FCal luminosity measurement Samir Arfaoui Stony Brook University
FCal luminosity measurement Samir Arfaoui Stony Brook University 21 September 2021 Samir Arfaoui - LAr Week 1
Measurement principle Total HV current Number of pairs created in the detector f: calorimeter sampling fraction K: suppression factor for electron response wrt mip W: liquid Argon ionization potential 21 September 2021 Total energy deposited in the detector Luminosity Pros: • Trigger independent • DAQ independent • Linear with luminosity Cons: • Low sampling rate (0. 2 Hz) • No bunch-by-bunch capabilities Samir Arfaoui - LAr Week 2
2011 Calibration 1. Subtract pedestal from current measured 2. Fit 1 st degree polynomial 3. Apply calibration to IFCal to obtain LFCal 21 September 2021 Samir Arfaoui - LAr Week 3
2011 Calibration One ATLAS run in 2011 (189280) and fit the selected FCal HV lines’ currents to extract calibration. Then apply calibration to the rest of the 2011 data. Equivalent to more than one straight month of stable beams! FCal-1 -C Current [u. A] FCal-1 -A 21 September 2021 2011 ATLAS preferred luminosity (BCM Event. OR) [1030 cm 2 s 1] (Luminosity range: 1033 cm 2 s-1 4 1033 cm 2 s-1) Samir Arfaoui - LAr Week 4
FCal vs. BCM_H_Event. OR One color per run All average One color per unique number of colliding bunches Versus luminosity è 2% variation edge-to-edge è Deviation as luminosity decreases Versus time è 2% variation edge-to-edge è Steps at technical stops è Depends on number of colliding bunches 21 September 2021 Samir Arfaoui - LAr Week 5
FCal vs. BCM_H_Event. OR One color per run All average One color per unique number of colliding bunches Pedestal correction Motivation: possible error in pedestal subtraction causing deviation at low luminosities è Corrects deviation è Ratios within +/- 0. 5% è Flattens time stability Source of this issue still under investigation 21 September 2021 Samir Arfaoui - LAr Week 6
September mu-scan Goal Understand mu-dependance of the different luminosity determinations LBCM [1030 cm 2 s-1] How Acquire collision data at very different instantaneous luminosities but under the same beam conditions by: Scanning the beams tranversally similarily to vd. M scans Peak luminosity: 1. 4 1033 cm 2 s-1 Time 21 September 2021 Samir Arfaoui - LAr Week 7
September mu-scan https: //indico. cern. ch/get. File. py/access? contrib. Id=2&res. Id=1&material. Id=slides&conf. Id=157844 21 September 2021 Samir Arfaoui - LAr Week 8
FCal linearity tests (1/2) • Goal: Estimate linearity of the power supply current measurement • Setup – One HV line at nominal voltage (250 V) – External digital currentmeter (LSB 1 n. A) – In between Position Resistance [MΩ] I @ 250 V [μA] 0 500 0. 5 1 250 1 2 166. 7 1. 5 3 125 2 4 100 2. 5 5 66. 7 3. 75 6 40 6. 25 7 22. 2 11. 25 10. 5 23. 75 5. 1 48. 75 3. 4 73. 75 2 123. 75 • Custom made 12 positions 8 resistor switch-box • Allows for different DC currents 9 to flow, probe wide range of 10 currents 11 21 September 2021 Samir Arfaoui - LAr Week 9
FCal linearity tests (2/2) M 82 C 4 M 84 C 4 F(x) = p 0 + p 1*x + p 2*x**2 Chi 2 = 103. 457 NDf = 22 p 0 = 2. 93406 +/- 0. 00134424 p 1 = 1. 0006 +/- 9. 54745 e-05 p 2 = 3. 93468 e-08 +/- 8. 26856 e-07 F(x) = p 0 + p 1*x + p 2*x**2 Chi 2 = 14. 8711 NDf = 16 p 0 = 2. 7965 +/- 0. 00143758 p 1 = 1. 00106 +/- 0. 000128213 p 2 = -6. 34343 e-07 +/- 1. 13507 e-06 Measurement is very linear over the probed range 21 September 2021 Samir Arfaoui - LAr Week 10
Summary • FCal HV lines successfully – Selected (low noise, no shorts) – Calibrated to BCM luminosity for a single run – Compared to luminosity for most of the 2011 data • Results very encouraging • Stable within 2% of the BCM reported luminosity • Mu-scan data – Goal is to estimate luminosity dependence of calibrated algorithms during a single data-taking period – Results consistent with normal physics data – FCal luminosity agrees with other luminosity determinations better than 2% for mu > 5 • The FCal results, combined with Tile. Cal, LUCID, BCM, and Vertex counting luminosity determinations allowed the evaluation of the preliminary systematic uncertainty on the 2011 dataset – 3. 7 % for β*=1. 5 m dataset – 4. 1 % for β*=1. 0 m dataset – Overall uncertainty for the 2011 dataset: 3. 9%
Summary • Investigation of the linearity of the current measurement by the power supply – – Limited test (two HV lines) on the production system Using resistor switch-box the probe large current range External digital current-meter for comparisons Results demonstrate very good linearity over the range [0, 120] μA • Next steps – Pinpoint source of deviation observed between FCal and BCM at low luminosity – Converge on decision regarding power supplies before March 2011 • Re-calibration at Iseg? • Acquisition of a few new, more precise, power supplies to populate the FCal -1? – Contribute actively to edition of the next ATLAS luminosity paper
Backup 21 September 2021 Samir Arfaoui - LAr Week - Munich 13
Run 189280 – Sep th 13 2011 https: //atlas. web. cern. ch/Atlas/GROUPS/DATAPREPARATION/Data. Summary/2011/run. py? run=189280 Peak luminosity: 3. 3 1033 cm-2 s-1 FCal-1 EMEC Inner Wheel EMB 21 September 2021 Samir Arfaoui - LAr Week 14
Summary of current draws Number of HV lines HV line current Max HVPS [μA] allowed current 7 Te. V [μA] 3. 3 1033 cm-2 s-1 HV line current [μA] 7 Te. V 1034 cm-2 s-1 EMEC IW 530 200/3000 20 60 EMEC OW 1006 200 2 -8 6 -24 HEC 1024 200/500 2. 5 7. 5 EMB 1008 75 4 12 FCal 1 128 6000/10000 50 150 Agrees with expected currents and well within allowed current output 21 September 2021 Samir Arfaoui - LAr Week 15
Legend – Run (Number of colliding bunches) 21 September 2021 Samir Arfaoui - LAr Week 16
FCal HV distribution One FCal readout cell One HV sector #HV lines = 4 FCal 1 (EM) FCal 1 module • 1008 readout cells • 16 HV sectors • 64 HV lines • Each sector is fed by 4 separate HV lines • Each HV line feeds ¼ of a readout cell (for redundancy) • Innermost (and edge) cells are fed by only one HV line ===> Current measured in one HV line corresponds roughly to ¼ of the current induced in the HV sector by minimum bias events 21 September 2021 Samir Arfaoui - LAr Week 17
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