Theγ-ray emission from the W51 complex is widely acknowledged to be attributed to the interaction between the cosmic rays(CRs)accelerated by the shock of supernova remnant(SNR)W51C and the dense molecular clouds in t...Theγ-ray emission from the W51 complex is widely acknowledged to be attributed to the interaction between the cosmic rays(CRs)accelerated by the shock of supernova remnant(SNR)W51C and the dense molecular clouds in the adjacent star-forming region,W51B.However,the maximum acceleration capability of W51C for CRs remains elusive.Based on observations conducted with the Large High Altitude Air Shower Observatory(LHAASO),we report a significant detection ofγrays emanating from the W51 complex,with energies from 2 to 200 TeV.The LHAASO measurements,for the first time,extend theγ-ray emission from the W51 complex beyond 100 TeV and reveal a significant spectrum bending at tens of TeV.By combining the"π^(0)-decay bump"featured data from Fermi-LAT,the broadbandγ-ray spectrum of the W51 region can be well-characterized by a simple pp-collision model.The observed spectral bending feature suggests an exponential cutoff at~400 TeV or a power-law break at~200 TeV in the CR proton spectrum,most likely providing the first evidence of SNRs serving as CR accelerators approaching the PeV regime.Additionally,two young star clusters within W51B could also be theoretically viable to produce the most energeticγrays observed by LHAASO.Our findings strongly support the presence of extreme CR accelerators within the W51 complex and provide new insights into the origin of Galactic CRs.展开更多
The full array of the Large High Altitude Air Shower Observatory(LHAASO)has been in operation since July 2021.For its kilometer-square array(KM2A),we optimized the selection criteria for very high and ultrahigh energy...The full array of the Large High Altitude Air Shower Observatory(LHAASO)has been in operation since July 2021.For its kilometer-square array(KM2A),we optimized the selection criteria for very high and ultrahigh energyγ-rays using data collected from August 2021 to August 2022,resulting in an improvement in significance of the detection in the Crab Nebula of approximately 15%,compared with that of previous cuts.With the implementation of these new selection criteria,the angular resolution was also significantly improved by approximately 10%at tens of TeV.Other aspects of the full KM2A array performance,such as the pointing error,were also calibrated using the Crab Nebula.The resulting energy spectrum of the Crab Nebula in the energy range of 10-1000 TeV are well fitted by a log-parabola model,which is consistent with the previous results from LHAASO and other experiments.展开更多
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
In the present study,we selected solutes to be added to the Cr Co Ni medium-entropy alloy(MEA)based on the mismatch of self-diffusion activation energy(SDQ)between the alloying elements and constituent elements of the...In the present study,we selected solutes to be added to the Cr Co Ni medium-entropy alloy(MEA)based on the mismatch of self-diffusion activation energy(SDQ)between the alloying elements and constituent elements of the matrix,and then investigated their grain growth behavior and mechanical properties.Mo and Al were selected as the solutes for investigation primarily because they have higher and lower SDQ,respectively,than those of the matrix elements;a secondary factor was their higher and lower shear modulus.Their concentrations were fixed at 3 at.%each because previous work had shown these compositions to be single-phase solid solutions with the face-centered cubic structure.Three alloys were produced by arc melting,casting,homogenizing,cold rolling and annealing at various temperatures and times to produce samples with different grain sizes.They were(a)the base alloy Cr Co Ni,(b)the base alloy plus 3 at.%Mo,and(c)the base alloy plus 3 at.%Al.The activation energies for grain growth of the Cr Co Ni,Cr Co Ni-3Mo and CrCo Ni-3Al MEAs were found to be^251,~368 and^219 k J/mol,respectively,consistent with the notion that elements with higher SDQ(in this study Mo)retard grain growth(likely by a solute-drag effect),whereas those with lower values(Al)accelerate grain growth.The roomtemperature tensile properties show that Mo increases the yield strength by^40%but Al addition has a smaller strengthening effect consistent with their relative shear moduli.The yield strength as a function of grain size for the three single-phase MEAs follows the classical Hall-Petch relationship with much higher slopes(>600 MPaμm-0.5)than traditional solid solutions.This work shows that the grain growth kinetics and solid solution strengthening of the Cr Co Ni MEA can be tuned by selecting solute elements that have appropriate diffusion and physical properties.展开更多
Two low-lying unbound states in ^(16)C are investigated by deuteron inelastic scattering in inverse kinematics.Besides the 2^(-) state at 5.45 MeV previously measured in a 1n knockout reaction,a new resonant state at ...Two low-lying unbound states in ^(16)C are investigated by deuteron inelastic scattering in inverse kinematics.Besides the 2^(-) state at 5.45 MeV previously measured in a 1n knockout reaction,a new resonant state at 6.89 MeV is observed for the first time.The inelastic scattering angular distributions of these two states are well reproduced by the distorted-wave Born approximation(DWBA)calculation with an l=1 excitation.In addition,the spinparities of the unbound states are discussed and tentatively assigned based on shell model calculations using the modified YSOX interaction.展开更多
Introduction One of main scientific goals of the Large High Altitude Air Shower Observatory(LHAASO)is to accurately measure the energy spectra of different cosmic ray compositions around the‘knee’region.The Wide Fiel...Introduction One of main scientific goals of the Large High Altitude Air Shower Observatory(LHAASO)is to accurately measure the energy spectra of different cosmic ray compositions around the‘knee’region.The Wide Field-of-View(FoV)Cherenkov Telescope Array(WFCTA),which is one of the main detectors of LHAASO and has 18 telescopes,is built to achieve this goal.Multiple telescopes are put together and point to connected directions for a larger FoV.Method Telescopes are deployed spatially as close as possible,but due to their own size,the distance between two adjacent telescopes is about 10 m.Therefore,the Cherenkov lateral distribution and the parallax between the two telescopes should be considered in the event building process for images crossing over the boundaries of FoVs of the telescopes.An event building method for Cherenkov images measured by multiple telescopes of WFCTA is developed.The performance of the shower measurements using the combined images is evaluated by comparing with showers that are fully contained by a virtual telescope in simulation.Results and conclusion It is proved that the developed event building process can help to increase the FoV of WFCTA by 30%while maintaining the same reconstruction quality,compared to the separate telescope reconstruction method.展开更多
KM2A is one of the main sub-arrays of LHAASO,working on gamma ray astronomy and cosmic ray physics at energies above 10 TeV.Detector simulation is the important foundation for estimating detector performance and data ...KM2A is one of the main sub-arrays of LHAASO,working on gamma ray astronomy and cosmic ray physics at energies above 10 TeV.Detector simulation is the important foundation for estimating detector performance and data analysis.It is a big challenge to simulate the KM2A detector in the framework of Geant4 due to the need to track numerous photons from a large number of detector units(>6000)with large altitude difference(30)and huge coverage(1.3).In this paper,the design of the KM2A simulation code G4KM2A based on Geant4 is introduced.The process of G4KM2A is optimized mainly in memory consumption to avoid memory overflow.Some simplifications are used to significantly speed up the execution of G4KM2A.The running time is reduced by at least 30 times compared to full detector simulation.The particle distributions and the core/angle resolution comparison between simulation and experimental data of the full KM2A array are also presented,which show good agreement.展开更多
基金supported by the National Natural Science Foundation of China(12393851,12261160362,12393852,12393853,12393854,12022502,2205314,12105301,12105292,12105294,12005246,and 12173039)Department of Science and Technology of Sichuan Province(24NSFJQ0060 and 2024NSFSC0449)+5 种基金Project for Young Scientists in Basic Research of Chinese Academy of Sciences(YSBR-061,2022010)Thailand by the National Science and Technology Development Agency(NSTDA)National Research Council of Thailand(NRCT):High-Potential Research Team Grant Program(N42A650868)the Chengdu Management Committee of Tianfu New Area for constant financial support to research with LHAASO datathe Milky Way Imaging Scroll Painting(MWISP)project,sponsored by the National Key R&D Program of China(2023YFA1608000 and 2017YFA0402701)the CAS Key Research Program of Frontier Sciences(QYZDJ-SSW-SLH047)。
文摘Theγ-ray emission from the W51 complex is widely acknowledged to be attributed to the interaction between the cosmic rays(CRs)accelerated by the shock of supernova remnant(SNR)W51C and the dense molecular clouds in the adjacent star-forming region,W51B.However,the maximum acceleration capability of W51C for CRs remains elusive.Based on observations conducted with the Large High Altitude Air Shower Observatory(LHAASO),we report a significant detection ofγrays emanating from the W51 complex,with energies from 2 to 200 TeV.The LHAASO measurements,for the first time,extend theγ-ray emission from the W51 complex beyond 100 TeV and reveal a significant spectrum bending at tens of TeV.By combining the"π^(0)-decay bump"featured data from Fermi-LAT,the broadbandγ-ray spectrum of the W51 region can be well-characterized by a simple pp-collision model.The observed spectral bending feature suggests an exponential cutoff at~400 TeV or a power-law break at~200 TeV in the CR proton spectrum,most likely providing the first evidence of SNRs serving as CR accelerators approaching the PeV regime.Additionally,two young star clusters within W51B could also be theoretically viable to produce the most energeticγrays observed by LHAASO.Our findings strongly support the presence of extreme CR accelerators within the W51 complex and provide new insights into the origin of Galactic CRs.
基金Supported by the National Key R&D Program of China(2018YFA0404201,2018YFA0404202,2018YFA0404203,2018YFA0404204)the National Natural Science Foundation of China(12022502,12205314,12105301,12261160362,12105294,U1931201)+2 种基金the Youth Innovation Promotion Association CAS(2022010)in Thailand by the National Science and Technology Development Agency(NSTDA)the National Research Council of Thailand(NRCT):High-Potential Research Team Grant Program(N42A650868)。
文摘The full array of the Large High Altitude Air Shower Observatory(LHAASO)has been in operation since July 2021.For its kilometer-square array(KM2A),we optimized the selection criteria for very high and ultrahigh energyγ-rays using data collected from August 2021 to August 2022,resulting in an improvement in significance of the detection in the Crab Nebula of approximately 15%,compared with that of previous cuts.With the implementation of these new selection criteria,the angular resolution was also significantly improved by approximately 10%at tens of TeV.Other aspects of the full KM2A array performance,such as the pointing error,were also calibrated using the Crab Nebula.The resulting energy spectrum of the Crab Nebula in the energy range of 10-1000 TeV are well fitted by a log-parabola model,which is consistent with the previous results from LHAASO and other experiments.
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 U.S.Department of Energy,Office of Science,Basic Energy Sciences,Materials Sciences and Engineering Division,E.P.Georgethe National Nature Science Foundation of China(No.51971099)+3 种基金the open fund of State Key Laboratory for Advanced Metals and Materials(No.2018-ZD03),X.W.Liuthe National Nature Science Foundation of China(No.51975425),L.C.Zengthe open fund of State Key Laboratory of Materials Processing and Die&Mould Technology(P2019-005),H.Duthe Research and Development Program of Jiangxi Academy of Sciences(No.2020-YZD-23),Q.Hu。
文摘In the present study,we selected solutes to be added to the Cr Co Ni medium-entropy alloy(MEA)based on the mismatch of self-diffusion activation energy(SDQ)between the alloying elements and constituent elements of the matrix,and then investigated their grain growth behavior and mechanical properties.Mo and Al were selected as the solutes for investigation primarily because they have higher and lower SDQ,respectively,than those of the matrix elements;a secondary factor was their higher and lower shear modulus.Their concentrations were fixed at 3 at.%each because previous work had shown these compositions to be single-phase solid solutions with the face-centered cubic structure.Three alloys were produced by arc melting,casting,homogenizing,cold rolling and annealing at various temperatures and times to produce samples with different grain sizes.They were(a)the base alloy Cr Co Ni,(b)the base alloy plus 3 at.%Mo,and(c)the base alloy plus 3 at.%Al.The activation energies for grain growth of the Cr Co Ni,Cr Co Ni-3Mo and CrCo Ni-3Al MEAs were found to be^251,~368 and^219 k J/mol,respectively,consistent with the notion that elements with higher SDQ(in this study Mo)retard grain growth(likely by a solute-drag effect),whereas those with lower values(Al)accelerate grain growth.The roomtemperature tensile properties show that Mo increases the yield strength by^40%but Al addition has a smaller strengthening effect consistent with their relative shear moduli.The yield strength as a function of grain size for the three single-phase MEAs follows the classical Hall-Petch relationship with much higher slopes(>600 MPaμm-0.5)than traditional solid solutions.This work shows that the grain growth kinetics and solid solution strengthening of the Cr Co Ni MEA can be tuned by selecting solute elements that have appropriate diffusion and physical properties.
基金Supported by the National Key R&D Program of China(2018YFA0404403)the National Natural Science Foundation of China(11775004,U1867214,11875074,11961141003)+1 种基金the funding from the State Key Laboratory of Nuclear Physics and Technology,Peking University(NPT2021ZZ01)the funding from Heavy Ion Research Facility in Lanzhou(HIR2021PY002)。
文摘Two low-lying unbound states in ^(16)C are investigated by deuteron inelastic scattering in inverse kinematics.Besides the 2^(-) state at 5.45 MeV previously measured in a 1n knockout reaction,a new resonant state at 6.89 MeV is observed for the first time.The inelastic scattering angular distributions of these two states are well reproduced by the distorted-wave Born approximation(DWBA)calculation with an l=1 excitation.In addition,the spinparities of the unbound states are discussed and tentatively assigned based on shell model calculations using the modified YSOX interaction.
基金supported by the National Key R&D program of China under grants 2018YFA0404201This research work is also supported by the National Natural Science Foundation of China,with NSFC Grants No.11635011,No.11761141001,No.11905240,No.12105293,No.12105294,No.U2031103,No.U1831208,No.11503021,No.11205126,No.11947404,and No.11675187+2 种基金by IHEP innovation project No.E25451U2by the Science and Technology Department of Sichuan Province 2021YFSY0031by the Xiejialin Foundation of IHEP No.E2546IU2,by RTA6280002 from Thailand Science Research and Innovation in Thailand.
文摘Introduction One of main scientific goals of the Large High Altitude Air Shower Observatory(LHAASO)is to accurately measure the energy spectra of different cosmic ray compositions around the‘knee’region.The Wide Field-of-View(FoV)Cherenkov Telescope Array(WFCTA),which is one of the main detectors of LHAASO and has 18 telescopes,is built to achieve this goal.Multiple telescopes are put together and point to connected directions for a larger FoV.Method Telescopes are deployed spatially as close as possible,but due to their own size,the distance between two adjacent telescopes is about 10 m.Therefore,the Cherenkov lateral distribution and the parallax between the two telescopes should be considered in the event building process for images crossing over the boundaries of FoVs of the telescopes.An event building method for Cherenkov images measured by multiple telescopes of WFCTA is developed.The performance of the shower measurements using the combined images is evaluated by comparing with showers that are fully contained by a virtual telescope in simulation.Results and conclusion It is proved that the developed event building process can help to increase the FoV of WFCTA by 30%while maintaining the same reconstruction quality,compared to the separate telescope reconstruction method.
基金supported by the following grants:The National Key R&D program of China under grants 2018YFA0404201the National Natural Science Foundation of China(NSFC)No.12022502,No.12205314,No.12105301,No.12261160362,No.12105294,No.U1931201,No.12393851,No.12393854+1 种基金In Thailand,support was provided by the National Science and Technology Development Agency(NSTDA)the National Research Council of Thailand(NRCT)under the High-Potential Research Team Grant Program(N42A650868).
文摘KM2A is one of the main sub-arrays of LHAASO,working on gamma ray astronomy and cosmic ray physics at energies above 10 TeV.Detector simulation is the important foundation for estimating detector performance and data analysis.It is a big challenge to simulate the KM2A detector in the framework of Geant4 due to the need to track numerous photons from a large number of detector units(>6000)with large altitude difference(30)and huge coverage(1.3).In this paper,the design of the KM2A simulation code G4KM2A based on Geant4 is introduced.The process of G4KM2A is optimized mainly in memory consumption to avoid memory overflow.Some simplifications are used to significantly speed up the execution of G4KM2A.The running time is reduced by at least 30 times compared to full detector simulation.The particle distributions and the core/angle resolution comparison between simulation and experimental data of the full KM2A array are also presented,which show good agreement.
