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ALICE simulations, predictions, comparisons with data

Explore ALICE simulations, data comparisons, and radiation effects on Inner Tracking System. Learn about ITS upgrades for RUN3+RUN4. Study beam-gas background contributions and mitigation measures.

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ALICE simulations, predictions, comparisons with data

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  1. ALICE simulations, predictions, comparisons with data Andrea Alici (Università and INFN, Bologna (IT)), Antonello Di Mauro (CERN) Workshop on radiation effects in the LHC experiments CERN, 12/02/2019

  2. A Large Ion Collider Experiment (ALICE) @ LHC The retired ITS 6 layers: 2 hybrid silicon pixel 2 silicon drift 2 silicon strip Inner-most layer: radial distance: 39 mm material: X/X0 = 1.14% • Dedicated to heavy-ion interactions (runs also in pp and pA) • Moderate collision rates in RUN1/RUN2: • pp: ~ 5∙1029Hz/cm2 • Pb-Pb : ~ 1∙1027 Hz/cm2 ALICE luminosity leveled to 2.6 Hz/μbarn pp Pb-Pb

  3. Radiation effects on Inner Tracking System integrated dose in RUN1+RUN2 (from simulation) x102 Given the operation at low luminosity, the total dose integrated by the retired ITS is considerably lower wrt other LHC experiments No impact on performance throughout RUN1+RUN2

  4. Radiation effects on Inner Tracking System SPD Increase in bulk leakage currents with delivered luminosity. Current limits tuned each year before starting the data taking, in 2018 it was necessary to adjust them also in August Pb-Pb 2018 • SSD • Observed SEU in the Front-End ReadOut Modules (racks are located in the cavern just outside the ALICE solenoid) • 7 SEUs recorded in RUN1. Mitigations added during LS1: • radiation tolerant PROM • firmware upgrade to allow a faster FPGA reload SEU cross section not increased throughout RUN2. 2017 2016 2015

  5. 1024 pixel / 3 cm The ITS Upgrade in LS2 7 layers: all Monolithic Active Pixel Sensors (ALPIDE), 10 m2 active Si, 12.5 G-pixel Inner-most layer: radial distance: 23 mm material: X/X0 = 0.3% R/O capability: pp: 400 kHz, Pb-Pb: 100 kHz • Alice Pixel Detector (ALPIDE): custom design, CMOS 180 nm Imaging Process (TowerJazz) • Pixel size: 29µm x 27µm • In pixel: Amplification, Zero suppression, 3-hit storage register • Ultra-low power consumption: ~ 40 mW/cm2 512 pixel / 1.38 cm 27 cm 147 cm OB half layer 6 IB half layers 0-1-2 100 μm (OB) or 50 μm (IB) 0.12 cm

  6. ALPIDE radiation tolerance • Non-irradiated and TID/NIEL chips similar performance • Big operational margin with only 10 masked pixels (0.002%), fake-hit rate < 10-10pixel/event and det. eff. > 99% • 5 mm resolution @ 200 e- threshold • Chip-to-chip negligible fluctuations • Sensor qualified up to TID ~ 2.7 Mrad and NIEL ~ 1.7 x 1013 1 MeV neq cm-2 (10x expected doses in RUN3+RUN4)

  7. Radiation load estimation in RUN3+RUN4 Simulationdetails in “Radiation Dose and Fluence in ALICE after LS2”,ALICE-PUBLIC-2018-012 (http://cds.cern.ch/record/2642401) Running scenario • Calculations based on 50000 minimum bias pp collisions @ √s = 5.5 TeV generated with PYTHIA (Perugia-2011) • Results for p-Pb, Pb-Pb and 13 TeVderived by scaling the pp/5.5 TeV values by the measured average charged multiplicity • Radiation calculations based on FLUKA RUN3+RUN4 TID and NIEL fluencefor the new ITS, including a safety factor of 10

  8. Radiation load estimation in RUN3+RUN4 Map of the Total Ionizing Dose (TID) for an integrated Pb-Pb luminosity of 10 nb-1 in the ALICE central barrel. Map of the Non−Ionizing Energy Loss (NIEL) weighted 1 MeV neutron equivalent fluence for an integrated Pb-Pb luminosity of 10 nb-1 in the ALICE central barrel.

  9. Radiation load estimation in RUN3+RUN4 Map of the fluence rate of hadrons with EK > 20 MEV for Pb-Pb collision rate of 50 kHz in the ALICE central barrel. Map of the charged particle fluence rate for Pb-Pb collision rate of 50 kHz in the ALICE central barrel.

  10. Contribution of beam-gas background • During RUN1, after the beam intensity ramp up in 2011, observed degradation of vacuum upstream the UX25, producing large beam-gas background reaching ~ 20% of the collision rates • Pressure bumps starting during the beam injection and reaching ~ 4-5 x 10-8 mbar, and lasting a large fraction of the fill duration; most of the ALICE detectors kept in SAFE mode until P < 10-8mbar • Contribution of different elements in the LSS2 (OD800 recombination chambers, TDI, TCTVB), due to e- cloud, heating, … • Modeling based on FLUKA simulation (A. Lechner, EN/STI), including detailed pressure profile measured by vacuum group → probability of inelastic nuclear interaction of a proton with a residual gas nucleus = 1.086x10-12 and rate of beam-gas collision = 1.086x10-12 x frev x Ibeam1(frev = 11245 Hz and Ibeam1= 2.1E14 protons) Particle fluxes from beam-gas interactionsat the UX25 entrance

  11. Contribution of beam-gas background • Quite effective mitigation measures during LS1 resulting in P ~ 2-3 10-9 mbar in RUN2 • Contribution of beam-gas background is also taken into account for RUN3+RUN4 TID and NIEL estimation by scaling down the RUN1 pressure profile • TID dominated by beam-gas background • NIEL dominated by IP collisions 2.5 0.3 3.9 0.5 4.4 0.6 5.1 0.7 4.4 0.6 2.7 0.6 2.7 0.6

  12. RadMonmeasurements in 2017 Verification of simulation models/results Total Ionizing Dose (TID) measured in 2017 by a RadMon sensor installed on the ALICE MiniFrame (z = 480 cm, r = 34 cm) upstream the LHC vacuum valve. Data from TIMBER (SIMA.ALICE12:TID2_INT)

  13. RadMon D12 –2017, pp collisions @ 13 TeV Simulation of TID per ppcollision @ 5.5 TeVat RadMon position (z = 480 cm and r = 34 cm): TIDcoll ~ 4.6 – 5.5 x 10-13krad

  14. RadMon D12 –2017, pp collisions @ 13 TeV • Expected TID(Gy): • ALICE Luminosity × sINEL,pp × TIDcoll(krad) × dNch(13TeV)/dNch(5.5TeV) × 10 • with sINEL,pp = 80 mb, TIDcoll(krad) = 5 x 10-13krad TOTEM (arXiv:1712.06153) sINEL,pp (13TeV) = (79.5 ± 1.8) mb ATLAS (Phys. Rev. Lett. 117, 182002) sINEL,pp (13TeV) = (78.51 ± 2.9) mb TIDcoll= 5x10-13krad

  15. RadMon D12 –2017, pp collisions @ 13 TeV • Expected TID(Gy): • ALICE Luminosity × sINEL,pp × TIDcoll(krad) × dNch(13TeV)/dNch(5.5TeV) × 10 • with sINEL,pp = 80 mb, TIDcoll(krad) = 5 x 10-13krad TIDcoll= 5x10-13krad goodagreement

  16. RadMon D12 –2017, pp collisions @ 13 TeV • Expected TID(Gy): • ALICE Luminosity × sINEL,pp × TIDcoll(krad) × dNch(13TeV)/dNch(5.5TeV) × 10 • with sINEL,pp = 80 mb, TIDcoll(krad) = 5 x 10-13krad After TS1, the RadMonsensor D12 wasdisplaced to monitor anothersystem, agreementiskept ! TIDcoll= 2.75x10-13krad TIDcoll= 5x10-13krad

  17. RadMonD12 –2017, beam-gas Beam 1 IP2 Beam gas contribution estimated using the RUN1 bad conditions, nevertheless the contribution in this position is negligible

  18. RadMonD12 in 2018 position • D12 RadMon D12 position not optimal to investigate possible beam-gas effects • In 2018 moved closer to beam axis and downstream the massive LHC valve (z= 340 cm, r= 20 cm) → comparable TID per interaction Expected TID per beam-gas interaction in the LSS2 Expected TID per pp collision @ 13 TeV

  19. RadMonD12 –2018, pp collisions + beam gas assuming: TIDcoll(pp) = 2x10-13krad TIDcoll(bg) = 2x10-13krad

  20. RadMon– 2018, Pb-Pbcollisions @ 5.02 TeV • During Pb-Pb runs the contribution from beam-gas is negligible, the expected TID (Gy) is estimated as: • ALICE Luminosity × 8 b × TIDcoll(krad) × dNch(Pb-Pb)/dNch(pp) × 10 . TID Discrepancy before end of run under investigations, loss of time alignment in D12 data?

  21. Summary • The limited radiation load corresponding to the low luminosity running of ALICE allowed smooth operation of the “retired” ITS without any major issue. • The ALPIDE silicon sensor of the new ITS has been qualified in several irradiation tests, showing a radiation tolerance an order of magnitude better than the load estimated for the running scenario planned in RUN3 and RUN4 • A verification of the FLUKA based simulation of TID and NIEL has been performed using RadMon measurements during RUN2: experimental results can be reproduced by simulation including pure pp collisions and beam-gas thus reassuring that the radiation load predictions for ALICE experiment in RUN3+RUN4are not significantly underestimated

  22. Backup slides

  23. LSS2 vacuum layout (in 2012) A1R2.X B1L2.X A1L2.X IP2 VGI.220.1L2.X VGI.220.1R2.X 22m -22m Vacuum Sector A4L2.X TDI ITL2 D2 VGPB.231.4L2 VGPB.123.4L2 OD800-L VGI.500.4L2 VGPB.120.4L2 80m 110m 70m Vacuum Sector A4R2.X ITR2 D2 OD800-R VGPB.123.4R2 VGI.514.4R2 VGPB.120.4R2 -110m -70m

  24. Bkgd observations in RUN1 (2011) • Linear dependence of beam-gas rate on product of beam intensity and total pressure • Bkgd rate reaching ~ 20% of total A-side C-side fill 2178 fill 2178 Exp: calculated using pressure fit parameters

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