2015 Vol. 39, No. 11

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New physics searches with Higgs-photon associated production at the Higgs factory
REN Hong-Yu
2015, 39(11): 113101. doi: 10.1088/1674-1137/39/11/113101
A future Higgs factory is being designed for precise measurement of Higgs characteristics and to search for new physics. In this paper we propose that the Higgs-photon associated production process, e+e-→γh could be a useful channel for new physics. We express new physics model-independently in the effective Lagrangian approach, and find that the new physics effects of γh have only two degrees of freedom, much fewer than the Higgsstrahlung process. This point could be used to reduce the degeneracies of Wilson coefficients. We also calculate for the first time the 95% confidence level(CL) bounds of γh at the Higgs factory, and prove that γh is more sensitive to some dimension-6 operators than the current experimental data. In the optimistic scenario new physics effects may be observed at the CEPC or FCC-ee after the first couple of years of their run.
Probing HZγ and Hγγ anomalous couplings in the process e+e-→Hγ
CAO Qing-Hong, WANG Hao-Ran, ZHANG Ya
2015, 39(11): 113102. doi: 10.1088/1674-1137/39/11/113102
We propose to measure the HZγ and Hγγ anomalous couplings in the process e+e-→Hγ with the sequential decay of H→bb. The discovery potential of observing the anomalous couplings are explored in detail. Our study shows that future electron-positron colliders have great potential to test the HZγ and Hγγ couplings. Conservative bounds on the two anomalous couplings are also derived when no new physics signal is detected on top of the SM backgrounds.
Meson electro-magnetic form factors in an extended Nambu-Jona-Lasinio model including heavy quark flavors
LUAN Yi-Long, CHEN Xiao-Lin, DENG Wei-Zhen
2015, 39(11): 113103. doi: 10.1088/1674-1137/39/11/113103
Based on an extended NJL model including heavy quark flavors, we calculate the form factors of pseudo-scalar and vector mesons. After taking into account the vector-meson-dominance effect, which introduces a form factor correction to the quark vector coupling vertices, the form factors and electric radii of π+ and K+ pseudo-scalar mesons in the light flavor sector fit the experimental data well. The magnetic moments of the light vector mesons ρ+ and K*+ are comparable with other theoretical calculations. The form factors in the light-heavy flavor sector are presented to compare with future experiments or other theoretical calculations.
Near-threshold η production in pp collisions
LI De-Min
2015, 39(11): 113104. doi: 10.1088/1674-1137/39/11/113104
We study near-threshold η meson production in pp collisions within an effective Lagrangian approach combined with the isobar model, by allowing for the various intermediate nucleon resonances due to the π, η, and ρ-meson exchanges. It is shown that the ρ-meson exchange is the dominant excitation mechanism for these resonances, and the contribution from the N*(1720) is dominant. The total cross section data can be reasonably reproduced, and the anisotropic angular distributions of the emitted η meson are consistent with experimental measurements. Besides, the invariant mass spectra of pp and ρη explain the data well at excess energy of 15 MeV, and are basically consistent with the data at excess energy of 40 MeV. However, our model calculations cannot reasonably account for the two-peak structure in the pη distribution at excess energies of 57 and 72 MeV, which suggests that a more complicated mechanism is needed at higher energy region.
Center-of-mass correction and rotational correction in covariant density functional theory
LI Zhao-Xi, LI Zhi-Pan
2015, 39(11): 114101. doi: 10.1088/1674-1137/39/11/114101
Center-of-mass (c.m.) correction and rotational correction in even-even Ge isotopes are systematically investigated within the triaxially deformed relativistic Hartree-Bogoliubov model using the PC-PK1 force. The shell effect and deformation effect on the microscopic c.m. correction and rotational correction are discussed, and the importance of both corrections on reproducing the binding energy is demonstrated.
Static versus energy-dependent nucleus-nucleus} potential for description of sub-barrier fusion dynamics of 816O+50112,116,120Sn reactions
Manjeet Singh Gautam
2015, 39(11): 114102. doi: 10.1088/1674-1137/39/11/114102
The static and energy-dependent nucleus-nucleus potentials are simultaneously used along with the Wong formula for exploration of fusion dynamics of 816O+50112,116,120Sn reactions. The role of internal structure degrees of freedom of colliding pairs, such as inelastic surface vibrations, are examined within the context of coupled channel calculations performed using the code CCFULL. Theoretical calculations based on the static Woods-Saxon potential along with the one-dimensional Wong formula fail to address the fusion data of 816O+50112,116,120Sn reactions. Such discrepancies can be removed if one uses couplings to internal structure degrees of freedom of colliding nuclei. However, the energy-dependent Woods-Saxon potential model (EDWSP model) accurately describes the sub-barrier fusion enhancement of 816O+50112,116,120Sn reactions. Therefore, in sub-barrier fusion dynamics, energy dependence in the nucleus-nucleus potential governs barrier modification effects in a closely similar way to that of the coupled channel approach.
Phase transition in odd-N Pd-isotopes
ZHOU Hou-Bing, DONG Guo-Xiang, SUN Xiao-Jun, XU Fu-Rong
2015, 39(11): 114103. doi: 10.1088/1674-1137/39/11/114103
Phase transition in odd-N isotopes 99,101,103Pd are investigated via the E-GOS (E-Gamma Over Spin) curves, which strongly suggest a structure evolution from vibration to rotation along the yrast lines with increasing spin. Theoretical calculations have been performed for the ground state bands of 99,101,103Pd in the framework of the cranked shell model (CSM) and the alignment properties observed experimentally are analyzed employing this model. The results show that the phase transition in the ground state bands of 99,101,103Pd can be interpreted as the valence nucleons start to occupy the g9/2 proton orbitals with increasing spin which would polarize the core to a small, but rigid quadrupole deformation.
Collective flow of K+ mesons in heavy-ion collisions predicted by the covariant Kaon dynamics
XING Yong-Zhong, DAI Yue-Qian
2015, 39(11): 114104. doi: 10.1088/1674-1137/39/11/114104
The directed and elliptic flow of positively charged kaons produced in 2858Ni+2858Ni reactions at incident kinetic energy 1.91 AGeV are studied within the covariant kaon dynamics and compared to new data. We observe that the influence of the Lorentz force on the directed and differential directed flow of K+ mesons is obvious. Our calculated results indicate that it is necessary for the Lorentz force to be included in the kaon dynamics in order to reasonably describe experimental data.
Energy dependent growth of nucleon and inclusive charged hadron distributions
WANG Hong-Min, HOU Zhao-Yu, SUN Xian-Jing
2015, 39(11): 114105. doi: 10.1088/1674-1137/39/11/114105
In the Color Glass Condensate formalism, charged hadron pT spectra in p+p and p+Pb collisions are studied by considering an energy-dependent broadening of nucleon density distribution. Then, in the glasma flux tube picture, the n-particle multiplicity distributions at different pseudo-rapidity ranges are investigated. Both the theoretical results show good agreement with the recent experimental data from ALICE and CMS at LHC energies. The predictive results for pT or multiplicity distributions in p+p and p+Pb collisions at the Large Hadron Collider are also given in this paper.
TOT measurement implemented in FPGA TDC
FAN Huan-Huan, CAO Ping, LIU Shu-Bin, AN Qi
2015, 39(11): 116101. doi: 10.1088/1674-1137/39/11/116101
Time measurement plays a crucial {role} for the purpose of particle identification in high energy physics experiments. With increasingly demanding physics goals and the development of electronics, modern time measurement systems need to meet the requirement of excellent resolution specification as well as high integrity. Based on Field Programmable Gate Arrays (FPGAs), FPGA time-to-digital converters (TDCs) have become one of the most mature and prominent time measurement methods in recent years. For correcting the time-walk effect caused by leading timing, a time-over-threshold (TOT) measurement should be added to the FPGA TDC. TOT can be obtained by measuring the interval between the signal leading and trailing {edges}. Unfortunately, a traditional TDC can recognize only one kind of signal edge, the leading or the trailing. Generally, to measure the interval, two TDC channels need to be used at the same time, one for leading, the other for trailing. However, this method unavoidably increases the amount of FPGA resources used and reduces the TDC's integrity. #br#This paper presents one method of TOT measurement implemented in a Xilinx Virtex-5 FPGA. In this method, TOT measurement can be achieved using only one TDC input channel. The consumed resources and time resolution can both be guaranteed. {Testing} shows that this TDC can achieve resolution better than 15ps for leading edge measurement and 37 ps for TOT measurement. Furthermore, the TDC measurement dead time is about {two} clock cycles, which makes it good for applications with higher physics event rates.
A data transmission method for particle physics experiments based on Ethernet physical layer
HUANG Xi-Ru, CAO Ping, ZHENG Jia-Jun
2015, 39(11): 116102. doi: 10.1088/1674-1137/39/11/116102
Due to its advantages of universality, flexibility and high performance, fast Ethernet is widely used in readout system design for modern particle physics experiments. However, Ethernet is usually used together with the TCP/IP protocol stack, which makes it difficult to implement readout systems because designers have to use the operating system to process this protocol. Furthermore, TCP/IP degrades the transmission efficiency and real-time performance. To maximize the performance of Ethernet in physics experiment applications, a data readout method based on the physical layer (PHY) is proposed. In this method, TCP/IP is replaced with a customized and simple protocol, which makes it easier to implement. On each readout module, data from the front-end electronics is first fed into an FPGA for protocol processing and then sent out to a PHY chip controlled by this FPGA for transmission. This kind of data path is fully implemented by hardware. From the side of the data acquisition system (DAQ), however, the absence of a standard protocol causes problems for the network related applications. To solve this problem, in the operating system kernel space, data received by the network interface card is redirected from the traditional flow to a specified memory space by a customized program. This memory space can easily be accessed by applications in user space. For the purpose of verification, a prototype system has been designed and implemented. Preliminary test results show that this method can meet the requirements of data transmission from the readout module to the DAQ {with} an efficient and simple manner.
A muti-channel distributed DAQ for n-TPC
CHENG Xiao-Lei, LIU Jian-Fang, YU Qian, NIU Li-Bo, LI Yu-Lan
2015, 39(11): 116103. doi: 10.1088/1674-1137/39/11/116103
A new fast neutron spectrometer named n-TPC has been designed by LPRI (Key Laboratory of Particle & Radiation Imaging, Ministry of Education) at Tsinghua University. The neutron energy spectrum can be calculated from the recoil angle and energy of the recoil proton detected by a 704-pad GEM-TPC. In beam tests at IHIP (Institute of Heavy Ion Physics, Peking University) in 2014, n-TPC performed better than 6%@6 MeV energy resolution and 5‰ detection efficiency. To find the best working parameters (the component and proportion of the gas, the high voltage between each GEM layer, etc.) of the n-TPC and support its application in various conditions, a multichannel distributed DAQ has been {designed} to read out the signals from the 704 channels. With over 25 Ms/s sampling rate and 12 bit resolution for each channel, it can record the time and amplitude information as well as traditional DAQs in the TPC application domain. The main design objective of this distributed DAQ, however, is more flexible parameter modulation and operation. It can support the n-TPC without the limitation of the chassis and categorize signals arriving from the 704 channels at the same time by different events without event triggers.
Digital pulse shape discrimination methods for n-γ separation in an EJ-301 liquid scintillation detector
WAN Bo, ZHANG Xue-Ying, CHEN Liang, GE Hong-Lin, MA Fei, ZHANG Hong-Bin, JU Yong-Qin, ZHANG Yan-Bin, LI Yan-Yan, XU Xiao-Wei
2015, 39(11): 116201. doi: 10.1088/1674-1137/39/11/116201
A digital pulse shape discrimination system based on a programmable module NI-5772 has been established and tested with an EJ-301 liquid scintillation detector. The module was operated by running programs developed in LabVIEW, with a sampling frequency up to 1.6 GS/s. Standard gamma sources 22Na, 137Cs and 60Co were used to calibrate the EJ-301 liquid scintillation detector, and the gamma response function was obtained. Digital algorithms for the charge comparison method and zero-crossing method have been developed. The experimental results show that both digital signal processing (DSP) algorithms can discriminate neutrons from γ-rays. Moreover, the zero-crossing method shows better n-γ discrimination at 80 keVee and lower, whereas the charge comparison method gives better results at higher thresholds. In addition, the figure-of-merit (FOM) for detectors of two different dimensions were extracted at 9 energy thresholds, and it was found that the smaller detector presented better n-γ separation for fission neutrons.
DAMPE silicon tracker on-board data compression algorithm
DONG Yi-Fan, ZHANG Fei, QIAO Rui, PENG Wen-Xi, FAN Rui-Rui, GONG Ke, WU Di, WANG Huan-Yu
2015, 39(11): 116202. doi: 10.1088/1674-1137/39/11/116202
The Dark Matter Particle Explorer (DAMPE) is an upcoming scientific satellite mission for high energy gamma-ray, electron and cosmic ray detection. The silicon tracker (STK) is a subdetector of the DAMPE payload. It has excellent position resolution (readout pitch of 242 μm), and measures the incident direction of particles as well as charge. The STK consists of 12 layers of Silicon Micro-strip Detector (SMD), equivalent to a total silicon area of 6.5 m2. The total number of readout channels of the STK is 73728, which leads to a huge amount of raw data to be processed. In this paper, we focus on the on-board data compression algorithm and procedure in the STK, and show the results of initial verification by cosmic-ray measurements.
Generating a uniform transverse distributed electronbeam along a beam line
JIAO Yi, CUI Xiao-Hao
2015, 39(11): 117001. doi: 10.1088/1674-1137/39/11/117001
It has been reported that transverse distribution shaping can help to further enhance the energy extraction efficiency in a terawatt, tapered X-ray free-electron laser. Thus, methods of creating and keeping an almost uniform transverse distributed (UTD) beam within undulators are required. This study shows that a UTD electron beam can be generated within evenly distributed drift sections where undulators can be placed, by means of octupoles and particular optics. A specific design is presented, and numerical simulations are performed to verify the proposed method.
Multipacting analysis for half wave resonators in the China ADS
ZHANG Cong, ZHANG Sheng-Hu, HE Yuan, YUE Wei-Ming, CHANG Wei
2015, 39(11): 117002. doi: 10.1088/1674-1137/39/11/117002
In the China ADS (CIADS) proton accelerator, multipacting is an issue of concern for the superconducting cavities. The parallel codes Omega3P and Track3P, developed at SLAC under the support of the DOE SciDAC program, have been used to calculate the electromagnetic field distribution and to analyze the multipacting barriers of such cavities. In this paper, two types of 162.5 MHz half wave resonator cavities, HWR-010 (cylinder type with β of 0.10) and HWR-015 (taper type with β of 0.15) have been analyzed, and the results of the multipacting analyses show that the resonant electrons occur at different regions with different accelerating gradients. The two-point 1st order multipacting on the short plate has also been researched and discussed.
Compensation-rematch for the major components of C-ADS injector-I
SUN Biao, YAN Fang, PEI Shi-Lun, MENG Cai, TANG Jing-Yu
2015, 39(11): 117003. doi: 10.1088/1674-1137/39/11/117003
The China-ADS project is a strategic plan launched by the Chinese Academy of Sciences to solve the nuclear waste problem and the resource problem for nuclear power in China. Under its long-term plan, it will last until about 2040. In order to achieve the extremely high reliability and availability required for the C-ADS accelerator, a fault tolerant strategy has been implanted. The failure effects of key elements such as the RF cavities and focusing elements in different locations of the injector-I part have been studied and schemes of compensation based on the local compensation-rematch method have been proposed. In addition, error analysis has been carried out to check the reliability of this method compared with the uncompensated situation, and it is found to be very effective. As the injector-I testing facility is coming into operation, it is possible to check and improve the compensation-rematch method with the beam testing experiment before the main linac operation.
Beam experiments with a non-intercepting beam induced fluorescence profile monitor for the ADS LINAC
XIE Hong-Ming, WU Jun-Xia, ZHANG Yong, ZHU Guang-Yu, XIA Jia-Wen, YE Min-You
2015, 39(11): 117004. doi: 10.1088/1674-1137/39/11/117004
An accelerator-driven subcritical system (ADS) project was launched in China in 2011, aiming to design and build an ADS demonstration facility with the capability of more than 1000 MW thermal power. The driver linac is defined to be a 10 mA current of high energy protons at 1.5 GeV in continuous wave operation mode. To meet the extremely high power and intense beam accelerator requirements, non-interceptive monitors for the beam transverse profile are required for this proton linac. Taking advantage of the residual gas as active material, the Beam Induced Fluorescence (BIF) monitor exploits gas-excited fluorescence in the visible spectrum region for transverse profile measurements. The advantages of this non-intercepting method are that nothing is installed in the vacuum pipe, component design is compact and there is no need for expensive signal processing electronics. Beam experiments have been performed under constant beam conditions. The helium spectrum has been verified with different optical filters, showing that a proper optical band-pass filter covering 400-500 nm is necessary for fluorescence experiments with helium. By changing gas pressure, it is shown that gas pressure is proportional to the signal amplitude but has no influence on detected profile width. Finally, a comparison experiment between the BIF monitor and a wire scanner shows that the detected profile width results of both methods agree well.
Experimental study on TiN coated racetrack-type ceramic pipe
WANG Jie, XU Yan-Hui, ZHANG Bo, WEI Wei, FAN Le, PEI Xiang-Tao, HONG Yuan-Zhi, WANG Yong
2015, 39(11): 117005. doi: 10.1088/1674-1137/39/11/117005
TiN film was coated on the internal surface of a racetrack-type ceramic pipe by three different methods: radio-frequency sputtering, DC sputtering and DC magnetron sputtering. The deposition rates of TiN film under different coating methods were compared. The highest deposition rate was 156 nm/h, which was obtained by magnetron sputtering coating. Based on AFM, SEM and XPS test results, the properties of TiN film, such as film roughness and surface morphology, were analyzed. Furthermore, the deposition rates were studied with two different cathode types, Ti wires and Ti plate. According to the SEM test results, the deposition rate of TiN/Ti film was about 800 nm/h with Ti plate cathode by DC magnetron sputtering. Using Ti plate cathode rather than Ti wire cathode can greatly improve the film deposition rate.
HOMs simulation and measurement results of IHEP02 cavity
ZHENG Hong-Juan, ZHAI Ji-Yuan, ZHAO Tong-Xian, GAO Jie
2015, 39(11): 117006. doi: 10.1088/1674-1137/39/11/117006
In accelerator RF cavities, there exists not only the fundamental mode which is used to accelerate the beam, but also higher order modes (HOMs). The higher order modes excited by the beam can seriously affect beam quality, especially for the higher R/Q modes. 1.3 GHz low-loss 9-cell superconducting cavity as a candidate for ILC high gradient cavity, the properties of higher order mode has not been studied carefully. IHEP based on existing low loss cavity, designed and developed a large grain size 1.3 GHz low-loss 9-cell superconducting cavity (IHEP02 cavity). The higher order mode coupler of IHEP02 used TESLA coupler's design. As a result of the limitation of the mechanical design, the distance between higher order mode coupler and end cell is larger than TESLA cavity. This paper reports on measured results of higher order modes in the IHEP02 1.3 GHz low-loss 9-cell superconducting cavity. Using different methods, Qe of the dangerous modes passbands have been obtained. The results are compared with TESLA cavity results. R/Q of the first three passbands have also been obtained by simulation and compared with the results of the TESLA cavity.