Proposal for SAC prototype basing on “Shashlyk” technique

INR (Moscow), University of Sofia

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.

Shashlyk fine sampling prototypes

N.proto Lead,mm Scint,mm R_Molier,mm

X0,mm Number of Layers

25.5X0

L,cm

Light Yield,

ph/MeV

(incident)

1 2.0 3.0 30 15.3 70 (60) 39(35) 15

2 1.5 3.0 35 18.5 93 (76) 47(41) 20

3 1.5 1.4 27 12.5 93 (76) 32(29) 9

4 0.7 1.4 38 20.0 200 (156) 50(43) 18

5 0.35 1.4 55 33 300 (210) 20X0->

65(49)

36

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

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:1. Molded scintillator with “lego” lock - > precise geometry2. No “dead” material between modules3. 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.

Mechanical design

Front view

Sampling structure

Al frame support

Assembly roads

Al front andback planes

Scintillator 1.5mm + Lead 1.5mm

Total weight is ~ 80kgfor 25x25cm2 area and 70 layers

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

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:

1. Mechanical design to be fixed - June

2. Choice of scintillator options – June

3. Production plan to be fixed by end of June

4. Delivery ( of components) to CERN ( and assembly) - September

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

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)

BACKUP slides

• Energy resolution

• Lateral uniformity

• Tilted holes effect

Shashlyk, fine sampling, results

Lateral uniformity

KOPIO results:

Light collection efficiency drops on the edge by ~10%

Chemical modification of the side edges of scintillator improves uniformity considerably.

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

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.