Yosuke Watanabe K.Utsunomiya, K.Ozawa, Y.Komatsu, S. Masumoto, T. Sato K. Aoki A,H.Enyo A, S. Yokkaichi A T. Gunji B, H. Hamagaki B, Y. Hori B, T.Tsuji B M. Sekimoto C University of Tokyo, RIKEN A, CNS B, KEK C, Development of GEM detectors for a large acceptance ф meson spectrometer 1

Outline 2 1. J-PARC E16 experiment 2. GEM tracker Setup Result of beamtests 3. Further improvement 4. Summary

J-PARC E16 experiment 3 p KEK –PS E325 φ Mass modification exist 30 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 Detection of φ meson mass spectrum modification in nuclear matter

E16 spectrometer 4 How to 100 times more statistic? × 10 beam intensity × 5 acceptance × 2 cross section Required ability for the tracker -100 μm position resolution with high rate events(5kHz/mm 2 ) New spectrometer GEM

GEM(Gas Electron Multiplier) 5 50 μm 100 μm 140 μm 70~90 μm 4 μm Copper 10cm Our GEM (made in Japan) schematic view Hole size : μm Pitch: 140 μm Most of the applications use 50 μ m GEM. Kapton LCP

GEM Chamber 6 １ 2 3 Collect ionized electrons (Drift gap) Length Electric field Amplify electrons setup1: 50 μ m GEM × 3 setup2: 50 μ m GEM+100 μ m GEM 2 D strip read out 700μ m pitch Chamber set up and parameters

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

Analysis procedure 8 Hit position determined by GEM chamber Hit position determined by Silicon Strip Detector(SSD) X1X1 X4X4 X3X3 X2X2 Q2Q2 Q3Q3 Q4Q4 Q1Q1 Q5Q5 X5X5 Center Of Gravity SSD GEM Events difference mm -Multiple scattering -Tracking Accuracy Position resolution beam

Test result 9 incident angle Drift gap Better resolution for inclined beam Achieved our goal ! angleFirst Second 0100 μm 160 μm μm 270 μm μm The effect of multiple scattering and tracking accuracy is subtracted Required performance position resolution : 100 μ m incident angle : 0 – 30 degree

Further improvement 10 Worse resolution for Second test Estimate of the number of electrons in drift gap. FirstSecond N primary x collection ～ 15 ～3～3 Collection efficiency ～ 0.2 ～ 0.15 Improve collection efficiency A setup with 3mm drift gap may get as many N primary x collection as the first test Drift gap collection efficiency: probablity for an electron in drift gap to be collected and multiplied

Better collection efficiency with narrow drift gap 11 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) disadvantage Setup with three layers of 50 μm GEM The collection efficiecy of the first test with three layers of 50 μm GEM is also bad.. First testNow ~90 μm ~75 μm The setup with current design of GEM has 2~3 times better collection efficiency.and 2 times larger gain (preliminary results) smaller hole + stronger E GEM - less optical transparency

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 tilted track. We obtained better collection efficiency with smaller hole GEM Another beam test will be performed at the end of the next month.

Back ups 13

Beam test setup 14 20cm 40cm SSD (silicon Strip Detector) scintilator GEM chamber pre-amplifierpost-amplifier charge sensitive ADC(v792) Read out circuits for GEM Trigger ← Scintillators 2 GeV electron ~5Hz600MeV positron ~100Hz

Remaining issues 2 15 What if collection efficiency = 100% ? How to deal with it ? (To be tested) simulation position resolution ( μm ) incident angle (degree) Not enough for our goal Narrower drift gap (1mm,2mm) Use arrival timing information

Estimation of collection efficiency 16 Fit with simulation Make primary and secondary electrons primary : poisson secondary: NIM Amplify those electrons Polya distribution( θ~0-5 ) Add noise experiment simulation Collection efficiency

laboratory Sr scintilater Pad read out 3cm 12cm 50 μmGEM×3 3mm experiment simulation Estimate the collection efficiency by comparing with simulation

Analysis procedure18 Hit position determined by GEM chamber X1X1 X4X3X3 X2X2 Q2Q2 Q3Q3 Q4Q4 Q1Q1 Q5Q5 X5X5 Center Of Gravity -Multiple scattering -Tracking Accuracy Q i /Q XiXi hit position resolution X i – X SSD mm ratio X GEM – X SSD mm SSD GEM