Instrumentation of the Forward Region of the TESLA Detector

Karsten Büßer

Instrumentation of the Forward Region of the TESLA Detector

International Europhysics Conference on High Energy Physics

Aachen, July 19th 2003

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TESLA

TeV Energy Superconducting Linear Accelerator

Main Parameters

• Energy: 90 to 800+ GeV• Luminosity (500GeV): 3.4 x 1034 cm-2 s-1

• Beam size (500 GeV): 553 x 5 nm

Physics Potential

Precision measurements and searches in:• Higgs physics• Supersymmetry• EW precision tests (GigaZ)• QCD and top thysics• yet unimagined physics

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The TESLA Detector

Detector Concept

• Precision vertex detector• Large gas filled central tracking detector• Highly segmented calorimeters• 4T magnetic field, tracking detectors and calorimeters inside the coil

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Beam Induced Backgrounds

Main background source for the detector are beamstrahlung pairs

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• Shielding of the tracking detectors against backscattered beamstrahlung background• Provide instrumentation for:

• Precision luminosity measurement• Hermeticity:

→ Extension of the energy flow measurement down to small angles • Beam diagnostics

Tasks for the Forward Region

GEANT3 simulation of 10 pair particles

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• Instrumented tungsten mask

• Two calorimeters:

• LAT Low Angle Tagger27.5 – 83.1 mradactual task :„Luminosity Calorimeter“

• LCAL Luminosity Calorimeter

4.6 – 30 mradactual task: „Beam Calorimeter“

TESLA Forward Calorimeters

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Physics Requirements: ΔL/L ≈ 0.02% (GigaZ)

Process: e+ e- → e+ e- elastic Bhabha Scatteringe+ e- → e+ e- γ radiative Bhabha Scattering

Statistics: for L = 3.4 x 1034 cm-2 s-1 rate R ≈ 170 Hz

Systematics:• from detector acceptance:

since σtot

(Θmin

,Θmax

) ~ Θmin

-2 – Θmax

-2 ≈ Θmin-2

then ΔL/L = 2ΔΘmin

/Θmin

with Θmin

= 27.5 mrad,

ΔL/L = 10-4 ΔΘmin

= 1.4 µrad (!)• from theory:

At LEP achieved: 5.0 x 10-4

Luminosity Measurement

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Geometry(as defined in the TESLA TDR)

• 14 cylinders in Θ 24 sectors in Φ 40 rings in z 13440 cells in MC studies

• Conical Setup

• r: 4 – 12 cm (not affected by beamstrahlung pairs) z: 140 – 200 cm

• Silicon/Tungsten sandwich 40 X

0

Low Angle Tagger

The LAT serves as a shield !

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Energy Response Energy Resolution

LAT Performance

GEANT3 simulation studies show the response to high energetic electrons

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Energy Response and Resolution Angular Resolution

Red: Cut on desposited energy (>2.5 GeV)

LAT Performance

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LAT Outlook• New TESLA beam optics are under development which would allow to move the quads out of the detector (increasing l* from 3m to ≤5m).

• Mask and calorimeters would move

• Flat LAT seems possible

• Simulation studies for a flat LAT are under way → angular resolutions down to 1.4 µrad are still challenging!

• Alignment tolerances for detectors are stringent:

• Δz < 60 µm

• Δr < 0.75 µm

Alignment monitor system probably needed

TESLA-TDRl*=3m

Design studyl*=4.1m

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Technology options under study:

• Diamond -Tungsten Sandwich, rm~ 1cm

• Crystal PbWO4, r

m~ 2cm

30 layers, 30 X0

The LCAL

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Pairs from Beamstrahlungper bunch crossing (BX)

Produced:#: ~130000, E

tot: ~360 TeV

on each LCAL:#: ~15000, E

tot: ~20 TeV

Deposited Energy, Diamond/W

LCAL and Pair Background

Dose: ≤ 10 MGy/y

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LCAL as Beam Monitor

• Number of produced pairs is a measure of the luminosity• Deposited energy on the LCAL is input for the TESLA fast feedback system• rΦ energy distribution on the LCAL is an indicator for beam misalignments

nominal beam

tilted beam: x‘=3.5 mrad

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One 250 GeV electron and pair background from one BX

Generated Background added Reconstructed

LCAL as Physics Device

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Simple algorithm:

• subtract average (10 BX) background• search for cells with signal > 3σ of background fluctuation• require longitudinal chain of signal cells

4.6 mrad30 mrad

Reconstruction

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Energy Resolution of the LCAL

Energy resolution is dominated by the background

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500 BX

Fake Rates

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ConclusionLAT

• Luminosity measurment with 0.02% accuracy will be challenging

LCAL

• Several technologies are under study• Detection of high energetic electrons is possible with high efficiency below 10 mrad• Energy resolution is dominated by background subtraction• Need to look into more clever algorithms

OUTLOOK

• TESLA interaction region might change (increasing l*)→ Redesign of the forward region, impact on

calorimeters ?• R&D has started

Test stand for Si and Diamond sensors in Zeuthen