1. The CMS muon system performance
Jesús Puerta-Pelayo
CIEMAT, Madrid (Spain)
on behalf of the CMS collaboration
Frontier Detectors for Frontier Physics Elba 24/May/09

2. Jesús_Puerta_Pelayo_CIEMAT_Madrid
Outline
CMS muon system description
Drift Tube chambers (DT)
Cathode Strip Chambers (CSC)
Resistive Plate Chambers (RPC)
Commissioning the CMS muon system
Detector performance results
Physics results
First LHC beams in CMS
Jesús_Puerta_Pelayo_CIEMAT_Madrid

3. The importance of muons in CMS
The design of CMS was strongly driven by the idea of a powerful, hermetic and redundant muon system, capable of exploiting the clearness of muon signals in hadron colliders.
A very precise muon spectrometer with high efficiency in muon reconstruction over a large momentum range was mandatory
Jesús_Puerta_Pelayo_CIEMAT_Madrid

4. CMS requirements on muon system
Magnetic field & particle rate
Muon pt resolution requirements
Standalone
200 GeV
1 TeV (η dependent)
Combining with the tracker
low pT
1 TeV
Muon trigger
μID → |η| = 2.4 with > 16 λ
Precise BX identification
1μ & 2 μ L1 triggers → |η| = 2.1
Alignment better than 100 μm
Jesús_Puerta_Pelayo_CIEMAT_Madrid

5. Muon system in CMS Redundant and hermetic coverage up to |η|< 2.4
Following these requirements, the chosen design in order to cope with them was…
Redundant and hermetic coverage up to |η|< 2.4
Gaseous detectors
3 different detectors, different technologies
Jesús_Puerta_Pelayo_CIEMAT_Madrid

6. Jesús_Puerta_Pelayo_CIEMAT_Madrid
Muon system in CMS
ENDCAP
BARREL
Detectors interleaved with the magnet yoke steel layers
4 stations in the endcaps
(0.9 < |η| < 2.4)
4 stations in the barrel
(|η| < 1.2)
Jesús_Puerta_Pelayo_CIEMAT_Madrid

7. Drift Tube Chambers (DT)
DTs are responsible for muon tracking and triggering in the barrel
250 chambers (50 per wheel)
5 wheels / 12 sectors / 4 stations
>170k RO channels
Basic unit: Drift cell
Drift signals collected in wire anodes.
Almost linear space-time relationship.
Vdrift ~ 55 μm/ns->
Max drift time ~380 ns
Single wire resolution ~ 250 μm
Local reconstruction (r-φ) ~ 100 μm
Efficient (Above 99.5%)
8 points in r-φ
4 points in r-θ
Redundant
DT chamber: 3/2 independent measuring units (SLs) composed of 4 layers of staggered drift cells each
Jesús_Puerta_Pelayo_CIEMAT_Madrid

8. Drift Tube Chambers (DT) trigger
Important feature is the trigger capability of muon tracking detectors
Higher trigger instances sort and select the 4 best barrel muons and pass them over to GMT
pt, position and charge are assigned
(Look-up-Tables)
Dedicated in-chamber trigger electronics
searche for hits alignment in each muon station.
Up to 2 muon segments per station are sent to higher trigger levels each BX, where trigger segments from each station are matched together
Jesús_Puerta_Pelayo_CIEMAT_Madrid

9. Drift Tube Chambers (DT) – Assembly and installation
Assembled in Italy, Spain and Germany
Installation from summer 2004 to November 07 (surface / underground)
DT test & storage area
ISR (CERN)
YB lowering
DT & RPC install
Jesús_Puerta_Pelayo_CIEMAT_Madrid

10. Cathode Strip Chambers (CSC)
Tracking and triggering in the endcaps.
Different technology needed (higher B and rate)
Trapezoidal shape multiwire proportional chambers
6 planes per chamber
Independent cathode and anode RO
468 chambers, >400k channels.
4 disks/endcap,
1, 2 or 3 rings/disk
18 or 36 sectors/ring
2 million cathode strip chamber wires.
Up to 6 points per track. Each point is the intersection of:
Centre of induced charge in 3-strip clusters (more accurate)
Signal in groups of 8 wires (faster)
Phi resolution ~ 100 μm
Detection eff > 99%
Jesús_Puerta_Pelayo_CIEMAT_Madrid

11. Cathode Strip Chambers (CSC) – Trigger
Similarly to DTs, CSCs also have trigger capability:
Cathode view: Pattern comparison in 6 layers provide a good (~ 1 mm) measurement of position in r-φ
Anode view: optimized for BX identification (~ 4 ns precision). The coincidence of ≥ 4 layers define a muon segment
CLCT
ALCT
CSC track finder: Reconstructs and assigns pt, φ and η, and selects the 4 best muon candidates to be sent to GMT
Jesús_Puerta_Pelayo_CIEMAT_Madrid

12. Cathode Strip Chambers (CSC) – Assembly and installation
Assembled in Russia, China & USA
CSC tests
CSC installation
YE lowering
Completed by March 2007
Jesús_Puerta_Pelayo_CIEMAT_Madrid

13. Resistive Plate Chambers (RPC)
Fast trigger dedicated detectors, both in endcap and barrel
96.2% C2H2F4
3.5% iso-C4H10
0.3% SF6
Double gap bakelite plates with graphite electrodes and strips readout
Avalanche mode & 2 gaps:
lower gain (to cope with high rate up to 1kHz/cm2)
higher amplification
A time resolution of ~3 ns allows BX tag without ambiguity
480 ch(barrel, 6 layers)
432 ch (end-caps, 3 layers)
At least 3 layers up to |η|=1.6
162k channels
Good space resolution (~1cm)
Trigger with pattern comparator
Jesús_Puerta_Pelayo_CIEMAT_Madrid

14. Resistive Plate Chambers (RPC) – Assembly and installation
Assembled in Italy, Bulgaria, China, Korea and Pakistan.
Installed:
Barrel:
Sum 04 – End 07
Endcap:
End 05 – End 07
Barrel RPCs
YE lowering
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Endcap RPCs installation

15. Jesús_Puerta_Pelayo_CIEMAT_Madrid
Nov 2000
Sep 2005
Mar 2006
Apr 2008
The muon detector is complete! It’s been a long way…
Feb 2007
Sep 2008
Jesús_Puerta_Pelayo_CIEMAT_Madrid

16. Commissioning the muon system
Several global cosmics data taking campaigns have been organised in the last ~3 years, progressively incorporating components of the whole experiment
MTCC (B on)
CRUZETs
CRAFT (B on)
MWGRs
A summary of most relevant results from all these runs will be presented (work in progress)
Extremely useful for system understanding, synchronisation, integration
Some physics results obtained from cosmics analysis
Jesús_Puerta_Pelayo_CIEMAT_Madrid

17. Jesús_Puerta_Pelayo_CIEMAT_Madrid
Some nice muon events…
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18. Jesús_Puerta_Pelayo_CIEMAT_Madrid
Some nice muon events…
Run 66533, Event
Jesús_Puerta_Pelayo_CIEMAT_Madrid

19. Jesús_Puerta_Pelayo_CIEMAT_Madrid
Some nice muon events…
p = 4.09 GeV/c
Run 66533, Event
Jesús_Puerta_Pelayo_CIEMAT_Madrid

20. DETECTOR PERFORMANCE RESULTS

21. DT cosmics performance
DT drift velocity is a key parameter for reconstruction and trigger performance
Affected by B in border regions (change in drift path of electrons)
Very precise calibrations performed
(see G.Mila’s poster)
Br magnetic field map
CRAFT
Alignment with tracks
DT single cell efficiency
For further info on DT commissioning,
see G.Cerminara’s poster
Correlation survey / tracks
Jesús_Puerta_Pelayo_CIEMAT_Madrid

22. RPC cosmics performance
X (cm) 20 40
Y (cm)
Single gap working region
RPC efficiency
Extrapolation of DT muon segments to the RPC area
“Muon radiography”
(occupancy of RPC based on reconstructed muons)
Barrel
For further info see D. Piccolo’s poster
Endcap
(rings 2 and 3)
Jesús_Puerta_Pelayo_CIEMAT_Madrid

23. CSC cosmics performance
Resolution vs distance to beamline
CSC resolution
1/σ2 (chamber) = 3/ σe2 + 3/σc2
Increasing strip width
σ(ME2/1) ~ 160 μm
σ(ME1/1) ~ μm
Gaussian fits to residuals distributions (ME2/2). Variation with track position within the strip
Average efficiencies for
each station/ring.
Single hit efficiency
Track segment efficiency
Jesús_Puerta_Pelayo_CIEMAT_Madrid

24. PHYSICS & FIRST BEAM RESULTS

25. Muon momenta and charge ratio
First ‘physics’ result obtained from CMS
Excellent exercise, helped understanding the muon system, magnetic field and alignment
MTCC 06
Momentum distribution of CRs
measured by DTs during MTCC
Jesús_Puerta_Pelayo_CIEMAT_Madrid

26. Muon origin extrapolation on surface
The overall distribution of triggered muons in the cavern clearly shows the
“shadows” of the service shafts
… and many more physics results will be extracted from CMS cosmics data
Work
in progress
Jesús_Puerta_Pelayo_CIEMAT_Madrid

27. ~2x109 protons on collimator ~150 m upstream of CMS
First beam in CMS
ME4
ME3
ME2
ME1
CSCs in negative endcap
CAL
DT hits
Barrel
Beam splash as seen from…
~2x109 protons on collimator ~150 m upstream of CMS
Jesús_Puerta_Pelayo_CIEMAT_Madrid

28. CSC Alignment with beam-halo muons
Halo muons were a powerful tool for CSC alignment
Almost parallel to beam pipe, incidence perpendicular to ring planes
Selection of tracks crossing the overlap region of two chambers
Accuracy achieved
270 μm in r-φ
0.35 mrad in φz
Mult. scattering
Initial alignment goal achieved in 9 min of LHC beam!
33k evs 9 min
Cross-check against photogrammetry
Jesús_Puerta_Pelayo_CIEMAT_Madrid

29. Looking forward to LHC data… We’re ready!
Conclusions
The three detectors constituting the CMS muon system have demonstrated the precision, reliability and stability of the chosen design for a muon spectrometer.
The construction, installation and pre-commissioning of the detectors was efficiently done, being the muon detectors on time for the global commissioning of the experiment.
Cosmic commissioning has been (is being!) a success. We exploited the possibilities and achieved a high level of understanding of our detectors (alignment / performances / calibration…).
Muon detectors have been the fundamental key for the commissioning of CMS as a whole.
Looking forward to LHC data… We’re ready!
Jesús_Puerta_Pelayo_CIEMAT_Madrid