Performance study of particle identification at the CEPC using TPC dE/dx information
EEur. Phys. J. C manuscript No. (will be inserted by the editor)
Performance study of particle identification at the CEPC using TPC dE / dx information F. An a,1,2 , S. Prell , C. Chen , J. Cochran , X. Lou , M. Ruan b,1 Institute of High Energy Physics, Chinese Academy of Science, Beijing, China Department of Physics and Astronomy, Iowa State University, Ames IA, USA Physics Department, University of Texas at Dallas, Richardson TX, USA University of Chinese Academy of Science (UCAS), Beijing, ChinaReceived: date / Accepted: date
Abstract
The kaon identification is crucial for the flavorphysics, and also benefits the flavor and charge reconstruc-tion of the jets. We explore the particle identification capa-bility for tracks with momenta ranging from 2-20 GeV/c us-ing the dE / dx measurements in the Time Projection Cham-ber at the future Circular Electron-Positron Collider. Basedon Monte Carlo simulation, we anticipate that an average3 . σ (2 . σ ) K / π separation can be achieved based on dE / dx information for an optimistic (conservative) extrap-olation of the simulated performance to the final system.Time-of-flight (TOF) information from the ElectromagneticCalorimeter can provide K / π separation around 1 GeV/cand reduce the K / p mis-identification rate. By combiningthe dE / dx and TOF information, we estimate that in the op-timistic scenario a kaon selection in inclusive hadronic Z de-cays with both the average efficiency and purity approaching95% can be achieved. The project of building a Circular Electron-Positron Collider(CEPC) [1] in China has been proposed. The CEPC will op-erate as a Higgs boson factory or a Z boson factory at center-of-mass energies of √ s ∼
240 or 91 GeV, respectively. Dur-ing the lifetime of the CEPC, one million Higgs bosons areexpected to be produced, allowing precision measurementsof the Higgs boson properties [2]. In addition, ten billion Z bosons will be delivered at the Z pole promising refinedmeasurements of electroweak and heavy flavor physics [3].A Time Projection Chamber (TPC) has been proposedas a candidate charged particle tracking device for the CEPCdetector. TPCs have been operated successfully in e + e − and a e-mail: [email protected] b e-mail: [email protected] hadron collider experiments and even in fixed-target experi-ments, such as the ALEPH [4] and ALICE [5] experimentsat CERN, the HISS experiment at BEVALEC [6], etc. ATPC provides precise momentum and position measurements,a low material budget, and good particle identification (PID)over a wide range of momentum. The PID information isbased on dE / dx measurements in the TPC, where dE / dx isdefined as the energy deposit per unit path length. There areseveral ongoing R&D efforts about the TPC proposal, suchas exploring novel technologies of the GEM-Micromegas[7] or GEM [8] readout detectors, the voxel occupancy in theTPC in decays at the Z pole [9], etc. Compared to previousTPCs, we expect an improved performance of the proposedTPC at the CEPC detector as a result of the increased num-ber of readout channels and recent developments in readoutelectronics.In this paper, the dE / dx performance of the CEPC TPCis investigated based on Monte Carlo (MC) simulation. PIDwill play an important role in measurements of the bottom( b ) and charm ( c ) hadron decays in heavy flavor physics. Itcan also be exploited to enhance the flavor tagging of the b / c -jets in Higgs and precision electroweak measurements.We study the PID of kaons, pions and protons in hadronicdecays at the Z pole, demonstrating that an effective kaonselection can be achieved by combining the dE / dx measure-ments of the TPC with the time-of-flight (TOF) informationprovided by the Electromagnetic Calorimeter (ECAL) at theCEPC detector.The paper is organized as follows. In section 2 we presentthe configuration of the CEPC TPC and the energy loss mea-surement of traversing charged particles. Section 3 describesthe key factors influencing the resolution of the dE / dx mea-surement and provides an estimate of the PID performanceat the CEPC. In section 4 a brief conclusion is given. a r X i v : . [ phy s i c s . i n s - d e t ] M a r The TPC concept was introduced in Ref. [10]. A TPC con-sists essentially of a wireless drift volume situated betweenparallel axial electric and magnetic fields, where the electricfield is set up between a central cathode plate and the endplates. When a charged particle traverses the gas-filled driftvolume, it generates electron-ion pairs by collisions with thegas molecules. The electrons drift towards the end plates,where the charges are amplified and collected.The default design of the TPC at the CEPC detector canbe found in Ref. [1]. It is a cylindrical detector that is 4.7 mlong with an inner and outer radii of 0.325 m and 1.8 m, re-spectively. The candidate gas is an argon-based gas compos-ite (93% Ar+5% CH +2% CO ) held at atmospheric pres-sure and room temperature. A solenoid provides a magneticfield of 3 T along the beam direction. In the endcaps, Mi-cromegas [11] detector modules with pad size of 6 mm alongthe radial direction (height) and 1 mm along the azimuthaldirection (width) are arranged in 222 concentrical rings.In the MC simulation, the description of the detector ge-ometry, material and the ionization process are implementedusing GEANT4 [12]. Single-particle events are generatedusing ParticleGun. Collision events of the Standard Modelprocesses are produced with the event generator WHIZARD[13]. The dE / dx measurement by each pad is defined as theenergy deposit divided by the track length in the correspond-ing drift volume, both of which are provided by GEANT4.Typically, the dE / dx measurements of a track follow a Lan-dau distribution with a large tail caused by high-energy δ -electrons. We estimate a representative average dE / dx for atrack, denoted as I , by using the common “truncated mean”method [14]. We calculate I as the mean of the lowest 90%of the dE / dx values associated with the track, where thetruncation ratio of 90% is determined to yield the optimal dE / dx resolution. The distribution of the truncated mean I can be well described by a Gaussian function with a widthdenoted as σ I . Unless explicitly stated, the dE / dx resolutionin the paper refers to the ratio σ I / I .For a particle with momentum p and mass m , the MCsimulation of the dependence of I as a function of β γ = p / ( mc ) is shown in the left plot of Fig. 1. Herein we usesingle-particle events requiring θ = o so that the trackstraverse the full TPC radius, where θ is defined as the po-lar angle of the tracks with respect to the beam direction.The simulated I dependence agrees well with the theoreticalprediction by the Bethe equation [15]. The values of all theparameters in the Bethe equation are taken from Ref. [16]except for the normalization scale factor and the maximumenergy transfer W max , which is free in the fit to the I dis-tribution following the procedure in Ref. [17]. In the rightplot of Fig. 1, the scatter plot of I versus p is presented us-ing a simulated sample of e + e − → Z → q ¯ q events. At the CEPC, the majority of the particles traversing the TPC havea momentum above 1 GeV/c and reside in the relativisticrise region, where TOF measurements can not effectivelydistinguish between the different particles types. Therefore,improving the dE / dx resolution will directly benefit the PIDperformance. In an ideal case, the dE / dx resolution for a given track de-pends on the number of the dE / dx measurements along theparticle trajectory and the number of the ionizing electronsper measurement. We name the induced resolution from thesefactors “intrinsic dE / dx resolution”. The resolution in realexperiments, named as “actual dE / dx resolution”, will bedeteriorated by the detector effects arising in the processesof electron drift, signal amplification and readout in TPC.A detailed study of those effects is beyond the scope of thepaper. In this paper, we study the intrinsic dE / dx resolu-tion of the CEPC TPC using MC simulation, and estimatethe degradation of the actual resolution by comparing theMC-based results with the experimental measurements ofprevious TPCs.3.1 Parameterization of the intrinsic dE / dx resolutionThe intrinsic dE / dx resolution arises from fluctuations atthe primary ionization stage. It depends on the number ofthe pad rings n , the pad height along the radial direction h , the density of the working gas ρ , the relativistic veloc-ity β γ and the polar angle θ of the particle trajectory. Theresolution dependence on these variables is studied usingsingle-particle MC events. We scan each variable to obtainits relationship with the intrinsic resolution. Except for thevariable under consideration, all others are kept constant attheir default values given in Sec. 2, i.e., n = h = ρ = ρ = and θ = o for pions with a momen-tum of 20 GeV/c. The MC results are shown in Fig. 2.The correlations between the variables are small. To agood approximation, the parameterization of σ I / I can befactorized as σ I I = . n . · ( h ρ ) . [ . + . ( β γ ) − . ] × [ . − . ( cos θ ) + . ( cos θ ) ] , (1)where h and ρ are in of mm and mg/cm , respectively. Tocheck the correlation between the variables, we validate thefactorization in the five-dimensional space by varying thevariables within the ranges shown in Fig. 2. In addition, theinfluence of the magnetic field is found to be negligible on γβ − × − × ) c m I ( M e V g Bethe Eq π Kp Fig. 1
The dependence of the truncated mean I of the track dE / dx , as a function of β γ (left) and p (right) for charged particles traversing theTPC of the CEPC detector. In the left plot the dots represent the MC result of single-particle events with the theoretical prediction by the Betheequation [15] overlaid. In the right plot the dots are from simulation of e + e − → Z → q ¯ q events. n d E / d x R e s o l u t i on ( % ) n ∝ /I I σ (a) h (mm) d E / d x R e s o l u t i on ( % ) h ∝ /I I σ (b) ρ / ρ d E / d x R e s o l u t i on ( % ) ρ ∝ /I I σ (c) γβ d E / d x R e s o l u t i on ( % ) π Kp ) γβ ∝ /I I σ (d) − − θ cos d E / d x R e s o l u t i on ( % ) ) θ ∝ /I I σ ) θ +3.9(cos(e) Fig. 2
The intrinsic dE / dx resolution versus the number of pad rings (a), the pad height along the radial direction (b), the ratio of gas density ρ over the default gas density ρ (equivalent to the ratio of corresponding pressures) (c), the relativistic velocity β γ (e) and cos θ (f) of the ionizingparticle. The default working point is indicated with a solid star symbol. Solid lines represent the fit projections. the dE / dx resolution. When the magnetic field is set to zero,the induced relative change of σ I / I is within 3% for particleswith momenta larger than 1 GeV/c.As Eq. (1) is derived from single-particle events, its ap-plicability to physics events is validated using kaons from e + e − → Z → q ¯ q MC events. The kinematic distributions areshown in Fig. 3. We integrate Eq. (1) over the cos θ distri-bution given in Fig. 3 and calculate the average dE / dx res-olution versus β γ . It is found to be consistent with the onedirectly obtained from MC. For example, for kaons with amomentum of 5 GeV/c in hadronic decays at the Z pole, theintrinsic dE / dx resolution is 3.1%.3.2 Expected actual dE / dx resolution of the CEPC TPCIn real experiments, both detector effects and imperfect cal-ibration can deteriorate the dE / dx resolution. We estimatethe potential degradation in previous TPCs by comparingtheir experimental achievements with the corresponding in-trinsic dE / dx resolutions obtained from MC simulation.The TPCs considered in this study are summarized inTable 1. The information about the experiments, unless ex-plicitly stated, is taken from the references listed in the firstrow. All the factors influencing the intrinsic resolution areimplemented in MC simulation, including the compositionof the working gas, the geometry of the TPC, the controlsamples and the truncation ratio used to remove the Lan-dau tail. In the MC study, we resort to single-particle eventsand make them have identical particle type and kinematicdistributions with the corresponding control samples usedin the experiments. For the case where minimum ionizingpions are used, we assume a flat cos θ distribution in thesimulation when their cos θ spectrum is not provided in thereferences. The relative uncertainty arising from such an ap-proximation is estimated to be within a few percent and canbe neglected.Besides the factors discussed above, the number of theeffective hits used for the dE / dx calculation, denoted as N eff , is also considered because it greatly influences the dE / dx resolution in the earlier experiments. In TOPAZ and DEL-PHI, for example, on average only 60-70% effective TPChits are available for tracks in jets due to the large size oftheir TPC readouts and resulting in serious hit overlap. STARand ALICE have made significant progress in exploiting high-granularity readouts to handle their dense tracking environ-ment. In ALICE, the fraction of N eff is about 93% or evenlarger in proton-proton collisions [27]. Compared to ALICE,the CEPC TPC will have a higher granularity and enduremuch smaller track multiplicities. Therefore we neglect thiseffect at the CEPC. Even if assuming that 5% of the hits arediscarded, the resulting relative change in the dE / dx resolu-tion is within 3% according to Eq. (1). In the last row of Table 1, the relative difference be-tween the intrinsic and actual dE / dx resolutions are listed.It varies from 0.15 to 0.50 between the different experi-ments. Studies performed by the ALICE TPC Collaboration[28, 29] show that the main detector effects causing the de-terioration include diffusion in the drift volume, fluctuationsin the amplification and DAQ processes, and cross talk be-tween the readout pads. Based on MC simulation, we esti-mate that these effects will cause a degradation of at least20% at the CEPC TPC. Therefore, we define two scenar-ios for further discussion about the dE / dx performance thatmight eventually be achieved by the CEPC, namely an “opti-mistic scenario” and a “conservative scenario”, correspond-ing to degradations of 20% and 50%, respectively, with re-spect to the intrinsic dE / dx resolution.3.3 Expected PID performance of the CEPC TPCA common figure of merit for the PID performance is theseparation power S . Between particle types A and B we de-fine S AB = | I A − I B | (cid:113) σ I A + σ I B , (2)where I A ( I B ) and σ I A ( σ I B ) are the average dE / dx measure-ment of particle type A (B) and the corresponding resolu-tion. In the ideal case assuming no degradation and σ I fol-lows Eq. (1), we estimate S K π at the CEPC as a function of p and cos θ (see Fig. 4).One often cares about the average separation power (cid:10) S (cid:11) versus momentum after integrating over the cos θ dimen-sion. Given the cos θ distribution in e + e − → Z → q ¯ q decays(see Fig. 3), the plots of (cid:10) S K π (cid:11) and (cid:10) S Kp (cid:11) as a function of p are shown in Fig. 5. In the left plot, the separation pow-ers using dE / dx for different TPC performance scenariosare illustrated. One can see that dE / dx alone is incapable of K / π separation around 1 GeV/c and yields poor K / p sep-aration beyond 1.5 GeV/c. To overcome this disadvantage,the exploitation of TOF information is considered.According to a recent study on the CMS high-granularitycalorimeter [30], precise TOF information could be providedby the CEPC ECAL with a precision of tens of picoseconds.Supposing TOF information with a 50 ps time resolution,and given the dE / dx measurements in the conservative sce-nario, the average K / π and K / p separation powers are cal-culated using both dE / dx and TOF. They are shown in themiddle and right plots of Fig. 5. Accounting for the time res-olution and the location of the ECAL, the TOF informationcan provide K / π ( K / p ) separation better than 2.5 σ up to2.1 (4.0) GeV/c. By combining TOF and dE / dx , more than − − θ cos − − l og ( p ) ( G e V / c ) (a) p (GeV/c) A . U . (b) − − θ cos A . U . (c) Fig. 3
Kinematic distribution of kaons in e + e − → Z → q ¯ q MC events as a function of log ( p ) and cos θ (a), p (b), and cos θ (c). Table 1
Properties of TPCs in previous experiments. Comparison of the relative dE / dx resolution between MC and experimental measurements.Experiment PEP-4 TOPAZ DELPHI ALEPH STAR ALICE CEPC[18–20] [21] [22, 23] [4, 24] [25, 26] [5, 27]Start of data taking 1982 1987 1989 1989 2000 2009 —Colliding Particles e − /e + e − /e + e − /e + e − /e + Au/Au p/p e − /e + E beam (GeV) 14.5 26 45.6 45.6 100 1380 125Ar: 0.8 Ar: 0.9 Ar: 0.8 Ar: 0.91 Ar: 0.9 Ne: 0.857 Ar: 0.93Gas CH : 0.2 CH : 0.1 CH : 0.2 CH : 0.09 CH : 0.1 CO : 0.095 CH : 0.05N : 0.048 CO : 0.02Pressure (atm) 8.5 3.5 1 1 1 1 1 ρ (mg/ml) 12.43 5.47 1.46 1.57 1.56 0.95 1.73 n
183 175 192 344 13, 32 h (mm) 4 4 4 4 12, 20 e π π e π π Kp (GeV/c) 14.5 0.4-0.6 0.4-0.6 45.6 0.4-0.6 6.0 5.0Truncation range 0-65% 0-65% 8-80% 8-60% 0-70% 0-60% 0-90% N eff n n n
338 44 149 n ( σ I / I ) MC ( σ I / I ) exp (cid:12)(cid:12)(cid:12) ( σ I / I ) exp ( σ I / I ) MC − (cid:12)(cid:12)(cid:12) It’s required that at least 78 hits are used for the dE / dx calculation [21]. Here we assume there are 70% effective hits.
65% tracks have more than 40 isolated hits, and 35% more than 100 [22]. We assume there are 60% effective hits. In the STAR and ALICE detectors, the inner, intermediate and outer subdetectors have different pad sizes. See Fig. 21 in Ref. [26]. σ K / π ( K / p ) separation can be achieved up to 20GeV/c.The PID performance depends on the kinematic distri-butions and relative abundance of the charged particles inthe sample under study. As an example, we take the pro-cess e + e − → Z → q ¯ q (see Fig. 3) with an average of 20charged particles per event, of which 85% are pions, 10% arekaons, and 4% are protons. We calculate the average separa-tion powers (cid:10) S K π (cid:11) and (cid:10) S Kp (cid:11) for particles with momenta inthe range from 2-20 GeV/c. They are listed in Table 2. Parti-cles with momenta smaller than 2 GeV/c are not consideredsince they can be clearly separated.Due to the importance of the kaon selection performancefor flavor physics, we also provide an estimation of the kaon selection efficiency ε K and the corresponding purity p K , to-gether with the probability of mis-identifying pions (pro-tons) as kaons p π ( p ) → K . They are defined as ε K = N K → K N K , p K = N K → K N K → K + N π → K + N p → K , p π → K = N π → K N π , p p → K = N p → K N p , (3)where N K , N π , N p are the total numbers of generated kaons,pions and protons that traverse the innermost pad ring of p (GeV/c) θ c o s Fig. 4
Separation power S K π between kaons and pions in the p -cos θ plane using dE / dx measurements of the CEPC TPC for the ideal sim-ulation. the TPC, N K → K is the number of correctly identified kaons,and N π ( p ) → K is the number of pions (protons) mistakenlyidentified as kaons.The kaon selection is performed based on the variable ( I − I K ) / σ I , where I and I K are the experimental measure-ment (either by dE / dx alone or by combining dE / dx andTOF) and the expected value for the kaon hypothesis re-spectively, and σ I denotes the experimental resolution. Theirspectra should be close to Gaussian distributions with a widthof 1. In Fig. 6 we illustrate the scaled spectra of kaons, pi-ons and protons with a momentum of 5 GeV/c using dE / dx alone assuming a 20% degradation. According to Eq. (2), thepeaks between the kaon and pion (proton) spectra should be √ S K π ( √ S Kp ) apart, where S K π ( S Kp ) is the correspond-ing separation power. The relative populations N π / N K and N K / N p vary versus momentum and are determined basedon MC simulation. We choose the intersections of the spec-tra as the cut points (marked by the arrows in the plot), inorder to calculate the kaon identification efficiency and pu-rity together with the mis-identification rates according toEq. (3). We calculate these parameters at each momentumpoint from 2-20 GeV/c in e + e − → Z → q ¯ q events (see Fig. 3)and provide in Table 2 the average values. The MC sampleunder study is large enough ( ∼ dE / dx measurements ulti-mately provide roughly 4 σ (1.5 σ ) separation between kaonand pion (proton) in inclusive e + e − → Z → q ¯ q decays. Theoverall kaon identification efficiency reaches 93.2% with apurity of 86.5%. The PID performance is limited by the pro-ton contamination. By combining the dE / dx and TOF mea-surements, the K / p separation is greatly enhanced from 1.5 σ to 3.2 σ . As a consequence, the kaon identification effi- Table 2
Expected PID performance parameters at the CEPC in differ-ent scenarios. Shown are the average value of particles with momentafrom 2-20 GeV/c in the e + e − → Z → q ¯ q decays.Deterioration 0 0.5 0.2 (cid:10) S K π (cid:11) (cid:10) S Kp (cid:11) dE / dx ε K (%) 93.2 84.5 90.9 p K (%) 86.5 76.1 82.4 p π → K (%) 0.1 1.3 0.5 p p → K (%) 33.0 47.2 40.1 (cid:10) S K π (cid:11) dE / dx (cid:10) S Kp (cid:11) ε K (%) 96.8 90.4 95.0TOF p K (%) 97.0 90.1 94.5 p π → K (%) 0.1 1.1 0.4 p p → K (%) 6.4 13.8. 9.6 ciency is improved to 96.8% with a corresponding purity of97.0%In the conservative scenario, the kaon identification ef-ficiency and purity degrade significantly mainly due to themore serious proton contamination. In this case, the TOFmeasurement plays a crucial role and can ameliorate theperformance back to an efficiency of 90.4% and a purityof 90.1%. If the optimistic scenario can be realized at theCEPC, by combining dE / dx and TOF, we expect the effi-ciency reaches 95.0% for kaon identification with a purityof 94.5%, which is only slightly degraded from the idealsimulation. In all scenarios, the pion mis-identification ratecan be controlled at a 1% level. Effective particle identification will enrich the CEPC physicsprogram, especially when operating at the Z pole. Using aGEANT4-based MC simulation, we study the PID perfor-mance at the CEPC based on the dE / dx measurements inthe TPC and the TOF information provided by the ECALwith an assumption of 50 ps time resolution.We explore the kaon identification performance in themomentum range from 2-20 GeV/c in inclusive hadronic Z decays, showing that an effective kaon identification can beachieved with the combined information of dE / dx and TOF.If the degradation of the dE / dx measurements due to detec-tor effects can be controlled to less than 20%, both the av-erage kaon identification efficiency and purity can approach95%. More detailed microscopic simulation and beam testsare expected to validate these conclusions in the future. Acknowledgements
We express our great appreciation to the techni-cal staff in our institutions for their discussion. In particular, we wouldlike to thank Prof. Peter Christiansen of Lund University for his veryhelpful suggestions. p (GeV/c) 〉 S 〈 π K/K/p p (GeV/c) 〉 S 〈 dE/dx π K/ TOF π K/ dE/dx+TOF π K/ p (GeV/c) 〉 S 〈 K/p dE/dxK/p TOFK/p dE/dx+TOF
Fig. 5
Average separation power (cid:10) S (cid:11) versus momentum between different particle types in hadronic decays at the Z pole. Left: only dE / dx isused. The bands delimit the area between the ideal simulation and the conservative scenario for the CEPC TPC. The optimistic scenario is shownas dash-dotted lines. Middle and right: dE / dx (in the conservative scenario) and/or TOF are used for K / π and K / p separation. The black solidline corresponds to 2.5 σ separation. − − − − − I σ )/ K (I I A . U . K π p Fig. 6
The scaled spectra of ( I − I K ) / σ I using dE / dx measurementsalone for particles with a momentum of 5 GeV/c, assuming a 20%degradation. The relative populations are N π = . N K and N K = . N p according to MC simulation.The intersections marked by the arrows are chosen as the cut points.This work was supported by National Key Program for S&T Re-search and Development under Contract Number 2016YFA0400400;the Hundred Talent programs of Chinese Academy of Science underContract Number Y3515540U1; National Natural Science Foundationof China under Contract Number 11675202; IHEP Innovation Grantunder Contract Number Y4545170Y2; Chinese Academy of ScienceFocused Science Grant under Contract Number QYZDY-SSW-SLH002;Chinese Academy of Science Special Grant for Large Scientific Projectunder Contract Number 113111KYSB20170005; National 1000 Tal-ents Program of China. References
1. M. Ahmad et al., CEPC-SPPC Pre-CDR, Chap. 6 (2015)163. 2. M. Ruan, Nucl. Part. Phys. Proc. 273 (2016) 857.3. J. Fan et al., JHEP09 (2015) 196.4. W. B. Atwood et al., Nucl. Instrum. and Meth. A306(1991) 446-458.5. J. Alme et al., Nucl. Instrum. and Meth. A622 (2010)316-367.6. G. Rai et al., LBL-27620 (1989).7. Y. Zhang et al., Chinese Physics C Vol. 38, No. 4 (2014)046001.8. D. Attie et al., Nucl. Instrum. and Meth. A856 (2017)109.9. M. Zhao et al., arXiv:1704.04401 [hep-ex].10. (a) D. Nygren, PEP-198-1975; (b) 1976 Proposal for aPEP Facility based on the TPC, PEP4-December 30.11. Y. Giomataris et al., Nucl. Instrum. and Meth. A 376(1996) 29.12. S. Agostinelli et al. (GEANT4 Collaboration), Nucl. In-strum. and Meth. Phys. Res., Sect. A 506, 250 (2003).13. W. Kilian, T. Ohl, and J. Reuter, Eur. Phys. J. C71(2011) 1742.14. D. Jeanne et al., Nucl. Instrum. and Meth. 111 (1973)287.15. C. Patrignani et al. (Particle Data Group), Chin. Phys.C, 40, 100001 (2016) 442.16. R.M. Sternheimer, M.J. Berger, S.M. Seltzer, At. DataNucl. Data Tables 30 (1984) 261.17. J. Va’Vra, Nucl. Instrum. and Meth. A453 (2000) 262.18. R.J. Madaras et al., LBL-17806, C84-03-04 Proceeding,413-444.19. G.R. Lynch, N.J. Hadley, 1982 Proceedings of the In-ternational Conference on Instrumentation for CollidingBeam Physics.20. A. Barbaro-Galtieri, 1982 Proceedings of the Interna-tional Conference on Instrumentation for Colliding BeamPhysics.1. M. Ahmad et al., CEPC-SPPC Pre-CDR, Chap. 6 (2015)163. 2. M. Ruan, Nucl. Part. Phys. Proc. 273 (2016) 857.3. J. Fan et al., JHEP09 (2015) 196.4. W. B. Atwood et al., Nucl. Instrum. and Meth. A306(1991) 446-458.5. J. Alme et al., Nucl. Instrum. and Meth. A622 (2010)316-367.6. G. Rai et al., LBL-27620 (1989).7. Y. Zhang et al., Chinese Physics C Vol. 38, No. 4 (2014)046001.8. D. Attie et al., Nucl. Instrum. and Meth. A856 (2017)109.9. M. Zhao et al., arXiv:1704.04401 [hep-ex].10. (a) D. Nygren, PEP-198-1975; (b) 1976 Proposal for aPEP Facility based on the TPC, PEP4-December 30.11. Y. Giomataris et al., Nucl. Instrum. and Meth. A 376(1996) 29.12. S. Agostinelli et al. (GEANT4 Collaboration), Nucl. In-strum. and Meth. Phys. Res., Sect. A 506, 250 (2003).13. W. Kilian, T. Ohl, and J. Reuter, Eur. Phys. J. C71(2011) 1742.14. D. Jeanne et al., Nucl. Instrum. and Meth. 111 (1973)287.15. C. Patrignani et al. (Particle Data Group), Chin. Phys.C, 40, 100001 (2016) 442.16. R.M. Sternheimer, M.J. Berger, S.M. Seltzer, At. DataNucl. Data Tables 30 (1984) 261.17. J. Va’Vra, Nucl. Instrum. and Meth. A453 (2000) 262.18. R.J. Madaras et al., LBL-17806, C84-03-04 Proceeding,413-444.19. G.R. Lynch, N.J. Hadley, 1982 Proceedings of the In-ternational Conference on Instrumentation for CollidingBeam Physics.20. A. Barbaro-Galtieri, 1982 Proceedings of the Interna-tional Conference on Instrumentation for Colliding BeamPhysics.