1. "Physics and astronomy results with the ARGO-YBJ experiment"
G. Marsella
Università del Salento and INFN Lecce - Italy
on behalf of ARGO-YBJ Collaboration
12/05/2019
NOW 2008, Conca Specchiulla - Italy

2. NOW 2008, Conca Specchiulla - Italy
Outline
Detector features and performance
Cosmic rays
Moon and Solar shadow
γ-astronomy
Conclusions
12/05/2019
NOW 2008, Conca Specchiulla - Italy

3. Tibet 4300 m a.s.l. High Altitude Cosmic Ray Laboratory @ YangBaJing
(Site Coordinates: longitude 90° 31’ 50” E, latitude 30° 06’ 38” N)
12/05/2019
NOW 2008, Conca Specchiulla - Italy

4. ARGO-YBJ layout Layer (92% active surface) of
Detector layout
ARGO-YBJ 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
12/05/2019
NOW 2008, Conca Specchiulla - Italy

5. NOW 2008, Conca Specchiulla - Italy
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
Experimental hall
VHE astronomy (range : few hundreds GeV – few tens TeV) oppure (range : 300 GeV – 10 TeV)
Search for GRB’s (full GeV / TeV energy range)
12/05/2019
NOW 2008, Conca Specchiulla - Italy

6. 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 : ~ TeV
ADC
RPC
BIG
PAD
3500 particles
54 clusters equipped to date
with the analog read-out
35 m
12/05/2019
NOW 2008, Conca Specchiulla - Italy
31 m

7. 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 (2π) and high “duty-cycle” (100%)
 continuous monitoring of the sky (-10°< <70°)
12/05/2019
NOW 2008, Conca Specchiulla - Italy

8. NOW 2008, Conca Specchiulla - Italy
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
12/05/2019
NOW 2008, Conca Specchiulla - Italy

9. NOW 2008, Conca Specchiulla - Italy
Cosmic Rays
12/05/2019
NOW 2008, Conca Specchiulla - Italy

10. High space/time granularity allows unprecedeted studies on
the EAS phenomenology (different topologies and time structures)
meters
Same trigger:
two showers
Conical shape
High energy
Conical shape in small shower
Lateral and density
12/05/2019
NOW 2008, Conca Specchiulla - Italy

11. Studies in progress on the shower time structure
shower curvature
q < 15°
shower thickness
We do not observe dependence on multiplicity
Strada per la separazione adroni - gamma
q < 15°
12/05/2019
NOW 2008, Conca Specchiulla - Italy

12. NOW 2008, Conca Specchiulla - Italy
Measurement of the flux attenuation and proton cross section
Use the shower frequency vs (secq -1)
for fixed energy and shower age (h0=vert. depth)
The absorption length L is connected to lint
through: h0 q 
L = k lint
sp-Air (mb) = 2.41 x 104 / lint (g/cm2)
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 ...
12/05/2019
NOW 2008, Conca Specchiulla - Italy

13. Inelastic p-air cross section
(only statistical errors)
12/05/2019
NOW 2008, Conca Specchiulla - Italy

14. Total p-p cross section
12/05/2019
NOW 2008, Conca Specchiulla - Italy

15. NOW 2008, Conca Specchiulla - Italy
Moon and Solar Shadow
12/05/2019
NOW 2008, Conca Specchiulla - Italy

16. NOW 2008, Conca Specchiulla - Italy
Moon Shadow
The largest signal: a “negative” source... The Moon shadow on cosmic rays
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
12/05/2019
NOW 2008, Conca Specchiulla - Italy

17. NOW 2008, Conca Specchiulla - Italy
Moon Shadow
E50 ≈ 2 TeV Emode ≈ 0.5 TeV
(for protons)
Nstr > 40
θ < 50°
Sample
2007 day day 229 (802 h)
ns ≈ 26
ns ≈ 26
12/05/2019
NOW 2008, Conca Specchiulla - Italy

18. NOW 2008, Conca Specchiulla - Italy
Moon Shadow
Nstr > 40
Nstr > 60
Nstr > 100
Nstr > 300
12/05/2019
NOW 2008, Conca Specchiulla - Italy

19. NOW 2008, Conca Specchiulla - Italy
Moon Shadow analysis
12/05/2019
NOW 2008, Conca Specchiulla - Italy

20. NOW 2008, Conca Specchiulla - Italy
Sun shadow
Nstr > 40
θ < 50°
All triggered events
2007 day day 229 (954 h)
≈25σ
12/05/2019
NOW 2008, Conca Specchiulla - Italy

21. NOW 2008, Conca Specchiulla - Italy
γ-astronomy
12/05/2019
NOW 2008, Conca Specchiulla - Italy

22. NOW 2008, Conca Specchiulla - Italy
Crab 2008
Nhit > 60
Nhit > 100
6 σ
Preliminary
Oservation Time ~1300 h
Nhit > 200
12/05/2019
NOW 2008, Conca Specchiulla - Italy

23. NOW 2008, Conca Specchiulla - Italy
Mrk day day 229 (1217 h)
nhit > 60
ns = 7
12/05/2019
NOW 2008, Conca Specchiulla - Italy

24. NOW 2008, Conca Specchiulla - Italy
RXTE-ASM
Mrk 421 Correlation with X rays
nhit > 40
nhit > 100
12/05/2019
NOW 2008, Conca Specchiulla - Italy

25. Mrk 421 Observation of a flare period 10 days: 86-95
Flux  Crab
Day 86-95:
Flux  3 Crab
events/day
10 days
130 days 10
obs. time  42 hours
min. PAD multiplicity
NPAD > 100
12/05/2019
NOW 2008, Conca Specchiulla - Italy

26. NOW 2008, Conca Specchiulla - Italy
NPAD > 100
Emed  2.4 TeV
declination ° < d < 70 °
NPAD > 100
time = 940 h (2007 days )
12/05/2019
NOW 2008, Conca Specchiulla - Italy

27. NOW 2008, Conca Specchiulla - Italy
time = 940 h (2007 days )
NPAD > 100
Emed  2.4 TeV
Crab
MILAGRO SOURCES 20 TeV
Cygnus region
17 hot spots > 4s in the 10°  10° Cygnus region (prob  )
12/05/2019
NOW 2008, Conca Specchiulla - Italy

28. 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 – March (ARGO f.o.v.: θ < 45°)
No excess observed
Fluence upper limits ~ 10-6 – 10-4 erg/cm2
(E = 1 – 100 GeV)
12/05/2019
NOW 2008, Conca Specchiulla - Italy

29. NOW 2008, Conca Specchiulla - Italy
Conclusions
ARGO-YBJ detector has been completely installed
Data taking with duty cycle > 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 > 6 s.d. Sky survey going on
Upper limits to GRB’s 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.
12/05/2019
NOW 2008, Conca Specchiulla - Italy