1. 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:  Introduction  Experimental set-up  Performance and experience  Summary

2. Proton 820/920GeV 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 HERA e ± 27.5GeV Central part of the ZEUS detectorFront side of the FCAL HES Electromagnetic cell 5 × 20cm 2 Radius 1.9m

3. 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 X 0 (maximum of intensity) Segmentation helps : e ±, g in jets Hadron Electron Separator Electromagnetic Calorimeter (26X 0, 1 l Nuclear )

4. 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 16.3×1.4cm 2 for -- 672 channels -- signals,power,cooling

5. Diode as Active Part Advantage: High charge in small space 400 m m, 33000 e-h-pairs/particle Active area : 3.32  2.96 cm 2 Compatible to shower size R Molière = 2cm Calorimeter cell 5  20cm 2  HES consists: 20518 diodes or 20m 2 silicon Experimental Set-up

6. Multilayer Board as central part of the mechanics   2 Functions:  Mechanical stability  Cable: 112 channels + support lines  Parameters:  18 Layers  Unusual: 4.6m long with special production  Effect on electrical signal  by small signal line: C  1nF  rise time: 50ns to 100ns (HERA: 96ns/bunch) Connectors

7. Construction of a Module Full coverage with Si-diodes Shifting and folding 2 boards Diode  opposite preamplifier  Diodes+electronics encapsulated Thickness = 0.1 X 0 Cooling needed: Low power = 90mW/channel but  low heat conductivity of surrounding calorimeter 4.6m long gap cut

8. Performance: Coverage  Cover full plane, no overlaps Reached by HES: 85 % of whole active 94% of accessible area Remaining gaps: -- Calorimeters wavelength shifter9.5% -- Diodes side by side Field stop ring2.5% -- Mechanics2.5% -- 4 diodes on one 4”-wafer (cost)0.5%

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

10. Calibration Muons 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

11. Clustering Cluster Algorithm: Take diode with highest signal Associate 8 neighbours   On Average: 96% of energy contained in cluster

12. Algorithm: x Cluster =     w(Energy i ) · x Diode i ) Result: Test beam with 25GeV electrons: 85% center of modules, away from edges5.4mm ZEUS, From Monte-Carlo, DIS ( ~ 25GeV) 5 mm Position reconstruction e ±, g  Cluster

13. 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

14. Running Performance Source for failures: Mainly connectors 100 channels/month single electronic cards  Continuously repaired Water leak 1999-2000 InstallationBad channels RHES 1992-1994 3 - 6 % FHES 1996-1998 2 - 3 % 

15. Major Problem: Water Leak What? Tubes inside the gap corroded from inside to outside When?After 6 to 8 years of running Involved parts:  Copper-tubes 3mm diameter, 0.3mm wall thickness  De-ionised water, sulphur (SO 4 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

16. Summary Hadron-Electron-Separator a shower maximum counter at ZEUS  20m 2 of silicon, 20518 diodes pulse height readout 94% coverage  Running since 1992 Reasonable rate of faults, Repaired in access days and maintenance periods  Signals from muons, electrons and hadrons Improvements: 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