1. Cosmic-Ray Detection at the ARGO-YBJ observatory P. Camarri University of Roma “Tor Vergata” INFN Roma Tor Vergata

2. P. Camarri - WAPP 2011 - Darjeeling, India - Dec 2011 2 TeV gamma-ray astronomy

3. P. Camarri - WAPP 2011 - Darjeeling, India - Dec 2011 3 TeV γ -ray astronomy: science topics

4. P. Camarri - WAPP 2011 - Darjeeling, India - Dec 2011 4 The gamma-ray spectrum 10 6 10 9 10 12 10 15 10 18 eV Satellites Cerenkov Telescopes EAS arrays HAFC EAS arrays 1 MeV 1 GeV 1 TeV 1 PeV 1 EeV  -ray sources: naturally multiwavelength Physics targets for  -ray astronomy Galactic sources  Supernova Remnants  Plerions  Shell type SNR  Pulsars  Diffuse emission from the galactic disk  Unidentified Sources Extragalactic sources  Active Galactic Nuclei (blazars)  Gamma Ray Bursts Cosmological γ –ray Horizon  Probe of the Extragalactic Background Light (EBL) Absolute necessity of multiwavelength observations

5. P. Camarri - WAPP 2011 - Darjeeling, India - Dec 2011 5 TeV γ -rays: production processes

6. P. Camarri - WAPP 2011 - Darjeeling, India - Dec 2011 6 TeV γ -rays: production processes

7. P. Camarri - WAPP 2011 - Darjeeling, India - Dec 2011 7 Satellite vs Ground-based detectors Satellite:  lower energy  primary detection  small effective area ~1m 2 lower sensitivity  large duty-cycle  large cost  low bkg Ground based:  higher energy  secondary detection  huge effective area ~10 4 m 2 higher sensitivity  Small/large duty-cycle  low cost  high bkg

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10. 10 Statistical significance Excess of events coming from the source over the estimated background standard deviations

11. P. Camarri - WAPP 2011 - Darjeeling, India - Dec 2011 11 …background showers induced by primary Cosmic Rays No possible veto with an anticoincidence shield as in satellite experiments  CRAB ( >1 TeV)  2 ·10 -11 ph/cm 2 · s  bkg ( >1 TeV) ·  (= 1 msr)  1.5 ·10 -8 nuclei/cm 2 ·s Cosmic Ray showers  γ -ray showers … fortunately, some difference does exist !! In addition… Ground based  -Ray Astronomy requires a severe control and rejection of the BKG. The main drawback of ground-based measurements

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15. P. Camarri - WAPP 2011 - Darjeeling, India - Dec 2011 15 Detecting Extensive Air Showers Classical EAS arrays High energy threshold (  50 TeV) Moderate bkg rejection (  50 %) Modest sensitivity (   crab ) Modest energy resolution High duty-cycle (> 90 %) Large field of view (~2 sr) detection of the charged particles in the shower Air Cherenkov Telescopes Very low energy threshold (  60 GeV) Good background rejection (99.7 %) High sensitivity (< 10 -2  crab ) Good energy resolution Low duty-cycle (~ 5-10 %) Small field of view  < 4° detection of the Cherenkov light from charged particles in the EAS The classical solution for ground based  –ray astronomy

16. P. Camarri - WAPP 2011 - Darjeeling, India - Dec 2011 16 The birth of TeV γ -ray astronomy Discovery of the emission of photons with E > 0.7 TeV coming from the Crab Nebula by the Whipple Cherenkov telescope in 1989: 50 h per 5σ HESS: 30 seconds !

17. P. Camarri - WAPP 2011 - Darjeeling, India - Dec 2011 17 The TeV sky

18. P. Camarri - WAPP 2011 - Darjeeling, India - Dec 2011 18 Why an EAS array ? Provides synoptic view of the sky Sees an entire hemisphere every day Large fov & high duty-cycle GRBs Transient astrophysics Extended objects New sources Excellent complement to satellites ACTs can monitor only a limited number of sources / year at stated sensitivity A sensitive EAS array is needed to extend the FERMI/GLAST measurements at > 100 GeV.

19. P. Camarri - WAPP 2011 - Darjeeling, India - Dec 2011 19 A new-generation EAS array Low energy threshold < 500 GeV Increased 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

20. P. Camarri - WAPP 2011 - Darjeeling, India - Dec 2011 20 The ARGO-YBJ experiment ARGO detects air-shower particles at ground level wide field of view gamma-ray telescope which operates in “scanning mode”ARGO is a wide field of view gamma-ray telescope which operates in “scanning mode” ARGO is optimized to work with showers induced by primaries of energy E > a few hundred GeV Excellent complement to AGILE/GLAST to extend satellite measurements at > 100 GeV This low energy threshold is achieved by:  operating at very high altitude (4300 m asl)  using a “full-coverage” detection surface

21. P. Camarri - WAPP 2011 - Darjeeling, India - Dec 2011 21 Longitude 90° 31’ 50” East Latitude 30° 06’ 38” North 90 Km North from Lhasa (Tibet) An Extensive Air Shower detector exploiting the full-coverage approach at very high altitude, with the goal of studying The ARGO-YBJ experiment Tibet AS γ ARGO The Yangbajing Cosmic Ray Laboratory VHE  -Ray Astronomy  -Ray Burst Physics Cosmic-Ray Physics 4300 m above the sea level

22. P. Camarri - WAPP 2011 - Darjeeling, India - Dec 2011 22 10 Pads = 1 RPC (2.80  1.25 m 2 ) Gas Mixture: Ar/ Iso/TFE = 15/10/75, HV = 7200 V 78 m 99 m74 m 111 m Layer of RPC covering  5600 m 2 (  92% active surface) (+ 0.5 cm lead converter) + sampling guard-ring Central Carpet: 130 Clusters 1560 RPCs 124800 Strips BIG PAD ADC RPC Read-out of the charge induced on “Big-Pads” 12 RPC =1 Cluster ( 5.7  7.6 m 2 ) 8 Strips = 1 Pad (56  62 cm 2 )

23. The ARGO-YBJ Resistive Plate Chambers P. Camarri - WAPP 2011 - Darjeeling, India - Dec 2011 Gas mixture: C 2 H 2 F 4 /Ar/iC 4 H 10 = 75/15/10 Operated in streamer mode Time resolution ~ 1.5 ns 23

24. P. Camarri - WAPP 2011 - Darjeeling, India - Dec 2011 24 Fired pads on the carpet Arrival time vs position time (ns) meters Shower recostruction

25. Analog read-out 0 Fs: 4000 -> 1300/m 2 It is crucial to extend the dynamics of the detector for E > 100 TeV, when the strip read-out information starts to become saturated. Max fs: 6500 part/m 2 0 4000 3500 3000 2500 2000 1500 1000 500 P. Camarri - WAPP 2011 - Darjeeling, India - Dec 2011 25

26. Detector Pixels Cluster = DAQ unit = 12 RPCs RPC Strip Strip = Strip = SPACE PIXEL, 6.5 x 62 cm 2, 124800 BigPa d BigPad = BigPad = CHARGE readout PIXEL, 120 x 145 cm 2, 3120 Pad Pad = Pad = TIME PIXEL, 56 x 62 cm 2, 15600 σ t ≈1 ns P. Camarri - WAPP 2011 - Darjeeling, India - Dec 2011 26

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28. P. Camarri - WAPP 2011 - Darjeeling, India - Dec 2011 Operational Modes Object: flaring phenomena (high energy tail of GRBs, solar flares) detector and environment monitor Recording the counting rates (N hit ≥1, ≥2, ≥3, ≥4) for each cluster at fixed time intervals (every 0.5 s) lowers the energy threshold down to ≈ 1 GeV. No information on the arrival direction and spatial distribution of the detected particles. :  Scaler Mode: Detection of Extensive Air Showers (direction, size, core …) Coincidence of different detector units (pads) within 420 ns Trigger : ≥ 20 fired pads on the central carpet (rate ~3.6 kHz) Object: Cosmic Ray physics (above ~1 TeV) VHE γ-astronomy (above ~300 GeV)  Shower Mode: INDEPENDENT DAQ 28

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30. P. Camarri - WAPP 2011 - Darjeeling, India - Dec 2011 30 The Moon Shadow Size of the deficit Position of the deficit Angular Resolution Pointing Error Geomagnetic Field: positively charged particles deflected towards the West and negatively charged particles towards the East. Ion spectrometer The observation of the Moon shadow can provide a direct check of the relation between size and primary energy Energy calibration Cosmic rays are hampered by the Moon Deficit of cosmic rays in the direction of the Moon Moon diameter ~0.5 deg

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32.  -ray astronomy Crab Nebula Mrk 421 MGRO 1908+06 Cygnus region and more… no γ/h discrimination applied so far P. Camarri - WAPP 2011 - Darjeeling, India - Dec 2011 32

33. γ/h discrimination Some algorithms developed based on  2-D topology  Time profile  Time distribution Q factor = 1.2 - 3 depending on the number of fired pads Very heavy, fine tuning needed Many months for data reprocessing P. Camarri - WAPP 2011 - Darjeeling, India - Dec 2011 33

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39. P. Camarri - WAPP 2011 - Darjeeling, India - Dec 2011 Cosmic-Ray Physics Spectrum of the light component (1-100 TeV) Medium and large scale anisotropies The anti-p/p ratio 39

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44. P. Camarri - WAPP 2011 - Darjeeling, India - Dec 2011 44 The Earth-Moon system as a spectrometer The shadow of the Moon can be used to put limits on antiparticle flux. In fact, if proton are deflected towards West, antiprotons are deflected towards East. If the displacement is large and the angular resolution small enough we can distinguish between the 2 shadows. If no event deficit on the antimatter side is observed an upper limit on antiproton content can be calculated.

45. P. Camarri - WAPP 2011 - Darjeeling, India - Dec 2011 (under peer reviewing for publication on PRD) 45

46. Conclusions (2)  -ray astronomy in the energy range above ~300 GeV can only be investigated by ground-based Cherenkov and EAS detectors. The ARGO-YBJ experiment, a full-coverage EAS array at high altitude, is giving very nice results in TeV  -ray astronomy and cosmic-ray physics at E > 1 TeV. By exploiting the analog read-out of its RPCs, it will be possible to study the energy region around the “knee” up to ~10 16 eV. P. Camarri - WAPP 2011 - Darjeeling, India - Dec 2011 46

47. P. Camarri - WAPP 2011 - Darjeeling, India - Dec 2011 47 A few references http://tevcat.uchicago.edu/reviews.html G. Di Sciascio and L.Saggese, Towards a solution of the knee problem with high altitude experiments Invited contribution to the Book "Frontiers in Cosmic Ray Research", 2007 Nova Science Publishers, New York, Ed. I.N. Martsch, Chapter 3, pp. 83 - 130.