cosmic-ray detection at the argo-ybj observatory
DESCRIPTION
Cosmic-Ray Detection at the ARGO-YBJ observatory. P. Camarri University of Roma “Tor Vergata ” INFN Roma Tor Vergata. TeV gamma-ray astronomy. TeV γ -ray astronomy: science topics. The gamma-ray spectrum. Cerenkov Telescopes. EAS arrays. HAFC EAS arrays. Satellites. - PowerPoint PPT PresentationTRANSCRIPT
Cosmic-Ray Detection at Cosmic-Ray Detection at the ARGO-YBJ observatorythe ARGO-YBJ observatory
P. CamarriP. CamarriUniversity of Roma “Tor Vergata”
INFN Roma Tor Vergata
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TeV gamma-ray astronomy
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TeV γ-ray astronomy: science topics
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The gamma-ray spectrum
106 109 1012 1015 1018 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 Physics targets for -ray astronomy-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)
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TeV γ-rays: production processes
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TeV γ-rays: production processes
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Satellite vs Ground-based detectors Satellite:
lower energy primary detection small effective area ~1m2
lower sensitivity large duty-cycle large cost low bkg
Ground based: higher energy secondary detection huge effective area ~104 m2
higher sensitivity Small/large duty-cycle low cost high bkg
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Statistical significance
source OFF Background OFF, - ON Signal
Background
Signal cesignifican S
Excess of events coming from the source over the estimated background
feffON QATS
1
standard deviations
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…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/cm2 ·s
bkg( >1 TeV) · (= 1 msr) 1.5 ·10-8 nuclei/cm2·sbkgsignal
10
3
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 measurementsThe main drawback of ground-based measurements
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Detecting Extensive Air Showers
Classical EAS arrays
High energy threshold ( 50 TeV)Moderate bkg rejection ( 50 %)Modest sensitivity ( crab)Modest energy resolutionHigh 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 resolutionLow duty-cycle (~ 5-10 %)Small field of view < 4°
detection of the Cherenkov light from charged particles in the EAS
The
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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 !
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The TeV sky
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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.
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A new-generation EAS array
• Low energy threshold < 500 GeV
• Increased sensitivity Φ Φcrab <10-1 Φcrab
The Goal
• High-altitude operation
• Secondary-photon conversion
• Increase the sampling (~1% 100%)
The Solution
MeVNMeVN
mNmN
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270054300
Improves angular resolutionLowers energy threshold
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The ARGO-YBJ experiment
• ARGO detects air-shower particles at ground level
• ARGO is a wide field of view gamma-ray telescope wide field of view gamma-ray telescope which operates in “scanning mode”which operates in “scanning mode”
• ARGO is optimized to work with showers induced by primaries of energy
EE > > a few hundred GeVa 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
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Longitude 90° 31’ 50” EastLatitude 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 ASTibet ASγγARGOARGO
The Yangbajing Cosmic Ray Laboratory
VHE -Ray Astronomy -Ray Burst Physics Cosmic-Ray Physics
4300 m above the sea level
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10 Pads = 1 RPC (2.80 1.25 m2)
Gas Mixture: Ar/ Iso/TFE = 15/10/75, HV = 7200 V78 m
99 m
74 m
111 m
Layer of RPC covering 5600 m2
( 92% active surface)(+ 0.5 cm lead converter)+ sampling guard-ring
Central Carpet:130 Clusters
1560 RPCs
124800 Strips
BIGPAD
ADC
RPC
Read-out of the charge induced on “Big-Pads”
12 RPC =1 Cluster ( 5.7 7.6 m2 ) 8 Strips = 1 Pad
(56 62 cm2)
The ARGO-YBJ Resistive Plate Chambers
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Gas mixture:C2H2F4/Ar/iC4H10 = 75/15/10
Operated in streamer mode
Time resolution ~ 1.5 ns
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Fired pads on the carpet Arrival time vs position
time (ns)
meters
Shower recostruction
Analog read-out
0
Fs: 4000 -> 1300/m2
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/m2
04000
3500
3000
2500
2000
1500
1000
500
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Detector Pixels
Cluster = DAQ Cluster = DAQ unit = 12 RPCsunit = 12 RPCs
RPCRPC
StripStrip
StripStrip = =SPACE PIXEL, 6.5 x 62 cm2,
124800
BigPBigPadad
BigPad =BigPad =CHARGE readout
PIXEL, 120 x 145 cm2, 3120
PadPad
Pad =Pad =TIME PIXEL, 56 x 62 cm2,
15600
σt≈1 ns
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Operational Modes
Object:• flaring phenomena (high energy tail of GRBs, solar
flares) • detector and environment monitor
Recording the counting 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. 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:
IND
EP
EN
DEN
T D
AQ
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The Moon Shadow
• Size of the deficit
• Position of the deficit
Angular Angular ResolutionResolution
Pointing ErrorPointing 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 calibrationEnergy calibration
Cosmic rays are hampered by the Moon
Deficit of cosmic rays in Deficit of cosmic rays in the direction of the Moonthe direction of the Moon
)(
6.1 0
TeVE
Moon diameter ~0.5 deg
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-ray astronomy
Crab Nebula Mrk 421 MGRO 1908+06 Cygnus region and more…
no γ/h discrimination applied so far
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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
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Cosmic-Ray Physics
•Spectrum of the light component (1-100 TeV)
•Medium and large scale anisotropies
•The anti-p/p ratio
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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.
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(under peer reviewing for publication on PRD)
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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 ~1016 eV.
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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 experimentsInvited contribution to the Book "Frontiers in Cosmic Ray Research", 2007 Nova Science Publishers, New York, Ed. I.N. Martsch, Chapter 3, pp. 83 - 130.