1. Introduction to the Compact Muon Solenoid Experiment for the LHC
Dave Barney, CMS Outreach Coordinator

2. Brief overview of the CMS experiment
Overview of Seminar
Brief overview of the CMS experiment
Motivation (not in-depth physics)
Layout
Sub-detectors
The CMS collaboration
Visiting the construction site at Cessy
Safety
What is in the assembly hall?
What is outside the hall?
Useful resources
Questions (and hopefully answers too!)

3. We don’t know what we will find at the LHC!
Physics goals of CMS
We don’t know what we will find at the LHC!
ATLAS and CMS are “general purpose” detectors – they need to be designed to be able to detect anything!
We believe that the Higgs boson, and/or Supersymmetric (SUSY) particles exist, and the LHC will provide collisions energetic enough to create them
But we cannot see Higgs/SUSY particles directly as they either decay to lighter (stable) particles or cannot be seen with any known detector
We have to design our detector to look for the stable particles and signs of “invisible” particles…..

4. Detecting signatures of the Higgs boson
Most likely mass of the Higgs boson (if it exists) is around GeV (1GeV = mass of proton)
If this is the case, the easiest way to detect it is via its decay to two photons
Need an excellent electromagnetic calorimeter - ECAL (to measure the energy of these photons)
Need excellent tracker to identify the primary interaction vertex
If the Higgs is heavier, it may be seen via its decay to electrons and/or muons
Need an excellent ECAL
Need excellent muon chambers (for muon identification and momentum measurement) and central tracking (for momentum measurement)

5. Detecting SUSY Signatures
Many SUSY particles decay to hadronic jets (many charged and neutral particles in a tight bunch)
Need good calorimeters – hadronic (HCAL) and ECAL
SUSY decays also lead to the production of the “lightest supersymmetric particle” (LSP), which is invisible in any known detector
Need excellent calorimetry coverage in order to detect “missing” energy (from simple conservation laws)

6. The best possible electromagnetic calorimeter
CMS Design Goals
A good and redundant muon system (= many layers – if one layer fails we can fall back on the others)
The best possible electromagnetic calorimeter
A high quality central tracking
A hadronic calorimeter that has good energy resolution and that is as hermetic as possible
Affordable! (= ~500 MCHF)

7. The Compact Muon Solenoid
ATLAS
CMS

8. The CMS Detector

9. The magnet systems of ATLAS and CMS
ATLAS A Toroidal LHC Apparatus
CMS Compact Muon Solenoid

10. The CMS Solenoid (1)
A solenoid is essentially a cylinder of wire. Passing an electrical current down the wire creates a magnetic field
The CMS solenoid is designed to provide an axial magnetic field of 4T – about times that of the earth’s magnetic field
The current required is ~20 kAmps  need to use a superconducting wire (zero resistance)
The superconductor chosen is Niobium Titanium (NbTi) wrapped with copper – needs to be cooled to ~4K
The CMS solenoid will be 13m long with an inner diameter of 5.9m – the largest superconducting solenoid ever made!

11. Superconducting cable
The CMS solenoid (2)
Solenoid piece at Cessy
Superconducting cable
Ultra-pure Aluminium - magnetic stabilizer
Aluminium alloy - mechanical stabilizer

12. The CMS Solenoid (3)

13. The solenoid vacuum vessel and return yoke
Solenoid needs to be maintained at ~4 K
Need to insert the coil into a vacuum vessel (a bit like a thermos flask)
The vacuum vessel = two concentric steel cylinders (both of which are at Cessy – see later) that surround the coil
Return yoke controls the field outside of the coil, and acts as a “filter” for muons (see later)
Return yoke = tonnes of steel, built in sections: 5 barrel “rings” and 3+3 endcap “disks”
Barrel rings are divided into layers, interspersed with muon chambers; muon chambers also on each endcap disk
All components of the yoke are at Cessy

14. The return yoke - parameters
Outer barrel rings
Endcap disks
Total weight
12500 tonnes
Diameter
15m
Length
21.6m
Magnetic field
4 Tesla
Central barrel ring
Central Ring
Outer Rings
Barrel ring
1250 tonnes
1174 tonnes
Vacuum vessel
264 tonnes -
Superconducting coil
234 tonnes
Support feet
72 tonnes
66 tonnes
Cabling on vacuum vessel
150 tonnes
Support for racks and cables
10 tonnes
Total
1980 tonnes
Endcap disk 1 (YE1)
~730 (disk) + 90 (cart) tonnes
Endcap disk 2 (YE2)
Endcap disk 3 (YE3)
~300 (disk) + 90 (cart) tonnes

15. The CMS Detector - Overview

16. The Tracker
214m2 of silicon sensors 11.4 million silicon strips 65.9 million pixels in final configuration!
Pixel endcap disks

17. The Electromagnetic Calorimeter - ECAL
Parameter
Barrel
Endcaps
Coverage
|h|<1.48
1.48<|h|<3.0
Df x Dh x
x to 0.05 x 0.05
Depth in X0
25.8
24.7
# of crystals
61200
14648
Volume
8.14m3
2.7m3
Xtal mass (t)
67.4
22.0

18. The Hadron Calorimeter - HCAL
CMS HCAL is constructed in 3 parts:
Barrel HCAL (HB)
Brass (laiton) plates interleaved with plastic scintillator embedded with wavelength-shifting optical fibres (photo top right)
Endcap HCAL (HE)
Brass plates interleaved with plastic scintillator
Forward HCAL (HF)
Steel wedges stuffed with quartz fibres (photo bottom right)
~10000 channels total
More photos later in presentation!

19. The Muon Chambers
Position measurement: Drift Tubes (DT) in barrel Cathode Strip Chambers (CSC) in endcaps
Trigger: Resistive Plate Chambers (RPCs) in barrel and endcaps
f superlayer of 4 DT layers
h superlayer of 4 DT layers
DT channels CSC channels RPC channels

20. The Trigger and Data Acquisition System (1)
Bunches of protons collide in CMS every 25ns (40 million times per second)
Each bunch crossing will result in ~1 Mbyte of data (after zero suppression)
Can only possibly write ~100 Mbytes / second to tape
CMS trigger system will try to decide (in a very short time!) if a bunch crossing has created something interesting
If yes, then the event is saved
If no, then the event is discarded for ever!

21. The Trigger and Data Acquisition System (2)
CMS Trigger system has two stages:
Level-1 trigger
Implemented in hardware
Uses coarse-grain information from calorimeters and muon chambers to make a quick decision – in <4msec – e.g.
are there 2 muons with momenta above certain thresholds?
Is there an electromagnetic energy deposit > 40 GeV?
Reduces rate from 40 MHz to a maximum of 100 kHz
High level triggers
100 kHz data passed through a high bandwidth switching network to a farm of ~1000 commercial PCs running data selection algorithms – effectively on-line data analysis
Use fine-grain information from all sub-detectors, e.g.
Is an ECAL energy deposit matched to hits in the pixel detector? (if so, this signifies the presence of an electron)
Reduces rate from 100 kHz to 100 Hz, for storage on tape

22. The Trigger and Data Acquisition System (3)
~same as whole world’s telecom network!

23. Visiting the Cessy Site - Safety First
Normally you should only go to the visitors gallery and outside areas
To enter the assembly hall (for private visits) you must:
Contact Jean-Pierre Girod (163703) and request permission
Wear safety helmets – failure to do so will result in visits to CMS being suspended
In case of an accident etc.
Call the Pompier (74444) – but bear in mind they are 15 minutes away….
Call J-P Girod (weekdays)
In case of fire etc. go to the main entrance assembly point

24. The CMS Construction Site at Cessy
PX56
PM54
2585
SX5
3580 VG
3584
Safety helmets
He gas tanks

25. Schematic of the surface buildings at Cessy

26. The Gas Cylinders Will be filled with Helium gas
Two cylinders will supply He for the CMS solenoid cryogenic system – about 5000 litres of liquid He are required
The time to cool the CMS solenoid to ~4K is about 3 weeks
Other 4 cylinders will supply He for the LHC cryogenic system

27. The Underground Areas

28. The PX56 Access Shaft ~21m diameter
Pieces of CMS detector will be lowered down this shaft into the UXC5 cavern
Walls around are to protect neighbours from noise
Problem: When constructing the PX56 shaft, the excavators hit the water table (nappe phreatique) at about 40m deep – and it is not easy to dig through water!
Solution: put small-bore pipes around the shaft (from surface down to below the water level) and circulate salt-water at ~-23oC for several months. Then replace the salt-water with liquid nitrogen to create a frozen cylinder around the shaft. Then excavate and concrete the shaft!

29. Status of Underground Caverns
Adding waterproof lining before final concrete layers Caverns will be completed by middle 2004

30. Inside SX5 – the barrel yoke rings
Connecting pieces from Czech republic
Main pieces from Russia
Central ring: ~2000 tonnes
Outer rings: ~1250 tonnes
Feet: ~35 tonnes each; from Pakistan (outer rings) or Germany (central ring)

31. Inside SX5 – the central barrel ring
Central ring supports solenoid
Outer vacuum vessel for solenoid
- manufactured in Lons Le Saunier by France Comte Industrie
- Transported to CERN in pieces and welded together at Cessy
Air-pads for moving rings etc.
-from Noell GmbH, Germany
Use compressed air at atmospheres from cylinders
Each pad can lift ~350 tonnes
4 pads per side
Rails used to guide the movement
Air-powered pistons push the rings

32. Inside SX5 – inserting the inner vacuum vessel
Manufactured by FCI as a single piece and transported by road to Cessy
Supported and rotated by platform made in Korea

33. Inside SX5 – the endcap yoke disks
Three disks for one endcap
One disk loaded with CSCs
- Disks constructed from wedges made in Japan, CERN - “Carts” made in China
Stabilization bolts from USA

34. Inside SX5 – the Hadron Calorimeter
Most of HCAL is in SX5 – two half-barrels and two endcaps (HF is still on the Meyrin site)
Brass for endcap HCAL has an interesting story……

35. Lowering the pieces of CMS into the cavern
Will rent a gantry crane capable of lifting 2500 tonnes
Crane will probably come from a shipyard in Rotterdam (Netherlands)

36. CMS Collaboration (Nov. 2003)
2008 scientists and engineers
160 institutes
36 countries
See

37. Some Important CMS Milestones
Task
Foreseen Date (as of November 2003)
Surface hall (SX5) finished construction
31 January 2000
Assembly of barrel yoke finished in SX5
31 August 2001
Assembly of endcap yokes finished in SX5
30 April 2002
Assembly of barrel HCAL finished in SX5
20 November 2002
Assembly of endcap HCAL finished in SX5
30 September 2003
Solenoid coil segments completed
30 June 2004
Underground experimental cavern completed
15 July 2004
Solenoid inserted into vacuum vessel
15 November 2004
Yoke closed and magnet test started in SX5
30 January 2005
End of magnet test in SX5
30 April 2005
Racks installed into underground service cavern
Start lowering large pieces into UXC5
30 May 2005
End of lowering of major pieces into UXC5
30 September 2005
End of installation and cabling in UXC5
30 June 2006
CMS ready for circulating beam
(including 20% computing capacity)
1 April 2007
Fully operational computing systems
1 April 2009
Full list can be found at

38. 2008 scientists and engineers
CMS Basic Parameters
Physical Parameters
Collaboration (Nov. 2003)
Length
21.6m
Diameter
14m
Mass
12500 Tonnes
Magnetic field
4 Tesla
2008 scientists and engineers
160 institutes
36 countries
Trigger and Data Acquisition Parameters
Channel Count
Parameter
Value
Bunch-crossing frequency
40 MHz
Average # of collisions / bunch-crossing 20
“interaction rate”
~109
Level-1 trigger rate
100 kHz
Average event size
1 Mbyte
Event builder bandwidth
100 Gbytes/sec
Event filter computing power required
106 SI95
Event rate saved to mass storage
100 Hz
Data production
10 Tbytes/day
Sub-Detector
Number of channels
Pixels
66 x 106
Silicon microstrips
11.4 x 106
ECAL crystals
0.076 x 106
Preshower strips
0.137 x 106
HCAL
0.01 x 106
Muon chambers
0.576 x 106
TOTAL
78.2 x 106

39. Puzzle
View along beam line of the inner tracking, with a H 4m event superimposed. The m are very high energy, so leave straight tracks originating from the centre and travelling to the outside

40. Puzzle solution Make a “cut” on the Transverse momentum
Of the tracks: pT>2 GeV