1. Yosuke Watanabe….. University of Tokyo, RIKEN A, KEK C, Development of a GEM tracker for E16 experiment @ J-PARC 1 Thanks to ???????????

2. Outline 2 1. J-PARC E16 experiment 2. Gas Electron Multiplier(GEM) 3. GEM tracker Setup Result of beamtests 4. Remaining issues 5. Summary

3. J-PARC E16 experiment 3 p KEK –PS E325 φ Mass modification exist 30 or 50 GeV 100 times more statistc 2 times better resolution Systematic study -Momentum dependence -Nuclear size depencence  M =11MeV,  <1.25  M =5MeV,  <0.5 J-PARC E16

4. E16 spectrometer 4 How to achieve 2 times better mass resolution 100 times more statistic? × 10 beam intensity × 5 acceptance × 2 cross section Required ability for the tracker -Torelance to high rate events -100 μm position resolution New spectrometer GEM

5. GEM(Gas Electron Multiplier) 5 50 μm 100 μm 140 μm 70μm70μm 4 μm Copper 10cm Our GEM (made in Japan) schematic view Hole size and pitch: Standard design developed at CERN Most of the applications use 50 μ m GEM. Kapton

6. GEM Chamber 6 １ 2 3 Collect ionized electrons (Drift gap) Length Electric field Amplify electrons 50 μ m GEM × 3 50 μ m GEM+100 μ m GEM 2 D strip read out 700μ m pitch Chamber set up and parameters

7. Test configuration 7 Drift gap 11mm, 500V/cm3mm, 1500V/cm Amplifing part 50 μm×3100μm+ 50 μm Read out strip pitch 700 μm Gas Ar90%CH 4 10% Feature More primary electrons Tolerant to inclined beam Second test 2mm First test 2mm good effective gain

8. Analysis procedure 8 Hit position determined by GEM chamber Hit position determined by Silicon Strip Detector(SSD) X1X1 X4X3X3 X2X2 Q2Q2 Q3Q3 Q4Q4 Q1Q1 Q5Q5 X5X5 Center Of Gravity SSD GEM Events difference mm -Multiple scattering -Tracking Accuracy Position resolution beam

9. Test result 9 First test (11mm drift gap) Second test(3mm drift gap) Incident angle 0153045 Position resolution 160 μ m270 μ m470 μ m810 μ m Incident angle 015 Position resolution 100 μ m470 μ m incident angle Drift gap Better resolution for inclined beam Achieved our goal !

10. Remaining issues 1 10 Worse resolution for Second test Problem of collection efficiency ? collection efficiency: probablity for an electron in drift gap to experience multiplication FirstSecond Estimated N primary electron ～ 15 ～2～2 How to improve it while keeping the drift gap narrow? ε collection = ε collection (GEM geometry, E GEM / E drift ) E GEM should be stronger E drift should be weaker 50 μ m100 μ m 340V 285V(/50 μ m) With 50 μ m GEM, we have ～ 5 times better collection efficiency now. disadvantage

11. Remaining issues 2 11 What if collection efficiency = 100% ? How to deal with it ? simulation position resolution ( μm ) incident angle (degree) Result of simulation It gives better resolution than reality. Not enough for our goal Narrower drift gap (1mm,2mm) Use arrival timing information

12. Summary 12 Developing of GEM tracker for E16 experiment is under way We achieved 100 resolution for 0 degree beam. Narrower drift gap leads to better resolution for inclined beam. We have not achieved 100 for inclined beam yet, but timing information may solve this problem. Another beam test will be performed at the end of the next month.

13. Back ups 13

14. Beam test setup 14 20cm 40cm SSD (silicon Strip Detector) scintilator GEM chamber Fuji @ KEKKakuriken@Tohoku pre-amplifierpost-amplifier charge sensitive ADC(v792) Read out circuits for GEM Trigger ← Scintillators 2 GeV electron ~5Hz400MeV positron ~100Hz

15. φ e+e+ E16 experiment 15 p+A → φ +X e + +e - e-e- Measurement of φ meson mass spectrum in the nuclear medium High statistic Good mass resolution lead glass calorimeter Gas Cerenkov e-e- p electron track 3 layers of a GEM chamber position resolution : 100 μm Gas Cerenkov : Next talk

16. Collection efficiency 16 50 μ m100 μ m 340V 285V(/50 μ m) Larger E GEM /E drift gap → Better collection efficiency Test @ laboratory 90 Sr scintilater Pad read out 3cm 12cm 200400 600 800 ADC value 50 μmGEM×3 3mm 600V/cm Improved collection efficiency : 5 times compared to the test @LNS