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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