[Paper Review] LATTES: a novel detector concept for a gamma-ray experiment in the Southern hemisphere

P. Assis, U. Barres de Almeida+11 more|arXiv (Cornell University)|Sep 27, 2017

Particle Detector Development and Performance3 citations

TL;DR

LATTES proposes a hybrid gamma-ray detector combining Resistive Plate Counters (RPCs) and Water Cherenkov Detectors (WCDs) at 5,200 m altitude in the Southern Hemisphere to bridge the sensitivity gap between satellite and ground-based experiments. With a 100 GeV energy threshold, wide field of view, and high duty cycle, it achieves 1.5° angular resolution at 100 GeV and gamma-hadron separation comparable to HAWC, enabling long-term monitoring of variable sources and real-time alerts for transient phenomena.

ABSTRACT

The Large Array Telescope for Tracking Energetic Sources (LATTES), is a novel concept for an array of hybrid EAS array detectors, composed of a Resistive Plate Counter array coupled to a Water Cherenkov Detector, planned to cover gamma rays from less than 100 GeV up to 100 TeVs. This experiment, to be installed at high altitude in South America, could cover the existing gap in sensitivity between satellite and ground arrays. The low energy threshold, large duty cycle and wide field of view of LATTES makes it a powerful tool to detect transient phenomena and perform long term observations of variable sources. Moreover, given its characteristics, it would be fully complementary to the planned Cherenkov Telescope Array (CTA) as it would be able to issue alerts. In this talk, a description of its main features and capabilities, as well as results on its expected performance, and sensitivity, will be presented.

Motivation & Objective

• Address the sensitivity gap between satellite (Fermi) and ground-based (HAWC, CTA) gamma-ray experiments in the 100 GeV–100 TeV energy range.
• Enable long-term monitoring of variable astrophysical sources and detection of transient phenomena in the Southern Hemisphere.
• Develop a low-cost, modular, and scalable detector system with high duty cycle and wide field of view to complement the Cherenkov Telescope Array (CTA).
• Achieve low energy threshold and high angular resolution for improved gamma-ray shower reconstruction and hadron rejection.
• Provide real-time alerts for transient sources through fast, high-precision shower reconstruction using hybrid RPC-WCD technology.

Proposed method

• Deploy a 20,000 m² array of modular hybrid stations, each combining two RPCs (1.5×1.5 m², 16 pads each) on top of a 3×1.5×0.5 m³ WCD with two PMTs.
• Use a 5.6 mm lead plate on top of RPCs to convert secondary photons into electron-positron pairs, enhancing shower axis correlation and improving geometric reconstruction.
• Apply a shower front plane model using time and position data from RPC pads to reconstruct shower core and direction, requiring at least 10 valid hits on RPCs over active WCDs.
• Use Geant4 and CORSIKA for end-to-end Monte Carlo simulation of 5×10⁶ gamma and proton showers (10 GeV–300 TeV) to model detector response and background.
• Implement a Fisher linear discriminant using two variables: (1) normalized signal sum from WCDs >40 m from core, and (2) compactness relative to average gamma-ray lateral distribution function (LDF).
• Compute differential sensitivity as flux for which N_excess / √N_bkg = 5 after one year, assuming 25% duty cycle and 25% visibility of galactic center.

Experimental results

Research questions

• RQ1 Can a hybrid RPC-WCD detector achieve a low energy threshold (~100 GeV) and high angular resolution for gamma-ray showers in the Southern Hemisphere?
• RQ2 How effective is the combination of RPCs and WCDs in distinguishing gamma-ray showers from hadronic showers at energies above 100 GeV?
• RQ3 To what extent can the LATTES array provide real-time alerts for transient gamma-ray sources due to its high duty cycle and wide field of view?
• RQ4 What is the expected sensitivity of LATTES to steady sources, particularly in the energy range between Fermi and HAWC?
• RQ5 Can the hybrid design maintain high reconstruction accuracy and low background at the array edges, especially with a simplified front plane model?

Key findings

• The LATTES detector achieves a 68% containment angular resolution of better than 1.5° at 100 GeV for showers reconstructed near the array center.
• At energies around 100 GeV, the angular resolution degrades near array edges due to limitations of the front plane model, indicating the need for a shower conic fit to account for front curvature.
• The gamma-hadron separation performance, based on two WCD-based variables (normalized distant signal and compactness), achieves a selection efficiency and hadron rejection comparable to the HAWC experiment.
• The detector’s differential sensitivity after one year of observation reaches the 100 GeV–100 TeV range, effectively bridging the sensitivity gap between Fermi (satellite) and HAWC (ground-based) experiments.
• With a 25% duty cycle and 25% visibility of the galactic center, LATTES achieves sensitivity comparable to or better than HAWC in the 100 GeV–1 TeV range, with potential for extension to 100 TeV using a sparse array.
• The modular, low-cost design with high segmentation and time resolution enables robust reconstruction of shower geometry and energy, supporting long-term monitoring and transient detection.