The ZEUS HadronElectronSeparator Performance and Experience Peter Gttlicher

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

ZEUS and HERA Central part of the ZEUS detector HERA Front side of the FCAL Radius 1. 9 m HERA e± 27. 5 Ge. V Proton 820/920 Ge. V HES e±, g : Ge. V to 100 Ge. V à Good separation of e± , g from hadrons in particular inside jets à Detector at shower maximum: called HES: Planes inside calorimeter Electromagnetic cell 5× 20 cm 2

Principle of HES Use: e±, g early and narrow shower Hadron Electron Separator Electromagnetic Calorimeter (26 X 0, 1 l. Nuclear) Strategy: Measure deposit of energy of particles at given longitudinal position Detector: Plane at 3 -5 X 0 (maximum of intensity) Segmentation helps : e±, g in jets

Constraints Low impact to energy measurement HES is at most sensitive position à Small depth: 1. 4 cm à Low absorption à Material Magnetic field Geometry: Gap surrounded by calorimeter parts à Access only from top 16. 3× 1. 4 cm 2 for -- 672 channels -- signals, power, cooling

Experimental Set-up Diode as Active Part Advantage: High charge in small space 400 mm, 33000 e-h-pairs/particle Active area : 3. 32× 2. 96 cm 2 Compatible to shower size RMolière= 2 cm Calorimeter cell 5× 20 cm 2 à HES consists: 20518 diodes or 20 m 2 silicon

Connectors Multilayer Board as central part of the mechanics à à 2 Functions: Mechanical stability à Cable: 112 channels + support lines à Parameters: à 18 Layers à Unusual: 4. 6 m long with special production à Effect on electrical signal by small signal line: C 1 n. F à rise time: 50 ns to 100 ns (HERA: 96 ns/bunch)

Construction of a Module cut Full coverage with Si-diodes Shifting and folding 2 boards Diodeó opposite preamplifier à Diodes+electronics encapsulated Thickness = 0. 1 X 0 Cooling needed: Low power = 90 m. W/channel but l low heat conductivity of surrounding calorimeter l 4. 6 m long gap

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%

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

Performance and Experience Calibration Muons in situ: l Minimum ionising particle l 1 MIP= Energy deposition of 120 ke. V Electronic calibration: l Charge injection to preamplifier l Only weekly performed Low drifts Mainly as check for faults

Clustering Cluster Algorithm: • Take diode with highest signal • Associate 8 neighbours à On Average: 96% of energy contained in cluster

Position reconstruction e±, g Algorithm: x = S ( w(Energy ) · x ) à à Cluster i Diode i Result: l Test beam with 25 Ge. V electrons: 85% center of modules, away from edges 5. 4 mm l ZEUS, From Monte-Carlo, DIS (~25 Ge. V) 5 mm

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:

Running Performance Installation RHES 1992 -1994 FHES 1996 -1998 Bad channels 3 -6% 2 -3% Source for failures: l Mainly connectors l 100 channels/month single electronic cards ÄContinuously repaired l Water leak 1999 -2000

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 3 mm diameter, 0. 3 mm wall thickness l De-ionised water, sulphur (SO 42 -) and carbon found Actions: l l l Complete exchange of cooling pipes Purification of tubes from oil Replacing long rubber tubes by copper Ion exchanger installed Continuous monitoring à Ready for new data taking

Summary Hadron-Electron-Separator a shower maximum counter at ZEUS l 20 m 2 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 Efficiency without redundancy is a problem