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Proposal for SAC prototype basing on “Shashlyk” technique

Proposal for SAC prototype basing on “Shashlyk” technique

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Proposal for SAC prototype basing on “Shashlyk” technique

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  1. Proposal for SAC prototype basing on “Shashlyk” technique INR (Moscow), University of Sofia E.Guschin, NA48(3) PhotonVetoes

  2. Basic requirements The proposal is based on the idea to construct a prototype of SAC as close as possible to the final design. Also “by product” to have identical approach for the IRC. Proposed structure and parameters: • SAC geometry: • active area: 20x20cm2 + shower size = 24-25 cm2 • Sampling 70 layers of 1.5mm Sci +1.5mm Lead -> X0=12.5mm , R_M=27mm • Depth of 18X0 to have “punch through” eff. less than 10^-5 = 22 cm + fiber bundle + read-out • WLS fibres : 1mm diameter Y-11(250)MSJ (Kuraray) • Pitch between holes is 9.5 mm, hole diameter is ~1.4mm • Energy resolution ~7%/sqrt(E) -> σ = 170MeV @ 6GeV • Time response is defined by WLS fiber type: Y-11 decay time is 10nsec + signal shaping in the read-out. • Light yield estimate is ~9 photons/MeV. E.Guschin, NA48(3) PhotonVetoes

  3. Shashlyk fine sampling prototypes Experience: 1996-97 – Fine sampling Prototypes, INR Various sampling: 0.35mm(Pb)+1.4mm(Sci); 0.7+1.4 ; 1.5+1.4 ; 1.5 + 3.0 ; 2.0 + 3.0 Measured energy resolution of ~4.5%/Sqrt(E) for prototype n.5 E.Guschin, NA48(3) PhotonVetoes

  4. Mechanical structure • Conventional mass-production Shashlyk technique is based on molded scintillator (press-form with holes punching) and stamped lead plates. • Another approach based on precise machining with hole drilling was also explored (E787, CMS, “spakebab”, DELPHI) . • KOPIO – like approach: • Molded scintillator with “lego” lock - > precise geometry • No “dead” material between modules • Mass-production technique • Lateral dimensions are 12x12 cm2, it could be used for SAC with lateral segmentation, but it is difficult to fit ring shape of IRC. • Therefore another option for SAC prototype is to machine the cast scintillator and lead and to drill holes using high precision numerical machine and/or face-molded jig. E.Guschin, NA48(3) PhotonVetoes

  5. Mechanical design Assembly roads Al front and back planes Scintillator 1.5mm + Lead 1.5mm Sampling structure Total weight is ~ 80kg for 25x25cm2 area and 70 layers Front view Al frame support E.Guschin, NA48(3) PhotonVetoes

  6. Materials • Lead+Sn(4%) alloy plates, 1.5mm thickness • Scintillator plates, 1.5mm thickness • TYVEK, 0.1mm • WLS fibres: Y11(250) MSJ, 1 mm diameter ~ 300 x 60 cm + • Tools • Support E.Guschin, NA48(3) PhotonVetoes

  7. Time schedule and responsibilities Market survey (preliminary) for the cast scintillator : StGobain vs Kharkov; the price difference is ~ tens times. Preliminary sharing of responsibilities: Lead + jig – Sofia, Scintillator with holes – INR, fibre – exist (?) INR, for others (TYVEK, mechanics, assembly, photo read-out) there are options to be fixed. Basic idea on time schedule: • Mechanical design to be fixed - June • Choice of scintillator options – June • Production plan to be fixed by end of June • Delivery ( of components) to CERN ( and assembly) - September E.Guschin, NA48(3) PhotonVetoes

  8. Photo read-out • For beam test 4 conventional PMT FEU-84 could be used • APD read-out is promising option: • Compact • Magnetic field insensitive But: • Smaller area: 1x1cm2 HAMAMATSU (CMS like) – 9 read-out channels • Charge particle direct ionization ~ 600 ph.el. (800MeV) • Stabilization of temperature (1%/degree C) and bias voltage is needed • It needs low noise amplifier + gain of 100-200 -> electronic noise <10 MeV/channel is achievable E.Guschin, NA48(3) PhotonVetoes

  9. Beam test program • Energy response for electrons and tagged gammas: • resolution • Lateral uniformity of the response • Effect on the holes vs angle. • Light yield • “Punch through” probability with (electrons?) gammas. With tagged gammas the set-up could be: • > tagged gamma -> veto scintillating counter -> SAC proto -> ECAL module (“shashlyk” or any available with good energy resolution) • Test of APD read-out (if ready) E.Guschin, NA48(3) PhotonVetoes

  10. BACKUP slides • Energy resolution • Lateral uniformity • Tilted holes effect E.Guschin, NA48(3) PhotonVetoes

  11. Shashlyk, fine sampling, results E.Guschin, NA48(3) PhotonVetoes

  12. Lateral uniformity KOPIO results: Light collection efficiency drops on the edge by ~10% Chemical modification of the side edges of scintillator improves uniformity considerably. E.Guschin, NA48(3) PhotonVetoes

  13. Design Proposal for Small Angle Photon Vetoes Requirements: • Extra high registration efficiency for gammas larger than 5 GeV (ineff <10^-5) -> thickness ~18-20X0 -> fibre axis is tilted to the beam more than 5 mrad • Timing better than 100 ps (?) -> light yield larger than 20 photons/MeV is sufficient *) *) following the result for KOPIO with 90ps/Sqrt(E) for 55 ph.el./MeV • Cell size / no cells, Molier’s radius - ? Occupancy is low? KOPIO Shashlyk eff. vs beam angle E.Guschin, NA48(3) PhotonVetoes

  14. SAC structure Hermeticity Few solutions: a) continuous layers of lead and scintillator with drilled holes ; b) non projective cracks ; c) with crack shift from layer to layer. E.Guschin, NA48(3) PhotonVetoes