02/10/2004

Minimum Bias Trigger Scintillator Counters (MBTS) for early ATLAS

running

M.Nessi

ATLAS week, Freiburg

02/10/2004 Marzio Nessi

MBTS

Why: In the commissioning phase of ATLAS, we need to have an effective means to trigger on physics and to veto halo events.

What : scintillator counters with some segmentation in eta and phi,

able to detect 1 minimum ionizing particle

Where : on the front face of the LAr endcap cryostat, covering the radial dimension of the Inner Detector

When : needed in 2007 for the first beam, 3-4 months at low luminosity (5*1032); it will be dismounted

during the first shut down

02/10/2004 Marzio Nessi

MBTS readout

It will be to difficult to bring inside ATLAS new PMTs, cables,..

The idea is to use the same optical path used for the existing crack scintillators. Optical cables will transmit the light signals from the counters to the existing connectors in place for the crack scintillators

Each PMT in the tile drawers, used for this purpose, will then be linked to the LVL1 trigger processor or equivalent

PHI segmentation of 8 should be enough. This can still be tested by simulation.

Eta segmentation of 2 is planned. Radius or eta of segmentation to be defined. Limit of Pixel detector?

02/10/2004 Marzio Nessi

MBTS Geometry

On each side a disk of scintillator Rmin=138 mm, Rmax=1200 mm

Rmax can still be optimized.

Two options:Each disk will either take the place of the JM moderator

disk or be mounted in front of it

Maximum thickness of the disk, including supports and eventual readout system Z= 30 +- 1 mm

02/10/2004 Marzio Nessi

MBTS Segmentation

Current design forMTBS counters

Inner eta segment covers pixel detector

Eta = 1.8 (1200 mm)

Eta = 2.8 (431 mm)

Eta = 3.8 (1.58 mm)

02/10/2004 Marzio Nessi

Possible mounting scheme

MICHIGAN STATE UNIVERSITYHIGH ENERGY PHYSICS

REV. SCALEDWG. NO.

TITLE

PARTS LIST

PART NO.ITEM DESCRIPTION QTY.

DATE 16 DEC 03

DRAWN RON RICHARDS

PROJECT MBTS

MATERIAL

UNLESS SPECIFIED:

DECIMALS ±

FRACTNS ±

ANGLES ±

BREAK ALL EDGES

DO NOT SCALE DWG

MBTS MTG. FRAMES

"NOSE" DETAIL:

OUTER RADIUS CLIP HOLES

ONLY TWO TYPES OF FRAMES

02/10/2004 Marzio Nessi

MBTS Optical readout

The requirement is to have enough light in the PMTs to easily detect minimum ionizing particles

The light budget should allow a degradation of the light output by a factor 2 because of radiation damage during its short lifetime

Standard technique is scintillator readout by wavelength-shifting (WLS) fibersalong edge of scintillatorcan also try fibers embedded in groove in scintillator

02/10/2004 Marzio Nessi

Prototype construction

Prototype construction currently proceeding using 2 cm thick scintillator provided by Dubna

This is the same type of high-quality scintillator used in the CDF central pre-radiator upgrade currently underwaysomewhat different

design but there we get >12 pe/mip

WLS fibers for prototype will be along crack in middle of scintillatorfabrication is more

efficient with scintillator in 2 pieces

inner

outer

02/10/2004 Marzio Nessi

Next steps for MBTS

Prototype counter will be completed this month We will test prototype counter with cosmic rays at CERN using ATLAS

readout If design and light-yield proves adequate, then

by end of 2004, define final design and write a technical proposal2005 go for procurementMarch ’06 install counters on the cryostatsApril ’06 commissioning, with the LVL1 trigger electronics

This project will be funded with ATLAS Common Fund resources as well as by US ATLAS

Project is proceeding with participation by:

Michigan State University (J. Huston is project leader)DubnaCERNUniversity of Texas-Arlington