RPCs in the ARGO-YBJ experiment

P. Camarri (University of Roma “Tor Vergata” and INFN Roma 2)

for the ARGO Collaboration

Workshop on Physics with Atmospheric Neutrinos and Neutrinos from Muon Storage RingsMumbai, August 1-2, 2005

The ARGO-YBJ Collaboration

INFN and Dpt. di Fisica Università, LecceINFN and Dpt. di Fisica Universita’, NapoliINFN and Dpt. di Fisica Universita’, PaviaINFN and Dpt di Fisica Università “Roma Tre”, RomaINFN and Dpt. di Fisica Università “Tor Vergata”, RomaIFSI/CNR and INFN, TorinoIFCAI/CNR, Palermo and INFN, Catania

IHEP, BeijingShandong University, JinanSouth West Jiaotong University, ChengduTibet University, LhasaYunnan University, KunmingZhenghou University, Henan

Spokesman: B. D’Ettorre Piazzoli Spokesman: Z. Cao

Collaboration Institutes: Chinese Academy of Science (CAS) Istituto Nazionale di Fisica Nucleare (INFN)

The YangBaJing High Altitude Cosmic Ray

LaboratoryLongitude 90° 31’ 50” EastLatitude 30° 06’ 38” North

4300 m above the sea level

90 Km North from Lhasa (Tibet)

Astrophysical Radiation withGround-based Observatory

The ARGO-YBJ site

Outline Introduction

The ARGO-YBJ experiment

Conclusions

Ground based -ray astronomy

Detector layout and RPC details

Physics goals and sensitivity

Present status and first measurements

Why ground-based detectors ?

Satellite measurements are limited by the E- ( = 2 ÷ 3) law for -ray flux

CRAB (>500 GeV) 6 · 10-11 photons/(cm2 s)

1 m2 detector needs 5 · 104 hours of observation to collect 100 photons

CRAB (>1 TeV) 2 · 10-11 photons/(cm2 s) 1.4· 105 hours

VHE -astronomy possible only by ground-based detectors exploiting the amplification effect of the Extensive Air Showers (EAS)

Detecting Extensive Air Showers

EAS arrays

High energy threshold ( 50 TeV)Moderate bkg rejection ( 50 %)Modest sensitivity ( crab)Modest energy resolutionHigh duty-cycle (> 90 %)Large field of view (~ 1-2 sr)

Air Cherenkov Telescopes

Very low energy threshold ( 60 GeV)Good background rejection (99.7 %)High sensitivity (< 10-2 crab)Good energy resolutionLow duty-cycle (~ 5-10 %)Small field of view < 4°- 5°

A new generation of EAS arrays

• Low energy threshold < 500 GeV

• Increase sensitivity Φ Φcrab 10-1 Φcrab

The Goal

• High altitude operation

• Secondary photon conversion

• Increase the sampling (~1% 100%)

The Solution

MeVNMeVN

mNmN

e

ee

171

270054300

Improves angular resolutionLowers energy threshold

ARGO-YBJ Physics Goals

-ray astronomy Search for point-like galactic and extra-galactic sources at few

hundreds GeV energy threshold

Diffuse -rays from the galactic plane and SNRs

GRB physics (full GeV / TeV energy range)

Cosmic ray physics• ratio at TeV energy

• Spectrum and composition around the “knee” (E > 10 TeV)

Sun and heliosphere physics (E > 10 GeV)

pp

The ARGO detector: bakelite Resistive Plate Chambersoperated in streamer mode

thickness of the gas volume : 2mm

Gas mixture: Ar/ i-C4H10 /C2H2F4 = 15/10/75Operating voltage = 7.2 kV (10.2 kV at sea level)Single RPC absorption current @ 7.2 kV = 3- ASingle RPC count rate @ 7.2 kV = 4 kHz

Gas gapBakelite plate

Graphite layer

Bakelite plateGraphite layer

PET spacer

ARGO RPC details (1)

Bakelite plate

Read-out strip panel

Front-end board

ARGO RPC details (2)

Closed ARGO chamber

High-voltage connection

Low-voltage connection

RPC performance in the ARGO preliminary test

• Efficiency

• Time resolution

• Altitude effect

TFE/ iBUT=97/3

TFE/Ar/ iBUT=75/15/10

Gas mixture: Ar/ i-C4H10 /C2H2F4 = 15/10/75

Operating voltage = 7.2 kV (10.2 kV at sea level)

Single RPC absorption current @ 7.2 kV = 3-4 A

Single RPC count rate @ 7.2 kV = 4 kHz

78 m

99 m

74 m

111 m

Detector Layout

10 Pads = 1 RPC (2.80 1.25 m2)

12 RPC =1 Cluster ( 5.7 7.6 m2 ) 8 Strips = 1 Pad

(56 62 cm2)

Layer of RPCs covering 5600 m2

( 92% active surface)+ 0.5 cm lead converter+ sampling guard ring

time resolution ~ 1 nsspace resolution = 6.5 62 cm2 (1 strip)

78 Clusters

Central Carpet:130 Clusters, 1560 RPCs, 124800 Strips

ARGO-YBJ Experimental Hall

RPC chamber

Cluster

Trigger and Data Acquisition

Shower modea minimum Pad multiplicity is required on the central detector,with space/time consistency as for a shower front

Scaler modemeasurement of the Pad rate from each Cluster(integration time: 0.5 s)

Aim - detection of unexpected increases in CR flux (GRB, Solar flares …)

Local Station(basic unit ofdistributed

DAQ System)

Central Station

• Trigger• Data storageTrigger

Pad Multiplicity info

DATA

Detector Control System (DCS) and Analog Charge readout

DCS

High voltage control and monitoring Monitoring of environmental parameters (indoor and outdoor

temperature, atmospheric pressure) HV fine tuning (to be implemented soon) RPC current monitoring RPC counting rate (for detailed diagnostics: to be added soon)

The DCS is crucial for detecting anomalous detector behaviours and performing the required actions to protect the system.

Analog Charge ReadoutBIGPAD

ADC

RPC

Read-outof the chargeinduced on“Big Pads”

Sensitivity to the Crab and angular resolution

Minimum Detectable Flux (5 in 1 y)

ARGO can observe, in 1 year, a Crab-like source of intensity 0.7 Crab units at energies E > 0.5 TeV, with a significance of 4 standard deviations.

ARGO

Veritas

Glast

HegraWhipple

Milagro

CRAB Whipple E-2.49 Opening angle

Zenith angle < 40°

4.3 h/day

≈ ψ/ 1.58

~ 1 TeV ~ 2 TeV ~ 5 TeV

0.55 TeV

N (>1 TeV) ~ 10

ARGO: without any /h discrimination ! Af = 80 80 m2

T5 (>1 TeV) ~ 3 months

-hadron discrimination

Development of an effective off-line procedure Multiscale image analysis has been showed to provide

an efficient tool for gamma/hadron discrimination Results are encouraging and allow to nearly double the

detector sensitivity. The best response is obtained in the few TeV range. The study is now being extended to all event categories The measurement of the muon content of the shower

allows hadron background rejection at higher energies

Summary of the main detector features and performance

pointing resolution (≤ 0.5 °)

detailed space-time image of the shower front

detection of small showers (low threshold energy)

large fov and high “duty-cycle”

continuous sky monitoring (-10° < < 70°)

Resistive Plate Chambers (RPC) as active elements

Space information from Strip (6.5 × 62 cm2 )

Time information from 8-strip pads (resolution 1 ns)

Large area ( 10000 m2 ) and full coverage (5600 m2 )

High altitude (4300 m a.s.l.)

Status of the experiment 16 clusters (~ 700 m2) in stable data taking

for 10 months (Jan 2004 till October 2004) gas mixture optimization fine tuning of electronics parameters long term test of the input-stage protection of the FE electronics, necessary to avoid damages due to high energy showers (tests at Roma 2 and in Tibet): fully successful monitoring of RPC efficiency time calibration operations check of the reconstruction algorithms

42 clusters (~ 1900 m2) in data taking since the end of 2004

detecting area large enough for Solar Flare and GRB searches.

100-110 clusters (~ 4500 m2) in data taking at the end of 2005

Completion of the central carpet in spring 2006

Trigger rates (threshold N > 60 pads)

Shower Front on

42 Clusters

(41 x 46 m2)

Event reconstruction with 42 clusters(PRELIMINARY)

<l> = -0.016<m> = 0.025

Zenith angle distribution

Direction cosinedistributions

DCS: HV monitoring (16 clusters, 10/02/2005)

DCS: RPC current monitoring (16 clusters, August 2004)

• Average Total RPC current

• Average barometric pressure

• Average hall temperature

Counting rate as a function of time

doublessingle pad

4 Clusters during 3.5 days

All Clusters react homogeneously to external changes

Analog Charge Readout: event on 4 Clusters (180 m2) at YBJ (PRELIMINARY)

Graphical elaborationADC Counts on each big-pad

~~30 part/m30 part/m22

1 m.i.p = 2 mV

Full scale = 4000 ADC counts = 300 mV

Some events…

Very big shower !!Very big shower !!

4000 ADC counts 4000 ADC counts ~ 90 p/m~ 90 p/m22

More events…

Conclusions The detector performance is turning out to be as good

as expected All the subsystems (DAQ, DCS, ACR) are fully

operational; further improvements are foreseen on the DCS for redundancy

The analysis of the data collected on a ~ 1900 m2 carpet is in progress: early results are going to be presented at ICRC 2005

The installation is in progress and will be completed in 2006

Most important, a stand-alone RPC apparatus is turning out to be a crucial tool for cosmic-ray astrophysics, apart from its already established applications as a muon-trigger detector in experiments at colliders