Physics and astronomy results with the ARGOYBJ experiment

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"Physics and astronomy results with the
ARGO-YBJ experiment"

• G. Marsella
• Università del Salento and INFN Lecce - Italy
• on behalf of ARGO-YBJ Collaboration

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Outline

• Detector features and performance
• Cosmic rays
• Moon and Solar shadow
• ?-astronomy
• Conclusions

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Tibet 4300 m a.s.l.
High Altitude Cosmic Ray Laboratory _at_
YangBaJing (Site Coordinates longitude 90 31
50 E, latitude 30 06 38 N)
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ARGO-YBJ layout
Detector layout
99 m
74 m
8 Strips (6.5 x 62 cm2) for each Pad
1 CLUSTER 12 RPC
(?43 m2)
78 m
10 Pads (56 x 62 cm2) for each RPC
111 m
Layer (?92 active surface) of Resistive Plate
Chambers (RPC), covering a large area (5600
m2) sampling guard ring 0.5 cm lead converter
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Operation modes Shower mode Detection of
Extensive Air Showers (direction, size, core
) Trigger minimum number of fired pads
within 420 ns ³ 20 fired pads on the central
carpet rate 4 kHz Aims cosmic-ray physics
(threshold 1 TeV) VHE g-astronomy (threshold
300 GeV) gamma-ray bursts Scaler
mode counting rates ( ³ 1, ³ 2, ³ 3, ³ 4
coincidences) for each cluster Aims detector
and environment monitor flaring phenomena (GRB,
solar flares) with a threshold of few GeV
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Analog read-out
Read-out of the charge induced on Big
Pads (other side with respect to strip read-out)
The analog signal of half chamber is recorded
and digitised in order to avoid saturation up to
104 particles/m2 (RPC calibration at BTF,
Frascati) Dynamical range for protons by
means of pads, strips and big pads 1 - 104 TeV
3500 particles
54 clusters equipped to date with the analog
read-out
35 m
31 m
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Main detector features and performances

• Active element Resistive Plate Chamber ? time
  resolution ?1 ns
• Time information from Pad (56 x 62 cm2)
• Space information from Strip (6.5 x 62 cm2)
• Full coverage and large area (? 10,000 m2)
• High altitude (4300 m a.s.l.)

• ?
• good pointing accuracy (0.5)
• detailed space-time image of the shower front
• capability of small shower detection (? low E
  threshold)
• large aperture (?2p) and high duty-cycle
  (?100)
• ? continuous monitoring of the sky (-10lt? lt70)

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ARGO-YBJ performance

• High space/time granularity of ARGO-YBJ detector
• ? capability of detecting several kinds of
  events, characterized by different topologies and
  time structures. Deeply inspect a wide and
  possibly unexpected EAS phenomenology.

A very energetic shower
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• Cosmic Rays

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High space/time granularity allows unprecedeted
studies on the EAS phenomenology (different
topologies and time structures)
Same trigger two showers
Conical shape
High energy
Conical shape in small shower
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Studies in progress on the shower time structure
shower curvature
q lt 15
shower thickness
q lt 15
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Measurement of the flux attenuationand proton
cross section
Use the shower frequency vs (secq -1) for fixed
energy and shower age (h0vert. depth) The
absorption length L is connected to lint
through
?
sp-Air (mb) 2.41 x 104 / lint (g/cm2)
L k lint

• The parameter k takes into account how the
  primary energy is dissipated in the shower
• It is determined by simulations and depends on
• interaction model
• shower fluctuations
• actual set of experimental observables
• energy ...

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Inelastic p-air cross section (only statistical
errors)
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From p-air to p-p cross section

• Several available models to obtain stotp-p from
  sinelp-air
• Glauber Matthiae theory
• Durand Pi
• Wibig Sobczynska
• .
• Models agree within few in our energy range
• ? systematic error 5

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Total p-p cross section
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Total p-pbar cross section
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• Moon and Solar Shadow

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The largest signal a negative source... The
Moon shadow on cosmic rays
Moon Shadow

• A powerful tool to check the detector
• Size of the deficit ? angular resolution
• Position ? pointing accuracy
• West displacement ? Energy calibration
• Geomagnetic bending
  ? 1.6 / E (TeV) towards West

Physics antiproton / proton ratio in cosmic rays
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Moon Shadow
E50 2 TeV Emode 0.5 TeV (for protons)
Nstr gt 40 ? lt 50
Sample 2007 day 347 - 2008 day 229 (802 h)
ns 26
ns 26
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Moon Shadow
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Moon Shadow analysis
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Antiproton/proton Ratio
VERY PRELIMINARY !!!
Nhit gt 40 16 s in 3 months antip/p 10 at
1.5 TeV (at 90 c.l.)
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Sun shadow
Nstr gt 40 ? lt 50
All triggered events
2007 day 347 - 2008 day 229 (954 h)
25s
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• ?-astronomy

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Crab 2008
Nhit gt 60
Nhit gt 100
6 s
Preliminary
Oservation Time 1300 h
Nhit gt 200
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Mrk 4212007 day 347 - 2008 day 229 (1217 h)
nhit gt 60
ns 7
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RXTE-ASM
Mrk 421Correlation with X rays
nhit gt 40
nhit gt 100
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Mrk 421 Observation of a flare period 10 days
86-95
Day 1-130 Flux ? Crab Day 86-95 Flux ? 3 Crab
events/day
10 days
130 days
10
obs. time ? 42 hours
min. PAD multiplicity
NPAD gt 100
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Crab Nebula - 2007 data
Only Central Carpet in DAQ
degrees
gt 5 s
Standard deviations
N PAD gt 100
time ? 241 hours (2007 days 25-110)
Equivalent time ? 41 days quality cuts applied,
no gamma-hadron discrimination
in one year ? 15 s
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NPAD gt 100 Emed ? 2.4 TeV
declination -10 lt d lt 70
NPAD gt 100
time 940 h (2007 days 25 - 110)
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time 940 h (2007 days 25 - 110)
NPAD gt 100 Emed ? 2.4 TeV
Crab
MILAGRO SOURCES 20 TeV
Cygnus region
17 hot spots gt 4s 2 in the 10 ?
10 Cygnus region (prob ? 5 10-3)
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Search for GRBs in Scaler Mode
GRBs are observable as a statistically
significant excess of events in coincidence with
a satellite event
No arrival direction measurement
38 GRBs observed by satellites (mainly SWIFT)
Dec. 2004 March 2008 (ARGO f.o.v. ? lt
45) No excess observed Fluence upper limits
10-6 10-4 erg/cm2 (E 1 100 GeV)
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Conclusions

• ARGO-YBJ detector has been completely installed
• Data taking with duty cycle gt 95 since Dec 2007
• Results from first data
• p-air and p-p cross section measurement
• Moon and Solar shadows observed
• Mrk421 flare observed in 2006 and 2008 flares
• Crab Nebula observed at gt 6 s.d. Sky survey
  going on
• Upper limits to GRBs flux at VHE range
• For the future
• Optimize the reconstruction
• Gamma-hadron discrimination
• More Physics items
• Argo is now working with a digital readout which
  allows physics up to 100 TeV.
• Next year also the analog readout will be
  operated, allowing to extend the
• cosmic ray physics up to the 'knee' region,and
  beyond, with unprecedented
• resolution.