1. Luca Spogli Università Roma Tre & INFN Roma Tre
Commissioning with cosmic rays of the Muon Spectrometer of the ATLAS Experiment at LHC
Luca Spogli
Università Roma Tre & INFN Roma Tre
LNF Frascati Spring School 2007

2. Outline The ATLAS experiment at LHC Muon Spectrometer
Commisioning Status
Test with cosmic rays
Summary

3. ATLAS detector Electromagnetic Calorimeter Muon Spectrometer
Forward Calorimeter
Solenoid
Endcap Toroid
Inner Detector
Barrel Toroid
Hadronic Calorimeter
Radiation Shielding

4. MDT (Monitored Drift Tubes)
good space resolution (~100 μm per point) 
pt/pt pt<200GeV/c
pt/pt pt  1TeV/c
Tubes per layer
Layer per multilayer
Chamber lenght (mm)
Chamber heigth (mm)
~1200 chambers / ~7000 m2
MDT
RPC
TGC
CSC
ECT
h=1
h=1.4

5. MDT Calibration: r(t) Drift time measurement
Determination of space-time relationship r(t) via autocalibration
rt-relation with a typical accuracy of 10µm
Time measurement

6. Muon Reconstruction In a single multilayer Track segments
MDT mutilayer
Momentum measurement from sagitta determination p=0.3 Br

7. Installation and commissioning
Installation in the pit started in Summer 2005
First tests with cosmic muons during Summer 2006
First curved muon (magnetic field on) in November 2006
MDT chamber installation completed in the barrel region

8. Installation
It is not an easy task...

9. Cosmics Sector 13 Side A 19-20 November data
Sector 13 with RPC timing informations
Magnetic field on-off
~1 Mevents
9 chambers
Many tests on MDT’s
Drift behavior
Calibration
Efficiency
Noise
Dead channels
Preliminary alignment
Some results in this talk
Sector 13
Side A

10. Event Display
BIL chamber

11. Fired tubes per event ...after noise reduction cuts
Accidental trigger coincidences
4 multilayers
2 multilayers
6 multilayers
Number of Fired Tubes / event

12. Impact of magnetic field on r(t)
B field expected to change drift-to-radius relationship by Lorentz angle
B field parallel to the wire
Electrons do not travel straight forward radially
They travel under an angle ψ
Drift time t for a certain radius r increases
τ: mean time between collisions

13. Measured muon spectra   µ- µ+ Z coordinate Momentum (GeV)
Ratio of µ+ / µ- = 1.48±0.27
Small shaft
Big shaft
According to P.D.G
Charge ratio of cosmic ray muons is between from 1 to 100 GeV
Effects of geometrical acceptance have to be taken into account 

14. Surface-Pit ~100m SIDE A SIDE C Sector 13 Side A Small Big shaft shaft
Muons coming from the shafts, are deviated in the upper part of Muon Spectrometer
before ending in sector 13; due to the magnetic field µ+, µ- result in different
angles.
SIDE A
SIDE C
Sector 13
Side A

15. Conclusions Barrel installations is completed
Test with cosmic muons: complete analysis of sector 13 data
Systematic study of the MDT performance over the all barrel sectors (magnetic field off)
Further tests with cosmics in June with B field on.

16. Backup slides...

17. Detection of Higgs decay final states:
GeV < mH < 1 TeV
Energy per Proton
7 TeV
Bunch spacing
25 ns
Bunch size
15 m  12 cm
Protons per bunch
1011
Bunches per ring
2835
Beam mean life
10 hours
Project Luminosity
1034 cm-2 s-1
Circumference
27 Km
Collisions per bunch 25
Detection of Higgs decay final states:
H  ZZ  4µ “Golden Channel”

18. MDT (Monitored Drift Tubes)
two multilayers of 3 (in Middle and Outer rings) or 4 (in the Inner ring) layers of staggered drift tubes each.
thin wall (400 μm thick) 3 cm diameter aluminum tubes.
low longitudinal diffusion gas mixture, 93%Ar−7%CO2, absolute pressure of 3 bar.
Gold-plated W-Re anode wire, 50 μm diameter is tensioned at 350 g crimped in copper pins.
low gas gain of 2×104 (3080 V andode voltage) to avoid ageing effects.
good space resolution (~100 μm per point)
robust and reliable operation for many years (no ageing problems).
Tubes per layer
Layer per multilayer
Chamber lenght (mm)
Chamber heigth (mm)
~1200 chambers / ~5500 m2
From F.Petrucci

19. (combined with Inner Detector tracking)
Impact of resolution
From TDR
Space resolution ~100 micron
Transverse momentum resolution
Z mass resolution
(combined with Inner Detector tracking)
Z->µµ
Invariant Mass (GeV)

20. ATLAS Installation Schedule 9.1

21. Setup h=0 13 Muon stations read-out BIL Side A BML BOL BOF BIL 3 BIL 2
From R. Nikolaidou

22. TDC vs ADC spectrum ADC counts Signal “double hits” Noise Background
When a tube has a second hit in the same event.
Noise
Background
TDC counts
From C.Bini

23. Magnetic field map
Magnetic field strongly inhomogeneous, in particular in BILs!
From C.Bini

24. Angle of tracks µ- µ+ µ- Big shaft degrees µ+ Muons coming
from the
small shaft
Angle of tracks
with respect to vertical axis. Shift in
spectrum for different signs (run with magnetic field on)
Big shaft
degrees
Angle of tracks:
superposition of run
with and without
magnetic field µ- µ+
µ- µ+ run with magnetic field on
µ run with no magnetic field
From R. Nikolaidou