1. Ideas and opportunities for a 2nd generation detector
Argo and beyond
Roma Tor vergata Jul
By R. Santonico

2. The scenario
In the next 6 years, during the Lhaaso construction, Argo will be the only experiment running in the YBJ laboratory
Outside of YBJ, Hawk will become in about 3-4 years, his main competitor. Lhaaso in turn could compete with Hawk by equipping in a shorter time one of his 4 pools
The opportunities offered by this scenario should be oriented in two directions
To complement the present Lhaaso project, mainly based on water Cerencov, scintillation and imaging Cerenckv detectors, with some other sub-detector based on a strong new idea
To improve the present Argo detector in order to fully exploit its potential and to produce results of excellence in competition with Hawk
In the long term Argo could become the “low energy” pole of Lhaaso
The main reason of this talk (and this workshop) is to stimulate ideas to take this opportunity

3. What is Argo
It is a full coverage array of RPCs, a detector with a 2 mm thick gaseous target at 0.6 bar pressure
A few numbers
central carpet area m2
guard ring m2
Number of pads
Number of strips
Minimum energy required to penetrate up to the gas few hundred keV
It has been running 4 years in the present configuration (plus 2 more years in a reduced configuration)
Negligible maintenance at the moment
17 Chambers off out of 1836.
A gas recirculation/purification system would make its running cost negligible thus creating the best conditions to continue the data taking for many years more

4. Single layer of Resistive Plate Chambers (RPCs)
with a full coverage (92% active surface) of a large area (5600 m2)
+ sampling guard ring (6700 m2 in total)
time resolution ~1-2 ns (pad)
space resolution = strip
10 Pads
(56 x 62 cm2)
for each RPC
8 Strips
(6.5 x 62 cm2)
for each Pad
1 CLUSTER = 12 RPCs
78 m
111 m
99 m
74 m
(5.7  7.6 m2)
Gas Mixture: Ar/ Iso/TFE = 15/10/75
HV = 7200 V
Central Carpet:
130 Clusters
1560 RPCs
Strips

5. The ARGO-YBJ Resistive Plate Chambers
Gas mixture:
C2H2F4/Ar/iC4H10 = 75/15/10
Operated in streamer mode
Time resolution ~ 1.5 ns
P. Camarri - Workshop di Dipartimento - Roma "Tor Vergata" - 8 giugno 2011

7. Upgrade of the analysis
Present event reconstruction methods require 1 year with (specify computing power) to reprocess 3 years data. This limits the possibility to test new ideas and new approach to the analysis
Great benefit from a more powerful approach to the event reconstruction: more manpower, new programs computers, storage
Try to optimize the shower front reconstruction (for a non usual detector) in order to improve angular resolution
Try to find some discriminating factor hadron/gamma
Conical shower front with variable angle (instead of fixed angle)  correlation with the hadron/gamma nature of the shower
Non conical shower fronts?
Search for gamma-hadron discriminating parameters

8. Lead on top of the existing carpet
According to the project and the relative MoU the Argo central carpet should have been covered with 5 mm (1 X0) Pb
Its effect would be to convert the photons which constitute >80% of the e.m. shower component.
According to the existing simulations this would increase the significance of the observed gamma sources by a factor 1.5 at least
It requires some 300 t of lead

9. Muon detection
Although there are no muons at 1 TeV a muon detector can be extremely helpful to discriminate hadronic showers in the energy range above 5 TeV which contains anyway about 20% of the statistics (some 700 Hz trigger rate) of the recorded Argo events
Two possibilities can be considered
An array of water Cerenkov detectors around the Argo laboratory
A muon detector installed inside small tunnels excavated below the laboratory

10. CR physics with Argo
Although Argo is optimized for low energy showers, the use of the analog read out offers the unprecedented opportunity to study the core of a 1 PeV shower at the 1 m distance scale
This focuses the importance of Argo for CR studies and the need to optimize it as a hadron shower detector

11. Analog read-out ARGO event
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
4000
3500
3000
2500
ARGO event
2000
1500
1000
500
Fs: > 1300/m2
P. Camarri - Workshop di Dipartimento - Roma "Tor Vergata" - 8 giugno 2011

12. Neutron detection
The detection of the neutron component is crucial to study hadron showers. This offer the opportunity for a very interesting R&D finalized to the neutron detection
Special scintillators (presented at the Lhaaso 2011 workshop
Gaseous detectors with the surface treated to convert the neutron

13. M-C
Yu.V. Stenkin, Beijing'2011

14. Detection of quasi horizontal showers
The detection of quasi horizontal showers can be used as the signature of the production and decay of a τ lepton from a ντ interaction
Horizontal showers detection can be improved with vertical chambers along the perimeter of the laboratory.
Two chambers with a 1 m concrete block in between would also give a signature of the muon component

16. Improving present RPC detector
Revision of the RPC signal pick up
A single large area pad (56x61 cm2) instead of 8 strips, with a substantial reduction of front end electronics channels
Amplitude recorded by ADCs which would substantially improve the amount of information
1 TDC + 1 ADC per pad
Avalanche operation (instead of streamer)
Lower operating current  lower gas consumption
Larger dynamic range
Allows to resolve a pair e+e- at a few mm distance
Calorimetric structure : 2-3 detector layers interleaved with 1 X0 of Pb would supply a relevant information about energy of the e.m. component
A relevant investment of simulation is crucial to test different ideas of optimization

17. Conclusions
Argo has still a relevant physics potential to express. To stop it at the end of 2012 as foreseen in the MoU long time ago, would be a big scientific mistake
The possibility to improve it to compete with Hawk should be seriously considered by a large Italian collaboration
In the longer term it could become the “low energy pole” of the big Lhaaso
Some original idea in the direction of Lhaaso would be very important for a qualified participation to this experiment