The ZEUS Hadron-Electron-Separator

Performance and ExperiencePeter Göttlicher (DESY) for the ZEUS-HES-group

Contributions to HESGermany, Israel, Japan, Korea, Russia, Spain, USA

Outline:

Introduction

Experimental set-up

Performance and experience

Summary

Proton820/920GeV

ZEUS and HERA

e±,g : GeV to 100 GeV Good separation of e± ,g from hadrons

in particular inside jets Detector at shower maximum: called HES:

Planes inside calorimeter

HERAHERA

e±

27.5GeV

Central part of the ZEUS detector Front side of the FCAL

HES

Electromagneticcell 5×20cm2

Radius 1.9m

Principle of HES

Use: e±,g early and narrow shower

Strategy: Measure deposit of energy of particles

at given longitudinal position

Detector: Plane at 3-5 X0 (maximum of intensity)

Segmentation helps : e±,g in jets

HadronElectronSeparator

Electromagnetic Calorimeter (26X0, 1lNuclear)

Constraints Low impact to energy measurement HES is at most sensitive position

Small depth: 1.4cm Low absorption Material

Magnetic field

Geometry:

Gap surrounded

by calorimeter parts

Access only from top

16.3×1.4cm2 for -- 672 channels -- signals,power,cooling

Diode as Active Part

Advantage: High charge in small space 400mm, 33000 e-h-pairs/particle

Active area : 3.322.96 cm2 Compatible to shower size RMolière= 2cm Calorimeter cell 520cm2

HES consists:

20518 diodes or 20m2 silicon

Experimental Set-up

Multilayer Board

as central part of the mechanics

2 Functions: Mechanical stability Cable: 112 channels + support linesParameters: 18 Layers Unusual: 4.6m long

with special production Effect on electrical signalby small signal line: C1nF rise time: 50ns to 100ns (HERA: 96ns/bunch)

Connectors

Construction of a Module

Full coverage with Si-diodes Shifting and folding 2 boards Diodeopposite preamplifier

Diodes+electronics encapsulated

Thickness = 0.1 X0

Cooling needed: Low power = 90mW/channel but low heat conductivity of surrounding calorimeter 4.6m long gap

cut

Performance: Coverage

Cover full plane , no overlaps

Reached by HES: 85 % of whole active 94% of accessible area

Remaining gaps:-- Calorimeters wavelength shifter 9.5%-- Diodes side by side Field stop ring 2.5%-- Mechanics 2.5%-- 4 diodes on one 4”-wafer (cost) 0.5%

ElectronicsRise time 2 HERA cycles (180ns) independent from multilayer board tolerable for low rate at ZEUS

CalibrationMuons in situ:

Minimum ionising particle

1MIP= Energy deposition of 120keV

Performance and Experience

Electronic calibration:

Charge injection to preamplifier

Only weekly performed Low drifts Mainly as check for faults

Clustering

Cluster Algorithm:

• Take diode with highest signal• Associate 8 neighbours

On Average: 96% of energy contained in cluster

Algorithm: x Cluster = w(Energy i ) · x Diode i)Result:

Test beam with 25GeV electrons:

85% center of modules, away from edges 5.4mm

ZEUS, From Monte-Carlo, DIS (~25GeV) 5 mm

Position reconstruction e±,g

Cluster

Electrons and Hadrons

Cut: 90% efficiency for electrons:

Test beam: Known particle identity

Well separation electron/hadron but some electrons have no shower and some hadrons showered

Misidentifiedhadrons [%] 2 3 5 9

by calorimeter

tower 20×20cm2

by HES alone 3.8 3.4 3.5 3.6combined 1.47 0.86 0.22 0.15factor of improvement 5.3 4.7 3.0 2.5

Energy [GeV]

7.79 4.03 0.65 0.37

RHES

020406080

100

FHES

020406080

100

1996 1998 2000Year

Running Performance

Source for failures:

Mainly connectors

100 channels/month

single electronic cards Continuously repaired

Water leak 1999-2000

Installation Bad channels RHES 1992-1994 3 - 6 % FHES 1996-1998 2 - 3 %

Major Problem: Water Leak

What? Tubes inside the gap corroded from inside to outsideWhen? After 6 to 8 years of running

Involved parts:Copper-tubes 3mm diameter, 0.3mm wall thicknessDe-ionised water, sulphur (SO4

2-) and carbon found

Actions: Complete exchange of cooling pipes Purification of tubes from oil Replacing long rubber tubes by copper Ion exchanger installed Continuous monitoring

Ready for new data taking

SummaryHadron-Electron-Separator

a shower maximum counter at ZEUS

20m2 of silicon, 20518 diodespulse height readout94% coverage

Running since 1992Reasonable rate of faults ,Repaired in access days and maintenance periods

Signals from muons, electrons and hadronsImprovements: Factor 5 for hadron rejection Factor 2 for the position resolution

Factor 10 in granularity Continuous use to check the e-finders

Efficiency without redundancy is a problem