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

2. 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. 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 115-130 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. 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 CMS Detector

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

9. 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 100000 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!

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

11. The CMS Solenoid (3)

12. 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 = 11000 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

13. The return yoke - parameters Central RingOuter Rings Barrel ring1250 tonnes1174 tonnes Vacuum vessel264 tonnes- Superconducting coil234 tonnes- Support feet72 tonnes66 tonnes Cabling on vacuum vessel150 tonnes- Support for racks and cables10 tonnes Total1980 tonnes1250 tonnes Endcap disk 1 (YE1)~730 (disk) + 90 (cart) tonnes Endcap disk 2 (YE2)~730 (disk) + 90 (cart) tonnes Endcap disk 3 (YE3)~300 (disk) + 90 (cart) tonnes Central barrel ring Outer barrel rings Endcap disks Total weight12500 tonnes Diameter15m Length21.6m Magnetic field4 Tesla

14. The CMS Detector - Overview

15. The Tracker Pixel endcap disks 214m 2 of silicon sensors 11.4 million silicon strips 65.9 million pixels in final configuration!

16. The Electromagnetic Calorimeter - ECAL ParameterBarrelEndcaps Coverage |  |<1.481.48<|  |<3.0  x  0.0175 x 0.0175 0.0175 x 0.0175 to 0.05 x 0.05 Depth in X 0 25.824.7 # of crystals6120014648 Volume8.14m 3 2.7m 3 Xtal mass (t)67.422.0

17. 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!

18. The Muon Chambers  superlayer of 4 DT layers  superlayer of 4 DT layers 195000 DT channels 210816 CSC channels 162282 RPC channels Position measurement: Drift Tubes (DT) in barrel Cathode Strip Chambers (CSC) in endcaps Trigger: Resistive Plate Chambers (RPCs) in barrel and endcaps

19. 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!

20. 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 <4  sec – 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

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

22. 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 J-P Girod (weekdays) Call the Pompier (74444) – but bear in mind they are 15 minutes away….

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

24. Schematic of the surface buildings at Cessy

25. 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

26. The Underground Areas

27. The PX56 Access Shaft ~20m 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 ~-5 o C for several months. Then replace the salt-water with liquid nitrogen to freeze the water in the shaft. Then dig-out the water and concrete the shaft!

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

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

30. 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 24 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

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

32. Inside SX5 – the endcap yoke disks Three disks for one endcap One disk loaded with CSCs - Disks constructed from wedges made in Japan, assembled @ CERN - “Carts” made in China Stabilization bolts from USA http://bulletin.cern.ch/eng/articles.php?bullno=47/2003&base=art&artno=BUL-NA-2003-141

33. 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……

34. Lowering the pieces of CMS into the cavern

35. CMS Collaboration (Nov. 2003) 2008 scientists and engineers160 institutes36 countries See http://cmsdoc.cern.ch/peopleCMS.shtml

36. Some Important CMS Milestones TaskForeseen Date (as of November 2003) Surface hall (SX5) finished construction31 January 2000 Assembly of barrel yoke finished in SX531 August 2001 Assembly of endcap yokes finished in SX530 April 2002 Assembly of barrel HCAL finished in SX520 November 2002 Assembly of endcap HCAL finished in SX530 September 2003 Solenoid coil segments completed30 June 2004 Underground experimental cavern completed15 July 2004 Solenoid inserted into vacuum vessel15 November 2004 Yoke closed and magnet test started in SX530 January 2005 End of magnet test in SX530 April 2005 Racks installed into underground service cavern30 April 2005 Start lowering large pieces into UXC530 May 2005 End of lowering of major pieces into UXC530 September 2005 End of installation and cabling in UXC530 June 2006 CMS ready for circulating beam (including 20% computing capacity) 1 April 2007 Fully operational computing systems1 April 2009 Full list can be found at http://cmsdoc.cern.ch/~cmstc

37. CMS Basic Parameters ParameterValue Bunch-crossing frequency40 MHz Average # of collisions / bunch-crossing20 “interaction rate”~10 9 Level-1 trigger rate100 kHz Average event size1 Mbyte Event builder bandwidth100 Gbytes/sec Event filter computing power required10 6 SI95 Event rate saved to mass storage100 Hz Data production10 Tbytes/day Sub-DetectorNumber of channels Pixels66 x 10 6 Silicon microstrips11.4 x 10 6 ECAL crystals0.076 x 10 6 Preshower strips0.137 x 10 6 HCAL0.01 x 10 6 Muon chambers0.576 x 10 6 TOTAL78.2 x 10 6 2008 scientists and engineers 160 institutes 36 countries Channel Count Trigger and Data Acquisition Parameters Length21.6m Diameter14m Mass12500 Tonnes Magnetic field4 Tesla Collaboration (Nov. 2003) Physical Parameters

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

39. Puzzle solution Make a “cut” on the Transverse momentum Of the tracks: p T >2 GeV