HpDIRC

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hpDIRC

Description

hpDIRC poster

The high-performance DIRC (hpDIRC) is a fast focusing DIRC (Detection of Internally Reflected Cherenkov light) counter, utilizing high-resolution 3D (x,y,t) reconstruction. The generic design of the hpDIRC for the EIC was developed by the eRD14 consortium, supported since 2011 by funding from the BNL program for Generic Detector R&D for an Electron Ion Collider. The goal was to extend the PID coverage well beyond the state-of-the-art of DIRC counters to 3 standard deviations or more for pi/K up to at least 6GeV/c, p/K up to at least 10GeV/c, and to make important contributions to low momentum e/pi separation.

Key elements required to achieve this performance are high-quality bars made of synthetic fused silica as Cherenkov radiators and lightguides, radiation-hard 3-layer spherical lenses to generate a flat focal plane, and lifetime-enhanced MCP-PMTs with small pixels and fast readout electronics to detect the photons with a precision of about 1mm and 100ps, and a compact fused silica prism as expansion volume.

The hpDIRC for ATHENA is divided into sixteen optically isolated sectors that comprise a bar box and a readout box, surrounding the beam line in a 16-sided polygonal barrel with an inner radius of about 97cm. The total length of the hpDIRC barrel, including the prisms, is 450cm.

To study the performance a detailed standalone Geant4 simulation was developed and validated with a joint PANDA/EIC DIRC prototype in test beams at GSI and CERN. The simulation uses wavelength-dependent properties of all optical components and sensors, including the measured features of commercially available MCP-PMTs, in particular the dimension, pixel size, efficiency and timing performance of the PHOTONIS Planacon XP85122.

The development of the HRPPD LAPPD by Incom Inc. is currently in progress. If this sensor will become available in time and provide the same quality of performance as commercial PHOTONIS or Photek MCP-PMTs, it will be an interesting alternative and offer potential cost reduction. The current hpDIRC design assumes narrow bars with a width of 35mm and a total length of about 4200mm. The width and thickness matches the dimensions of the BaBar DIRC bars and reuse of the disassembly and reuse of the BaBar DIRC bars is the cost-saving baseline solution for the ATHENA hpDIRC.

Specs

PID goals: Separation of pions from kaons with at least 3s.d. up to at least 6GeV/c; separation of electrons from pions with at least 3s.d. up to at least 1GeV/c

Detector

  • barrel with a radius of 970mm and a length of approx. 4500mm (bars plus prism)
  • barrel is composed of 16 sectors in azimuth, separated by small gaps for the support structure (azimuthal coverage expected to be ~92%)
  • one sector comprises one bar box and one readout box, light-tight and made of CFRP, with ~2-3mm wall thickness
  • one bar box comprises
    • 10 long synthetic fused silica bars per sector, 17mm (T) x 35mm (W) x 4200mm (L), separated by a ~0.1mm air gap
      • each long bar is made of three reused BABAR bars glued together plus one additional 525mm-long bar or plate glued to the end
    • 10 three-layer spherical lenses, one lens glued to the readout end of each long bar and the lenses glued to each other side-by-side
    • 10 flat mirrors, one mirror coupled with an air gap to the other end of each long long bar
  • one readout box comprises
    • one synthetic fused silica prism as expansion volume, 240mm (H) x 360mm (W) x 300mm (L)
    • 24 MCP-PMTs with 3mm x 3mm pixel size (for the commercial 2’’ MCP-PMT option, fewer units for the 10cm x 10cm LAPPD option)
    • ~13cm longitudinal space behind the prism for sensors, readout boards, and cables
    • fast readout electronics with single photon sensitivity (details to be determined)
      • required timing precision per photon: 100ps (includes sensor, electronics, and synchronization)
  • total number of bars: up to 640 (for BABAR DIRC reuse option and short bars)
  • total number of readout channels: up to 98304
  • material budget: ~16% of a radiation length at normal incidence
  • total weight of hpDIRC components (without support structure): ~1500kg

Materials

  • support structure - could be extruded aluminum alloy, details to be determined
  • bar boxes, readout boxes: CFRP with 2-3mm wall thickness
  • bars and prisms: synthetic fused silica
  • lenses: synthetic fused silica and either sapphire, lead fluoride, or lanthanum crown glass, details to be determined
  • photodetector: MCP-PMT (commercial or LAPPD)

Services

  • high voltage cables for MCP-PMTs (commercial or LAPPD), one HV cable per MCP-PMT - details to be determined
  • low voltage cables for readout electronics, likely few cables per readout box, local DCDC converters - details to be determined
  • digital signal out via optical fibers, likely only one fiber per readout box
  • laser light pulser via optical fibers, likely 1-2 fibers per readout box
  • dry nitrogen flow to each bar box and readout box to keep optical surfaces clean (few liters per hour per bar box and readout box)
  • compressed air or water cooling of readout electronics, details to be determined