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Development of a Time Projection Chamber Using Gas Electron Multipliers (GEM-TPC) Susumu Oda, H. Hamagaki, K. Ozawa, M. Inuzuka, T. Sakaguchi, T. Isobe, T. Gunji, S. Saito, Y. Morino, Y.L. Yamaguchi1, S. Sawada2 and S. Yokkaichi3 CNS, University of Tokyo, 1Waseda University, 2KEK, 3RIKEN 1. Motivation of GEM-TPC Development 2. GEM-TPC prototype 3. Performance Evaluation of GEM-TPC 4. Summary 2005/10/25 Puerto Rico IEEE NSS 2005 N17-8 1/13 2/13 Motivation of GEM-TPC development Study hot and dense matter, Quark Gluon Plasma (QGP), by high energy heavy ion collision. – e.g. PHENIX-RHIC-BNL, ALICE-LHC-CERN A high resolution (position, double track and energy) tracker under high collision rate and high particle density is needed. – Interested pT region is 0.2 - 20GeV/c magnetic field should be kept low ~1T. – Required resolution dpT/pT2~10-3 (GeV/c)-1 : to resolve Upsilon states etc. – If 1-m radius solenoidal tracker, 200mm of spatial resolution is required. – Since particle density is high, double tracks with >1cm should be separated. TPC using GEM(Gas Electron Multiplier)may satisfy the above requirements. – Ion feedback suppression. – No incidental angle dependence by 2-dimension symmetry. – Flexibility for magnification. 3/13 GEM-TPC prototype Field cage : 35cm(drift direction) x 17cm x 17cm Triple-GEM : 10cm x 10cm (effective region), made in CERN. Pad : rectangular & zigzag 1.09mm x 12mm Charge sensitive preamplifier : time constant 1ms 24ch signals are read out using 100MHz FADC. Beam direction Beam direction 4/13 Gas 3 kinds of gases with different drift velocity and diffusion coefficient were used for measurement. Energy resolution was s=1013% with 55Fe X-ray source. Electric field Drift velocity Transverse diffusion @1cm Longitudinal diffusion @1cm Ar(90%)-CH4(10%) 130 V/cm 5.48 cm/ms 570 mm 378 mm Ar(70%)-C2H6(30%) 390 V/cm 5.01 cm/ms 306 mm 195 mm CF4 570 V/cm 8.90 cm/ms 104 mm 82 mm 55Fe X-ray (5.9keV) spectrum with CF4 s=13% 5/13 Beam test A beam test was performed at KEK PS to evaluate the performance of the GEM-TPC. Three kinds of gases – Ar-CH4(P10), Ar-C2H6 and CF4 Evaluated items – – – – – Detection efficiency (1GeV/c p) Spatial resolution (1GeV/c p) Effect of beam rate (2GeV/c e,p,p) PID by dE/dx measurement (0.5-3GeV/c、e,m,p,p,d) Double track resolution (2GeV/c e,p,p) Without magnetic field. Setup schematic view 6/13 Typical GEM-TPC signal ADC Track Ar-C2H6, drift length 85mm, rectangular pad 1GeV/c electron beam Time (6.4ms=640bin, 1bin=10ns) 7/13 Result 1: Detection efficiency 2. For events with hits in 1st pad row and 3rd pad row, the fraction of hit in 2nd pad row. The plateau reaches 99.5%. To be updated – Detection efficiencies of Ar+C2H6 and CF4 are also >99.5% 99.5% 8/13 Result 2: Spatial resolution 1. 2. Hit positions in pad-row direction (X) and drift direction (Z) are determined by weighted mean of charge. Spatial resolution is estimated from residuals between position of inner row and interpolated position. 1 2 Res X X 1 2 X 0 X 2 , s X 6 s Res x Result Best resolution was 80mm (X-direction) and 310mm(Z-direction) with Ar-C2H6 gas, with rectangular pad, for drift length of 13mm. Zigzag pad and rectangular pad have similar spatial resolution. 9/13 Result 3: Beam rate dependence Purpose To study the effect of ion feedback on the GEM-TPC performance, detection efficiency and spatial resolution were evaluated as indexes. Beam rate was changed by changing the width of beam slit. Beam rate was monitored by 2.5x2.5cm2 plastic scintillator. Ar-CH4 gas and 85mm drift Result Under large beam rate (<5000cps/cm2, ~105cps), high detection efficiency was obtained. Spatial resolution worsen by a factor of 10%. RHIC (Au-Au, sNN=200GeV) <dNch/dh>|h=0=170, Luminosity=1.4x1027/cm2/s, sinel=7barn ⇒300cps/cm2 : 30cm away from vertex LHC (Pb-Pb, sNN=5.5 TeV) <dNch/dh>|h=0~1000, Luminosity~1x1027/cm2/s, sinel~8barn ⇒1400cps/cm2 : 30cm away from vertex 10/13 Result 4: Particle identification Energy loss was measured in momentum range of 0.5 - 3.0GeV/c with Ar-CH4. Since gain fluctuated between each momentum, energy loss was corrected as the measured values of pion agree with calculated values of pion (max. 30%) Energy resolution of a larger TPC was evaluated from measured distribution (1.0GeV/c beam) – – With a 50cm track, energy resolution is expected to be 9.1% for pion and 8.0% for proton Better than STAR TPC • sE/E=8% with a 67cm track Expected energy loss spectra of 1.0GeV/c p+ and p beams with 50cm track For proton efficiency of 99%, p rejection factor is 180 p p Energy loss 1.0GeV/c p+ 11/13 Result 5: Double track resolution Double track resolution was evaluated by the distribution of distance between two hits in drift direction Multiple hits in one event (6.4ms) were generated by high beam rate (~4000cps/cm2) and a lead block (1X0) Since distance between scattered secondary particles is generally less than 20mm, those distribution was evaluated from data with low beam rate For Ar+CH4 gas and 85mm of drift length, diffusion is 1.7mm(transeverse) and 1.0mm(longitudinal) Two tracks with 12mm distance can be distinguished Longitudinal diffusion is 1mm and electric noise limits double track resolution Secondary particle Accidental coincidence 12/13 Summary and Outlook A GEM-TPC prototype was constructed toward a tracker works under high rate and high multiplicity circumstance Beam test for evaluation of GEM-TPC was done To be updated – Detection efficiency : 99.5% – Spatial resolution : 80mm (X direction), 310mm (Z direction) (Ar(70%)+C2H6(30%)) – Beam Rate : Spatial resolution was unchanged even with 5000cps/cm2 – Energy loss : Fluctuation of gain was 12% in maximum – Adjacent track resolution : 12mm (Z direction) Our expectation was mostly satisfied GEM 13/13 Development of GEM in Japan We succeeded in fabricating a new type of GEM (CNS-GEM) using a dry etching method. CERN-GEM Etching method wet etching CNS-GEM dry etching The cross section of a hole A hole with double-conical shape A hole with cylindrical shape Gain stability of CNS-GEM is better than that of CERN-GEM. – The shape of holes in GEM significantly affect gain stability.