1. RPC 2007 - Mumbai, February 13-16, 2008 Operation and performance of RPCs in the ARGO-YBJ experiment P. Camarri University of Roma “Tor Vergata” and INFN Roma Tor Vergata

2. RPC 2007 - Mumbai, February 13-16, 2008 The ARGO-YBJ Collaboration 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 Spokesman: B. D’Ettorre Piazzoli Spokesman: Z. Cao Collaboration Institutes: Chinese Academy of Science (CAS) Istituto Nazionale di Fisica Nucleare (INFN)

3. RPC 2007 - Mumbai, February 13-16, 2008 The ARGO-YBJ site

4. RPC 2007 - Mumbai, February 13-16, 2008 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 of Lhasa A strophysical R adiation with G round-based O bservatory

5. RPC 2007 - Mumbai, February 13-16, 2008 A new generation of EAS arrays Low energy threshold < 500 GeV Increase sensitivity Φ  Φ crab  10 -1 Φ crab The Goal High altitude operation Secondary photon conversion Increase the sampling (~1%  100%) The Solution - Improves angular resolution - Lowers energy threshold

6. RPC 2007 - Mumbai, February 13-16, 2008 ARGO-YBJ Physics Goals   -ray astronomy Search for point-like galactic and extra-galactic sources at few hundreds GeV energy threshold 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 ratio at TeV energy Spectrum and composition around the “knee” (E > 10 TeV)Spectrum and composition around the “knee” (E > 10 TeV)  Sun and heliosphere physics (E > 10 GeV)

7. RPC 2007 - Mumbai, February 13-16, 2008 The ARGO detector: bakelite Resistive Plate Chambers operated in streamer mode Gas-volume thickness : 2mm Gas gap Bakelite plate Graphite layer Bakelite plate Graphite layer PET spacers

8. RPC 2007 - Mumbai, February 13-16, 2008 RPC performance in the ARGO preliminary test (1998) Efficiency Time resolution Gas mixture: Ar / i-C 4 H 10 / C 2 H 2 F 4 = 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

9. RPC 2007 - Mumbai, February 13-16, 2008 Installation of the experiment 16 clusters (~ 700 m 2 ) in stable data taking for 10 months (Jan 2004 till October 2004) 42 clusters (~ 1900 m 2 ) in data taking since the end of 2004. 100-110 clusters (~ 4500 m 2 ) started taking data at the end of 2005. 130 clusters (complete full-coverage central carpet) taking data since July 2006. 153 clusters (full-coverage central carpet plus 23 guard-ring clusters) in data taking since October 2007.

10. RPC 2007 - Mumbai, February 13-16, 2008 78 m 99 m74 m 111 m Operating Detector Layout (since October 2007) 10 Pads = 1 RPC (2.80  1.25 m 2 ) 12 RPC =1 Cluster ( 5.7  7.6 m 2 ) 8 Strips = 1 Pad (56  62 cm 2 ) time resolution ~ 1 ns space resolution = 6.5  62 cm 2 (1 strip) Overall: 153 Clusters, 1836 RPCs, 146880 FE channels angular resolution 2 TeV, θ < 40 °

11. RPC 2007 - Mumbai, February 13-16, 2008 ARGO-YBJ Experimental Hall RPC chamber Cluster

12. RPC 2007 - Mumbai, February 13-16, 2008 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 ( trigger rate: 4 - 4.5 kHz for N > 20 )  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 …) Local Station (basic unit of distributed DAQ System) Central Station Trigger Data storage Trigger Pad Multiplicity info DATA

13. RPC 2007 - Mumbai, February 13-16, 2008 Detector Control System (DCS) and Analog Charge readout DCS  High voltage control and monitoring  Monitoring of environmental parameters (indoor and outdoor temperature, atmospheric pressure, relative humidity)  HV fine tuning (to be implemented soon)  RPC current monitoring The DCS is crucial for detecting anomalous detector behaviour and performing the required actions to protect the system. Analog Charge Readout BIG PAD ADC RPC Measurement of the charge induced on the big pads

14. RPC 2007 - Mumbai, February 13-16, 2008 DCS: environmental-parameter monitoring (January-February 2008) TEMPERATURE @ YBJ: OUISIDE (blue) AND INSIDE (purple) BAROMETRIC PRESSURE @ YBJ

15. RPC 2007 - Mumbai, February 13-16, 2008 RPC current distribution OVERALL RPC CURRENT DISTRIBUTION  The current distribution is mainly contained between 2 and 6  A,  At present, no current value greater than 8  A is recorded.  A great number of chambers has been working for over 4 years (with interruptions only due to maintenance interventions) with no sign of irreversible current increase.  Almost all the RPCs with high current in the past were found to have problems with the gas flow (e.g. pipe obstruction or disconnection)

16. RPC 2007 - Mumbai, February 13-16, 2008 Temperature – gap current correlation The current trends are extremely stable after 4 months of continuous operation The current trends are extremely stable after 4 months of continuous operation The RPC current is correlated linearly with the temperature. The linear correlation is a maximum if a delay of about 70 mins between the measured temperature and the measured RPC current is accounted for The RPC current is correlated linearly with the temperature. The linear correlation is a maximum if a delay of about 70 mins between the measured temperature and the measured RPC current is accounted for A regular measurement of the slope of the linear fit (typical value: 0.5 - 0.6  / °C) is another tool to check the system stability. A regular measurement of the slope of the linear fit (typical value: 0.5 - 0.6  / °C) is another tool to check the system stability.

17. RPC 2007 - Mumbai, February 13-16, 2008 RPC time calibration RPC time calibration  The off-line time-calibration procedure (using a conical-fit algorithm for the shower front) was able to equalize the time responses of the ARGO pads. The standard deviation of the residual distribution turns out to be less than 60 ps.

18. RPC 2007 - Mumbai, February 13-16, 2008 Shower recostruction Fired pads on the carpetArrival time vs position Arrival direction measurement:  Core reconstruction: Maximum Likelihood Method applied to the lateral density profile of the shower (Li and Ma, 1983)  Fit of the shower front with a cone of slope 0.03 ns m -1 time (ns) meters

19. RPC 2007 - Mumbai, February 13-16, 2008 An event on 130 clusters Palette colour = number of fired strips on a pad

20. RPC 2007 - Mumbai, February 13-16, 2008 Angular resolution - from MC Definition:  72 = radius of the circular window containing 72% of the signal If the PSF is gaussian  72 is the value that maximizes the signal to noise ratio and  =  72 / 2

21. RPC 2007 - Mumbai, February 13-16, 2008 The ARGO detector can perform a continuous observation of a large fraction of the sky searching for  unknown g ray sources  transient events as AGN flares and GRBs  Large field of view ( > 2 sr)  High duty cycle (  100 %) Gamma-ray astronomy

22. RPC 2007 - Mumbai, February 13-16, 2008 The first signal: a “negative” source... Geomagnetic bending  1.6° / E (TeV)

23. RPC 2007 - Mumbai, February 13-16, 2008 Moon shadow – ARGO-YBJ data Number of PADS > 500 Median energy  5 TeV time  500 hours (from July 2006 to February 2007) Position of the maximum deficit: x = 0.04 ° y = 0.14 ° Simulations x = - 0.3 ° y = 0.0 °  10 standard deviations West East Geomagnetic shift

24. RPC 2007 - Mumbai, February 13-16, 2008 Width of the Moon shadow  = 0.43°  0.06  = 0.51°  0.09 West-East South-North

25. RPC 2007 - Mumbai, February 13-16, 2008 Sun shadow – ARGO data degrees Excess distribution Standard deviations Sun shadow  6 standard deviations time = 208 hours (from July to October 2006) Number of PADS > 500

26. RPC 2007 - Mumbai, February 13-16, 2008 First gamma-ray sources observations...

27. RPC 2007 - Mumbai, February 13-16, 2008 Mrk 421 ASM/RXTE X-rays data July-August 2006 active period 7.5 years data Julian date Counts/s one day average

28. RPC 2007 - Mumbai, February 13-16, 2008 Mrk 421 - ARGO-YBJ data degrees > 5 standard deviations time  80 hours (July - August 2006) Excess distribution Standard deviations Number of PADS > 60 Mrk421 preliminary

29. RPC 2007 - Mumbai, February 13-16, 2008 Crab Nebula - ARGO data degrees  5 standard deviations time  290 hours (July 2006 – March 2007) Equivalent time  50 days Excess distribution Standard deviations Number of PADS > 200 Crab preliminary

30. RPC 2007 - Mumbai, February 13-16, 2008 Conclusions  The complete ARGO RPC carpet has been fully operational since October 2007.  All the subsystems (DAQ, DCS) are working good.  No problems with high current seen, except isolated cases due to bad gas flow.  Angular resolution as expected  Moon and Sun shadows observed  Mrk421 flare observed in July-August 2006 at > 5 s.d.  Crab Nebula observed at > 5 s.d. in  50 days.  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.

31. RPC 2007 - Mumbai, February 13-16, 2008 ARGO RPC details (1) Bakelite plate Read-out strip panel Front-end board

32. RPC 2007 - Mumbai, February 13-16, 2008 ARGO RPC details (2) Closed ARGO chamber High-voltage connection Low-voltage connection

33. RPC 2007 - Mumbai, February 13-16, 2008 Angular resolution – from data “even-odd” method Good agreement with MC To be divided by 2 to have the angular resolution

34. RPC 2007 - Mumbai, February 13-16, 2008 Gap-width rescaling TFE/ iBUT=97/3 TFE/Ar/ iBUT=75/15/10