1. The ARGO-YBJ experiment
CSNII, 30/09/08 Villa Mondragone, Frascati
M. Iacovacci- Napoli

2. ARGO-YBJ 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)

3. ARGO-YBJ since Dec 2007
1) Electric power system has been upgraded to 139 kVA.
2) 17 ring clusters are in DAQ since December Better reconstruction of the shower features, then better pointing accuracy.
3) Data transfer: link to Mbps is operational since January 6th, Data are now reconstructed at CNAF within a month.
4) Summer operation: Temperature problem has been solved Little humidity increase, but under control with ventilation.
Argo is taking data continuously since the end of 2007.
5) Detector performance (efficiency, time resolution) are continuously monitored by a RPC telescope.
6) Analog readout switched off in March because of LV power supply problems, due to bad heat dissipation (low air density). Designed a new LV power supply in Naples, prototype already tested at the YBJ pressure conditions. Prototype in operation at YBJ quite soon.
7) Gas System completed: Container with Big Tanks at YBJ.

4. Temperature and Humidity
Operation stopped (July 4th, 2007)
Covered the skylight windows (about 570 m2) + ventilation in the nigth (June 11th , 2008)
Tin(oC)
1 m level)
Red: 2008 Blue:2007
Tdn(oC)
Day in the year
0 m level)
RHup(%)
(above the RPC)
Some tens of RPCs (over 1764) suffered from Humidity increase.

5. Detector performance RPC telescope Ground
Time resolution and efficiency Profile - May 18 to May 25
Time Resolution (ns )
RPC telescope
RPC 0
RPC 4
RPC 3
RPC 2
RPC 1
wood
Ground
Walking floor
lead
HV1
HV0
7cm
Efficiency of the 20 PADs (%)
23cm
Temperature near cluster91 (oC)
Day

6. Analog Readout Status New Low Voltage power supply
Already mounted (104 Clusters)
Ready for DAQ, apart from LV PowerSupply (54 Clusters)
New Low Voltage power supply

7. New PS Test : Low Pressure Test Facility P can be dynamically set
P=600 mb,
I_trans=4.7 A, (full current)
W_all= 40 W
Low Pressure Test Facility
P can be dynamically set

8. Gas System : Big Tanks
The container with the Big Tanks goes beside the GasRoom, that directly comunicate whith.
Shipping: the container is in Beijing, it will arrive at YBJ in a couple of weeks
Mounting is foreseen by October-November

9. Physics Results p-p cross section measurement in a wider enery range.
GRB upper limits, both in scaler mode and in shower mode.
Moon shadow at 26 sigma
Mrk421 Flare (2008) and X rays correlation

10. 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:
hadronic interaction
shower fluctuations
detector features and location (atmospheric depth)
actual set of experimental observables and analysis cuts
energy ...

11. Inelastic p-air cross section Total p-p cross section
(only statistical errors)
Total p-p cross section

12. No arrival direction reconstruction
Search for GRBs in Scaler Mode
GRBs are observable as a significant excess of counting rate in coincidence with a satellite observation
No arrival direction reconstruction
39 GRBs observed by satellites (mainly SWIFT)
in the period December 2004 – July 2008
visible by ARGO-YBJ (f.o.v. θ<45°)
No excess observed
Fluence upper limits down to ~ 10-5 erg/cm2
for E = 1 – 100 GeV
mean  = 0.26
Search for GRBs in Shower Mode
No significant excess found for 20 GRBs analyzed
in the period July July 2008
Fluence upper limits (~ 10-5 erg/cm2) in the 10 GeV  1 TeV range

13. Moon Shadow ns ≈ 26 E50 ≈ 2 TeV Emode ≈ 0.5 TeV Nstr > 40
(for protons)
Nstr > 40
θ < 50°
Sample (802 h)
day 347, day 229, 2008
ns ≈ 26
Nstr > 40
Nstr > 60
ns ≈ 26
Nstr > 100
Nstr > 300

14. Moon Shadow Data (collected in 2006, 2007 and 2008)
in agreement with simulation about angular
resolution and west shift

15. Sun Shadow ns ≈ 25 E50 ≈ 2 TeV Emode ≈ 0.5 TeV Nstr > 40 θ < 50°
(for protons)
Nstr > 40
θ < 50°
Sample (954 h)
day 347, day 229, 2008
ns ≈ 25

16. Markarian 421 Observation Time = 1217 h day 347, 2007 - day 229, 2008
nhit > 60
median Eg = 1.6 TeV
nhit > 40    median energy = 1.1 TeV nhit > 60    median energy = 1.6 nhit > 100   median energy = 2.4 nhit > 200   median energy = 4.0
ns = 7

17. 2008 flare of Markarian 421 Data collected in 10 days (86-95) 10 days
Nhit > 100
median Eg = 2.4 TeV
10 days
events/day
130 days
minimal hit multiplicity
Days 1-130: the average flux is about the Crab flux
Days 86-95: the flux is 3 times higher than the Crab flux

18. 2008 flare of Markarian 421 Correlation with X rays RXTE-ASM
nhit > 40
median Eg = 1.1 TeV
nhit > 100
median Eg = 2.4 TeV

19. ARGO Plan 2009
Beginning 2009:
Complete Guard Ring in DAQ (+6 clusters)
Replace broken RPCs
Spring 2009:
AnalogRO on the central carpet
Summer 2009:
AnalogRO on the Guard Ring
Continous Data unless Preparing for Pb mounting.

20. Conclusions
Continuous Data Taking is going on with high duty cycle (> 95%) since December 2007
Moon and Solar shadows observed with high significance
Confirmed Angular resolution.
Detector systematics better understood
Mrk421 flare observed in 2006 and 2008 flares
Sky survey is going on
1 paper published , 1 accepted for pubblication
3 papers in preparation (GRB UL, p-p xsect, Mrk 421)

21. Richieste 2009

22. Richiesta sblocco sj ME 2008
Previsti circa 5 turni da 3/4 persone per fine anno.Saranno leggermente piu’ lunghi. Gli obiettivi: 1. Montaggio UPS spare + sostituzione batterie. Cablaggi vari 2. Installazione analogico (su due turni). 3. Installazione bombolone del gas 4. Recupero RPC 5. Maintanance Local Station