the barrel muon system of cms
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The BArreLMUON SYSTEM
Of cms
International Meeting on Fundamental Physics
El EscorialApril 5th 2006
Marcos Fernández GarcíaUniversidad Autónoma de Madrid
CMS at a glance
ECAL: PbWO4 crystals, short 0 and fast response, but low light yieldIntrinsic gain photodetectors: Silicon APD barrel,VPT for EEElectrons: (E)/E~0.5-1% (E>20 GeV)
HCAL: Brass+plastic scint. tiles readout by WLS+CFHadronization leaks after magnet caught by scint Hadron Outer (barrel)HCAL Energy resolution: Pions (E)/E~20%@50 GeV, ~15%(E>100 GeV)
Solenoid: Superconductor 4T L=13 m, 5.9 mMagnetic Field returns throughiron yoke
Tracker@ -20ºCPixel: =10(20) µm r (z)Strip Tracker: µstrips Silicon TIB~20 µm,TOB~40 µm
Trigger:Approx. 20 ev/bx @ L=1034/cm2s bx=40Mhz 109 ev/sL1 FPGAs,ASICs, 312 µs output rate 105 HzDecision photon,e,µ,jets > pT cutsHLT output 100 ev/sReduction info, farm CPUs
Muon System: key for trigger. 250 DTs, 540 CSCs, 912 RPCs in 12 sectorsModerate pT resolution (comp. tracker)
Barrel: <1.2, B< & uniform, R(µ) 1 Hz/cm2, R(n bkgd)=1-10 Hz/cm2
Endcaps: 0.9<<2.4, B upto 3.5T, R(µ) 200 Hz/cm2, R(n bkgd)<1kHz/cm2
RPC:t~1 ns, identification bx
Length: 21.6 mDiameter: 14.6 m
12500 TonsReady to close: 30th July 2007
CMS three years ago
CMS now: MUONS
YB+2
YB-0
YB-1
YE+1 CSCs
YE+1
YB+2
Forward HFCAL(cabled)
Assembled on surface at point 5 in LHC ring
CSCs all @ CERN(>80% cosmics comm.)
Barrel~50% installed
CMS now: Magnet + HCAL
Magnetouter case+SC
YB+0
Magnet closedCooled downCoil powered May
HCAL on itstransport structure
Completed, 1st lowered
HCAL slid insidemagnet bore
Transport structure(will be removed)
Muon measurement
1) In the Inner Tracker2) With the muon system3) Inner Tracker+ Muon System
Muons are measured at the tracker with higher resolution. Why using Muon Chambers anyway?
Easier to find muon in the chambers than in the tracker. Once found in the barrel, the track isextrapolated backwards
The L1 trigger (decision taken 128 bx after current event) can not wait for tracker reconstruction
Tracker will not be fully aligned at the beggining of the experiment. Muons measured onlyusing Muon System
Muons measured in 3 different ways(central muons with enough pT):
=0
=1.5
Muon chambersActually they are ionization gas detectors. They detect only muons, because these are the only (charged) particles reaching that far in CMS.
Why Ar/CO2 (85/15)%?Ar=monoatomic e– undergo only elastic scattering with low energy loss
Only Ar excited atoms emit photons which induce new avalanches discharges
CO2 quencher required. Absorbs photons
Time (ns)Avalanche Constant vd
Øwire =50 µmWire positioning error=100 µmCell spatial resolution=250 µm
5 electrostaticelements
Vstrip
Vwire
Vbeams
= 1800
= 3600=-1200
Muon chamber’s core: Drift cell
Drift Cell:Muon ionises the gasElectrodes shape the fieldConstant drift velocity (roughly 50 µ/ns)TDC µ crossing position known
Half cell staggering solves the left-right uncertainty
A superLayer is just 4 layers of
staggeredcells
3 SLs Muon Chamber
2
1
Honeycomb
Muon chambers
R 150 µm 200 µm Angle=1 mrad
RPC
Muon Chamber, cabled on cosmic calibration bench
Scintillator trigger panels
(not scaled)
Muon Chambers in Level 1 trigger systemOn-chamber Local Trigger Logic
1
1
2
• Muon L1 Trigger based on custom electronics
BTI: alignment in 4 layers, bx identificationTRACO: Combines segments from the SLs.TS: Selects best two segments/chamber
Track Finder: Connects segments of chambers in sectorAssigns pT, angle and quality
Local trigger (on-chamber):
Regional trigger (off-chamber)
Regional Trigger
Chamber certification at the ISR lab
Muon chamber storage and certification area at CERN uses the (dismantled) ISR facilityNote: ISR was the world’s first pp collider (1971-1984), 62 GeV cdm, record L @ hadron collider till 2004
As of March 2006, 117 chambers pending for installation (133 already certified and installed)
Currently 3 physicist, one engineer, 2-3 technicians devoted full time to this task
Chamber certification process takes approx. 2 months. With current buffer of chambers, we certify 2-3 chambers/week
After certification, chambers are installed at a rate of 2-4 chambers/day (depends on schedule)
After installation chambers are commissioned in the wheels, approx. 5 chambers/week
ReceptionCertification Installation Commissioning
Work acknowledged to all those pictured below, as well as casual collaborators from institutes
J. PuertaCERN J.M. Ahijado
CIEMAT
VincenzoINFN Bo
A. BenvenutiINFN Bo
S. Di VincezoCERNM. Chamizo
CIEMAT
+ Vittorio (INFN Bo), G. Fetchenhauer (Aa)(…)
Reception
Chamber dressing
SurveyUnload
Gas MFHV CablesPADC
ChamberCertification
@ ISRSTEP I
Storage
ChamberCertification
@ ISRSTEP II
Intervention
Curr
ents
time
CosmicsProblemidentification
2-3 interventions/chamber
Intervention
Insertion
Commissioning
From ISRto SX5
Insertion
Commissioning of 2 sectors simultaneouslyTrigger logical AND of all 4 chambers (across 2 sectors!)
…and actually, everything works
Perspectives
CMS installation progressing on a daily basisHeavy lowering [July 2006-March 2007]
…and Conclusions
2007 LHC related dates:
[Sept-Oct] Pilot RunFirst collisions: 1+1 bunches-43+43 bunchesL1027 1030 cm-2s-1
Up to 10 pb-1, enough for subdetector calibrations
[Nov-Dec] First PhysicsRuns at 75 ns (936 bunches) and 25 ns (2808)L~ 1032 cm-2s-1 (75ns,936b)…21033 (25ns,2808)
[Jan-Mar 08] ShutdownInstallation of staged detectors
[Apr 08-…] Expected 7 months run
The LHC time is already here
CMS close to completion. Final detectorsbeing installed:
Magnet and HCAL … doneRest follow the path (and the schedule)
Muon chambers key trigger detectorsand very important for high pT muons
Chambers certified prior to installation…and commissioned after installationSo many tests ensure a performant µ system
Packed schedule from now on:Magnet test/Cosmic ChallengeFinal installation (surface and pit)First collisions … and last holidays!
First endcap wheel lowering by October 2006Last DT chamber installed by Dec06-Jan07
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