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From Tibet to the Southern hemisphere: an RPC-based detector for astroparticle physics

From Tibet to the Southern hemisphere: an RPC-based detector for astroparticle physics. Lisboa , LIP - Laboratório de Instrumentação e Física Experimental de Partículas , 20 May 2019 Paolo Camarri University of Roma “Tor Vergata ” and INFN. The reason to start from ARGO-YBJ.

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From Tibet to the Southern hemisphere: an RPC-based detector for astroparticle physics

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  1. From Tibet to the Southern hemisphere: an RPC-based detector for astroparticle physics Lisboa, LIP - Laboratório de Instrumentação e Física Experimental de Partículas, 20 May 2019 Paolo Camarri University of Roma “Tor Vergata” and INFN

  2. The reason to start from ARGO-YBJ • ARGO-YBJ was a ground-based CR detector with unprecedentedfeatures: • Full-coverage core surrounded by a samplingguard ring • Located in a very high mountain laboratory (YBJ 4300 m asl) • Exclusive use of Resistive PlateChambersas a particle detector • Aimed to reach a verylowenergythreshold to overlap the maximum energiesachievable with satellite detectors. • The resultsachieved by thisexperimentstronglyencourage to go on with thisapproach to CR physics with a second-generation experiment. The experience made with ARGO-YBJ is a solid starting point to extrapolate the performance of a second generation experiment. • The main challenge should be the detection of gamma rays in the energy range down to 100 GeV or below and, at the same time, to study cosmic rays through the shower core, up to about 10-20 PeV. • A wide FoV gamma-ray detector, with the above characteristics, located in the Southern Hemisphere, would have a great discovery potential.

  3. The ARGO-YBJ experiment • Longitude: 90º 31’ 50’’ East4300 m above sea level ∾ 600 g/cm2 • Latitude: 30º 06’ 38’’ North • 90 km North from Lhasa (Tibet) • INFN • IHEP/CAS

  4. Basic concepts for an unconventional air shower detector • HIGH ALTITUDE SITE • (YBJ - Tibet 4300 m asl– 600 g/cm2) • FULL COVERAGE • (Resistive Plate Chambers, 92% coverage) • HIGH READOUTSEGMENTATION • Space pixels: 146,880 strips (7×62 cm2) • Time pixels: 18,360 pads (56×62 cm2) •  image the shower front with unprecedented details • get an energy threshold of a few hundreds of GeV

  5. time resolution ~1.5-2 ns (pad) space resolution = strip CentralCarpet: 130 Clusters 1560 RPCs 124800 Strips 99 m 74 m 8 Strips (6.5 x 62 cm2) for each Pad 10 Pads (56 x 62 cm2) for each RPC 1 CLUSTER = 12 RPCs (5.7  7.6 m2) Gas Mixture: Ar/ Iso/TFE = 15/10/75 HV = 7200 V 78 m 111 m 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) The ARGO-YBJ detector

  6. Status and performance • Running from July 2004 (with increasing portions of the detector) • Stable data taking with the complete lay-out since November 2007 • End/Stop data taking: January 2013 • Very modest maintenance effort in a hostile environment • Average duty cycle ~87% Dead time mostly due to frequent cuts of electric power • Trigger rate ~3.5 kHz @ 20 pad threshold • N. recorded events: ≈ 5·1011 from 100 GeV to 10 PeV • 100 TB/year data • Duty-cycle Intrinsic Trigger Rate stability 0.5%(after corrections for T/p effects)

  7. Effective Area • ARGO-YBJ • Central Carpet: 76 X 75 m2 • Coverage factor: 92 % • Segmentation of the Read-out: 6 X 62 cm • HAWC • Instrumented Area: 140 X 140 m2 • Coverage factor: 57 % • Segmentation of the Read-out: >15 m HAWC is a factor of 3.5 larger than ARGO-YBJ but the effective areas are similar below few TeV. ARGO-YBJwas a telescope optimized for the detection of small-size air showers

  8. Energy-scale calibration N ≈ 21 · (ETeV/Z)1.5 10% uncertainty estimated in the energy range 1 – 30 (TeV/Z).

  9. Scheme of the ARGO-YBJ Resistive Plate Chamber • A RPC is just a gas-filled plane capacitor with high-resistivity electrodes • External signal pick-up electrodes can be easily tailored with any shape • Chamber size: 1.25x2.80 m2; Time resolution ~ 1.5 ns • Argo gas mixture: C2H2F4/Ar/iC4H10 = 75/15/10; Operated in Streamer Mode • Two “big pads” of 1.25x1.40 m2 allows the analog readout H HV

  10. The RPC range of applications • The RPCs found a wide range of applications • Due to their simplicity and robustness they were used as Cosmic-Ray detectors in ARGO-YBJ • They are used as muon trigger detectors in 3 out of the 4 LHC main experiments (ATLAS, CMS and ALICE) • They are also used, in the multi-gap configuration, as Time of Flight detectors for mass identification, with a time resolution of 50 ps • On the other hand, it must also be stressed that a wide range of applications is essential for the production of components, like e.g. a full-custom front-end circuit, that is only possible on a large-scale base

  11. Higgs boson 4 muons decay in Atlas

  12. Operation of a large-size detector at 4300 m asl • Efficient detector control system (DCS) to monitor • External temperature and pressure • Detector temperature • Operating currents of each chamber • Trigger rate

  13. Temperature annual oscillations

  14. Operating currentdistribution for the 1681 RPCs (3.5 m2each)

  15. Gamma-Ray Astronomy with ARGO-YBJ • Energy threshold: few hundreds of GeV → Overlaps with Cherenkov detectors • Large duty cycle: 86% • Large field of view: ~2 sr • Declination band from -10° to 70° • Integrated sensitivity in 5 y at ~1 TeV: 0.25 Crab for dec 15° - 45° Crab Nebula 5 years data

  16. Gamma-rayAstromomyARGO-YBJ 5-year survey of the Northern Sky Gamma-rayastronomy • Integrated sensitivity in 5 y at ~1 TeV: 0.25 Crab for dec 15° - 45° • ApJ 779 (2013) 27

  17. ARGO-YBJ 5-year Survey of Inner Galactic Plane 20◦ < l < 90◦, |b| < 10◦ • HESS J1841-055 • HESS J1912+101 • MGRO J1908+06 • MGRO J2031+41 • E50≈ 0.7 TeV • E50≈1.8 TeV

  18. Study of the flaring sky: Mrk421 During 4.5 years (August 2008 – Feb 2013), Mrk 421 was continuously monitored by ARGO-YBJ and Fermi-LAT, covering the energy range from0.1 GeV to 10 TeV without any gap. Using the data of many different detectors, the MWL SEDs (from radio to TeV gamma rays) have been studied during 7 flares, one outburst phase and 2 quiescent periods • ARGO-YBJ (E > 300 GeV) • FERMI-LAT (E > 0.3 GeV) • SWIFT-BAT (E = 15-50 keV) • RXTE-AMS (E = 2-12 keV) • MAXI-GSC (E = 2-20 keV) • SWIFT-XRT (E = 0.3-10 keV) • SWIFT-UVOT (UVW1) • OVRO (radio 15 GHz) • By analysing the public data, we have evaluated: • Light curves • SEDs • for 4.5 years Cherenkov data exist for limited periods All these data provide a unique chance to investigate the multi-wavelength SED evolution during different states of activity of Mrk421. The multi wavelenght emission can be reasonably described by the one-zone SSC model, however different models cannot be excluded by these data.

  19. Mrk421 emission

  20. CR energy spectrum One of the most interesting ARGO-YBJ results concerns the measurement of the CR spectrum up to several PeV energy This was possible thanks to the analog readout of the signals which allowed to observe the shower core density with unprecedented detail High-altitude operation (4300 m asl) offered the following advantages Small fluctuations: near the shower maximum p and Fe produce showers with similar size Low energy threshold Absolute energy scale calibration with the Moon Shadow technique and overlapping with direct measurements

  21. The RPC analogreadout • Extending the dynamical range up to PeV • Is crucial to extend the covered energy range above 100 TeV, where the strip read-out saturates • Max digital density ~20/m2 Max analog dens ~104/m2 • Access the LDF inthe shower core • Sensitivity to primary mass • Info/checks on Hadronic Interactions 0 4000 3500 3000 ARGO event 2500 2000 1500 0 4000 0 1000 3500 500 d 3000 2500 Fs: 4000 -> 1300/m2

  22. The RPC signal vs the calorimeter signal Intrinsic linearity: test at the BTF facility • Linearity of the RPC @ BTF in INFN Frascati Lab: • electrons (or positrons) • E=25-750MeV(0.5%resolution) • <N>=1÷108particles/pulse • 10 ns pulses, 1-49 Hz • beam spot uniform on 3⨉5 cm 4 RPCs60 x 60 cm2 Good overlap between 4 scales with the maximum density of the showers spanning over three decades ➔ Linearity up to ≈ 2・104 particle/m2 Astrop. Phys. 67 (2015) 47

  23. All-particle spectrum by ARGO-YBJ ARGO-YBJ reports evidence for the all-particle knee at the expected energy

  24. Light component spectrum (3 TeV - 5 PeV) by ARGO-YBJ • ARGO-YBJ preliminary • ARGO-YBJ reported evidence for a proton knee starting at about 650 TeV and not at 4 PeV (“standard model”) • Pamela • CREAM • Horandel model

  25. The overall picture

  26. Large scale anisotropy by ARGO-YBJ 2 years data: 2008 - 2009, during minimum of solar activity E ≈1 TeV, 3.6 × 1010 events in the declination band -10º < δ < +70º

  27. Cygnus Region Medium/Small Scale Anisotropy CRAB Data: November 8, 2007 - May 20, 2012 ≈ 3.70×1011 events dec. region δ ∼ -20◦÷ 80◦ Galactic center Galactic plane Map smoothed with the detected PSF for CRs, obtained with the Moon Shadow analysis Proton median energy ≈ 1 TeV CRs excess ≈ 0.1 % with significance up to 15 s.d. Phys. Rev. D 88 (2013) 082001

  28. A look at the future: motivationfor a Southern experiment • The results of 5 years running with ARGO-YBJ suggest that this approach to ground-based CR detection is very promising and should continue with a second-generation experiment • Moreover, based on the ARGO-YBJ experience, a number of relevant upgrades can be conceived to improve the sensitivity of a similar detector, in particular for low-energy gamma rays • There are strong reasons for a Southern Experiment • The Southern skyisextremelyrich and important for astrophysics • No large-FOV TeVexperimentsare running in the Southern hemisphereatpresent • Goodopportunitytoday for an ambitiousproject in the South based on the convergence of differentgroups. • The collaborationLATTES (Brasil, Portugal…) hasalreadyproposed an RPC Cosmic-Ray detector to be locatedat a high-altitude site in the Southern hemisphere

  29. Southern TeV Astrophysics & CosmicRays Experiment: STACEX

  30. Upgrades suggested by the ARGO-YBJ experience in view of a future experiment:larger detection area and photon conversion (1) The results of ARGO-YBJ in gamma-ray astronomy and CR physics were achieved with a substantially downgradeddetector with respect the initial proposal, which was based on • A RPC carpet of 120x120 m2 • A 1X0Pb converter on top of it The real detector was a carpet of 5600 m2 without any photon converter on top. An obvious upgrade: • increase the area to 10 000-20 000 m2 • Much higher statistics • photon-hadron discrimination possible (the small size of ARGO-YBJ did not allow this discrimination) • A 1X0Pb photon converter would substantially increase the number of detected shower particles

  31. Gamma vs Hadronicshower concentrated sparse Largespreadof arrivaltimes

  32. Gamma-protonshower discrimination 1 Tevphotons 1 Tev protons

  33. Primaryphotonsof100GeV,500GeVand5TeVat 5000 m asl Photons arethe main component of theshower 6part/m2 0.3part/m2 0.02part/m2

  34. Operating at higher altitudes, ~5000 m, would be a further important advantage, mainly for low-energy photons • Extrapolationfrom 4300 m to 5000 m (about -1.4 X0 ) gives an increase of almost a factor of 2 for the number of particlesproduced by a 100 GeV primary photon Upgrades: Operation at higher altitudes

  35. Upgrades:Improving the detector performance (1) • Fully analog read out • The experience with ARGO-YBJ suggests that for a shower detection the analog read out is more effective than the digital one and should be extended from the “big pad” to the full signal read out • With this approach, squared pick up electrodes of area e.g. 20x20 cm2 or 30x30 cm2, would be more effective than substantially longer strips. The signal amplitude recorded by ADCs would substantially improve the amount of information • 1 TDC + 1 ADC per pad •  Space-time sampling of the shower front with an unprecedented detail ! • Avalanche-mode operation (ARGO-YBJ was operated in streamer mode) • Lower delivered charge and loweroperating current  lower gas consumption • Much wider dynamic range of the analog read out • Should allow to resolve a very closed e+e- pair produced by a photon annihilation, its signal amplitude being twice the m.i.p. • Better timing. Sub-nanosecond resolution possible but should be compared with the intrinsic shower-front fluctuations • A relevant investment of simulation is crucial to test different ideas for optimization

  36. Upgrades:Improving the detector performance (2) • Front-end electronics • A new full-custom front-end circuit, dedicated to the RPCs, has been developed (by R. Cardarelli) and will replace the one used for ARGO-YBJ • Final front-end electronics optimized for the avalanche-mode operation • The full-custom circuit will integrate the ADC and TDC functions • The output for each fired pad will be a shaped signal, suitable for coincidence logics, equipped with two numbers digitizing the Amplitude and the Time respectively • A crucial solution to avoid a huge complexity of interconnected circuits needed to discriminate and to digitize the input signal • A relevant investment of simulation is crucial to test different upgrade ideas and to optimize the detector, balancing performance and complexity • Collaborators interested in a full-detector simulation would be highly welcome

  37. Upgrades: the gas system • The ARGO-YBJ gas system was operated in open flow. The operation in closed loop, foreseen in the proposal, remained at the prototype level and was never implemented • A gas recirculation/purification system would make the running cost negligible thus creating the best conditions for a very-long-term data acquisition

  38. Some ideas about a future detector. Summary • Lay-out • Acentral carpet 120x120 m2hosted inside a very light and cheap building • Surrounded by a sampling array of similar sensitive area but spread on an area some 10 times larger. Some experience has been already achieved on the “outdoors” RPC operation • Read out • Fully analogread out with pads of area about 20x20 cm2 • “big pads” of about 1 m2 for very high multiplicities • New front-end full-custom circuit integrating the time and amplitude digitization • RPC operation • Avalanche mode • Gas mixture properly chosen for avalanche operation • Gas system • Closed loop with a few volumes/day flux indoors • Open loop outdoors with minimal gas supply (to be checked) • Altitude: > 5000 m

  39. The challenge of 50-100 GeVthreshold and the site choice • Itis a big challengerequiring a carefulevaluation of allparametersdetermining the detector sensitivity • Low-energy gamma showerswould be detected, in any case, muchbelow the point of the maximum showerdevelopment. The laboratoryaltitudeistherefore, to some extent, the mostimportantparameterand thisrequires to evaluate: • The human limits:  maximum altitudeconceivable for a large-size and complexexperiment • The ARGO-YBJ laboratory, at 4300 m asl, wasstilllivable, although with some difficulty. Whatabout 5000 m or higher? • The human limitshave to be included in the overallprojectoptimizationtogether with othertechnologicalparameters. • Strong requirements on the technology to minimize the permanence of the personnelat the experiment site. • A supportlaboratotyclose to the experimentbutlocatedatloweraltitudewould be veryimportant for the finaltestingof the modulesbefore the installation. Local manpowermay be crucial in the deployment of the experiment. • A small-sizetest in the selected site would be essential to evaluate the feasibility of the experiment and the robustnessof the project

  40. STACEX site: 5000 m altitude or more. ARGO-YBJ: 4300 m • RPC detectors possiblywith Pb absorber; no Pb • Area: 14,000 m2(full coverage); 6000 m2full cov+ surrounded by a comparablesampling array 1000 m2guard ring • Energy ranges: • Photons: 100 GeV – > 20 TeV300 GeV – 10 TeV • CRs: 300 GeV – 20 PeV600 GeV – 5/10 PeV • 1-year gamma-ray sensitivity (@ 1 TeV): 50 mCrab½ Crab

  41. Results from Fermi at Energies E > 50 GeVconfirmthe importance of a low-energythreshold The VHE sky (IACTs) TeV sources (HESS, MAGIC, VERITAS) (courtesy of P. Giommi) F > ~ 10 mC.U.

  42. The VHE sky (IACTs+Fermi 2FHL) E > 50 GeV sources (Fermi-LAT, 2FHL) (courtesy of P. Giommi) F > ~ 10 mC.U. F > ~ 10 mC.U.

  43. Supernova Remnant IC 443

  44. AGN-BL Lac, Markarian 421

  45. Conclusions • The combination of high-altitude site, full coverage and high segmentation of the read out, made ARGO-YBJ a unique experiment, which achieved relevant results even beyond the expectations of the proposal. The extension of this original approach to a new upgraded experiment will offer a relevant discovery potential • ARPC wide FoV gamma-ray detector, in the energy range 100 GeV-10 TeV, located in the Southern Hemisphere, would be unique and complementary to other experiments planning to take data in the next decade • The experience of ARGO-YBJ has clearly identified a list of improvements for a future experiment: higher altitude site, increased area, addition of a photon converter, RPC avalanche-mode operation with improved timing and fully analogread-out achievable with new front-end electronic • Twocollaborations, Lattes, Stacex, havealreadyconsideredthispossibility. A common proposalwould create a veryambitiousproject with a large internationalparticipation • Severalcollaborationitems can be foundeven in the short/middle term: computer simulation, site choice and preparationof a pilottest to be performed in the chosen site

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