Forward Muon System for the D0 Experiment

1. D0 Note 4061 November 2002 Forward Muon System for the D0 Experiment Presented by Dmitri Denisov Fermilab For the D0 Collaboration 644 members 73 institutions 18 countries 2002 IEEE NSS Dmitri Denisov, Fermilab

2. Run 1b Run 2a Run 2b Bunches in Turn 6  6 36  36 140 103 s (TeV) 1.8 1.96 1.96 Typical L (cm-2s-1) 1.6 1030 8.6 1031 5.2 1032  Ldt (pb-1/week) 3.2 17.3 105 Bunch xing (ns) 3500 396 132 Interactions / xing 2.5 2.3 4.8 Run 1Run 2a Run 2b 0.1 fb-1 24 fb-115 fb-1 Fermilab Tevatron Upgrade Tevatron Run 1 (1992-1996) produced reach harvest of interesting physics results, including top quark discovery In order to continue studies at the energy frontier Tevatron underwent serious upgrade in 1997-2001 factor of ~10 higher luminosity factor of ~10 smaller bunch spacing Physics goals for Tevatron Run 2: precision studies of weak bosons, top, QCD, B-physics searches for Higgs, supersymmetry, extra dimensions, other new phenomena 2002 IEEE NSS Dmitri Denisov, Fermilab

3. Challenges for the Tevatron Run 2 Detectors • In order to fully exploit Tevatron capabilities in Run 2 D0 detector has been substantially upgraded • smaller bunch crossing of 132ns (vs 3.1ms) required replacement of electronics as well as some of the slow detectors • higher luminosity provides higher radiation fluxes and requires more radiation hard detectors • higher event rate requires better trigger systems in order to select only ~10-5 of the interactions which can be written to tapes • new detectors have been added in order to improve detection of displaced vertices and provide momentum measurement in the central region • Forward muon system of the D0 detector covers rapidity region between 1.0 and 2.0 and has been fully redesigned for Run 2 • separated functions of muon tracking and trigger detectors • fast detectors with internal resolution time below 60ns • radiation hard detectors • detectors capable of operating in the magnetic field of the muon toroid and central solenoid • time and coordinate resolution provide efficient muon detection and backgrounds suppression 2002 IEEE NSS Dmitri Denisov, Fermilab

4. D0 Detector for Run II Forward MDT Layers C B A Pixel Counter Layers A B C Outer Counters PDT Chambers C B A A- Counters Shielding Shielding Preshower Silicon Tracker New 2T Solenoid Fiber Tracker Electronics 2002 IEEE NSS Dmitri Denisov, Fermilab

5. Forward Muon System • Forward muon system consists of the following major elements • shielding around Tevatron beam pipe • provides factor of ~100 reduction in backgrounds • trigger system based on 3 layers of scintillation trigger counters • 4608 scintillation counters with ~1ns time resolution • tracking system based on 3 layers of mini-drift tubes • 50,000 wires assembled in 8 wires extrusion assemblies • maximum drift time is 60ns • coordinate resolution is 0.7mm Forward scintillation counters Shielding Mini-drift tubes 2002 IEEE NSS Dmitri Denisov, Fermilab

6. Shielding • There are two major sources of backgrounds(non-muon) hits in muon detectors at hadron colliders • background particles coming from the accelerator tunnel • background particles originated in interactions of p-pbar collision products propagating at small angles with accelerator and detector equipment • Both of these backgrounds can be substantially reduced by placing shielding around beam pipe • consists of 3 layers • 50 cm of steel - absorb hadrons and e/gamma • 12 cm of polyethylene - absorb neutrons • 5 cm of lead - absorb gamma rays • calculations based on GEANT/MARS codes demonstrate reduction in particle fluxes for shielded/unshielded detectors by a factor of 50-100 • Run 1 muon detector occupancies have been in the 5-10% level • Run 2 muon detector occupancies are in the 0.05-0.1% level in good agreement with calculations • use of detectors less sensitive to backgrounds (high time resolution, small sensitive volume, etc.) provides advantages as well 2002 IEEE NSS Dmitri Denisov, Fermilab

7. Shielding Effect of the shielding on background fluxes: factor of 50-100 reduction Hadron e/gamma Without Shielding With Shielding 2002 IEEE NSS Dmitri Denisov, Fermilab

8. Trigger Scintillation Counters • 3 planes of ~10x10m2 on both sides of the interaction region • Counters arranged in R-f geometry matching central fiber tracker trigger • Total number of counters 4608 • Major specifications • fine segmentation • time resolution of ~1ns to separate tracks coming from interaction region from cosmic and accelerator tunnel • low radiation aging • operation in magnetic field up to ~350Gs • Simple and reliable design has been developed • based on 12mm thick Bicron 404A scintillator • light collection is performed using WLS bars • fast 25mm diameter phototubes are used for light collection 10x10m2 plane of counters assembled in “fish scale”design in the collision hall 2002 IEEE NSS Dmitri Denisov, Fermilab

9. Trigger Scintillation Counters • Cut to shape 404A scintillator with two Kumarin WLS bars attached • collect light on the 25mm photocathode of 115M (MELZ) • phototube • Tyvek wrapping is used for better light collection • Counters sizes are from 10x10cm2 to 1x1m2 • Average number of phe for large counters is 60 • Time resolution is 0.5-1ns depending on counter size • limited by photoelectron statistics and amplitude fluctuations • (single threshold discriminator) • Amplitude response uniformity is ~10% Counter Design Radiation aging for 15fb-1 integrated luminosity (Run II Tevatron goal) Pair Kumarin(WLS)+404A(Scintillator) demonstrates 10% light loss for 20krad irradiation. We expect doses for the hottest regions to be well below 1krad (15fb-1) Phototube 115M losses 10% of gain for anode accumulated charge of 100C (15fb-1). This could be easily compensatedby HV adjustment 2002 IEEE NSS Dmitri Denisov, Fermilab

10. Magnetic Shielding • Magnetic shielding is provided with • 1.2mm thick mu-metal • 3mm or 6mm tick soft iron shield • transverse to tube axis field has no effect up to ~700Gs • field parallel to the tube affects phototubes • 3mm iron shield (closed circles): 10% gain loss at 250Gs • used in layers outside muon toroid • 6mm iron shield (open circles): 10% gain loss at 350Gs • used in layer inside muon toroid • LED tests with/without field • less then 1-2% effect for all 4608 tubes 2002 IEEE NSS Dmitri Denisov, Fermilab

11. Counters Performance During Data Taking • During collider data collection performance of all counters is monitored • efficiency of individual planes and counters based on reconstructed muon tracks • stable above 99% • gain of all phototubes with respect to reference calibration set using LED system • peak position stable within ~2% over one year of operation • typical variations in the gain do not exceed ~5% • timing characteristics • peak of LED pulse is stable within 0.5ns over a year of operation • peak and width of the timing spectra for muon tracks • Total number of “dead” counters after 1 year of operation is 5 (0.1%) 1 year LED timing stability Timing peak for muon tracks s=0.5ns s=1.8ns 2002 IEEE NSS Dmitri Denisov, Fermilab

12. Forward Muon Tracking Detector • Forward muon tracking detector is based on mini-drift tubes • 1x1cm2 drift cell • 8 cell aluminum extrusion comb with 0.7mm thick walls (to reduce dead zones) • stainless steel cover and PVC sleeve provides electrical field configuration and gas tight volume • Tubes length vary between 1m and 6m • 50mm gold plated tungsten wire is supported every meter • Total number of wires in the system is 50,000 • Tubes are assembled into 8 octants per layer with wires parallel to magnetic field lines • There are 4 planes of wires in layer before toroid and 3 planes of wires in each of two layers after toroid • muon has 10 hits on track average 2002 IEEE NSS Dmitri Denisov, Fermilab

13. Working Gas for Mini-drift Tubes • We are using CF4(90%)+CH4(10%) gas mixture • non-flammable • very fast • re-circulation with small losses (~5%) reduces gas cost • no radiation aging • wide 100% efficiency mip platou • 2.9kV-3.4kV • Time-to-distance dependence has been measured and simulated • maximum drift time for tracks perpendicular to the plane is ~40ns • maximum dirft time for 45 degree tracks is ~60ns • Coordinate resolution of the mini-drift tube system is defined by electronics • TDC bin is 19ns (cost driven) • s=0.7mm • starts affect “muon system only” coordinate resolution for muon momentum above 50GeV/c Accumulated charge for 15fb-1 is estimated at 30mC/cm Aging test with Sr90 r/a source demonstrates no aging effects up to 2C/cm With large safety factor mini-drift tubes radiation aging is not an issue 2002 IEEE NSS Dmitri Denisov, Fermilab

14. Mini-drift Tubes Performance • During data collection many parameters of the mini-drift tubes are monitored • gas flow • ~32 tubes are connected in serial with input/output flow monitoring • high voltage values and currents • all 50,000 wires operates at the same high voltage of 3.25kV • individual planes efficiency using reconstructed muon segments • typical efficiency is in the range above 99% • plane coordinate accuracy using reconstructed segments • Reliability • total number of disabled wires • 0.3% after commissioning • dead or noisy • increase in number of disabled wires is less then 0.1% per year of operation RMS=0.7mm Coordinate resolution of mini-drift tube plane based on local segment reconstruction 2002 IEEE NSS Dmitri Denisov, Fermilab

15. M = 3.08  0.04 GeV  = 0.78  0.08 GeV Forward Muon System Performance • Low occupancy of the forward muon detectors due to well designed shielding and use of fast detectors proved to be very low • at the 0.05%-0.1% level • simple and reliable muon triggering • after Level 1 trigger (scintillation counters only) 50% of events have good muon reconstructed off-line • after Level 2 trigger (mini-drift tubes and scintillation counters) 80% of events have good track reconstructed off-line • writing to tapes background free samples • simple and background free muon off-line reconstruction • High reliability of forward muon detectors provided above 99% “up-time” during physics data collection • Based on efficient muon hits detection, triggering, and reconstruction D0 forward muon system is providing data for wide spectrum of physics studies at the energy frontier at the Tevatron • Some important issues like alignment, electronics, triggering, reconstruction are not addressed due to limited talk time Single Muon Event 2002 IEEE NSS Dmitri Denisov, Fermilab

16. Summary: D0 Forward Muon System • D0 experiment developed and constructed multi-layer steel+poly+lead shielding which reduced background fluxes on the muon detectors by a factor of 50-100 • reduction in detectors aging, trigger rates, fake tracks • Separation of triggering and tracking capabilities in the D0 forward muon system provides background free muon samples to be written to tapes • Forward muon trigger system based on 4608 scintillation counters • simple and reliable counter design for counters from 10x10cm2 to 1x1m2 • time resolution of ~1ns • provides above 60 phe per mip • radiation hard to well above 100kRad • phototube magnetic shield provides reliable operation up to 350Gs • Forward muon tracking system • 50,000 wires of mini-drift tubes with 1x1cm2 drift cells and length up to 6m • modular extrusion based tube design • CF4(90%)+CH4(10%) gas mixture • fast, 60ns max drift time • non-flammable • radiation hard above 2C/cm • wide HV operating plateau of 0.5kV • All system elements reached or exceeded Run II specifications and operate smoothly during over a year of data taking 2002 IEEE NSS Dmitri Denisov, Fermilab