The Large High Altitude Air Shower Observatory(LHAASO)has three sub-arrays,KM2A,WCDA,and WFCTA.The flux variations of cosmic ray air showers were studied by analyzing the KM2A data during a thunderstorm on June 10,202...The Large High Altitude Air Shower Observatory(LHAASO)has three sub-arrays,KM2A,WCDA,and WFCTA.The flux variations of cosmic ray air showers were studied by analyzing the KM2A data during a thunderstorm on June 10,2021.The number of shower events that meet the trigger conditions increases significantly in atmospheric electric fields,with a maximum fractional increase of 20%.The variations in trigger rates(increases or decreases)were found to be strongly dependent on the primary zenith angle.The flux of secondary particles increased significantly,following a trend similar to that of shower events.To better understand the observed behavior,Monte Carlo simulations were performed with CORSIKA and G4KM2A(a code based on GEANT4).We found that the experimental data(in saturated negative fields)were in good agreement with the simulations,assuming the presence of a uniform electric field of-700 V/cm with a thickness of 1500 m in the atmosphere above the observation level.Due to the acceleration/deceleration by the atmospheric electric field,the number of secondary particles with energy above the detector threshold was modified,resulting in the changes in shower detection rate.展开更多
The ground-based EAS array is usually operated with a high duty cycle （〉 90%） and a large field of view （- 2sr）, which can continuously monitor the sky. It is essential and irreplaceable to understand the gamma-r...The ground-based EAS array is usually operated with a high duty cycle （〉 90%） and a large field of view （- 2sr）, which can continuously monitor the sky. It is essential and irreplaceable to understand the gamma-ray emission mechanism and intrinsic physics progress of the variable source AGN. The EAS arrays, AS-y experiment （since 1990） and ARGO-YBJ experiment （since 2007）, have continuously monitored the northern sky at energies above 3 TeV and 0.3 TeV, respectively. They have made substantial contributions for long-term monitoring of Mrk 421 and Mrk 501. In this paper, we will review the results obtained by the EAS arrays. The next generation of EAS array, LHAASO project, will boost the sensitivity of current EAS array at least up to 30 times with a much wider energy range from 40 GeV to 1 PeV. Beside increasing the number of VHE gamma-ray sources, it will guide us look sight into the properties of jet, and throw light on the determining of the EBL, intergalactic magnetic fields, and the validity of the Lorentz Invariance.展开更多
Gamma ray source detection above 30 TeV is an encouraging approach for finding galactic cosmic ray sources. All sky survey for gamma ray sources using wide field of view detector is essential for population accumulati...Gamma ray source detection above 30 TeV is an encouraging approach for finding galactic cosmic ray sources. All sky survey for gamma ray sources using wide field of view detector is essential for population accumulation for various types of sources above 100 GeV. In order to target those goals, a large air shower particle detector array of 1 km^2 （the LHAASO project） at 4300 m a.s.l, is proposed, By adding two MagicⅡ- type telescopes in the array as proposed, LHAASO will be enhanced in source morphologic investigation power. The proposed array will be utilized also for energy spectrum measurement for individual cosmic ray species above 30 TeV. By re-configuring the wide field of view telescopes into fluorescence light detector array, the aperture of the detector array can be enlarged to cover an energy region above 100 PeV where the second knee is located. Cosmic ray spectrum and composition will be measured in order to transfer an energy scale to ultra high energy cosmic ray experiments.展开更多
Aiming at the observation of cosmic-ray chemical composition in the ＂knee＂ energy region, we have been developing a new type of air-shower core detector （YAC, Yangbajing Air shower Core detector array） to be set u...Aiming at the observation of cosmic-ray chemical composition in the ＂knee＂ energy region, we have been developing a new type of air-shower core detector （YAC, Yangbajing Air shower Core detector array） to be set up at Yangbajing （90.522° E, 30.102° N, 4300 m above sea level, atmospheric depth： 606 g/m2） in Tibet, China. YAC works together with the Tibet air-shower array （Tibet-Ⅲ） and an underground water Cherenkov muon detector array （MD） as a hybrid experiment. Each YAC detector unit consists of lead plates of 3.5 cm thickness and a scintillation counter which detects the burst size induced by high energy particles in the air-shower cores. The burst size can be measured from 1 MIP （Minimum Ionization Particle） to 106 MIPs. The first phase of this experiment, named ＂YAC- I ＂, consists of 16 YAC detectors each with a size of 40 cm×50 cm and distributed in a grid with an effective area of 10 m2. YAC- I is used to check hadronic interaction models. The second phase of the experiment, called ＂YAC-Ⅱ＂, consists of 124 YAC detectors with coverage of about 500 m2. The inner 100 detectors of 80 cm×50 cm each are deployed in a 10×10 matrix with a 1.9 m separation; the outer 24 detectors of 100 cm×50 cm each are distributed around these to reject non-core events whose shower cores are far from the YAC- Ⅱ array. YAC- Ⅱ is used to study the primary cosmic-ray composition, in particular, to obtain the energy spectra of protons, helium and iron nuclei between 5× 1013 eV and 1016 eV, covering the ＂knee＂ and also connected with direct observations at energies around 100 TeV. We present the design and performance of YAC- Ⅱ in this paper.展开更多
Extensive Air Showers(EAS)induced by cosmic ray particles of very low energies,owing to the significantly steep cosmic ray energy spectrum,dominate the secondary particle flux measured by single detectors and small sh...Extensive Air Showers(EAS)induced by cosmic ray particles of very low energies,owing to the significantly steep cosmic ray energy spectrum,dominate the secondary particle flux measured by single detectors and small shower arrays.Such arrays connected in extended networks can be used to determine potentially interesting spatial correlations between showers,which may shed new light on the nature of ultra high-energy cosmic rays.The quantitative interpretation of showers recorded by small local arrays requires a methodology that differs from that used by ordinary large EAS arrays operating in the"knee"region and above.We present"small EAS generator,"a semi-analytical method for integrating cosmic ray spectra over energies of interest and summing over the mass spectra of primary nuclei in arbitrary detector configurations.Furthermore,we provide results on the EAS electron and muon fluxes and particle density spectra.展开更多
By a Monte Carlo simulation, the arrival time (delay time) distribution o?shower particles at large distance (>100 m) from the air shower core has been simulated.The characteristics of the distribution are expresse...By a Monte Carlo simulation, the arrival time (delay time) distribution o?shower particles at large distance (>100 m) from the air shower core has been simulated.The characteristics of the distribution are expressed by three parameters. An approximate formula for the distribution has also been derived. The distribution is found depending strongly on the distance from the core, but almost independent of the age, zenith angle, primary energy, primary compositions. An apparent difference is seen in some cases in the distribution from event to event when the number of particles is small. This is only due to statistical fluctuation. Therefore it is important to take into account the experimental conditions in the comparison of the present results with experimental data.展开更多
Introduction The Large High Altitude Air Shower Observatory plans to build a hybrid extensive air shower array with an area of about 1 km^(2) at an altitude of 4,410 m a.s.l.in Sichuan province,China,to explore the or...Introduction The Large High Altitude Air Shower Observatory plans to build a hybrid extensive air shower array with an area of about 1 km^(2) at an altitude of 4,410 m a.s.l.in Sichuan province,China,to explore the origin of high-energy cosmic rays.KM2A LHAASO-KM2A will detect gamma ray sources with a sensitivity of about 1%Crab Unit at 100 TeV.It covers an area of 1 km^(2) with a total of 5195 scintillation detectors.Its angular resolution reaches about 0.3 degrees,and the energy resolution is better than 25%.With the help of 1171 muon detectors,cosmic nuclei background will be rejected to a level of 10-4 at 50 TeV.The design and performances of the scintillation detectors and muon detectors are described in detail.WCDA LHAASO-WCDA focuses on surveying the northern sky for steady and transient sources from 100 GeV to 20 TeV,with a very high background rejection power and a good angular resolution.The WCDA consists of three water ponds with a total area of 78,000 m^(2),and the effective water depth is 4 m.Each water pond is divided into 5m×5m cells partitioned by black plastic curtains to prevent penetration of the light from neighboring cells.An 8-inch PMT sits at the bottom center of each cell,looking upward to collect Cherenkov light generated by shower secondary particles in water.WFCTA LHAASO-WFCTA is composed of 12 wide-field-of-view Cherenkov/fluorescence telescopes.Each telescope consists of a spherical light collector of about 4.7 m^(2) and focal plane camera of 32×32 pixels with a pixel size of 0.5 degree.LHAASO prototype arrays A prototype array about 1%of LHAASO has been constructed at Yangbajing Cosmic Ray Observatory and has been in operation for more than 2 years.Its performance fully meets the design requirements.Conclusion The LHAASO detectors are designed to fulfill the physical goals in gamma ray astronomy and cosmic ray physics.One-fourth of LHAASO will be constructed and put into operation to produce physical data by the end of 2018.The whole array will be finished in the beginning of 2021.展开更多
基金Supported in China by National Key R&D program of China(2018YFA0404201,2018YFA0404202,2018YFA0404203,2018YFA0404204)NSFC(U2031101,11475141,12147208)in Thailand by RTA6280002 from Thailand Science Research and Innovation。
文摘The Large High Altitude Air Shower Observatory(LHAASO)has three sub-arrays,KM2A,WCDA,and WFCTA.The flux variations of cosmic ray air showers were studied by analyzing the KM2A data during a thunderstorm on June 10,2021.The number of shower events that meet the trigger conditions increases significantly in atmospheric electric fields,with a maximum fractional increase of 20%.The variations in trigger rates(increases or decreases)were found to be strongly dependent on the primary zenith angle.The flux of secondary particles increased significantly,following a trend similar to that of shower events.To better understand the observed behavior,Monte Carlo simulations were performed with CORSIKA and G4KM2A(a code based on GEANT4).We found that the experimental data(in saturated negative fields)were in good agreement with the simulations,assuming the presence of a uniform electric field of-700 V/cm with a thickness of 1500 m in the atmosphere above the observation level.Due to the acceleration/deceleration by the atmospheric electric field,the number of secondary particles with energy above the detector threshold was modified,resulting in the changes in shower detection rate.
基金the National Natural Science Foundation of China (Grant No. 11205165)the Xiejialin Fund of the Institute of High Energy Physics, Chinese Academy of Sciences (Grant No. Y3546140U2)
文摘The ground-based EAS array is usually operated with a high duty cycle （〉 90%） and a large field of view （- 2sr）, which can continuously monitor the sky. It is essential and irreplaceable to understand the gamma-ray emission mechanism and intrinsic physics progress of the variable source AGN. The EAS arrays, AS-y experiment （since 1990） and ARGO-YBJ experiment （since 2007）, have continuously monitored the northern sky at energies above 3 TeV and 0.3 TeV, respectively. They have made substantial contributions for long-term monitoring of Mrk 421 and Mrk 501. In this paper, we will review the results obtained by the EAS arrays. The next generation of EAS array, LHAASO project, will boost the sensitivity of current EAS array at least up to 30 times with a much wider energy range from 40 GeV to 1 PeV. Beside increasing the number of VHE gamma-ray sources, it will guide us look sight into the properties of jet, and throw light on the determining of the EBL, intergalactic magnetic fields, and the validity of the Lorentz Invariance.
基金Supported by Knowledge Innovation Fund (U-526) of IHEP,China
文摘Gamma ray source detection above 30 TeV is an encouraging approach for finding galactic cosmic ray sources. All sky survey for gamma ray sources using wide field of view detector is essential for population accumulation for various types of sources above 100 GeV. In order to target those goals, a large air shower particle detector array of 1 km^2 （the LHAASO project） at 4300 m a.s.l, is proposed, By adding two MagicⅡ- type telescopes in the array as proposed, LHAASO will be enhanced in source morphologic investigation power. The proposed array will be utilized also for energy spectrum measurement for individual cosmic ray species above 30 TeV. By re-configuring the wide field of view telescopes into fluorescence light detector array, the aperture of the detector array can be enlarged to cover an energy region above 100 PeV where the second knee is located. Cosmic ray spectrum and composition will be measured in order to transfer an energy scale to ultra high energy cosmic ray experiments.
基金Supported by grants from the National Natural Science Foundation of China(11078002,11275212,11165013)the Chinese Academy of Sciences(H9291450S3,Y4293211S5)the Knowledge Innovation Fund of Institute of High Energy Physics(IHEP),China(H95451D0U2,H8515530U1)
文摘Aiming at the observation of cosmic-ray chemical composition in the ＂knee＂ energy region, we have been developing a new type of air-shower core detector （YAC, Yangbajing Air shower Core detector array） to be set up at Yangbajing （90.522° E, 30.102° N, 4300 m above sea level, atmospheric depth： 606 g/m2） in Tibet, China. YAC works together with the Tibet air-shower array （Tibet-Ⅲ） and an underground water Cherenkov muon detector array （MD） as a hybrid experiment. Each YAC detector unit consists of lead plates of 3.5 cm thickness and a scintillation counter which detects the burst size induced by high energy particles in the air-shower cores. The burst size can be measured from 1 MIP （Minimum Ionization Particle） to 106 MIPs. The first phase of this experiment, named ＂YAC- I ＂, consists of 16 YAC detectors each with a size of 40 cm×50 cm and distributed in a grid with an effective area of 10 m2. YAC- I is used to check hadronic interaction models. The second phase of the experiment, called ＂YAC-Ⅱ＂, consists of 124 YAC detectors with coverage of about 500 m2. The inner 100 detectors of 80 cm×50 cm each are deployed in a 10×10 matrix with a 1.9 m separation; the outer 24 detectors of 100 cm×50 cm each are distributed around these to reject non-core events whose shower cores are far from the YAC- Ⅱ array. YAC- Ⅱ is used to study the primary cosmic-ray composition, in particular, to obtain the energy spectra of protons, helium and iron nuclei between 5× 1013 eV and 1016 eV, covering the ＂knee＂ and also connected with direct observations at energies around 100 TeV. We present the design and performance of YAC- Ⅱ in this paper.
文摘Extensive Air Showers(EAS)induced by cosmic ray particles of very low energies,owing to the significantly steep cosmic ray energy spectrum,dominate the secondary particle flux measured by single detectors and small shower arrays.Such arrays connected in extended networks can be used to determine potentially interesting spatial correlations between showers,which may shed new light on the nature of ultra high-energy cosmic rays.The quantitative interpretation of showers recorded by small local arrays requires a methodology that differs from that used by ordinary large EAS arrays operating in the"knee"region and above.We present"small EAS generator,"a semi-analytical method for integrating cosmic ray spectra over energies of interest and summing over the mass spectra of primary nuclei in arbitrary detector configurations.Furthermore,we provide results on the EAS electron and muon fluxes and particle density spectra.
文摘By a Monte Carlo simulation, the arrival time (delay time) distribution o?shower particles at large distance (>100 m) from the air shower core has been simulated.The characteristics of the distribution are expressed by three parameters. An approximate formula for the distribution has also been derived. The distribution is found depending strongly on the distance from the core, but almost independent of the age, zenith angle, primary energy, primary compositions. An apparent difference is seen in some cases in the distribution from event to event when the number of particles is small. This is only due to statistical fluctuation. Therefore it is important to take into account the experimental conditions in the comparison of the present results with experimental data.
基金This work is supported in China by NSFC(Nos.11205165,11375210,11375224,11405181,11475190 and 11635011)the Chinese Academy of Sciences,Institute of High Energy Physics,the Key Laboratory of Particle Astrophysics,CAS.
文摘Introduction The Large High Altitude Air Shower Observatory plans to build a hybrid extensive air shower array with an area of about 1 km^(2) at an altitude of 4,410 m a.s.l.in Sichuan province,China,to explore the origin of high-energy cosmic rays.KM2A LHAASO-KM2A will detect gamma ray sources with a sensitivity of about 1%Crab Unit at 100 TeV.It covers an area of 1 km^(2) with a total of 5195 scintillation detectors.Its angular resolution reaches about 0.3 degrees,and the energy resolution is better than 25%.With the help of 1171 muon detectors,cosmic nuclei background will be rejected to a level of 10-4 at 50 TeV.The design and performances of the scintillation detectors and muon detectors are described in detail.WCDA LHAASO-WCDA focuses on surveying the northern sky for steady and transient sources from 100 GeV to 20 TeV,with a very high background rejection power and a good angular resolution.The WCDA consists of three water ponds with a total area of 78,000 m^(2),and the effective water depth is 4 m.Each water pond is divided into 5m×5m cells partitioned by black plastic curtains to prevent penetration of the light from neighboring cells.An 8-inch PMT sits at the bottom center of each cell,looking upward to collect Cherenkov light generated by shower secondary particles in water.WFCTA LHAASO-WFCTA is composed of 12 wide-field-of-view Cherenkov/fluorescence telescopes.Each telescope consists of a spherical light collector of about 4.7 m^(2) and focal plane camera of 32×32 pixels with a pixel size of 0.5 degree.LHAASO prototype arrays A prototype array about 1%of LHAASO has been constructed at Yangbajing Cosmic Ray Observatory and has been in operation for more than 2 years.Its performance fully meets the design requirements.Conclusion The LHAASO detectors are designed to fulfill the physical goals in gamma ray astronomy and cosmic ray physics.One-fourth of LHAASO will be constructed and put into operation to produce physical data by the end of 2018.The whole array will be finished in the beginning of 2021.
