Status of LHAASO-WCDA Mingjun Chen Jul 14th , 2017
LHAASO L arge H igh A ltitude A ir S hower O bservatory LHAASO site Location: Four types of detectors: 29 21’30.7”N, 100 08’14.7”E; The Electromagnetic particle Detector • (ED) array --5195 units 4,400 m a.s.l; Muon Detectors Array --1171 units. • 2 700 km to Chengdu; Wide Field Cherenkov Telescope Array • 8 km to airport; WCDA • 50 km to Daocheng City.
WCDA - Water Cherenkov Detector Array 3 water ponds : 78,000 m 2 in total; 4.4 m water depth; 3,120 cells, with an 8”/9” PMT in each cell; Cells are partitioned with black curtains. Detect shower secondary particles: Electrons/positrons; Muons; Gammas. 3
Physics Goals VHE gamma sky survey (100 GeV-30 TeV): Extragalactic sources & flares; VHE emission from Gamma Ray Bursts; Galactic sources; Diffused Gamma rays. Cosmic Ray physics (1 TeV-10 PeV): Anisotropy of VHE cosmic rays; Cosmic ray spectrum; Cosmic electrons; Hadronic interaction models. Miscellaneous: Gamma rays from dark matter; Sun storm & IMF. 4
Schematics of WCDA Nine Nine FEE Clock system Cells Cells FEE FEE FEE HV system Nine Nine Cells Cells DAQ & Data storage Time calibration system Slow control system Water purification & recirculation system 3,120 cells
Engineering of Water Pond Major pollution is TOC/DOC: UV185 + 0.22 m. Water flow: 1 volume/month 6
Photo Multiplier Tube 8-in/9-in Large area Candidates ： P/V>2.0 Single Photonelectron R5912 • Anode & Dynode outputs Large dynamic range CR365 • TTS<4.0ns High time performance XP1805 • Noise rate<5KHz Low noise rate Work gain:3*10 6 HZC XP1805 FEE Average Amplitude of SPE: ~5mV HV Polarity of HV: Positive Three 30m cables: Two signals + One HV 7
Readout Electronics Time Measurement Data PMT Charge Measurement Readout Buffer Anode FPGA Dynode 8 Buffer Charge Measurement 9 PMTs share a FEE board. • Charge/ADC: filter & shaping with RC 2 ， peak finding with FPGA; • Time/TDC: leading edge discriminating, time being measured with FPGA-TDC (bin-size 0.333 ns); • 8
DAQ & Data Online Computer Room Disk Array Online Farm A computer cluster consists of （ Blade servers ） File&Manager Fiber Storage ~4,000 CPU cores; server × 2 Twisted-pair Server × 2 Software implementation is based on the ATLAS TDAQ framework. Control Room Web server To Internet Switches DAQ PC × 2 Data are transferred to a computing • center at IHEP (or other site) via commercial network links; Data are stored (disk + tape), accessed • and processed in the infrastructure of the computer center. 9
Slow Control system Monitor environment parameters(temperature, pressure, humidity, water depth, …); Monitor & control of HV of PMTs; Water attenuation length measurement. 10
Time Calibration Cluster-based, cross-calibrated: 2 fibers per PMT seperatively; 2 LEDs per cluster, lit in turn; 2-4 fibers are crossed over neighboring clusters; Frequency of LED pulsing: 5-10 Hz. 11
Charge Calibration Low range: single rate (peak-i) ~20 kHz; SPE signal dominated; Including PMT Gain + cable + pre-amp + low range electronics. High range: muon peak (peak-iii) ~10 Hz; Vertical muons hitting the photo-cathode; PMT high range gain + QE + CE + cable + pre-amp + high 12 range electronics.
Sensitivity 积分灵敏度 0.013crab@2TeV 13
WCDA Specifications Item Value 25 m 2 Cell area Effective water depth 4 m Water transparency > 15 m (400 nm) Precision of time measurement 0.5 ns Dynamic range 1-4,000 PEs Time resolution <2 ns Charge resolution 50% @ 1 PE 5% @ 4000 PEs Accuracy of charge calibration <2% Accuracy of time calibration <0.2 ns 78,000 m 2 Total area Total cells 3,120 14
R&D work(I): a prototype unit Diameter:7m Height: 5m 15
R&D work(II): Nine cells engineering array at Yabajing A reconstructed shower-core distribution from ARGO-YBJ for the GPStime-matched events of the prototype array and ARGO-YBJ. The space angles of the reconstructed shower directions between the two experiments for 16 the matched shower events.
Collaborators & Schedule University of Science and Technology of Electronics, PMTs China National Space Science Center, CAS Slow control system Tsinghua University WR Clock system Institute of High Energy Physics, CAS Detector installation, DAQ, data, etc.
Collaborators & Schedule University of Science and Technology of China Electronics, PMTs National Space Science Center, CAS Slow control system Tsinghua University WR Clock system Institute of High Energy Physics, CAS Detector installation, DAQ, data, etc. Start detector installation of the 1 st pond. 2018.6 Installation finished of the 1 st pond. End of 2018 Beginning of 2021 Completed. 18
Summary LHAASO-WCDA, as a component of LHAASO project, aims at playing an important role in the Gamma astronomy. WCDA already started construction. And one quarter of array will start operation in the end of 2018. 19
Thank you all. 20
Backup 21
VHE -astronomy: Two Techniques IACTs: H.E.S.S., VERITAS, MAGIC, … Good angular resolution (~0.1 ); Fair background rejection power; Short duty cycle (~10%); Narrow FOV (<5 ); Low energy threshold (~100 GeV); Mainly focused on deep observation. Ground particle array: AS , ARGO-YBJ, Milagro , HAWC, … Not-so-good angular resolution (~0.5 ); Poor background rejection power (but much elaborated in water Cherenkov); Full duty cycle (>95% ， ~10 IACT); Wide FOV （ >2/3 ， ~150 IACT); High energy threshold improved by construction at high altitude (~1 TeV); Good at sky survey, extended sources and flares. 22
Unknown TeV Sources Kifune’s plot: new detectors on TeV Gamma rays are awaited to keep the discovery pace. The LHAASO detectors will do help. Can the number of sources climb to ~1000 by 2020? 23
WCDA project- - 触发模式 以 12*12 个单元为一组； 相邻组由一半重叠； 各个通道的阈值设置 1/3PE 组内 250ns 有多个 PMT 着火时 触发 , 比如 12 个，就只有小于 1KHz 的噪声触发。 Noise trigger 依赖于簇射芯位距阵列中心的距离（ R ）： nPMT 20 ： >60% 的事例能够触发； 24 nPMT 30 ： >90% 的事例能够触发。
Gamma/proton Discrimination Gamma Proton Brightest “sub - core”: Signal of the brightest PMT outside the shower core region (e.g., 45 m); “Compactness” can be employed to reject cosmic ray background efficiently. Q-factor: 7 @ 1 TeV; 22 @ 5 TeV. 25
Effective Area & Angular Resolution Effective area: ~1,000 m 2 @ 100 GeV; >80,000 m 2 @ 5 TeV. Angular resolution: Optimized bin size: 0.55 @ 1 TeV; 0.23 @ 5 TeV. 26
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