The ZEUS HadronElectronSeparator Performance and Experience

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The ZEUS Hadron-Electron-Separator Performance
and Experience
Peter Göttlicher (DESY) for the
ZEUS-HES-group Contributions to HES Germany,
Israel, Japan, Korea, Russia, Spain,
USA Outline l Introduction l Experimental
set-up l Performance and experience l Summary
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ZEUS and HERA
Central part of the ZEUS detector
Front side of the FCAL
Radius 1.9m
HERA
HERA
e 27.5GeV
Proton 820/920GeV
HES
e,g GeV to 100 GeV à Good separation of e
,g from hadrons in particular inside jets
à Detector at shower maximum called HES
Planes inside calorimeter
Electromagnetic cell 520cm2
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Principle of HES
Hadron Electron Separator
Electromagnetic Calorimeter (26X0, 1lNuclear)
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
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Constraints
Low impact to energy measurement HES is at
most sensitive position à Small depth 1.4cm à
Low absorption à Material Magnetic field
Geometry Gap surrounded by calorimeter
parts à Access only from top 16.31.4cm2
for -- 672 channels --
signals,power,cooling
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Diode as Active Part
Experimental Set-up
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 à HES consists 20518
diodes or 20m2 silicon
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Multilayer Board as central part of the mechanics
Connectors
à 2 Functions à Mechanical stability
à Cable 112 channels
support lines à Parameters à 18
Layers à Unusual 4.6m long with special
production à Effect on electrical
signal by small signal line C 1nF
à rise time 50ns to 100ns
(HERA 96ns/bunch)
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Construction of a Module
Full coverage with Si-diodes Shifting and
folding 2 boards Diodeóopposite
preamplifier à Diodeselectronics encapsulated
Thickness 0.1 X0 Cooling needed Low
power 90mW/channel but l low heat
conductivity of surrounding
calorimeter l 4.6m long gap
cut
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Performance Coverage
à 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
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Electronics
Rise time 2 HERA cycles (180ns) à independent
from multilayer board à tolerable for low rate
at ZEUS
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Calibration
Performance and Experience
Muons in situ l Minimum ionising particle l
1MIP Energy deposition of 120keV
Electronic calibration l Charge injection to
preamplifier l Only weekly performed Low
drifts Mainly as check for faults
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Clustering

• Cluster Algorithm
• Take diode with highest signal
• Associate 8 neighbours

à On Average 96 of energy contained in
cluster
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Position reconstruction e,g
Algorithm x Cluster S ( w(Energy i ) x
Diode i) Result l Test beam with 25GeV
electrons 85 center of modules, away
from edges 5.4mm l ZEUS, From Monte-Carlo,
DIS (25GeV) 5 mm
à
à
Cluster
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Electrons and Hadrons
Test beam Known particle identity
à Well separation electron/hadron but some
electrons have no shower and some hadrons
showered
Cut 90 efficiency for electrons
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Running Performance
Installation Bad channels RHES 1992-1994
3 - 6 FHES 1996-1998 2 - 3

Source for failures l Mainly connectors l
100 channels/month single electronic cards
Ä Continuously repaired l Water leak
1999-2000
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Major Problem Water Leak
What? Tubes inside the gap corroded from inside
to outside When? After 6 to 8 years of
running Involved parts l Copper-tubes 3mm
diameter, 0.3mm wall thickness l De-ionised
water, sulphur (SO42-) and carbon
found Actions l Complete exchange of cooling
pipes l Purification of tubes from oil l
Replacing long rubber tubes by copper l Ion
exchanger installed l Continuous monitoring
à Ready for new data taking
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Summary
Hadron-Electron-Separator a shower maximum
counter at ZEUS l 20m2 of silicon, 20518
diodes pulse height readout 94 coverage l
Running since 1992 Reasonable rate of faults
, Repaired in access days and maintenance
periods l Signals from muons, electrons and
hadrons Improvements Factor 5 for hadron
rejection Factor 2 for
the position resolution
Factor 10 in granularity
l Continuous use to check the e-finders Efficienc
y without redundancy is a problem