2017 Vol. 41, No. 7

Status of the chiral magnetic effect and collisions of isobars
Volker Koch, Soeren Schlichting, Vladimir Skokov, Paul Sorensen, Jim Thomas, Sergei Voloshin, Gang Wang, Ho-Ung Yee
2017, 41(7): 072001. doi: 10.1088/1674-1137/41/7/072001
In this review, we examine the current theoretical and experimental status of the chiral magnetic effect. We discuss possible future strategies for resolving uncertainties in interpretation including recommendations for theoretical work, recommendations for measurements based on data collected in the past five years, and recommendations for beam use in the coming years of RHIC. We specifically investigate the case for colliding nuclear isobars (nuclei with the same mass but different charge) and find the case compelling. We recommend that a program of nuclear isobar collisions to isolate the chiral magnetic effect from background sources be placed as a high priority item in the strategy for completing the RHIC mission.
Particles and fields
Excited state mass spectra, decay properties and Regge trajectories of charm and charm-strange mesons
Virendrasinh Kher, Nayneshkumar Devlani, Ajay Kumar Rai
2017, 41(7): 073101. doi: 10.1088/1674-1137/41/7/073101
The framework of a phenomenological quark-antiquark potential (Coulomb plus linear confinement) model with a Gaussian wave function is used for detailed study of masses of the ground, orbitally and radially excited states of heavy-light Qq(Q=c,q=u/d,s) mesons. We incorporate a O(1/m) correction to the potential energy term and relativistic corrections to the kinetic energy term of the Hamiltonian. The spin-hyperfine, spin-orbit and tensor interactions incorporating the effect of mixing are employed to obtain the pseudoscalar, vector, radially and orbitally excited state meson masses. The Regge trajectories in the (J,M2) and (nr,M2.) planes for heavy-light mesons are investigated with their corresponding parameters. Leptonic and radiative leptonic decay widths and corresponding branching ratios are computed. The mixing parameters are also estimated. Our predictions are in good agreement with experimental results as well as lattice and other theoretical models.
Dynamical mass generation in QED3 beyond the instantaneous approximation
Hai-Xiao Xiao, Jian-Feng Li, Wei Wei, Pei-Lin Yin, Hong-Shi Zong
2017, 41(7): 073102. doi: 10.1088/1674-1137/41/7/073102
In this paper, we investigate dynamical mass generation in (2+1)-dimensional quantum electrodynamics at finite temperature. Many studies are carried out within the instantaneous-exchange approximation, which ignores all but the zero-frequency component of the boson propagator and fermion self-energy function. We extend these studies by taking the retardation effects into consideration. In this paper, we get the explicit frequency n and momentum p dependence of the fermion self-energy function and identify the critical temperature for different fermion flavors in the chiral limit. Also, the phase diagram for spontaneous symmetry breaking in the theory is presented in Tc-Nf space. The results show that the chiral condensate is just one-tenth of the scale of previous results, and the chiral symmetry is restored at a smaller critical temperature.
Z→li±lj processes in the BLMSSM
Xing-Xing Dong, Shu-Min Zhao, Xi-Jie Zhan, Zhong-Jun Yang, Hai-Bin Zhang, Tai-Fu Feng
2017, 41(7): 073103. doi: 10.1088/1674-1137/41/7/073103
In a supersymmetric extension of the Standard Model (SM) where baryon and lepton numbers are local gauge symmetries (BLMSSM), we investigate the charged lepton flavor violating (CLFV) processes Z→li±lj after introducing new gauginos and right-handed neutrinos. In this model, the branching ratios of Z→li±lj are around (10-8-10-10), which approach the present experimental upper bounds. We hope that the branching ratios for these CLFV processes can be detected in the near future.
Nuclear physics
Sub-leading flow modes in PbPb collisions at sNN = 2.76 TeV from the HYDJET++ model
P. Cirkovic, D. Devetak, M. Dordevic, J. Milosevic, M. Stojanovic
2017, 41(7): 074001. doi: 10.1088/1674-1137/41/7/074001
Recent LHC results on the appearance of sub-leading flow modes in PbPb collisions at 2.76 TeV, related to initial-state fluctuations, are analyzed and interpreted within the HYDJET++ model. Using the newly introduced Principal Component Analysis (PCA) method applied to two-particle azimuthal correlations extracted from the model calculations, the leading and sub-leading flow modes are studied as a function of the transverse momentum (pT) over a wide centrality range. The leading modes of the elliptic (v2(1)) and triangular (v3(1)) flow calculated with the HYDJET++ model reproduce rather well the v2{2} and v3{2} coefficients measured experimentally using the two-particle correlations. Within the pT ≤ 3 GeV/c range, where hydrodynamics dominates, the sub-leading flow effects are greatest at the highest pT of around 3 GeV/c. The sub-leading elliptic flow mode (v2(2)), which corresponds to the n = 2 harmonic, has a small non-zero value and slowly increases from central to peripheral collisions, while the sub-leading triangular flow mode (v3(2)), which corresponds to the n = 3 harmonic, is even smaller and does not depend on centrality. For n = 2, the relative magnitude of the effect measured with respect to the leading flow mode shows a shallow minimum for semi-central collisions and increases for very central and for peripheral collisions. For the n = 3 case, there is no centrality dependence. The sub-leading flow mode results obtained from the HYDJET++ model are in rather good agreement with the experimental measurements of the CMS Collaboration.
Magnetic moments and g-factors in odd-A Ho isotopes
E. Tabar, H. Yakut, A. A. Kuliev, H. Quliyev, G. Ho?gör
2017, 41(7): 074101. doi: 10.1088/1674-1137/41/7/074101
The ground-state magnetic moment, gK factor and quenching spin gyromagnetic ratio have been calculated using the microscopic method based on the Quasiparticle Phonon Nuclear Model (QPNM) for 155-169Ho nuclei for the first time. It is shown that the residual spin-spin interactions are responsible for the core polarization, and because of the core polarization the spin gyromagnetic factors are quenched. By considering the core polarization effects, a satisfactory agreement is obtained for the computed ground state gK factor, which gives an intrinsic contribution to the magnetic moments. In order to assess the collective contribution to the magnetic moments, the rotational gyromagnetic factors gR have been also calculated within the cranking approximation using the single particle wave function of the axially symmetric Woods-Saxon potential. For the ground-state magnetic moments of odd-proton 155-165Ho nuclei, a good description of the experimental data is obtained with an accuracy of 0.01-0.1 μN. From systematic trends, the quenching spin gyromagnetic factor, gK factor and magnetic moment have also been theoretically predicted for 167,169Ho where there is no existing experimental data.
The ΛΛ4n system
H. Garcilazo, A. Valcarce, J. Vijande
2017, 41(7): 074102. doi: 10.1088/1674-1137/41/7/074102
Using local central Yukawa-type Malfliet-Tjon interactions reproducing the low-energy parameters and phase shifts of the m nn system, and the latest updates of the m nΛ and ΛΛ Nijmegen ESC08c potentials, we study the possible existence of a ΛΛ4 n bound state. Our results indicate that the ΛΛ4 n is unbound, being just above threshold. We discuss the role played by the 1S0 m nn repulsive term of the Yukawa-type Malfliet-Tjon interaction.
A nucleon-pair and boson coexistent description of nuclei
Lianrong Dai, Feng Pan, J. P. Draayer
2017, 41(7): 074103. doi: 10.1088/1674-1137/41/7/074103
We study a mixture of s-bosons and like-nucleon pairs with the standard pairing interaction outside an inert core. Competition between the nucleon-pairs and s-bosons is investigated in this scenario. The robustness of the BCS-BEC coexistence and crossover phenomena are examined through an analysis of pf-shell nuclei with realistic single-particle energies, in which two configurations with Pauli blocking of nucleon-pair orbits due to the formation of the s-bosons is taken into account. When the nucleon-pair orbits are considered to be independent of the s-bosons, the BCS-BEC crossover becomes smooth, with the number of the s-bosons noticeably more than that of the nucleon-pairs near the half-shell point, a feature that is demonstrated in the pf-shell for several values of the standard pairing interaction strength. As a further test of the robustness of the BCS-BEC coexistence and crossover phenomena in nuclei, results are given for B(E2; 01+→21+) values of even-even 102-130Sn with 100Sn taken as a core and valence neutron pairs confined within the 1d5/2, 0g7/2, 1d3/2, 2s1/2, 1h11/2 orbits in the nucleon-pair orbit and the s-boson independent approximation. The results indicate that the B(E2) values are reproduced well.
Study of X(5568) in a unitary coupled-channel approximationof BK and Bsπ
Bao-Xi Sun, Fang-Yong Dong, Jing-Long Pang
2017, 41(7): 074104. doi: 10.1088/1674-1137/41/7/074104
The potential of the m B meson and the pseudoscalar meson is constructed up to the next-to-leading order Lagrangian, and then the m BK and m Bs π interaction is studied in the unitary coupled-channel approximation. A resonant state with a mass about 5568 MeV and JP=0+ is generated dynamically, which can be associated with the X(5568) state announced by the D0 Collaboration recently. The mass and the decay width of this resonant state depend on the regularization scale in the dimensional regularization scheme, or the maximum momentum in the momentum cutoff regularization scheme. The scattering amplitude of the vector B meson and the pseudoscalar meson is calculated, and an axial-vector state with a mass near 5620 MeV and JP=1+ is produced. Their partners in the charm sector are also discussed.
Quasiparticle structure of superheavy nuclei in α-decay chains of 285Fl and 291,293Lv
V. G. Kartavenko, N. V. Antonenko, A. N. Bezbakh, L. A. Malov, N. Yu. Shirikova, A. V. Sushkov, R. V. Jolos
2017, 41(7): 074105. doi: 10.1088/1674-1137/41/7/074105
Two mean-field potentials, Woods-Saxon and Skyrme based potentials, are used to calculate the energies of low-lying one-quasiparticle states. The spectra of the low-lying states and the α-decay spectra of nuclei belonging to the α-decay chains of 285Fl and 291,293Lv are calculated and compared with the available experimental data. Dependence of the splitting of the pseudospin doublets and of the energies of the unique parity neutron one-quasiparticle states on the mean field potential are discussed. As shown, the α-decay spectra could be different in the α-decay chain and at the direct production of the nucleus in a fusion reaction.
Predictions of decay modes for the superheavy nuclei most suitable for synthesis
Jun-Hong Liu, Shu-Qing Guo, Xiao-Jun Bao, Hong-Fei Zhang
2017, 41(7): 074106. doi: 10.1088/1674-1137/41/7/074106
The competition between α-decay and spontaneous fission of superheavy nuclei (SHN) is investigated by the generalized liquid drop model (GLDM) and the modified Swiatecki's formula respectively. The theoretical decay modes are in good agreement with the experimental results. Predictions are made for as-yet unobserved superheavy nuclei. The theoretical calculations show that the nuclei 298120, 295119, 290118, 291117, 287117, 294116, 289116, 286116, 285116, 284115, 283115, 283114, 282114, 280113, 276112, 275112, 274112, 273111, 272110, 265109 may be synthesized experimentally in the near future since they not only have relatively large predicted cross sections but can also be identified via α-decay chains.
A comprehensive revisit of the ρ meson with improved Monte-Carlo based QCD sum rules
Qi-Nan Wang, Zhu-Feng Zhang, T. G. Steele, Hong-Ying Jin, Zhuo-Ran Huang
2017, 41(7): 074107. doi: 10.1088/1674-1137/41/7/074107
We improve the Monte-Carlo based QCD sum rules by introducing the rigorous Hölder-inequality-determined sum rule window and a Breit-Wigner type parametrization for the phenomenological spectral function. In this improved sum rule analysis methodology, the sum rule analysis window can be determined without any assumptions on OPE convergence or the QCD continuum. Therefore, an unbiased prediction can be obtained for the phenomenological parameters (the hadronic mass and width etc.). We test the new approach in the ρ meson channel with re-examination and inclusion of αs corrections to dimension-4 condensates in the OPE. We obtain results highly consistent with experimental values. We also discuss the possible extension of this method to some other channels.
The Λ(1405) state in a chiral unitary approach with off-shell corrections to dimensional regularized loop functions
Fang-Yong Dong, Bao-Xi Sun, Jing-Long Pang
2017, 41(7): 074108. doi: 10.1088/1674-1137/41/7/074108
The Bethe-Salpeter equation is solved in the framework of the unitary coupled-channel approximation by using the pseudoscalar meson-baryon octet interaction. The loop function of the intermediate meson and baryon is deduced in a dimensional regularization scheme, where the relativistic kinetic effect and off-shell corrections are taken into account. Based on the experimental data at the K-p threshold, the subtraction constants in the loop function are determined. The squared amplitude is suppressed strongly and only one Λ(1405) state is generated dynamically in the strangeness S=-1 and isospin I=0 sector.
Neutrino emissivity of the nucleon direct URCA process for rotational traditional and hyperonic neutron stars
Nai-Bo Zhang, Shou-Yu Wang, Bin Qi, Jian-Hua Gao, Bao-Yuan Sun
2017, 41(7): 075101. doi: 10.1088/1674-1137/41/7/075101
Based on covariant density functional theory, we study the effects of rotation on the nucleon direct URCA (N-DURCA) process for traditional and hyperonic neutron stars. The calculated results indicate that, for a fixed mass sequence of rotational traditional neutron stars, the neutrino emissivity of the star is nearly invariant with increasing frequency, while it always increases for rotational hyperonic neutron stars. Thus, rotation has different effects on the N-DURCA process for these two kinds of neutron stars.
Detectors, Related Electronics and Experimental Methods
Study of TTS for a 20-inch dynode PMT
Dong-Hao Liao, Hong-Bang Liu, Yi-Xiong Zhou, Feng-Jiao Luo, Zhi-Min Wang, An-Bo Yang, Mei-Hang Xu, Wan Xie, Zhong-Hua Qin
2017, 41(7): 076001. doi: 10.1088/1674-1137/41/7/076001
The neutrino detector for the Jiangmen Underground Neutrino Observatory (JUNO) requires a large number of photomultiplier tubes (PMTs), including 15000 MCP PMTs and 5000 dynode PMTs. The TTS (transit time spread) of the PMTs is very important for vertex and track reconstruction of the neutrinos in the detector. In this paper, we study the TTS of a 20-inch dynode PMT (R12860) from Hamamatsu for different high voltage, light intensity, light spot size and different photocathode regions. The impact from Earth's magnetic field is also studied. The results achieved in this paper will be very useful for the JUNO experiment.
Beam distribution reconstruction simulation for electron beam probe
Yong-Chun Feng, Rui-Shi Mao, Peng Li, Xin-Cai Kang, Yan Yin, Tong Liu, Yao-Yao You, Yu-Cong Chen, Tie-Cheng Zhao, Zhi-Guo Xu, Yan-Yu Wang, You-Jin Yuan
2017, 41(7): 077001. doi: 10.1088/1674-1137/41/7/077001
An electron beam probe (EBP) is a detector which makes use of a low-intensity and low-energy electron beam to measure the transverse profile, bunch shape, beam neutralization and beam wake field of an intense beam with small dimensions. While it can be applied to many aspects, we limit our analysis to beam distribution reconstruction. This kind of detector is almost non-interceptive for all of the beam and does not disturb the machine environment. In this paper, we present the theoretical aspects behind this technique for beam distribution measurement and some simulation results of the detector involved. First, a method to obtain a parallel electron beam is introduced and a simulation code is developed. An EBP as a profile monitor for dense beams is then simulated using the fast scan method for various target beam profiles, including KV distribution, waterbag distribution, parabolic distribution, Gaussian distribution and halo distribution. Profile reconstruction from the deflected electron beam trajectory is implemented and compared with the actual profile, and the expected agreement is achieved. Furthermore, as well as fast scan, a slow scan, i.e. step-by-step scan, is considered, which lowers the requirement for hardware, i.e. Radio Frequency deflector. We calculate the three-dimensional electric field of a Gaussian distribution and simulate the electron motion in this field. In addition, a fast scan along the target beam direction and slow scan across the beam are also presented, and can provide a measurement of longitudinal distribution as well as transverse profile simultaneously. As an example, simulation results for the China Accelerator Driven Sub-critical System (CADS) and High Intensity Heavy Ion Accelerator Facility (HIAF) are given. Finally, a potential system design for an EBP is described.
Design study of a radio-frequency quadrupole for high-intensity beams
Jungbae Bahng, Eun-San Kim, Bong-Hyuk Choi
2017, 41(7): 077002. doi: 10.1088/1674-1137/41/7/077002
The Rare isotope Accelerator Of Newness (RAON) heavy-ion accelerator has been designed for the Rare Isotope Science Project (RISP) in Korea. The RAON will produce heavy-ion beams from 660-MeV-proton to 200-MeV/u-uranium with continuous wave (CW) power of 400 kW to support research in various scientific fields. Its system consists of an ECR ion source, LEBTs with 10 keV/u, CW RFQ accelerator with 81.25 MHz and 500 keV/u, a MEBT system, and a SC linac. In detail, the driver linac system consists of a Quarter Wave Resonator (QWR) section with 81.25 MHz and a Half Wave Resonator (HWR) section with 162.5 MHz, Linac-1, and a Spoke Cavity section with 325 MHz, Linac-2. These linacs have been designed to optimize the beam parameters to meet the required design goals. At the same time, a light-heavy ion accelerator with high-intensity beam, such as proton, deuteron, and helium beams, is required for experiments. In this paper, we present the design study of the high intensity RFQ for a deuteron beam with energies from 30 keV/u to 1.5 MeV/u and currents in the mA range. This system is composed of an Penning Ionization Gauge ion source, short LEBT with a RF deflector, and shared SC Linac. In order to increase acceleration efficiency in a short length with low cost, the 2nd harmonic of 162.5 MHz is applied as the operation frequency in the m D+ RFQ design. The m D+ RFQ is designed with 4.97 m, 1.52 bravery factor. Since it operates with 2nd harmonic frequency, the beam should be 50% of the duty factor while the cavity should be operated in CW mode, to protect the downstream linac system. We focus on avoiding emittance growth by the space-charge effect and optimizing the RFQ to achieve a high transmission and low emittance growth. Both the RFQ beam dynamics study and RFQ cavity design study for two and three dimensions will be discussed.
Simulation of longitudinal dynamics of laser-cooled and RF-bunched C3+ ion beams at heavy ion storage ring CSRe
Xiao-Ni Li, Wei-Qiang Wen, Heng Du, Peng Li, Xiao-Hu Zhang, Xue-Jing Hu, Guo-Feng Qu, Zhong-Shan Li, Wen-Wen Ge, Jie Li, Han-Bing Wang, Jia-Wen Xia, Jian-Cheng Yang, Xin-Wen Ma, You-Jin Yuan
2017, 41(7): 077003. doi: 10.1088/1674-1137/41/7/077003
Laser cooling of Li-like C3+ and O4+ relativistic heavy ion beams is planned at the experimental Cooler Storage Ring (CSRe). Recently, a preparatory experiment to test important prerequisites for laser cooling of relativistic 12C3+ ion beams using a pulsed laser system has been performed at the CSRe. Unfortunately, the interaction between the ions and the pulsed laser cannot be detected. In order to study the laser cooling process and find the optimized parameters for future laser cooling experiments, a multi-particle tracking method has been developed to simulate the detailed longitudinal dynamics of laser-cooled ion beams at the CSRe. Simulations of laser cooling of the 12C3+ ion beams by scanning the frequency of the RF-buncher or continuous wave (CW) laser wavelength have been performed. The simulation results indicate that ion beams with a large momentum spread could be laser-cooled by the combination of only one CW laser and the RF-buncher, and show the requirements of a successful laser cooling experiment. The optimized parameters for scanning the RF-buncher frequency or laser frequency have been obtained. Furthermore, the heating effects have been estimated for laser cooling at the CSRe. The Schottky noise spectra of longitudinally modulated and laser-cooled ion beams have been simulated to fully explain and anticipate the experimental results. The combination of Schottky spectra from the highly sensitive resonant Schottky pick-up and the simulation methods developed in this paper will be helpful to investigate the longitudinal dynamics of RF-bunched and ultra-cold ion beams in the upcoming laser cooling experiments at the CSRe.
Synchrotron Radiation, Free Electron Lasers, Applications of Nuclear Technology, etc
Preliminary study of EEHG-based superradiant undulator radiation at the HLS-II storage ring
Wei-Wei Gao, He-Ting Li, Lin Wang
2017, 41(7): 078101. doi: 10.1088/1674-1137/41/7/078101
We investigate storage ring-based Echo-Enabled Harmonic Generation (EEHG) superradiant undulator radiation as a possible scheme to obtain shorter wavelengths at the HLS-II (Hefei Light Source-II) storage ring. In this paper we give the designation of the storage ring based EEHG up to the 26th harmonic, where 31 nm vacuum ultraviolet light is radiated from an 800 nm seeded laser. The novelty of our design is that both the two dispersion sections of EEHG are realized by the storage ring's own magnet structure. In particular, the whole ring is used as the first dispersion section, and two modulators of the traditional EEHG can be done with the same undulator. These two dispersion sections are realized by changing the superperiod of the present lattice structure, and more precisely by changing the focusing strengths of the present structure. Since no additional magnets and chicanes are used, the beam circulates around the storage ring repeatedly, and thus this storage ring-based EEHG can have a higher repetition rate than a linac-based EEHG.