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

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

P. Camarri - WAPP 2011 - Darjeeling, India - Dec 2011 2

TeV gamma-ray astronomy


TeV γ-ray astronomy: science topics


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


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


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


…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


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 !


The TeV sky


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.


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

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270054300

Improves angular resolutionLowers energy threshold


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


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


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

P. Camarri - WAPP 2011 - Darjeeling, India - Dec 2011

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

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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



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

-ray astronomy

Crab Nebula Mrk 421 MGRO 1908+06 Cygnus region and more…

no γ/h discrimination applied so far


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



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.


(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.



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.

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

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