LAWCA for Air Shower Detection at High Altitude

IHEP, BeijingZhiguo Yao

VCI, 11-15/02/2013

LAWCA - Large Area Water Cherenkov Array

Physics GoalsVHE 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.

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 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.

Instrumentation History

2007

1980Whipple0.2 CrabCrab detected!

VERITAS0.008 Crab ARGO-YBJ

0.6 Crab

Tibet-AS1.5 Crab

Milagro0.9 Crab

20122015

HAWC0.06 Crab

LAWCA0.06 Crab

2004H.E.S.S.0.008 Crab

MAGIC0.02 Crab

2009

2001

1989

CTA0.001 Crab

LHAASO-WCDA0.01 Crab

Usually IACT is 10 better in sensitivity.

143 Sources observed

6 Sources

2017?

HEGRA, CANGAROO, CAT … 0.04 Crab

10 years delay!

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.

“Sub-core” of Hadronic ShowersProton

Gamma

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

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 m depth; 916 cells, with an 8” PMT in each cell; Cells are partitioned with black curtains. Original idea is credited

to Milagro/HAWC.

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.

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

Sensitivity to Flares Minimum requirements:

30 events; 5 s.d.

Mainly limited by statistics.

Duration Sensitivity (Crab)

1 year 0.0630 days 0.210 days 0.43 days 11 day 23 hours 42 hours 51 hour 10

3 days’ flare

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.

Engineering of Water Pool

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.

LAWCAPMT 8”/9”Input polarity PositiveSingle rate 50 kHzCharge dynamic range

1-4000 p.e.

Charge resolution

50% @ 1 p.e.5% @ 4000 p.e.

Discriminator threshold

0.25 p.e.

Time range 0-2000 nsTime resolution

0.5 ns

Multi-hit separation

100 ns

Channels 3600Cable length 30 m

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.

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

Trigger Rate & Data VolumeTrigger rate:

~17 kHz.Data volume after trigger:

240 Mbps = 1 PB/year.

DAQ data volume (input, soft trigger): 4.6 Gbps = 18 PB/year.

Huge amount of data: an online- reconstruction solution is under investigation.

Trigger rate

Data volume

PMT Readout

D 1 , F 2F 1 , F 3 D 2 D 3 D 4 D 5 D 6

D 7

D 8

D 9

D 1 0

O u t 1 O u t 2

A n o d e

R

1 . 1

R

1 . 3

R

1 F

R

2

R

3

R

4

R

5

R

6

R

7

R

8

R

9

R

1 0

R

a

R

d 8

R

d 9

R

i 1 0

1 0 0 k

R

i 8

C

6

C

8

C

1 0

C

7

C

9

C

c

C

c 8

R

b 8

C a t h o d e

R

1 . 2

+ H V

C

f

R

f

5 0

1 0 0 k

2 2 n

5 0 0 k

C a t h o d e D Y 1 D Y 2 D Y 3 D Y 4 D Y 5 D Y 6 D Y 7 D Y 8 D Y 9 D Y 1 0 A n o d e

5 . 4 1 . 7 7 2 . 2 1 . 5 0 . 8 2 0 . 4 7 0 . 5 6 0 . 6 8 1 . 0 1 . 5 1 . 2

1 0 0 k

R

d 1 0

5 1

R

b 1 0

1 0 0 k

1 0 0 k

5 1

5 1

1 0 n

C

c 1 0

1 0 n

2 2 n

2 2 n2 2 n

2 2 n

R

b

1 0 n

R

i

2 2 n

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%.

Electronics

DY10

DY8

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).

Charge Calibration: Low Range

Method: single rate ~50 kHz; SPE signal dominated; Including PMT Gain + cable + pre-amp

+ electronics low range; Precision:

2% per 30 seconds; Real time (hardware trigger): 2% per 30

minutes. Temperature effect: PMT + cable

Variation over a month

Fitted with a convolution of power law Poisson Gaussian + SPE noise

Charge Calibration: High Range

Method: muon peak ~10 Hz; muons hitting the photo-cathode; PMT gain + QE + CE + cable +

pre-amp + electronics high range. Precision:

2% per 30 minutes; Real time (hardware trigger): 2%

per day.

Gaussian fitting after a power law of charge is multiplied.

Variation over a month

Temperature effect: PMT + cable

Time CalibrationCluster-based, cross-

calibrated: 2 fibers per PMT (naming: short

& long); 2 LEDs per cluster, lightened in

turn; 2-4 fibers are crossed among

neighboring clusters; Frequency of LED pulsing: 5-10

Hz.

Requirements: Time offset measurement: ~0.1

ns.

Time Calibration: Test Results

Two fibers on a PMT

Two fibers on 2 PMTs

Short fibers of 2 PMTs: = 0.07 ns.

Long fibers of 2 PMTs: = 0.12 ns.

Distribution of mean offset, 3 months. Mean value: 10 minutes @ 5 Hz.

unit: 1/5.6 ns

Distribution of single measurements, 5 minutes @ 1 kHz, different thresholds.

Prototype Detector (2009-2010)

Single rate: 16 kHz 30-50 kHz (4300 m a.s.l.)

-peak is first observed.

2 layers of 1 m1 m Scintillators

1 layer of 1 m1 m Scintillator

5 m

7 m

Engineering Array (2010-now)

9 cells, effective area 225 m2, 1% scale of LAWCA.

Installation

2011/03: dry run2011/07: wet run

>10 TB test and physics data obtained so far.

Event Reconstruction and Coincidence with ARGO-YBJ

Support & ScheduleProvisional 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.

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.