1. The ARGO-YBJ Experiment
Collaboration Institutes:
Chinese Academy of Science (CAS)
Istituto Nazionale di Fisica Nucleare (INFN)
IHEP, Beijing
Shandong University, Jinan
South West Jiaotong University, Chengdu
Tibet University, Lhasa
Yunnan University, Kunming
ZhengZhou University, ZhengZhou
Hong Kong University, Hong Kong
INFN and Dpt. di Fisica Università, Lecce
INFN and Dpt. di Fisica Universita’, Napoli
INFN and Dpt. di Fisica Universita’, Pavia
INFN and Dpt di Fisica Università “Roma Tre”, Roma
INFN and Dpt. di Fisica Univesità “Tor Vergata”, Roma
INAF/IFSI and INFN, Torino
INAF/IASF, Palermo and INFN, Catania
Michele Iacovacci (Napoli),
CSNII, Roma 1 Ottobre 09

2. Basic concepts HIGH ALTITUDE SITE (YBJ, 4300 m a.s.l)
for an unconventional air shower detector
HIGH ALTITUDE SITE (YBJ, 4300 m a.s.l)
FULL COVERAGE (RPC technology, 92%)
HIGH SEGMENTATION  see next slides
… in order to:
image the shower front
get a energy threshold of a few hundreds GeV

7. Current status Data taking since November 2007 Duty cycle ~ 90%
Trigger rate 3.6 kHz
Dead time 4%
220 GB/day transferred to CNAF

8. Physical Goals multi-purpose experiment
Sky survey -10%  δ  70% (-sources, anisotropies)
High exposure for flaring activity ( -sources, GRBs, solar flares)
C.R. 1 TeV  104 TeV
p/p at TeV energies
hadronic interactions
Helium spectrum
Proton “knee”
Knee region

9. Detector Pixels ... to be put in operation
Strip
Strip =SPACE PIXEL, 6 x 62 cm2,
Pad
Pad =TIME PIXEL, 60 x 62 cm2, 15600
σt≈1 ns
BigPad
BigPad =CHARGE readout PIXEL, 120 x 145 cm2, 3120
Cluster = DAQ unit = 12 RPCs
RPC
... to be put in operation

10.  astronomy Crab Mrk 421 Geminga Sky survey/galactic plane
no /h discrimination applied so far

11. Crab energy spectrum N PAD Events /day Emed (TeV) 40 – 100 128  24
0.85
100 – 300
17.9  6.3
1.8
> 300
9.2  2.3
5.2
dN/dE = 3.73  E –2.67 0.25 ev cm –2 s –1 TeV –1

12. Mrk 421 X-rays ASM/RXTE July-August 2006 2006 2007 2008 TEST DATA
FULL ARGO
2006
2007
2008

13. Mrk 421 - 2006 July-August (test data)
N PAD > 40
Excess distribution
degrees
6 s.d.
Mrk 421
Standard deviations
obs. time  109 hours
Flux  3-4 Crab

14. Mrk 421 - 2008 10 days average ARGO NPAD > 100 ASM/RXTE
days from

15. Gamma Rays vs X-rays in 2008 10 days average Correlation coefficient

16. Mrk421 spectrum (2008 days 41 – 180)  2  Crab
Integral flux (E > 1 TeV)
4.9  ev cm –2 s –1
 2  Crab
from: Primack et al.
AIP conf Proc 745, 23,2005
Power law spectrum + EBL absorption :
dN/dE = 7.5  E –2.51 0.29 e-t(E) ev cm –2 s –1 TeV –1

17. Mrk 421 - June 2008 NPAD > 100 3 days average ARGO 1 day average
ASM/RXTE

18. June 11-13
4.2 s

19. Event rate
NPAD > 100
Expected from theoretical SED

20. SED
7 Crab units

21. Geminga In this case two selection cuts have been applied:
Geminga has been observed for 466 Days and a total of h
Geminga is a diffuse source (Milagro claims 3° x 3°)
The next slide show the result of analysis for different multiplicities and
with a smoothing angle of 4.9°
At low mulitplicities no signal is evident while, as expected by Milagro’s
observation, at higher multiplicities the significance becomes interesting
In this case two selection cuts have been applied:
χ2<20ns2 & core in Area 95.5 x 87.5 m2

22. Geminga new χ2<20 ns2 & Area3
Ω = 4.9o
Nhit>500

23. nhit > 40 Smoothing window radius = 1.3°
Galactic plane
542 days
2007 day 311–2009 day 220
PSR J
HESS J
MGRO J
CRAB
nhit > Smoothing window radius = 1.3°

24. GRB Scaler mode 1-100 GeV Shower mode 10-1000 GeV
Upper limits to the fluence ( erg/cm2)
Upper limits to the cutoff energy as a function of the spectral index (1-100 GeV)

25. Referenced Papers
Search for Gamma Ray Bursts with the ARGO-YBJ detector in
scaler mode, Astrophysical Journal 699 (2009) 128
→ Upper limits to the fluence of 62 GRBs (9 with redshift z)
in the energy range 1100 GeV
2) ARGO-YBJ constraints on very high energy emission from GRBs,
Astroparticle Physics 32 (2009) 47
→ Upper limits to the fluence of 26 GRBs (6 with z) in the
ranges 10100 and 101000 GeV

26. Cosmic Rays Spectrum of the light component (1-100 TeV)
The Helium puzzle
Medium scale anisotropies
Moon shadow and the anti-p/p ratio

27. Strip distribution Rexp = RP + Rα + Rh R= ΔNev / ΔNs
10 %
R= ΔNev / ΔNs
Jα(E) with < 30% uncertainty if systematic  10%

28. Strip distribution (Ns<104)

29. E  100 TeV
Strip
Big Pad

30. Strip
E  1000 TeV
Big Pad

31. E  1000 TeV
Big Pad
Strip

32. Medium scale anisotropy
542 days
2007 day 311–2009 day 220
Smoothing window radius = 5°
nhit > 40

33. MILAGRO
ARGO

34. The Moon shadow on cosmic rays
Size of the deficit  angular resolution
Position  pointing accuracy
West displacement  Energy calibration
Geomagnetic bending  1.57° × Z / E (TeV)

35. The angular width in N-S direction using Moon shadow
Based on the Robust method reconstruction

36. 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.

37. Significance: ~ 43 s Data (2006 + 2007 + 2008) n Pad > 100
 10 standard deviation /month

38. Moon shadow: all data (2006+2007+2008)
43 s.d.
N > 60
θ < 50°
PSF of the detector
2063 hours on-source
 9 standard deviations / month

39. Antiproton/proton ratio at TeV energies
G. Di Sciascio et al. ICRC 2009
arXiv:

40. Proton-air cross section measurement
Xmax X0
Xrise
XDM h0 q
Use the shower frequency vs (secq -1)
for fixed energy and shower age.
The lenght L is not the p interaction lenght mainly because of collision inelasticity, shower fluctuations and detector resolution.
It has been shown that L = k lint , where k is determined by simulations and depends on:
Take care of shower fluctuations
Constrain XDO = Xdet – X0 or
XDM = Xdet – Xmax
Select deep showers (large Xmax,
i.e. small XDM)
Exploit detector features (space-time pattern) and location (depth).
hadronic interactions
detector features and location (atm. depth)
actual set of experimental observables
analysis cuts
energy, ...
Then:
sp-Air (mb) = / lint(g/cm2)

41. Experimental data Clear exponential behaviour
Weather effects, namely the atmospheric pressure dependence on time, have been shown to be at the level of 1 %
h0MC = g/cm2 (4300m a.s.l. standard atm.) h0MC / h0 = ± 0.007
Clear exponential behaviour
Full consistency with MC simulation at each selection step

42. The proton-air cross section
arXiv:
Extending the energy range
with the analog readout

44. Conclusions excellent detector performance
smooth running of the experiment with good parameters
duty cycle 90%
trigger rate 3.6 kHz
dead time 4%
minimum shower size 20 particles
Total integrated events > 2 × 1011
imaging of the shower front successfully implemented
to be extended beyond 100 TeV
studies to better the reconstruction and improve sensitivity in progress
many relevant results on the road

45. Richieste 2010 Sezione M.I. M.E. Cons. Inv. C.App. Trasp. Totale
Catania
5.5
14.5 3 1 25
Lecce
20.5 39 5
71.5
Napoli 20 60
366 24 15
485
Pavia 9 17 2 30
Roma 2 12
51.5 7
10.5 86
Roma 3 33 44
116
Torino
21.5
36.5 71
Totali
103.5
251.5
398 82
38.5 11
884.5

46. Milagro Sky Survey Cygnus region shows two new TeV gamma-ray sources
Diffuse emission from Cygnus region: ~ 2 x Fcrab (120 square degrees) l (65,85), b (-3,3)
A new TeV source at low declinations

47. E  100 TeV
Strip
Big Pad

48. GRB090902B Detected by Fermi GBM at 11:05:08 UT (T0) and zenith angle
 = 23.1° (uncertainty = 1.0), with a duration T90 = 25 s
Detected by Fermi LAT at 11:05:15 UT (uncertainty = 2.4):
within 100 s → >30 events with E >1 GeV
82 s after T0 → photon with E = 33.4 GeV (record!)
extended emission at GeV energies
(common feature of high energy emission?)
Scaler data analysis
Shower data analysis