The dynamic range extension system for the LHAASO-WCDA experiment Cheng LIU On behalf of the LHAASO collaboration 2017/7/18

Outline The LHAASO-WCDA experiment The dynamic range extension system Motivation System design Summary

The LHAASO-WCDA Experiment 3 water ponds (78,000 m2 ) 3120 cells, with an 8”/9” PMT; Dynamic range: 1 - 4000 PEs; Angular resolution: <0.4° @2TeV Sensitivity: <1.3% ICrab @2TeV Physics Goal: To survey the northern sky for γ sources from 100 GeV to 30 TeV.

The LHAASO Experiment —— a hybrid air shower detector Direction Multi-parameter measurement of air showers  Identify the composition of the primary particles Muon Energy & Image shape

Why do we need the dynamic range extension system for LHAASO proton iron The lateral distributions of the particle density log10 ( Energy / TeV ) log10( Npe core ) The NPE distribution of the large PMT in the core cell The dynamic range of the large PMT Motivation: To measure the shower cores from 100 TeV to 10 PeV (~knee region)

The dynamic range extension system 1 water pond (22,500 m2 ) 900 cells, with 1.5” PMT Dynamic range: 50 – 500,000PEs

1.5” Photo Multiplier Tube Candidates： CR285 (HAMAMATSU), XP3960 (HZC Photonics) Polarity of HV: Positive Gain: ~2 × 105 XP3960 CR285

The dynamic range base design The pulse shape of the PMT Anode 500 mV/bin Dy7 5 mV/bin Anode & the 7th Dynode readout Schematic diagram of voltage-divider circuit CR285 Typical non-linearity of PMTs Non-linearity (%) Dynamic range Anode DY7 The requirements of the 4 orders of dynamic range can be reached.

the waterproof package design of the large PMT Waterproof design Scheme B Large PMT PACTAN 6010 Stainless steel Heat shrink tube the waterproof package design of the large PMT Scheme A Directly measure the Cherenkov light produced in the water Measure the large signals and the absorption effect of glass can be neglected.

Waterproof test system Prototype test Waterproof test system Scheme A Pressure sensor RH&T sensor Scheme B Pressure tank Air compressor The estimate of these two schemes is still in progress

Design of charge digitizing module for readout electronics. Signals from the anode and the dynode of one PMT are digitized by a two-channel ADC after being manipulated by the amplification and shaping circuit. the digitized signals are sent to the FPGA for digital peaking. All digitized data is transmitted to DAQ (Data Acquisition) via a simplified White Rabbit protocol. Design of charge digitizing module for readout electronics.

Design of the Charge calibration Charge calibration system based on an array of LEDs and plastic optical fiber bundle is designed The LEDs array can be turned on individually or in any combination. Using the different light emitted by the LEDs array, we can measured the SPE spectrum and the high voltage response of each PMT. Schematic of charge calibration for small PMTs.

Summary The dynamic range extension system of the LHAASO-WCDA is to precisely measure the shower cores of events at the energy range from 100 TeV to 10 PeV; 900 cells of the WCDA array are planned to add another 1.5 inch PMT at side of the large PMT; Using all detector arrays in LHAASO, combining the shower cores information, it will be powerful to identify the composition of the primary particles.

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Effective Area & Angular Resolution At 500 GeV, the effective area can reach 3,000 m2, the angular resolution is 0.6◦ and the energy resolution for -rays is 95%. The corresponding values are 10,000 m2, 0.4◦, 90% at 1 TeV, and 50,000 m2, 0.2◦, 60% at 10 TeV. The highest sensitivity is 1.3% of the Crab nebula flux at the energy around 2 TeV.

Muon Detector Water Cherenkov detector Underneath soil Eth ~ 1 GeV Item Value Area 36 m2 Detection efficiency >95% Purity of N Time resolution <10 ns Dynamic range 1-10,000 particles Particle counting resolution 25% @ 1 particle 5% @ 10,000 particles Aging (<20%) >10 years Spacing 30 m Number 1171 Muon Detector Water Cherenkov detector Underneath soil Eth ~ 1 GeV