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2002 IEEE NSS Dmitri Denisov, Fermilab

Forward Muon System for the D0 Experiment

Presented by Dmitri DenisovFermilab

For the D0 Collaboration

644 members73 institutions18 countries

D0 Note 4061November 2002

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2002 IEEE NSS Dmitri Denisov, Fermilab

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

4.82.32.5Interactions / xing

1323963500Bunch xing (ns)

10517.33.2 Ldt (pb-1/week)

5.2 10328.6 10311.6 1030Typical L (cm-2s-1)

1.961.961.8s (TeV)

140 10336 366 6Bunches in Turn

Run 2bRun 2aRun 1b

Run 1 Run 2a Run 2b 0.1 fb-1 24 fb-1 15 fb-1

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2002 IEEE NSS Dmitri Denisov, Fermilab

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 3.1s) 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

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2002 IEEE NSS Dmitri Denisov, Fermilab

D0 Detector for Run IIForward MDT Layers C B A

A- Counters

Pixel Counter LayersA B C

New 2T Solenoid

PDT Chambers C B A

Outer Counters

Shielding Shielding

PreshowerFiber Tracker

Silicon Tracker

Electronics

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2002 IEEE NSS Dmitri Denisov, Fermilab

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 scintillationcounters

Shielding

Mini-drift tubes

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2002 IEEE NSS Dmitri Denisov, Fermilab

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

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2002 IEEE NSS Dmitri Denisov, Fermilab

Shielding

Effect of the shielding on background fluxes:factor of 50-100 reduction

Without Shielding With Shielding

Hadron

e/gamma

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2002 IEEE NSS Dmitri Denisov, Fermilab

Trigger Scintillation Counters

3 planes of ~10x10m2 on both sides of the interaction region

Counters arranged in R- 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

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2002 IEEE NSS Dmitri Denisov, Fermilab

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%

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 compensated by HV adjustment

Counter Design

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2002 IEEE NSS Dmitri Denisov, Fermilab

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

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2002 IEEE NSS Dmitri Denisov, Fermilab

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 stabilityTiming peak for muon tracks

=1.8ns =0.5ns

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2002 IEEE NSS Dmitri Denisov, Fermilab

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

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2002 IEEE NSS Dmitri Denisov, Fermilab

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) =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/cmWith large safety factor mini-drift

tubes radiation aging is not an issue

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2002 IEEE NSS Dmitri Denisov, Fermilab

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

Coordinate resolution of mini-drift tube plane

based on local segment reconstruction

RMS=0.7mm

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2002 IEEE NSS Dmitri Denisov, Fermilab

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

M = 3.08 0.04 GeV

= 0.78 0.08 GeV

Single Muon Event

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2002 IEEE NSS Dmitri Denisov, Fermilab

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