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LAWCA for Air Shower Detection at High Altitude

LAWCA for Air Shower Detection at High Altitude. IHEP, Beijing Zhiguo Yao VCI, 11-15/02/2013. LAWCA - L arge A rea W ater C herenkov A rray. Physics Goals. VHE gamma sky survey (100 GeV-30 TeV ): Extragalactic sources & flares; VHE emission from Gamma Ray Bursts;

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LAWCA for Air Shower Detection at High Altitude

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  1. LAWCA for Air Shower Detection at High Altitude IHEP, Beijing Zhiguo Yao VCI, 11-15/02/2013

  2. LAWCA - Large Area Water Cherenkov Array

  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 electrons / positrons; • Cosmic ray spectrum; • Hadronic interaction models. • Miscellaneous: • Gamma rays from dark matter; • Sun storm & IMF.

  4. 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, … • not-so-good angular resolution(~0.5); • poor background rejection power (but much elaboratedin 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.

  5. Instrumentation History Usually IACT is10 better in sensitivity. Whipple 0.2 Crab 1980 Tibet-AS 1.5 Crab Crab detected! 1989 HEGRA, CANGAROO, CAT … 0.04 Crab 2001 Milagro 0.9 Crab H.E.S.S. 0.008 Crab 2004 VERITAS 0.008 Crab 2007 ARGO-YBJ 0.6 Crab MAGIC 0.02 Crab 2009 6Sources 10 years delay! 2012 143Sources observed LAWCA 0.06 Crab HAWC 0.06 Crab 2015 CTA 0.001 Crab LHAASO-WCDA 0.01 Crab 2017?

  6. Water Cherenkov for Air Showers • Developed by Milagro, Auger, IceTop, etc. • to detect shower secondary particles: • electrons/positions; • muons; • gammas: ~10x more, a benefit of water Cherenkov. • What are actually measured: energy flux in the water. • VHE: Two kinds of layouts: pool / tank.

  7. “Sub-core” of Hadronic Showers Proton • Brightest “sub-core”: • signal of the brightest PMT outside the shower core region (e.g., 45 m); • mainly caused by muon (mean PE = 20, fluctuating with a long tail). • “Compactness” ( invented by Milagro): •  nPMT/cxPE; • proton: small; • gamma: big. • “Compactness” can be employed to reject cosmic ray background efficiently Gamma

  8. Detector Layout of LAWCA • An L-shape water pool: • 4300 m a.s.l. • North-East of ARGO-YBJ hall; • 23,000 m2; • 4.5 mdepth; • 916 cells, with an 8” PMT in each cell; • Cells are partitioned with black curtains. Original idea is credited toMilagro/HAWC.

  9. Angular Resolution & Background Rejection • Good angular resolution: • Optimized bin size: 0.85 @ 1 TeV; 0.45 @ 5 TeV. • Fair background rejection power: • Q-factor: 3 @ 1 TeV; 14 @ 5 TeV.

  10. Effective Area & Sensitivity • Effective area: • 500 m2 @ 100 GeV; • 30,000 m2 @ 1 TeV; • 60,000 m2 @ 5 TeV. • Sensitivity per year: • 0.1 CRAB @ 1 TeV; • 0.06 CRAB @ 5 TeV。 • ~10x better than ARGO-YBJ. 4个¼ 阵列

  11. Sensitivity to Flares • Minimum requirements: • 30 events; • 5 s.d. • Mainly limited by statistics. 3 days’ flare

  12. Engineering of Water Pool • Requirements: • water-proof: loss <1/1000 volume/day; • light-proof: luminous flux(300-650 nm) <100k photons/m2/s; • tolerance to snow, rain, wind, dust, earth-quake; • anti-icing; • clean water compatible; • light roof and top materials.

  13. Water Purifying & Circulation • Purifying: • Absorption length >30 m@ 400 nm; • Water in pool: • Absorption length >20 m@ 400 nm; • Uniformity: >85%. • Circulation speed: • 30 days per pool volume.

  14. PMT / Electronics Specifications • Single counting rate is very high: robust DAQ system; • Single PE, large dynamic range: low noise, dynodes readout; • Time resolution: essential for shower direction measurement.

  15. Trigger Scheme • Cluster-based; • Neighboring clusters are half-overlapped; • Pattern: • Multiplicity during 250 ns of any cluster 12; • Noise trigger <1 kHz. • Besides a hardware solution, a software-based trigger mechanism is also proposed. Noise trigger

  16. Trigger Rate & Data Volume • Trigger rate: • ~17 kHz. • Data volume after trigger: • 240 Mbps = 1 PB/year. • DAQ data volume (input, soft trigger): • 4.6 Gbps = 18 PB/year. Trigger rate • Huge amount of data: an online- reconstruction solution is under investigation. Data volume

  17. PMT Readout • Tapered voltage divider circuit; • A specialized decoupling circuit to reduce the effect of charge piled-up; • Two dynode outputs set for SPE resolution and dynamic range; • Dynamic range 1-4000 PE can be achieved with a linearity level 5%.

  18. Electronics • Charge: analog shaping, digital peak detecting; • Timing: pulse front discrimination; • 9 PMTs share 1 FEE board; • FEEs are synchronized with central station via White Rabbit protocol; • Hit signals are transferred to the central DAQ system via TCP/IP network, shared with WR; • DAQ: based on Atlas TDAQ software framework (soft trigger compatible). DY8 DY10

  19. Charge Calibration: Low Range • Method: single rate • ~50 kHz; • SPE signal dominated; • Including PMTGain + cable + pre-amp + electronics low range; • Precision: • 2% per 30 seconds; • Real time (hardware trigger): 2%per 30 minutes. Variation over a month Fitted with a convolution of power law  Poisson  Gaussian + SPE noise Temperature effect: PMT + cable

  20. Charge Calibration:High Range • Method: muon peak • ~10 Hz; • muons hitting the photo-cathode; • PMTgain + QE + CE + cable + pre-amp + electronics high range. • Precision: • 2% per 30 minutes; • Real time (hardware trigger): 2%per day. Variation over a month Gaussian fitting after a power law of charge is multiplied. Temperature effect: PMT + cable

  21. Time Calibration • Cluster-based, cross-calibrated: • 2 fibers per PMT (naming: short & long); • 2 LEDs per cluster, lightened in turn; • 2-4fibers are crossed among neighboring clusters; • Frequency of LED pulsing: 5-10 Hz. • Requirements: • Time offset measurement: ~0.1 ns.

  22. Time Calibration: Test Results Distribution of mean offset, 3 months. Mean value: 10 minutes @ 5 Hz. Distribution of single measurements, 5 minutes @ 1 kHz, different thresholds. Two fibers on a PMT Short fibers of 2 PMTs:  = 0.07 ns. unit: 1/5.6 ns Two fibers on 2 PMTs Long fibers of 2 PMTs:  = 0.12 ns.

  23. Prototype Detector(2009-2010) 2 layers of 1 m1 m Scintillators Single rate: 16 kHz  30-50 kHz (4300 ma.s.l.) 5 m 7 m 1 layer of 1 m1 m Scintillator -peak is first observed.

  24. Engineering Array(2010-now) 9 cells, effective area 225 m2, 1% scale of LAWCA.

  25. Installation 2011/03: dry run 2011/07: wet run >10 TB test and physics data obtained so far.

  26. Event Reconstruction and Coincidence with ARGO-YBJ

  27. Support & Schedule • Provisional support from IHEP-Beijing is available: • ~2 M$; • Land preparation is going to start in 04/2013; • Preparation for production has started, including PMTs, electronics, detector installation facilities, DAQ, data storage, … • Full support from NSFC is to be decided in 06/2013: • ~10 M$; • Pool construction will then start soon and is to be completed in 10/2013; • Detector installation is to be completed in 07/2014; • Physics run may start in 10/2014.

  28. Summary • A new VHE air shower detection instrument “LAWCA” is proposed to be built at YBJ in 2 years. • Similar to HAWC, it employs water Cherenkov techniques, aimed mainly at a full sky survey for new gamma ray sources; • The detector has been designed and partially tested with the prototype and the engineering array.

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