Study Of Sensitivity To CP Violation In ?~±?K_S~0?~±v_? Decays At The Super Tau-Charm Facility

In the standard model(SM),CKM mechanism is the only source of charge parity violation(CPV).Experimentally,CPV has been observed in K?B?D mesons and all re-sults to date are consistent with the predictions of the CKM mechanism in the SM.How-ever,the matter-antimatter asymmetry observed in the universe illustrates the existence of additional sources of CPV beyond the CKM mechanism.The Super Tau-Charm Fa-cility(STCF)proposed by China is a symmetrical electron-positron collider.Its center-of-mass energy(?)is from 2.0 to 7.0 GeV.The peak luminosity over 0.5 × 1035 cm-2s-1 at(?)=4 GeV is a good venue to search CPV.Currently,the main way of searching CPV is study of ? decays because of its heavy mass which is relevant to the prediction of many new physics models.? decays provide a good way of searching CPV due to the abundant hadron final states which are beneficial for constructing CP observables.Moreover,? pair processes have advantages at(?)=4.26 GeV in STCF,such as high statistics,high cross section and low background,etc.We choose ?±?KS0?±v? de-cays which have larger branch fraction and contain K0 to study the sensitivity of CPV in STCF.This work applies fast simulation software package to describe STCF.It is able to describe the detector responses properly.Generating simulated collision data can be analysed the influence of sub-detector.The ? leptons are detected by using dou-ble tag method which is divided by two sides,one side is selected with ?(?)decay to leptons(?(?)?l(?)vlv?,l=e,?),other side is selected with signal process(?±?KS0?±V?).In the meanwhile,using multi-variable method is to suppress the background processes and optimised the event selection.The signal process is selected by identify-ing final state particles(e±,?±,?±,photon)and reconstructed particles(KS0,?0).Then the numbers of signal process can be obtained by fitting the mass spectrum of KS0?±.The statistical error can be calculated by measuring the difference number of events between ?+?KS?+v? and ?-?Ks?-v?.The statistical error reflects the sensi-tivity to CPV in ?+?KS0?±v?decays.The fast simulation software package varies the efficiency of charged tracks,the efficiency of momentum/spatial resolution and ?/?separation.Analysing the sensitivity to CPV in ?±?KS0?±v? decays can provide standard to optimised performance parameters of detector.After above analysis,the optimized performance parameters of detector are obtained and the final signal effi-ciency is increased by 44%to 32.82%.With an expected luminosity of 1 ab-1 collected by STCF per year at(?)=4.26 GeV,the sensitivity for the CPV is determined to be of order 9.7 × 10-4.Furthermore,STCF plans to collect data with 10 ab-1 integrated luminosity.In order to analysis the sensitivity of combining multiple center-of-mass in(?)decays in the energy region with 10 ab-1 integrated luminosity,we calcu-late the selection efficiency and the result illustrates selection efficiency is little change within 1%.Hence the energy-dependent efficiencies for reconstructing ?-?KS?-v?are presented and the expected CP sensitivity is proportional to 1/(?)in the energy region from 4.0 to 5.0 GeV.With 10 ab-1 integrated luminosity,the sensitivity of CPV is of order 3.1 × 10-4,which is comparable with accuracy of SM predicted value and BelleII experiment measurement.At the same time,it's the first time to study the CPV in the r-charm region.It has great potential and guiding significance for the future experiments.From the analysis of sensitivity of CPV in ?(?)?l(?)vlv?(1=e,?),?+?KS0?±v?decays,? faked as ? has great influence for selection efficiency.For higher momentum,?,? can be identified by MUD in STCF.However,?,? can not be identified very well in lower momentum.Owing to some events(?(?)?l(?)vlv?)are located in lower momen-tum,there are positive impact on improving the sensitivity to CPV by reducing the rate of ? faked as ?.In STCF,particle-identification(PID)is used in the Ringing Imaging CHerenkov detector(RICH)as barrel part and the Detection of Internal total-Reflected Cherenkov light(DIRC)as endcap part.The radiator for RICH and DIRC is liquid C6F14 and high purity quartz plate,respectively.RICH in STCF can provide the seper-ated ability between ? and ? which improves the sensitivity to CPV in ?±?KS0?±v?decays.For RICH in STCF,the performance of PID is simulated for ?,K,proton in high momentum and ?,? in low momentum.The likelihood function ratio is used to calculate the performance of PID,At the meanwhile,GEANT4 is used to simulate the physical process of particles which are transported in matter and interacted between particles and matter.Since the performance is related by polar angle,some structures of RICH are designed to optimised the situation of large angle incidence.The above simulation indicates that the performance has good result for ?,K,proton in high mo-mentum.The separation significance of K/? and K/p are 3.32? and 4.42? in 2 GeV/c and 0°incidence.For ?,? in low momentum,some specific areas(0.3-0.5 GeV/c and 0°-40°)still have good PID performance.The other areas can be identified combining dE/dx in MDC.In summary,the performance of PID can be higher in all momentum and angle ranges which are interested by STCF.The PID in RICH wich is relevant to ?and ? is being applied in fast simulation software package to improve the sensitivity to CPV in ?±?KS0?±v? decays.