1. Gap Production for Upscope of the Endcap RPCs Sung Keun Park Korea Detector Laboratory Korea University February 5, 2010 Workshop on the Forward CMS RPC Upscope

2. 1. Contributions to Forward RPC 1)R&D of Gap production - Since 1997 2)Gap production KODEL in charge of production and QC for gaps for all the RE RPCs. - Low eta : RE 1/2, 1/3, 2/2, 2/3, 3/2, 3/3 (432 RPCs, 1548 gaps produced) - Upscope Low eta : RE2bis (288 RPCs) - High eta : RE1/1, RE2/1, RE3/1 3)Installation of 4 prototypes of RE1/1 4)R&D of HPLs 5)R&D for Upgrade

3. Silk screen method for graphite coating (100 ~ 200 k  /square) PET film coating

4. Gap assemblyLinseed oil coating

5. 200 mCi 137 Cs gamma irradiation facility & DAQ + electronics

6. Barrel RPCs Low-η Forward RPCs High-η Forward RPCs (Plan) 4-th station (Plan) RE1/1 1) R&D of RE1/1 RPCs at CMS nose cones 2. R&D activities

7. RE1/1 Design for RE1/1 in 1.6<  <2.1 - 6 RE1/1 RPC modules tested for cosmic rays - 4 RE1/1 RPCs installed RE1/1 RPCs : 10 degree trapezoidal 36 RPC modules on each wing

9. 2) R&D of HPLs Feasibility study for HPLs - A local HPL factory in Korea (Meltech). - Thin melamine-paper cladding on both surfaces of bakelite - The range of resistivity : 2 ~ 10 ⅹ 10 10  cm. - Maximum size of HPLs : 2450 mm ⅹ 1245 mm Quality Assurance for the HPL - KODEL built tools for resistivity measurement Recent procurement of HPLs for multigap RPCs - Thickness : 0.5 - 1 mm for the multigap structure - The test results of the small prototype to be presented in RPC2010 workshop

10. Resistivity tests for HPLs consisting of Melamine + Phenol sheets Batch1 : 20 samples of 0.5 mm melamine-phenol-melamine Batch2 : 20 samples of 0.5 mm melamine-phenol-melamine Batch3 : 15 samples of 1.0 mm melamine-phenol-melamine Batch 1 Batch 2 Batch 3 α = 0.12/°C Mean humidity ~ 75 %

11. 3) R&D of multigap RPCs R&D for high-rate triggers at RE1/1 for future CMS Higher rate capability ← lower avalanche charge - Rate capability ~ 1 / - Rate capability ~ 1/ ρ Then, what if multigap RPCs with HPLs ? - ~ 10 times smaller than CMS RPCs - HPL : Melamine+Phenol → ρ < 10 11 - Oiling required to reduce noises 0.6 ~1.1 pC 80 ~150 fC

12. For 6-gap RPCs (without gamma rays) TDC threshold = 1 mV ADC thresholds = 80 ~ 150 fC (in offline analysis) Mean q e at the efficiency plateau region → At 11.8 kV, ε = 0.97 (by TDC) and q e = 0.61 pC → At 12.7 kV, ε = 0.98 (by TDC) and q e = 1.12 pC ε = 0.96

13. Tests with gamma rays A 6-gap RPC installed at a 200 mCi 137 Cs gamma source (0.662 MeV) for high-rate background test - Accidental coincidences (geometrical) ~ 10 % 45 cm S - Current activity of the source ~ 156 mCi = 5.77 GBq Distances N γ (kHz/cm 2 ) N γ (signal) (kHz/cm 2 ) -------------------------------------------------------------------------- 35 cm 375.0 3.38 (estimation) 45 cm 226.9 2.02 (measured at 13.97 kV) 55 cm 151.9 1.37 (estimation)

14. Muon data with gamma background - Shifts in HV ~ 1.5 kV at 2.02 kHz/cm 2 - Caused by increase in resistivity of HPL ρ 20 = (6.9 ± 3.5) ⅹ 10 10 Ωcm (at H = 75%) in Jul. 15, 2009 (right after the production) ρ 20 = (3.3 ± 0.8) ⅹ 10 11 Ωcm (at H = 47%) in Jan. 6, 2010 (final measurement) - Resistivity of HPL should be ≤ 10 11 Ωcm after fully polymerized. Mean charges Efficiencies & mean chargesEfficiencies & cluster sizes Future R&Ds - QC for HPL - Test of prototype 6-gap RPCs for RE1/1 - Aging study with high gamma backgrounds

15. 3. Summary and Conclusion 1)Gap production - KODEL is ready for production and QC of the gaps for upscope - Gap production facility is well maintained 2)Other areas to contribute - Assembly of chambers - Electronics - High eta : RE1/1 (72 RPCs), RE2/1 (36 RPCs), and RE3/1 (36 RPCs) 3) R&Ds - HPL - RE1/1 (Multigap RPC, GEM)