Presentation on theme: "1 ALICE EMCal Electronics Outline: PHOS Electronics review Design Specifications –Why PHOS readout is suitable –Necessary differences from PHOS Shaping."— Presentation transcript:
1 ALICE EMCal Electronics Outline: PHOS Electronics review Design Specifications –Why PHOS readout is suitable –Necessary differences from PHOS Shaping time / data volume problem EMCal vs PHOS comparison summary
8 Tower/module structure: “shashlik” design Total Pb depth = 124 mm = 22.1 X 0 Comparisons: PHOS = 180 mm/8.9 mm = 20.2 X 0 ATLAS LiqAr/Pb = 25 X 0 CMS PbWO = 25 X 0 Trapezoidal module: transverse size varies in depth from 63x63 to 63x67 mm 2 78 layers of 1.6 mm scint/1.6 mm Pb Moliere radius ~ 2 cm Pb absorber has dimensions of module Towers defined by smaller optically isolated scintillator tiles Going to Shashlik design allows to use thinner sampling layers to improve intrinsic energy resolution.
9 Use PHOS APD + Charge Sensitive PreAmplifier Must operate in Magnetic Field. Need gain (and gain adjustment for trigger) Light yield from EMCal similar to PHOS
10 inclusive jets 10 Hz @ 50 GeV few x 10 4 /year for E T >150 GeV E FS = 250 GeV (PHOS 80 GeV) Full Scale energy… From Peter Jacobs
11 Light yield Light Yield (in photo- electrons) measured at WSU with Cosmic rays in prototype tower using well-calibrated PMT. For APD, with Gain M=1 expect ~2.5 photoelectrons/MeV Compare PHOS: 4.4 pe/MeV @ M=1. For same fullscale signal amplitude M Emcal = 50(M PHOS )*(4.4*80GeV)/(2.5*250GeV)=28
12 Intrinsic Energy Resolution GEANT Simulation results: Sampling fraction 8.1% Intrinsic energy resolution ~12% Calculations by Aleksei Pavlinov
13 The PHOS APD + CSP Electronic Noise PHOS measurement 625e @ 2 s shaping : 625/(4.4*50)=2.8 MeV If EMCal uses 100ns shaping, expect ~1500e : 1500/(2.5*50)=12 MeV (36MeV 3x3) from PHOS Electronics Document
14 Energy Resolution: All contributions Even with pessimistic assumptions (eNC=2000) electronics contributions to resolution are unimportant in energy region of primary interest. Important open question: slow neutrons drives choice to investigate short shaping time ~100 ns. 12% intrinsic 1% calibration Digitization (full scale=250 GeV) PA/shaper eNC=2000 (60MeV) Dual 10-bit ADCs (high and low gain)
15 EMCal Resolution: The ALICE “Environment” EMCAL onlyAll ALICE material GEANT Simulations for single photons (i.e. p+p) Significant degradation of resolution A. Pavlinov
16 The ALICE “Environment” Before 30ns After 30 ns Large background from moderately slow neutrons. Central HIJING Simulations: Production point of particles with E Deposit Calculations by Heather Gray
17 Soft,Slow (neutron) Background Calculations by Heather Gray Total EMCal E Deposit vs Time Tower neutron E Deposit Mean neutron E Deposit =36 MeV (i.e. 3 times electronic noise!) with rms=41MeV Note: This is for Central HIJING (worse case, the problem is centrality dependent).
18 Bandwidth: Another shaping time argument Propose to use peak = 100ns with 20MHz sampling Ex: PHOS Bandwidth –Number of samples = 5* peak / t sample = 5*4 s/100ns = 200 –Average hit rate (>30MeV) = 200Hz –GTL bus rate = (14FEE)(32chan)(2Gain)(10bit)(200samples)(200Hz)=44.8MB/s –RCU data rate = 2*GTL/RCU partition=89MB/s (limit 100MB/s) EMCal Bandwidth –Number of samples = 5* peak / t sample = 5*200ns/50ns = 20 –Average hit rate (>30MeV) = 2000Hz (from 6x6/2x2, or 80% occupancy in central Pb+Pb(GEANT) -> 25% min bias -> 2kHz) –GTL bus rate = (12FEE)(32chan)(2Gain)(10bit)(20samples)(2000Hz)=38.4MB/s –RCU data rate = 2*GTL/RCU partition=77MB/s –If peak = 4 s with 200 samples then GTL bus rate=384MB/s - Death!
20 PHOS vs EMCal Readout comparison Commonalities: –Same APD + preamplifier –Same GTL bus (but not identical) –~Same FEE –Same RCU,TRU, etc Differences –Different T-Card: FEE located far away, need signals driver on T- card+twisted pair –Same FEE but with shorter shaping time, 100ns –Numerology, FEE to GTL to RCU, TRU –New (later option) TRU’ to form larger area energy sums for jet trigger. Other –Power consumption: 63mW*1152 = 73W in SM, 450W in FEE region of SM
21 TowerAPD+PreAmpTransition CardFEE-card w/ ALTRO 8 4 TRU = Trigger Router Unit 36 RCU = Read-out Control Unit 2(1.5) RCU/SuperModule = 1152 Towers (cf. 896 PHOS) Level 0 Level 1 3 OR per SM EMCal Electronics: Numerology 32 Channels 384 Towers 1152 Towers (768 + 384) 12 TRU’ = Trigger Router Unit’ 36 13824 Towers Level 1,..
22 Totals/SuperModule 36 FEE cards 3 GTL bus 3 TRU 1 RCU EMCal Readout Matrix per Supermodule
30 EMCAL: main jet physics capabilities 1.Level 1 trigger for jets, 0 / essential for jet E T >50 GeV 2.Improved jet energy resolution charged-only jets: poor resolution (>50%) TPC+EMCAL: resolution ~30% main effect: out-of-cone energy (R~0.3 for heavy ions) also: intrinsic resolution; missing n, K 0 L, discrimination to p T ~30-40 GeV (cross section limit for +jet coincidences in acceptance) S. Blyth, QM04
31 Tower granularity (cont’d) 0 opening angle shower shape discrimination Heather Gray, LBNL/Cape Town rejection for p T <~30 GeV/c More sophisticated SSA underway, possible large improvements Additional +jet issues: other backgrounds: fragmentation , radiative decays, … isolation cuts +jet is important but limited measurement fixed $$$: maximize acceptance for jets, granularity driven by cost preliminary
32 Soft,Slow (neutron) Background Tower Cut 1 100MeV 2 150MeV 3 200MeV 4 500MeV Time Integ. 0 20ns 1 30ns 2 50ns 3 100ns 4 200ns 5 500ns 6 1000ns Calculations by Heather Gray Kill the number of neutron hits by tower threshold or (integration) time cut. Tower threshold cut of ~150MeV is effective, but it doesn’t remove neutron energy deposit in tower with real gamma hit! Integration time cut can also reduce the number of neutron hits. Benefit also applies to tower with real hit. Note: Using PHOS cluster algorithm without splitting.
33 Soft,Slow (neutron) Background Tower Cut 1 100MeV 2 150MeV 3 200MeV 4 500MeV Time Integ. 0 20ns 1 30ns 2 50ns 3 100ns 4 200ns 5 500ns 6 1000ns 10-20 GeV/c + HIJING (b<3fm) Full ALICE Calculations by Heather Gray Tower energy threshold and integration time cuts are correlated. Shortening integration time allows to lower tower energy resolution, which will improve performance especially at low p T. Note: Using PHOS cluster algorithm without splitting. Feasible to use a shaping time of ~100ns with PHOS electronics?
34 Soft,Slow (neutron) Background Calculations by Heather Gray The Alarming Plot… Taking the shower core only… Conclusion: Neutrons cause large occupancy - difficulty for cluster finding. Will need to use shower core with high tower threshold. Shorter shaping time will improve the situation. Again: This is for Central HIJING (worse case, the problem is centrality dependent). due to large clusters
35 EMCal L0 trigger input concerns … Upon receipt of L0, the ALTRO chip keeps 14 presamples: –For PHOS with 10MHz sampling this is region of 1.4 s prior to L0. –For EMCal with 20MHz sampling this is region of 700ns prior to L0. –With ALICE L0 latency of 1.2 s For 10MHz sampling this is just okay with ~no presamples For 20MHz sampling this is 300ns after 200ns peaking time - Death! Proposed PHOS solution is to use local PHOS L0 trigger output as ALTRO L0 trigger input. Would “solve” problem for EMCal also, but… –This seems to be a very dangerous solution… L0(PHOS).ne. L0(CTP): might have L0(CTP) without L0(PHOS) then L2 request when there was no L0… Danger of filling ALTRO buffer with noisely local L0’s? –Only alternative for EMCal seems to be to keep 10MHz sampling and go to 200ns shaping time.
36 EMCal Jet Trigger (TRU’?) Calculations by Bill Mayes Conclusion: Increasing trigger region requires in increase trigger threshold for same trigger rejection factor (e.g. central HIJING). Not much difference in trigger efficiency (on PYTHIA jets) versus trigger region size - except for large patch sizes. PHOS TRU size (4x4 tower) works quite well…
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