Data from the Tibet air shower array were used to examine the cosmic ray shadows of the Moon and the Sun at energies around 10Tev.The shadowing effect was clearly observed at the 5.8level for the Moon,while the shadow...Data from the Tibet air shower array were used to examine the cosmic ray shadows of the Moon and the Sun at energies around 10Tev.The shadowing effect was clearly observed at the 5.8level for the Moon,while the shadow of the Sun was found in the direction away from the sun by 0.86°tothe west and 0.43°to the south.The effect of the geomagnetic field has also been observed in the shadow of cosmic rays by the Moon.The observed deflection of the sun’s shadow is briefly discussed in connection with the effect of the magnetic fields between the sun and the Earth.This is the first observation of the effects of such magnetic fields on the cosmic ray shadow.The maximum-likelihood analysis of the Moon data set shows that the angular resolutions of the array for showers with its mode energies 7TeVand 35TeV are 0.87°-0.13°+0.10°and 0.54°-0.08°+0.11°,respectively.展开更多
A sub-array of the Large High Altitude Air Shower Observatory(LHAASO),KM2A is mainly designed to observe a large fraction of the northern sky to hunt for γ-ray sources at energies above 10 TeV.Even though the detecto...A sub-array of the Large High Altitude Air Shower Observatory(LHAASO),KM2A is mainly designed to observe a large fraction of the northern sky to hunt for γ-ray sources at energies above 10 TeV.Even though the detector construction is still underway,half of the KM2A array has been operating stably since the end of 2019.In this paper,we present the KM2A data analysis pipeline and the first observation of the Crab Nebula,a standard candle in very high energy γ-ray astronomy.We detect γ-ray signals from the Crab Nebula in both energy ranges of 10-100 TeV and>100 TeV with high significance,by analyzing the KM2A data of 136 live days between December 2019 and May 2020.With the observations,we test the detector performance,including angular resolution,pointing accuracy and cosmic-ray background rejection power.The energy spectrum of the Crab Nebula in the energy range 10-250 TeV fits well with a single power-law function dN/dE=(1.13±0.05stat±0.08sys)×10^(-14).(E/20 TeV)-309±0.06stat±0.02syscm^(-2) s^(-1) TeV^(-1).It is consistent with previous measurements by other experiments.This opens a new window of γ-ray astronomy above 0.1 PeV through which new ultrahigh-energy γ-ray phenomena,such as cosmic PeVatrons,might be discovered.展开更多
The superτ-charm facility(STCF)is an electron–positron collider proposed by the Chinese particle physics community.It is designed to operate in a center-of-mass energy range from 2 to 7 GeV with a peak luminosity of...The superτ-charm facility(STCF)is an electron–positron collider proposed by the Chinese particle physics community.It is designed to operate in a center-of-mass energy range from 2 to 7 GeV with a peak luminosity of 0.5×10^(35) cm^(–2)·s^(–1) or higher.The STCF will produce a data sample about a factor of 100 larger than that of the presentτ-charm factory—the BEPCII,providing a unique platform for exploring the asymmetry of matter-antimatter(charge-parity violation),in-depth studies of the internal structure of hadrons and the nature of non-perturbative strong interactions,as well as searching for exotic hadrons and physics beyond the Standard Model.The STCF project in China is under development with an extensive R&D program.This document presents the physics opportunities at the STCF,describes conceptual designs of the STCF detector system,and discusses future plans for detector R&D and physics case studies.展开更多
The first Water Cherenkov detector of the LHAASO experiment(WCDA-1)has been operating since April 2019.The data for the first year have been analyzed to test its performance by observing the Crab Nebula as a standard ...The first Water Cherenkov detector of the LHAASO experiment(WCDA-1)has been operating since April 2019.The data for the first year have been analyzed to test its performance by observing the Crab Nebula as a standard candle.The WCDA-1 achieves a sensitivity of 65 mCU per year,with a statistical threshold of 5 cr.To accomplish this,a 97.7%cosmic-ray background rejection rate around 1 TeV and 99.8%around 6 TeV with an ap proximate photon acceptance of 50%is achieved after applying an algorithm to separate gamma-induced showers.The angular resolution is measured using the Crab Nebula as a point source to be approximately 0.45°at 1 TeV and better than 0.2°above 6 TeV,with a pointing accuracy better than 0.05°.These values all match the design specifications.The energy resolution is found to be 33%for gamma rays around 6 TeV.The spectral energy distribution of the Crab Nebula in the range from 500 GeV to 15.8 TeV is measured and found to be in agreement with the results from other TeV gamma ray observatories.展开更多
The Large High Altitude Air Shower Observatory(LHAASO) is a composite cosmic ray observatory consisting of three detector arrays: kilometer square array(KM2 A), which includes the electromagnetic detector array and mu...The Large High Altitude Air Shower Observatory(LHAASO) is a composite cosmic ray observatory consisting of three detector arrays: kilometer square array(KM2 A), which includes the electromagnetic detector array and muon detector array, water Cherenkov detector array(WCDA) and wide field-of-view Cherenkov telescope array(WFCTA). One of the main scientific objectives of LHAASO is to precisely measure the cosmic rays energy spectrum of individual components from 10^14 eV to 10^18 eV. The hybrid observation will be employed by the LHAASO experiment, in which the lateral and longitudinal distributions of extensive air shower can be observed simultaneously. Thus, many kinds of parameters can be used for primary nuclei identification. In this paper, high purity cosmic ray simulation samples of the light nuclei component are obtained using multi-variable analysis. The apertures of 1/4 LHAASO array for pure proton and mixed proton and helium(H&He) samples are 900 m^2 Sr and1800 m^2 Sr, respectively. Prospect of obtaining proton and H&He spectra from 100 TeV to 4 PeV is discussed.展开更多
The LHAASO-WFCTA experiment,which aims to observe cosmic rays in the sub-EeV range using the fluorescence technique,uses a new generation of high-performance telescopes.To ensure that the experiment has ex-cellent det...The LHAASO-WFCTA experiment,which aims to observe cosmic rays in the sub-EeV range using the fluorescence technique,uses a new generation of high-performance telescopes.To ensure that the experiment has ex-cellent detection capability associated with the measurement of the energy spectrum,the primary composition of cosmic rays,and so on,an accurate geometrical reconstruction of air-shower events is fundamental.This paper de-scribes the development and testing of geometrical reconstruction for stereo viewed events using the WFCTA(Wide Field of view Cherenkov/Fluorescence Telescope Array)detectors.Two approaches,which take full advantage ofthe WFCTA detectors.are investigated.One is the stereo-angular method,which uses the pointing of triggered SiPMs in the shower trajectory,and the other is the stereo-timing method,which uses the triggering time of the fired SiPMs.The results show that both methods have good geometrical resolution:the resolution of the stereo-timing method is slightly better than the stereo-angular method because the resolution of the latter is slightly limited by the shower track length.展开更多
Purpose The main scientific goal of LHAASO-WCDA is to survey gamma-ray sources with energy from 100 GeV to 30 TeV.To observe high-energy shower events,especially to measure the energy spectrum of cosmic rays from 100 ...Purpose The main scientific goal of LHAASO-WCDA is to survey gamma-ray sources with energy from 100 GeV to 30 TeV.To observe high-energy shower events,especially to measure the energy spectrum of cosmic rays from 100 TeV to 10 PeV,a dynamic range extension system(WCDA++)is designed to use a 1.5-inch PMT with a dynamic range of four orders of magnitude for each cell in WCDA-1.Method The dynamic range is extended by using these PMTs to measure the effective charge density in the core region of air shower events,which is an important parameter for identifying the composition of primary particles.Result and Conclusion The system has been running for more than one year.In this paper,the details of the design and performance of WCDA++are presented.展开更多
Purpose Observation of high energy and very high emission from Gamma Ray Bursts(GRBs)is crucial to study the gigantic explosion and the underline processes.With a large field-of-view and almost full duty cycle,the Wat...Purpose Observation of high energy and very high emission from Gamma Ray Bursts(GRBs)is crucial to study the gigantic explosion and the underline processes.With a large field-of-view and almost full duty cycle,the Water Cherenkov Detector Array(WCDA),a sub-array of the Large High Altitude Air Shower Observatory(LHAASO),is appropriate to monitor the very high energy emission from unpredictable transients such as GRBs.Method Nevertheless,the main issue for an extensive air shower array is the high energy threshold which limits the horizon of the detector.To address this issue a new trigger method is developed in this article to lower the energy threshold of WCDA for GRB observation.Result The proposed method significantly improves the detection efficiency of WCDA for gamma-rays around the GRB direction at 10-300 GeV.The sensitivity of the WCDA for GRB detection with the new trigger method is estimated.The achieved sensitivity of the quarter WCDA array above 10 GeV is comparable with that of Fermi-LAT.The data analysis process and corresponding fluence upper limit for GRB 190719C is presented as an example.展开更多
基金We are grateful to Prof.J.Arafune of ICRR,University of Tokyo and Prof.S.X.Fan of IHEP,Chinese Academy of Science for their support and encouragement.
文摘Data from the Tibet air shower array were used to examine the cosmic ray shadows of the Moon and the Sun at energies around 10Tev.The shadowing effect was clearly observed at the 5.8level for the Moon,while the shadow of the Sun was found in the direction away from the sun by 0.86°tothe west and 0.43°to the south.The effect of the geomagnetic field has also been observed in the shadow of cosmic rays by the Moon.The observed deflection of the sun’s shadow is briefly discussed in connection with the effect of the magnetic fields between the sun and the Earth.This is the first observation of the effects of such magnetic fields on the cosmic ray shadow.The maximum-likelihood analysis of the Moon data set shows that the angular resolutions of the array for showers with its mode energies 7TeVand 35TeV are 0.87°-0.13°+0.10°and 0.54°-0.08°+0.11°,respectively.
基金Supported in China by National Key R&D program of China under the grants(2018YF A0404201.2018YFA0404202.2018YF A0404203)by NSFC(12022502,190527,135011,11761141001.U1931112,11775131,U1931201,11905043,U1931108)by NSFSPC(ZR2019MA014),and in Thailand by RTA6280002 from Thailand Science Research and Innovation。
文摘A sub-array of the Large High Altitude Air Shower Observatory(LHAASO),KM2A is mainly designed to observe a large fraction of the northern sky to hunt for γ-ray sources at energies above 10 TeV.Even though the detector construction is still underway,half of the KM2A array has been operating stably since the end of 2019.In this paper,we present the KM2A data analysis pipeline and the first observation of the Crab Nebula,a standard candle in very high energy γ-ray astronomy.We detect γ-ray signals from the Crab Nebula in both energy ranges of 10-100 TeV and>100 TeV with high significance,by analyzing the KM2A data of 136 live days between December 2019 and May 2020.With the observations,we test the detector performance,including angular resolution,pointing accuracy and cosmic-ray background rejection power.The energy spectrum of the Crab Nebula in the energy range 10-250 TeV fits well with a single power-law function dN/dE=(1.13±0.05stat±0.08sys)×10^(-14).(E/20 TeV)-309±0.06stat±0.02syscm^(-2) s^(-1) TeV^(-1).It is consistent with previous measurements by other experiments.This opens a new window of γ-ray astronomy above 0.1 PeV through which new ultrahigh-energy γ-ray phenomena,such as cosmic PeVatrons,might be discovered.
基金supported by the National Key R&D Program of China under Contract No.2022YFA1602200the International Partnership Program of the Chineses Academy of Sciences under Grant No.211134KYSB20200057the STCF Key Technology Research and Development Project.
文摘The superτ-charm facility(STCF)is an electron–positron collider proposed by the Chinese particle physics community.It is designed to operate in a center-of-mass energy range from 2 to 7 GeV with a peak luminosity of 0.5×10^(35) cm^(–2)·s^(–1) or higher.The STCF will produce a data sample about a factor of 100 larger than that of the presentτ-charm factory—the BEPCII,providing a unique platform for exploring the asymmetry of matter-antimatter(charge-parity violation),in-depth studies of the internal structure of hadrons and the nature of non-perturbative strong interactions,as well as searching for exotic hadrons and physics beyond the Standard Model.The STCF project in China is under development with an extensive R&D program.This document presents the physics opportunities at the STCF,describes conceptual designs of the STCF detector system,and discusses future plans for detector R&D and physics case studies.
基金Supported by the following grants:the National Key R&D program of China(2018YFA0404201,2018YFA0404202,2018YFA0404203)the National Natural Science Foundation of China(12022502,11905227,U1931112,11635011,11761141001,Y811A35,11675187,U1831208,U1931111)in Thailand by RTA6280002 from Thailand Science Research and Innovation。
文摘The first Water Cherenkov detector of the LHAASO experiment(WCDA-1)has been operating since April 2019.The data for the first year have been analyzed to test its performance by observing the Crab Nebula as a standard candle.The WCDA-1 achieves a sensitivity of 65 mCU per year,with a statistical threshold of 5 cr.To accomplish this,a 97.7%cosmic-ray background rejection rate around 1 TeV and 99.8%around 6 TeV with an ap proximate photon acceptance of 50%is achieved after applying an algorithm to separate gamma-induced showers.The angular resolution is measured using the Crab Nebula as a point source to be approximately 0.45°at 1 TeV and better than 0.2°above 6 TeV,with a pointing accuracy better than 0.05°.These values all match the design specifications.The energy resolution is found to be 33%for gamma rays around 6 TeV.The spectral energy distribution of the Crab Nebula in the range from 500 GeV to 15.8 TeV is measured and found to be in agreement with the results from other TeV gamma ray observatories.
基金Supported by the National Key R&D Program of China(2018YFA0404201,2018YFA0404202)the Key Laboratory of Particle Astrophysics,Institute of High Energy Physics,CAS(Y5113D005C)National Natural Science Foundation(NSFC)(11563004,11775248)
文摘The Large High Altitude Air Shower Observatory(LHAASO) is a composite cosmic ray observatory consisting of three detector arrays: kilometer square array(KM2 A), which includes the electromagnetic detector array and muon detector array, water Cherenkov detector array(WCDA) and wide field-of-view Cherenkov telescope array(WFCTA). One of the main scientific objectives of LHAASO is to precisely measure the cosmic rays energy spectrum of individual components from 10^14 eV to 10^18 eV. The hybrid observation will be employed by the LHAASO experiment, in which the lateral and longitudinal distributions of extensive air shower can be observed simultaneously. Thus, many kinds of parameters can be used for primary nuclei identification. In this paper, high purity cosmic ray simulation samples of the light nuclei component are obtained using multi-variable analysis. The apertures of 1/4 LHAASO array for pure proton and mixed proton and helium(H&He) samples are 900 m^2 Sr and1800 m^2 Sr, respectively. Prospect of obtaining proton and H&He spectra from 100 TeV to 4 PeV is discussed.
基金National Natural Science Foundation of China(11903005,11563004,11475190)。
文摘The LHAASO-WFCTA experiment,which aims to observe cosmic rays in the sub-EeV range using the fluorescence technique,uses a new generation of high-performance telescopes.To ensure that the experiment has ex-cellent detection capability associated with the measurement of the energy spectrum,the primary composition of cosmic rays,and so on,an accurate geometrical reconstruction of air-shower events is fundamental.This paper de-scribes the development and testing of geometrical reconstruction for stereo viewed events using the WFCTA(Wide Field of view Cherenkov/Fluorescence Telescope Array)detectors.Two approaches,which take full advantage ofthe WFCTA detectors.are investigated.One is the stereo-angular method,which uses the pointing of triggered SiPMs in the shower trajectory,and the other is the stereo-timing method,which uses the triggering time of the fired SiPMs.The results show that both methods have good geometrical resolution:the resolution of the stereo-timing method is slightly better than the stereo-angular method because the resolution of the latter is slightly limited by the shower track length.
基金This research work is also supported by following grants.The National Key R&D program of China under the Grant 2018YFA0404201,2018YFA0404202 and 2018YFA0404203by the National Natural Science Foundation of China(NSFC Grants Nos.12022502,No.11905227,No.U1931112,No.11635011,No.11761141001,No.Y811A35,No.11675187,No.U1831208,No.11873005)+1 种基金by the Key R&D Program of SiChuan Province under the Grant 2019ZYZF0001in Thailand by RTA6280002 from Thailand Science Research and Innovation.
文摘Purpose The main scientific goal of LHAASO-WCDA is to survey gamma-ray sources with energy from 100 GeV to 30 TeV.To observe high-energy shower events,especially to measure the energy spectrum of cosmic rays from 100 TeV to 10 PeV,a dynamic range extension system(WCDA++)is designed to use a 1.5-inch PMT with a dynamic range of four orders of magnitude for each cell in WCDA-1.Method The dynamic range is extended by using these PMTs to measure the effective charge density in the core region of air shower events,which is an important parameter for identifying the composition of primary particles.Result and Conclusion The system has been running for more than one year.In this paper,the details of the design and performance of WCDA++are presented.
基金This work is supported by the National Key R&D Program of China under the Grant 2018YFA0404201the Natural Sciences Foundation of China under the Grants 12022502,11635011the Key R&D Program of SiChuan Province under the Grant 2019ZYZF0001.
文摘Purpose Observation of high energy and very high emission from Gamma Ray Bursts(GRBs)is crucial to study the gigantic explosion and the underline processes.With a large field-of-view and almost full duty cycle,the Water Cherenkov Detector Array(WCDA),a sub-array of the Large High Altitude Air Shower Observatory(LHAASO),is appropriate to monitor the very high energy emission from unpredictable transients such as GRBs.Method Nevertheless,the main issue for an extensive air shower array is the high energy threshold which limits the horizon of the detector.To address this issue a new trigger method is developed in this article to lower the energy threshold of WCDA for GRB observation.Result The proposed method significantly improves the detection efficiency of WCDA for gamma-rays around the GRB direction at 10-300 GeV.The sensitivity of the WCDA for GRB detection with the new trigger method is estimated.The achieved sensitivity of the quarter WCDA array above 10 GeV is comparable with that of Fermi-LAT.The data analysis process and corresponding fluence upper limit for GRB 190719C is presented as an example.
