can be much lighter than h). We find that at a 250 GeV e+e- collider the production rates of e+e-→Zh1 can reach 60 fb.
The fusion dynamic mechanism of heavy ions at energies near the Coulomb barrier is complicated and still not very clear up to now. Accordingly, a self-consistent method based on the CCFULL calculations has been developed and applied for an ongoing study of the effect of the positive Q-value neutron transfer (PQNT) channels in this work. The typical experimental fusion data of Ca+Ca and Ni+Ni is analyzed within the unified calculation scheme. The PQNT effect in near-barrier fusion is further confirmed based on the self-consistent analysis and extracted quantitatively.
We have developed an event mixing technique to observe Bose-Einstein correlations (BEC) between two identical neutral pions produced in photo-induced reactions in the non-perturbative QCD energy region. It is found that the missing-mass consistency cut and the pion-energy cut are essential for the event mixing method to effectively extract BEC observables. A Monte Carlo (MC) simulation is used to validate these constraints and confirms the efficiency of this method. Our work paves the way for similar BEC studies at lower energies where the multiplicity of emitted bosons is limited.
Ground state properties for Mg isotopes, including binding energies, one- and two-neutron separation energies, pairing energies, nuclear matter radii and quadrupole deformation parameters, are obtained from the self-consistent relativistic mean field (RMF) model with the pairing correlations treated by a shell-mode-like approach (SLAP), in which the particle-number is conserved and the blocking effects are treated exactly. The experimental data, including the binding energies and the one- and two-neutron separation energies, which are sensitive to the treatment of pairing correlations and block effects, are well reproduced by the RMF+SLAP calculations.
Origen2.1 is a widely used computer code for calculating the burnup, decay, and processing of radioactive materials. However, the nuclide library of Origen2.1 is used for existing reactors like pressurized water reactors. To calculate the photon spectrum released by the decay of spallation products, we have made specific libraries for the ADS tungsten spallation target, based on the results given by the FLUKA Monte Carlo code. All the data used to make the Origen2.1 libraries are obtained from Nuclear structure & decay Data (NuDat2.6). The accumulated activity of spallation products and the contribution of nuclides to photon emission are given in this paper.
Two parameter expressions for rotational spectra viz. variable moment of inertia (VMI), ab formula and three parameter Harris ω2 expansion are used to assign the band head spins (I0) of four rotational superdeformed bands in 86Zr. The least-squares fitting method is employed to obtain the band head spins of these four bands in the A~80 mass region. Model parameters are extracted by fitting of intraband γ-ray energies, so as to obtain a minimum root-mean-square (rms) deviation between the calculated and the observed transition energies. The calculated transition energies are found to depend sensitively on the assigned spins. Whenever an accurate band head spin is assigned, the calculated transition energies are in agreement with the experimental transition energies. The dynamic moment of inertia is also extracted and its variation with rotational frequency is investigated. Since a better agreement of band head spin with experimental results is found using the VMI model, it is a more powerful tool than the ab formula and Harris ω2 expansion.
The asymptotic normalization coefficients (ANCs) of the virtual decay 16N→15N+n are extracted from the 15N(7Li, 6Li)16N reaction populating the ground and first three excited states in 16N. The root-mean-square (rms) radii of the valence neutron in these four low-lying 16N states are then derived by using the ANCs. The probabilities of the valence neutron staying out of the core potentials are found to be 31%±8%, 58%±12%, 32%±8%, and 60%±12%. The present results support the conclusion that a one-neutron halo may be formed in the 16N first and third excited states, while the ground and second excited states do not have a one-neutron halo structure. However, the core excitation effect has a strong influence on the one-neutron halo structure of the ground and first excited states in 16N.
The standard model of cosmic ray propagation has been very successful in explaining all kinds of galactic cosmic ray spectra. However, high precision measurement have recently revealed an appreciable discrepancy between data and model expectations, from spectrum observations of gamma-rays, e+/e- and probably the B=C ratio starting from ~10 GeV energy . In this work, we propose that a hard galactic plane component, supplied by the fresh cosmic ray sources and detained by local magnetic elds, can contribute additional secondary particles interacting with local materials. By properly choosing the intensity and spectral index of the harder component up to multi-T eV energy , a two-component gamma-ray spectrum is obtained and agrees very well with the observation. Simultaneously , the expected neutrino numbers from the galactic plane could contribute ~60% of IceCube observed neutrino number below a few hundreds of TeV under our model. In addition to these studies, we nd that the same pp-collision process responsible for the excess gamma ray emission could account for a signi cant amount of the positron excess, but a more detailed mechanism is needed for a full agreement. It is expected that the excesses in the p=p and B=C ratio will show up when energy is above ~10 GeV. We look forward this model being tested in the near future by new observations from AMS02, IceCube, AS-gamma, HA WC and future experiments such as LHASSO, HiSCORE and CTA.
Based on cosmic ray events without a magnetic field taken with the BESIII detector during the summer shutdown of BEPCII in 2012 and di-muon events from a data sample taken at center-of-mass energy of 3.686 GeV in 2009, we compare the coordinates of hits registered in the BESIII muon counter with the expected interaction point extrapolated from reconstructed tracks from the inner tracking system in the absence of a magnetic field. By minimizing the difference, we align the muon counter with the inner tracking system. Moreover, the strength of the magnetic field in the muon counter is measured for the first time with di-muon events from data taken at a center-of-mass energy of 3.686 GeV. After the alignment and the magnetic field strength measurement, the offsets in the reconstructed hit positions for muon tracks are reduced, which improves the muon identification. The alignment and magnetic field strength measurement have been adopted in the latest version of the BESIII offline software system. This addition to the software reduces the systematic uncertainty for the physics analysis in cases where the muon counter information is used.
The China Dark Matter Experiment (CDEX) is a low background experiment at China Jinping Underground Laboratory (CJPL) designed to directly detect dark matter with a high-purity germanium (HPGe) detector. In the second phase, CDEX-10, which has a 10 kg germanium array detector system, a liquid argon (LAr) anti-Compton active shielding and cooling system is proposed. To study the properties of the LAr detector, a prototype with an active volume of 7 liters of liquid argon was built and operated. The photoelectron yields, as a critically important parameter for the prototype detector, have been measured to be 0.051-0.079 p.e./keV for 662 keV γ rays at different positions. The good agreement between the experimental and simulation results has provided a reasonable understanding and determination of the important parameters such as the surviving fraction of the Ar2* excimers, the absorption length for 128 nm photons in liquid argon, the reflectivity of Teflon and so on.
DArk Matter Particle Explorer (DAMPE) is the first Chinese astronomical satellite, successfully launched on Dec. 17 2015. As the most important payload of DAMPE, the BGO calorimeter contains 308 bismuth germanate crystals, with 616 photomultiplier tubes, one coupled to each end of every crystal. Environmental tests have been carried out to explore the environmental adaptability of the flight model of the BGO calorimeter. In this work we report the results of the vibration tests. During the vibration tests, no visible damage occurred in the mechanical assembly. After random or sinusoidal vibrations, the change of the first order natural frequency of BGO calorimeter during the modal surveys is less than 5%. The shift ratio of Most Probable Value of MIPs changes in cosmic-ray tests are shown, the mean value of which is about -4%. The comparison of results of cosmic-ray tests before and after the vibration shows no significant change in the performance of the BGO calorimeter. All these results suggest that the calorimeter and its structure have passed through the environment tests successfully.
The breakup reactions of weakly-bound nuclei at energies around the Coulomb barrier and the corresponding coupling effect on the other reaction channels are hot topics nowadays. To overcome the difficulty in identifying both heavier and lighter fragments simultaneously, a new kind of ionization-chamber based detector telescope has been designed and manufactured. It consists of a PCB ionization chamber and three different thickness silicon detectors installed inside the chamber, which form a multilayer ΔE-ER telescope. The working conditions were surveyed by using an α source. An in-beam test experiment shows that the detector has good particle identification for heavy particles like 17F and 16O as well as light particles like protons and alpha particles. The measured quasi-elastic scattering angular distribution and the related discussions for 17F+208Pb are presented.
Liquid argon (LAr) is an attractive target for the direct detection of WIMPs. A LAr prototype detector was designed to study the technology and properties of LAr detectors. The prototype detector had an active volume containing 0.65 kg of liquid argon. A liquid nitrogen (LN) cooling system allowed the temperature fluctuation of the liquid argon to be controlled within less than 0.1 K during a one month run. In the 22Na calibration run, the LAr prototype obtained 1.59±0.02 p.e./keV light yield for 511 keV gamma rays using a domestic-made argon purification system.
The Compact Muon Solenoid (CMS) at LHC intends to use a high rate trapezoid MRPC for the muon system upgrade, but the size of the MRPC is limited by the dimensions of low resistivity glass. We have designed a prototype of a large MRPC in which the electrodes are developed by gluing two pieces of glass plates. Simulation of the weighting field and cosmic ray test shows that the efficiency of the glued MRPC is higher than 96% and the time resolution is better than 71 ps.
The Silicon Tracker (STK) is one of the detectors of the DAMPE satellite used to measure the incidence direction of high energy cosmic rays. It consists of 6 X-Y double layers of silicon micro-strip detectors with 73728 readout channels. It is a great challenge to read out the channels and process the huge volume of data in the harsh environment of space. 1152 Application Specific Integrated Circuits (ASIC) and 384 ADCs are used to read out the detector channels. 192 Tracker Front-end Hybrid (TFH) modules and 8 identical Tracker Readout Board (TRB) modules are designed to control and digitalize the front signals. In this paper, the design of the readout electronics for the STK and its performance are presented in detail.
A Flash-ADC data acquisition (DAQ) system has been developed for the drift chamber array designed for the External-Target-Experiment at the Cooling Storage Ring at the Heavy Ion Research Facility, Lanzhou. The simplified readout electronics system has been developed using the Flash-ADC modules and the whole waveform in the sampling window is obtained, with which the time and energy information can be deduced with an offline processing. A digital filter algorithm has been developed to discriminate the noise and the useful signal. With the digital filtering process, the signal to noise ratio (SNR) is increased and a better time and energy resolution can be obtained.
High precision and large dynamic range measurement are required in the readout systems for the Water Cherenkov Detector Array (WCDA) in the Large High Altitude Air Shower Observatory (LHAASO). This paper presents a prototype of a 12-bit 40 MSPS Analog-to-Digital Converter (ADC) Application Specific Integrated Circuit (ASIC) designed for the readout of the LHAASO WCDA. Combining this ADC and the front-end ASIC finished in our previous work, high precision charge measurement can be achieved based on the digital peak detection method. This ADC is implemented based on a power-efficient Successive Approximation Register (SAR) architecture, which incorporates key parts such as a Capacitive Digital-to-Analog Converter (CDAC), dynamic comparator and asynchronous SAR control logic. The simulation results indicate that the Effective Number Of Bits (ENOB) with a sampling rate of 40 MSPS is better than 10 bits in an input frequency range below 20 MHz, while its core power consumption is 6.6 mW per channel. The above results are good enough for the readout requirements of the WCDA.
At the CEPC (Circular Electron Positron Collider), which is proposed by the Chinese high energy physics community, the dominant background comes from radiative Bhabha scattering and the beamstrahlung effect according to preliminary research. Therefore, it is necessary to incorporate a collimator system to intercept particles that may be lost near the interaction region (IR). In this paper, we introduce some limitations in choosing the position and width of the collimators. A certain parameter range is determined which is confined by the β function and the width of the collimators. A suitable choice of the half width is made by exploring this parameter range. A simulation of the particle loss rate in the IR and the hit density in the vertex detector with and without the collimators shows that the set of parameters of the collimators we designed is appropriate and effective.
The target thickness for nitrogen was determined from the beam energy loss in HIRFL-CSRe during the experimental study of the K-REC process in 197 MeV/u Xe54+-N2 collisions. Furthermore, the corresponding integrated luminosity of (1.15±0.06)×1030 cm-2 was obtained. As an independent check on the energy-loss method, we have also determined the integrated luminosity by measuring the produced X-rays from the K-REC process with a known differential cross section. The values of (1.12±0.06)×1030 and (1.09±0.06)×1030 cm-2 were obtained by using two high-purity germanium (HPGe) detectors which were oriented at 90° and 120° with respect to the beam path, respectively. The consistent results confirmed the feasibility of the energy-loss method, which may have an important impact on future internal target experiments at HIRFL-CSRe.
For modern and future circular accelerators, especially high-intensity proton synchrotrons or colliders, the electron cloud effect is a key issue. So, in order to reduce the electron cloud effect, exploring very low secondary electron yield (SEY) material or coating used in vacuum tubes becomes necessary. In this article, we studied the SEY characteristics of graphene films with different thicknesses which were deposited on copper substrates using chemical vapor deposition. The SEY tests were done at temperatures of 25℃ and vacuum pressure of (2-6)×10-9 torr. The properties of the deposited graphene films were investigated by X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. The SEY curves show that the number of graphene layers has a great effect on the SEY of graphene films. The maximum SEY of graphene films decreases with the increase of the number of layers. The maximum SEY of 6-8 layers of graphene film is 1.25. These results have a great significance for next-generation particle accelerators.
To make full use of the photocathode material and improve its quantum efficiency lifetime, it can be necessary to operate the laser away from the cathode center in photoinjectors. In RF guns, the off-axis emitted beam will see a time-dependent RF effect, which would generate a significant growth in transverse emittance. It has been demonstrated that such an emittance growth can be almost completely compensated by orienting the beam on a proper orbit in the downstream RF cavities along the injector . In this paper we analyze in detail the simulation techniques used in reference  and the issues associated with them. The optimization of photoinjector systems involving off-axis beams is a challenging problem. To solve this problem, one needs advanced simulation tools including both genetic algorithms and an efficient algorithm for 3D space charge. In this paper, we report on simulation studies where the two codes ASTRA and IMPACT-T are used jointly to overcome these challenges, in order to optimize a system designed to compensate for the emittance growth in a beam emitted off axis.
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