Construction and performance test of charged particle detector array for MATE

A charged particle array named MATE-PA,which serves as an auxiliary detector system for a Multi-purpose Active-target Time projection chamber used in nuclear astrophysical and exotic beam Experiments(MATE),was constructed.The array comprised of 20 single-sided strip-silicon detectors covering approximately 10%of the solid angle.The detectors facilitated the detection of reaction-induced charged particles that penetrate the active volume of the MATE.The performance of MATE-PA has been experimentally studied using an alpha source and a 36-MeV 14 N beam injected into the MATE chamber on the radioactive ion beam line in Lanzhou(RIBLL).The chamber was filled with a gas mixture of 95%4 He and 5%CO_(2) at a pressure of 500 mbar.The results indicated good separation of light-charged particles using the forward double-layer silicon detectors of MATE-PA.The energy resolution of the Si detectors was deduced to be approximately 1%(σ)for an energy loss of approximately 10 MeV caused by theαparticles.The inclusion of MATE-PA improves particle identification and increases the dynamic range of the kinetic energy of charged particles,particularly that of theαparticles,up to approximately 15 MeV.

NνDEx-100 conceptual design report

Observing nuclear neutrinoless double beta (0vββ) decay would be a revolutionary result in particle physics.Observing such a decay would prove that the neutrinos are their own antiparticles,help to study the absolute mass of neutrinos,explore the origin of their mass,and may explain the matter-antimatter asymmetry in our universe by lepton number violation.We propose developing a time projection chamber (TPC) using high-pressure ^(82)SeF_(6) gas and Topmetal silicon sensors for readout in the China Jinping Underground Laboratory (CJPL) to search for neutrinoless double beta decay of82Se,called the NvDEx experiment.Besides being located at CJPL with the world’s thickest rock shielding,NvDEx combines the advantages of the high Qββ(2.996 MeV) of82Se and the TPC’s ability to distinguish signal and background events using their different topological characteristics.This makes NvDEx unique,with great potential for low-background and high-sensitivity 0 vββsearches.NvDEx-100,a NvDEx experiment phase with 100 kg of SeF_(6)gas,is being built,with plans to complete installation at CJPL by 2025.This report introduces 0 vββ physics,the NvDEx concept and its advantages,and the schematic design of NvDEx-100,its subsystems,and background and sensitivity estimation.

A new analytical algorithm for computing probability distribution of project completion time

An analytical algorithm was presented for the exact computation of the probability distribution of the project completion time in stochastic networks,where the activity durations are mutually independent and continuously distributed random variables. Firstly,stochastic activity networks were modeled as continuous-time Markov process with a single absorbing state by the well-know method of supplementary variables and the time changed from the initial state to absorbing state is equal to the project completion time.Then,the Markov process was regarded as a special case of Markov skeleton process.By taking advantage of the backward equations of Markov skeleton processes,a backward algorithm was proposed to compute the probability distribution of the project completion time.Finally,a numerical example was solved to demonstrate the performance of the proposed methodology.The results show that the proposed algorithm is capable of computing the exact distribution function of the project completion time,and the expectation and variance are obtained.

Approach Evaluating an Investment Project under Uncertainty by Risky Index of Time

The effectiveness of evaluating an investment project based on predicting cash flows depends on the uncertainty of its future cash flows. The remoter the cash flows are, the higher the uncertainty is. Because of this, this paper suggests to discount cash flows by applying risky index of time （RIT）. Thus, the discount rate used to discount the distant cash flows is higher that the discount rate used to discount the near cash flows. By this systematic method, the risk caused by the uncertainty of future cash flows can be hedged in making investment decision. To a certain degree, this approach is reasonable in evaluating investment alternatives under uncertainty. Furthermore, the paper puts forward a practical approach on determining RIT in practice.

Advances in nuclear detection and readout techniques

“A Craftsman Must Sharpen His Tools to Do His Job,”said Confucius.Nuclear detection and readout techniques are the foundation of particle physics,nuclear physics,and particle astrophysics to reveal the nature of the universe.Also,they are being increasingly used in other disciplines like nuclear power generation,life sciences,environmental sciences,medical sciences,etc.The article reviews the short history,recent development,and trend of nuclear detection and readout techniques,covering Semiconductor Detector,Gaseous Detector,Scintillation Detector,Cherenkov Detector,Transition Radiation Detector,and Readout Techniques.By explaining the principle and using examples,we hope to help the interested reader underst and this research field and bring exciting information to the community.

On proportional scintillation in very large liquid xenon detectors

The charge readout of a liquid xenon(LXe)detector via proportional scintillation in the liquid phase was first realized by the Waseda group 40 years ago,but the technical challenges involved were overwhelming.Although the tests were successful,this method was finally discarded and eventually nearly forgotten.Currently,this approach is not considered for large LXe dark matter detectors.Instead,the dual-phase technology was selected despite many limitations and challenges.In two independent studies,two groups from Columbia University and Shanghai Jiao Tong University reevaluated proportional scintillation in the liquid phase.Both studies established the merits for very large LXe detectors,but the Columbia group also encountered apparent limitations,namely the shadowing of the light by the anode wires,and a dependence of the pulse shape on the drift path of the electrons in the anode region.The differences between the two studies,however,are not intrinsic to the technique,but a direct consequence of the chosen geometry.Taking the geometrical differences into account,the results match without ambiguity.They also agree with the original results from the Waseda group.

A LN2-based cooling system for a next-generation liquid xenon dark matter detector

In recent years, cooling technology for liquid xenon(LXe) detectors has advanced driven by the development of dark matter(DM) detectors with target mass in the 100–1000 kg range. The next generation of DM detectors based on LXe will be in the 50,000 kg(50 t)range requiring more than 1 k W of cooling power. Most of the prior cooling methods become impractical at this level.For cooling a 50 t scale LXe detector, a method is proposed in which liquid nitrogen(LN2) in a small local reservoir cools the xenon gas via a cold finger. The cold finger incorporates a heating unit to provide temperature regulation. The proposed cooling method is simple, reliable, and suitable for the required long-term operation for a rare event search. The device can be easily integrated into present cooling systems, for example the ‘‘Cooling Bus’ ’employed for the Panda X I and II experiments. It is still possible to cool indirectly with no part of the cooling or temperature control system getting in direct contact with the clean xenon in the detector. Also, the cooling device can be mounted at a large distance, i.e., the detector is cooled remotely from a distance of 5–10 m. The method was tested in a laboratory setup at Columbia University to carry out different measurements with a small LXe detector and behaved exactly as predicted.

Non-Markovian dynamics of a qubit in a reservoir: different solutions of non-Markovian master equation

We present a non-Markovian master equation for a qubit interacting with a general reservoir, which is derived according to the Nakajima-Zwanzig and the time convolutionless projection operator technique. The non-Markovian solutions and Markovian solution of dynamical decay of a qubit are compared. The results indicate the validity of non-Markovian approach in different coupling regimes and also show that the Markovian master equation may not precisely describe the dynamics of an open quantum system in some situation. The non-Markovian solutions may be effective for many qubits independently interacting with the heated reservoirs.

Non-Markovian dynamics of two non-coupled qubits interacting with two separate reservoirs with different spectral densities

The dynamics of two non-coupled qubits independently interacting with their reservoirs is solved by the time convolutionless projection operator method. We study two-qubit quantum correlation dynamics for two different types of spectral densities, which are a Lorentzian distribution and an Ohmic spectral density with a Lorentzian–Drude cutoff function. For two qubits initially prepared in the initial Bell state, quantum discord can keep longer time and reach larger values in nonMarkovian reservoirs for the first spectral distribution or by reducing the cutoff frequency for the second case. For the initial Bell-like state, the dynamic behaviors of quantum discord and entanglement are compared. The results show that a long time of quantum correlation can be obtained by adjusting some parameters in experiment and further confirm that the discord can capture quantum correlation in addition to entanglement.

M-TIMES SECANT-LIKE MULTI-PROJCTION METHOD FOR SPARSE MINIMIZATION PROBLEM

In this paper, we present m time secant like multi projection algorithm for sparse unconstrained minimization problem. We prove this method are all q superlinearly convergent to the solution about m≥1 . At last, we from some numerical results, discuss how to choose the number m to determine the approximating matrix properly in practical use.

Optimization of PERT Network and Compression of Time

In the traditional methods of program evaluation and review technique （PERT） network optimization and compression of time limit for project, the uncertainty of free time difference and total time difference were not considered as well as its time risk. The authors of this paper use the theory of dependent-chance programming to establish a new model about compression of time for project and multi-objective network optimization, which can overcome the shortages of traditional methods and realize the optimization of PERT network directly. By calculating an example with genetic algorithms, the following conclusions are drawn： （ 1 ） compression of time is restricted by cost ratio and completion probability of project; （2） activities with maximal standard difference of duration and minimal cost will be compressed in order of precedence; （3） there is no optimal solutions but noninferior solutions between chance and cost, and the most optimal node time depends on decision-maker＇s preference.

A gaseous time projection chamber with Micromegas readout for low-radioactive material screening

Purpose Low-radioactive material screening is becoming essential for rare event search experiments,such as neutrinoless double beta decay and dark matter searches in underground laboratories.A gaseous time projection chamber(TPC)can be used for such purposes with large active areas and high efficiency.Methods A gaseous TPC with a Micromegas readout plane of approximately 20×20 cm^(2)is successfully constructed for surface alpha contamination measurements.Results We have characterized the energy resolution,gain stability,and tracking capability with calibration sources.Conclusion With the unique track-related background suppression cuts of the gaseous TPC,we have established that the alpha background rate of the TPC is(0.13±0.03)×10^(−6)Bq/cm^(2),comparable to the leading commercial solutions.

Waveform simulation in PandaX-4T

Signal reconstruction through software processing is a crucial component of the background and signal models in the PandaX-4T experiment,which is a multi-tonne dark matter direct search experiment.The accuracy of signal reconstruction is influenced by various detector artifacts,including noise,dark count of photomultiplier,photoionization of impurities in the detector,and other relevant considerations.In this study,we presented a detailed description of a semi-data-driven approach designed to simulate a signal waveform.This work provides a reliable model for the efficiency and bias of the signal reconstruction in the data analysis of PandaX-4T.By comparing critical variables that relate to the temporal shape and hit pattern of the signals,we found good agreement between the simulation and data.

Studies of the 2α and 3α channels of the ^(12)C+^(12)C reaction in the range of E_(c.m.)=8.9 MeV to 21 MeV using the active target Time Projection Chamber

The ^(12)C+^(12)C fusion reaction was studied in the range of E_(c.m.)=8.9 to 21 MeV using the active-target Time Projection Chamber.With full information on all tracks of the reaction products,cross sections of the^(12)C(^(12)C,^(8)Be)^(16)O_(g.s.)channel and the ^(12)C(^(12)C,3a)^(12)C channel could be measured down to the level of a few milibarns.The ^(12)C(^(12)C,^(8)Be)^(16)O_(g.s.)reaction channel was determined to be 10_(-8)^(+24) mb at E_(c.m.)=11.1 MeV,supporting the direct a transfer reaction mechanism.The ^(12)C(^(12)C,3α)^(12)C reaction channel was studied for the first time using an exclusive measurement.Our result does not confirm the anomaly behavior reported in the previous inclusive measurement by Kolata et al.[Phys.Rev.C 21,579(1980)].Our comparisons with statistical model calculations suggest that the 3 a channel is dominated by the fusion evaporation process at E_(c.m.)>19 MeV.The additional contribution of the 3 a channel increases the fusion reaction cross section by 10% at energies above 20 MeV.We also find that an additional reaction mechanism is needed to explain the measured cross section at E_(c.m.)<15 MeV at which point the statistical model prediction vanishes.

Outboard abnormal noise source localization method with curved surface projection based on time delay matching and weighting criterion

An improved localization method consisting of ＂filtering-time delay estimationhyperbolic localization＂ is proposed. Combining the empirical mode decomposition（EMD）and time delay estimation method based on generalized average magnitude difference function,the original signals are decomposed into intrinsic mode function（IMF） components. The energy distribution criterion and spectrum consistency criterion are used to select the IMFs, which can represent the physical characteristics of the source signal. Several sets of signals are applied to estimate the time delay, and then a vector matching criterion is proposed to select the correct time delay estimation. Considering the hydrophones location, a shell model is established and projected to a plane according to the quadrant before the hyperbolic localization. Results of mooring and sailing tests show that the proposed method improves the localization accuracy,and reduces the error caused by time delay estimation.

Comparison of two projection methods for modeling incompressible flows in MPM

Material point method（MPM）was originally introduced for large deformation problems in solid mechanics applications.Later,it has been successfully applied to solve a wide range of material behaviors.However,previous research has indicated that MPM exhibits numerical instabilities when resolving incompressible flow problems.We study Chorin＇s projection method in MPM algorithm to simulate material incompressibility.Two projection-type schemes,non-incremental projection and incremental projection,are investigated for their accuracy and stability within MPM.Numerical examples show that the non-incremental projection scheme provides stable results in single phase MPM framework.Further,it avoids artificial pressure oscillations and small time steps that are present in the explicit MPM approach.

Cross section measurement for the^(232)Th(n,f)reaction in the 4.50−5.40 MeV region using a time projection chamber

Accurate cross sections of neutron induced fission reactions are required in the design of advanced nuclear systems and the development of fission theory.Time projection chambers(TPCs),with their track reconstruction and particle identification capabilities,are considered the best detectors for high-precision fission cross section measurements.The TPC developed by the back-streaming white neutron source(Back-n)team of the China Spallation Neutron Source(CSNS)was used as the fission fragment detector in measurements.In this study,the cross sections of the ^(232)Th(n,f)reaction at five neutron energies in the 4.50−5.40 MeV region were measured.The fission fragments and α particles were well identified using our TPC,which led to a higher detection efficiency of the fission fragments and smaller uncertainty of the measured cross sections.Ours is the first measurement of the ^(232)Th(n,f)reaction using a TPC for the detection of fission fragments.With uncertainties less than 5%,our cross sections are consistent with the data in different evaluation libraries,including JENDL-4.0,ROSFOND-2010,CENDL-3.2,ENDF/B-VⅢ.0,and BROND-3.1,whose uncertainties can be reduced after future improvement of the measurement.

PandaX: a liquid xenon dark matter experiment at CJPL

PandaX is a large liquid-xenon detector experiment usable for direct dark-matter detection and 136Xe double-beta decay search.The central vessel was designed to accommodate a staged target volume increase from initially 120 kg(stage I)to 0.5 t(stage II)and eventually to a multi-ton scale.The experiment is located in the Jinping Deep-Underground Laboratory in Sichuan,China.The detector operates in dual-phase mode,allowing detection of both prompt scintillation,and ionization charge through proportional scintillation.In this paper a detailed description of the stage I detector design and performance as well as results established during the commissioning phase are presented.

Design and construction of a TPC prototype based on GEM detector readout

A time projection chamber （TPC） readout by gas electron multipliers （GEM） detector is a very promising candidate for the central tracking system of ILC （International Linear Collider）. A prototype is designed and set up in our lab and introduced here. The tests during and after the assembly prove that the prototype TPC has been constructed successfully. It is ready for further study.