RPCs in the ARGO-YBJ experiment

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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 Rings
• Mumbai, August 1-2, 2005

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The ARGO-YBJ Collaboration

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

Spokesman Z. Cao
Spokesman B. DEttorre Piazzoli
INFN and Dpt. di Fisica Università, Lecce INFN
and Dpt. di Fisica Universita, Napoli INFN and
Dpt. di Fisica Universita, Pavia INFN and Dpt di
Fisica Università Roma Tre, Roma INFN and Dpt.
di Fisica Università Tor Vergata, Roma IFSI/CNR
and INFN, Torino IFCAI/CNR, Palermo and INFN,
Catania
IHEP, Beijing Shandong University, Jinan South
West Jiaotong University, Chengdu Tibet
University, Lhasa Yunnan University,
Kunming Zhenghou University, Henan
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The YangBaJing High Altitude Cosmic Ray Laboratory
Longitude 90 31 50 East Latitude 30 06
38 North 4300 m above the sea level 90 Km
North from Lhasa (Tibet)
Astrophysical Radiation with Ground-based
Observatory
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The ARGO-YBJ site
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Outline

• Introduction

Ground based g-ray astronomy

• The ARGO-YBJ experiment

Detector layout and RPC details Physics goals and
sensitivity Present status and first measurements

• Conclusions

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Why ground-based detectors ?
Satellite measurements are limited by the E- ? (?
2 3) law for g-ray flux
?CRAB (gt500 GeV) ? 6 10-11 photons/(cm2 s)
1 m2 detector needs ? 5 104 hours of
observation to collect 100 photons
?CRAB (gt1 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)
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Detecting Extensive Air Showers
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A new generation of EAS arrays
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ARGO-YBJ Physics Goals

• g-ray astronomy
• Search for point-like galactic and
  extra-galactic sources at few hundreds GeV energy
  threshold
• Diffuse g-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 gt
  10 TeV)
• Sun and heliosphere physics (E gt 10 GeV)

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The ARGO detector bakelite Resistive Plate
Chambers operated in streamer mode
Graphite layer
Bakelite plate
Gas gap
Bakelite plate
Graphite layer
PET spacer
thickness of the gas volume 2mm
Gas mixture Ar/ i-C4H10 /C2H2F4
15/10/75 Operating voltage 7.2 kV (10.2 kV at
sea level) Single RPC absorption current _at_ 7.2 kV
3- mA Single RPC count rate _at_ 7.2 kV 4 kHz
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ARGO RPC details (1)
Bakelite plate
Read-out strip panel
Front-end board
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ARGO RPC details (2)
High-voltage connection
Closed ARGO chamber
Low-voltage connection
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RPC performance in the ARGO preliminary test

• Altitude effect

• Efficiency

TFE/ iBUT97/3
TFE/Ar/ iBUT75/15/10

• Time resolution

Gas mixture Ar/ i-C4H10 /C2H2F4
15/10/75 Operating voltage 7.2 kV (10.2 kV at
sea level) Single RPC absorption current _at_ 7.2 kV
3-4 mA Single RPC count rate _at_ 7.2 kV 4 kHz
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Detector Layout
8 Strips 1 Pad (56 62 cm2)
10 Pads 1 RPC (2.80 1.25 m2)
Central Carpet 130 Clusters, 1560 RPCs, 124800
Strips
Layer of RPCs covering ?5600 m2 ( ? 92 active
surface) 0.5 cm lead converter sampling
guard ring
time resolution 1 ns space resolution 6.5
62 cm2 (1 strip)
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ARGO-YBJ Experimental Hall
Cluster
RPC chamber
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Trigger and Data Acquisition

• Shower mode
• a minimum Pad multiplicity is required on the
  central detector,
• with space/time consistency as for a shower
  front
• Scaler mode
• measurement of the Pad rate from each Cluster
• (integration time 0.5 s)
• Aim - detection of unexpected increases in
  CR flux (GRB, Solar flares )

Pad Multiplicity info
Local Station (basic unit of distributed DAQ
System)

• Central Station
• Trigger
• Data storage

DATA
Trigger
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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 Readout

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Sensitivity to the Crab and angular resolution
Minimum Detectable Flux (5 ? in 1 y)
N? (gt1 TeV) 10
T5? (gt1 TeV) 3 months
ARGO without any ?/h discrimination !
ARGO can observe, in 1 year, a Crab-like source
of intensity 0.7 Crab units at energies E gt 0.5
TeV, with a significance of 4 standard deviations.
Af 80 ? 80 m2
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g-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

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Summary of the main detector features and
performance

• 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.)

• 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 lt ? lt 70)

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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

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Trigger rates (threshold N gt 60 pads)
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Shower Front on 42 Clusters (41 x 46 m2)
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Event reconstruction with 42 clusters (PRELIMINARY
)
Zenith angle distribution
Direction cosine distributions
ltlgt -0.016 ltmgt 0.025
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DCS HV monitoring (16 clusters, 10/02/2005)
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DCS RPC current monitoring (16 clusters, August
2004)

• Average Total RPC current

• Average barometric pressure

• Average hall temperature

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Counting rate as a function of time
4 Clusters during 3.5 days
All Clusters react homogeneously to external
changes
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Analog Charge Readout event on 4 Clusters (180
m2) at YBJ (PRELIMINARY)
Full scale 4000 ADC counts 300 mV
1 m.i.p 2 mV
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Some events
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More events
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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