1. INSTR08 1.03.08 L.Shekhtman 1 Triple-GEM detectors for KEDR tagging system V.M.Aulchenko, A.V.Bobrov,A.E.Bondar, L.I.Shekhtman, E.V.Usov, V.N.Zhilich, V.V.Zhulanov Budker Institute of Nuclear Physics, Novosibirsk

2. INSTR08 1.03.08 L.Shekhtman 2 Tagging system: The primary physics problems to investigate with the help of the TS are: * study of the total cross-section of two photons into hadrons at low Q 2 ; into hadrons at low Q 2 ; * study of C-even resonances, * search for exotic states.

3. INSTR08 1.03.08 L.Shekhtman 3 Motivation for the upgrade: - improvement of spatial resolution in the orbit plane down to ~<0.1 mm orbit plane down to ~<0.1 mm - measurement of track position in the direction - measurement of track position in the direction perpendicular to orbit plane for suppression of perpendicular to orbit plane for suppression of the background from single Bremsstrahlung the background from single Bremsstrahlung Detectors must have rate capability better than 10 5 cm -2 s -1 and double track resolution ~1mm

4. INSTR08 1.03.08 L.Shekhtman 4 140  m 80  m Gas Electron Multiplier: F. Sauli, Nucl. Instr. and Meth. A 386 (1997) 531.

5. INSTR08 1.03.08 L.Shekhtman 5 Triple-GEM detector for the tagging system: GEM parameters: holes 80  m holes pitch 140  m (hexagonal structure) kapton thickness 50  m copper thickness 5  m Front-end electronics 3mm 1mm 1mm 2mm Driftelectrode GEM1 GEM2 GEM3 PCB

6. INSTR08 1.03.08 L.Shekhtman 6 Readout structure Detectors dimensions: 9 p. – 128х100mm 3p. - 256х100mm strip widths are determined such that charge is shared equally between layers

7. INSTR08 1.03.08 L.Shekhtman 7 Capability of clusters association in multi-track environment: 1. 1.If clusters from different layers are separated by more than 36 channels, they belong to different tracks. 2. Charges of clusters of one track are correlated (equal) Correlation of cluster charge in direct and stereo layers (prototype, 2000) V.M.Aulchenko et.al., NIM A494 (2002),241

8. INSTR08 1.03.08 L.Shekhtman 8 Detector components GEM Sensitive part assembled

9. INSTR08 1.03.08 L.Shekhtman 9 Detector components Front-end hybrids Large module completed

10. INSTR08 1.03.08 L.Shekhtman 10 Installation at VEPP-4M St.4 e - side St.1,2 e- side 7 modules are installed at VEPP-4M 3 modules are used for cosmic tests

11. INSTR08 1.03.08 L.Shekhtman 11 Cosmic tests: Det1 Det2 Det3 Sc1 Sc2 Measured value is variance of residuals: X2 – (X1+X3)/2  meas =  det  meas =  det x 1.225

12. INSTR08 1.03.08 L.Shekhtman 12 Gain in 3 detectors measured with Sr 90 Ar-CO 2 (3-1)

13. INSTR08 1.03.08 L.Shekhtman 13 Charge clusters 1 2 3 1 2 3

14. INSTR08 1.03.08 L.Shekhtman 14 Demonstration of 2D capability: Sr 90 10 30 5 10mm

15. INSTR08 1.03.08 L.Shekhtman 15 Spatial resolution:  det = 0.073 mm  det = 0.219 channnel (to be compared to 0.289 chan)

16. INSTR08 1.03.08 L.Shekhtman 16 Efficiency as a function of the width of corridor around track: ~10% of tracks have poor localization 100% of clusters are associated with tracks

17. INSTR08 1.03.08 L.Shekhtman 17 Clusters overlapping the gaps between GEM segments: Clusters COG distribution (direct strips) Gap between GEM segments

18. INSTR08 1.03.08 L.Shekhtman 18 Spatial resolution as a function of track angle: sqrt((0.089) 2 +(tg  *3/sqrt(12)) 2 ) Maximal angle of signal tracks

19. INSTR08 1.03.08 L.Shekhtman 19 Efficiency as a function of gain:

20. INSTR08 1.03.08 L.Shekhtman 20 Correlation of signals induced on direct and stereo strips: Prototype 2000 Final detector – layers exchanged stereo strips direct strips

21. INSTR08 1.03.08 L.Shekhtman 21 Cluster width: Direct strips. Cluster FWHM = 1.58 Stereo strips. Cluster FWHM = 1.78

22. INSTR08 1.03.08 L.Shekhtman 22 Conclusions and plans - All triple-GEM detectors for the upgrade of TS are produced. 7 detectors are installed at VEPP-4M, are produced. 7 detectors are installed at VEPP-4M, 3 detectors are being used for cosmic tests. 3 detectors are being used for cosmic tests. - Spatial resolution in the orbit plane for tracks with incident angle below 0.05 rad is ~70  m incident angle below 0.05 rad is ~70  m - Efficiency is close to 98%. About 10% of events have poor localization, probably due to overlapping with poor localization, probably due to overlapping with the gaps between GEM segments. Modification of COG the gaps between GEM segments. Modification of COG algorithm might help. algorithm might help. -Complete start-up of the system at VEPP-4M is planned for spring 2008 for spring 2008