Hadron background rejection for Very for Very Hadron background rejection High Energy gamma ray astronomy High Energy gamma ray astronomy with ARGO- -YBJ YBJ with ARGO Ivan DE MITRI Ivan DE MITRI Dipartimento di di Fisica Fisica – – Università Università di di Lecce Lecce Dipartimento and Istituto Istituto Nazionale Nazionale di di Fisica Fisica Nucleare Nucleare and Lecce Lecce, ITALY , ITALY On behalf of the ARGO- -YBJ Collaboration YBJ Collaboration On behalf of the ARGO HE γ -ray workshop, Bari, June 2004
Physics goals goals Physics � γ -Ray Astronomy : Search for point-like galactic and extra-galactic sources at few hundreds GeV energy threshold � Diffuse γ -Rays from the Galactic plane and SuperNova Remnants � Gamma Ray Burst physics (full GeV / TeV energy range) � Cosmic ray physics : • anti-p / p ratio at TeV energy • spectrum and composition around “knee” (E th ∼ 10 TeV) � Sun and Heliosphere physics (E th ∼ 10 GeV) through the observation of Extensive Air Showers produced in the atmosphere by γ ’s and primary nuclei I. De Mitri I. De Mitri Hadron background rejection Hadron background rejection for for VHE gamma VHE gamma ray ray astronomy astronomy with with ARGO ARGO- -YBJ YBJ 2 2
The ARGO- -YBJ YBJ experiment experiment The ARGO • Collaboration between: • Collaboration between: � Istituto Istituto Nazionale Nazionale di di Fisica Fisica Nucleare Nucleare (INFN) (INFN) – – Italy Italy � � Chinese Academy of Science (CAS) Chinese Academy of Science (CAS) � • Site: Site: Cosmic Ray Observatory @ Cosmic Ray Observatory @ Yangbajing Yangbajing (Tibet), 4300 m a.s.l. (Tibet), 4300 m a.s.l. • I. De Mitri I. De Mitri Hadron background rejection Hadron background rejection for for VHE gamma VHE gamma ray ray astronomy astronomy with with ARGO ARGO- -YBJ YBJ 3 3
Astrophysical Radiation Ground-based Observatory @ YangBaJing I. De Mitri I. De Mitri Hadron background Hadron background rejection rejection for for VHE gamma VHE gamma ray ray astronomy astronomy with with ARGO ARGO- -YBJ YBJ 4 4
High Altitude Cosmic Ray Laboratory @ YangBaJing (Site Coordinates: longitude 90° 31’ 50” E, latitude 30° 06’ 38” N) I. De Mitri I. De Mitri Hadron background Hadron background rejection rejection for for VHE gamma VHE gamma ray ray astronomy astronomy with with ARGO ARGO- -YBJ YBJ 5 5
ARGO- -YBJ layout YBJ layout ARGO Detector layout time resolution ~1 ns space resolution = strip 99 m 74 m 10 Pads 8 Strips 1 CLUSTER = 12 RPC (56 x 62 cm 2 ) (6.5 x 62 cm 2 ) ( ∼ 43 m 2 ) for each RPC for each Pad 78 m 111 m Read-out Layer ( ∼ 92% active surface) of BIG of the charge PAD Resistive Plate Chambers (RPC), ADC induced on covering a large area “Big Pads” + sampling guard ring RPC + 0.5 cm lead converter I. De Mitri I. De Mitri Hadron background Hadron background rejection rejection for for VHE gamma VHE gamma ray ray astronomy astronomy with with ARGO ARGO- -YBJ YBJ 6 6
Main detector features and performance Main detector features and performance � Active element: Resistive Plate Chamber ⇒ time resolution ∼ 1 ns � Time information from Pad (56 x 62 cm 2 ) � Space information from Strip (6.5 x 62 cm 2 ) � Full coverage and large area ( ∼ 10,000 m 2 ) � High altitude (4300 m a.s.l.) ▼ • good pointing accuracy ( ≤ 1°) • detailed space-time image of the shower front • capability of small shower detection ( ⇒ low E threshold) • large aperture ( → 2 π ) and high “duty-cycle” ( → 100%) ⇒ continuous monitoring of the sky (-10°< δ <70°) I. De Mitri I. De Mitri Hadron background rejection Hadron background rejection for for VHE gamma VHE gamma ray ray astronomy astronomy with with ARGO ARGO- -YBJ YBJ 7 7
Experiment Hall I. De Mitri I. De Mitri Hadron background Hadron background rejection rejection for for VHE gamma VHE gamma ray ray astronomy astronomy with with ARGO ARGO- -YBJ YBJ 8 8
I. De Mitri I. De Mitri Hadron background Hadron background rejection rejection for for VHE gamma VHE gamma ray ray astronomy astronomy with with ARGO ARGO- -YBJ YBJ 9 9
pady:padx - 16 Clusters (Data: Feb 2003) Pads Pads 3D view of the same event Run = 2840 - Ev = 11 Entries Entries 512 512 Space view of an event with 512 hits 80 detected by Pad-Y 75 16 Clusters 200 70 Time (ns) (pixel ≡ Pad) 65 180 60 160 55 50 140 140 135 X d - P a 130 125 45 120 115 110 120 105 100 100 Space-Time projection Projected 80 Time (ns) space-time view 200 60 180 of the same event: 160 40 140 120 20 100 80 0 60 100 105 110 115 120 125 130 135 140 80 75 40 70 65 X - d Pad-Y 60 a P 55 50 20 45 0 45 50 55 60 65 70 75 80 100 105 110 115 120 125 130 135 140 Pad number I. De Mitri I. De Mitri Hadron background Hadron background rejection rejection for for VHE gamma VHE gamma ray ray astronomy astronomy with with ARGO ARGO- -YBJ YBJ 10 10
pady:padx - 16 Clusters (Data: Feb 2003) Pads Pads Entries Entries 797 797 Run = 537 - Ev = 970 View of an event with ~ 800 hits 80 P detected by a d - Y 75 16 Clusters 70 65 60 55 50 140 135 - X a d 130 P 45 125 120 115 110 105 100 Space-Time projection Time (ns) 200 180 160 140 120 100 80 60 40 20 0 140 135 130 125 120 115 110 105 100 80 75 70 65 60 55 50 45 Pad number I. De Mitri I. De Mitri Hadron background rejection Hadron background rejection for for VHE gamma VHE gamma ray ray astronomy astronomy with with ARGO ARGO- -YBJ YBJ 11 11
ARGO-YBJ (16 Clusters) - Run: 545, Event:2558 Pads Pads Entries Entries 444 444 A shower giving 444 hits Mean x Mean x 110.2 110.2 Mean y Mean y 60.09 60.09 RMS x RMS x 10.41 10.41 on 16 Clusters. RMS y RMS y 9.59 9.59 80 The shower core is 75 well contained into 70 the detector area. 65 60 55 50 140 135 130 125 45 120 115 110 105 100 Time (ns) 200 180 160 140 120 100 80 60 40 20 0 80 75 70 65 60 55 50 45 100 105 110 115 120 125 130 135 140 Pad number I. De Mitri I. De Mitri Hadron background rejection Hadron background rejection for for VHE gamma VHE gamma ray ray astronomy astronomy with with ARGO ARGO- -YBJ YBJ 12 12
Distribution of reconstructed zenith angle Distribution of reconstructed zenith angle Sample of 122,000 events on 16 Clusters (Trigger: N_pad ≥ 20) 3000 2500 2000 1500 1000 500 0 0 10 20 30 40 50 60 70 80 90 Zenith (degree) I. De Mitri I. De Mitri Hadron background Hadron background rejection rejection for for VHE gamma VHE gamma ray ray astronomy astronomy with with ARGO ARGO- -YBJ YBJ 13 13
Even- -odd angle difference odd angle difference vs vs pad pad multiplicity multiplicity Even (run on 6 Clusters) (run on 6 Clusters) σ θ (°) Very preliminary Very preliminary multiplicity I. De Mitri I. De Mitri Hadron background Hadron background rejection rejection for for VHE gamma VHE gamma ray ray astronomy astronomy with with ARGO ARGO- -YBJ YBJ 14 14
Real Event taken with a fraction of the detector I. De Mitri I. De Mitri Hadron background Hadron background rejection rejection for for VHE gamma VHE gamma ray ray astronomy astronomy with with ARGO ARGO- -YBJ YBJ 15 15
Real Event taken with a fraction of the detector I. De Mitri I. De Mitri Hadron background Hadron background rejection rejection for for VHE gamma VHE gamma ray ray astronomy astronomy with with ARGO ARGO- -YBJ YBJ 16 16
Simulated Photon Event I. De Mitri I. De Mitri Hadron background Hadron background rejection rejection for for VHE gamma VHE gamma ray ray astronomy astronomy with with ARGO ARGO- -YBJ YBJ 17 17
Gamma/hadron discrimination discrimination Gamma/hadron Photon Shower Proton Shower The photon signal is statistically identified by looking for an excess, coming from a given direction, over the isotropic background due to charged cosmic rays (H, He, Li, .. nuclei) In addition to this tool the study of the shower 1) space (and time) patterns 2) muon content can be useful to have higher discrimination power and then a larger sensitivity I. De Mitri I. De Mitri Hadron background rejection Hadron background rejection for for VHE gamma VHE gamma ray ray astronomy astronomy with with ARGO ARGO- -YBJ YBJ 18 18
The multiscale approach The multiscale approach m m n th step 1 st step m m l 1 = m/2 l n = m/2 n l 1 = m/2 l n = m/2 n m φ ( x , y , l ) = p ( x , y , l ) N th step N tot 2 N = m m φ = ( x , y , l ) content of the cell at position (x,y) as seen at scale length l l N = 1 N tot = total map content l N = 1 I. De Mitri I. De Mitri Hadron background rejection Hadron background rejection for for VHE gamma VHE gamma ray ray astronomy astronomy with with ARGO ARGO- -YBJ YBJ 19 19
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