1. The ATLAS Beam Conditions Monitor Marko Mikuž University of Ljubljana & Jožef Stefan Institute IEEE NSS’07 N31-7 Hawaii, October 31, 2007

2. NSS’07, Hawaii, Oct 31, 2007ATLAS BCM (M.Mikuž, Ljubljana)2 The ATLAS BCM collaboration CERN  D. Dabos, H. Pernegger, P. Weilhammer Fotec & Univ. Wiener Neustadt  E. Griesmayer, H. Frais-Kölbl, M. Niegl JSI & Univ. Ljubljana  V. Cindro, I. Dolenc, A. Gorišek, G.Kramberger, B. Maček, I. Mandić, E. Margan, M. Zavrtanik, M. Mikuž OSU, Columbus  H. Kagan, S. Smith Univ. Toronto  M. Cadabeschi, D. Tardif, W. Trischuk  ~20 people from 5 institutes

3. NSS’07, Hawaii, Oct 31, 2007ATLAS BCM (M.Mikuž, Ljubljana)3 Aim of the ATLAS BCM Goal of the BCM detector system inside the ATLAS Inner Detector:  Monitor instantaneous background rate and collision rate during normal running Measure background rate close to vertex Compare to rate of collisions and provide basic bunch-by-bunch luminosity measurement  Protection in case of larger beam losses Detect early signs of beam instabilities (e.g. wrong magnet settings, trips,…) Issue warning and alarm signals for equipment protection Input to ATLAS Detector Safety system and LHC beam abort

4. NSS’07, Hawaii, Oct 31, 2007ATLAS BCM (M.Mikuž, Ljubljana)4 Timing of background vs. interactions Distinguish collisions from background through time-of-flight measurement with detectors at either side of the IP  Is measured for every bunch crossing (25ns)  Requires fast and radiation hard detector + electronics ( rise time ~ 1ns, pulse width ~ 3ns, baseline restoration < 10ns)  Out of collision time hits signatures of beam anomalies Time difference Interactions:  t = 0, 25, … ns Upstream background:  t = 2z/c = 12ns BCM Side A - Side C

5. NSS’07, Hawaii, Oct 31, 2007ATLAS BCM (M.Mikuž, Ljubljana)5 The Beam Conditions Monitor 4 BCM stations on each side of the Pixel detector  Mounted on Pixel support structure at z = +/- 183.8 cm and r = 5.5 cm  Each station: 1 cm 2 detector element + front-end analogue readout 183cm 38 cm

6. NSS’07, Hawaii, Oct 31, 2007ATLAS BCM (M.Mikuž, Ljubljana)6 The BCM is installed in ATLAS BCM installed on Pixel detector, lowered into ATLAS pit in June 2007

7. NSS’07, Hawaii, Oct 31, 2007ATLAS BCM (M.Mikuž, Ljubljana)7 The BCM Module Sensors are poly-crystalline CVD diamonds  Developed by RD42 and Element Six Ltd Radiation hard  Shown to withstand > 10 15 p/cm 2 Fast & short signal (FWHM~2ns, rise time<1ns)‏  Large charge carrier drift velocity (10 7 cm/s) (operates at high drift field ~2 V/  m)‏ Very low leakage current after irradiation  Does not require detector cooling 2 diamonds each with: Thickness 500  m CCD @1V/  m ~ 200  m Size: 10 x 10 mm 2 Contact size: 8 x 8 mm 2 BCM operation: 2 V/  m

8. NSS’07, Hawaii, Oct 31, 2007ATLAS BCM (M.Mikuž, Ljubljana)8 Front-end readout: RF amplifier 2-stage amplification of ionization current pulse  RF amplifier, no feed-back Parameters  Bandwidth 500 MHz (1 st stage)  Amplification ~40 dB Radiation hard to ~10 15 n/cm 2  Tested at Ljubljana TRIGA reactor and CERN PS  Find gain reduction of 20% after 5x10 14 n/cm 2 plus 5x10 14 p/cm 2 at constant noise

9. NSS’07, Hawaii, Oct 31, 2007ATLAS BCM (M.Mikuž, Ljubljana)9 BCM system overview Inside Pixel Package At PP2 (~1 st muon chamber)Counting room USA15 ~30 Mrad detector ~1 krad TOT “digitization”

10. NSS’07, Hawaii, Oct 31, 2007ATLAS BCM (M.Mikuž, Ljubljana)10 Functional tests of BCM chain BCM modules and performance of the signal processing chain have been tested in several lab tests and test beams We currently use beam tests to commission the readout electronics using three spare modules The next slides will show an overview of the tests done:  Module tests during production  Analogue signal response during beam tests  Performance after analogue-to-digital conversion and optical link  Efficiency & Noise  Timing resolution

11. NSS’07, Hawaii, Oct 31, 2007ATLAS BCM (M.Mikuž, Ljubljana)11 Module tests Diamonds  IV curve & CCD measurements before assembly to modules Use 90 Sr source test setup to characterize each module  Measure signal distribution and noise in HV scan from -1000V to +1000V  Done before and after burn-in (80°C@12hrs) and thermal cycling (10 cycles -20 to +40°C) while modules are operated Measure on modules a most probable SNR = (7.3 ± 0.56) :1 for 90° impact  Meets our requirement of 10:1 in final configuration at 45° ( x √2) S mp ~ 2.7mV Noise rms ~330  V 200 MHz BWL

12. NSS’07, Hawaii, Oct 31, 2007ATLAS BCM (M.Mikuž, Ljubljana)12 Test beam (CERN SPS) Test BCM modules in high energy pion beam at CERN SPS Goal:  Evaluate analogue signals  Test NINO time-over-threshold (TOT) conversion and opto-link  Measure efficiency, noise rate and timing resolution  Test V1.0 of FPGA readout board Setup:  Telescope with 5 scintillators and 2x2 mm 2 trigger area, BCM modules moved across beam  BCM stations connected via 16 m coax cable to Ortec 300 MHz amplifier for analogue measurements and VME 2 Gs/s ADC  BCM stations connected via 16 m coaxial cable to NINO board + opto transmitter + fibre + opto receiver going to VME readout and FPGA readout

13. NSS’07, Hawaii, Oct 31, 2007ATLAS BCM (M.Mikuž, Ljubljana)13 Signal uniformity & time resolution Efficiency versus beam position  Analogue signal > 150 ADC counts  Scans in steps of 1x1 mm 2 Exhibits very efficient and uniform response over active area Time difference of NINO outputs between 2 BCM stations  NINO threshold fixed to 200 mV Easily meets requirement of 1 ns NINO Time res ~ 490ps No tails ! Efficiency

14. NSS’07, Hawaii, Oct 31, 2007ATLAS BCM (M.Mikuž, Ljubljana)14 Time resolution Time difference between 2 BCM stations Two measurement sets:  Offline analysis of analogue signals assuming a start time at 50% amplitude (“constant-fraction-discriminator”)  Time resolution of NINO output with fixed threshold in NINO operational range (200mV) Analog Time res ~ 360ps NINO Time res ~ 490ps No tails !

15. NSS’07, Hawaii, Oct 31, 2007ATLAS BCM (M.Mikuž, Ljubljana)15 Efficiency and noise rate Efficiency and noise rate measured after analogue-to-digital conversion with NINO and optical link Median signal 335mV on NINO discriminator Slope = 31mV rms noise * * Baseline noise of NINO without input connected = 13.5mV rms Efficiency >99% for threshold of 180mV or less Median SNR after full signal chain ~ 11:1 Beam blocker IN Muons “leaking” through beam blocker Machine development – lower muon rate

16. NSS’07, Hawaii, Oct 31, 2007ATLAS BCM (M.Mikuž, Ljubljana)16 Operation in ATLAS For operation want to maximize efficiency at minimal number of noise hits per LHC BX (25 ns) Threshold optimized with efficiency versus noise occupancy per module and BX:  Horizontal axis is calculated from fit to previous noise vs threshold plot e.g. 180 mV threshold: Efficiency is 99% at noise occupancy of 3 x 10 -8 /module/BX At low luminosity (5x10 32 cm -2 s -1 ) expect ~13% of BX’s have Side A-C coincidence

17. NSS’07, Hawaii, Oct 31, 2007ATLAS BCM (M.Mikuž, Ljubljana)17 Radiation test of complete module Radiation hardness of sensors, electronics and components verified separately up to level of 10 15 cm -2 (30 MRad) Want to assess performance of complete module Irradiation/test of one module  Test in beam – June 07  Irradiate to 10 14 p/cm 2 – July 07  Test in beam – August 07  Irradiate to 3x10 14 p/cm 2 – September 07  Test in beam – now  Irradiate to 10 15 p/cm 2 – Spring 08  Test in beam – Summer 08 non-irradiated 10 14 p/cm 2 ~20 % of signal loss observed in test beam after 10 14 p/cm 2  Diamonds not properly pumped – need to cover complete sensor  Loss consistent with that of samples irradiated to same fluence with neutrons – see talk N44-5 tomorrow  Expect complete signal recovery after pumping  Tests with module irradiated to 3x10 14 p/cm 2 ongoing

18. NSS’07, Hawaii, Oct 31, 2007ATLAS BCM (M.Mikuž, Ljubljana)18 Summary ATLAS BCM will monitor beam conditions close to the IP in ATLAS using a time-of-flight measurement Based on pCVD diamonds readout by fast RF amplifiers to achieve very fast signal response and required radiation hardness  Rise time 1.3ns & ~2ns FWHM pulse width We have tested the full set of BCM modules in beam tests demonstrating the required performance  Efficiency of ~99% at operational threshold with noise occupancy /module/BX <10 -7  Time resolution ~500ps All BCM modules were installed in ATLAS together with the ATLAS Pixel detector in June 2007

19. NSS’07, Hawaii, Oct 31, 2007ATLAS BCM (M.Mikuž, Ljubljana)19 Backup slides …

20. NSS’07, Hawaii, Oct 31, 2007ATLAS BCM (M.Mikuž, Ljubljana)20 LHC beam losses E.g. wrong magnet settings or trips can lead to beam scraping on collimators  Simulations of beam orbits with wrong magnet settings near ATLAS IP ( D. Bocian Accidental Beam Losses during Injection in the Interaction Region IR1 Dariusz Bocian / EST-LEA and ATLAS ) Time constants of failures (trips,…) are often large (~ms) If signs are detected early, the beam can be aborted

21. NSS’07, Hawaii, Oct 31, 2007ATLAS BCM (M.Mikuž, Ljubljana)21 Signal optimization Step 1: 2 Diamonds read out in parallel increase signal by factor 2, noise increases only by ~30% Step 2: Place at 45 degrees ->  2 signal increase, no noise increase Step 3: Adding ~200-300MHz BWL on NINO input improves SNR by 30% (timing resolution worsens by ~ 10%) Step 4: operate at 2V/  m instead of 1V/  m -> increases signal by up to 50% amplitudenoise SNR no BWL 200MHz BWL RMS=0.66mV RMS=0.33mV MP=3.7mV MP=2.5mV

22. NSS’07, Hawaii, Oct 31, 2007ATLAS BCM (M.Mikuž, Ljubljana)22 Analogue response in test beam Single event and signal distribution =1.3 ns and = 2.1 ns Signal and noise well separated

23. NSS’07, Hawaii, Oct 31, 2007ATLAS BCM (M.Mikuž, Ljubljana)23 5 x 10 32 2.8 x 10 34 1 x 10 34 Number of BCM hits & coincidences Number of BCM station hits/BCO  At low luminosity expect ~ 50% of BCO have >= 1 hit Coincidences  Plots as # Side A * # Side C  At low luminosity expect ~13% of BCM have a coincidence No timing cut

24. NSS’07, Hawaii, Oct 31, 2007ATLAS BCM (M.Mikuž, Ljubljana)24 Radiation Test results Measure response of irradiated 1st stage after full irradiation with Si- diode and 90Sr source Noise constant Overall gain reduction of ~ 20% after full irradiation

25. NSS’07, Hawaii, Oct 31, 2007ATLAS BCM (M.Mikuž, Ljubljana)25 LHC Beam loss scenario Simulation by CMS: single proton lost on collimator (“TAS”) (dose [Gy]) (M. Huhtinen, LHC Machine Protection WG, Oct. 2003) ~ MIPs/cm 2 per proton

26. NSS’07, Hawaii, Oct 31, 2007ATLAS BCM (M.Mikuž, Ljubljana)26 Passive signal summation Increase signal by using 2 diamonds acting as one current source (“Double diamond assembly”)  2 independent current signals summed at input signal HV drift voltage

27. NSS’07, Hawaii, Oct 31, 2007ATLAS BCM (M.Mikuž, Ljubljana)27 FPGA backend  Have developed the V1.0 signal processing code  Rocket I/O acquisition of BCM signals from optical board (2.6 GHz sampling)‏  Edge detection, pulse width calculation  DDR2 circular buffers  Ethernet + Client Software on PC  In-time/out-of-time coincidences  Tested in most recent beam tests with full signal chain and two BCM stations  Data analysis is ongoing  Plan second run with FPGA end October in SPS testbeam

28. NSS’07, Hawaii, Oct 31, 2007ATLAS BCM (M.Mikuž, Ljubljana)28 BCM simulations Simulations in full ATHENA framework Average number of tracks in BCM diamonds per p-p collision: 0.375 Surprise: half of events from decays and scattering in material Studies of coincidences to establish FPGA algorithms ongoing BCM Pixels Beam pipe Decays

29. NSS’07, Hawaii, Oct 31, 2007ATLAS BCM (M.Mikuž, Ljubljana)29 BCM simulations – movement of vertex Explored sensitivity of BCM rates to vertex displacements Vertex displaced to z = +10 cm Surprise: more BCM hits on side C – secondaries dominate dP A /dz = (-0.11 ± 0.05) m -1, effect at % level ( dP A /dz = +0.12 m -1 for primaries only Vertex at z=0Vertex at z=+10 More material towards Side C