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The ARGO-YBJ experiment: results and perspectives

The ARGO-YBJ experiment: results and perspectives. Paolo Camarri on behalf of the ARGO-YBJ collaboration. University of Roma “Tor Vergata” and INFN. WAPP 2009. Darjeeling, India, December 10-11-12, 2009. The ARGO-YBJ Experiment. Collaboration Institutes: Chinese Academy of Science (CAS)

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The ARGO-YBJ experiment: results and perspectives

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  1. The ARGO-YBJ experiment: results and perspectives Paolo Camarri on behalf of the ARGO-YBJ collaboration University of Roma “Tor Vergata” and INFN WAPP 2009 Darjeeling, India, December 10-11-12, 2009 WAPP 2009 - Darjeeling, India December 10-11-12, 2009

  2. The ARGO-YBJ Experiment • Collaboration Institutes: • Chinese Academy of Science (CAS) • Istituto Nazionale di Fisica Nucleare (INFN) 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 Univesità “Tor Vergata”, Roma INAF/IFSI and INFN, Torino INAF/IASF, Palermo and INFN, Catania IHEP, Beijing Shandong University, Jinan South West Jiaotong University, Chengdu Tibet University, Lhasa Yunnan University, Kunming ZhengZhou University, ZhengZhou Hong Kong University, Hong Kong WAPP 2009 - Darjeeling, India December 10-11-12, 2009

  3. Outlook • Introduction • ARGO-YBJ detector features and performance • g-ray astronomy with ARGO-YBJ • Cosmic-ray astronomy with ARGO-YBJ • Conclusions WAPP 2009 - Darjeeling, India December 10-11-12, 2009

  4. Basic concepts for an unconventional air shower detector • HIGH ALTITUDE SITE (YBJ, 4300 m a.s.l) • FULL COVERAGE (RPC technology, 92%) • HIGH SEGMENTATION  see next slides … in order to: • image the shower front • reach an energy threshold of a few hundreds of GeV WAPP 2009 - Darjeeling, India December 10-11-12, 2009

  5. WAPP 2009 - Darjeeling, India December 10-11-12, 2009

  6. WAPP 2009 - Darjeeling, India December 10-11-12, 2009

  7. Current status • Data taking since November 2007 • Duty cycle ~ 90% • Trigger rate 3.6 kHz • Dead time 4% • 220 GB/day transferred to CNAF WAPP 2009 - Darjeeling, India December 10-11-12, 2009

  8. Sky survey -10° <δ< 70° (g-sources, anisotropies) • High exposure for flaring activity ( g-sources, GRBs, solar flares) • C.R. 1 TeV  104 TeV • p/p at TeV energies • hadronic interactions Helium spectrum Proton “knee” Knee region Physical Goals multi-purpose experiment by 2 operation modes: • scaler mode (counting rate, > 1 GeV) • shower mode (full reconstruction, > 300 GeV) WAPP 2009 - Darjeeling, India December 10-11-12, 2009

  9. The ARGO-YBJ detector WAPP 2009 - Darjeeling, India December 10-11-12, 2009

  10. The ARGO detector: bakelite Resistive Plate Chambers operated in streamer mode Graphite layer Bakelite plate Gas gap Bakelite plate Graphite layer PET spacers Gas-volume thickness: 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 @ 7.2 kV = 3 - 4 mA Single RPC count rate @ 7.2 kV = 4 kHz WAPP 2009 - Darjeeling, India December 10-11-12, 2009

  11. Digital and analog read-out Big Pad for charge read-out (1.40 × 1.25 m2) Space time pixel (56 × 62 cm2) Pixel for digital read-out (6.7 × 62 cm2) WAPP 2009 - Darjeeling, India December 10-11-12, 2009

  12. Operation Modes • Shower Mode: • Detection of Extensive Air Showers (direction, size, core …) • Trigger : minimum number of fired pads within 420 ns • ≥ 20 fired pads on the central carpet: rate ~3.6 kHz • Aims: • cosmic-ray physics (above ~1 TeV) • VHE γ-astronomy (above ~300 GeV) • Scaler Mode: • Recording thecounting rates ( Nhit ≥1, ≥2, ≥3, ≥4) for each cluster at fixed time intervals (every 0.5 s) lowers the energy threshold down to ≈1 GeV • Aims: • flaring phenomena (high energy tail of GRBs, solar flares) • detector and environment monitor WAPP 2009 - Darjeeling, India December 10-11-12, 2009

  13. Environmental Parameters • All the parameters relevant to the detector operation are regularly monitored: temperature, pressure, etc. WAPP 2009 - Darjeeling, India December 10-11-12, 2009

  14. Detector stability Accounting for the monitored changes in the atmospheric pressure the trigger rate is pretty stable, with relative fluctuation ~ 0.5% @ 1s WAPP 2009 - Darjeeling, India December 10-11-12, 2009

  15. Shower recostruction Fired pads on the carpet Arrival time vs position time (ns) meters Arrival direction measurement: • Core reconstruction: Maximum Likelihood Method applied to the lateral density profile of the shower • Fit of the shower front with a conical shape WAPP 2009 - Darjeeling, India December 10-11-12, 2009

  16. Analog readout Strip E ~ 1000 TeV Big Pad This will extend the dynamics of the detector up to and beyond 1 PeV WAPP 2009 - Darjeeling, India December 10-11-12, 2009

  17.  astronomy • Crab • Mrk 421 • Sky survey/galactic plane no /h discrimination applied so far WAPP 2009 - Darjeeling, India December 10-11-12, 2009

  18. Sources at > 3 s2007, day 311 - 2009, day 89 (424 equivalent days) Galactic • Crab 7.8s • MGRO J2031+41 (LAT pulsar) 3.6 s • PSR J2021+4026 (LAT pulsar, gamma Cygni SNR) 3.5 s • HESS J1841-055 (unidentified) 3.2 s Extragalactic • Mrk421 7.5s • Blazar B3 0650+453 (FSRQ z=0.993) 3.2 s WAPP 2009 - Darjeeling, India December 10-11-12, 2009

  19. Crab energy spectrum dN/dE = (3.73 ± 0.80)·10-11 E –2.67 ±0.25 ev cm –2 s –1 TeV –1 WAPP 2009 - Darjeeling, India December 10-11-12, 2009

  20. Mrk 421 X-rays ASM/RXTE TEST DATA July-August 2006 FULL ARGO 2006 2008 2007 WAPP 2009 - Darjeeling, India December 10-11-12, 2009

  21. Mrk 421 - July-August 2006 (test data) N PAD > 40 Excess distribution degrees 6 s.d. Mrk 421 Standard deviations obs. time ≈ 109 hours Flux ≈ 3-4 Crab WAPP 2009 - Darjeeling, India December 10-11-12, 2009

  22. Mrk 421 - 2008 10 days average ARGO NPAD > 100 ASM/RXTE days from 1-1-08 WAPP 2009 - Darjeeling, India December 10-11-12, 2009

  23. Mrk 421 spectrum (2008, days 41 – 180) Integral flux (E > 1 TeV) (4.9 ± 2.0) ·10-11 ev cm –2 s –1 ≈2 ×Crab from:Primack et al. AIP conf Proc 745, 23, 2005 Power law spectrum + EBL absorption : dN/dE = (7.5 ± 1.7)· 10-11 E –2.51 ±0.29 e-t(E) ev cm –2 s –1 TeV –1 WAPP 2009 - Darjeeling, India December 10-11-12, 2009

  24. Mrk 421 - June 2008 June 11-13 4.2 s June 5-7 3.0 s NPAD > 100 3 days average ARGO 1 day average ASM/RXTE WAPP 2009 - Darjeeling, India December 10-11-12, 2009

  25. June 11-13, 2008 4.2 s WAPP 2009 - Darjeeling, India December 10-11-12, 2009

  26. Event rate NPAD > 100 Expected from theoretical SED WAPP 2009 - Darjeeling, India December 10-11-12, 2009

  27. Comments on the MRK 421 2008 flares • Considering the first flare, the integral flux measured by ARGO-YBJ above 1 TeV and averaged over 3 days is about 1.5 times higher than the flux measured by VERITAS on June 6, but still marginally consistent with it. • The intensity of the second flare allows us to assess its spectral shape. The deabsorbed spectrum can be fitted by a power law extending up to several TeV. This spectrum appears definitively harder than that predicted on the basis of June 12-13 data collected up to GeV energies (AGILE; Donnarumma et al., ApJ 691, L13, 2009). • However, the ARGO-YBJ data fully satisfy the relation between the spectral index and the flux obtained analyzing the Whipple measurements of Mrk421 since 1995 (Krennrich et al., ApJ 575, L9, 2002). • ARGO-YBJ paper: “GAMMA RAY FLARES FROM MRK421 IN 2008 OBSERVED WITH THE ARGO-YBJ DETECTOR”, submitted to ApJ Letters on Nov. 27th, 2009. WAPP 2009 - Darjeeling, India December 10-11-12, 2009

  28. 542 days 2007, day 311–2009, day 220 Galactic plane PSR J2021+4026 MGRO J2031+41 HESS J1841-055 CRAB WAPP 2009 - Darjeeling, India December 10-11-12, 2009 nhit > 40Smoothing window radius = 1.3°

  29. HESS J1841-055 Tobs = 10 h 10.7 s Extension 0.8° 0.5° dN/dE = (1.28 ±0.13) 10-11 E-2.41g cm-2 s-1 TeV-1 for E = 0.5 – 80 TeV ~ 30% Crab In ARGO: 8.5 ev/day WAPP 2009 - Darjeeling, India December 10-11-12, 2009 Aharonian et al., A&A 477, 353-363 (2008)

  30. GRB • Scaler mode 1-100 GeV • Shower mode 10-1000 GeV • Upper limits to the fluence ( 10-5 erg/cm2) • Upper limits to the cutoff energy as a function of the spectral index (1-100 GeV) WAPP 2009 - Darjeeling, India December 10-11-12, 2009

  31. GRB Sample (for ICRC09) • Total number of GRBs analyzed: 66 • With known redshift: 11 • Long duration GRBs (> 2s): 58 • Short duration GRBs (≤ 2s): 8 mean s = 0.06 The distribution of the statistical significances is compared with a standard normal distribution WAPP 2009 - Darjeeling, India December 10-11-12, 2009

  32. Referenced Papers • Search for Gamma Ray Bursts with the ARGO-YBJ detector in • scaler mode, Astrophysical Journal 699 (2009) 128 • → Upper limits to the fluence of 62 GRBs (9 with redshift z) • in the energy range 1- 100 GeV • 2) ARGO-YBJ constraints on very high energy emission from GRBs, • Astroparticle Physics 32 (2009) 47 • → Upper limits to the fluence of 26 GRBs (6 with z) in the • ranges 10- 100 GeV and 10 - 1000 GeV WAPP 2009 - Darjeeling, India December 10-11-12, 2009

  33. GRB090902B • Detected by Fermi GBM at 11:05:08 UT (T0) and zenith angle • θ = 23.1° (uncertainty = 1.0°), with a duration T90 = 25 s • Detected by Fermi LAT at 11:05:15 UT (uncertainty = 2.4 '): • within 100 s → >30 events with E >1 GeV • 82 s after T0 → photon with E = 33.4 GeV (record!) • extended emission at GeV energies • (common feature of high energy emission?) • Scaler data analysis WAPP 2009 - Darjeeling, India December 10-11-12, 2009

  34. GRB090902B: Upper Limit • The spectrum obtained with both GBM and LAT data is well • fitted by a Band function + underlying single power law • Fluences of the Band component: F = 3.74104 erg/cm2 • Fluence of the whole GBM + LAT emission: • F(8 keV30 GeV) = 4.86104 erg/cm2 • Extrapolated fluence, considering absorption in EBL (z =1.8): • F(1100 GeV) = 5.9105 erg/cm2 • Upper limit to fluence during T90, considering absorption: • F(1100 GeV) = 1.4104 erg/cm2 • Upper limit to the cutoff energy, without absorption in EBL: • Ecut = 130 GeV WAPP 2009 - Darjeeling, India December 10-11-12, 2009

  35. Cosmic Rays • Medium scale anisotropies • Moon shadow and the anti-p/p ratio • Proton-air cross section WAPP 2009 - Darjeeling, India December 10-11-12, 2009

  36. Medium scale anisotropy(preliminary) 542 days 2007 day 311–2009 day 220 Smoothing window radius = 5° nhit > 40  0.06%  0.1% Proton median energy  2 TeV WAPP 2009 - Darjeeling, India December 10-11-12, 2009

  37. MILAGRO ARGO WAPP 2009 - Darjeeling, India December 10-11-12, 2009

  38. The Moon shadow on cosmic rays • Size of the deficit Þangular resolution • Position Þ pointing accuracy • West displacement Þ Energy calibration Geomagnetic bending »1.57° × Z / E (TeV) WAPP 2009 - Darjeeling, India December 10-11-12, 2009

  39. The angular width in the N-S direction using the Moon shadow Based on the Robust method reconstruction WAPP 2009 - Darjeeling, India December 10-11-12, 2009

  40. The Earth-Moon system as a spectrometer The Moon shadow can be used to put limits on the antiparticle flux. In fact, if protons are deflected towards the West, antiprotons are deflected towards the East. If the displacement is large and the angular resolution is small enough, we can distinguish between the 2 shadows. If no event deficit on the antimatter side is observed, an upper limit on the antiproton content can be calculated. WAPP 2009 - Darjeeling, India December 10-11-12, 2009

  41. Data (2006 + 2007 + 2008) n Pad > 100 Significance: ~ 43 s  9 standard deviations /month WAPP 2009 - Darjeeling, India December 10-11-12, 2009

  42. 43 s.d. PSF of the detector Moon shadow: all data (2006+2007+2008) N > 60 θ < 50° 2063 hours on-source »9 standard deviations / month WAPP 2009 - Darjeeling, India December 10-11-12, 2009

  43. Antiproton/proton ratio at TeV energies G. Di Sciascio et al. ICRC 2009 arXiv:0907.1164 WAPP 2009 - Darjeeling, India December 10-11-12, 2009

  44. Proton-air cross section measurement(Physical Review D 80, 092004, 2009) Use the shower frequency vs (sec q -1) for fixed energy and shower age. The lenght Ldiffers from the p interaction lenght mainlybecause of collision inelasticity, shower fluctuations and detector resolution. It has been shown that L = k lint , where k is determined by simulations and depends on: • Take care of shower fluctuations • Constrain XDO = Xdet – X0 or • XDM = Xdet – Xmax • Select deep showers (large Xmax, • i.e. small XDM) • Exploit the detector features (space-time pattern) and location (depth). • hadronic interactions • detector features and location (atm. depth) • actual set of experimental observables • analysis cuts • energy, ... Then: sp-Air (mb) = 2.4· 104 / lint(g/cm2) WAPP 2009 - Darjeeling, India December 10-11-12, 2009

  45. Experimental data Weather effects, namely the atmospheric pressure dependence on time, have been shown to be at the level of less than 1 % h0MC = 606.7 g/cm2 (4300m a.s.l. standard atm.) h0MC / h0 = 0.988 ± 0.007 Clear exponential behaviour Full consistency with MC simulation at each selection step WAPP 2009 - Darjeeling, India December 10-11-12, 2009

  46. The proton-air cross section arXiv:0904.4198 Extending the energy range with the analog readout WAPP 2009 - Darjeeling, India December 10-11-12, 2009

  47. WAPP 2009 - Darjeeling, India December 10-11-12, 2009

  48. Conclusions and perspectives • excellent detector performance • smooth running of the experiment with good parameters • duty cycle: 90% • trigger rate: 3.6 kHz • dead time: 4% • minimum shower size: 20 particles • Total integrated events > 2 × 1011 • imaging of the shower front successfully implemented • analysis to be extended beyond 100 TeV • studies to improve the reconstruction and the sensitivity in progress • many more relevant results on the way… WAPP 2009 - Darjeeling, India December 10-11-12, 2009

  49. WAPP 2009 - Darjeeling, India December 10-11-12, 2009

  50. Effective area for g-ray detection in ARGO-YBJ WAPP 2009 - Darjeeling, India December 10-11-12, 2009

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