CMS Tracking Detector case study

Transcription

1 CMS Tracking Detector case study This lecture is based on a PG lecture generously provided by Prof G Hall of Imperial College, London Updated in December 2016 Prof Peter R Hobson C.Phys M.Inst.P. Department of Electronic and Computer Engineering Brunel University London, Uxbridge Peter.Hobson@brunel.ac.uk /

2 Development of a tracking detector for physics at the Large Hadron Collider Geoff Hall

3 CMS = Compact Muon Solenoid detector missing element in current theoretical framework - mass t Total weight 12,500 tons Diameter 15m Length 21.6m Magnetic field 4T Tracking system 10 million microstrips Diameter 2.6m Length 7m Power ~50kW G Hall 3

4 LHC parameters (CMS) pp Pb-Pb Luminosity cm -2.s cm -2.s -1 Consequences Annual integrated L 5x10 40 cm -2? CM energy 14 TeV 5.5 TeV/ N σ inelastic ~70mb ~6.5 b interactions/bunch ~ tracks/unit rapidity ~ beam diameter 20µm 20µm bunch length 75mm 75mm beam crossing rate 40MHz 8MHz Level 1 trigger delay - 3.2µsec - 3.2µsec L1 (average) trigger rate Š100kHz < 8kHz High speed signal processing Signal pile-up High (low) radiation exposure High (low) B field operation Very large data volumes New technologies G Hall 4

5 Design philosophy Large solenoidal (4T) magnet iron yoke - returns B field, absorbs particles technically challenging but smaller detector, p resolution, trigger, cost Muon detection high p T lepton signatures for new physics Electromagnetic calorimeter high ( E) resolution, for H => γγ (low mass mode) Tracking system momentum measurements of charged particles pattern recognition & efficiency complex, multi-particle events complement muon & ECAL measurements improved p measurement (high p) E/p for e/γ identification G Hall 5

6 Parameters for hadronic collider physics E, p, cosθ, φ transform e.g E, p T, p L, φ p T rapidity prefer variables which easily Lorentz divergences from simple behaviour could imply new physics eg heavy particle decay => high p T lepton (or hadron) Lorentz boost pseudorapidity LHC y = 1 2 ln( E + p L E p L ) dy = dp L E y y = y ln(1 + β 1 β ) dn => dy y = 1 cos 2 (θ 2) + m 2 2 ln( 4 p sin 2 (θ 2) + m2 4p 2 d 2 N ch arg ed dη.dp T H. f ( p T ) H~ 6 η < 2.5 invariant +... ) ln tan(θ 2) η G Hall 6

7 Physics requirements (I) Mass peak - one means of discovery m = E i p i i => small σ(p T ) eg H => ZZ or ZZ * => 4l ± typical p T (µ) ~ 5-50GeV/c Background suppression measure lepton charges good geometrical acceptance - 4 leptons background channel t => b => l require m(l + l - ) = m Z Γ Z ~ 2.5GeV precise vertex measurement identify b decays, or reduce fraction in data G Hall 7

8 Physics requirements (II) p resolution σ( p T ) σ ~ p meas p T T B.L 2 N pts large B and L high precision space points detector with small intrinsic σ meas well separated particles good time resolution low occupancy => many channels good pattern recognition minimise multiple scattering minimal bremsstrahlung, photon conversions material in tracker most precise points close to beam p T p T 0.15p T (TeV) 0.5% G Hall 8

9 Silicon diodes as position detectors ~25µm ~1pF/cm Spatial measurement precision defined by strip dimensions ultimately limited by charge diffusion σ ~ 5-10µm ~300µm ~0.1pF/cm +V bias G Hall 9

10 Vertex detector ~1990 G Hall 10

11 Interactions in CMS 7 TeV p 7 TeV p G Hall 11

12 Microstrip tracker system 2.4m ~10M detector channels ~ 6m G Hall 12

13 Event in the tracker G Hall 13

14 Silicon detector modules Constraints on tracker minimal material high spatial precision sensitive detectors requiring low noise readout power dissipation ~50kW in 4T magnetic field radiation hard Budget Requirements large number of channels limited energy resolution limited dynamic range G Hall 14

15 Radiation environment Particle fluxes Charged and neutral particles from interactions ~ 1/r 2 Neutrons from calorimeter nuclear backsplash + thermalisation more uniform gas only E > 100keV damaging Dose energy deposit per unit volume Gray = 1Joule/kg = 100rad mostly due to charged particles G Hall 15

16 Imperial College contributions to Tracker APV25 APVMUX/PLL FED Hardware development Hardware construction Beam tests & studies Preparation for physics G Hall 16

17 APV µm CMOS 1 of the 128 channels Analogue unity gain inverter 192-cell analogue pipeline S/H programmable gain 128:1 MUX Differential current O/P signal processing amplifiers pipeline & memory MUX SF Low noise charge preamplifier SF 50 ns CR- RC shaper APSP control logic APV25-S1 (Aug 2000) Chip Size 7.1 x 8.1 mm Final APV25-S0 (Oct 1999) G Hall 17

18 Irradiations of 0.25µm technology Extensive studies CMS tracker data from IC, Padova, CERN ALL POSITIVE and well beyond LHC range CMOS hard against bulk damage Qualify chips from wafers with ionising sources Typical irradiation conditions 50kV X-ray source Dose rate ~ 0.5Mrad/Hour to 10, 20, 30 & 50Mrad Noise [µv/hz 1/2 ] Id [A] PMOS 2000/ µA Vg [V] pre-rad 10 Mrad 20 Mrad 30 Mrad 50 Mrad anneal Pre-rad 50 Mrad Anneal PMOS Frequency [Hz] G Hall 18

19 APV25 irradiations (IC & Padova) IC x-ray source Normal operational bias during irradiation clocked & triggered Post irradiation noise change insignificant pre-rad APV25-S1 10 Mrad also 1 0 MeV linac electrons(80mrad) and 2. 1 x reactor n. cm - 2 G Hall 19

20 CMS Silicon Strip Tracker Front End Driver 96 Tracker Opto Fibres 12 CERN Opto- Rx Analogue/Digital 9U VME64x JTAG Data Rates 9U VME64x Form Factor FE-FPGA Cluster Finder FPGA Configuration VME-FPGA VME Interface Modularity matched Opto Links Analogue: 96 ADC channels 40 MHz ) 12 BE-FPGA Event Builder L1 Trigger : processes 25K MUXed silicon strips / FED TTC TTCrx Buffers DAQ Interface Raw Input: 3 Gbytes/sec* after Zero Suppression... DAQ Output: ~ 200 MBytes/sec Temp Monitor Power DC-DC ~440 FEDs required for entire SST Readout System Front-End Modules x 8 Double-sided board Xilinx Virtex-II FPGA TCS : Trigger Control System G Hall 20 *(@ L1 max rate = 100 khz)

21 CMS Silicon Strip Tracker FED Front-End FPGA Logic per adc channel phase compensation required to bring data into step Cluster Finding FPGA VERILOG Firmware 1x 2x 4x DLL Clock 40 MHz ADC 1 ADC Temp Sensor Phase Registers 4x Phase Registers sync sync trig1 trig Ped sub header Ped sub header trig2 11 trig x 256 cycles 256 cycles nx256x16 Re-order cm sub status Re-order cm sub trig3 11 trig3 11 Hit finding 256 cycles 256 cycles status Hit finding trig4 8 s-data 8 s-addr hit No hits averages 8 8 s-data 8 s-addr hit No hits averages 8 Sequencer-mux Sequencer-mux 16 d DPM d 16 8 a a 8 16 nx256x16 d DPM d 16 8 a a 8 mux Serial Int Packetiser Control Synch Synch in Synch out emulator in Synch error Global reset Sub resets Full flags control 4 data 160 MHz Serial I/O Opto Rx Delay Line Local IO + Raw Data mode, Scope mode, Test modes... B Scan Config G Hall 21

22 The CMS Tracking Strategy Rely on few measurement layers, each able to provide robust (clean) and precise coordinate determination Radius ~ 110cm, Length/2 ~ 270cm 6 layers TOB 2-3 Silicon Pixel Silicon Strip Layers Number of hits by tracks: Total number of hits Double-side hits Double-side hits in thin detectors Double-side hits in thick detectors 4 layers TIB 3 disks TID 9 disks TEC G Hall 22

23 Vertex Reconstruction Primary vertices: use pixels! At high luminosity, the trigger primary vertex is found in >95% of the events G Hall 23

24 High Level Trigger & Tracker 40 MHZ 100 KHz 100 Hz DAQ HLT Track finding In High Level trigger reconstruction only 0.1% of the events should survive. How can I kill these events using the least CPU time? This can be interpreted as: o The fastest (most approx.) reconstruction o The minimal amount of precise reconstruction o A mixture of the two Same SW would be use in HLT and off-line : Events rejected at HLT are irrecoverably lost! algorithms should be high quality algorithms should be fast enough G Hall 24

25 References (updated by P Hobson) N. Ellis & T. Virdee. Experimental Challenges in High Luminosity Collider Physics. Ann. Rev. Nucl. Part. Sci 44 (1994) G.Hall Modern charged particle detectors Contemporary Physics 33 (1992) 1-14 & refs therein G.Hall Semiconductor particle tracking detectors Reports on Progress in Physics.57 (1994) A. Schwarz 1993 Heavy Flavour Physics at Colliders with silicon strip vertex detectors. Physics Reports 238 (1994) C. Damerell Vertex detectors: The state of the art and future prospects. Rutherford Appleton Laboratory report RAL-P A pdf version is available on the CERN library Web site.(search preprints) The CMS experiment at the CERN LHC, Journal of Instrumentation, 3 (2008) S08004 Performance studies of the CMS Strip Tracker before installation, Journal of Instrumentation, 4 (2009) P06009 Stand-alone cosmic muon reconstruction before installation of the CMS silicon strip tracker, Journal of Instrumentation, 4 (2009) P05004 G Hall 25

26 How does it perform at the LHC? P Hobson

27 How does it perform at the LHC? P Hobson

28 How does it perform at the LHC? P Hobson

29 How does it perform at the LHC? P Hobson

30 How does it perform at the LHC? Kaons, Protons, Deuterons P Hobson

31 Published results VERTEX 2012 P Hobson 31 December 2015

32 Efficiency P Hobson 32 November 2015

33 de/dx Using de/dx data to fit the KK invariant mass distribution to detect the φ(1020). 13 TeV data P Hobson 33

34 Photon conversions in the pixel layers Reconstructed photon conversions (photon radiography ) P Hobson 34 December 2015

35 Finding the cooling pipes! G Hall 35

36 IP within jets G Hall 36

37 Secondary vertex b-tagging G Hall 37

38 Leakage Currents in Strips Leakage current vs radius Leakage current (top) and simulated 1 MeV neutron equivalent dose (bottom) P Hobson 38 December 2015

39 Even more from CMS From JINST 9 (2014) P Tracker performance plots (public) P Hobson 39 December 2016