Hadronic Interaction Studies with ARGO-YBJ Ivan De Mitri University of Salento and Istituto Nazionale di Fisica Nucleare Lecce, Italy On behalf of the ARGO-YBJ Collaboration Hadron-Hadron & Cosmic Ray Interactions at multi-TeV Energies ECT*, Trento, Nov 29-Dec 3, 2010
The ARGO-YBJ experiment ARGO-YBJ High Altitude Cosmic Ray Observatory @ YangBaJing,Tibet, China Site Altitude: 4,300 m a.s.l. , ~ 600 g/cm 2 ECT* - HH & CR - 2010 I.De Mitri: Hadronic Interaction studies with ARGO-YBJ 2
ARGO-YBJ physics goals � Cosmic ray physics : spectrum and composition (E th few TeV), study of the shower space-time structure , p-Air cross section measurement and hadint studies anti-p / p ratio at TeV energies, ….. � VHE γ -Ray Astronomy : ( search for)/(study of) point-like (and diffuse) galactic and extra-galactic sources at few hundreds GeV energy threshold � Search for GRB’s (full GeV / TeV energy range) � … through the… Observation of Extensive Air Showers produced in the atmosphere by primary γ ’s and nuclei ECT* - HH & CR - 2010 I.De Mitri: Hadronic Interaction studies with ARGO-YBJ 3
The ARGO-YBJ detector 99 m 74 m 8 Strips 10 Pads 1 CLUSTER = 12 RPC (6.5 x 62 cm 2 ) (56 x 62 cm 2 ) ( ∼ 43 m 2 ) for each Pad for each RPC 78 m 111 m RPC Strip = space pixel Pad = time pixel + Analog charge read-out on “Big Pads” Time resolution ~1.7 ns ECT* - HH & CR - 2010 I.De Mitri: Hadronic Interaction studies with ARGO-YBJ 4
RPC performance and linearity range By means of the RPC analog readout ECT* - HH & CR - 2010 I.De Mitri: Hadronic Interaction studies with ARGO-YBJ 5
EAS reconstruction Event Rate ~ 3.6 kHz for N hit >20 High space/time granularity detailed study on the + Full coverage EAS space/time structure + High altitude with unique capabilities 3-D view of a detected shower Top view of the same shower ECT* - HH & CR - 2010 I.De Mitri: Hadronic Interaction studies with ARGO-YBJ 6
The Moon Shadow 55 s.d. Number of sigma’s 3200 hours on-source � Size of the deficit ⇒ angular resolution � Position ⇒ pointing accuracy � West displacement ⇒ Energy calibration (Geomagnetic bending ≈ 1.57 ° / E (TeV) ) � Antiprotons should give a shadow on the opposite side ⇒ Upper limit ECT* - HH & CR - 2010 I.De Mitri: Hadronic Interaction studies with ARGO-YBJ 7
VHE gamma-ray astronomy All sky survey in the 1 – – 30 30 TeV TeV energy band energy band All sky survey in the 1 3 sources with significance >5 σ in ~800 days (July 06 – Dec. 09) Crab 14 σ , Mrk421 12 σ , MGRO J1908+06 6 σ Interesting results on long term variabilities, correlation with Xrays, spectra,…. Evidence for a signal at ≈ 4 s.d. from Mean = -9.3 ± 2.1 10 -3 the MGRO J2031+41 region. Sigma = 1.008 ± 0.002 Crab Mrk421 8 ECT* - HH & CR - 2010 I.De Mitri: Hadronic Interaction studies with ARGO-YBJ 8
Light- -component spectrum of component spectrum of CRs CRs Light Measurement of the light-component (p+He) spectrum of primary CRs in the energy region (5 – 250) TeV via a Bayesian unfolding procedure. EAS-TOP + MACRO Horandel p+He CREAM p+He The contribution of heavier nuclei to the trigger is a few % CREAM He ARGO data agree with CREAM results CREAM p Evidence that the proton ARGO p+He p+He preliminary preliminary ARGO spectrum is flatter than in the lower energy region For the first time direct and ground- -based measurements overlap for a wide based measurements overlap for a wide For the first time direct and ground energy range thus making possible the cross- -calibration of the experiments. calibration of the experiments. energy range thus making possible the cross ECT* - HH & CR - 2010 I.De Mitri: Hadronic Interaction studies with ARGO-YBJ 9
Proton-air cross section measurement Use the shower frequency vs (sec θ -1) 0 X X rise h ( ) − θ − o sec 1 θ = ⋅ h 0 Λ I ( ) I ( 0 ) e x X DM a for fixed energy and shower age. m X θ The lenght Λ is not the p interaction lenght mainly because of collision inelasticity, shower fluctuations and detector resolution. It has been shown that Λ = k λ int , where k is Take care of shower fluctuations determined by simulations and depends on: • Constrain X DO = X det – X 0 or � hadronic interactions � detector features and location (atm. depth) X DM = X det – X max � actual set of experimental observables • Select deep showers (large X max , � analysis cuts i.e. small X DM ) � energy, ... • Exploit detector features (space- σ p-Air (mb) = 2.4 10 4 / λ int (g/cm 2 ) time pattern) and location (depth). Then: ECT* - HH & CR - 2010 I.De Mitri: Hadronic Interaction studies with ARGO-YBJ 10
The position of the shower maximum (and its rms) ARGO-YBJ vertical depth ECT* - HH & CR - 2010 I.De Mitri: Hadronic Interaction studies with ARGO-YBJ 11
Data selection � Event selection based on: (a) “shower size” on detector, N strip (strip multiplicity) R 70 : radius of circle including (b) core reconstructed in a fiducial area (64 x 64 m 2 ) 70% of hits (c) constraints on Strip density (> 0.2/m 2 within R 70 ) and shower extension (R 70 < 30m) N strip is used to get different E sub-samples Full Monte Carlo simulation: Corsika showers QGSJET-I and QGSJET-II , SYBILL int. models GEANT detector simulation ECT* - HH & CR - 2010 I.De Mitri: Hadronic Interaction studies with ARGO-YBJ 12
MC vs DATA The distribution of the observable quantities before and after the analysis cuts are in good agreement with the MC data The fraction of events passing the analysis cut is consistent (at each step) with the correponding MC estimate ECT* - HH & CR - 2010 I.De Mitri: Hadronic Interaction studies with ARGO-YBJ 13
Cuts in-dependence on the zenith angle Energy X det –X max No significant zenith angle dependence below 30 degrees. A slight shift might be seen above 40 degrees. In this analysis we stop at 40 degrees ECT* - HH & CR - 2010 I.De Mitri: Hadronic Interaction studies with ARGO-YBJ 14
Experimental data Weather effects, namely the atmospheric Clear exponential behaviour pressure dependence on time, have been shown to be at the level of 1 % Full consistency with MC MC = 606.7 g/cm 2 ( 4300m a.s.l. standard atm .) h 0 simulation at each selection step MC / h 0 = 0.988 ± 0.007 h 0 ECT* - HH & CR - 2010 I.De Mitri: Hadronic Interaction studies with ARGO-YBJ 15
Heavy primaries proton contribution Hoerandel AP 19 (2003) 193 taken as reference. JACEE and RUNJOB for the evaluation of systematic error − γ ⎛ ⎞ Z dN E = Φ = Φ ⋅ ⎜ ⎟ 0 ( E ) helium Z ⎝ ⎠ dE TeV ECT* - HH & CR - 2010 I.De Mitri: Hadronic Interaction studies with ARGO-YBJ 16
QGSJET-I The spread among the models has been used in order to have a conservative estimate of QGSJET-II.03 the associated systematic uncertainties SIBYLL 2.1 k = k 0 ( inelasticity,CR spectrum, … )×k det ( det. Features,, analysis, … ) Correction factor for Glauber theory applied heavier primaries ( model differences contribute in the sys error ) ECT* - HH & CR - 2010 I.De Mitri: Hadronic Interaction studies with ARGO-YBJ 17
The proton-air cross section ARGO-YBJ Coll. Phys. Rev D 80, 092004 (2009) Extending the energy range with the analog readout ECT* - HH & CR - 2010 I.De Mitri: Hadronic Interaction studies with ARGO-YBJ 18
The total p-p cross section � No p-p (and pbar-p) accelerator data available at these energies � The log 2 (s) asymptotic behaviour is favoured ARGO-YBJ Coll. Phys. Rev D 80, 092004 (2009) Extending the energy range with the analog readout ECT* - HH & CR - 2010 I.De Mitri: Hadronic Interaction studies with ARGO-YBJ 19
Physics History Corner The reaction can occur only if the energy density in the overlap region is high enough to produce at least a pion pair Then ln 2 s σ → k ⋅ ( ) As → ∞ s ECT* - HH & CR - 2010 I.De Mitri: Hadronic Interaction studies with ARGO-YBJ 20
Next steps in the cross section analysis • Use the analog RPC charge readout to extend the Energy range • Better estimate of systematics Improvements are expected from: (a) More detailed informations on the shower time structure, longitudinal development and lateral density profile (LDF) (b) Better constraints on shower Xmax ( → lower systematics) ... also given by the RPC charge information ECT* - HH & CR - 2010 I.De Mitri: Hadronic Interaction studies with ARGO-YBJ 21
Shower front time structure New observables are being studied, mainly shape and width, and their correlation with the longitudinal shower development ECT* - HH & CR - 2010 I.De Mitri: Hadronic Interaction studies with ARGO-YBJ 22
Shower front time structure Look for detectable differences among various hadint models and data protons Look for correlations with Xmax 0.06 0.055 α 0.05 photon conicity coefficient proton 0.045 0.04 0.035 0.03 0.025 0.02 protons 0.015 0.01 350 400 450 500 550 600 650 -2 Xmax (g cm ) ECT* - HH & CR - 2010 I.De Mitri: Hadronic Interaction studies with ARGO-YBJ 23
Info from the analog readout Real event Strips (digital) 0 4000 3500 BigPads 3000 (analog) 2500 2000 1500 1000 500 ECT* - HH & CR - 2010 I.De Mitri: Hadronic Interaction studies with ARGO-YBJ 24
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