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Future Upgrade and Physics Perspectives of the ALICE TPC

Future Upgrade and Physics Perspectives of the ALICE TPC. Taku Gunji On behalf of the ALICE Collaboration Center for Nuclear Study, The University of Tokyo. ALICE upgrade after Long Shutdown 2 (LS2) ALICE TPC u pgrade with micro-pattern gaseous detectors

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Future Upgrade and Physics Perspectives of the ALICE TPC

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  1. Future Upgrade and Physics Perspectives of the ALICE TPC Taku Gunji On behalf of the ALICE Collaboration Center for Nuclear Study, The University of Tokyo

  2. ALICE upgrade after Long Shutdown 2 (LS2) ALICE TPC upgrade with micro-pattern gaseous detectors Status of R&D activities Summary and Outlook Outline ALICE TPC Upgrade Technical Design Report (submitted in 2013) http://cds.cern.ch/record/1622286

  3. Detailed characterization of the QGP at the highest LHC energy • Main Physics topics. Uniquely accessible with ALICE after LHC luminosity and detector upgrade. • Heavy-flavors (charm, beauty): • Diffusion coefficient – azimuthal anisotropy and RAA • In-medium thermalization and hadronization – meson-baryon • Low-mass and low–pt di-leptons: • Chiral symmetry restoration – vector meson spectral function • Space-time evolution and thermodynamical properties – radial and elliptic flow of emitted radiation • Quarkonia (J/y, y’, U) : • Charm and bottom thermalization, regeneration – RAA, flow • Jet quenching and fragmentation: • Energy loss, transport properties vs. Q2 – RAA, flow • Heavy-nuclei, exotic hadrons: • Confinement, Coalescence, quasi-state in QGP – RAA, flow ALICE Physics Program in Run3 ALICE Upgrade LoI: http://cds.cern.ch/record/1475243

  4. Operate ALICE at high rate, record all MB events • Goal: 50kHz in Pb-Pb (~10nb-1 in Run3 and Run4) • Upgrade detectors and electronics during Long Shutdown 2 (2018) • New Inner Tracking Systems • Improved vertexing, tracking at low pT, and improved rate capability • GEM TPC with continuous readout • High rate capability, preserve PID and tracking performance • Muon Forward Tracker • Electronics, Trigger, online-offline upgrade ALICE Upgrade Strategy Talk by S. Siddhanta (172) Posters by R. Romita(M-23), C. Terrevoli(M-27), J. Stiller(M-26) Posters by L. V. Palomo(M-29), A. Uras(F-56)

  5. High statistics + Dalitz, conversion and charm rejection in new ITS, TPC+TOF for eID Reduced systematic uncertainties from charm decay Example: Low Mass Di-electrons ALICE Simulation TPC High rate New ITS B=0.2T ALICE Simulation TPC Current rate New ITS B= 0.2T dedicated low-field run dedicated low-field run

  6. Diameter: 5m, length: 5 m • Acceptance: |h|<0.9, Df=2p • Readout Chambers: total = 72 • Outer (OROC): 18 x 2 • Inner (IROC): 18 x 2 • Pad size • Inner: 4×7.5 mm2, Outer: 6×10&15 mm2 • Pad channel number = 557,568 • Gas: Ne-CO2 (90-10) (in Run1) at drift field = 400V/cm • sT~sL ~0.2mm /√cm, vd~2.7cm/ms • Total drift time: 92ms • MWPC + Gating Grid Operation • Rate limitation < 3.5kHz 114cm 50cm ALICE TPC Central Electrode (-100kV) E E 5m 5m Readout chamber OROC IROC

  7. Operation of MWPC w/o Gating Grid in 50 kHz Pb-Pb would lead to massive space-charge distortion due to back-drifting ions. • Continuous readout with GEMs • GEM has advantages in: • Reduction of ion backflow (IBF) • High rate capability • No ion tail • Requirement • IBF < 1% at Gain =2000 • dE/dx resolution < 12% for 55Fe • Stable operation under LHC condition GEM TPC upgrade Standard GEM Pitch=140mm Hole f=70mm

  8. Ions from 8000 events pile up in the drift volume in 50kHz Pb-Pb collisions (tion=160ms) • 1% of IBF at Gain = 2000 (e=20) • At small r and z, dr=20cm and drf = 8cm • For the largest part of drift volume, dr<10 cm • Corrections to a few 10-3 are required for final resolution (s(rf) ~ 200um) Space Charge Distortions

  9. Extensive studies started in 2012. • Technology choice • Baseline: GEM stacks of standard (S) and large-pitch (LP) • COBRA-GEM • 2 GEM + MicroMegas(MMG) • Ion backflow • Gain stability • Discharge probability • Large-size prototype • Single mask technology • Electronics R&D • Garfield simulations • Physics and Performance simulations • Collaboration with RD51 at CERN GEM TPC R&D Program 280um

  10. IBF and Resolution studies for baseline solution • Different foil configurations, VGEM, transfer field ET • IBF optimized setting = high ET1 & ET2, and low ET3, VGEM1~VGEM2~VGEM3<<VGEM4 • 0.6-0.8% IBF at s(5.9keV)~12% 4 GEM setup with S and LP foils 140um pitch 280um pitch 4 GEM S-LP-LP-S

  11. Garfield++/Magboltz simulations • Field calculation by ANSYS • IBF quantitatively well described by simulations based on Garfield++. Garfield Simulations GEM1(S) GEM2(LP) GEM3(LP) GEM4(S)

  12. dE/dx studies with 3 GEM Prototype • Prototype IROC was built in 2012. • With 3 single-mask GEMs • Beam test at PS (e/p/p) in 2012 • Good e/p separation • sdE/dx/<dE/dx> ~ 10.5% • Comparable to the current • TPC resolution (~9.5% with IROC) G=1000 6000

  13. IBF and Resolution studies • VMesh, VGEM, transfer field ET • It is possible to reach < 0.2% IBF at s(5.9keV)~12%. Alternative: 2 GEM + MicroMegas Large-scale solution and operational stability still to be verified Ne-CO2 (90-10) Gain~1850-2150 UMMG UGEM

  14. New ASIC “SAMPA” • Integration of the functionality of the present preamp/shaper and ALTRO ADC+DSP • Both polarity, Continuous/Triggered RO • SAR ADC (10M or 20MSPS) • First MWP submission in April Electronics Upgrade of ALICE Electronics & Trigger System (Technical Design Report) http://cds.cern.ch/record/1603472

  15. Twostage reconstruction scheme: • Cluster finding and cluster-to-track association in the TPC • Data compression by x20 : 1 TB/s  50 GB/s • Scaled average space-charge distortion map • Full tracking with ITS-TRD matching • High resolution space-charge map (time interval~5ms) for full distortion calibration Reconstruction Scheme

  16. Space charge fluctuations (~3%) are taken into account.(Nevt,dNch/dh,etc) ITS-TPC track matching and pT resolution are practically recovered after 2nd reconstruction stage. Expected Performance

  17. The ALICE program after LS2 requires an upgrade of the TPC. • MWPC-based readout chambers will be replaced by detectors employing micro-pattern detectors including GEMs to allow TPC operation in continuous mode. • Extensive R&D of the GEM TPC upgrade • 4 GEMs, 2GEM+MMG • IBF<1%, Resolution for 55Fe<12% • Performance of the present TPC will be maintained in 50kHz Pb-Pb collisions. • Stability, discharge probability under study • Beam test of IROCs at PS and SPS in 2014 • Construction (GEM, FEE) from 2015 Summary and Outlook

  18. Backup slides

  19. Measurement at CERN(RD51)/TUM/FRA/Tokyo. • 3 or 4 standard GEM settings • standard and/or large pitch foils • X-ray from top or side, • current readout from each electrode IBF with conventional GEMs

  20. COBRA-GEM • SciEnergy, 400um pitch • 2 GEM + MicroMegas Other options

  21. Parameterization of collection, extraction, gain, resolution, and IBF vs. VGEM, Ed, Et, Eind, S/LP Calculator Collection vs. Ed/UGEM1 Extraction vs. ET/UGEM2

  22. Parameterization of collection, extraction, gain, resolution, and IBF vs. VGEM, Ed, Et, Eind, S/LP Calculator RMS/Gain vs. Total Multiplication*sqrt(collection) # of ions in drift/Effective Gain vs. Ed/UGEM1

  23. Source of space-charge fluctuations • The number of pile up events, Multiplicity • Charge of the tracks, Granularity Space-charge fluctuation • At 8000 ion pile up events, • space-charge fluctuation is • 2-3%. • Dominant source: • Nevt fluctuation • Multiplicity fluctuation • Need take into account these • fluctuations for distortion corrections.

  24. Study of space-charge distortions based on real Pb-Pb data Space-charge map 50kHz Pb-Pb collisions. 8000 pileup events in ion drift time=160msec Overlapped 130k events are used to estimate time-averaged space- charge distortion.

  25. Time shifted space-charge map Space-charge fluctuation • Simulation inputs: • Use fluctuating space-charge map for track distortion and • Correction • Use time-shifted map • ~5msec is the time-scale to update the space-charge map during the online-calibration procedure

  26. Simulate statistics of typical calibration interval (~5msec. 250Hz) • Pre-reconstruct by scaled average SC map • Then, use ITS-TRD track interpolation • Map residual local distortions and 2-D correction analysis to get (dr, drf) Distortion correction in 2nd stage Spatial Patterns of dr and drf are well reproduced.

  27. Large-size GEM foils by CERN using single mask technology. 3 standard GEM foils in prototype IROC Prototype

  28. MWPC without GG • Best estimate: ion back flow (IBF) rate of ~5% at gain = 6000 • Simulation shows a large distortion in electric field impossible • Tolerable limit • IBF rate of 1% at gain 2000; ~20 back flow ions per electron TPC Operation without GG

  29. Front-end Electronics Data ratesandbandwidthrequirements Comparisonof FEE parametersfor RUN 1 and 3

  30. 98% tracking efficiency in pp. 1-3% lower for central Pb-Pb Momentum resolution ~ 1% at 1GeV, 5% at 50GeV dE/dx resolution= 5.5% in pp and 7% in Pb-Pb Current TPC Performance

  31. GG close 100us after collisions GG closed for 180us (ion arrival time to the GG) IBF<10-4 but event rate < 3.5kHz GG open results in 5-8% IBF Gating Grid Operation

  32. 3 stacked GEMs with 90Sr for Ne/CO2 (90/10) • Single-wire chamber as a reference for correction of the gain fluctuation due to P/T Gain Stability Gain Variation within 0.5% at gain=1800

  33. IROC Prototype (3 standard GEMs) beamtest at CERN-PS T10 • e, p, p: 1-3 GeV for negative, 1&6 GeV for positive • PCA16 + ALTRO Readout from LCTPC collaboration • dE/dx resolution for standard and IBF setting Prototype Beamtest at PS in 2012

  34. Garfield++ simulations • Field calculation by ANSYS • Mis-alignment of GEMs • Measurements are understood. Garfield Simulations

  35. Systematic studies for 4 GEM • different foil configurations, VGEM, transfer field ET • IBF optimized setting = high ET1 & ET2, and low ET3, VGEM1<VGEM2<VGEM3<VGEM4 • 0.6-0.8% IBF and s(5.9keV)=11-12% IBF and Energy Resolution 4 GEM S-LP-LP-S

  36. Space-charge distortion correction

  37. Average pileup = 5 MB events • 2500 tracks in average • ~7500 tracks is maximum • Maximum occupancy : 70% at IROC Occupancy

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